//  * This file is part of `fmt` from the uutils coreutils package.
//  *
//  * (c) kwantam <kwantam@gmail.com>
//  *
//  * For the full copyright and license information, please view the LICENSE
//  * file that was distributed with this source code.

// spell-checker:ignore (ToDO) INFTY MULT PSKIP accum aftertab beforetab breakwords fmt's formatline linebreak linebreaking linebreaks linelen maxlength minlength nchars noformat noformatline ostream overlen parasplit pfxind plass pmatch poffset posn powf prefixindent punct signum slen sstart tabwidth tlen underlen winfo wlen wordlen wordsplits xanti xprefix

use std::io::{BufRead, Lines};
use std::iter::Peekable;
use std::slice::Iter;
use unicode_width::UnicodeWidthChar;

use crate::FileOrStdReader;
use crate::FmtOptions;

fn char_width(c: char) -> usize {
    if (c as usize) < 0xA0 {
        // if it is ASCII, call it exactly 1 wide (including control chars)
        // calling control chars' widths 1 is consistent with OpenBSD fmt
        1
    } else {
        // otherwise, get the unicode width
        // note that we shouldn't actually get None here because only c < 0xA0
        // can return None, but for safety and future-proofing we do it this way
        UnicodeWidthChar::width(c).unwrap_or(1)
    }
}

// lines with PSKIP, lacking PREFIX, or which are entirely blank are
// NoFormatLines; otherwise, they are FormatLines
#[derive(Debug)]
pub enum Line {
    FormatLine(FileLine),
    NoFormatLine(String, bool),
}

impl Line {
    // when we know that it's a FormatLine, as in the ParagraphStream iterator
    fn get_formatline(self) -> FileLine {
        match self {
            Self::FormatLine(fl) => fl,
            Self::NoFormatLine(..) => panic!("Found NoFormatLine when expecting FormatLine"),
        }
    }

    // when we know that it's a NoFormatLine, as in the ParagraphStream iterator
    fn get_noformatline(self) -> (String, bool) {
        match self {
            Self::NoFormatLine(s, b) => (s, b),
            Self::FormatLine(..) => panic!("Found FormatLine when expecting NoFormatLine"),
        }
    }
}

// each line's prefix has to be considered to know whether to merge it with
// the next line or not
#[derive(Debug)]
pub struct FileLine {
    line: String,
    indent_end: usize, // the end of the indent, always the start of the text
    pfxind_end: usize, // the end of the PREFIX's indent, that is, the spaces before the prefix
    indent_len: usize, // display length of indent taking into account tabs
    prefix_len: usize, // PREFIX indent length taking into account tabs
}

// iterator that produces a stream of Lines from a file
pub struct FileLines<'a> {
    opts: &'a FmtOptions,
    lines: Lines<&'a mut FileOrStdReader>,
}

impl<'a> FileLines<'a> {
    fn new<'b>(opts: &'b FmtOptions, lines: Lines<&'b mut FileOrStdReader>) -> FileLines<'b> {
        FileLines { opts, lines }
    }

    // returns true if this line should be formatted
    fn match_prefix(&self, line: &str) -> (bool, usize) {
        if !self.opts.use_prefix {
            return (true, 0);
        }

        FileLines::match_prefix_generic(&self.opts.prefix[..], line, self.opts.xprefix)
    }

    // returns true if this line should be formatted
    fn match_anti_prefix(&self, line: &str) -> bool {
        if !self.opts.use_anti_prefix {
            return true;
        }

        match FileLines::match_prefix_generic(
            &self.opts.anti_prefix[..],
            line,
            self.opts.xanti_prefix,
        ) {
            (true, _) => false,
            (_, _) => true,
        }
    }

    fn match_prefix_generic(pfx: &str, line: &str, exact: bool) -> (bool, usize) {
        if line.starts_with(pfx) {
            return (true, 0);
        }

        if !exact {
            // we do it this way rather than byte indexing to support unicode whitespace chars
            for (i, char) in line.char_indices() {
                if line[i..].starts_with(pfx) {
                    return (true, i);
                } else if !char.is_whitespace() {
                    break;
                }
            }
        }

