//
//  CustomSchemaMappingProvider.swift
//  CoreStore
//
//  Copyright © 2017 John Rommel Estropia
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import CoreData
import Foundation


// MARK: - CustomSchemaMappingProvider

open class CustomSchemaMappingProvider: Hashable, SchemaMappingProvider {
    
    public let sourceVersion: ModelVersion
    public let destinationVersion: ModelVersion
    
    public required init(from sourceVersion: ModelVersion, to destinationVersion: ModelVersion, entityMappings: Set<CustomMapping> = []) {
        
        CoreStore.assert(
            cs_lazy {
                
                let sources = entityMappings.flatMap({ $0.entityMappingSourceEntity })
                let destinations = entityMappings.flatMap({ $0.entityMappingDestinationEntity })
                return sources.count == Set(sources).count
                    && destinations.count == Set(destinations).count
            },
            "Duplicate source/destination entities found in provided \"entityMappings\" argument."
        )
        self.sourceVersion = sourceVersion
        self.destinationVersion = destinationVersion
        self.entityMappings = entityMappings
    }
    
    
    // MARK: - CustomMapping
    
    public enum CustomMapping: Hashable {
        
        public typealias Transformer = (_ sourceObject: UnsafeSourceObject, _ createDestinationObject: () -> UnsafeDestinationObject) throws -> Void
        
        case deleteEntity(sourceEntity: EntityName)
        case insertEntity(destinationEntity: EntityName)
        case copyEntity(sourceEntity: EntityName, destinationEntity: EntityName)
        case transformEntity(sourceEntity: EntityName, destinationEntity: EntityName, transformer: Transformer)
        
        static func inferredTransformation(_ sourceObject: UnsafeSourceObject, _ createDestinationObject: () -> UnsafeDestinationObject) throws -> Void {
            
            let destinationObject = createDestinationObject()
            destinationObject.enumerateAttributes { (attribute, sourceAttribute) in
                
                if let sourceAttribute = sourceAttribute {
                    
                    destinationObject[attribute] = sourceObject[sourceAttribute]
                }
            }
        }
        
        var entityMappingSourceEntity: EntityName? {
            
            switch self {
                
            case .deleteEntity(let sourceEntity),
                 .copyEntity(let sourceEntity, _),
                 .transformEntity(let sourceEntity, _, _):
                return sourceEntity
                
            case .insertEntity:
                return nil
            }
        }
        
        var entityMappingDestinationEntity: EntityName? {
            
            switch self {
                
            case .insertEntity(let destinationEntity),
                 .copyEntity(_, let destinationEntity),
                 .transformEntity(_, let destinationEntity, _):
                return destinationEntity
                
            case .deleteEntity:
                return nil
            }
        }
        
        
        // MARK: Equatable
        
        public static func == (lhs: CustomMapping, rhs: CustomMapping) -> Bool {
            
            switch (lhs, rhs) {
                
            case (.deleteEntity(let sourceEntity1), .deleteEntity(let sourceEntity2)):
                return sourceEntity1 == sourceEntity2
                
            case (.insertEntity(let destinationEntity1), .insertEntity(let destinationEntity2)):
                return destinationEntity1 == destinationEntity2
                
            case (.copyEntity(let sourceEntity1, let destinationEntity1), .copyEntity(let sourceEntity2, let destinationEntity2)):
                return sourceEntity1 == sourceEntity2
                    && destinationEntity1 == destinationEntity2
                
            case (.transformEntity(let sourceEntity1, let destinationEntity1, _), .transformEntity(let sourceEntity2, let destinationEntity2, _)):
                return sourceEntity1 == sourceEntity2
                    && destinationEntity1 == destinationEntity2
                
            default:
                return false
            }
        }
        
        
        // MARK: Hashable
        
        public var hashValue: Int {
            
            switch self {
                
            case .deleteEntity(let sourceEntity):
                return sourceEntity.hashValue
                
            case .insertEntity(let destinationEntity):
                return destinationEntity.hashValue
                
            case .copyEntity(let sourceEntity, let destinationEntity):
                return sourceEntity.hashValue
                    ^ destinationEntity.hashValue
                
            case .transformEntity(let sourceEntity, let destinationEntity, _):
                return sourceEntity.hashValue
                    ^ destinationEntity.hashValue
            }
        }
    }
    
