// This file is part of the uutils coreutils package.
//
// (c) Virgile Andreani <virgile.andreani@anbuco.fr>
// (c) kwantam <kwantam@gmail.com>
//     * 2015-04-28 ~ updated to work with both UTF-8 and non-UTF-8 encodings
//
// For the full copyright and license information, please view the LICENSE
// file that was distributed with this source code.

// spell-checker:ignore (ToDO) ctype cwidth iflag nbytes nspaces nums tspaces uflag

#[macro_use]
extern crate uucore;

use clap::{crate_version, App, Arg, ArgMatches};
use std::fs::File;
use std::io::{stdin, stdout, BufRead, BufReader, BufWriter, Read, Write};
use std::str::from_utf8;
use unicode_width::UnicodeWidthChar;

static ABOUT: &str = "Convert tabs in each FILE to spaces, writing to standard output.
 With no FILE, or when FILE is -, read standard input.";

pub mod options {
    pub static TABS: &str = "tabs";
    pub static INITIAL: &str = "initial";
    pub static NO_UTF8: &str = "no-utf8";
    pub static FILES: &str = "FILES";
}

static LONG_HELP: &str = "";

static DEFAULT_TABSTOP: usize = 8;

fn get_usage() -> String {
    format!("{0} [OPTION]... [FILE]...", executable!())
}

/// The mode to use when replacing tabs beyond the last one specified in
/// the `--tabs` argument.
enum RemainingMode {
    None,
    Slash,
    Plus,
}

/// Decide whether the character is either a space or a comma.
///
/// # Examples
///
/// ```rust,ignore
/// assert!(is_space_or_comma(' '))
/// assert!(is_space_or_comma(','))
/// assert!(!is_space_or_comma('a'))
/// ```
fn is_space_or_comma(c: char) -> bool {
    c == ' ' || c == ','
}

/// Parse a list of tabstops from a `--tabs` argument.
///
/// This function returns both the vector of numbers appearing in the
/// comma- or space-separated list, and also an optional mode, specified
/// by either a "/" or a "+" character appearing before the final number
/// in the list. This mode defines the strategy to use for computing the
/// number of spaces to use for columns beyond the end of the tab stop
/// list specified here.
fn tabstops_parse(s: String) -> (RemainingMode, Vec<usize>) {
    // Leading commas and spaces are ignored.
    let s = s.trim_start_matches(is_space_or_comma);

    // If there were only commas and spaces in the string, just use the
    // default tabstops.
    if s.is_empty() {
        return (RemainingMode::None, vec![DEFAULT_TABSTOP]);
    }

    let mut nums = vec![];
    let mut remaining_mode = RemainingMode::None;
    for word in s.split(is_space_or_comma) {
        let bytes = word.as_bytes();
        for i in 0..bytes.len() {
            match bytes[i] {
                b'+' => {
                    remaining_mode = RemainingMode::Plus;
                }
                b'/' => {
                    remaining_mode = RemainingMode::Slash;
                }
                _ => {
                    // Parse a number from the byte sequence.
                    let num = from_utf8(&bytes[i..]).unwrap().parse::<usize>().unwrap();

                    // Tab size must be positive.
                    if num == 0 {
                        crash!(1, "{}\n", "tab size cannot be 0");
                    }

                    // Tab sizes must be ascending.
                    if let Some(last_stop) = nums.last() {
                        if *last_stop >= num {
                            crash!(1, "tab sizes must be ascending");
                        }
                    }

                    // Append this tab stop to the list of all tabstops.
                    nums.push(num);
                    break;
                }
            }
        }
    }
    // If no numbers could be parsed (for example, if `s` were "+,+,+"),
    // then just use the default tabstops.
    if nums.is_empty() {
        nums = vec![DEFAULT_TABSTOP];
    }
    (remaining_mode, nums)
}

struct Options {
    files: Vec<String>,
    tabstops: Vec<usize>,
    tspaces: String,
    iflag: bool,
    uflag: bool,