        (false, 0)
    }

    fn compute_indent(&self, string: &str, prefix_end: usize) -> (usize, usize, usize) {
        let mut prefix_len = 0;
        let mut indent_len = 0;
        let mut indent_end = 0;
        for (os, c) in string.char_indices() {
            if os == prefix_end {
                // we found the end of the prefix, so this is the printed length of the prefix here
                prefix_len = indent_len;
            }

            if (os >= prefix_end) && !c.is_whitespace() {
                // found first non-whitespace after prefix, this is indent_end
                indent_end = os;
                break;
            } else if c == '\t' {
                // compute tab length
                indent_len = (indent_len / self.opts.tabwidth + 1) * self.opts.tabwidth;
            } else {
                // non-tab character
                indent_len += char_width(c);
            }
        }
        (indent_end, prefix_len, indent_len)
    }
}

impl<'a> Iterator for FileLines<'a> {
    type Item = Line;

    fn next(&mut self) -> Option<Line> {
        let n = match self.lines.next() {
            Some(t) => match t {
                Ok(tt) => tt,
                Err(_) => return None,
            },
            None => return None,
        };

        // if this line is entirely whitespace,
        // emit a blank line
        // Err(true) indicates that this was a linebreak,
        // which is important to know when detecting mail headers
        if n.chars().all(char::is_whitespace) {
            return Some(Line::NoFormatLine(String::new(), true));
        }

        let (pmatch, poffset) = self.match_prefix(&n[..]);

        // if this line does not match the prefix,
        // emit the line unprocessed and iterate again
        if !pmatch {
            return Some(Line::NoFormatLine(n, false));
        }

        // if the line matches the prefix, but is blank after,
        // don't allow lines to be combined through it (that is,
        // treat it like a blank line, except that since it's
        // not truly blank we will not allow mail headers on the
        // following line)
        if pmatch
            && n[poffset + self.opts.prefix.len()..]
                .chars()
                .all(char::is_whitespace)
        {
            return Some(Line::NoFormatLine(n, false));
        }

        // skip if this line matches the anti_prefix
        // (NOTE definition of match_anti_prefix is TRUE if we should process)
        if !self.match_anti_prefix(&n[..]) {
            return Some(Line::NoFormatLine(n, false));
        }

        // figure out the indent, prefix, and prefixindent ending points
        let prefix_end = poffset + self.opts.prefix.len();
        let (indent_end, prefix_len, indent_len) = self.compute_indent(&n[..], prefix_end);

        Some(Line::FormatLine(FileLine {
            line: n,
            indent_end,
            pfxind_end: poffset,
            indent_len,
            prefix_len,
        }))
    }
}

// a paragraph : a collection of FileLines that are to be formatted
// plus info about the paragraph's indentation
// (but we only retain the String from the FileLine; the other info
// is only there to help us in deciding how to merge lines into Paragraphs
#[derive(Debug)]
pub struct Paragraph {
    lines: Vec<String>,     // the lines of the file
    pub init_str: String,   // string representing the init, that is, the first line's indent
    pub init_len: usize,    // printable length of the init string considering TABWIDTH
    init_end: usize,        // byte location of end of init in first line String
    pub indent_str: String, // string representing indent
    pub indent_len: usize,  // length of above
    indent_end: usize, // byte location of end of indent (in crown and tagged mode, only applies to 2nd line and onward)
    pub mail_header: bool, // we need to know if this is a mail header because we do word splitting differently in that case
}

