# Source code for propertyestimator.properties.enthalpy

    """
    A collection of enthalpy physical property definitions.
    """

    from collections import namedtuple

    from propertyestimator import unit
    from propertyestimator.datasets.plugins import register_thermoml_property
    from propertyestimator.properties.plugins import register_estimable_property
    from propertyestimator.properties.properties import PhysicalProperty, PropertyPhase
    from propertyestimator.protocols import analysis, groups, miscellaneous, reweighting, storage
    from propertyestimator.protocols.groups import ProtocolGroup
    from propertyestimator.protocols.utils import generate_base_reweighting_protocols, generate_base_simulation_protocols, \
        generate_gradient_protocol_group
    from propertyestimator.storage import StoredSimulationData
    from propertyestimator.storage.dataclasses import StoredDataCollection
    from propertyestimator.thermodynamics import Ensemble
    from propertyestimator.utils.quantities import EstimatedQuantity
    from propertyestimator.utils.statistics import ObservableType
    from propertyestimator.workflow import WorkflowOptions
    from propertyestimator.workflow.schemas import ProtocolReplicator, WorkflowSchema, \
        WorkflowDataCollectionToStore
    from propertyestimator.workflow.utils import ProtocolPath, ReplicatorValue

    @register_estimable_property()
    @register_thermoml_property(thermoml_string='Excess molar enthalpy (molar enthalpy of mixing), kJ/mol',
                                supported_phases=PropertyPhase.Liquid)
    class EnthalpyOfMixing(PhysicalProperty):
        """A class representation of an enthalpy of mixing property"""

        EnthalpyWorkflow = namedtuple('EnthalpySchema', 'build_coordinates '
                                                        'assign_topology '
                                                        'energy_minimisation '
                                                        'npt_equilibration '
                                                        'converge_uncertainty '
                                                        'subsample_trajectory '
                                                        'subsample_statistics ')

        @property
        def multi_component_property(self):
            return True

        @property
        def required_data_class(self):
            return StoredSimulationData

        @staticmethod
        def get_default_workflow_schema(calculation_layer, options=None):

            if calculation_layer == 'SimulationLayer':
                return EnthalpyOfMixing.get_default_simulation_workflow_schema(options)
            elif calculation_layer == 'ReweightingLayer':
                return EnthalpyOfMixing.get_default_reweighting_workflow_schema(options)

            return None

        @staticmethod
        def _get_simulation_protocols(id_suffix, gradient_replicator_id, replicator_id=None, weight_by_mole_fraction=False,
                                      component_substance_reference=None, full_substance_reference=None, options=None):

            """Returns the set of protocols which when combined in a workflow
            will yield the enthalpy of a substance.

            Parameters
            ----------
            id_suffix: str
                A suffix to append to the id of each of the returned protocols.
            gradient_replicator_id: str
                The id of the replicator which will clone those protocols which will
                estimate the gradient of the enthalpy with respect to a given parameter.
            replicator_id: str, optional
                The id of the replicator which will be used to clone these protocols.
                This will be appended to the id of each of the returned protocols if
                set.
            weight_by_mole_fraction: bool
                If true, an extra protocol will be added to weight the calculated
                enthalpy by the mole fraction of the component.
            component_substance_reference: ProtocolPath or PlaceholderInput, optional
                An optional protocol path (or replicator reference) to the component substance
                whose enthalpy is being estimated.
            full_substance_reference: ProtocolPath or PlaceholderInput, optional
                An optional protocol path (or replicator reference) to the full substance
                whose enthalpy of mixing is being estimated. This cannot be `None` if
                `weight_by_mole_fraction` is `True`.
            options: WorkflowOptions
                The options to use when setting up the workflows.

            Returns
            -------
            BaseSimulationProtocols
                The protocols used to estimate the enthalpy of a substance.
            ProtocolPath
                A reference to the estimated enthalpy.
            WorkflowSimulationDataToStore
                An object which describes the default data from a simulation to store,
                such as the uncorrelated statistics and configurations.
            ProtocolGroup
                The group of protocols which will calculate the gradient of the reduced potential
                with respect to a given property.
            ProtocolReplicator
                The protocol which will replicate the gradient group for every gradient to
                estimate.
            ProtocolPath
                A reference to the value of the gradient.
            """

            if replicator_id is not None:
                id_suffix = f'{id_suffix}_$({replicator_id})'

            if component_substance_reference is None:
                component_substance_reference = ProtocolPath('substance', 'global')

            if weight_by_mole_fraction is True and full_substance_reference is None:

                raise ValueError('The full substance reference must be set when weighting by'
                                 'the mole fraction')

            # Define the protocol which will extract the average enthalpy from
            # the results of a simulation.
            extract_enthalpy = analysis.ExtractAverageStatistic(f'extract_enthalpy{id_suffix}')
            extract_enthalpy.statistics_type = ObservableType.Enthalpy

            # Define the protocols which will run the simulation itself.
            simulation_protocols, value_source, output_to_store = generate_base_simulation_protocols(extract_enthalpy,
                                                                                                     options,
                                                                                                     id_suffix)

            number_of_molecules = ProtocolPath('output_number_of_molecules', simulation_protocols.build_coordinates.id)
            built_substance = ProtocolPath('output_substance', simulation_protocols.build_coordinates.id)

            # Divide the enthalpy by the number of molecules in the system
            extract_enthalpy.divisor = number_of_molecules

            # Use the correct substance.
            simulation_protocols.build_coordinates.substance = component_substance_reference
            simulation_protocols.assign_parameters.substance = built_substance
            output_to_store.substance = built_substance

            conditional_group = simulation_protocols.converge_uncertainty

            if weight_by_mole_fraction:

