import Foundation

// ──────────────────────────────────────────────────────────────────────
// PendingOperationsQueue.swift
// Persistent queue for companion API operations that failed due to
// network issues. Retries automatically when the WebSocket reconnects.
// Stored as JSON in Documents so it survives app restarts.
// ──────────────────────────────────────────────────────────────────────

struct PendingOperation: Codable, Identifiable {
    let id: UUID
    let type: OperationType
    let payload: [String: String]
    let createdAt: Date
    var retryCount: Int
    let maxRetries: Int
    
    enum OperationType: String, Codable {
        case metadataEdit       // PATCH /batch-edit-metadata
        case coverArtUpload     // POST /library/cover-art-by-path
        case coverArtDelete     // DELETE /library/cover-art/{id}
        case tagCleanup         // POST /tag-cleanup
    }
    
    init(type: OperationType, payload: [String: String], maxRetries: Int = 5) {
        self.id = UUID()
        self.type = type
        self.payload = payload
        self.createdAt = Date()
        self.retryCount = 0
        self.maxRetries = maxRetries
    }
    
    var isExpired: Bool { retryCount >= maxRetries }
    
    var displayDescription: String {
        switch type {
        case .metadataEdit:
            return "Edit: \(payload["album"] ?? payload["artist"] ?? "metadata")"
        case .coverArtUpload:
            return "Cover art: \(payload["path"] ?? "upload")"
        case .coverArtDelete:
            return "Remove cover: \(payload["songId"] ?? "")"
        case .tagCleanup:
            return "Tag cleanup: \(payload["path"] ?? "")"
        }
    }
}

class PendingOperationsQueue: ObservableObject {
    static let shared = PendingOperationsQueue()
    
    @Published private(set) var operations: [PendingOperation] = []
    
    private let fileURL: URL
    private var isProcessing = false
    
    var count: Int { operations.count }
    var isEmpty: Bool { operations.isEmpty }
    
    private init() {
        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        fileURL = docs.appendingPathComponent("pending_operations.json")
        loadFromDisk()
    }
    
    // MARK: - Enqueue
    
    func enqueue(_ op: PendingOperation) {
        operations.append(op)
        saveToDisk()
        DebugLogger.shared.log(
            "Pending op queued: \(op.type.rawValue) (\(operations.count) total)",
            category: "PendingOps"
        )
    }
    
    /// Convenience: enqueue a metadata edit that failed.
    func enqueueMetadataEdit(paths: [String], tags: [String: String]) {
        var payload = tags
        payload["_paths"] = paths.joined(separator: "\n")
        enqueue(PendingOperation(type: .metadataEdit, payload: payload))
    }
    
    /// Convenience: enqueue a cover art upload that failed.
    func enqueueCoverArtUpload(relativePath: String) {
        enqueue(PendingOperation(
            type: .coverArtUpload,
            payload: ["path": relativePath]
        ))
    }
    
    // MARK: - Process
    
    /// Retry all pending operations. Call when WebSocket reconnects
    /// or when the app returns to foreground with a connection.
    func processAll() {
        guard !isProcessing, !operations.isEmpty else { return }
        isProcessing = true
        
        DebugLogger.shared.log(
            "Processing \(operations.count) pending operations",
            category: "PendingOps"
        )
        
        Task {
            var remaining: [PendingOperation] = []
            
            for var op in operations {
                if op.isExpired {
                    DebugLogger.shared.log(
                        "Dropping expired op: \(op.displayDescription) (\(op.retryCount) retries)",
                        category: "PendingOps"
                    )
                    continue
                }
                
                let success = await retryOperation(op)
                if !success {
                    op.retryCount += 1
                    remaining.append(op)
                }
            }
            
            // Copy to let for safe capture in MainActor.run (Swift 6 concurrency)
            let finalRemaining = remaining
            
            await MainActor.run {
                self.operations = finalRemaining
                self.saveToDisk()
                self.isProcessing = false
                
                if finalRemaining.isEmpty {
                    DebugLogger.shared.log("All pending ops completed", category: "PendingOps")
                } else {
                    DebugLogger.shared.log(
                        "\(finalRemaining.count) ops still pending after retry",
                        category: "PendingOps"
                    )
                }
            }
        }
    }
    
    private func retryOperation(_ op: PendingOperation) async -> Bool {
        let api = CompanionAPIService.shared
        
        switch op.type {
        case .metadataEdit:
            let paths = (op.payload["_paths"] ?? "").split(separator: "\n").map(String.init)
            guard !paths.isEmpty else { return true } // nothing to do = success
            var tags: [String: String] = op.payload
            tags.removeValue(forKey: "_paths")
            
            let request = BatchMetadataEditRequest(
                relativePaths: paths,
                title: tags["title"],
                artist: tags["artist"],
                album: tags["album"],
                albumArtist: tags["album_artist"],
                genre: tags["genre"],
                year: tags["year"].flatMap { Int($0) }
            )
            
            do {
                _ = try await api.batchEditMetadata(request)
                return true
            } catch {
                return false
            }
            
        case .coverArtUpload:
            // Cover art data isn't persisted in the queue (too large).
            // Mark as expired — user will need to re-apply.
            return false
            
        case .coverArtDelete:
            guard let songId = op.payload["songId"] else { return true }
            do {
                try await api.deleteCoverArt(songId: songId)
                return true
            } catch {
                return false
            }
            
        case .tagCleanup:
            // Tag cleanup is idempotent — safe to retry
            return false // Not implemented yet
        }
    }
    
    // MARK: - Remove
    
    func remove(_ op: PendingOperation) {
        operations.removeAll { $0.id == op.id }
        saveToDisk()
    }
    
    func clearAll() {
        operations.removeAll()
        saveToDisk()
    }
    
    // MARK: - Persistence
    
    private func saveToDisk() {
        if let data = try? JSONEncoder().encode(operations) {
            try? data.write(to: fileURL, options: .atomic)
        }
    }
    
    func loadFromDisk() {
        guard let data = try? Data(contentsOf: fileURL),
              let ops = try? JSONDecoder().decode([PendingOperation].self, from: data)
        else { return }
        operations = ops
    }
    
    // MARK: - Export/Import (for backup system)
    
    func exportData() -> Data? {
        try? JSONEncoder().encode(operations)
    }
    
    func importData(_ data: Data) {
        guard let ops = try? JSONDecoder().decode([PendingOperation].self, from: data) else { return }
        operations = ops
        saveToDisk()
    }
}