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    //! Text formatter.

    use crate::util::{header_text, unwrap};
    use crate::EventIter;
    use anyhow::{bail, Error};
    use pulldown_cmark::{Alignment, Event, HeadingLevel, LinkType, Tag};
    use std::fmt::Write;
    use std::mem;
    use url::Url;

    pub struct TextFormatter {
        url: Option<Url>,
    }

    impl TextFormatter {
        pub fn new(url: Option<Url>) -> TextFormatter {
            TextFormatter { url }
        }
    }

    impl super::Formatter for TextFormatter {
        fn render(&self, input: &str) -> Result<String, Error> {
            TextRenderer::render(input, self.url.clone(), 0)
        }

        fn render_options_start(&self) -> &'static str {
            // Tell pulldown_cmark to ignore this.
            // This will be stripped out later.
            "<![CDATA[\n"
        }

        fn render_options_end(&self) -> &'static str {
            "]]>\n"
        }

        fn render_option(
            &self,
            params: &[&str],
            block: &str,
            _man_name: &str,
        ) -> Result<String, Error> {
            let rendered_options = params
                .iter()
                .map(|param| TextRenderer::render(param, self.url.clone(), 0))
                .collect::<Result<Vec<_>, Error>>()?;
            let trimmed: Vec<_> = rendered_options.iter().map(|o| o.trim()).collect();
            // Wrap in HTML tags, they will be stripped out during rendering.
            Ok(format!(
                "<dt>{}</dt>\n<dd>\n{}</dd>\n<br>\n",
                trimmed.join(", "),
                block
            ))
        }

        fn linkify_man_to_md(&self, name: &str, section: u8) -> Result<String, Error> {
            Ok(format!("`{}`({})", name, section))
        }
    }

    struct TextRenderer<'e> {
        output: String,
        indent: usize,
        /// The current line being written. Once a line break is encountered (such
        /// as starting a new paragraph), this will be written to `output` via
        /// `flush`.
        line: String,
        /// The current word being written. Once a break is encountered (such as a
        /// space) this will be written to `line` via `flush_word`.
        word: String,
        parser: EventIter<'e>,
        /// The base URL used for relative URLs.
        url: Option<Url>,
        table: Table,
    }

    impl<'e> TextRenderer<'e> {
        fn render(input: &str, url: Option<Url>, indent: usize) -> Result<String, Error> {
            let parser = crate::md_parser(input, url.clone());
            let output = String::with_capacity(input.len() * 3 / 2);
            let mut mr = TextRenderer {
                output,
                indent,
                line: String::new(),
                word: String::new(),
                parser,
                url,
                table: Table::new(),
            };
            mr.push_md()?;
            Ok(mr.output)
        }

        fn push_md(&mut self) -> Result<(), Error> {
            // If this is true, this is inside a cdata block used for hiding
            // content from pulldown_cmark.
            let mut in_cdata = false;
            // The current list stack. None if unordered, Some if ordered with the
            // given number as the current index.
            let mut list: Vec<Option<u64>> = Vec::new();
            // Used in some cases where spacing isn't desired.
            let mut suppress_paragraph = false;
            // Whether or not word-wrapping is enabled.
            let mut wrap_text = true;

