LeStorage/LeStorage/StoredCollection.swift

//
//  StoredCollection.swift
//  LeStorage
//
//  Created by Laurent Morvillier on 02/02/2024.
//

import Foundation

enum StoredCollectionError: Error {
    case unmanagedHTTPMethod(method: String)
    case missingApiCallCollection
    case missingInstance
}

protocol CollectionHolder {
    associatedtype Item
    
    var items: [Item] { get }
    func reset()
}

protocol SomeCollection: CollectionHolder, Identifiable {
    var resourceName: String { get }
    var synchronized: Bool { get }
    var hasLoaded: Bool { get }

    func allItems() -> [any Storable]
    
    func loadDataFromServerIfAllowed() async throws
    func loadCollectionsFromServerIfNoFile() async throws
    
}

extension Notification.Name {
    public static let CollectionDidLoad: Notification.Name = Notification.Name.init("notification.collectionDidLoad")
    public static let CollectionDidChange: Notification.Name = Notification.Name.init("notification.collectionDidChange")
}

public class StoredCollection<T: Storable>: RandomAccessCollection, SomeCollection, CollectionHolder {
    
    /// If true, will synchronize the data with the provided server located at the Store's synchronizationApiURL
    let synchronized: Bool
    
    /// Doesn't write the collection in a file
    fileprivate var _inMemory: Bool = false
    
    /// Indicates if the synchronized collection sends update to the API
    fileprivate var _sendsUpdate: Bool = true
    
    /// The list of stored items
    @Published public fileprivate(set) var items: [T] = []
    
    /// The reference to the Store
    fileprivate var _store: Store
    
    /// Provides fast access for instances if the collection has been instanced with [indexed] = true
    fileprivate var _indexes: [T.ID : T]? = nil
    
    /// Indicates whether the collection has changed, thus requiring a write operation
    fileprivate var _hasChanged: Bool = false {
        didSet {
            if self._hasChanged == true {
                
                self._scheduleWrite()
                DispatchQueue.main.async {
                    NotificationCenter.default.post(name: NSNotification.Name.CollectionDidChange, object: self)
                }
                self._hasChanged = false
            }
        }
    }
    
    /// Denotes a collection that loads and writes asynchronously
    fileprivate var asynchronousIO: Bool = true
    
    /// Indicates if the collection has loaded locally, with or without a file
    fileprivate(set) public var hasLoaded: Bool = false
    
    init(synchronized: Bool, store: Store, indexed: Bool = false, asynchronousIO: Bool = true, inMemory: Bool = false, sendsUpdate: Bool = true) {
        self.synchronized = synchronized
        self.asynchronousIO = asynchronousIO
        if indexed {
            self._indexes = [:]
        }
        self._inMemory = inMemory
        self._sendsUpdate = sendsUpdate
        self._store = store
        
        self._load()
    }
    
    fileprivate init() {
        self.synchronized = false
        self._store = Store.main
    }
    
    public static func placeholder() -> StoredCollection<T> {
        return StoredCollection<T>()
    }
    
    var resourceName: String {
        return T.resourceName()
    }
    
    // MARK: - Loading
    
    /// Migrates if necessary and asynchronously decodes the json file
    fileprivate func _load() {
        
        do {
            if self._inMemory {
                Task {
                    try await self.loadDataFromServerIfAllowed()
                }
            } else {
                try self._loadFromFile()
            }
        } catch {
            Logger.error(error)
        }
        
    }
    
    /// Starts the JSON file decoding synchronously or asynchronously
    fileprivate func _loadFromFile() throws {
            
        if self.asynchronousIO {
            Task(priority: .high) {
                try self._decodeJSONFile()
            }
        } else {
            try self._decodeJSONFile()
        }
            
    }
    
    /// Decodes the json file into the items array
    fileprivate func _decodeJSONFile() throws {
        
        let fileURL = try self._store.fileURL(type: T.self)
        
        if FileManager.default.fileExists(atPath: fileURL.path()) {
            let jsonString: String = try FileUtils.readFile(fileURL: fileURL)
            let decoded: [T] = try jsonString.decodeArray() ?? []
            for var item in decoded {
                item.store = self._store
            }
            if self.asynchronousIO {
                DispatchQueue.main.async {
                    self._setItems(decoded)
                    self._setAsLoaded()
                }
            } else {
                self._setItems(decoded)
                self._setAsLoaded()
            }
        } else {
            self._setAsLoaded()
        }
    }
    