                # The component workflows need an extra step to multiply their enthalpies by their
                # relative mole fraction.
                weight_by_mole_fraction = miscellaneous.WeightByMoleFraction(f'weight_by_mole_fraction{id_suffix}')
                weight_by_mole_fraction.value = ProtocolPath('value', extract_enthalpy.id)
                weight_by_mole_fraction.full_substance = full_substance_reference
                weight_by_mole_fraction.component = component_substance_reference

                conditional_group.add_protocols(weight_by_mole_fraction)

                value_source = ProtocolPath('weighted_value', conditional_group.id, weight_by_mole_fraction.id)

            if options.convergence_mode != WorkflowOptions.ConvergenceMode.NoChecks:

                # Make sure the convergence criteria is set to use the per component
                # uncertainty target.
                conditional_group.conditions[0].right_hand_value = ProtocolPath('per_component_uncertainty', 'global')

                if weight_by_mole_fraction:
                    # Make sure the weighted uncertainty is being used in the conditional comparison.
                    conditional_group.conditions[0].left_hand_value = ProtocolPath('weighted_value.uncertainty',
                                                                                   conditional_group.id,
                                                                                   weight_by_mole_fraction.id)

            # Set up the gradient calculations
            reweight_enthalpy_template = reweighting.ReweightStatistics('')
            reweight_enthalpy_template.statistics_type = ObservableType.PotentialEnergy
            reweight_enthalpy_template.statistics_paths = [ProtocolPath('statistics_file_path',
                                                                        conditional_group.id,
                                                                        simulation_protocols.production_simulation.id)]

            coordinate_source = ProtocolPath('output_coordinate_file', simulation_protocols.equilibration_simulation.id)
            trajectory_source = ProtocolPath('trajectory_file_path', simulation_protocols.converge_uncertainty.id,
                                             simulation_protocols.production_simulation.id)
            statistics_source = ProtocolPath('statistics_file_path', simulation_protocols.converge_uncertainty.id,
                                             simulation_protocols.production_simulation.id)

            gradient_group, gradient_replicator, gradient_source = \
                generate_gradient_protocol_group(reweight_enthalpy_template,
                                                 [ProtocolPath('force_field_path', 'global')],
                                                 ProtocolPath('force_field_path', 'global'),
                                                 coordinate_source,
                                                 trajectory_source,
                                                 statistics_source,
                                                 replicator_id=gradient_replicator_id,
                                                 substance_source=built_substance,
                                                 id_suffix=id_suffix)

            # Remove the group id from the path.
            gradient_source.pop_next_in_path()

            if weight_by_mole_fraction:

                # The component workflows need an extra step to multiply their gradients by their
                # relative mole fraction.
                weight_gradient = miscellaneous.WeightByMoleFraction(f'weight_gradient_by_mole_fraction{id_suffix}')
                weight_gradient.value = gradient_source
                weight_gradient.full_substance = full_substance_reference
                weight_gradient.component = component_substance_reference

                gradient_group.add_protocols(weight_gradient)
                gradient_source = ProtocolPath('weighted_value', weight_gradient.id)

            scale_gradient = miscellaneous.DivideValue(f'scale_gradient{id_suffix}')
            scale_gradient.value = gradient_source
            scale_gradient.divisor = number_of_molecules

            gradient_group.add_protocols(scale_gradient)
            gradient_source = ProtocolPath('result', gradient_group.id, scale_gradient.id)

            return (simulation_protocols, value_source, output_to_store,
                    gradient_group, gradient_replicator, gradient_source)

        @staticmethod
        def _get_reweighting_protocols(id_suffix, gradient_replicator_id, data_replicator_id, replicator_id=None,
                                       weight_by_mole_fraction=False, substance_reference=None, options=None):

            """Returns the set of protocols which when combined in a workflow
            will yield the enthalpy of a substance by reweighting cached data.

            Parameters
            ----------
            id_suffix: str
                A suffix to append to the id of each of the returned protocols.
            gradient_replicator_id: str
                The id of the replicator which will clone those protocols which will
                estimate the gradient of the enthalpy with respect to a given parameter.
            data_replicator_id: str
                The id of the replicator which will be used to clone these protocols
                for each cached simulation data.
            replicator_id: str, optional
                The optional id of the replicator which will be used to clone these
                protocols, e.g. for each component in the system.
            weight_by_mole_fraction: bool
                If true, an extra protocol will be added to weight the calculated
                enthalpy by the mole fraction of the component.
            substance_reference: ProtocolPath or PlaceholderInput, optional
                An optional protocol path (or replicator reference) to the substance
                whose enthalpy is being estimated.
            options: WorkflowOptions
                The options to use when setting up the workflows.

            Returns
            -------
            BaseReweightingProtocols
                The protocols used to estimate the enthalpy of a substance.
            ProtocolPath
                A reference to the estimated enthalpy.
            ProtocolReplicator
                The replicator which will replicate each protocol for each
                cached simulation datum.
            ProtocolGroup
                The group of protocols which will calculate the gradient of the reduced potential
                with respect to a given property.
            ProtocolPath
                A reference to the value of the gradient.
            """

            if replicator_id is not None:
                id_suffix = f'{id_suffix}_$({replicator_id})'

            full_id_suffix = id_suffix

            if data_replicator_id is not None:
                full_id_suffix = f'{id_suffix}_$({data_replicator_id})'

            if substance_reference is None:
                substance_reference = ProtocolPath('substance', 'global')

            extract_enthalpy = analysis.ExtractAverageStatistic(f'extract_enthalpy{full_id_suffix}')
            extract_enthalpy.statistics_type = ObservableType.Enthalpy
            reweight_enthalpy = reweighting.ReweightStatistics(f'reweight_enthalpy{id_suffix}')
            reweight_enthalpy.statistics_type = ObservableType.Enthalpy

