//
//  ObjectProxy.swift
//  CoreStore
//
//  Copyright © 2020 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: - ObjectProxy

/**
 An `ObjectProxy` is only used when overriding getters and setters for `CoreStoreObject` properties. Custom getters and setters are implemented as a closure that "overrides" the default property getter/setter. The closure receives an `ObjectProxy<O>`, which acts as a fast, type-safe KVC interface for `CoreStoreObject`. The reason a `CoreStoreObject` instance is not passed directly is because the Core Data runtime is not aware of `CoreStoreObject` properties' static typing, and so loading those info every time KVO invokes this accessor method incurs a heavy performance hit (especially in KVO-heavy operations such as `ListMonitor` observing.) When accessing the property value from `ObjectProxy<O>`, make sure to use `ObjectProxy<O>.$property.primitiveValue` instead of `ObjectProxy<O>.$property.value`, which would execute the same accessor again recursively.
 */
@dynamicMemberLookup
public struct ObjectProxy<O: CoreStoreObject> {

    /**
     Returns the value for the property identified by a given key.
     */
    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Stored<V>>) -> FieldProxy<V> {

        return .init(rawObject: self.rawObject, keyPath: member)
    }

    /**
     Returns the value for the property identified by a given key.
     */
    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Virtual<V>>) -> FieldProxy<V> {

        return .init(rawObject: self.rawObject, keyPath: member)
    }

    /**
     Returns the value for the property identified by a given key.
     */
    public subscript<OBase, V>(dynamicMember member: KeyPath<O, FieldContainer<OBase>.Coded<V>>) -> FieldProxy<V> {

        return .init(rawObject: self.rawObject, keyPath: member)
    }


    // MARK: Internal

    internal let rawObject: CoreStoreManagedObject

    internal init(_ rawObject: CoreStoreManagedObject) {

        self.rawObject = rawObject
    }


    // MARK: - FieldProxy

    public struct FieldProxy<V> {

        // MARK: Public

        /**
         Returns the value for the specified property from the object’s private internal storage.

         Accessing this property does not invoke the access notification methods (`willAccessValue(forKey:)` and `didAccessValue(forKey:)`). This method is used primarily to implement custom accessor methods that need direct access to the object's private storage.
         */
        public var primitiveValue: V? {

            get {

                return self.getPrimitiveValue()
            }
            nonmutating set {

                self.setPrimitiveValue(newValue)
            }
        }

        /**
         Returns the value for the property identified by a given key.

         Accessing this property triggers the access notification methods (`willAccessValue(forKey:)` and `didAccessValue(forKey:)`).
         */
        public var value: V {

            get {

                return self.getValue()
            }
            nonmutating set {

                self.setValue(newValue)
            }
        }


        // MARK: Internal

        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Stored<V>>) {

            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
        }

        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Virtual<V>>) {

            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
        }

        internal init<OBase>(rawObject: CoreStoreManagedObject, keyPath: KeyPath<O, FieldContainer<OBase>.Coded<V>>) {

            self.init(rawObject: rawObject, field: O.meta[keyPath: keyPath])
        }

        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Stored<V>) {

            let keyPathString = field.keyPath
            self.getValue = {

                return type(of: field).read(field: field, for: rawObject) as! V
            }
            self.setValue = {

                type(of: field).modify(field: field, for: rawObject, newValue: $0)
            }
            self.getPrimitiveValue = {

                return V.cs_fromFieldStoredNativeType(
                    rawObject.primitiveValue(forKey: keyPathString) as! V.FieldStoredNativeType
                )
            }
            self.setPrimitiveValue = {

                rawObject.setPrimitiveValue(
                    $0.cs_toFieldStoredNativeType(),
                    forKey: keyPathString
                )
            }
        }

        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Virtual<V>) {

            let keyPathString = field.keyPath
            self.getValue = {

                return type(of: field).read(field: field, for: rawObject) as! V
            }
            self.setValue = {

                type(of: field).modify(field: field, for: rawObject, newValue: $0)
            }
            self.getPrimitiveValue = {

                switch rawObject.primitiveValue(forKey: keyPathString) {

                case let value as V:
                    return value

                case nil,
                     is NSNull,
                     _? /* any other unrelated type */ :
                    return nil
                }
            }
            self.setPrimitiveValue = {

                rawObject.setPrimitiveValue(
                    $0,
                    forKey: keyPathString
                )
            }
        }

        internal init<OBase>(rawObject: CoreStoreManagedObject, field: FieldContainer<OBase>.Coded<V>) {

            let keyPathString = field.keyPath
            self.getValue = {

                return type(of: field).read(field: field, for: rawObject) as! V
            }
            self.setValue = {

                type(of: field).modify(field: field, for: rawObject, newValue: $0)
            }
            self.getPrimitiveValue = {

                switch rawObject.primitiveValue(forKey: keyPathString) {

                case let valueBox as Internals.AnyFieldCoder.TransformableDefaultValueCodingBox:
                    rawObject.setPrimitiveValue(valueBox.value, forKey: keyPathString)
                    return valueBox.value as? V

                case let value as V:
                    return value

                case nil,
                     is NSNull,
                      _? /* any other unrelated type */ :
                     return nil
                }
            }
            self.setPrimitiveValue = {

                rawObject.setPrimitiveValue(
                    $0,
                    forKey: keyPathString
                )
            }
        }


        // MARK: Private

        private let getValue: () -> V
        private let setValue: (V) -> Void
        private let getPrimitiveValue: () -> V?
        private let setPrimitiveValue: (V?) -> Void
    }
}