    
    // MARK: - UnsafeSourceObject
    
    public final class UnsafeSourceObject {
        
        public subscript(attribute: KeyPath) -> Any? {
            
            return self.rawObject.cs_accessValueForKVCKey(attribute)
        }
        
        public subscript(attribute: NSAttributeDescription) -> Any? {
            
            return self.rawObject.cs_accessValueForKVCKey(attribute.name)
        }
        
        public func enumerateAttributes(_ closure: (_ attribute: NSAttributeDescription) -> Void) {
            
            for case let attribute as NSAttributeDescription in self.rawObject.entity.properties {
                
                closure(attribute)
            }
        }
        
        
        // MARK: Internal
        
        internal init(_ rawObject: NSManagedObject) {
            
            self.rawObject = rawObject
        }
        
        
        // MARK: Private
        
        private let rawObject: NSManagedObject
    }
    
    
    // MARK: - UnsafeDestinationObject
    
    public final class UnsafeDestinationObject {
        
        public subscript(attribute: KeyPath) -> Any? {
            
            get { return self.rawObject.cs_accessValueForKVCKey(attribute) }
            set { self.rawObject.cs_setValue(newValue, forKVCKey: attribute) }
        }
        
        public subscript(attribute: NSAttributeDescription) -> Any? {
            
            get { return self.rawObject.cs_accessValueForKVCKey(attribute.name) }
            set { self.rawObject.cs_setValue(newValue, forKVCKey: attribute.name) }
        }
        
        public func enumerateAttributes(_ closure: (_ attribute: NSAttributeDescription, _ sourceAttribute: NSAttributeDescription?) -> Void) {
            
            for case let attribute as NSAttributeDescription in self.rawObject.entity.properties {
                
                closure(attribute, self.sourceAttributesByDestinationKey[attribute.name])
            }
        }
        
        
        // MARK: Internal
        
        internal init(_ rawObject: NSManagedObject, _ sourceAttributesByDestinationKey: [KeyPath: NSAttributeDescription]) {
            
            self.rawObject = rawObject
            self.sourceAttributesByDestinationKey = sourceAttributesByDestinationKey
        }
        
        
        // MARK: Private
        
        private let rawObject: NSManagedObject
        private let sourceAttributesByDestinationKey: [KeyPath: NSAttributeDescription]
    }
    
    
    // MARK: Equatable
    
    public static func == (lhs: CustomSchemaMappingProvider, rhs: CustomSchemaMappingProvider) -> Bool {
        
        return lhs.sourceVersion == rhs.sourceVersion
            && lhs.destinationVersion == rhs.destinationVersion
            && type(of: lhs) == type(of: rhs)
    }
    
    
    // MARK: Hashable
    
    public var hashValue: Int {
        
        return self.sourceVersion.hashValue
            ^ self.destinationVersion.hashValue
    }
    
    
    // MARK: SchemaMappingProvider
    
    public func createMappingModel(from sourceSchema: DynamicSchema, to destinationSchema: DynamicSchema, storage: LocalStorage) throws -> (mappingModel: NSMappingModel, migrationType: MigrationType) {
        
        let sourceModel = sourceSchema.rawModel()
        let destinationModel = destinationSchema.rawModel()
        
        let mappingModel = NSMappingModel()
        
        let (deleteMappings, insertMappings, copyMappings, transformMappings) = self.resolveEntityMappings(
            sourceModel: sourceModel,
            destinationModel: destinationModel
        )
        func expression(forSource sourceEntity: NSEntityDescription) -> NSExpression {
            
            return NSExpression(format: "FETCH(FUNCTION($\(NSMigrationManagerKey), \"fetchRequestForSourceEntityNamed:predicateString:\" , \"\(sourceEntity.name!)\", \"\(NSPredicate(value: true))\"), $\(NSMigrationManagerKey).\(#keyPath(NSMigrationManager.sourceContext)), \(false))")
        }
        
        let sourceEntitiesByName = sourceModel.entitiesByName
        let destinationEntitiesByName = destinationModel.entitiesByName
        
        var entityMappings: [NSEntityMapping] = []
        for case .deleteEntity(let sourceEntityName) in deleteMappings {
            
            let sourceEntity = sourceEntitiesByName[sourceEntityName]!
            
