//! Windows subprocess backend. Launch details follow libuv and Rust's
//! standard library as adapted by Deno: CRT descriptor inheritance through
//! `lpReserved2`, MSVC argument quoting, and verbatim path simplification.

use std::ffi::{OsStr, OsString, c_void};
use std::io;
use std::os::windows::ffi::{OsStrExt, OsStringExt};
use std::os::windows::fs::OpenOptionsExt;
use std::os::windows::io::{AsRawHandle, BorrowedHandle, FromRawHandle, OwnedHandle};
use std::os::windows::process::ExitStatusExt;
use std::path::{Component, Path, PathBuf, Prefix};
use std::process::ExitStatus;
use std::sync::atomic::{AtomicU64, Ordering};

use crate::Launch;
use futures::FutureExt;
use tokio::net::windows::named_pipe::{NamedPipeServer, PipeMode, ServerOptions};
use windows_sys::Win32::Foundation::{
    HANDLE, HANDLE_FLAG_INHERIT, INVALID_HANDLE_VALUE, MAX_PATH, SetHandleInformation,
    WAIT_OBJECT_0, WAIT_TIMEOUT,
};
use windows_sys::Win32::Storage::FileSystem::{
    FILE_GENERIC_READ, FILE_GENERIC_WRITE, FILE_READ_ATTRIBUTES, FILE_SHARE_READ, FILE_TYPE_CHAR,
    FILE_TYPE_DISK, FILE_TYPE_PIPE, FILE_WRITE_ATTRIBUTES, GetFileType, GetShortPathNameW,
};
use windows_sys::Win32::System::JobObjects::{
    JOB_OBJECT_LIMIT_BREAKAWAY_OK, JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK,
};
use windows_sys::Win32::System::Threading::{
    CREATE_UNICODE_ENVIRONMENT, CreateProcessW, DeleteProcThreadAttributeList,
    EXTENDED_STARTUPINFO_PRESENT, GetExitCodeProcess, INFINITE, InitializeProcThreadAttributeList,
    LPPROC_THREAD_ATTRIBUTE_LIST, PROC_THREAD_ATTRIBUTE_HANDLE_LIST,
    PROC_THREAD_ATTRIBUTE_JOB_LIST, PROCESS_INFORMATION, STARTF_USESTDHANDLES, STARTUPINFOEXW,
    TerminateProcess, UpdateProcThreadAttribute, WaitForSingleObject,
};

/// A handle handed to the child at its declared CRT descriptor number.
pub type Endpoint = OwnedHandle;
/// The parent's end of a stdio pipe.
pub type Pipe = NamedPipeServer;
/// Terminals are not supported on Windows yet.
pub enum Window {}
/// The CRT's inherited descriptor table holds at most 255 entries.
pub const MAX_DESCRIPTOR: u32 = 254;

const SIGNALS: [&str; 16] = [
    "SIGHUP", "SIGINT", "SIGQUIT", "SIGABRT", "SIGKILL", "SIGUSR1", "SIGUSR2", "SIGPIPE",
    "SIGALRM", "SIGTERM", "SIGCONT", "SIGSTOP", "SIGTSTP", "SIGTTIN", "SIGTTOU", "SIGWINCH",
];

/// Like libuv, the signals that end a process all terminate it immediately:
/// Windows has no general way to ask a process to stop.
pub fn validate_signal(name: &str) -> io::Result<()> {
    if matches!(name, "SIGKILL" | "SIGTERM" | "SIGINT" | "SIGQUIT") {
        Ok(())
    } else if SIGNALS.contains(&name) {
        Err(io::Error::new(
            io::ErrorKind::Unsupported,
            "Windows subprocesses accept only SIGTERM, SIGKILL, SIGINT, and SIGQUIT",
        ))
    } else {
        Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            "Unsupported subprocess signal",
        ))
    }
}

pub fn exit_signal(_: &ExitStatus) -> Option<String> {
    None
}

fn last_error() -> io::Error {
    io::Error::last_os_error()
}

fn wide(value: &OsStr) -> Vec<u16> {
    value.encode_wide().chain([0]).collect()
}

