module os

fn C.setpgid(pid i32, pgid i32) i32

fn env_value_from_entries(env []string, name string) ?string {
    prefix := '${name}='
    for entry in env {
        if entry.starts_with(prefix) {
            return entry[prefix.len..]
        }
    }
    return none
}

fn (p &Process) unix_resolve_filename() !string {
    if is_abs_path(p.filename) {
        return p.filename
    }
    if p.filename.contains(path_separator) {
        if p.work_folder != '' {
            return abs_path(p.filename)
        }
        return p.filename
    }
    path := env_value_from_entries(p.env, 'PATH') or { return error_failed_to_find_executable() }
    return find_abs_path_of_executable_in_path_env(p.filename, path)
}

fn (mut p Process) unix_spawn_process() int {
    mut pipeset := [6]int{}
    if p.use_stdio_ctl {
        mut dont_care := C.pipe(&pipeset[0]) // pipe read end 0 <- 1 pipe write end
        dont_care = C.pipe(&pipeset[2]) // pipe read end 2 <- 3 pipe write end
        dont_care = C.pipe(&pipeset[4]) // pipe read end 4 <- 5 pipe write end
        _ = dont_care // using `_` directly on each above `pipe` fails to avoid C compiler generate an `-Wunused-result` warning
    }
    pid := fork()
    if pid != 0 {
        // This is the parent process after the fork.
        // Note: pid contains the process ID of the child process
        if p.use_stdio_ctl {
            p.stdio_fd[0] = pipeset[1] // store the write end of child's in
            p.stdio_fd[1] = pipeset[2] // store the read end of child's out
            p.stdio_fd[2] = pipeset[4] // store the read end of child's err
            // close the rest of the pipe fds, the parent does not need them
            fd_close(pipeset[0])
            fd_close(pipeset[3])
            fd_close(pipeset[5])
        }
        return pid
    }
    //
    // Here, we are in the child process.
    // It still shares file descriptors with the parent process,
    // but it is otherwise independent and can do stuff *without*
    // affecting the parent process.
    //
    if p.use_pgroup {
        C.setpgid(0, 0)
    }
    if p.use_stdio_ctl {
        // Redirect the child standard in/out/err to the pipes that
        // were created in the parent.
        // Close the parent's pipe fds, the child do not need them:
        fd_close(pipeset[1])
        fd_close(pipeset[2])
        fd_close(pipeset[4])
        // redirect the pipe fds to the child's in/out/err fds:
        C.dup2(pipeset[0], 0)
        C.dup2(pipeset[3], 1)
        C.dup2(pipeset[5], 2)
        // close the pipe fdsx after the redirection
        fd_close(pipeset[0])
        fd_close(pipeset[3])
        fd_close(pipeset[5])
    }
    p.filename = p.unix_resolve_filename() or {
        eprintln(err)
        exit(1)
    }
    if p.work_folder != '' {
        chdir(p.work_folder) or {}
    }
    execve(p.filename, p.args, p.env) or {
        eprintln(err)
        exit(1)
    }
    return 0
}

fn (mut p Process) unix_stop_process() {
    C.kill(p.pid, C.SIGSTOP)
}

fn (mut p Process) unix_resume_process() {
    C.kill(p.pid, C.SIGCONT)
}

fn (mut p Process) unix_term_process() {
    C.kill(p.pid, C.SIGTERM)
}

fn (mut p Process) unix_kill_process() {
    C.kill(p.pid, C.SIGKILL)
}

fn (mut p Process) unix_kill_pgroup() {
    C.kill(-p.pid, C.SIGKILL)
}

fn (mut p Process) unix_wait() {
    p.impl_check_pid_status(false, 0)
}

fn (mut p Process) unix_is_alive() bool {
    return p.impl_check_pid_status(true, C.WNOHANG)
}

fn (mut p Process) impl_check_pid_status(exit_early_on_ret0 bool, waitpid_options int) bool {
    mut cstatus := 0
    mut ret := -1
    $if !emscripten ? {
        ret = C.waitpid(p.pid, &cstatus, waitpid_options)
    }
    p.code = ret
    if ret == -1 {
        p.err = posix_get_error_msg(C.errno)
        return false
    }
    if exit_early_on_ret0 && ret == 0 {
        return true
    }
    mut pret, is_signaled := posix_wait4_to_exit_status(cstatus)
    if is_signaled {
        p.status = .aborted
        p.err = 'Terminated by signal ${pret:2d} (${sigint_to_signal_name(pret)})'
        pret += 128
    } else {
        p.status = .exited
    }
    p.code = pret
    return false
}

// these are here to make v_win.c/v.c generation work in all cases:
fn (mut p Process) win_spawn_process() int {
    return 0
}

fn (mut p Process) win_stop_process() {
}

fn (mut p Process) win_resume_process() {
}

fn (mut p Process) win_term_process() {
}

fn (mut p Process) win_kill_process() {
}

fn (mut p Process) win_kill_pgroup() {
}

fn (mut p Process) win_wait() {
}

fn (mut p Process) win_is_alive() bool {
    return false
}

fn (mut p Process) win_write_string(_idx int, _s string) {
}

fn (mut p Process) win_read_string(_idx int, _maxbytes int) (string, int) {
    return '', 0
}

fn (mut p Process) win_is_pending(_idx int) bool {
    return false
}

fn (mut p Process) win_slurp(_idx int) string {
    return ''
}