LeStorage/LeStorage/StoredCollection+Sync.swift

//
//  StoredCollection.swift
//  LeStorage
//
//  Created by Laurent Morvillier on 11/10/2024.
//

import Foundation

extension StoredCollection: SomeSyncedCollection where T : SyncedStorable {
    
    /// Migrates if necessary and asynchronously decodes the json file
    func load() async {
        do {
            if self.inMemory {
                try await self.loadDataFromServerIfAllowed()
            } else {
                try self.loadFromFile()
            }
        } catch {
            Logger.error(error)
        }
    }
    
    /// 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()
        }
    }
    
    func loadDataFromServerIfAllowed() async throws {
        try await self.loadDataFromServerIfAllowed(clear: false)
    }
    
    /// Retrieves the data from the server and loads it into the items array
    public func loadDataFromServerIfAllowed(clear: Bool = false) async throws {
        guard !(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 {
                    if clear {
                        self.clear()
                    }
                    self.addOrUpdateNoSync(contentOfs: items)
                }
            }
        } catch {
            Logger.error(error)
        }
        self.setAsLoaded()
    }
    
    /// Updates a local item from a server instance. This method is typically used when the server makes update
    /// to an object when it's inserted. The StoredCollection possibly needs to update its own copy with new values.
    /// - serverInstance: the instance of the object on the server
    func updateFromServerInstance(_ serverInstance: T) {
        DispatchQueue.main.async {
            if let localInstance = self.findById(serverInstance.id) {
                localInstance.copy(from: serverInstance)
                self.setChanged()
//                let modified = localInstance.copyFromServerInstance(serverInstance)
//                if modified {
//                    self.setChanged()
//                }
            }
        }
    }
    
    // MARK: - Basic operations
    
    /// Adds or update an instance without synchronizing it
    func addOrUpdateNoSync(_ instance: T) throws {
        self.addOrUpdateItem(instance: instance)
    }
    
    /// Adds or update a sequence of elements without synchronizing it
    func addOrUpdateNoSync(contentOfs sequence: any Sequence<T>) {
        self.addSequence(sequence)
    }
    
    /// Deletes the instance in the collection without synchronization
    func deleteNoSync(instance: T) throws {
        defer {
            self.setChanged()
        }
        self.deleteItem(instance)
    }
    
    /// Deletes the instance in the collection without synchronization
    func deleteByStringIdNoSync(_ id: String) {
        defer {
            self.setChanged()
        }
        let realId = T.buildRealId(id: id)
        if let instance = self.findById(realId) {
            self.deleteItem(instance)
        }
    }

    /// Adds or update an instance and writes
    public func addOrUpdate(instance: T) {
        defer {
            self.setChanged()
        }
        
        instance.lastUpdate = Date()
        if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
            self.updateItem(instance, index: index)
            self._sendUpdate(instance)
        } else {
            self.addItem(instance: instance)
            self._sendInsertion(instance)
        }
    }
    
    /// Adds or update a sequence and writes
    public func addOrUpdate(contentOfs sequence: any Sequence<T>) {
        defer {
            self.setChanged()
        }
        
        let date = Date()
        let batch = OperationBatch<T>()
        
        for instance in sequence {
            instance.lastUpdate = date
            if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
                self.updateItem(instance, index: index)
                batch.addUpdate(instance)
//                self._sendUpdateIfNecessary(instance)
            } else { // insert
                self.addItem(instance: instance)
                batch.addInsert(instance)
//                self._sendInsertionIfNecessary(instance)
            }
        }
        
        self._sendOperationBatch(batch)

    }
    
    /// Proceeds to delete all instance of the collection, properly cleaning up dependencies and sending API calls
    public func deleteAll() throws {
        self.delete(contentOfs: self.items)
    }

    /// Deletes all items of the sequence by id and sets the collection as changed to trigger a write
    public func delete(contentOfs sequence: any Sequence<T>) {

        defer {
            self.setChanged()
        }

        for instance in sequence {
            self.deleteItem(instance)
            StoreCenter.main.createDeleteLog(instance)
        }
        
        let batch = OperationBatch<T>()
        batch.deletes = Array(sequence)
        self._sendOperationBatch(batch)
    }
    
    /// Deletes an instance and writes
    public func delete(instance: T) {
        defer {
            self.setChanged()
        }
        self._deleteNoWrite(instance: instance)
    }
    
    /// Deletes an instance without writing, logs the operation and sends an API call
    fileprivate func _deleteNoWrite(instance: T) {
        self.deleteItem(instance)
        StoreCenter.main.createDeleteLog(instance)
        
        self._sendDeletion(instance)
    }
    
    public func deleteDependencies(_ items: any Sequence<T>) {
        self.delete(contentOfs: items)
    }
    
    // MARK: - Send requests
    
    fileprivate func _sendInsertion(_ instance: T) {
        self._sendOperationBatch(OperationBatch(insert: instance))
    }
    
    fileprivate func _sendUpdate(_ instance: T) {
        self._sendOperationBatch(OperationBatch(update: instance))
    }
    
    fileprivate func _sendDeletion(_ instance: T) {
        self._sendOperationBatch(OperationBatch(delete: instance))
    }
    
    fileprivate func _sendOperationBatch(_ batch: OperationBatch<T>) {
        Task {
            do {
                let success = try await StoreCenter.main.sendOperationBatch(batch)
                for item in success {
                    self.updateFromServerInstance(item)
                }
            } catch {
                Logger.error(error)
            }
        }
    }
    
    /// 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) {
//
//        Task {
//            do {
//                if let result = try await self.store.sendInsertion(instance) {
//                    self.updateFromServerInstance(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) {
//        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) {
//        Task {
//            do {
//                try await self.store.sendDeletion(instance)
//            } catch {
//                Logger.error(error)
//            }
//        }
//    }
    
    // MARK: - Synchronization
    
    /// Adds or update an instance if it is newer than the local instance 
    func addOrUpdateIfNewer(_ instance: T, shared: Bool) {
        defer {
            self.setChanged()
        }

        if let index = self.items.firstIndex(where: { $0.id == instance.id }) {
            let localInstance = self.items[index]
            if instance.lastUpdate > localInstance.lastUpdate {
                self.updateItem(instance, index: index)
            }
        } else { // insert
            if shared {
                instance.shared = true
            }
            self.addItem(instance: instance)
        }

    }
    
    // MARK: - Migrations
    
    /// Sends a POST request for the instance, and changes the collection to perform a write
    public func writeChangeAndInsertOnServer(instance: T) {
        defer {
            self.setChanged()
        }
        self._sendInsertion(instance)
    }
    
}

class OperationBatch<T> {
    var inserts: [T] = []
    var updates: [T] = []
    var deletes: [T] = []
    
    init() {
        
    }
    init(insert: T) {
        self.inserts = [insert]
    }
    init(update: T) {
        self.updates = [update]
    }
    init(delete: T) {
        self.deletes = [delete]
    }
    
    func addInsert(_ instance: T) {
        self.inserts.append(instance)
    }
    func addUpdate(_ instance: T) {
        self.updates.append(instance)
    }
    func addDelete(_ instance: T) {
        self.deletes.append(instance)
    }
}