// an iterator producing a stream of paragraphs from a stream of lines
// given a set of options.
pub struct ParagraphStream<'a> {
    lines: Peekable<FileLines<'a>>,
    next_mail: bool,
    opts: &'a FmtOptions,
}

impl<'a> ParagraphStream<'a> {
    pub fn new<'b>(opts: &'b FmtOptions, reader: &'b mut FileOrStdReader) -> ParagraphStream<'b> {
        let lines = FileLines::new(opts, reader.lines()).peekable();
        // at the beginning of the file, we might find mail headers
        ParagraphStream {
            lines,
            next_mail: true,
            opts,
        }
    }

    // detect RFC822 mail header
    fn is_mail_header(line: &FileLine) -> bool {
        // a mail header begins with either "From " (envelope sender line)
        // or with a sequence of printable ASCII chars (33 to 126, inclusive,
        // except colon) followed by a colon.
        if line.indent_end > 0 {
            false
        } else {
            let l_slice = &line.line[..];
            if l_slice.starts_with("From ") {
                true
            } else {
                let colon_posn = match l_slice.find(':') {
                    Some(n) => n,
                    None => return false,
                };

                // header field must be nonzero length
                if colon_posn == 0 {
                    return false;
                }

                l_slice[..colon_posn]
                    .chars()
                    .all(|x| !matches!(x as usize, y if !(33..=126).contains(&y)))
            }
        }
    }
}

impl<'a> Iterator for ParagraphStream<'a> {
    type Item = Result<Paragraph, String>;

    fn next(&mut self) -> Option<Result<Paragraph, String>> {
        // return a NoFormatLine in an Err; it should immediately be output
        let noformat = match self.lines.peek() {
            None => return None,
            Some(l) => match *l {
                Line::FormatLine(_) => false,
                Line::NoFormatLine(_, _) => true,
            },
        };

        // found a NoFormatLine, immediately dump it out
        if noformat {
            let (s, nm) = self.lines.next().unwrap().get_noformatline();
            self.next_mail = nm;
            return Some(Err(s));
        }

        // found a FormatLine, now build a paragraph
        let mut init_str = String::new();
        let mut init_end = 0;
        let mut init_len = 0;
        let mut indent_str = String::new();
        let mut indent_end = 0;
        let mut indent_len = 0;
        let mut prefix_len = 0;
        let mut pfxind_end = 0;
        let mut p_lines = Vec::new();

        let mut in_mail = false;
        let mut second_done = false; // for when we use crown or tagged mode
        loop {
            {
                // peek ahead
                // need to explicitly force fl out of scope before we can call self.lines.next()
                let fl = match self.lines.peek() {
                    None => break,
                    Some(l) => match *l {
                        Line::FormatLine(ref x) => x,
                        Line::NoFormatLine(..) => break,
                    },
                };

                if p_lines.is_empty() {
                    // first time through the loop, get things set up
                    // detect mail header
                    if self.opts.mail && self.next_mail && ParagraphStream::is_mail_header(fl) {
                        in_mail = true;
                        // there can't be any indent or pfxind because otherwise is_mail_header
                        // would fail since there cannot be any whitespace before the colon in a
                        // valid header field
                        indent_str.push_str("  ");
                        indent_len = 2;
                    } else {
                        if self.opts.crown || self.opts.tagged {
                            init_str.push_str(&fl.line[..fl.indent_end]);
                            init_len = fl.indent_len;
                            init_end = fl.indent_end;
                        } else {
                            second_done = true;
                        }

                        // these will be overwritten in the 2nd line of crown or tagged mode, but
                        // we are not guaranteed to get to the 2nd line, e.g., if the next line
                        // is a NoFormatLine or None. Thus, we set sane defaults the 1st time around
                        indent_str.push_str(&fl.line[..fl.indent_end]);
                        indent_len = fl.indent_len;
                        indent_end = fl.indent_end;

                        // save these to check for matching lines
                        prefix_len = fl.prefix_len;
                        pfxind_end = fl.pfxind_end;