            let entityMapping = NSEntityMapping()
            entityMapping.sourceEntityName = sourceEntity.name
            entityMapping.sourceEntityVersionHash = sourceEntity.versionHash
            entityMapping.mappingType = .removeEntityMappingType
            entityMapping.sourceExpression = expression(forSource: sourceEntity)
            
            entityMappings.append(entityMapping)
        }
        for case .insertEntity(let destinationEntityName) in insertMappings {
            
            let destinationEntity = destinationEntitiesByName[destinationEntityName]!
            
            let entityMapping = NSEntityMapping()
            entityMapping.destinationEntityName = destinationEntity.name
            entityMapping.destinationEntityVersionHash = destinationEntity.versionHash
            entityMapping.mappingType = .addEntityMappingType
            entityMapping.attributeMappings = autoreleasepool { () -> [NSPropertyMapping] in
                
                var attributeMappings: [NSPropertyMapping] = []
                for (_, destinationAttribute) in destinationEntity.attributesByName {
                    
                    let propertyMapping = NSPropertyMapping()
                    propertyMapping.name = destinationAttribute.name
                    attributeMappings.append(propertyMapping)
                }
                return attributeMappings
            }
            entityMapping.relationshipMappings = autoreleasepool { () -> [NSPropertyMapping] in
                
                var relationshipMappings: [NSPropertyMapping] = []
                for (_, destinationRelationship) in destinationEntity.relationshipsByName {
                    
                    let propertyMapping = NSPropertyMapping()
                    propertyMapping.name = destinationRelationship.name
                    relationshipMappings.append(propertyMapping)
                }
                return relationshipMappings
            }
            entityMappings.append(entityMapping)
        }
        for case .copyEntity(let sourceEntityName, let destinationEntityName) in copyMappings {
            
            let sourceEntity = sourceEntitiesByName[sourceEntityName]!
            let destinationEntity = destinationEntitiesByName[destinationEntityName]!
            
            let entityMapping = NSEntityMapping()
            entityMapping.sourceEntityName = sourceEntity.name
            entityMapping.sourceEntityVersionHash = sourceEntity.versionHash
            entityMapping.destinationEntityName = destinationEntity.name
            entityMapping.destinationEntityVersionHash = destinationEntity.versionHash
            entityMapping.mappingType = .copyEntityMappingType
            entityMapping.sourceExpression = expression(forSource: sourceEntity)
            entityMapping.attributeMappings = autoreleasepool { () -> [NSPropertyMapping] in
                
                let sourceAttributes = sourceEntity.cs_resolvedAttributeRenamingIdentities()
                let destinationAttributes = destinationEntity.cs_resolvedAttributeRenamingIdentities()
                
                var attributeMappings: [NSPropertyMapping] = []
                for (renamingIdentifier, destination) in destinationAttributes {
                    
                    let sourceAttribute = sourceAttributes[renamingIdentifier]!.attribute
                    let destinationAttribute = destination.attribute
                    let propertyMapping = NSPropertyMapping()
                    propertyMapping.name = destinationAttribute.name
                    propertyMapping.valueExpression = NSExpression(format: "$\(NSMigrationSourceObjectKey).\(sourceAttribute.name)")
                    attributeMappings.append(propertyMapping)
                }
                return attributeMappings
            }
            let entityMappingName = entityMapping.name!
            entityMapping.relationshipMappings = autoreleasepool { () -> [NSPropertyMapping] in
                
                let destinationRelationships = destinationEntity.cs_resolvedRelationshipRenamingIdentities()
                var relationshipMappings: [NSPropertyMapping] = []
                for (_, destination) in destinationRelationships {
                    
                    let destinationRelationship = destination.relationship
                    let propertyMapping = NSPropertyMapping()
                    propertyMapping.name = destinationRelationship.name
                    propertyMapping.valueExpression = NSExpression(format: "FUNCTION($\(NSMigrationManagerKey), \"\(#selector(NSMigrationManager.destinationInstances(forEntityMappingName:sourceInstances:)))\" , \"\(entityMappingName)\", $\(NSMigrationSourceObjectKey))[0]")
                    relationshipMappings.append(propertyMapping)
                }
                return relationshipMappings
            }
            entityMappings.append(entityMapping)
        }
        for case .transformEntity(let sourceEntityName, let destinationEntityName, let transformEntity) in transformMappings {
            
            let sourceEntity = sourceEntitiesByName[sourceEntityName]!
            let destinationEntity = destinationEntitiesByName[destinationEntityName]!
            