            while let Some((event, range)) = self.parser.next() {
                let this_suppress_paragraph = suppress_paragraph;
                // Always reset suppression, even if the next event isn't a
                // paragraph. This is in essence, a 1-token lookahead where the
                // suppression is only enabled if the next event is a paragraph.
                suppress_paragraph = false;
                match event {
                    Event::Start(tag) => {
                        match tag {
                            Tag::Paragraph => {
                                if !this_suppress_paragraph {
                                    self.flush();
                                }
                            }
                            Tag::Heading(level, ..) => {
                                self.flush();
                                if level == HeadingLevel::H1 {
                                    let text = header_text(&mut self.parser)?;
                                    self.push_to_line(&text.to_uppercase());
                                    self.hard_break();
                                    self.hard_break();
                                } else if level == HeadingLevel::H2 {
                                    let text = header_text(&mut self.parser)?;
                                    self.push_to_line(&text.to_uppercase());
                                    self.flush();
                                    self.indent = 7;
                                } else {
                                    let text = header_text(&mut self.parser)?;
                                    self.push_indent((level as usize - 2) * 3);
                                    self.push_to_line(&text);
                                    self.flush();
                                    self.indent = (level as usize - 1) * 3 + 1;
                                }
                            }
                            Tag::BlockQuote => {
                                self.indent += 3;
                            }
                            Tag::CodeBlock(_kind) => {
                                self.flush();
                                wrap_text = false;
                                self.indent += 4;
                            }
                            Tag::List(start) => list.push(start),
                            Tag::Item => {
                                self.flush();
                                match list.last_mut().expect("item must have list start") {
                                    // Ordered list.
                                    Some(n) => {
                                        self.push_indent(self.indent);
                                        write!(self.line, "{}.", n)?;
                                        *n += 1;
                                    }
                                    // Unordered list.
                                    None => {
                                        self.push_indent(self.indent);
                                        self.push_to_line("o ")
                                    }
                                }
                                self.indent += 3;
                                suppress_paragraph = true;
                            }
                            Tag::FootnoteDefinition(_label) => unimplemented!(),
                            Tag::Table(alignment) => {
                                assert!(self.table.alignment.is_empty());
                                self.flush();
                                self.table.alignment.extend(alignment);
                                let table = self.table.process(&mut self.parser, self.indent)?;
                                self.output.push_str(&table);
                                self.hard_break();
                                self.table = Table::new();
                            }
                            Tag::TableHead | Tag::TableRow | Tag::TableCell => {
                                bail!("unexpected table element")
                            }
                            Tag::Emphasis => {}
                            Tag::Strong => {}
                            // Strikethrough isn't usually supported for TTY.
                            Tag::Strikethrough => self.word.push_str("~~"),
                            Tag::Link(link_type, dest_url, _title) => {
                                if dest_url.starts_with('#') {
                                    // In a man page, page-relative anchors don't
                                    // have much meaning.
                                    continue;
                                }
                                match link_type {
                                    LinkType::Autolink | LinkType::Email => {
                                        // The text is a copy of the URL, which is not needed.
                                        match self.parser.next() {
                                            Some((Event::Text(_), _range)) => {}
                                            _ => bail!("expected text after autolink"),
                                        }
                                    }
                                    LinkType::Inline
                                    | LinkType::Reference
                                    | LinkType::Collapsed
                                    | LinkType::Shortcut => {}
                                    // This is currently unused. This is only
                                    // emitted with a broken link callback, but I
                                    // felt it is too annoying to escape `[` in
                                    // option descriptions.
                                    LinkType::ReferenceUnknown
                                    | LinkType::CollapsedUnknown
                                    | LinkType::ShortcutUnknown => {
                                        bail!(
                                            "link with missing reference `{}` located at offset {}",
                                            dest_url,
                                            range.start
                                        );
                                    }
                                }
                            }
                            Tag::Image(_link_type, _dest_url, _title) => {
                                bail!("images are not currently supported")
                            }
                        }
                    }
                    Event::End(tag) => match &tag {
                        Tag::Paragraph => {
                            self.flush();
                            self.hard_break();
                        }
                        Tag::Heading(..) => {}
                        Tag::BlockQuote => {
                            self.indent -= 3;
                        }
                        Tag::CodeBlock(_kind) => {
                            self.hard_break();
                            wrap_text = true;
                            self.indent -= 4;
                        }
                        Tag::List(_) => {
                            list.pop();
                        }
                        Tag::Item => {
                            self.flush();
                            self.indent -= 3;
                            self.hard_break();
                        }
                        Tag::FootnoteDefinition(_label) => {}
                        Tag::Table(_) => {}
                        Tag::TableHead => {}
                        Tag::TableRow => {}
                        Tag::TableCell => {}
                        Tag::Emphasis => {}
                        Tag::Strong => {}
                        Tag::Strikethrough => self.word.push_str("~~"),
                        Tag::Link(link_type, dest_url, _title) => {
                            if dest_url.starts_with('#') {
                                continue;
                            }
                            match link_type {
                                LinkType::Autolink | LinkType::Email => {}
                                LinkType::Inline
                                | LinkType::Reference
                                | LinkType::Collapsed
                                | LinkType::Shortcut => self.flush_word(),
                                _ => {
                                    panic!("unexpected tag {:?}", tag);
                                }
                            }
                            self.flush_word();
                            write!(self.word, "<{}>", dest_url)?;
                        }
                        Tag::Image(_link_type, _dest_url, _title) => {}
                    },
                    Event::Text(t) | Event::Code(t) => {
                        if wrap_text {
                            let chunks = split_chunks(&t);
                            for chunk in chunks {
                                if chunk == " " {
                                    self.flush_word();
                                } else {
                                    self.word.push_str(chunk);
                                }
                            }
                        } else {
                            for line in t.lines() {
                                self.push_indent(self.indent);
                                self.push_to_line(line);
                                self.flush();
                            }
                        }
                    }
                    Event::Html(t) => {
                        if t.starts_with("<![CDATA[") {
                            // CDATA is a special marker used for handling options.
                            in_cdata = true;
                            self.flush();
                        } else if in_cdata {
                            if t.trim().ends_with("]]>") {
                                in_cdata = false;
                            } else {
                                let trimmed = t.trim();
                                if trimmed.is_empty() {
                                    continue;
                                }
                                if trimmed == "<br>" {
                                    self.hard_break();
                                } else if trimmed.starts_with("<dt>") {
                                    let opts = unwrap(trimmed, "<dt>", "</dt>");
                                    self.push_indent(self.indent);
                                    self.push_to_line(opts);
                                    self.flush();
                                } else if trimmed.starts_with("<dd>") {
                                    let mut def = String::new();
                                    while let Some((Event::Html(t), _range)) = self.parser.next() {
                                        if t.starts_with("</dd>") {
                                            break;
                                        }
                                        def.push_str(&t);
                                    }
                                    let rendered =
                                        TextRenderer::render(&def, self.url.clone(), self.indent + 4)?;
                                    self.push_to_line(rendered.trim_end());
                                    self.flush();
                                } else {
                                    self.push_to_line(&t);
                                    self.flush();
                                }
                            }
                        } else {
                            self.push_to_line(&t);
                            self.flush();
                        }
                    }
                    Event::FootnoteReference(_t) => {}
                    Event::SoftBreak => self.flush_word(),
                    Event::HardBreak => self.flush(),
                    Event::Rule => {
                        self.flush();
                        self.push_indent(self.indent);
                        self.push_to_line(&"_".repeat(79 - self.indent * 2));
                        self.flush();
                    }
                    Event::TaskListMarker(_b) => unimplemented!(),
                }
            }
            Ok(())
        }