            (protocols,
             data_replicator) = generate_base_reweighting_protocols(analysis_protocol=extract_enthalpy,
                                                                    mbar_protocol=reweight_enthalpy,
                                                                    workflow_options=options,
                                                                    replicator_id=data_replicator_id,
                                                                    id_suffix=id_suffix)

            # Make sure we use the reduced internal potential when re-weighting enthalpies
            protocols.reduced_reference_potential.use_internal_energy = True
            protocols.reduced_target_potential.use_internal_energy = True

            # Make sure to use the correct substance.
            protocols.build_target_system.substance = substance_reference

            value_source = ProtocolPath('value', protocols.mbar_protocol.id)

            # Set up the protocols which will be responsible for adding together
            # the component enthalpies, and subtracting these from the full system enthalpy.
            weight_enthalpy = None

            if weight_by_mole_fraction is True:

                weight_enthalpy = miscellaneous.WeightByMoleFraction(f'weight_enthalpy{id_suffix}')
                weight_enthalpy.value = ProtocolPath('value', protocols.mbar_protocol.id)
                weight_enthalpy.full_substance = ProtocolPath('substance', 'global')
                weight_enthalpy.component = substance_reference

                value_source = ProtocolPath('weighted_value', weight_enthalpy.id)

            # Divide by the component enthalpies by the number of molecules in the system
            number_of_molecules = ProtocolPath('total_number_of_molecules', protocols.
                                               unpack_stored_data.id.replace(f'$({data_replicator_id})', '0'))

            divide_by_molecules = miscellaneous.DivideValue(f'divide_by_molecules{id_suffix}')
            divide_by_molecules.value = value_source
            divide_by_molecules.divisor = number_of_molecules

            value_source = ProtocolPath('result', divide_by_molecules.id)

            # Set up the gradient calculations.
            reweight_potential_template = reweighting.ReweightStatistics('')
            reweight_potential_template.statistics_type = ObservableType.PotentialEnergy
            reweight_potential_template.frame_counts = ProtocolPath('number_of_uncorrelated_samples',
                                                                    protocols.decorrelate_statistics.id)

            coordinate_path = ProtocolPath('output_coordinate_path', protocols.concatenate_trajectories.id)
            trajectory_path = ProtocolPath('output_trajectory_path', protocols.concatenate_trajectories.id)

            gradient_group, _, gradient_source = \
                generate_gradient_protocol_group(reweight_potential_template,
                                                 ProtocolPath('force_field_path', protocols.unpack_stored_data.id),
                                                 ProtocolPath('force_field_path', 'global'),
                                                 coordinate_path,
                                                 trajectory_path,
                                                 replicator_id=gradient_replicator_id,
                                                 id_suffix=id_suffix,
                                                 substance_source=substance_reference,
                                                 use_subset_of_force_field=False,
                                                 effective_sample_indices=ProtocolPath('effective_sample_indices',
                                                                                       protocols.mbar_protocol.id))

            # Remove the group id from the path.
            gradient_source.pop_next_in_path()

            if weight_by_mole_fraction is True:

                # The component workflows need an extra step to multiply their gradients by their
                # relative mole fraction.
                weight_gradient = miscellaneous.WeightByMoleFraction(f'weight_gradient_$({gradient_replicator_id})_'
                                                                     f'by_mole_fraction{id_suffix}')
                weight_gradient.value = gradient_source
                weight_gradient.full_substance = ProtocolPath('substance', 'global')
                weight_gradient.component = substance_reference

                gradient_group.add_protocols(weight_gradient)
                gradient_source = ProtocolPath('weighted_value', weight_gradient.id)

            scale_gradient = miscellaneous.DivideValue(f'scale_gradient_$({gradient_replicator_id}){id_suffix}')
            scale_gradient.value = gradient_source
            scale_gradient.divisor = number_of_molecules

            gradient_group.add_protocols(scale_gradient)
            gradient_source = ProtocolPath('result', gradient_group.id, scale_gradient.id)

            all_protocols = (*protocols, divide_by_molecules)

            if weight_enthalpy is not None:
                all_protocols = (*all_protocols, weight_enthalpy)

            return all_protocols, value_source, data_replicator, gradient_group, gradient_source

        @staticmethod
        def get_default_simulation_workflow_schema(options=None):
            """Returns the default workflow to use when estimating this property
            from direct simulations.

            Parameters
            ----------
            options: WorkflowOptions
                The default options to use when setting up the estimation workflow.

            Returns
            -------
            WorkflowSchema
                The schema to follow when estimating this property.
            """

            # Define the id of the replicator which will clone the gradient protocols
            # for each gradient key to be estimated.
            gradient_replicator_id = 'gradient_replicator'

            # Set up a workflow to calculate the enthalpy of the full, mixed system.
            (full_system_protocols,
             full_system_enthalpy,
             full_output,
             full_system_gradient_group,
             full_system_gradient_replicator,
             full_system_gradient) = EnthalpyOfMixing._get_simulation_protocols('_full',
                                                                                gradient_replicator_id,
                                                                                options=options)

            # Set up a general workflow for calculating the enthalpy of one of the system components.
            component_replicator_id = 'component_replicator'
            component_substance = ReplicatorValue(component_replicator_id)