/// Returns the parent's end and the child's end of a new pipe. The parent's
/// end is overlapped for async IO; the child's end is synchronous, which is
/// what most programs expect of their standard streams.
pub fn pipe(parent_writes: bool) -> io::Result<(Pipe, Endpoint)> {
    static NEXT: AtomicU64 = AtomicU64::new(0);
    let name = format!(
        r"\\.\pipe\avril-{}-{}-{:016x}",
        std::process::id(),
        NEXT.fetch_add(1, Ordering::Relaxed),
        getrandom::u64().map_err(io::Error::other)?,
    );
    // first_pipe_instance refuses a squatted name; max_instances keeps out
    // a second client.
    let server = ServerOptions::new()
        .first_pipe_instance(true)
        .max_instances(1)
        .reject_remote_clients(true)
        .pipe_mode(PipeMode::Byte)
        .access_inbound(!parent_writes)
        .access_outbound(parent_writes)
        .create(&name)?;
    // libuv's access masks: the child may adjust its end's pipe state.
    let access = if parent_writes {
        FILE_GENERIC_READ | FILE_WRITE_ATTRIBUTES
    } else {
        FILE_GENERIC_WRITE | FILE_READ_ATTRIBUTES
    };
    let client = std::fs::OpenOptions::new()
        .access_mode(access)
        .share_mode(0)
        .open(&name)?;
    match server.connect().now_or_never() {
        Some(result) => result?,
        None => return Err(io::Error::other("Subprocess pipe did not connect")),
    }
    Ok((server, client.into()))
}

pub fn null(read: bool) -> io::Result<Endpoint> {
    Ok(std::fs::OpenOptions::new()
        .read(read)
        .write(!read)
        .open("NUL")?
        .into())
}

pub fn inherit(fd: u32) -> io::Result<Endpoint> {
    let handle = match fd {
        0 => std::io::stdin().as_raw_handle(),
        1 => std::io::stdout().as_raw_handle(),
        _ => std::io::stderr().as_raw_handle(),
    };
    // Without a console or redirection there is nothing to inherit.
    if handle.is_null() || handle == INVALID_HANDLE_VALUE {
        return null(fd == 0);
    }
    unsafe { BorrowedHandle::borrow_raw(handle) }.try_clone_to_owned()
}

pub fn duplicate(endpoint: &Endpoint) -> io::Result<Endpoint> {
    endpoint.try_clone()
}

pub struct Pty {
    pub reader: Pipe,
    pub writer: Pipe,
    pub endpoints: [Endpoint; 3],
    pub window: Window,
}

pub fn pty(_columns: u16, _rows: u16) -> io::Result<Pty> {
    Err(io::Error::new(
        io::ErrorKind::Unsupported,
        "Subprocess terminals are not supported on Windows",
    ))
}

pub fn resize(window: &Window, _columns: u16, _rows: u16) -> io::Result<()> {
    match *window {}
}

pub fn is_executable(metadata: &std::fs::Metadata) -> bool {
    metadata.is_file()
}

/// Names without an executable extension also try `.com` and `.exe`, like
/// libuv's search. Batch extensions are never added: they need a shell.
pub fn expand(path: PathBuf) -> Vec<PathBuf> {
    let extension = path.extension().map(OsStr::to_ascii_lowercase);
    if extension
        .as_deref()
        .is_some_and(|extension| extension == "com" || extension == "exe")
    {
        return vec![path];
    }
    let mut paths = Vec::new();
    for suffix in [".com", ".exe"] {
        let mut name = path.clone().into_os_string();
        name.push(suffix);
        paths.push(name.into());
    }
    if extension.is_some() {
        paths.insert(0, path);
    }
    paths
}

/// CreateProcess runs `.bat` and `.cmd` files through cmd.exe, with its own
/// quoting rules; there is no implicit shell, so they need an explicit one.
/// Path normalization drops trailing dots and spaces, so CreateProcess does
/// too (the BatBadBut lesson in Rust's standard library).
fn is_batch(path: &Path) -> bool {
    path.file_name().is_some_and(|name| {
        let name = name.to_string_lossy().to_ascii_lowercase();
        let name = name.trim_end_matches(['.', ' ']);
        name.ends_with(".bat") || name.ends_with(".cmd")
    })
}