            let entityMapping = NSEntityMapping()
            entityMapping.sourceEntityName = sourceEntity.name
            entityMapping.sourceEntityVersionHash = sourceEntity.versionHash
            entityMapping.destinationEntityName = destinationEntity.name
            entityMapping.destinationEntityVersionHash = destinationEntity.versionHash
            entityMapping.mappingType = .customEntityMappingType
            entityMapping.sourceExpression = expression(forSource: sourceEntity)
            entityMapping.entityMigrationPolicyClassName = NSStringFromClass(CustomEntityMigrationPolicy.self)
            
            var userInfo: [AnyHashable: Any] = [
                CustomEntityMigrationPolicy.UserInfoKey.transformer: transformEntity
            ]
            autoreleasepool {
                
                let sourceAttributes = sourceEntity.cs_resolvedAttributeRenamingIdentities()
                let destinationAttributes = destinationEntity.cs_resolvedAttributeRenamingIdentities()
                
                let transformedRenamingIdentifiers = Set(destinationAttributes.keys)
                    .intersection(sourceAttributes.keys)

                var sourceAttributesByDestinationKey: [KeyPath: NSAttributeDescription] = [:]
                for renamingIdentifier in transformedRenamingIdentifiers {
                    
                    let sourceAttribute = sourceAttributes[renamingIdentifier]!.attribute
                    let destinationAttribute = destinationAttributes[renamingIdentifier]!.attribute
                    sourceAttributesByDestinationKey[destinationAttribute.name] = sourceAttribute
                }
                userInfo[CustomEntityMigrationPolicy.UserInfoKey.sourceAttributesByDestinationKey] = sourceAttributesByDestinationKey
            }
            let entityMappingName = entityMapping.name!
            entityMapping.relationshipMappings = autoreleasepool { () -> [NSPropertyMapping] in
                
                let destinationRelationships = destinationEntity.cs_resolvedRelationshipRenamingIdentities()
                var relationshipMappings: [NSPropertyMapping] = []
                for (_, destination) in destinationRelationships {
                    
                    let destinationRelationship = destination.relationship
                    let propertyMapping = NSPropertyMapping()
                    propertyMapping.name = destinationRelationship.name
                    propertyMapping.valueExpression = NSExpression(format: "FUNCTION($\(NSMigrationManagerKey), \"\(#selector(NSMigrationManager.destinationInstances(forEntityMappingName:sourceInstances:)))\" , \"\(entityMappingName)\", $\(NSMigrationSourceObjectKey))[0]")
                    relationshipMappings.append(propertyMapping)
                }
                return relationshipMappings
            }
            entityMapping.userInfo = userInfo
            entityMappings.append(entityMapping)
        }
        
        mappingModel.entityMappings = entityMappings
        return (
            mappingModel,
            .heavyweight(
                sourceVersion: self.sourceVersion,
                destinationVersion: self.destinationVersion
            )
        )
    }
    
    
    // MARK: Private
    
    // MARK: - CustomEntityMigrationPolicy
    
    private final class CustomEntityMigrationPolicy: NSEntityMigrationPolicy {
        
        // MARK: NSEntityMigrationPolicy
        
        override func createDestinationInstances(forSource sInstance: NSManagedObject, in mapping: NSEntityMapping, manager: NSMigrationManager) throws {
            
            let userInfo = mapping.userInfo!
            let transformer = userInfo[CustomEntityMigrationPolicy.UserInfoKey.transformer]! as! CustomMapping.Transformer
            let sourceAttributesByDestinationKey = userInfo[CustomEntityMigrationPolicy.UserInfoKey.sourceAttributesByDestinationKey] as! [KeyPath: NSAttributeDescription]
            