            # Make sure to weight by the mole fractions of the actual full system as these may be slightly
            # different to the mole fractions of the measure property due to rounding.
            full_substance = ProtocolPath('output_substance', full_system_protocols.build_coordinates.id)

            (component_protocols,
             component_enthalpies,
             component_output,
             component_gradient_group,
             component_gradient_replicator,
             component_gradient) = EnthalpyOfMixing._get_simulation_protocols('_component',
                                                                              gradient_replicator_id,
                                                                              replicator_id=component_replicator_id,
                                                                              weight_by_mole_fraction=True,
                                                                              component_substance_reference=
                                                                                      component_substance,
                                                                              full_substance_reference=full_substance,
                                                                              options=options)

            # Finally, set up the protocols which will be responsible for adding together
            # the component enthalpies, and subtracting these from the mixed system enthalpy.
            add_component_enthalpies = miscellaneous.AddValues('add_component_enthalpies')
            add_component_enthalpies.values = component_enthalpies

            calculate_enthalpy_of_mixing = miscellaneous.SubtractValues('calculate_enthalpy_of_mixing')
            calculate_enthalpy_of_mixing.value_b = full_system_enthalpy
            calculate_enthalpy_of_mixing.value_a = ProtocolPath('result', add_component_enthalpies.id)

            # Create the replicator object which defines how the pure component
            # enthalpy estimation protocols will be replicated for each component.
            component_replicator = ProtocolReplicator(replicator_id=component_replicator_id)
            component_replicator.template_values = ProtocolPath('components', 'global')

            # Combine the gradients.
            add_component_gradients = miscellaneous.AddValues(f'add_component_gradients'
                                                              f'_$({gradient_replicator_id})')
            add_component_gradients.values = component_gradient

            combine_gradients = miscellaneous.SubtractValues(f'combine_gradients_$({gradient_replicator_id})')
            combine_gradients.value_b = full_system_gradient
            combine_gradients.value_a = ProtocolPath('result', add_component_gradients.id)

            # Combine the gradient replicators.
            gradient_replicator = ProtocolReplicator(replicator_id=gradient_replicator_id)
            gradient_replicator.template_values = ProtocolPath('parameter_gradient_keys', 'global')

            # Build the final workflow schema
            schema = WorkflowSchema(property_type=EnthalpyOfMixing.__name__)
            schema.id = '{}{}'.format(EnthalpyOfMixing.__name__, 'Schema')

            schema.protocols = {
                component_protocols.build_coordinates.id: component_protocols.build_coordinates.schema,
                component_protocols.assign_parameters.id: component_protocols.assign_parameters.schema,
                component_protocols.energy_minimisation.id: component_protocols.energy_minimisation.schema,
                component_protocols.equilibration_simulation.id: component_protocols.equilibration_simulation.schema,
                component_protocols.converge_uncertainty.id: component_protocols.converge_uncertainty.schema,

                full_system_protocols.build_coordinates.id: full_system_protocols.build_coordinates.schema,
                full_system_protocols.assign_parameters.id: full_system_protocols.assign_parameters.schema,
                full_system_protocols.energy_minimisation.id: full_system_protocols.energy_minimisation.schema,
                full_system_protocols.equilibration_simulation.id: full_system_protocols.equilibration_simulation.schema,
                full_system_protocols.converge_uncertainty.id: full_system_protocols.converge_uncertainty.schema,

                component_protocols.extract_uncorrelated_trajectory.id:
                    component_protocols.extract_uncorrelated_trajectory.schema,
                component_protocols.extract_uncorrelated_statistics.id:
                    component_protocols.extract_uncorrelated_statistics.schema,

                full_system_protocols.extract_uncorrelated_trajectory.id:
                    full_system_protocols.extract_uncorrelated_trajectory.schema,
                full_system_protocols.extract_uncorrelated_statistics.id:
                    full_system_protocols.extract_uncorrelated_statistics.schema,

                add_component_enthalpies.id: add_component_enthalpies.schema,
                calculate_enthalpy_of_mixing.id: calculate_enthalpy_of_mixing.schema,

                component_gradient_group.id: component_gradient_group.schema,
                full_system_gradient_group.id: full_system_gradient_group.schema,
                add_component_gradients.id: add_component_gradients.schema,
                combine_gradients.id: combine_gradients.schema
            }

            schema.replicators = [gradient_replicator, component_replicator]

            # Finally, tell the schemas where to look for its final values.
            schema.gradients_sources = [ProtocolPath('result', combine_gradients.id)]
            schema.final_value_source = ProtocolPath('result', calculate_enthalpy_of_mixing.id)

            schema.outputs_to_store = {
                'full_system': full_output,
                f'component_$({component_replicator_id})': component_output
            }

            return schema

        @staticmethod
        def get_default_reweighting_workflow_schema(options=None):
            """Returns the default workflow to use when estimating this property
            by reweighting existing data.

            Parameters
            ----------
            options: WorkflowOptions
                The default options to use when setting up the estimation workflow.