        fn flush(&mut self) {
            self.flush_word();
            if !self.line.is_empty() {
                self.output.push_str(&self.line);
                self.output.push('\n');
                self.line.clear();
            }
        }

        fn hard_break(&mut self) {
            self.flush();
            if !self.output.ends_with("\n\n") {
                self.output.push('\n');
            }
        }

        fn flush_word(&mut self) {
            if self.word.is_empty() {
                return;
            }
            if self.line.len() + self.word.len() >= 79 {
                self.output.push_str(&self.line);
                self.output.push('\n');
                self.line.clear();
            }
            if self.line.is_empty() {
                self.push_indent(self.indent);
                self.line.push_str(&self.word);
            } else {
                self.line.push(' ');
                self.line.push_str(&self.word);
            }
            self.word.clear();
        }

        fn push_indent(&mut self, indent: usize) {
            for _ in 0..indent {
                self.line.push(' ');
            }
        }

        fn push_to_line(&mut self, text: &str) {
            self.flush_word();
            self.line.push_str(text);
        }
    }

    /// Splits the text on whitespace.
    ///
    /// Consecutive whitespace is collapsed to a single ' ', and is included as a
    /// separate element in the result.
    fn split_chunks(text: &str) -> Vec<&str> {
        let mut result = Vec::new();
        let mut start = 0;
        while start < text.len() {
            match text[start..].find(' ') {
                Some(i) => {
                    if i != 0 {
                        result.push(&text[start..start + i]);
                    }
                    result.push(" ");
                    // Skip past whitespace.
                    match text[start + i..].find(|c| c != ' ') {
                        Some(n) => {
                            start = start + i + n;
                        }
                        None => {
                            break;
                        }
                    }
                }
                None => {
                    result.push(&text[start..]);
                    break;
                }
            }
        }
        result
    }

    struct Table {
        alignment: Vec<Alignment>,
        rows: Vec<Vec<String>>,
        row: Vec<String>,
        cell: String,
    }

    impl Table {
        fn new() -> Table {
            Table {
                alignment: Vec::new(),
                rows: Vec::new(),
                row: Vec::new(),
                cell: String::new(),
            }
        }

        /// Processes table events and generates a text table.
        fn process(&mut self, parser: &mut EventIter<'_>, indent: usize) -> Result<String, Error> {
            while let Some((event, _range)) = parser.next() {
                match event {
                    Event::Start(tag) => match tag {
                        Tag::TableHead
                        | Tag::TableRow
                        | Tag::TableCell
                        | Tag::Emphasis
                        | Tag::Strong => {}
                        Tag::Strikethrough => self.cell.push_str("~~"),
                        // Links not yet supported, they usually won't fit.
                        Tag::Link(_, _, _) => {}
                        _ => bail!("unexpected tag in table: {:?}", tag),
                    },
                    Event::End(tag) => match tag {
                        Tag::Table(_) => return self.render(indent),
                        Tag::TableCell => {
                            let cell = mem::replace(&mut self.cell, String::new());
                            self.row.push(cell);
                        }
                        Tag::TableHead | Tag::TableRow => {
                            let row = mem::replace(&mut self.row, Vec::new());
                            self.rows.push(row);
                        }
                        Tag::Strikethrough => self.cell.push_str("~~"),
                        _ => {}
                    },
                    Event::Text(t) | Event::Code(t) => {
                        self.cell.push_str(&t);
                    }
                    Event::Html(t) => bail!("html unsupported in tables: {:?}", t),
                    _ => bail!("unexpected event in table: {:?}", event),
                }
            }
            bail!("table end not reached");
        }

