//===----------------------------------------------------------------------===//
// Copyright © 2026 Apple Inc. and the Containerization project authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//===----------------------------------------------------------------------===//

#if os(Linux)

import ContainerizationOS
import Foundation
import LCShim
import Logging
import Synchronization

final class TerminalIO: ManagedProcess.IO & Sendable {
    private struct State {
        var stdinSocket: Socket?
        var stdoutSocket: Socket?

        var stdin: IOPair?
        var stdout: IOPair?
        var parent: Terminal?
    }

    private let log: Logger?
    private let hostStdio: HostStdio
    private let state: Mutex<State>

    init(
        stdio: HostStdio,
        log: Logger?
    ) throws {
        self.hostStdio = stdio
        self.log = log
        self.state = Mutex(State())
    }

    func resize(size: Terminal.Size) throws {
        try self.state.withLock {
            if let parent = $0.parent {
                try parent.resize(size: size)
            }
        }
    }

    func start(process: inout Command) throws {
        try self.state.withLock {
            process.stdin = nil
            process.stdout = nil
            process.stderr = nil

            // [Nucleic vendored patch] Close whatever connected on a partial failure —
            // these sockets are closeOnDeinit: false, so a discarded IO object would leak
            // the earlier fd in PID-1.
            do {
                if let stdinPort = self.hostStdio.stdin {
                    let type = VsockType(
                        port: stdinPort,
                        cid: VsockType.hostCID
                    )
                    let stdinSocket = try Socket(type: type, closeOnDeinit: false)
                    do {
                        try stdinSocket.connect()
                    } catch {
                        try? stdinSocket.close()
                        throw error
                    }
                    $0.stdinSocket = stdinSocket
                }

                if let stdoutPort = self.hostStdio.stdout {
                    let type = VsockType(
                        port: stdoutPort,
                        cid: VsockType.hostCID
                    )
                    let stdoutSocket = try Socket(type: type, closeOnDeinit: false)
                    do {
                        try stdoutSocket.connect()
                    } catch {
                        try? stdoutSocket.close()
                        throw error
                    }
                    $0.stdoutSocket = stdoutSocket
                }
            } catch {
                if let stdinSocket = $0.stdinSocket {
                    try? stdinSocket.close()
                    $0.stdinSocket = nil
                }
                throw error
            }
        }
    }

    func attach(pid: Int32, fd: Int32) throws {
        try self.state.withLock {
            let containerFd = CZ_pidfd_open(pid, 0)
            guard containerFd != -1 else {
                throw POSIXError.fromErrno()
            }
            defer { Foundation.close(Int32(containerFd)) }

            let hostFd = CZ_pidfd_getfd(containerFd, fd, 0)
            guard hostFd != -1 else {
                throw POSIXError.fromErrno()
            }

            let term = try Terminal(descriptor: Int32(hostFd), setInitState: false)
            $0.parent = term

            if let stdinSocket = $0.stdinSocket {
                // [Nucleic vendored patch] The stdin relay's destination is a dup of the
                // terminal fd, NOT the terminal fd itself: both relays sharing one number
                // meant the stdin side's EPOLLOUT backpressure registration collided with
                // the stdout side's read registration (see DupIOCloser) — one bulk paste
                // permanently killed the terminal's stdout relay.
                let pair = IOPair(
                    readFrom: stdinSocket,
                    writeTo: try DupIOCloser(duplicating: term.fileDescriptor),
                    reason: "TerminalIO stdin",
                    logger: log
                )
                do {
                    try pair.relay(ignoreHup: true)
                } catch {
                    pair.close()
                    throw error
                }
                $0.stdin = pair
            }

            if let stdoutSocket = $0.stdoutSocket {
                let pair = IOPair(
                    readFrom: term,
                    writeTo: stdoutSocket,
                    reason: "TerminalIO stdout",
                    logger: log
                )
                do {
                    try pair.relay(ignoreHup: true)
                } catch {
                    // [Nucleic vendored patch] The stdin pair (and its relay) is already
                    // live; a discarded IO object would leave it registered and pumping
                    // forever (the supervisor's handler map retains it).
                    pair.close()
                    $0.stdin?.close()
                    $0.stdin = nil
                    throw error
                }
                $0.stdout = pair
            }
        }
    }

    func close() throws {
        self.state.withLock {
            // stdout closes first: it registered the Terminal fd with epoll (as its read
            // source) and unregisters it while the fd is still valid. The stdin pair's
            // write destination is its own dup of the terminal (see attach), so its
            // close-time flush stays valid regardless of ordering — the shared open file
            // description outlives the stdout side's close until the dup closes too.
            if let stdout = $0.stdout {
                stdout.close()
                $0.stdout = nil
            }
            if let stdin = $0.stdin {
                stdin.close()
                $0.stdin = nil
            }

            // If IOPairs were never created (process exited before attach),
            // close the raw sockets directly since they have closeOnDeinit
            // disabled.
            if let stdinSocket = $0.stdinSocket {
                try? stdinSocket.close()
                $0.stdinSocket = nil
            }
            if let stdoutSocket = $0.stdoutSocket {
                try? stdoutSocket.close()
                $0.stdoutSocket = nil
            }

            $0.parent = nil
        }
    }

    // NOP
    func closeAfterExec() throws {}

    func closeStdin() throws {
        self.state.withLock {
            if let stdin = $0.stdin {
                stdin.close()
                $0.stdin = nil
            }
        }
    }
}

#endif