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 SomeCollection : Identifiable {
    func allItems() -> [any Storable]
    func deleteById(_ id: String) throws
    func deleteApiCallById(_ id: String) 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 {
    
    /// If true, will synchronize the data with the provided server located at the Store's synchronizationApiURL
    let synchronized: Bool
    
    /// The list of stored items
    @Published public fileprivate(set) var items: [T] = []
    
    /// The reference to the Store
    fileprivate var _store: Store
    
    /// Notifies the closure when the loading is done
    fileprivate var loadCompletion: ((StoredCollection<T>) -> ())? = nil
    
    /// Provides fast access for instances if the collection has been instanced with [indexed] = true
    fileprivate var _index: [String : T]? = nil
    
    fileprivate var apiCallsCollection: StoredCollection<ApiCall<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 asynchronousIO
    fileprivate var asynchronousIO: Bool = true
    
    init(synchronized: Bool, store: Store, indexed: Bool = false, asynchronousIO: Bool = true, loadCompletion: ((StoredCollection<T>) -> ())? = nil) {
        self.synchronized = synchronized
        self.asynchronousIO = asynchronousIO
        if indexed {
            self._index = [:]
        }
        self._store = store
        self.loadCompletion = loadCompletion
        
        if synchronized {
            self.apiCallsCollection = StoredCollection<ApiCall<T>>(synchronized: false, store: store, loadCompletion: { apiCallCollection in
                self._rescheduleApiCalls()
            })
        }
        
        self._load()
    }
    
    // MARK: - Loading
    
    /// Migrates if necessary and asynchronously decodes the json file
    fileprivate func _load() {
        do {
            let url = try FileUtils.directoryURLForFileName(T.fileName())
            if FileManager.default.fileExists(atPath: url.path()) {
                
                if self.asynchronousIO {
                    Task(priority: .high) {
                        try await Store.main.performMigrationIfNecessary(self)
                        try self._decodeJSONFile()
                    }
                } else {
                    try self._decodeJSONFile()
                }
                
            }
            //            else {
            //                try? self.loadDataFromServer()
            //            }
        } catch {
            Logger.log(error)
        }
        
    }
    
    /// Decodes the json file into the items array
    fileprivate func _decodeJSONFile() throws {
        let jsonString = try FileUtils.readDocumentFile(fileName: T.fileName())
        if let decoded: [T] = try jsonString.decodeArray() {
            DispatchQueue.main.async {
                Logger.log("loaded \(T.fileName()) with \(decoded.count) items")
                self.items = decoded
                self._updateIndexIfNecessary()
                self.loadCompletion?(self)
                
                NotificationCenter.default.post(name: NSNotification.Name.CollectionDidLoad, object: self)
            }
        }
    }
    
    /// Updates the whole index with the items array
    fileprivate func _updateIndexIfNecessary() {
        if let _ = self._index {
            self._index = self.items.dictionary(handler: { $0.stringId })
        }
    }
    
    /// Retrieves the data from the server and loads it into the items array
    public func loadDataFromServer() throws {
        guard self.synchronized else {
            throw StoreError.unSynchronizedCollection
        }
        Task {
            do {
                self.items = try await self._store.getItems()
                self._hasChanged = true
            } catch {
                Logger.error(error)
            }
        }
    }
    
    // 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
        }
        
        // update
        if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
            self.items[index] = instance
            try self._sendUpdateIfNecessary(instance)
        } else { // insert
            self.items.append(instance)
            self._index?[instance.stringId] = instance
            try self._sendInsertionIfNecessary(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._index?.removeValue(forKey: instance.stringId)
        try self._sendDeletionIfNecessary(instance)
        
    }
    
    /// Inserts the whole sequence into the items array, no updates
    public func append(contentOfs sequence: any Sequence<T>) throws {
        defer {
            self._hasChanged = true
        }
        self.items.append(contentsOf: sequence)
        for instance in sequence {
            try self._sendInsertionIfNecessary(instance)
        }
    }
    
    /// Returns the instance corresponding to the provided [id]
    public func findById(_ id: String) -> T? {
        if let index = self._index, 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: String) throws {
        if let instance = self.findById(id) {
            try self.delete(instance: instance)
        }
    }
    
    /// Proceeds to "hard" delete the items without synchronizing them
    public func deleteDependencies(_ items: any Sequence<T>) {
        defer {
            self._hasChanged = true
        }
        for item in items {
            self.items.removeAll(where: { $0.id == item.id })
        }
    }
    
    // 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() {
        if self.asynchronousIO {
            DispatchQueue(label: "lestorage.queue.write", qos: .utility).sync { // 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...")
        do {
            let jsonString: String = try self.items.jsonString()
            let _ = try FileUtils.writeToDocumentDirectory(content: jsonString, fileName: T.fileName())
        } catch {
            Logger.error(error) // TODO how to notify the main project
        }
        Logger.log("End write")
    }
    