            Returns
            -------
            WorkflowSchema
                The schema to follow when estimating this property.
            """

            # Set up a replicator that will re-run the component reweighting workflow for each
            # component in the system.
            component_replicator = ProtocolReplicator(replicator_id='component_replicator')
            component_replicator.template_values = ProtocolPath('components', 'global')

            gradient_replicator = ProtocolReplicator('gradient')
            gradient_replicator.template_values = ProtocolPath('parameter_gradient_keys', 'global')

            # Set up the protocols which will reweight data for the full system.
            full_data_replicator_id = 'full_data_replicator'

            (full_protocols,
             full_enthalpy,
             full_data_replicator,
             full_gradient_group,
             full_gradient_source) = EnthalpyOfMixing._get_reweighting_protocols('_full',
                                                                                 gradient_replicator.id,
                                                                                 full_data_replicator_id,
                                                                                 options=options)

            # Set up the protocols which will reweight data for each component.
            component_data_replicator_id = f'component_{component_replicator.placeholder_id}_data_replicator'

            (component_protocols,
             component_enthalpies,
             component_data_replicator,
             component_gradient_group,
             component_gradient_source) = EnthalpyOfMixing._get_reweighting_protocols('_component',
                                                                                      gradient_replicator.id,
                                                                                      component_data_replicator_id,
                                                                                      replicator_id=component_replicator.id,
                                                                                      weight_by_mole_fraction=True,
                                                                                      substance_reference=ReplicatorValue(
                                                                                          component_replicator.id),
                                                                                      options=options)

            # Make sure the replicator is only replicating over component data.
            component_data_replicator.template_values = ProtocolPath(f'component_data[$({component_replicator.id})]',
                                                                     'global')

            add_component_potentials = miscellaneous.AddValues('add_component_potentials')
            add_component_potentials.values = component_enthalpies

            calculate_excess_enthalpy = miscellaneous.SubtractValues('calculate_excess_potential')
            calculate_excess_enthalpy.value_b = full_enthalpy
            calculate_excess_enthalpy.value_a = ProtocolPath('result', add_component_potentials.id)

            # Combine the gradients.
            add_component_gradients = miscellaneous.AddValues(f'add_component_gradients'
                                                              f'_{gradient_replicator.placeholder_id}')
            add_component_gradients.values = component_gradient_source

            combine_gradients = miscellaneous.SubtractValues(f'combine_gradients_{gradient_replicator.placeholder_id}')
            combine_gradients.value_b = full_gradient_source
            combine_gradients.value_a = ProtocolPath('result', add_component_gradients.id)

            # Build the final workflow schema.
            schema = WorkflowSchema(property_type=EnthalpyOfMixing.__name__)
            schema.id = '{}{}'.format(EnthalpyOfMixing.__name__, 'Schema')

            schema.protocols = dict()

            schema.protocols.update({protocol.id: protocol.schema for protocol in full_protocols})
            schema.protocols.update({protocol.id: protocol.schema for protocol in component_protocols})

            schema.protocols[add_component_potentials.id] = add_component_potentials.schema
            schema.protocols[calculate_excess_enthalpy.id] = calculate_excess_enthalpy.schema

            schema.protocols[full_gradient_group.id] = full_gradient_group.schema
            schema.protocols[component_gradient_group.id] = component_gradient_group.schema
            schema.protocols[add_component_gradients.id] = add_component_gradients.schema
            schema.protocols[combine_gradients.id] = combine_gradients.schema

            schema.replicators = [
                full_data_replicator,
                component_replicator,
                component_data_replicator,
                gradient_replicator
            ]

            schema.gradients_sources = [ProtocolPath('result', combine_gradients.id)]
            schema.final_value_source = ProtocolPath('result', calculate_excess_enthalpy.id)

            return schema

    @register_estimable_property()
    @register_thermoml_property('Molar enthalpy of vaporization or sublimation, kJ/mol',
                                supported_phases=PropertyPhase.Liquid | PropertyPhase.Gas)
    class EnthalpyOfVaporization(PhysicalProperty):
        """A class representation of an enthalpy of vaporization property"""

        @property
        def multi_component_property(self):
            """Returns whether this property is dependant on properties of the
            full mixed substance, or whether it is also dependant on the properties
            of the individual components also.
            """
            return False

        @property
        def required_data_class(self):
            return StoredDataCollection

        @staticmethod
        def get_default_workflow_schema(calculation_layer, options=None):

            if calculation_layer == 'SimulationLayer':
                return EnthalpyOfVaporization.get_default_simulation_workflow_schema(options)
            elif calculation_layer == 'ReweightingLayer':
                return EnthalpyOfVaporization.get_default_reweighting_workflow_schema(options)

            return None

        @staticmethod
        def get_default_simulation_workflow_schema(options=None):
            """Returns the default workflow to use when estimating this property
            from direct simulations.

            Parameters
            ----------
            options: WorkflowOptions
                The default options to use when setting up the estimation workflow.

            Returns
            -------
            WorkflowSchema
                The schema to follow when estimating this property.
            """

            # Define the number of molecules for the liquid phase
            number_of_liquid_molecules = 1000

            # Define a custom conditional group.
            converge_uncertainty = groups.ConditionalGroup(f'converge_uncertainty')
            converge_uncertainty.max_iterations = 100

            # Define the protocols to perform the simulation in the liquid phase.
            extract_liquid_energy = analysis.ExtractAverageStatistic('extract_liquid_energy')
            extract_liquid_energy.statistics_type = ObservableType.PotentialEnergy
            extract_liquid_energy.divisor = number_of_liquid_molecules

            liquid_protocols, liquid_value_source, liquid_output_to_store = \
                generate_base_simulation_protocols(extract_liquid_energy, options, '_liquid', converge_uncertainty)

            # Make sure the number of molecules in the liquid is consistent.
            liquid_protocols.build_coordinates.max_molecules = number_of_liquid_molecules

            # Define the protocols to perform the simulation in the gas phase.
            extract_gas_energy = analysis.ExtractAverageStatistic('extract_gas_energy')
            extract_gas_energy.statistics_type = ObservableType.PotentialEnergy

            gas_protocols, gas_value_source, gas_output_to_store = \
                generate_base_simulation_protocols(extract_gas_energy, options, '_gas', converge_uncertainty)

