import ByreAPI
import Darwin
import Foundation
import OpenAPIRuntime

typealias ClientRequest = Components.Schemas.ClientRequest
typealias ClientReply = Components.Schemas.ClientReply

private let retryAfter = Duration.seconds(2)
private let maxOutput = 64 << 10
private let maxMessage = 256 << 20
private let maxRead = 64 << 20
private let copyTimeoutMs = 10 * 60 * 1000

@MainActor
final class Remote {
    let api: API
    private let hands = Hands()
    private var ws: URLSessionWebSocketTask?
    private var stopped = false

    init(api: API) {
        self.api = api
    }

    func start() {
        guard !stopped else {
            return
        }
        let task = api.session.webSocketTask(with: api.url("/api/clients/connect", scheme: "wss"))
        task.maximumMessageSize = maxMessage
        ws = task
        task.resume()
        receive(task)
    }

    func stop() {
        stopped = true
        ws?.cancel(with: .normalClosure, reason: nil)
        ws = nil
        hands.stop()
    }

    private func receive(_ task: URLSessionWebSocketTask) {
        task.receive { result in
            Task { @MainActor in
                guard self.ws === task, !self.stopped else {
                    return
                }
                switch result {
                case .success(.string(let s)):
                    self.handle(task, Data(s.utf8))
                    self.receive(task)
                case .success(.data(let d)):
                    self.handle(task, d)
                    self.receive(task)
                case .success:
                    self.receive(task)
                case .failure(let error):
                    log.info("client connection closed: \(errorText(error), privacy: .public)")
                    self.ws = nil
                    try? await Task.sleep(for: retryAfter)
                    self.start()
                }
            }
        }
    }

    private func handle(_ task: URLSessionWebSocketTask, _ data: Data) {
        let req: ClientRequest
        do {
            req = try jsonDecoder().decode(ClientRequest.self, from: data)
        } catch {
            log.error("decode client request: \(String(describing: error), privacy: .public)")
            return
        }
        log.info("client request \(req.id, privacy: .public): \(req.op.rawValue, privacy: .public)")
        Task {
            var reply: ClientReply
            do {
                reply = try await perform(req)
            } catch {
                reply = ClientReply(id: req.id, error: errorText(error))
            }
            do {
                try await task.send(.string(String(decoding: try JSONEncoder().encode(reply), as: UTF8.self)))
            } catch {
                log.error("send client reply \(req.id, privacy: .public): \(errorText(error), privacy: .public)")
            }
        }
    }

    private func perform(_ req: ClientRequest) async throws -> ClientReply {
        switch req.op {
        case .bash:
            let home = FileManager.default.homeDirectoryForCurrentUser.path
            let (code, output) = try await spawn(["/bin/zsh", "-l", "-c", req.command ?? ""], in: home, timeoutMs: req.timeoutMs ?? 120_000)
            return ClientReply(id: req.id, exitCode: code, output: output)
        case .upload:
            try await upload(transfer: req.transfer ?? "", to: req.dest ?? "")
            return ClientReply(id: req.id)
        case .download:
            try await download(req.path ?? "", transfer: req.transfer ?? "")
            return ClientReply(id: req.id)
        case .readFile:
            let path = req.path ?? ""
            let data = try await Task.detached {
                try readFile(path)
            }.value
            return ClientReply(id: req.id, data: Base64EncodedData(data))
        case .writeFile:
            let path = req.path ?? ""
            let data = Data(req.data?.data ?? [])
            try await Task.detached {
                try writeFile(path, data)
            }.value
            return ClientReply(id: req.id)
        case .hands:
            let result = try await hands.call(req.tool ?? "", req.arguments?.additionalProperties ?? OpenAPIObjectContainer())
            return ClientReply(id: req.id, result: .init(additionalProperties: result))
        }
    }

    private func download(_ path: String, transfer: String) async throws {
        let source = expand(path)
        let archive = FileManager.default.temporaryDirectory.appending(path: "byre-download-\(UUID().uuidString).tgz")
        defer {
            try? FileManager.default.removeItem(at: archive)
        }
        let parent = source.deletingLastPathComponent().path
        let (status, output) = try await spawn(["/usr/bin/tar", "-czf", archive.path, "-C", parent, "--", source.lastPathComponent], in: parent, timeoutMs: copyTimeoutMs)
        if status != 0 {
            throw ApiError(status: 0, message: "pack: tar exited \(status): \(output)")
        }

        var request = URLRequest(url: api.url("/api/clients/transfers/\(transfer)"))
        request.httpMethod = "PUT"
        request.setValue("application/gzip", forHTTPHeaderField: "Content-Type")
        let (body, response) = try await api.session.upload(for: request, fromFile: archive)
        let code = (response as! HTTPURLResponse).statusCode
        if code != 204 {
            throw ApiError(status: code, message: "upload transfer: \(code) \(String(decoding: body, as: UTF8.self))")
        }
    }