    // MARK: - Synchronization
    
    fileprivate func _callForInstance(_ instance: T, method: Method) throws -> ApiCall<T>? {
        guard let apiCallCollection = self.apiCallsCollection else {
            throw StoredCollectionError.missingApiCallCollection
        }

        if let existingCall = apiCallCollection.first(where: { $0.dataId == instance.id }) {
            switch existingCall.method {
            case Method.post.rawValue, Method.put.rawValue:
                existingCall.body = try instance.jsonString()
                return existingCall
            case Method.delete.rawValue:
                try self.deleteApiCallById(existingCall.id)
                return nil
            default:
                throw StoredCollectionError.unmanagedHTTPMethod(method: existingCall.method)
            }

        } else {
            return try self._createCall(instance, method: method)
        }
    }
    
    fileprivate func _createCall(_ instance: T, method: Method) throws -> ApiCall<T> {
        guard let baseURL = _store.service?.baseURL else {
            throw StoreError.missingService
        }
        let jsonString = try instance.jsonString()
        let url = baseURL + T.resourceName() + "/"
        return ApiCall(url: url, method: method.rawValue, dataId: String(instance.id), body: jsonString)
    }

    fileprivate func _prepareCall(apiCall: ApiCall<T>) throws {
        apiCall.lastAttemptDate = Date()
        apiCall.attemptsCount += 1
        try self.apiCallsCollection?.addOrUpdate(instance: apiCall)
    }
    
    /// Sends an insert api call for the provided [instance]
    fileprivate func _sendInsertionIfNecessary(_ instance: T) throws {
        guard self.synchronized else {
            return
        }
        
        if let apiCall = try self._callForInstance(instance, method: Method.post) {
            try self._prepareCall(apiCall: apiCall)
            
            Task {
                do {
                    _ = try await self._store.execute(apiCall: apiCall)
                } catch {
                    self.rescheduleApiCallsIfNecessary()
                    Logger.error(error)
                }
            }

        }
        
    }
    
    /// Sends an update api call for the provided [instance]
    fileprivate func _sendUpdateIfNecessary(_ instance: T) throws {
        guard self.synchronized else {
            return
        }
        
        if let apiCall = try self._callForInstance(instance, method: Method.put) {
            try self._prepareCall(apiCall: apiCall)
            Task {
                do {
                    _ = try await self._store.execute(apiCall: apiCall)
                } catch {
                    Logger.error(error)
                    self.rescheduleApiCallsIfNecessary()
                }
            }
        }

        
        
//        Task {
//            do {
//                if let apiCall = try self._callForInstance(instance, method: Method.put) {
//                    try self._prepareCall(apiCall: apiCall)
//                    _ = try await self._store.execute(apiCall: apiCall)
//                }
//                
////                let _ = try await self._store.service?.update(instance)
//            } catch {
//                Logger.error(error)
//                self.rescheduleApiCallsIfNecessary()
//            }
//        }
        
    }
    
    /// Sends an delete api call for the provided [instance]
    fileprivate func _sendDeletionIfNecessary(_ instance: T) throws {
        guard self.synchronized else {
            return
        }
        
        if let apiCall = try self._callForInstance(instance, method: Method.delete) {
            try self._prepareCall(apiCall: apiCall)
            Task {
                do {
                    _ = try await self._store.execute(apiCall: apiCall)
                } catch {
                    Logger.error(error)
                    self.rescheduleApiCallsIfNecessary()
                }
            }
            
        }
        
        
    }
    
    // MARK: - Reschedule calls
    
    /// number of time an execution loop has been called
    fileprivate var _attemptLoops: Int = 0
    
    /// Indicates if the collection is currently retrying ApiCalls
    fileprivate var _isRetryingCalls: Bool = false
    
    func rescheduleApiCallsIfNecessary() {
        if !self._isRetryingCalls {
            self._rescheduleApiCalls()
        }
    }
    
    fileprivate func _rescheduleApiCalls() {

        guard let apiCallsCollection, apiCallsCollection.isNotEmpty else {
            return
        }
        
        self._isRetryingCalls = true
        self._attemptLoops += 1
        
        Task {
            
            let delay = pow(2, self._attemptLoops)
            let seconds = NSDecimalNumber(decimal: delay).intValue
            Logger.log("wait for \(seconds) sec")
            try await Task.sleep(until: .now + .seconds(seconds))
            
            let apiCallsCopy = apiCallsCollection.items
            for apiCall in apiCallsCopy {
                apiCall.attemptsCount += 1
                apiCall.lastAttemptDate = Date()
                do {
                    let _ = try await Store.main.execute(apiCall: apiCall)
                } catch {
                    Logger.error(error)
                }
            }
            
            if apiCallsCollection.isEmpty {
                self._isRetryingCalls = false
            } else {
                self._rescheduleApiCalls()
            }
            
        }
        
    }
        
    func deleteApiCallById(_ id: String) throws {
        guard let apiCallsCollection else {
            throw StoreError.apiCallCollectionNotRegistered(type: T.resourceName())
        }
        try apiCallsCollection.deleteById(id)
    }
    
    // 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
        }
    }

//    public func append(_ newElement: T) {
//        self.addOrUpdate(instance: newElement)
//    }
    
}