            # Create only a single molecule in vacuum
            gas_protocols.build_coordinates.max_molecules = 1

            # Run the gas phase simulations in the NVT ensemble
            gas_protocols.energy_minimisation.enable_pbc = False
            gas_protocols.equilibration_simulation.ensemble = Ensemble.NVT
            gas_protocols.equilibration_simulation.enable_pbc = False
            gas_protocols.production_simulation.ensemble = Ensemble.NVT
            gas_protocols.production_simulation.steps_per_iteration = 15000000
            gas_protocols.production_simulation.output_frequency = 5000
            gas_protocols.production_simulation.checkpoint_frequency = 100
            gas_protocols.production_simulation.enable_pbc = False

            # Due to a bizarre issue where the OMM Reference platform is
            # the fastest at computing properties of a single molecule
            # in vacuum, we enforce those inputs which will force the
            # gas calculations to run on the Reference platform.
            gas_protocols.equilibration_simulation.high_precision = True
            gas_protocols.equilibration_simulation.allow_gpu_platforms = False
            gas_protocols.production_simulation.high_precision = True
            gas_protocols.production_simulation.allow_gpu_platforms = False

            # Combine the values to estimate the final energy of vaporization
            energy_of_vaporization = miscellaneous.SubtractValues('energy_of_vaporization')
            energy_of_vaporization.value_b = ProtocolPath('value', extract_gas_energy.id)
            energy_of_vaporization.value_a = ProtocolPath('value', extract_liquid_energy.id)

            ideal_volume = miscellaneous.MultiplyValue('ideal_volume')
            ideal_volume.value = EstimatedQuantity(1.0 * unit.molar_gas_constant,
                                                   0.0 * unit.joule / unit.mole / unit.kelvin,
                                                   'Universal Constant')
            ideal_volume.multiplier = ProtocolPath('thermodynamic_state.temperature', 'global')

            enthalpy_of_vaporization = miscellaneous.AddValues('enthalpy_of_vaporization')
            enthalpy_of_vaporization.values = [
                ProtocolPath('result', energy_of_vaporization.id),
                ProtocolPath('result', ideal_volume.id)
            ]

            # Add the extra protocols and conditions to the custom group.
            converge_uncertainty.add_protocols(energy_of_vaporization,
                                               ideal_volume,
                                               enthalpy_of_vaporization)

            if options.convergence_mode != WorkflowOptions.ConvergenceMode.NoChecks:

                condition = groups.ConditionalGroup.Condition()
                condition.condition_type = groups.ConditionalGroup.ConditionType.LessThan

                condition.left_hand_value = ProtocolPath('result.uncertainty', converge_uncertainty.id,
                                                                               enthalpy_of_vaporization.id)
                condition.right_hand_value = ProtocolPath('target_uncertainty', 'global')

                gas_protocols.production_simulation.total_number_of_iterations = ProtocolPath('current_iteration',
                                                                                              converge_uncertainty.id)

                liquid_protocols.production_simulation.total_number_of_iterations = ProtocolPath('current_iteration',
                                                                                                 converge_uncertainty.id)

                converge_uncertainty.add_condition(condition)

            # Set up the liquid gradient calculations
            reweight_potential_template = reweighting.ReweightStatistics('')
            reweight_potential_template.statistics_type = ObservableType.PotentialEnergy

            liquid_coordinate_source = ProtocolPath('output_coordinate_file', liquid_protocols.equilibration_simulation.id)
            liquid_trajectory_source = ProtocolPath('trajectory_file_path', converge_uncertainty.id,
                                                    liquid_protocols.production_simulation.id)
            liquid_statistics_source = ProtocolPath('statistics_file_path', liquid_protocols.converge_uncertainty.id,
                                                    liquid_protocols.production_simulation.id)

            liquid_gradient_group, liquid_gradient_replicator, liquid_gradient_source = \
                generate_gradient_protocol_group(reweight_potential_template,
                                                 [ProtocolPath('force_field_path', 'global')],
                                                 ProtocolPath('force_field_path', 'global'),
                                                 liquid_coordinate_source,
                                                 liquid_trajectory_source,
                                                 liquid_statistics_source,
                                                 id_suffix='_liquid')

            # Set up the gas gradient calculations
            gas_coordinate_source = ProtocolPath('output_coordinate_file', gas_protocols.equilibration_simulation.id)
            gas_trajectory_source = ProtocolPath('trajectory_file_path', converge_uncertainty.id,
                                                    gas_protocols.production_simulation.id)
            gas_statistics_source = ProtocolPath('statistics_file_path', gas_protocols.converge_uncertainty.id,
                                                 gas_protocols.production_simulation.id)

            gas_gradient_group, gas_gradient_replicator, gas_gradient_source = \
                generate_gradient_protocol_group(reweight_potential_template,
                                                 [ProtocolPath('force_field_path', 'global')],
                                                 ProtocolPath('force_field_path', 'global'),
                                                 gas_coordinate_source,
                                                 gas_trajectory_source,
                                                 gas_statistics_source,
                                                 id_suffix='_gas',
                                                 enable_pbc=False)

            # Combine the gradients.
            scale_liquid_gradient = miscellaneous.DivideValue('scale_liquid_gradient_$(repl)')
            scale_liquid_gradient.value = liquid_gradient_source
            scale_liquid_gradient.divisor = number_of_liquid_molecules

            combine_gradients = miscellaneous.SubtractValues('combine_gradients_$(repl)')
            combine_gradients.value_b = gas_gradient_source
            combine_gradients.value_a = ProtocolPath('result', scale_liquid_gradient.id)