                        // in tagged mode, add 4 spaces of additional indenting by default
                        // (gnu fmt's behavior is different: it seems to find the closest column to
                        // indent_end that is divisible by 3. But honestly that behavior seems
                        // pretty arbitrary.
                        // Perhaps a better default would be 1 TABWIDTH? But ugh that's so big.
                        if self.opts.tagged {
                            indent_str.push_str("    ");
                            indent_len += 4;
                        }
                    }
                } else if in_mail {
                    // lines following mail headers must begin with spaces
                    if fl.indent_end == 0 || (self.opts.use_prefix && fl.pfxind_end == 0) {
                        break; // this line does not begin with spaces
                    }
                } else if !second_done {
                    // now we have enough info to handle crown margin and tagged mode

                    // in both crown and tagged modes we require that prefix_len is the same
                    if prefix_len != fl.prefix_len || pfxind_end != fl.pfxind_end {
                        break;
                    }

                    // in tagged mode, indent has to be *different* on following lines
                    if self.opts.tagged
                        && indent_len - 4 == fl.indent_len
                        && indent_end == fl.indent_end
                    {
                        break;
                    }

                    // this is part of the same paragraph, get the indent info from this line
                    indent_str.clear();
                    indent_str.push_str(&fl.line[..fl.indent_end]);
                    indent_len = fl.indent_len;
                    indent_end = fl.indent_end;

                    second_done = true;
                } else {
                    // detect mismatch
                    if indent_end != fl.indent_end
                        || pfxind_end != fl.pfxind_end
                        || indent_len != fl.indent_len
                        || prefix_len != fl.prefix_len
                    {
                        break;
                    }
                }
            }

            p_lines.push(self.lines.next().unwrap().get_formatline().line);

            // when we're in split-only mode, we never join lines, so stop here
            if self.opts.split_only {
                break;
            }
        }

        // if this was a mail header, then the next line can be detected as one. Otherwise, it cannot.
        // NOTE next_mail is true at ParagraphStream instantiation, and is set to true after a blank
        // NoFormatLine.
        self.next_mail = in_mail;

        Some(Ok(Paragraph {
            lines: p_lines,
            init_str,
            init_len,
            init_end,
            indent_str,
            indent_len,
            indent_end,
            mail_header: in_mail,
        }))
    }
}

pub struct ParaWords<'a> {
    opts: &'a FmtOptions,
    para: &'a Paragraph,
    words: Vec<WordInfo<'a>>,
}

impl<'a> ParaWords<'a> {
    pub fn new<'b>(opts: &'b FmtOptions, para: &'b Paragraph) -> ParaWords<'b> {
        let mut pw = ParaWords {
            opts,
            para,
            words: Vec::new(),
        };
        pw.create_words();
        pw
    }

    fn create_words(&mut self) {
        if self.para.mail_header {
            // no extra spacing for mail headers; always exactly 1 space
            // safe to trim_start on every line of a mail header, since the
            // first line is guaranteed not to have any spaces
            self.words.extend(
                self.para
                    .lines
                    .iter()
                    .flat_map(|x| x.split_whitespace())
                    .map(|x| WordInfo {
                        word: x,
                        word_start: 0,
                        word_nchars: x.len(), // OK for mail headers; only ASCII allowed (unicode is escaped)
                        before_tab: None,
                        after_tab: 0,
                        sentence_start: false,
                        ends_punct: false,
                        new_line: false,
                    }),
            );
        } else {
            // first line
            self.words.extend(if self.opts.crown || self.opts.tagged {
                // crown and tagged mode has the "init" in the first line, so slice from there
                WordSplit::new(self.opts, &self.para.lines[0][self.para.init_end..])
            } else {
                // otherwise we slice from the indent
                WordSplit::new(self.opts, &self.para.lines[0][self.para.indent_end..])
            });

            if self.para.lines.len() > 1 {
                let indent_end = self.para.indent_end;
                let opts = self.opts;
                self.words.extend(
                    self.para
                        .lines
                        .iter()
                        .skip(1)
                        .flat_map(|x| WordSplit::new(opts, &x[indent_end..])),
                );
            }
        }
    }

