const Child = @This();

const builtin = @import("builtin");
const native_os = builtin.os.tag;

const std = @import("../std.zig");
const Io = std.Io;
const process = std.process;
const File = std.Io.File;
const assert = std.debug.assert;
const Allocator = std.mem.Allocator;

pub const Id = switch (native_os) {
    .windows => std.os.windows.HANDLE,
    .wasi => void,
    else => std.posix.pid_t,
};

/// After `wait` or `kill` is called, this becomes `null`.
/// On Windows this is the hProcess.
/// On POSIX this is the pid.
id: ?Id,
thread_handle: if (native_os == .windows) std.os.windows.HANDLE else void,
/// The writing end of the child process's standard input pipe.
/// Usage requires `process.SpawnOptions.StdIo.pipe`.
stdin: ?File,
/// The reading end of the child process's standard output pipe.
/// Usage requires `process.SpawnOptions.StdIo.pipe`.
stdout: ?File,
/// The reading end of the child process's standard error pipe.
/// Usage requires `process.SpawnOptions.StdIo.pipe`.
stderr: ?File,
/// This is available after calling wait if
/// `request_resource_usage_statistics` was set to `true` before calling
/// `spawn`.
/// TODO move this data into `Term`
resource_usage_statistics: ResourceUsageStatistics = .{},
request_resource_usage_statistics: bool,

pub const ResourceUsageStatistics = struct {
    rusage: @TypeOf(rusage_init) = rusage_init,

    /// Returns the peak resident set size of the child process, in bytes,
    /// if available.
    pub inline fn getMaxRss(rus: ResourceUsageStatistics) ?usize {
        switch (native_os) {
            .dragonfly, .freebsd, .netbsd, .openbsd, .illumos, .linux, .serenity => {
                if (rus.rusage) |ru| {
                    return @as(usize, @intCast(ru.maxrss)) * 1024;
                } else {
                    return null;
                }
            },
            .windows => {
                if (rus.rusage) |ru| {
                    return ru.PeakWorkingSetSize;
                } else {
                    return null;
                }
            },
            .driverkit, .ios, .maccatalyst, .macos, .tvos, .visionos, .watchos => {
                if (rus.rusage) |ru| {
                    // Darwin oddly reports in bytes instead of kilobytes.
                    return @as(usize, @intCast(ru.maxrss));
                } else {
                    return null;
                }
            },
            else => return null,
        }
    }

    const rusage_init = switch (native_os) {
        .dragonfly,
        .freebsd,
        .netbsd,
        .openbsd,
        .illumos,
        .linux,
        .serenity,
        .driverkit,
        .ios,
        .maccatalyst,
        .macos,
        .tvos,
        .visionos,
        .watchos,
        => @as(?std.posix.rusage, null),
        .windows => @as(?std.os.windows.VM_COUNTERS, null),
        else => {},
    };
};

pub const Term = union(enum) {
    exited: u8,
    signal: std.posix.SIG,
    stopped: u32,
    unknown: u32,
};

/// Requests for the operating system to forcibly terminate the child process,
/// then blocks until it terminates, then cleans up all resources.
///
/// Idempotent and does nothing after `wait` returns.
///
/// Uncancelable. Ignores unexpected errors from the operating system.
pub fn kill(child: *Child, io: Io) void {
    if (child.id == null) {
        assert(child.stdin == null);
        assert(child.stdout == null);
        assert(child.stderr == null);
        return;
    }
    io.vtable.childKill(io.userdata, child);
    assert(child.id == null);
}

pub const WaitError = error{
    AccessDenied,
} || Io.Cancelable || Io.UnexpectedError;

/// Blocks until child process terminates and then cleans up all resources.
pub fn wait(child: *Child, io: Io) WaitError!Term {
    assert(child.id != null);
    return io.vtable.childWait(io.userdata, child);
}

pub const CollectOutputError = error{
    StreamTooLong,
    ConcurrencyUnavailable,
} || Allocator.Error || Io.File.Reader.Error;

pub const CollectOutputOptions = struct {
    stdout: *std.ArrayList(u8),
    stderr: *std.ArrayList(u8),
    allocator: Allocator,
    stdout_limit: Io.Limit = .unlimited,
    stderr_limit: Io.Limit = .unlimited,
};

/// Collect the output from the process's stdout and stderr. Will return once
/// all output has been collected. This does not mean that the process has
/// ended. `wait` should still be called to wait for and clean up the process.
///
/// The process must have been started with stdout and stderr set to
/// `process.SpawnOptions.StdIo.pipe`.
pub fn collectOutput(child: *const Child, io: Io, options: CollectOutputOptions) CollectOutputError!void {
    var stdout = try io.concurrent(collectStream, .{
        io, options.allocator, child.stdout.?, options.stdout, options.stdout_limit,
    });
    defer stdout.cancel(io) catch {};

    var stderr = try io.concurrent(collectStream, .{
        io, options.allocator, child.stderr.?, options.stderr, options.stderr_limit,
    });
    defer stderr.cancel(io) catch {};

    try stdout.await(io);
    try stderr.await(io);
}

fn collectStream(io: Io, gpa: Allocator, file: File, list: *std.ArrayList(u8), limit: Io.Limit) CollectOutputError!void {
    var fr = file.readerStreaming(io, &.{});
    fr.interface.appendRemaining(gpa, list, limit) catch |err| switch (err) {
        error.ReadFailed => return fr.err.?,
        else => |e| return e,
    };
}