/*
    MIT License

    Copyright (c) 2020 Philipp Schuster

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE.
*/

pub use crate::data::{CmdChain, BasicCmd, CmdChainBuilder, BasicCmdBuilder, Builder, ProcessState};
// public in case someone want to use this abstraction
pub use crate::pipe::Pipe;

mod libc_util;
mod data;
mod pipe;


/// Runs a command chain. The parent process creates n childs and
/// connects them (stdout => stdin) together via pipes.
pub fn execute_piped_cmd_chain(cmds: &CmdChain) -> Vec<ProcessState> {
    let mut pids: Vec<libc::pid_t> = vec![];

    let mut pipe_to_current: Option<Pipe> = Option::None;
    let mut pipe_to_next: Option<Pipe> = Option::None;
    for i in 0..cmds.length() {
        let cmd = &cmds.cmds()[i];

        if pipe_to_next.is_some() {
            pipe_to_current.replace(
                pipe_to_next.take().unwrap()
            );
        }

        if !cmd.is_last() {
            pipe_to_next.replace(Pipe::new());
        }

        let pid = unsafe { libc::fork() };
        if pid == -1 {
            panic!("Fork failed! {}", errno::errno());
        }

        // parent code
        if pid > 0 {
            pids.push(pid);

            // We MUST close all FDs in the Parent
            if pipe_to_current.is_some() {
                pipe_to_current.as_mut().unwrap().parent_close_all();
            }
        }
        // child code
        else {
            // handle optional initial '< in.file' redirect
            if cmd.is_first() && cmd.in_red_path().is_some() {
                initial_ir(cmd);
            }
            // handle optional final '> out.file' redirect
            if cmd.is_last() && cmd.out_red_path().is_some() {
                final_or(cmd);
            }

            if pipe_to_current.is_some() {
                pipe_to_current.as_mut().unwrap().as_read_end();
            }
            if pipe_to_next.is_some() {
                pipe_to_next.as_mut().unwrap().as_write_end();
            }

            let _res = unsafe {
                libc::execvp(
                    cmd.executable_cstring().as_ptr(),
                    cmd.args_to_c_argv()
                )
            };
            panic!("Exec failed! {}", errno::errno());
        }
    }

    let mut i = 0;
    let mut process_states: Vec<ProcessState> = pids.into_iter()
        .map(|pid| {
            let executable = cmds.cmds()[i].executable().to_owned();
            i += 1;
            ProcessState::new(executable, pid)
        })
        .collect();

    update_process_states(&mut process_states, cmds.background());

    process_states
}

/// Updates the process state values if the pid is done running.
/// Returns true if all pids are finished, otherwise false.
///
///  * `wnohang` if waitpid uses WNOHANG-flag. In other words: true means "wait blocking"
///     and false means "update but don't block".
pub fn update_process_states(states: &mut Vec<ProcessState>, wnohang: bool) -> bool {
    // decide whether we wait blocking or non blocking
    let wait_flags: libc::c_int = if wnohang { libc::WNOHANG } else { 0 };
    let mut all_finished = true;

    // only check those that are not finished yet!
    // Important, otherwise failures happen
    states.into_iter()
        .filter(|state| !state.finished())
        .for_each(|state| {
            let mut status_code: libc::c_int = 0;
            let status_code_ptr = &mut status_code as * mut libc::c_int;

            let res = unsafe { libc::waitpid(state.pid(), status_code_ptr, wait_flags) };

            // IDE doesn't find this functions but they exist
            // returns true if the child terminated normally
            let exited_normally: bool = unsafe { libc::WIFEXITED(status_code) };

            if wait_flags == libc::WNOHANG && res == 0 {
                all_finished = false;
                // not done yet
            } else if res == -1 {
                panic!("Failure during waitpid! {}", errno::errno());
            } else {
                if !exited_normally {
                    eprintln!("Process did not exited normally! {:#?}", state);
                }
                // exit code (only if exited_normally is true)
                let exit_code: libc::c_int = unsafe { libc::WEXITSTATUS(status_code) };

                state.finish(exit_code);
                println!("Process {} finished with status code {}", state.pid(), status_code);
            }
        });
    all_finished
}

/// Handles initial input redirect (from file).
fn initial_ir(cmd: &BasicCmd) {
    let fd = unsafe {
        libc::open(
            cmd.in_red_path_cstring().unwrap().as_ptr(),
            libc::O_RDONLY,
        )
    };
    if fd == -1 {
        panic!("Input redirect path {} can't be opened/read! {}", cmd.in_red_path().as_ref().unwrap(), errno::errno());
    }
    let ret = unsafe { libc::dup2(fd, libc::STDIN_FILENO) };
    if ret == -1 {
        panic!("Error dup2() input redirect! {}", errno::errno());
    }
}

/// Handles final output redirect (to file).
fn final_or(cmd: &BasicCmd) {
    let fd = unsafe {
        // note that append won't work here because we only use the
        // '> out.file' functionality but not '>> out.file' which
        // would require the O_APPEND flag!

        // open() doesn't work; file remains empty
        // somehow fopen does some more magic..
        /*libc::open(
            cmd.out_red_path_cstring().unwrap().as_ptr(),
            libc::O_WRONLY | libc::O_CREAT,
            0644,
        );*/
        let file = libc::fopen(
            cmd.out_red_path_cstring().unwrap().as_ptr(),
            "w".as_ptr() as * const i8
        );
        // get file descriptor
        libc::fileno(file)
    };
    if fd == -1 {
        panic!("Output redirect path {} can't be opened/written! {}", cmd.out_red_path().as_ref().unwrap(), errno::errno());
    }
    let ret = unsafe { libc::dup2(fd, libc::STDOUT_FILENO) };
    if ret == -1 {
        panic!("Error dup2() output redirect! {}", errno::errno());
    }
}

#[cfg(test)]
mod tests {
    use crate::data::{CmdChainBuilder, BasicCmdBuilder, Builder};
    use crate::execute_piped_cmd_chain;

    #[test]
    fn test_execute_chain() {
        // this test works if "2" is printed to stdout

        let cmd_chain = CmdChainBuilder::new()
            .add_cmd(
                BasicCmdBuilder::new()
                    .set_executable("echo")
                    .add_arg("echo")
                    .add_arg("Hallo\nAbc\n123\nAbc123")
            ).add_cmd(
            BasicCmdBuilder::new()
                .set_executable("grep")
                .add_arg("grep")
                .add_arg("-i")
                .add_arg("abc"))
            .add_cmd(
                BasicCmdBuilder::new()
                    .set_executable("wc")
                    .add_arg("wc")
                    .add_arg("-l")
            ).build();

        execute_piped_cmd_chain(&cmd_chain);
    }
}