    /// Strategy for expanding tabs for columns beyond those specified
    /// in `tabstops`.
    remaining_mode: RemainingMode,
}

impl Options {
    fn new(matches: &ArgMatches) -> Options {
        let (remaining_mode, tabstops) = match matches.value_of(options::TABS) {
            Some(s) => tabstops_parse(s.to_string()),
            None => (RemainingMode::None, vec![DEFAULT_TABSTOP]),
        };

        let iflag = matches.is_present(options::INITIAL);
        let uflag = !matches.is_present(options::NO_UTF8);

        // avoid allocations when dumping out long sequences of spaces
        // by precomputing the longest string of spaces we will ever need
        let nspaces = tabstops
            .iter()
            .scan(0, |pr, &it| {
                let ret = Some(it - *pr);
                *pr = it;
                ret
            })
            .max()
            .unwrap(); // length of tabstops is guaranteed >= 1
        let tspaces = " ".repeat(nspaces);

        let files: Vec<String> = match matches.values_of(options::FILES) {
            Some(s) => s.map(|v| v.to_string()).collect(),
            None => vec!["-".to_owned()],
        };

        Options {
            files,
            tabstops,
            tspaces,
            iflag,
            uflag,
            remaining_mode,
        }
    }
}

pub fn uumain(args: impl uucore::Args) -> i32 {
    let usage = get_usage();
    let matches = uu_app().usage(&usage[..]).get_matches_from(args);

    expand(Options::new(&matches));
    0
}

pub fn uu_app() -> App<'static, 'static> {
    App::new(executable!())
        .version(crate_version!())
        .about(ABOUT)
        .after_help(LONG_HELP)
        .arg(
            Arg::with_name(options::INITIAL)
                .long(options::INITIAL)
                .short("i")
                .help("do not convert tabs after non blanks"),
        )
        .arg(
            Arg::with_name(options::TABS)
                .long(options::TABS)
                .short("t")
                .value_name("N, LIST")
                .takes_value(true)
                .help("have tabs N characters apart, not 8 or use comma separated list of explicit tab positions"),
        )
        .arg(
            Arg::with_name(options::NO_UTF8)
                .long(options::NO_UTF8)
                .short("U")
                .help("interpret input file as 8-bit ASCII rather than UTF-8"),
        ).arg(
            Arg::with_name(options::FILES)
                .multiple(true)
                .hidden(true)
                .takes_value(true)
        )
}

fn open(path: String) -> BufReader<Box<dyn Read + 'static>> {
    let file_buf;
    if path == "-" {
        BufReader::new(Box::new(stdin()) as Box<dyn Read>)
    } else {
        file_buf = match File::open(&path[..]) {
            Ok(a) => a,
            Err(e) => crash!(1, "{}: {}\n", &path[..], e),
        };
        BufReader::new(Box::new(file_buf) as Box<dyn Read>)
    }
}

/// Compute the number of spaces to the next tabstop.
///
/// `tabstops` is the sequence of tabstop locations.
///
/// `col` is the index of the current cursor in the line being written.
///
/// If `remaining_mode` is [`RemainingMode::Plus`], then the last entry
/// in the `tabstops` slice is interpreted as a relative number of
/// spaces, which this function will return for every input value of
/// `col` beyond the end of the second-to-last element of `tabstops`.
///
/// If `remaining_mode` is [`RemainingMode::Plus`], then the last entry
/// in the `tabstops` slice is interpreted as a relative number of
/// spaces, which this function will return for every input value of
/// `col` beyond the end of the second-to-last element of `tabstops`.
fn next_tabstop(tabstops: &[usize], col: usize, remaining_mode: &RemainingMode) -> usize {
    let num_tabstops = tabstops.len();
    match remaining_mode {
        RemainingMode::Plus => match tabstops[0..num_tabstops - 1].iter().find(|&&t| t > col) {
            Some(t) => t - col,
            None => tabstops[num_tabstops - 1] - 1,
        },
        RemainingMode::Slash => match tabstops[0..num_tabstops - 1].iter().find(|&&t| t > col) {
            Some(t) => t - col,
            None => tabstops[num_tabstops - 1] - col % tabstops[num_tabstops - 1],
        },
        RemainingMode::None => {
            if num_tabstops == 1 {
                tabstops[0] - col % tabstops[0]
            } else {
                match tabstops.iter().find(|&&t| t > col) {
                    Some(t) => t - col,
                    None => 1,
                }
            }
        }
    }
}