            var dInstance: NSManagedObject?
            try transformer(
                UnsafeSourceObject(sInstance),
                {
                    let rawObject = NSEntityDescription.insertNewObject(
                        forEntityName: mapping.destinationEntityName!,
                        into: manager.destinationContext
                    )
                    dInstance = rawObject
                    return UnsafeDestinationObject(rawObject, sourceAttributesByDestinationKey)
                }
            )
            if let dInstance = dInstance {
                
                manager.associate(
                    sourceInstance: sInstance,
                    withDestinationInstance: dInstance,
                    for: mapping
                )
            }
        }
        
        override func createRelationships(forDestination dInstance: NSManagedObject, in mapping: NSEntityMapping, manager: NSMigrationManager) throws {
            
            try super.createRelationships(forDestination: dInstance, in: mapping, manager: manager)
        }
        
        
        // MARK: FilePrivate
        
        fileprivate enum UserInfoKey {
            
            fileprivate static let transformer = "CoreStore.CustomEntityMigrationPolicy.transformer"
            fileprivate static let sourceAttributesByDestinationKey = "CoreStore.CustomEntityMigrationPolicy.sourceAttributesByDestinationKey"
        }
    }
    
    
    // MARK: -
    
    private let entityMappings: Set<CustomMapping>
    
    private func resolveEntityMappings(sourceModel: NSManagedObjectModel, destinationModel: NSManagedObjectModel) -> (delete: Set<CustomMapping>, insert: Set<CustomMapping>, copy: Set<CustomMapping>, transform: Set<CustomMapping>) {
        
        var deleteMappings: Set<CustomMapping> = []
        var insertMappings: Set<CustomMapping> = []
        var copyMappings: Set<CustomMapping> = []
        var transformMappings: Set<CustomMapping> = []
        var allMappedSourceKeys: [KeyPath: KeyPath] = [:]
        var allMappedDestinationKeys: [KeyPath: KeyPath] = [:]
        
        let sourceRenamingIdentifiers = sourceModel.cs_resolvedRenamingIdentities()
        let sourceEntityNames = sourceModel.entitiesByName
        let destinationRenamingIdentifiers = destinationModel.cs_resolvedRenamingIdentities()
        let destinationEntityNames = destinationModel.entitiesByName
        
        let removedRenamingIdentifiers = Set(sourceRenamingIdentifiers.keys)
            .subtracting(destinationRenamingIdentifiers.keys)
        let addedRenamingIdentifiers = Set(destinationRenamingIdentifiers.keys)
            .subtracting(sourceRenamingIdentifiers.keys)
        let transformedRenamingIdentifiers = Set(destinationRenamingIdentifiers.keys)
            .subtracting(addedRenamingIdentifiers)
            .subtracting(removedRenamingIdentifiers)
        
        // First pass: resolve source-destination entities
        for mapping in self.entityMappings {
            
            switch mapping {
                
            case .deleteEntity(let sourceEntity):
                CoreStore.assert(
                    sourceEntityNames[sourceEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the source \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    allMappedSourceKeys[sourceEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for source entity name \"\(sourceEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                deleteMappings.insert(mapping)
                allMappedSourceKeys[sourceEntity] = ""
                
            case .insertEntity(let destinationEntity):
                CoreStore.assert(
                    destinationEntityNames[destinationEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the destination \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    allMappedDestinationKeys[destinationEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for destination entity name \"\(destinationEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                insertMappings.insert(mapping)
                allMappedDestinationKeys[destinationEntity] = ""
                
            case .transformEntity(let sourceEntity, let destinationEntity, _):
                CoreStore.assert(
                    sourceEntityNames[sourceEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the source \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    destinationEntityNames[destinationEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the destination \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    allMappedSourceKeys[sourceEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for source entity name \"\(sourceEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                CoreStore.assert(
                    allMappedDestinationKeys[destinationEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for destination entity name \"\(destinationEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                transformMappings.insert(mapping)
                allMappedSourceKeys[sourceEntity] = destinationEntity
                allMappedDestinationKeys[destinationEntity] = sourceEntity
                
