use std::env;
use std::ffi::OsString;
use std::io::{self, Write};
use std::path::PathBuf;
use std::process::{Child, Command, Stdio};

use shell_words;

use crate::errors::*;
use crate::less::retrieve_less_version;
use crate::PagingMode;

#[derive(Debug)]
pub enum OutputType {
    Pager(Child),
    Stdout(io::Stdout),
}

impl OutputType {
    pub fn from_mode(mode: PagingMode, pager: Option<&str>) -> Result<Self> {
        use self::PagingMode::*;
        Ok(match mode {
            Always => OutputType::try_pager(false, pager)?,
            QuitIfOneScreen => OutputType::try_pager(true, pager)?,
            _ => OutputType::stdout(),
        })
    }

    /// Try to launch the pager. Fall back to stdout in case of errors.
    fn try_pager(quit_if_one_screen: bool, pager_from_config: Option<&str>) -> Result<Self> {
        let mut replace_arguments_to_less = false;

        let pager_from_env = match (env::var("BAT_PAGER"), env::var("PAGER")) {
            (Ok(bat_pager), _) => Some(bat_pager),
            (_, Ok(pager)) => {
                // less needs to be called with the '-R' option in order to properly interpret the
                // ANSI color sequences printed by bat. If someone has set PAGER="less -F", we
                // therefore need to overwrite the arguments and add '-R'.
                //
                // We only do this for PAGER (as it is not specific to 'bat'), not for BAT_PAGER
                // or bats '--pager' command line option.
                replace_arguments_to_less = true;
                Some(pager)
            }
            _ => None,
        };

        let pager_from_config = pager_from_config.map(|p| p.to_string());

        if pager_from_config.is_some() {
            replace_arguments_to_less = false;
        }

        let pager = pager_from_config
            .or(pager_from_env)
            .unwrap_or_else(|| String::from("less"));

        let pagerflags =
            shell_words::split(&pager).chain_err(|| "Could not parse pager command.")?;

        match pagerflags.split_first() {
            Some((pager_name, args)) => {
                let mut pager_path = PathBuf::from(pager_name);

                if pager_path.file_stem() == Some(&OsString::from("bat")) {
                    pager_path = PathBuf::from("less");
                }

                let is_less = pager_path.file_stem() == Some(&OsString::from("less"));

                let mut process = if is_less {
                    let mut p = Command::new(&pager_path);
                    if args.is_empty() || replace_arguments_to_less {
                        p.arg("--RAW-CONTROL-CHARS");
                        if quit_if_one_screen {
                            p.arg("--quit-if-one-screen");
                        }

                        // Passing '--no-init' fixes a bug with '--quit-if-one-screen' in older
                        // versions of 'less'. Unfortunately, it also breaks mouse-wheel support.
                        //
                        // See: http://www.greenwoodsoftware.com/less/news.530.html
                        match retrieve_less_version() {
                            Some(version) if version < 530 => {
                                p.arg("--no-init");
                            }
                            _ => {}
                        }
                    } else {
                        p.args(args);
                    }
                    p.env("LESSCHARSET", "UTF-8");
                    p
                } else {
                    let mut p = Command::new(&pager_path);
                    p.args(args);
                    p
                };

                Ok(process
                    .stdin(Stdio::piped())
                    .spawn()
                    .map(OutputType::Pager)
                    .unwrap_or_else(|_| OutputType::stdout()))
            }
            None => Ok(OutputType::stdout()),
        }
    }

    fn stdout() -> Self {
        OutputType::Stdout(io::stdout())
    }

    pub fn handle(&mut self) -> Result<&mut dyn Write> {
        Ok(match *self {
            OutputType::Pager(ref mut command) => command
                .stdin
                .as_mut()
                .chain_err(|| "Could not open stdin for pager")?,
            OutputType::Stdout(ref mut handle) => handle,
        })
    }
}

impl Drop for OutputType {
    fn drop(&mut self) {
        if let OutputType::Pager(ref mut command) = *self {
            let _ = command.wait();
        }
    }
}