/// The authorized executable, opened without delete or write sharing so
/// it cannot be replaced or renamed until CreateProcess has mapped it.
pub struct Executable {
    _image: std::fs::File,
}

impl Executable {
    pub fn open(target: &Path) -> io::Result<(Self, std::fs::Metadata)> {
        if is_batch(target) {
            return Err(io::Error::new(
                io::ErrorKind::Unsupported,
                "Batch files need an explicit cmd.exe invocation",
            ));
        }
        let file = std::fs::OpenOptions::new()
            .read(true)
            .share_mode(FILE_SHARE_READ)
            .open(target)?;
        let metadata = file.metadata()?;
        Ok((Self { _image: file }, metadata))
    }
}

pub fn controlling_foreground() -> bool {
    false
}

/// Canonical paths are verbatim (`\\?\C:\…`), which CreateProcess and many
/// programs mishandle as a working directory or image path; use the plain
/// spelling, as Deno's `strip_unc_prefix` does, but only where Win32
/// normalization leaves it alone. Otherwise it would name another file:
/// trailing dots and spaces are dropped, device names are remapped, and
/// long paths need the prefix.
fn simplify(path: &Path) -> PathBuf {
    let mut components = path.components();
    let Some(Component::Prefix(prefix)) = components.next() else {
        return path.to_owned();
    };
    let mut plain = match prefix.kind() {
        Prefix::VerbatimDisk(letter) => PathBuf::from(format!("{}:\\", letter as char)),
        Prefix::VerbatimUNC(server, share) => {
            let mut root = OsString::from(r"\\");
            root.push(server);
            root.push(r"\");
            root.push(share);
            root.push(r"\");
            PathBuf::from(root)
        }
        _ => return path.to_owned(),
    };
    plain.extend(components.filter(|component| !matches!(component, Component::RootDir)));
    if plain.as_os_str().encode_wide().count() < MAX_PATH as usize
        && std::path::absolute(&plain).is_ok_and(|absolute| absolute == plain)
    {
        plain
    } else {
        path.to_owned()
    }
}

/// MSVC command-line quoting, as in Rust's standard library: arguments with
/// whitespace (or none at all) are quoted, and backslashes are doubled only
/// where they precede a quote.
fn append_argument(line: &mut Vec<u16>, argument: &OsStr) {
    let quote = argument.is_empty()
        || argument
            .encode_wide()
            .any(|unit| unit == b' ' as u16 || unit == b'\t' as u16);
    if quote {
        line.push(b'"' as u16);
    }
    let mut backslashes = 0;
    for unit in argument.encode_wide() {
        if unit == b'\\' as u16 {
            backslashes += 1;
        } else {
            if unit == b'"' as u16 {
                line.extend(std::iter::repeat_n(b'\\' as u16, backslashes + 1));
            }
            backslashes = 0;
        }
        line.push(unit);
    }
    if quote {
        line.extend(std::iter::repeat_n(b'\\' as u16, backslashes));
        line.push(b'"' as u16);
    }
}

pub struct Child {
    pid: u32,
    process: OwnedHandle,
    /// Kill-on-close: if this process dies, so does the job's tree.
    job: std::sync::Arc<crate::job::Job>,
}
impl Child {
    pub fn id(&self) -> u32 {
        self.pid
    }
    fn status(&self) -> io::Result<ExitStatus> {
        let mut code = 0;
        if unsafe { GetExitCodeProcess(self.process.as_raw_handle(), &mut code) } == 0 {
            return Err(last_error());
        }
        Ok(ExitStatus::from_raw(code))
    }
    pub fn wait(&mut self) -> io::Result<ExitStatus> {
        if unsafe { WaitForSingleObject(self.process.as_raw_handle(), INFINITE) } != WAIT_OBJECT_0 {
            return Err(last_error());
        }
        self.status()
    }
    pub fn observe_exit(&self) -> io::Result<Option<ExitStatus>> {
        match unsafe { WaitForSingleObject(self.process.as_raw_handle(), 0) } {
            WAIT_OBJECT_0 => self.status().map(Some),
            WAIT_TIMEOUT => Ok(None),
            _ => Err(last_error()),
        }
    }
    /// Group scope terminates the child's job, which holds its descendants
    /// unless they explicitly broke away (as setsid would on Unix).
    pub fn signal(&self, group: bool, name: &str) -> io::Result<bool> {
        validate_signal(name)?;
        if group {
            return self.job.terminate();
        }
        if self.observe_exit()?.is_some() {
            return Ok(false);
        }
        if unsafe { TerminateProcess(self.process.as_raw_handle(), 1) } == 0 {
            let error = last_error();
            // Termination races with a natural exit.
            return if self.observe_exit()?.is_some() {
                Ok(false)
            } else {
                Err(error)
            };
        }
        Ok(true)
    }
}

