//! Text parsing.

use std::{borrow::Cow, fmt, io::Write, mem, str};

use quick_xml::events::{BytesStart, Event};
use termcolor::{Color, ColorSpec, WriteColor};

use super::{map_utf8_error, parse_classes, ParseError, Parsed};
use crate::{
    test::color_diff::ColorSpansWriter,
    utils::{normalize_newlines, RgbColor},
};

pub(super) struct TextReadingState {
    pub plaintext_buffer: String,
    html_buffer: String,
    color_spans_writer: ColorSpansWriter,
    open_tags: usize,
}

impl fmt::Debug for TextReadingState {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter
            .debug_struct("TextReadingState")
            .field("plaintext_buffer", &self.plaintext_buffer)
            .finish_non_exhaustive()
    }
}

impl Default for TextReadingState {
    fn default() -> Self {
        Self {
            html_buffer: String::new(),
            color_spans_writer: ColorSpansWriter::default(),
            plaintext_buffer: String::new(),
            open_tags: 1,
        }
    }
}

impl TextReadingState {
    pub fn is_empty(&self) -> bool {
        self.plaintext_buffer.is_empty()
    }

    pub fn open_tags(&self) -> usize {
        self.open_tags
    }

    // We only retain `<span>` tags in the HTML since they are the only ones containing color info.
    pub fn process(&mut self, event: Event<'_>) -> Result<Option<Parsed>, ParseError> {
        match event {
            Event::Text(text) => {
                let unescaped_str = text.unescape()?;
                let unescaped_str = normalize_newlines(&unescaped_str);

                self.html_buffer.push_str(&unescaped_str);
                self.plaintext_buffer.push_str(&unescaped_str);
                self.color_spans_writer
                    .write_all(unescaped_str.as_bytes())
                    .expect("cannot write to ANSI buffer");
            }
            Event::Start(tag) => {
                self.open_tags += 1;
                if tag.name().as_ref() == b"span" {
                    self.html_buffer.push('<');
                    let tag_str = str::from_utf8(&tag).map_err(map_utf8_error)?;
                    self.html_buffer.push_str(tag_str);
                    self.html_buffer.push('>');

                    let color_spec = Self::parse_color_from_span(&tag)?;
                    if !color_spec.is_none() {
                        self.color_spans_writer
                            .set_color(&color_spec)
                            .expect("cannot set color for ANSI buffer");
                    }
                }
            }
            Event::End(tag) => {
                self.open_tags -= 1;

                if tag.name().as_ref() == b"span" {
                    self.html_buffer.push_str("</span>");

                    // FIXME: check embedded color specs (should never be produced).
                    self.color_spans_writer
                        .reset()
                        .expect("cannot reset color for ANSI buffer");
                }

                if self.open_tags == 0 {
                    let html = mem::take(&mut self.html_buffer);
                    let plaintext = mem::take(&mut self.plaintext_buffer);
                    let color_spans = mem::take(&mut self.color_spans_writer).into_inner();
                    return Ok(Some(Parsed {
                        plaintext,
                        color_spans,
                        html,
                    }));
                }
            }
            _ => { /* Do nothing */ }
        }
        Ok(None)
    }

    /// Parses color spec from a `span`.
    ///
    /// **NB.** Must correspond to the span creation logic in the `html` module.
    fn parse_color_from_span(span_tag: &BytesStart) -> Result<ColorSpec, ParseError> {
        let class_attr = parse_classes(span_tag.attributes())?;
        let mut color_spec = ColorSpec::new();
        Self::parse_color_from_classes(&mut color_spec, &class_attr);

        let mut style = Cow::Borrowed(&[] as &[u8]);
        for attr in span_tag.attributes() {
            let attr = attr.map_err(quick_xml::Error::InvalidAttr)?;
            if attr.key.as_ref() == b"style" {
                style = attr.value;
            }
        }
        Self::parse_color_from_style(&mut color_spec, &style)?;

        Ok(color_spec)
    }

    fn parse_color_from_classes(color_spec: &mut ColorSpec, class_attr: &[u8]) {
        let classes = class_attr.split(u8::is_ascii_whitespace);
        for class in classes {
            // Note that `class` may be empty because of multiple sequential whitespace chars.
            // This is OK for us.
            match class {
                b"bold" => {
                    color_spec.set_bold(true);
                }
                b"dimmed" => {
                    color_spec.set_dimmed(true);
                }
                b"italic" => {
                    color_spec.set_italic(true);
                }
                b"underline" => {
                    color_spec.set_underline(true);
                }