            case .copyEntity(let sourceEntity, let destinationEntity):
                CoreStore.assert(
                    sourceEntityNames[sourceEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the source \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    destinationEntityNames[destinationEntity] != nil,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' passed to \(cs_typeName(CustomSchemaMappingProvider.self)) could not be mapped to any \(cs_typeName(NSEntityDescription.self)) from the destination \(cs_typeName(NSManagedObjectModel.self))."
                )
                CoreStore.assert(
                    sourceEntityNames[sourceEntity]!.versionHash == destinationEntityNames[destinationEntity]!.versionHash,
                    "A \(cs_typeName(CustomMapping.self)) with value '\(mapping)' was passed to \(cs_typeName(CustomSchemaMappingProvider.self)) but the \(cs_typeName(NSEntityDescription.self))'s \"versionHash\" of the source and destination entities do not match."
                )
                CoreStore.assert(
                    allMappedSourceKeys[sourceEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for source entity name \"\(sourceEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                CoreStore.assert(
                    allMappedDestinationKeys[destinationEntity] == nil,
                    "Duplicate \(cs_typeName(CustomMapping.self))s found for destination entity name \"\(destinationEntity)\" in \(cs_typeName(CustomSchemaMappingProvider.self))."
                )
                copyMappings.insert(mapping)
                allMappedSourceKeys[sourceEntity] = destinationEntity
                allMappedDestinationKeys[destinationEntity] = sourceEntity
            }
            
            for renamingIdentifier in transformedRenamingIdentifiers {
                
                let sourceEntity = sourceRenamingIdentifiers[renamingIdentifier]!.entity
                let destinationEntity = destinationRenamingIdentifiers[renamingIdentifier]!.entity
                let sourceEntityName = sourceEntity.name!
                let destinationEntityName = destinationEntity.name!
                switch (allMappedSourceKeys[sourceEntityName], allMappedDestinationKeys[destinationEntityName]) {
                    
                case (nil, nil):
                    if sourceEntity.versionHash == destinationEntity.versionHash {
                        
                        copyMappings.insert(
                            .copyEntity(
                                sourceEntity: sourceEntityName,
                                destinationEntity: destinationEntityName
                            )
                        )
                    }
                    else {
                        
                        transformMappings.insert(
                            .transformEntity(
                                sourceEntity: sourceEntityName,
                                destinationEntity: destinationEntityName,
                                transformer: CustomMapping.inferredTransformation
                            )
                        )
                    }
                    allMappedSourceKeys[sourceEntityName] = destinationEntityName
                    allMappedDestinationKeys[destinationEntityName] = sourceEntityName
                    
                case (""?, nil):
                    insertMappings.insert(.insertEntity(destinationEntity: destinationEntityName))
                    allMappedDestinationKeys[destinationEntityName] = ""
                    
                case (nil, ""?):
                    deleteMappings.insert(.deleteEntity(sourceEntity: sourceEntityName))
                    allMappedSourceKeys[sourceEntityName] = ""
                    
                default:
                    continue
                }
            }
            for renamingIdentifier in removedRenamingIdentifiers {
                
                let sourceEntity = sourceRenamingIdentifiers[renamingIdentifier]!.entity
                let sourceEntityName = sourceEntity.name!
                switch allMappedSourceKeys[sourceEntityName] {
                    
                case nil:
                    deleteMappings.insert(.deleteEntity(sourceEntity: sourceEntityName))
                    allMappedSourceKeys[sourceEntityName] = ""
                    
                default:
                    continue
                }
            }
            for renamingIdentifier in addedRenamingIdentifiers {
                
                let destinationEntity = destinationRenamingIdentifiers[renamingIdentifier]!.entity
                let destinationEntityName = destinationEntity.name!
                switch allMappedDestinationKeys[destinationEntityName] {
                    
                case nil:
                    insertMappings.insert(.insertEntity(destinationEntity: destinationEntityName))
                    allMappedDestinationKeys[destinationEntityName] = ""
                    
                default:
                    continue
                }
            }
        }
        return (deleteMappings, insertMappings, copyMappings, transformMappings)
    }
}