            # Combine the gradient replicators.
            gradient_replicator = ProtocolReplicator(replicator_id=liquid_gradient_replicator.id)
            gradient_replicator.template_values = ProtocolPath('parameter_gradient_keys', 'global')

            # Build the workflow schema.
            schema = WorkflowSchema(property_type=EnthalpyOfVaporization.__name__)
            schema.id = '{}{}'.format(EnthalpyOfVaporization.__name__, 'Schema')

            schema.protocols = {
                liquid_protocols.build_coordinates.id: liquid_protocols.build_coordinates.schema,
                liquid_protocols.assign_parameters.id: liquid_protocols.assign_parameters.schema,
                liquid_protocols.energy_minimisation.id: liquid_protocols.energy_minimisation.schema,
                liquid_protocols.equilibration_simulation.id: liquid_protocols.equilibration_simulation.schema,

                gas_protocols.build_coordinates.id: gas_protocols.build_coordinates.schema,
                gas_protocols.assign_parameters.id: gas_protocols.assign_parameters.schema,
                gas_protocols.energy_minimisation.id: gas_protocols.energy_minimisation.schema,
                gas_protocols.equilibration_simulation.id: gas_protocols.equilibration_simulation.schema,

                converge_uncertainty.id: converge_uncertainty.schema,

                liquid_protocols.extract_uncorrelated_trajectory.id:
                    liquid_protocols.extract_uncorrelated_trajectory.schema,
                liquid_protocols.extract_uncorrelated_statistics.id:
                    liquid_protocols.extract_uncorrelated_statistics.schema,

                gas_protocols.extract_uncorrelated_trajectory.id: gas_protocols.extract_uncorrelated_trajectory.schema,
                gas_protocols.extract_uncorrelated_statistics.id: gas_protocols.extract_uncorrelated_statistics.schema,

                liquid_gradient_group.id: liquid_gradient_group.schema,
                gas_gradient_group.id: gas_gradient_group.schema,

                scale_liquid_gradient.id: scale_liquid_gradient.schema,
                combine_gradients.id: combine_gradients.schema
            }

            schema.replicators = [gradient_replicator]

            data_to_store = WorkflowDataCollectionToStore()

            data_to_store.data['liquid'] = liquid_output_to_store
            data_to_store.data['gas'] = gas_output_to_store

            schema.outputs_to_store = {'full_system_data': data_to_store}

            schema.gradients_sources = [ProtocolPath('result', combine_gradients.id)]
            schema.final_value_source = ProtocolPath('result', converge_uncertainty.id, enthalpy_of_vaporization.id)

            return schema

        @staticmethod
        def get_default_reweighting_workflow_schema(options):
            """Returns the default workflow to use when estimating this property
            by reweighting existing data.

            Parameters
            ----------
            options: WorkflowOptions
                The default options to use when setting up the estimation workflow.

            Returns
            -------
            WorkflowSchema
                The schema to follow when estimating this property.
            """

            # Set up the data replicator (we use the same one for the gas and liquid phase)
            data_replicator = ProtocolReplicator('data_replicator')
            data_replicator.template_values = ProtocolPath('full_system_data', 'global')
            # Set up the gradient replicator
            gradient_replicator = ProtocolReplicator('gradient_replicator')
            gradient_replicator.template_values = ProtocolPath('parameter_gradient_keys', 'global')

            # Set up a protocol to extract both the liquid and gas phase data
            unpack_data_collection = storage.UnpackStoredDataCollection(f'unpack_data_collection_'
                                                                        f'{data_replicator.placeholder_id}')
            unpack_data_collection.input_data_path = ReplicatorValue(data_replicator.id)

            # Set up a protocol to extract the liquid phase energy from the existing data.
            extract_liquid_energy = analysis.ExtractAverageStatistic(f'extract_liquid_energy_'
                                                                     f'{data_replicator.placeholder_id}')
            extract_liquid_energy.statistics_type = ObservableType.PotentialEnergy

            reweight_liquid_energy = reweighting.ReweightStatistics('reweight_liquid_energy')
            reweight_liquid_energy.statistics_type = ObservableType.PotentialEnergy

            liquid_protocols, _ = generate_base_reweighting_protocols(extract_liquid_energy,
                                                                      reweight_liquid_energy,
                                                                      options,
                                                                      id_suffix='_liquid',
                                                                      replicator_id=data_replicator.id)

            liquid_protocols.unpack_stored_data.simulation_data_path = ProtocolPath('collection_data_paths[liquid]',
                                                                                    unpack_data_collection.id)

            # Extract the number of liquid phase molecules from the first data collection.
            number_of_liquid_molecules = ProtocolPath('total_number_of_molecules', liquid_protocols.unpack_stored_data.
                                                      id.replace(data_replicator.placeholder_id, '0'))

            divide_by_liquid_molecules = miscellaneous.DivideValue('divide_by_liquid_molecules')
            divide_by_liquid_molecules.value = ProtocolPath('value', liquid_protocols.mbar_protocol.id)
            divide_by_liquid_molecules.divisor = number_of_liquid_molecules

            # Set up a protocol to extract the gas phase energy from the existing data.
            extract_gas_energy = analysis.ExtractAverageStatistic('extract_gas_energy_'
                                                                  f'{data_replicator.placeholder_id}')
            extract_gas_energy.statistics_type = ObservableType.PotentialEnergy
            reweight_gas_energy = reweighting.ReweightStatistics('reweight_gas_energy')
            reweight_gas_energy.statistics_type = ObservableType.PotentialEnergy

            gas_protocols, _ = generate_base_reweighting_protocols(extract_gas_energy,
                                                                   reweight_gas_energy,
                                                                   options,
                                                                   id_suffix='_gas',
                                                                   replicator_id=data_replicator.id)

