//===----------------------------------------------------------------------===//
// 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 Cgroup
import Containerization
import ContainerizationError
import ContainerizationOCI
import ContainerizationOS
import Foundation
import Logging
import Synchronization

final class ManagedProcess: ContainerProcess, Sendable {
    // swiftlint: disable type_name
    protocol IO {
        func attach(pid: Int32, fd: Int32) throws
        func start(process: inout Command) throws
        func resize(size: Terminal.Size) throws
        func close() throws
        func closeStdin() throws
        func closeAfterExec() throws
    }
    // swiftlint: enable type_name

    private struct State {
        init(io: IO) {
            self.io = io
        }

        let io: IO
        var waiters: [CheckedContinuation<ContainerExitStatus, Never>] = []
        var exitStatus: ContainerExitStatus? = nil
        var pid: Int32?
    }

    private static let ackPid = "AckPid"
    private static let ackConsole = "AckConsole"

    let id: String

    private let log: Logger
    private let command: Command
    private let state: Mutex<State>
    private let owningPid: Int32?
    // [Nucleic vendored patch] Parent cgroup for this exec's OWN per-exec child (`<parent>/<id>`);
    // nil means the legacy flat layout (join the container/init cgroup via `owningPid`).
    private let execCgroupParent: String?
    private let ackPipe: Pipe
    private let syncPipe: Pipe
    private let errorPipe: Pipe
    private let terminal: Bool
    private let bundle: ContainerizationOCI.Bundle

    var pid: Int32? {
        self.state.withLock {
            $0.pid
        }
    }

    init(
        id: String,
        stdio: HostStdio,
        bundle: ContainerizationOCI.Bundle,
        owningPid: Int32? = nil,
        execCgroupParent: String? = nil,  // [Nucleic vendored patch]
        log: Logger
    ) throws {
        self.id = id
        var log = log
        log[metadataKey: "id"] = "\(id)"
        self.log = log
        self.owningPid = owningPid
        self.execCgroupParent = execCgroupParent

        let syncPipe = Pipe()
        try syncPipe.setCloexec()
        self.syncPipe = syncPipe

        let ackPipe = Pipe()
        try ackPipe.setCloexec()
        self.ackPipe = ackPipe

        let errorPipe = Pipe()
        try errorPipe.setCloexec()
        self.errorPipe = errorPipe

        let args: [String]
        if let owningPid {
            args = [
                "exec",
                "--parent-pid",
                "\(owningPid)",
                "--process-path",
                bundle.getExecSpecPath(id: id).path,
            ]
        } else {
            args = ["run", "--bundle-path", bundle.path.path]
        }

        var command = Command(
            "/sbin/vmexec",
            arguments: args,
            extraFiles: [
                syncPipe.fileHandleForWriting,
                ackPipe.fileHandleForReading,
                errorPipe.fileHandleForWriting,
            ]
        )

        var io: IO
        if stdio.terminal {
            log.info("setting up terminal I/O")
            let attrs = Command.Attrs(setsid: false, setctty: false)
            command.attrs = attrs
            io = try TerminalIO(
                stdio: stdio,
                log: log
            )
        } else {
            command.attrs = .init(setsid: false)
            io = StandardIO(
                stdio: stdio,
                log: log
            )
        }

        log.info("starting I/O")

        // Setup IO early. We expect the host to be listening already.
        try io.start(process: &command)

        self.command = command
        self.terminal = stdio.terminal
        self.bundle = bundle
        self.state = Mutex(State(io: io))
    }
}

extension ManagedProcess {
    /// [Nucleic vendored patch] Run the blocking start sequence OFF the cooperative executor / gRPC
    /// event loop. `startBlocking()` does synchronous, potentially slow pipe reads (waiting for
    /// `vmexec` to hand back the pid, then for the error pipe to close) while holding `state`'s Mutex.
    /// Upstream ran that directly on the calling task, so a slow exec start parked the event loop and
    /// head-of-line-blocked sibling execs' control RPCs multiplexed on the same loop (each host `exec`
    /// dials its own connection, but NIO pins several connections per loop). Dispatching to a worker
    /// keeps the loop responsive; the body has no `await` and `ManagedProcess` is `Sendable`, so it is
    /// safe off-actor, and the per-exec Mutex still serializes only this exec's own operations.
    func start() async throws -> Int32 {
        try await withCheckedThrowingContinuation { (cont: CheckedContinuation<Int32, Error>) in
            DispatchQueue.global(qos: .userInitiated).async {
                do {
                    cont.resume(returning: try self.startBlocking())
                } catch {
                    cont.resume(throwing: error)
                }
            }
        }
    }

    private func startBlocking() throws -> Int32 {
        do {
            return try self.state.withLock {
                log.info(
                    "starting managed process",
                    metadata: [
                        "id": "\(id)"
                    ])

                // Start the underlying process.
                try command.start()

                defer {
                    try? self.ackPipe.fileHandleForWriting.close()
                    try? self.syncPipe.fileHandleForReading.close()
                    try? self.ackPipe.fileHandleForReading.close()
                    try? self.syncPipe.fileHandleForWriting.close()
                    try? self.errorPipe.fileHandleForWriting.close()
                }

                // Close our side of any pipes.
                try $0.io.closeAfterExec()
                try self.ackPipe.fileHandleForReading.close()
                try self.syncPipe.fileHandleForWriting.close()
                try self.errorPipe.fileHandleForWriting.close()

                let size = MemoryLayout<Int32>.size
                guard let piddata = try syncPipe.fileHandleForReading.read(upToCount: size) else {
                    throw ContainerizationError(.internalError, message: "no PID data from sync pipe")
                }

                guard piddata.count == size else {
                    throw ContainerizationError(.internalError, message: "invalid payload")
                }

                let pid = piddata.withUnsafeBytes { ptr in
                    ptr.load(as: Int32.self)
                }

                log.info(
                    "got back pid data",
                    metadata: [
                        "pid": "\(pid)"
                    ])
                $0.pid = pid