#[derive(PartialEq, Eq, Debug)]
enum CharType {
    Backspace,
    Tab,
    Other,
}

fn expand(options: Options) {
    use self::CharType::*;

    let mut output = BufWriter::new(stdout());
    let ts = options.tabstops.as_ref();
    let mut buf = Vec::new();

    for file in options.files.into_iter() {
        let mut fh = open(file);

        while match fh.read_until(b'\n', &mut buf) {
            Ok(s) => s > 0,
            Err(_) => buf.is_empty(),
        } {
            let mut col = 0;
            let mut byte = 0;
            let mut init = true;

            while byte < buf.len() {
                let (ctype, cwidth, nbytes) = if options.uflag {
                    let nbytes = char::from(buf[byte]).len_utf8();

                    if byte + nbytes > buf.len() {
                        // don't overrun buffer because of invalid UTF-8
                        (Other, 1, 1)
                    } else if let Ok(t) = from_utf8(&buf[byte..byte + nbytes]) {
                        match t.chars().next() {
                            Some('\t') => (Tab, 0, nbytes),
                            Some('\x08') => (Backspace, 0, nbytes),
                            Some(c) => (Other, UnicodeWidthChar::width(c).unwrap_or(0), nbytes),
                            None => {
                                // no valid char at start of t, so take 1 byte
                                (Other, 1, 1)
                            }
                        }
                    } else {
                        (Other, 1, 1) // implicit assumption: non-UTF-8 char is 1 col wide
                    }
                } else {
                    (
                        match buf[byte] {
                            // always take exactly 1 byte in strict ASCII mode
                            0x09 => Tab,
                            0x08 => Backspace,
                            _ => Other,
                        },
                        1,
                        1,
                    )
                };

                // figure out how many columns this char takes up
                match ctype {
                    Tab => {
                        // figure out how many spaces to the next tabstop
                        let nts = next_tabstop(ts, col, &options.remaining_mode);
                        col += nts;

                        // now dump out either spaces if we're expanding, or a literal tab if we're not
                        if init || !options.iflag {
                            if nts <= options.tspaces.len() {
                                safe_unwrap!(output.write_all(options.tspaces[..nts].as_bytes()));
                            } else {
                                safe_unwrap!(output.write_all(" ".repeat(nts).as_bytes()));
                            };
                        } else {
                            safe_unwrap!(output.write_all(&buf[byte..byte + nbytes]));
                        }
                    }
                    _ => {
                        col = if ctype == Other {
                            col + cwidth
                        } else if col > 0 {
                            col - 1
                        } else {
                            0
                        };

                        // if we're writing anything other than a space, then we're
                        // done with the line's leading spaces
                        if buf[byte] != 0x20 {
                            init = false;
                        }

                        safe_unwrap!(output.write_all(&buf[byte..byte + nbytes]));
                    }
                }

                byte += nbytes; // advance the pointer
            }

            safe_unwrap!(output.flush());
            buf.truncate(0); // clear the buffer
        }
    }
}

#[cfg(test)]
mod tests {
    use super::next_tabstop;
    use super::RemainingMode;

    #[test]
    fn test_next_tabstop_remaining_mode_none() {
        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::None), 1);
        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::None), 2);
        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::None), 1);
    }

    #[test]
    fn test_next_tabstop_remaining_mode_plus() {
        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::Plus), 1);
        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::Plus), 4);
        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::Plus), 4);
    }

    #[test]
    fn test_next_tabstop_remaining_mode_slash() {
        assert_eq!(next_tabstop(&[1, 5], 0, &RemainingMode::Slash), 1);
        assert_eq!(next_tabstop(&[1, 5], 3, &RemainingMode::Slash), 2);
        assert_eq!(next_tabstop(&[1, 5], 6, &RemainingMode::Slash), 4);
    }
}