    private func upload(transfer: String, to dest: String) async throws {
        let target = expand(dest)
        let parent = target.deletingLastPathComponent()
        let fm = FileManager.default
        try fm.createDirectory(at: parent, withIntermediateDirectories: true)

        let (archive, response) = try await api.session.download(from: api.url("/api/clients/transfers/\(transfer)"))
        defer {
            try? fm.removeItem(at: archive)
        }
        let code = (response as! HTTPURLResponse).statusCode
        if code != 200 {
            throw ApiError(status: code, message: "download transfer: \(code) \(String(decoding: (try? Data(contentsOf: archive)) ?? Data(), as: UTF8.self))")
        }

        let tmp = parent.appending(path: ".byre-upload-\(UUID().uuidString)", directoryHint: .isDirectory)
        try fm.createDirectory(at: tmp, withIntermediateDirectories: false)
        defer {
            try? fm.removeItem(at: tmp)
        }
        let (status, output) = try await spawn(["/usr/bin/tar", "-xzf", archive.path, "-C", tmp.path], in: tmp.path, timeoutMs: copyTimeoutMs)
        if status != 0 {
            throw ApiError(status: 0, message: "unpack: tar exited \(status): \(output)")
        }
        let entries = try fm.contentsOfDirectory(at: tmp, includingPropertiesForKeys: nil)
        guard entries.count == 1 else {
            throw ApiError(status: 0, message: "unpack: the archive holds \(entries.count) entries, not 1")
        }
        if (try? fm.attributesOfItem(atPath: target.path)) != nil {
            try fm.removeItem(at: target)
        }
        try fm.moveItem(at: entries[0], to: target)
    }
}

private func expand(_ path: String) -> URL {
    URL(filePath: (path as NSString).expandingTildeInPath)
}

private func readFile(_ path: String) throws -> Data {
    let source = expand(path).resolvingSymlinksInPath()
    let type = try FileManager.default.attributesOfItem(atPath: source.path)[.type] as? FileAttributeType
    guard type == .typeRegular else {
        throw ApiError(status: 0, message: "\(path) isn't a regular file")
    }
    let h = try FileHandle(forReadingFrom: source)
    defer {
        try? h.close()
    }
    let data = try h.read(upToCount: maxRead + 1) ?? Data()
    if data.count > maxRead {
        throw ApiError(status: 0, message: "\(path) is over the \(maxRead >> 20) MiB read limit; use client_download")
    }
    return data
}

private func writeFile(_ path: String, _ data: Data) throws {
    let target = expand(path).resolvingSymlinksInPath()
    let fm = FileManager.default
    if let attrs = try? fm.attributesOfItem(atPath: target.path), attrs[.type] as? FileAttributeType != .typeRegular {
        throw ApiError(status: 0, message: "\(path) isn't a regular file")
    }
    try fm.createDirectory(at: target.deletingLastPathComponent(), withIntermediateDirectories: true)
    try data.write(to: target)
}

private final class Flag: @unchecked Sendable {
    private let lock = NSLock()
    private var value = false

    func set() -> Bool {
        lock.withLock {
            let was = value
            value = true
            return !was
        }
    }
}

private func spawn(_ argv: [String], in dir: String, timeoutMs: Int) async throws -> (Int, String) {
    let out = FileManager.default.temporaryDirectory.appending(path: "byre-\(UUID().uuidString).log")
    defer {
        try? FileManager.default.removeItem(at: out)
    }

    var attr: posix_spawnattr_t?
    unsafe posix_spawnattr_init(&attr)
    defer {
        unsafe posix_spawnattr_destroy(&attr)
    }
    unsafe posix_spawnattr_setflags(&attr, Int16(POSIX_SPAWN_SETPGROUP))
    unsafe posix_spawnattr_setpgroup(&attr, 0)

    var actions: posix_spawn_file_actions_t?
    unsafe posix_spawn_file_actions_init(&actions)
    defer {
        unsafe posix_spawn_file_actions_destroy(&actions)
    }
    unsafe posix_spawn_file_actions_addopen(&actions, 0, "/dev/null", O_RDONLY, 0)
    unsafe posix_spawn_file_actions_addopen(&actions, 1, out.path, O_WRONLY | O_CREAT | O_TRUNC, 0o600)
    unsafe posix_spawn_file_actions_adddup2(&actions, 1, 2)
    unsafe posix_spawn_file_actions_addchdir(&actions, dir)

    var cargs = unsafe argv.map { unsafe strdup($0) } + [nil]
    defer {
        for unsafe p in unsafe cargs {
            unsafe free(p)
        }
    }
    var spawned: pid_t = 0
    let rc = unsafe posix_spawn(&spawned, argv[0], &actions, &attr, &cargs, environ)
    if rc != 0 {
        throw ApiError(status: 0, message: "start \(argv[0]): \(unsafe String(cString: strerror(rc)))")
    }
    let pid = spawned

