//
//  From.swift
//  CoreStore
//
//  Copyright © 2018 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 Foundation
import CoreData


// MARK: - From

/**
 A `From` clause specifies the source entity and source persistent store for fetch and query methods. A common usage is to just indicate the entity:
 ```
 let person = transaction.fetchOne(From<Person>())
 ```
 For cases where multiple `NSPersistentStore`s contain the same entity, the source configuration's name needs to be specified as well:
 ```
 let person = transaction.fetchOne(From<Person>("Configuration1"))
 ```
 */
public struct From<O: DynamicObject> {
    
    /**
     The associated `NSManagedObject` or `CoreStoreObject` entity class
     */
    public let entityClass: O.Type
    
    /**
     The `NSPersistentStore` configuration names to associate objects from.
     May contain `String`s to pertain to named configurations, or `nil` to pertain to the default configuration
     */
    public let configurations: [ModelConfiguration]?
    
    /**
     Initializes a `From` clause.
     ```
     let people = transaction.fetchAll(From<MyPersonEntity>())
     ```
     */
    public init() {
        
        self.init(
            entityClass: O.self,
            configurations: nil
        )
    }
    
    /**
     Initializes a `From` clause with the specified entity type.
     ```
     let people = transaction.fetchAll(From<MyPersonEntity>())
     ```
     - parameter entity: the associated `NSManagedObject` or `CoreStoreObject` type
     */
    public init(
        _ entity: O.Type
    ) {

        self.init(
            entityClass: entity,
            configurations: nil
        )
    }
    
    /**
     Initializes a `From` clause with the specified configurations.
     ```
     let people = transaction.fetchAll(From<MyPersonEntity>(nil, "Configuration1"))
     ```
     - parameter configuration: the `NSPersistentStore` configuration name to associate objects from. This parameter is required if multiple configurations contain the created `NSManagedObject` or `CoreStoreObject`'s entity type. Set to `nil` to use the default configuration.
     - parameter otherConfigurations: an optional list of other configuration names to associate objects from (see `configuration` parameter)
     */
    public init(
        _ configuration: ModelConfiguration,
        _ otherConfigurations: ModelConfiguration...
    ) {

        self.init(
            entityClass: O.self,
            configurations: [configuration] + otherConfigurations
        )
    }
    
    /**
     Initializes a `From` clause with the specified configurations.
     ```
     let people = transaction.fetchAll(From<MyPersonEntity>(["Configuration1", "Configuration2"]))
     ```
     - parameter configurations: a list of `NSPersistentStore` configuration names to associate objects from. This parameter is required if multiple configurations contain the created `NSManagedObject` or `CoreStoreObject`'s entity type. Set to `nil` to use the default configuration.
     */
    public init(
        _ configurations: [ModelConfiguration]
    ) {

        self.init(
            entityClass: O.self,
            configurations: configurations
        )
    }
    
    /**
     Initializes a `From` clause with the specified configurations.
     ```
     let people = transaction.fetchAll(From(MyPersonEntity.self, nil, "Configuration1"))
     ```
     - parameter entity: the associated `NSManagedObject` or `CoreStoreObject` type
     - parameter configuration: the `NSPersistentStore` configuration name to associate objects from. This parameter is required if multiple configurations contain the created `NSManagedObject` or `CoreStoreObject`'s entity type. Set to `nil` to use the default configuration.
     - parameter otherConfigurations: an optional list of other configuration names to associate objects from (see `configuration` parameter)
     */
    public init(
        _ entity: O.Type,
        _ configuration: ModelConfiguration,
        _ otherConfigurations: ModelConfiguration...
    ) {

        self.init(
            entityClass: entity,
            configurations: [configuration] + otherConfigurations
        )
    }
    
    /**
     Initializes a `From` clause with the specified configurations.
     ```
     let people = transaction.fetchAll(From(MyPersonEntity.self, ["Configuration1", "Configuration1"]))
     ```
     - parameter entity: the associated `NSManagedObject` or `CoreStoreObject` type
     - parameter configurations: a list of `NSPersistentStore` configuration names to associate objects from. This parameter is required if multiple configurations contain the created `NSManagedObject` or `CoreStoreObject`'s entity type. Set to `nil` to use the default configuration.
     */
    public init(
        _ entity: O.Type,
        _ configurations: [ModelConfiguration]
    ) {

        self.init(
            entityClass: entity,
            configurations: configurations
        )
    }
    
    
    // MARK: Internal
    
    internal let findPersistentStores: (_ context: NSManagedObjectContext) -> [NSPersistentStore]?
    
    internal init(
        entityClass: O.Type,
        configurations: [ModelConfiguration]?,
        findPersistentStores: @escaping (
            _ context: NSManagedObjectContext
        ) -> [NSPersistentStore]?
    ) {

        self.entityClass = entityClass
        self.configurations = configurations
        self.findPersistentStores = findPersistentStores
    }
    
    internal func applyToFetchRequest<U>(
        _ fetchRequest: Internals.CoreStoreFetchRequest<U>,
        context: NSManagedObjectContext,
        applyAffectedStores: Bool = true
    ) throws(CoreStoreError) {

        guard let parentStack = context.parentStack else {

            Internals.log(
                .warning,
                message: "Attempted to perform a fetch but the \(Internals.typeName(DataStack.self)) has already been deallocated."
            )
            throw CoreStoreError.unknown
        }
        fetchRequest.entity = parentStack.entityDescription(for: Internals.EntityIdentifier(self.entityClass))!
        guard applyAffectedStores else {
            
            return
        }
        do {

            try self.applyAffectedStoresForFetchedRequest(fetchRequest, context: context)
        }
        catch {

            Internals.log(
                error,
                "Attempted to perform a fetch but could not find any persistent store for the entity \(Internals.typeName(fetchRequest.entityName))"
            )
            throw error
        }
    }
    
    internal func applyAffectedStoresForFetchedRequest<U>(
        _ fetchRequest: Internals.CoreStoreFetchRequest<U>,
        context: NSManagedObjectContext
    ) throws(CoreStoreError) {

        let stores = self.findPersistentStores(context)
        fetchRequest.affectedStores = stores
        if stores?.isEmpty == false {

            return
        }
        throw CoreStoreError.persistentStoreNotFound(entity: self.entityClass)
    }
    
    
    // MARK: Private
    
    private init(
        entityClass: O.Type,
        configurations: [ModelConfiguration]?
    ) {

        self.entityClass = entityClass
        self.configurations = configurations
        
        let entityIdentifier = Internals.EntityIdentifier(entityClass)
        if let configurations = configurations {
            
            let configurationsSet = Set(configurations.map({ $0 ?? DataStack.defaultConfigurationName }))
            self.findPersistentStores = { (context: NSManagedObjectContext) -> [NSPersistentStore]? in
                
                return context.parentStack?.persistentStores(for: entityIdentifier)?.filter {
                    
                    return configurationsSet.contains($0.configurationName)
                }
            }
        }
        else {
            
            self.findPersistentStores = { (context: NSManagedObjectContext) -> [NSPersistentStore]? in
                
                return context.parentStack?.persistentStores(for: entityIdentifier)
            }
        }
    }
}