    /// Sets the collection as loaded
    /// Send a CollectionDidLoad event
    fileprivate func _setAsLoaded() {
        self.hasLoaded = true
        DispatchQueue.main.async {
            NotificationCenter.default.post(name: NSNotification.Name.CollectionDidLoad, object: self)
        }
    }
    
    /// Sets a collection of items and indexes them
    fileprivate func _setItems(_ items: [T]) {
        self.items = items
        self._updateIndexIfNecessary()
    }
    
    /// Updates the whole index with the items array
    fileprivate func _updateIndexIfNecessary() {
        if let _ = self._indexes {
            self._indexes = self.items.dictionary { $0.id }
        }
    }
    
    /// Retrieves the data from the server and loads it into the items array
    public func loadDataFromServerIfAllowed() async throws {
        guard self.synchronized, !(self is StoredSingleton<T>) else {
            throw StoreError.cannotSyncCollection(name: self.resourceName)
        }
        do {
            let items: [T] = try await self._store.getItems()
            if items.count > 0 {
                DispatchQueue.main.async {
                    self._addOrUpdate(contentOfs: items, shouldSync: false)
                }
            }
        } catch {
            Logger.error(error)
        }
        self._setAsLoaded()
    }
    
    /// Loads the collection using the server data only if the collection file doesn't exists
    func loadCollectionsFromServerIfNoFile() async throws {
        let fileURL: URL = try self._store.fileURL(type: T.self)
        if !FileManager.default.fileExists(atPath: fileURL.path()) {
            try await self.loadDataFromServerIfAllowed()
        }
    }
    
    // MARK: - Basic operations
    
    /// Adds or updates the provided instance inside the collection
    /// Adds it if its id is not found, and otherwise updates it
    public func addOrUpdate(instance: T) throws {
        
        defer {
            self._hasChanged = true
        }
        
        var item = instance
        item.store = self._store
        
        // update
        if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
            self.items[index] = instance
            self._sendUpdateIfNecessary(instance)
        } else { // insert
            self.items.append(instance)
            self._sendInsertionIfNecessary(instance)
        }
        self._indexes?[instance.id] = instance

    }
    
    /// Sends a POST request for the instance, and changes the collection to perform a write
    public func writeChangeAndInsertOnServer(instance: T) {
        defer {
            self._hasChanged = true
        }
        self._sendInsertionIfNecessary(instance)
    }
    
    /// A method the treat the collection as a single instance holder
    func setSingletonNoSync(instance: T) {
        defer {
            self._hasChanged = true
        }
        self.items.removeAll()
        self.items.append(instance)
    }
    
    /// Deletes the instance in the collection by id
    public func delete(instance: T) throws {
        
        defer {
            self._hasChanged = true
        }
        
        try instance.deleteDependencies()
        self.items.removeAll { $0.id == instance.id }
        self._indexes?.removeValue(forKey: instance.id)
        
        self._sendDeletionIfNecessary(instance)
    }
    
    /// Deletes all items of the sequence by id
    public func delete(contentOfs sequence: any Sequence<T>) throws {
        
        defer {
            self._hasChanged = true
        }
        
        for instance in sequence {
            try instance.deleteDependencies()
            self.items.removeAll { $0.id == instance.id }
            self._indexes?.removeValue(forKey: instance.id)
            self._sendDeletionIfNecessary(instance)
        }
    }
    
    /// Adds or update a sequence of elements
    public func addOrUpdate(contentOfs sequence: any Sequence<T>) throws {
        self._addOrUpdate(contentOfs: sequence)
    }
    
    /// Adds or update a sequence of elements without synchronizing it
    func addOrUpdateNoSync(contentOfs sequence: any Sequence<T>) throws {
        self._addOrUpdate(contentOfs: sequence, shouldSync: false)
    }
    
    /// Inserts or updates all items in the sequence
    fileprivate func _addOrUpdate(contentOfs sequence: any Sequence<T>, shouldSync: Bool = true) {
        defer {
            self._hasChanged = true
        }
        
        for var instance in sequence {
            if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
                self.items[index] = instance
                if shouldSync {
                    self._sendUpdateIfNecessary(instance)
                }
            } else { // insert
                self.items.append(instance)
                if shouldSync {
                    self._sendInsertionIfNecessary(instance)
                }
            }
            instance.store = self._store
            self._indexes?[instance.id] = instance
        }
        