/// Owns an initialized attribute list.
struct Attributes(Vec<usize>);
impl Attributes {
    fn new(count: u32) -> io::Result<Self> {
        let mut size = 0;
        unsafe {
            InitializeProcThreadAttributeList(std::ptr::null_mut(), count, 0, &mut size);
        }
        let mut list = Self(vec![0; size.div_ceil(std::mem::size_of::<usize>())]);
        if unsafe { InitializeProcThreadAttributeList(list.as_ptr(), count, 0, &mut size) } == 0 {
            list.0.clear();
            return Err(last_error());
        }
        Ok(list)
    }
    fn as_ptr(&mut self) -> LPPROC_THREAD_ATTRIBUTE_LIST {
        self.0.as_mut_ptr().cast()
    }
    /// The value is borrowed, not copied, until CreateProcess returns.
    fn set<T>(&mut self, attribute: u32, value: &[T]) -> io::Result<()> {
        if unsafe {
            UpdateProcThreadAttribute(
                self.as_ptr(),
                0,
                attribute as usize,
                value.as_ptr().cast(),
                std::mem::size_of_val(value),
                std::ptr::null_mut(),
                std::ptr::null(),
            )
        } == 0
        {
            return Err(last_error());
        }
        Ok(())
    }
}
impl Drop for Attributes {
    fn drop(&mut self) {
        if !self.0.is_empty() {
            unsafe { DeleteProcThreadAttributeList(self.as_ptr()) }
        }
    }
}

pub(crate) fn spawn(launch: Launch) -> io::Result<Child> {
    let Launch {
        executable,
        program,
        args,
        env,
        cwd,
        group,
        join,
        terminal,
        endpoints,
    } = launch;
    if terminal {
        return Err(io::Error::new(
            io::ErrorKind::Unsupported,
            "Subprocess terminals are not supported on Windows",
        ));
    }
    let program = simplify(program);
    let application = wide(program.as_os_str());
    // MSVC's parser takes argv[0] verbatim up to the closing quote, and
    // Windows paths cannot contain quotes.
    let mut line = vec![b'"' as u16];
    line.extend(program.as_os_str().encode_wide());
    line.push(b'"' as u16);
    for argument in args {
        line.push(b' ' as u16);
        append_argument(&mut line, OsStr::new(argument));
    }
    line.push(0);
    // Names arrive sorted by their case-insensitive key, as CreateProcess
    // expects.
    let mut environment = Vec::new();
    for (name, value) in &env {
        environment.extend(OsStr::new(name).encode_wide());
        environment.push(b'=' as u16);
        environment.extend(OsStr::new(value).encode_wide());
        environment.push(0);
    }
    if environment.is_empty() {
        environment.push(0);
    }
    environment.push(0);
    let mut directory = simplify(cwd);
    // libuv: a working directory of MAX_PATH or more needs its short form.
    if directory.as_os_str().encode_wide().count() >= MAX_PATH as usize {
        let long = wide(cwd.as_os_str());
        let mut short = vec![0u16; long.len()];
        let length =
            unsafe { GetShortPathNameW(long.as_ptr(), short.as_mut_ptr(), short.len() as u32) };
        if length == 0 || length as usize >= short.len() {
            return Err(last_error());
        }
        short.truncate(length as usize);
        directory = simplify(Path::new(&OsString::from_wide(&short)));
    }
    let directory = wide(directory.as_os_str());