        fn render(&self, indent: usize) -> Result<String, Error> {
            // This is an extremely primitive layout routine.
            // First compute the potential maximum width of each cell.
            // 2 for 1 space margin on left and right.
            let width_acc = vec![2; self.alignment.len()];
            let mut col_widths = self
                .rows
                .iter()
                .map(|row| row.iter().map(|cell| cell.len()))
                .fold(width_acc, |mut acc, row| {
                    acc.iter_mut()
                        .zip(row)
                        // +3 for left/right margin and | symbol
                        .for_each(|(a, b)| *a = (*a).max(b + 3));
                    acc
                });
            // Shrink each column until it fits the total width, proportional to
            // the columns total percent width.
            let max_width = 78 - indent;
            // Include total len for | characters, and +1 for final |.
            let total_width = col_widths.iter().sum::<usize>() + col_widths.len() + 1;
            if total_width > max_width {
                let to_shrink = total_width - max_width;
                // Compute percentage widths, and shrink each column based on its
                // total percentage.
                for width in &mut col_widths {
                    let percent = *width as f64 / total_width as f64;
                    *width -= (to_shrink as f64 * percent).ceil() as usize;
                }
            }
            // Start rendering.
            let mut result = String::new();

            // Draw the horizontal line separating each row.
            let mut row_line = String::new();
            row_line.push_str(&" ".repeat(indent));
            row_line.push('+');
            let lines = col_widths
                .iter()
                .map(|width| "-".repeat(*width))
                .collect::<Vec<_>>();
            row_line.push_str(&lines.join("+"));
            row_line.push('+');
            row_line.push('\n');

            // Draw top of the table.
            result.push_str(&row_line);
            // Draw each row.
            for row in &self.rows {
                // Word-wrap and fill each column as needed.
                let filled = fill_row(row, &col_widths, &self.alignment);
                // Need to transpose the cells across rows for cells that span
                // multiple rows.
                let height = filled.iter().map(|c| c.len()).max().unwrap();
                for row_i in 0..height {
                    result.push_str(&" ".repeat(indent));
                    result.push('|');
                    for filled_row in &filled {
                        let cell = &filled_row[row_i];
                        result.push_str(cell);
                        result.push('|');
                    }
                    result.push('\n');
                }
                result.push_str(&row_line);
            }
            Ok(result)
        }
    }

    /// Formats a row, filling cells with spaces and word-wrapping text.
    ///
    /// Returns a vec of cells, where each cell is split into multiple lines.
    fn fill_row(row: &[String], col_widths: &[usize], alignment: &[Alignment]) -> Vec<Vec<String>> {
        let mut cell_lines = row
            .iter()
            .zip(col_widths)
            .zip(alignment)
            .map(|((cell, width), alignment)| fill_cell(cell, *width - 2, *alignment))
            .collect::<Vec<_>>();
        // Fill each cell to match the maximum vertical height of the tallest cell.
        let max_lines = cell_lines.iter().map(|cell| cell.len()).max().unwrap();
        for (cell, width) in cell_lines.iter_mut().zip(col_widths) {
            if cell.len() < max_lines {
                cell.extend(std::iter::repeat(" ".repeat(*width)).take(max_lines - cell.len()));
            }
        }
        cell_lines
    }

    /// Formats a cell. Word-wraps based on width, and adjusts based on alignment.
    ///
    /// Returns a vec of lines for the cell.
    fn fill_cell(text: &str, width: usize, alignment: Alignment) -> Vec<String> {
        let fill_width = |text: &str| match alignment {
            Alignment::None | Alignment::Left => format!(" {:<width$} ", text, width = width),
            Alignment::Center => format!(" {:^width$} ", text, width = width),
            Alignment::Right => format!(" {:>width$} ", text, width = width),
        };
        if text.len() < width {
            // No wrapping necessary, just format.
            vec![fill_width(text)]
        } else {
            // Word-wrap the cell.
            let mut result = Vec::new();
            let mut line = String::new();
            for word in text.split_whitespace() {
                if line.len() + word.len() >= width {
                    // todo: word.len() > width
                    result.push(fill_width(&line));
                    line.clear();
                }
                if line.is_empty() {
                    line.push_str(word);
                } else {
                    line.push(' ');
                    line.push_str(&word);
                }
            }
            if !line.is_empty() {
                result.push(fill_width(&line));
            }

            result
        }
    }