            # Turn of PBC for the gas phase.
            gas_protocols.reduced_reference_potential.enable_pbc = False
            gas_protocols.reduced_target_potential.enable_pbc = False

            gas_protocols.unpack_stored_data.simulation_data_path = ProtocolPath('collection_data_paths[gas]',
                                                                                 unpack_data_collection.id)

            extract_gas_energy.statistics_path = ProtocolPath('statistics_file_path',
                                                              gas_protocols.unpack_stored_data.id)

            # Combine the values to estimate the final enthalpy of vaporization
            energy_of_vaporization = miscellaneous.SubtractValues('energy_of_vaporization')
            energy_of_vaporization.value_b = ProtocolPath('value', gas_protocols.mbar_protocol.id)
            energy_of_vaporization.value_a = ProtocolPath('result', divide_by_liquid_molecules.id)

            ideal_volume = miscellaneous.MultiplyValue('ideal_volume')
            ideal_volume.value = EstimatedQuantity(1.0 * unit.molar_gas_constant,
                                                   0.0 * unit.joule / unit.mole / unit.kelvin,
                                                   'Universal Constant')
            ideal_volume.multiplier = ProtocolPath('thermodynamic_state.temperature', 'global')

            enthalpy_of_vaporization = miscellaneous.AddValues('enthalpy_of_vaporization')
            enthalpy_of_vaporization.values = [
                ProtocolPath('result', energy_of_vaporization.id),
                ProtocolPath('result', ideal_volume.id)
            ]

            # Set up the liquid phase gradient calculations
            reweight_potential_template = reweighting.ReweightStatistics('')
            reweight_potential_template.statistics_type = ObservableType.PotentialEnergy

            liquid_coordinate_path = ProtocolPath('output_coordinate_path', liquid_protocols.concatenate_trajectories.id)
            liquid_trajectory_path = ProtocolPath('output_trajectory_path', liquid_protocols.concatenate_trajectories.id)

            liquid_gradient_group, _, liquid_gradient_source = \
                generate_gradient_protocol_group(reweight_potential_template,
                                                 ProtocolPath('force_field_path', liquid_protocols.unpack_stored_data.id),
                                                 ProtocolPath('force_field_path', 'global'),
                                                 liquid_coordinate_path,
                                                 liquid_trajectory_path,
                                                 replicator_id=gradient_replicator.id,
                                                 id_suffix='_liquid',
                                                 use_subset_of_force_field=False,
                                                 effective_sample_indices=ProtocolPath('effective_sample_indices',
                                                                                       liquid_protocols.mbar_protocol.id))

            # Set up the gas phase gradient calculations
            gas_coordinate_path = ProtocolPath('output_coordinate_path', gas_protocols.concatenate_trajectories.id)
            gas_trajectory_path = ProtocolPath('output_trajectory_path', gas_protocols.concatenate_trajectories.id)

            gas_gradient_group, _, gas_gradient_source = \
                generate_gradient_protocol_group(reweight_potential_template,
                                                 ProtocolPath('force_field_path', gas_protocols.unpack_stored_data.id),
                                                 ProtocolPath('force_field_path', 'global'),
                                                 gas_coordinate_path,
                                                 gas_trajectory_path,
                                                 replicator_id=gradient_replicator.id,
                                                 id_suffix='_gas',
                                                 use_subset_of_force_field=False,
                                                 enable_pbc=False,
                                                 effective_sample_indices=ProtocolPath('effective_sample_indices',
                                                                                       gas_protocols.mbar_protocol.id))

            # Combine the gradients.
            divide_liquid_gradient = miscellaneous.DivideValue(f'divide_liquid_gradient_'
                                                               f'{gradient_replicator.placeholder_id}')
            divide_liquid_gradient.value = liquid_gradient_source
            divide_liquid_gradient.divisor = number_of_liquid_molecules

            combine_gradients = miscellaneous.SubtractValues(f'combine_gradients_{gradient_replicator.placeholder_id}')
            combine_gradients.value_b = gas_gradient_source
            combine_gradients.value_a = ProtocolPath('result', divide_liquid_gradient.id)

            # Build the workflow schema.
            schema = WorkflowSchema(property_type=EnthalpyOfVaporization.__name__)
            schema.id = '{}{}'.format(EnthalpyOfVaporization.__name__, 'Schema')

            schema.protocols[unpack_data_collection.id] = unpack_data_collection.schema

            schema.protocols.update({protocol.id: protocol.schema for protocol in liquid_protocols})
            schema.protocols.update({protocol.id: protocol.schema for protocol in gas_protocols})

            schema.protocols[divide_by_liquid_molecules.id] = divide_by_liquid_molecules.schema
            schema.protocols[energy_of_vaporization.id] = energy_of_vaporization.schema
            schema.protocols[ideal_volume.id] = ideal_volume.schema
            schema.protocols[enthalpy_of_vaporization.id] = enthalpy_of_vaporization.schema

            schema.protocols[liquid_gradient_group.id] = liquid_gradient_group.schema
            schema.protocols[gas_gradient_group.id] = gas_gradient_group.schema
            schema.protocols[divide_liquid_gradient.id] = divide_liquid_gradient.schema
            schema.protocols[combine_gradients.id] = combine_gradients.schema

            schema.replicators = [data_replicator, gradient_replicator]

            schema.gradients_sources = [ProtocolPath('result', combine_gradients.id)]
            schema.final_value_source = ProtocolPath('result', enthalpy_of_vaporization.id)

            return schema