    // The CRT reads inherited descriptors from lpReserved2: a count, one
    // flag byte per descriptor, then one unaligned handle per descriptor.
    const FOPEN: u8 = 0x01;
    const FPIPE: u8 = 0x08;
    const FDEV: u8 = 0x40;
    let count = endpoints
        .iter()
        .map(|(fd, _)| *fd as usize + 1)
        .max()
        .unwrap_or(0)
        .max(3);
    let handle_size = std::mem::size_of::<HANDLE>();
    let mut descriptors = vec![0u8; 4 + count + count * handle_size];
    descriptors[..4].copy_from_slice(&(count as u32).to_ne_bytes());
    for fd in 0..count {
        let at = 4 + count + fd * handle_size;
        descriptors[at..at + handle_size]
            .copy_from_slice(&(INVALID_HANDLE_VALUE as usize).to_ne_bytes());
    }
    let mut standard = [INVALID_HANDLE_VALUE; 3];
    let mut inherited = Vec::with_capacity(endpoints.len());
    for (fd, endpoint) in &endpoints {
        let handle = endpoint.as_raw_handle();
        if unsafe { SetHandleInformation(handle, HANDLE_FLAG_INHERIT, HANDLE_FLAG_INHERIT) } == 0 {
            return Err(last_error());
        }
        let flags = match unsafe { GetFileType(handle) } {
            FILE_TYPE_DISK => FOPEN,
            FILE_TYPE_PIPE => FOPEN | FPIPE,
            FILE_TYPE_CHAR => FOPEN | FDEV,
            _ => FOPEN | FDEV,
        };
        let fd = *fd as usize;
        descriptors[4 + fd] = flags;
        let at = 4 + count + fd * handle_size;
        descriptors[at..at + handle_size].copy_from_slice(&(handle as usize).to_ne_bytes());
        if fd < 3 {
            standard[fd] = handle;
        }
        inherited.push(handle);
    }

    // Child scope keeps only the child in its job; descendants silently
    // stay out, as they stay out of termination on Unix.
    let flags = if group {
        JOB_OBJECT_LIMIT_BREAKAWAY_OK
    } else {
        JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK
    };
    let job = match join {
        Some(group) => group.job()?,
        None => std::sync::Arc::new(crate::job::Job::new(flags)?),
    };
    let jobs = [job.as_raw_handle()];

    // Only the listed handles reach the child, even when other threads
    // spawn with inheritable handles of their own; the job list places the
    // child in its job before it runs.
    let mut attributes = Attributes::new(2)?;
    attributes.set(PROC_THREAD_ATTRIBUTE_HANDLE_LIST, &inherited)?;
    attributes.set(PROC_THREAD_ATTRIBUTE_JOB_LIST, &jobs)?;
    let mut startup: STARTUPINFOEXW = unsafe { std::mem::zeroed() };
    startup.StartupInfo.cb = std::mem::size_of::<STARTUPINFOEXW>() as u32;
    startup.StartupInfo.dwFlags = STARTF_USESTDHANDLES;
    startup.StartupInfo.hStdInput = standard[0];
    startup.StartupInfo.hStdOutput = standard[1];
    startup.StartupInfo.hStdError = standard[2];
    startup.StartupInfo.cbReserved2 = descriptors.len() as u16;
    startup.StartupInfo.lpReserved2 = descriptors.as_mut_ptr();
    startup.lpAttributeList = attributes.as_ptr();
    let mut information: PROCESS_INFORMATION = unsafe { std::mem::zeroed() };
    let created = unsafe {
        CreateProcessW(
            application.as_ptr(),
            line.as_mut_ptr(),
            std::ptr::null(),
            std::ptr::null(),
            1,
            CREATE_UNICODE_ENVIRONMENT | EXTENDED_STARTUPINFO_PRESENT,
            environment.as_ptr().cast::<c_void>(),
            directory.as_ptr(),
            &raw const startup.StartupInfo,
            &mut information,
        )
    };
    let error = last_error();
    drop(attributes);
    drop(executable);
    if created == 0 {
        return Err(error);
    }
    unsafe {
        drop(OwnedHandle::from_raw_handle(information.hThread));
    }
    Ok(Child {
        pid: information.dwProcessId,
        process: unsafe { OwnedHandle::from_raw_handle(information.hProcess) },
        job,
    })
}