                // This should probably happen in vmexec, but we don't need to set any cgroup
                // toggles so the problem is much simpler to just do it here.
                if let parent = execCgroupParent {
                    // [Nucleic vendored patch] Per-exec cgroup: place this exec in its OWN child cgroup
                    // (`<parent>/<id>`) with memory.oom.group (a runaway session's OOM kills only its
                    // tree), a fair cpu.weight, and a pids.max fork-bomb backstop — so one session can't
                    // OOM-kill / starve / fork-bomb its siblings in the shared container. Best-effort:
                    // on ANY error fall back to the container/init cgroup so a cgroup hiccup never blocks
                    // the exec from starting.
                    do {
                        let execCg = Cgroup2Manager(group: URL(filePath: parent + "/" + id), logger: log)
                        try execCg.create()
                        try? execCg.setOomGroup(true)
                        try? execCg.setCpuWeight(100)
                        try? execCg.setPidsMax(4096)
                        try execCg.addProcess(pid: pid)
                    } catch {
                        log.error("per-exec cgroup for \(id) failed; joining the container cgroup: \(error)")
                        if let owningPid {
                            try? Cgroup2Manager.loadFromPid(pid: owningPid).addProcess(pid: pid)
                        }
                    }
                } else if let owningPid {
                    let cgManager = try Cgroup2Manager.loadFromPid(pid: owningPid)
                    try cgManager.addProcess(pid: pid)
                }

                log.info(
                    "sending pid acknowledgement",
                    metadata: [
                        "pid": "\(pid)"
                    ])
                try self.ackPipe.fileHandleForWriting.write(contentsOf: Self.ackPid.data(using: .utf8)!)

                if self.terminal {
                    log.info(
                        "wait for PTY FD",
                        metadata: [
                            "id": "\(id)"
                        ])

                    // Wait for a new write that will contain the pty fd if we asked for one.
                    guard let ptyFd = try self.syncPipe.fileHandleForReading.read(upToCount: size) else {
                        throw ContainerizationError(
                            .internalError,
                            message: "no PTY data from sync pipe"
                        )
                    }
                    let fd = ptyFd.withUnsafeBytes { ptr in
                        ptr.load(as: Int32.self)
                    }
                    log.info(
                        "received PTY FD from container, attaching",
                        metadata: [
                            "id": "\(id)"
                        ])

                    try $0.io.attach(pid: pid, fd: fd)
                    try self.ackPipe.fileHandleForWriting.write(contentsOf: Self.ackConsole.data(using: .utf8)!)
                }

                // Wait for the errorPipe to close (after exec).
                if let errorData = try? self.errorPipe.fileHandleForReading.readToEnd(),
                    let errorString = String(data: errorData, encoding: .utf8),
                    !errorString.isEmpty
                {
                    throw ContainerizationError(
                        .internalError,
                        message: "vmexec error: \(errorString.trimmingCharacters(in: .whitespacesAndNewlines))"
                    )
                }

                log.info(
                    "started managed process",
                    metadata: [
                        "pid": "\(pid)",
                        "id": "\(id)",
                    ])

                return pid
            }
        } catch {
            if let errorData = try? self.errorPipe.fileHandleForReading.readToEnd(),
                let errorString = String(data: errorData, encoding: .utf8),
                !errorString.isEmpty
            {
                throw ContainerizationError(
                    .internalError,
                    message: "vmexec error: \(errorString.trimmingCharacters(in: .whitespacesAndNewlines))",
                    cause: error
                )
            }
            throw error
        }
    }

    func setExit(_ status: Int32) {
        self.state.withLock { state in
            self.log.info(
                "managed process exit",
                metadata: [
                    "status": "\(status)"
                ])

            let exitStatus = ContainerExitStatus(exitCode: status, exitedAt: Date.now)
            state.exitStatus = exitStatus

            do {
                try state.io.close()
            } catch {
                self.log.error("failed to close I/O for process: \(error)")
            }

            for waiter in state.waiters {
                waiter.resume(returning: exitStatus)
            }

            self.log.debug("\(state.waiters.count) managed process waiters signaled")
            state.waiters.removeAll()
        }
    }

    /// Wait on the process to exit
    func wait() async -> ContainerExitStatus {
        await withCheckedContinuation { cont in
            self.state.withLock {
                if let status = $0.exitStatus {
                    cont.resume(returning: status)
                    return
                }
                $0.waiters.append(cont)
            }
        }
    }

    func kill(_ signal: Int32) async throws {
        try self.state.withLock {
            guard let pid = $0.pid else {
                throw ContainerizationError(.invalidState, message: "process PID is required")
            }

            guard $0.exitStatus == nil else {
                return
            }

            self.log.info("sending signal \(signal) to process \(pid)")
            guard Foundation.kill(pid, signal) == 0 else {
                throw POSIXError.fromErrno()
            }
        }
    }

    func resize(size: Terminal.Size) throws {
        try self.state.withLock {
            guard $0.exitStatus == nil else {
                return
            }
            try $0.io.resize(size: size)
        }
    }

    func closeStdin() throws {
        let io = self.state.withLock { $0.io }
        try io.closeStdin()
    }

    func delete() async throws {
        // vmexec doesn't require explicit cleanup - the process is cleaned up
        // when it exits and IO is closed via setExit()
    }
}

#endif