    pub fn words(&'a self) -> Iter<'a, WordInfo<'a>> {
        self.words.iter()
    }
}

struct WordSplit<'a> {
    opts: &'a FmtOptions,
    string: &'a str,
    length: usize,
    position: usize,
    prev_punct: bool,
}

impl<'a> WordSplit<'a> {
    fn analyze_tabs(&self, string: &str) -> (Option<usize>, usize, Option<usize>) {
        // given a string, determine (length before tab) and (printed length after first tab)
        // if there are no tabs, beforetab = -1 and aftertab is the printed length
        let mut beforetab = None;
        let mut aftertab = 0;
        let mut word_start = None;
        for (os, c) in string.char_indices() {
            if !c.is_whitespace() {
                word_start = Some(os);
                break;
            } else if c == '\t' {
                if beforetab.is_none() {
                    beforetab = Some(aftertab);
                    aftertab = 0;
                } else {
                    aftertab = (aftertab / self.opts.tabwidth + 1) * self.opts.tabwidth;
                }
            } else {
                aftertab += 1;
            }
        }
        (beforetab, aftertab, word_start)
    }
}

impl<'a> WordSplit<'a> {
    fn new<'b>(opts: &'b FmtOptions, string: &'b str) -> WordSplit<'b> {
        // wordsplits *must* start at a non-whitespace character
        let trim_string = string.trim_start();
        WordSplit {
            opts,
            string: trim_string,
            length: string.len(),
            position: 0,
            prev_punct: false,
        }
    }

    fn is_punctuation(c: char) -> bool {
        matches!(c, '!' | '.' | '?')
    }
}

pub struct WordInfo<'a> {
    pub word: &'a str,
    pub word_start: usize,
    pub word_nchars: usize,
    pub before_tab: Option<usize>,
    pub after_tab: usize,
    pub sentence_start: bool,
    pub ends_punct: bool,
    pub new_line: bool,
}

// returns (&str, is_start_of_sentence)
impl<'a> Iterator for WordSplit<'a> {
    type Item = WordInfo<'a>;

    fn next(&mut self) -> Option<WordInfo<'a>> {
        if self.position >= self.length {
            return None;
        }

        let old_position = self.position;
        let new_line = old_position == 0;

        // find the start of the next word, and record if we find a tab character
        let (before_tab, after_tab, word_start) =
            match self.analyze_tabs(&self.string[old_position..]) {
                (b, a, Some(s)) => (b, a, s + old_position),
                (_, _, None) => {
                    self.position = self.length;
                    return None;
                }
            };

        // find the beginning of the next whitespace
        // note that this preserves the invariant that self.position
        // points to whitespace character OR end of string
        let mut word_nchars = 0;
        self.position = match self.string[word_start..].find(|x: char| {
            if !x.is_whitespace() {
                word_nchars += char_width(x);
                false
            } else {
                true
            }
        }) {
            None => self.length,
            Some(s) => s + word_start,
        };

        let word_start_relative = word_start - old_position;
        // if the previous sentence was punctuation and this sentence has >2 whitespace or one tab, is a new sentence.
        let is_start_of_sentence =
            self.prev_punct && (before_tab.is_some() || word_start_relative > 1);

        // now record whether this word ends in punctuation
        self.prev_punct = match self.string[..self.position].chars().rev().next() {
            Some(ch) => WordSplit::is_punctuation(ch),
            _ => panic!("fatal: expected word not to be empty"),
        };

        let (word, word_start_relative, before_tab, after_tab) = if self.opts.uniform {
            (&self.string[word_start..self.position], 0, None, 0)
        } else {
            (
                &self.string[old_position..self.position],
                word_start_relative,
                before_tab,
                after_tab,
            )
        };

        Some(WordInfo {
            word,
            word_start: word_start_relative,
            word_nchars,
            before_tab,
            after_tab,
            sentence_start: is_start_of_sentence,
            ends_punct: self.prev_punct,
            new_line,
        })
    }
}