    let done = Flag()
    DispatchQueue.global().asyncAfter(deadline: .now() + .milliseconds(timeoutMs)) {
        if done.set() {
            kill(-pid, SIGKILL)
        }
    }
    let status: Int32 = await withCheckedContinuation { c in
        DispatchQueue.global().async {
            var s: Int32 = 0
            while unsafe waitpid(pid, &s, 0) == -1 && errno == EINTR {}
            c.resume(returning: s)
        }
    }
    let timedOut = !done.set()

    let output = tail(out)
    if timedOut {
        return (-1, output)
    }
    if status & 0x7f == 0 {
        return (Int((status >> 8) & 0xff), output)
    }
    return (128 + Int(status & 0x7f), output)
}

private func tail(_ file: URL) -> String {
    guard let h = try? FileHandle(forReadingFrom: file) else {
        return ""
    }
    defer {
        try? h.close()
    }
    let size = (try? h.seekToEnd()) ?? 0
    try? h.seek(toOffset: size > UInt64(maxOutput) ? size - UInt64(maxOutput) : 0)
    return String(decoding: (try? h.readToEnd()) ?? Data(), as: UTF8.self)
}

private struct HandsRequest: Encodable {
    struct Params: Encodable {
        let name: String
        let arguments: OpenAPIObjectContainer
    }

    let jsonrpc = "2.0"
    let id: Int
    let method = "tools/call"
    let params: Params
}

private struct HandsResponse: Decodable {
    struct RPCError: Decodable {
        let message: String
    }

    let id: Int
    let result: OpenAPIObjectContainer?
    let error: RPCError?
}

private final class Helper: @unchecked Sendable {
    let process = Process()
    let input: FileHandle
    var buffer = Data()
    var pending: [Int: CheckedContinuation<OpenAPIObjectContainer, any Error>] = [:]

    init(input: FileHandle) {
        self.input = input
    }
}

private final class Hands: @unchecked Sendable {
    private let lock = NSLock()
    private var helper: Helper?
    private var next = 0

    func call(_ tool: String, _ arguments: OpenAPIObjectContainer) async throws -> OpenAPIObjectContainer {
        try await withCheckedThrowingContinuation { c in
            lock.withLock {
                next += 1
                let id = next
                var target: Helper?
                do {
                    let h = try running()
                    target = h
                    var line = try JSONEncoder().encode(HandsRequest(id: id, params: .init(name: tool, arguments: arguments)))
                    line.append(0x0a)
                    h.pending[id] = c
                    try h.input.write(contentsOf: line)
                } catch {
                    target?.pending[id] = nil
                    c.resume(throwing: error)
                }
            }
        }
    }

    func stop() {
        lock.withLock {
            helper?.process.terminate()
        }
    }

    private func running() throws -> Helper {
        if let helper, helper.process.isRunning {
            return helper
        }
        signal(SIGPIPE, SIG_IGN)
        let stdin = Pipe()
        let stdout = Pipe()
        let h = Helper(input: stdin.fileHandleForWriting)
        let p = h.process
        p.executableURL = Bundle.main.executableURL!.deletingLastPathComponent().appending(path: "byre-hands")
        p.standardInput = stdin
        p.standardOutput = stdout
        p.standardError = FileHandle.nullDevice
        stdout.fileHandleForReading.readabilityHandler = { [weak self] fh in
            self?.read(h, fh.availableData)
        }
        p.terminationHandler = { [weak self] _ in
            self?.exited(h)
        }
        try p.run()
        log.info("byre-hands started: pid \(p.processIdentifier)")
        helper = h
        return h
    }

    private func read(_ h: Helper, _ data: Data) {
        let lines: [Data] = lock.withLock {
            h.buffer.append(data)
            var out: [Data] = []
            while let nl = h.buffer.firstIndex(of: 0x0a) {
                out.append(h.buffer[h.buffer.startIndex..<nl])
                h.buffer = Data(h.buffer[(nl + 1)...])
            }
            return out
        }
        for line in lines {
            guard let resp = try? JSONDecoder().decode(HandsResponse.self, from: line) else {
                log.error("byre-hands sent an unreadable line")
                continue
            }
            let c = lock.withLock {
                h.pending.removeValue(forKey: resp.id)
            }
            if let result = resp.result {
                c?.resume(returning: result)
            } else {
                c?.resume(throwing: ApiError(status: 0, message: "byre-hands: \(resp.error?.message ?? "no result")"))
            }
        }
    }

    private func exited(_ h: Helper) {
        let waiting = lock.withLock {
            let all = h.pending
            h.pending = [:]
            if helper === h {
                helper = nil
            }
            return all
        }
        let status = h.process.terminationStatus
        log.info("byre-hands exited: status \(status)")
        for c in waiting.values {
            c.resume(throwing: ApiError(status: 0, message: "byre-hands exited with status \(status) before replying"))
        }
    }
}