    }
    
    /// Returns the instance corresponding to the provided [id]
    public func findById(_ id: T.ID) -> T? {
        if let index = self._indexes, let instance = index[id] {
            return instance
        }
        return self.items.first(where: { $0.id == id })
    }
    
    /// Deletes the instance corresponding to the provided [id]
    public func deleteById(_ id: T.ID) throws {
        if let instance = self.findById(id) {
            try self.delete(instance: instance)
        }
    }
    
    /// Proceeds to "hard" delete the items without synchronizing them
    /// Also removes related API calls
    public func deleteDependencies(_ items: any Sequence<T>) {
        defer {
            self._hasChanged = true
        }
        for item in items {
            if let index = self.items.firstIndex(where: { $0.id == item.id }) {
                self.items.remove(at: index)
            }
            
            Task {
                do {
                    try await StoreCenter.main.deleteApiCallByDataId(type: T.self, id: item.stringId)
                } catch {
                    Logger.error(error)
                }
            }
        }
        
    }
    
    /// Proceeds to delete all instance of the collection, properly cleaning up dependencies and sending API calls
    public func deleteAll() throws {
        try self.delete(contentOfs: self.items)
    }
    
    // MARK: - Migrations

    /// Makes POST ApiCall for all items in the collection
    public func insertAllIntoCurrentService() {
        for item in self.items {
            self._sendInsertionIfNecessary(item)
        }
    }
    
    /// Makes POST ApiCall for the provided item
    public func insertIntoCurrentService(item: T) {
        self._sendInsertionIfNecessary(item)
    }
    
    // MARK: - SomeCall
    
    /// Returns the collection items as [any Storable]
    func allItems() -> [any Storable] {
        return self.items
    }
    
    // MARK: - File access
    
    /// Schedules a write operation
    fileprivate func _scheduleWrite() {
        
        guard !self._inMemory else { return }
        
        if self.asynchronousIO {
            DispatchQueue(label: "lestorage.queue.write", qos: .utility).asyncAndWait { // sync to make sure we don't have writes performed at the same time
                self._write()
            }
        } else {
            self._write()
        }
    }
    
    /// Writes all the items as a json array inside a file
    fileprivate func _write() {
//        Logger.log("Start write to \(T.fileName())...")
        do {
            let jsonString: String = try self.items.jsonString()
            try self._store.write(content: jsonString, fileName: T.fileName())
        } catch {
            Logger.error(error) // TODO how to notify the main project
        }
//        Logger.log("End write")
    }
    
    /// Simply clears the items of the collection
    func clear() {
        self.items.removeAll()
    }
    
    /// Removes the items of the collection and deletes the corresponding file
    public func reset() {
        self.items.removeAll()
        self._store.removeFile(type: T.self)
    }
    
    // MARK: - Reschedule calls
    
    /// Sends an insert api call for the provided
    /// Calls copyFromServerInstance on the instance with the result of the HTTP call
    /// - Parameters:
    ///   - instance: the object to POST
    fileprivate func _sendInsertionIfNecessary(_ instance: T) {
        guard self.synchronized else {
            return
        }
        Task {
            do {
                if let result = try await self._store.sendInsertion(instance) {
                    DispatchQueue.main.async {
                        self._hasChanged = instance.copyFromServerInstance(result)
                    }
                }
            } catch {
                Logger.error(error)
            }
        }
    }
    
    /// Sends an update api call for the provided [instance]
    /// - Parameters:
    ///   - instance: the object to PUT
    fileprivate func _sendUpdateIfNecessary(_ instance: T) {
        guard self.synchronized, self._sendsUpdate else {
            return
        }
        Task {
            do {
                try await self._store.sendUpdate(instance)
            } catch {
                Logger.error(error)
            }
        }
    }
    
    /// Sends an delete api call for the provided [instance]
    /// - Parameters:
    ///   - instance: the object to DELETE
    fileprivate func _sendDeletionIfNecessary(_ instance: T) {
        guard self.synchronized else {
            return
        }
        Task {
            do {
                try await self._store.sendDeletion(instance)
            } catch {
                Logger.error(error)
            }
        }
    }
    
    // MARK: - RandomAccessCollection
    
    public var startIndex: Int { return self.items.startIndex }

    public var endIndex: Int { return self.items.endIndex }

    public func index(after i: Int) -> Int {
       return self.items.index(after: i)
    }

    open subscript(index: Int) -> T {
        get {
            return self.items[index]
        }
        set(newValue) {
            self.items[index] = newValue
            self._hasChanged = true
        }
    }

}