// yt - A fully featured command line YouTube client
//
// Copyright (C) 2025 Benedikt Peetz <benedikt.peetz@b-peetz.de>
// Copyright (C) 2025 uutils developers
// SPDX-License-Identifier: MIT
//
// This file is part of Yt.
//
// You should have received a copy of the License along with this program.
// If not, see <https://www.gnu.org/licenses/gpl-3.0.txt>.

// This file is part of the uutils coreutils package.
//
// For the full copyright and license information, please view the LICENSE
// file that was distributed with this source code.

use std::iter::Peekable;
use std::slice::Iter;
use unicode_width::UnicodeWidthChar;

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(super) 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(super) struct FileLine {
    line: String,
    /// The end of the indent, always the start of the text
    indent_end: usize,

    /// The end of the PREFIX's indent, that is, the spaces before the prefix
    prefix_indent_end: usize,

    /// Display length of indent taking into account tabs
    indent_len: usize,

    /// PREFIX indent length taking into account tabs
    prefix_len: usize,
}

/// Iterator that produces a stream of Lines from a file
pub(super) struct FileLines<'a> {
    opts: &'a FmtOptions,
    lines: std::str::Lines<'a>,
}

impl FileLines<'_> {
    fn new<'b>(opts: &'b FmtOptions, lines: std::str::Lines<'b>) -> FileLines<'b> {
        FileLines { opts, lines }
    }

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

        FileLines::match_prefix_generic(prefix, line, self.opts.exact_prefix)
    }

    /// returns true if this line should be formatted
    fn match_anti_prefix(&self, line: &str) -> bool {
        let Some(anti_prefix) = &self.opts.anti_prefix else {
            return true;
        };

        match FileLines::match_prefix_generic(anti_prefix, line, self.opts.exact_anti_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 Iterator for FileLines<'_> {
    type Item = Line;

    fn next(&mut self) -> Option<Line> {
        let n = self.lines.next()?;

        // 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.to_owned(), 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.as_ref().map_or(0, String::len)..]
                .chars()
                .all(char::is_whitespace)
        {
            return Some(Line::NoFormatLine(n.to_owned(), 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.to_owned(), false));
        }

        // figure out the indent, prefix, and prefixindent ending points
        let prefix_end = poffset + self.opts.prefix.as_ref().map_or(0, String::len);
        let (indent_end, prefix_len, indent_len) = self.compute_indent(n, prefix_end);

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

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

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

impl ParagraphStream<'_> {
    pub(super) fn new<'b>(opts: &'b FmtOptions, text: &'b str) -> ParagraphStream<'b> {
        let lines = FileLines::new(opts, text.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 Some(colon_posn) = l_slice.find(':') else {
                    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 Iterator for ParagraphStream<'_> {
    type Item = Result<Paragraph, String>;

    #[allow(clippy::cognitive_complexity)]
    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()? {
            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 prefix_indent_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 Some(Line::FormatLine(fl)) = self.lines.peek() else {
                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 prefixindent 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_margin || self.opts.tagged_paragraph {
                        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;
                    prefix_indent_end = fl.prefix_indent_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_paragraph {
                        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.prefix.is_some() && fl.prefix_indent_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 || prefix_indent_end != fl.prefix_indent_end {
                    break;
                }

                // in tagged mode, indent has to be *different* on following lines
                if self.opts.tagged_paragraph
                    && 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
                    || prefix_indent_end != fl.prefix_indent_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(super) struct ParaWords<'a> {
    opts: &'a FmtOptions,
    para: &'a Paragraph,
    words: Vec<WordInfo<'a>>,
}

impl<'a> ParaWords<'a> {
    pub(super) fn new(opts: &'a FmtOptions, para: &'a Paragraph) -> Self {
        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_margin || self.opts.tagged_paragraph {
                    // 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(super) 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 WordSplit<'_> {
    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 WordSplit<'_> {
    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(super) 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) =
            if let (b, a, Some(s)) = self.analyze_tabs(&self.string[old_position..]) {
                (b, a, s + old_position)
            } else {
                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() {
                true
            } else {
                word_nchars += char_width(x);
                false
            }
        }) {
            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().next_back() {
            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,
        })
    }
}