                // Indexed foreground color candidate.
                fg if fg.starts_with(b"fg") => {
                    if let Some(color) = Self::parse_indexed_color(&fg[2..]) {
                        color_spec.set_fg(Some(color));
                    }
                }
                // Indexed background color candidate.
                bg if bg.starts_with(b"bg") => {
                    if let Some(color) = Self::parse_indexed_color(&bg[2..]) {
                        color_spec.set_bg(Some(color));
                    }
                }

                _ => { /* Ignore other classes. */ }
            }
        }
    }

    // **NB.** This parser is pretty rudimentary (e.g., does not understand comments).
    fn parse_color_from_style(color_spec: &mut ColorSpec, style: &[u8]) -> Result<(), ParseError> {
        for style_property in style.split(|&ch| ch == b';') {
            let name_and_value: Vec<_> = style_property.splitn(2, |&ch| ch == b':').collect();
            let [property_name, property_value] = name_and_value.as_slice() else {
                continue;
            };

            let property_name = str::from_utf8(property_name)
                .map_err(map_utf8_error)?
                .trim();
            let property_value = str::from_utf8(property_value)
                .map_err(map_utf8_error)?
                .trim();

            match property_name {
                "color" => {
                    if let Ok(color) = property_value.parse::<RgbColor>() {
                        color_spec.set_fg(Some(color.into_ansi_color()));
                    }
                }
                "background" | "background-color" => {
                    if let Ok(color) = property_value.parse::<RgbColor>() {
                        color_spec.set_bg(Some(color.into_ansi_color()));
                    }
                }
                _ => { /* Ignore other properties. */ }
            }
        }
        Ok(())
    }

    fn parse_indexed_color(class: &[u8]) -> Option<Color> {
        Some(match class {
            b"0" => Color::Black,
            b"1" => Color::Red,
            b"2" => Color::Green,
            b"3" => Color::Yellow,
            b"4" => Color::Blue,
            b"5" => Color::Magenta,
            b"6" => Color::Cyan,
            b"7" => Color::White,
            b"8" | b"9" => Color::Ansi256(class[0] - b'0'),
            b"10" | b"11" | b"12" | b"13" | b"14" | b"15" => Color::Ansi256(10 + class[1] - b'0'),
            _ => return None,
        })
    }
}

impl RgbColor {
    fn into_ansi_color(self) -> Color {
        Color::Rgb(self.0, self.1, self.2)
    }
}

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

    #[test]
    fn parsing_color_index() {
        assert_eq!(
            TextReadingState::parse_indexed_color(b"0"),
            Some(Color::Black)
        );
        assert_eq!(
            TextReadingState::parse_indexed_color(b"3"),
            Some(Color::Yellow)
        );
        assert_eq!(
            TextReadingState::parse_indexed_color(b"9"),
            Some(Color::Ansi256(9))
        );
        assert_eq!(
            TextReadingState::parse_indexed_color(b"10"),
            Some(Color::Ansi256(10))
        );
        assert_eq!(
            TextReadingState::parse_indexed_color(b"15"),
            Some(Color::Ansi256(15))
        );

        assert_eq!(TextReadingState::parse_indexed_color(b""), None);
        assert_eq!(TextReadingState::parse_indexed_color(b"17"), None);
        assert_eq!(TextReadingState::parse_indexed_color(b"01"), None);
        assert_eq!(TextReadingState::parse_indexed_color(b"333"), None);
    }

    #[test]
    fn parsing_color_from_classes() {
        let mut color_spec = ColorSpec::new();
        TextReadingState::parse_color_from_classes(&mut color_spec, b"bold fg3 underline bg11");

        assert!(color_spec.bold(), "{color_spec:?}");
        assert!(color_spec.underline(), "{color_spec:?}");
        assert_eq!(color_spec.fg(), Some(&Color::Yellow));
        assert_eq!(color_spec.bg(), Some(&Color::Ansi256(11)));
    }

    #[test]
    fn parsing_color_from_style() {
        let mut color_spec = ColorSpec::new();
        TextReadingState::parse_color_from_style(
            &mut color_spec,
            b"color: #fed; background: #c0ffee",
        )
        .unwrap();

        assert_eq!(color_spec.fg(), Some(&Color::Rgb(0xff, 0xee, 0xdd)));
        assert_eq!(color_spec.bg(), Some(&Color::Rgb(0xc0, 0xff, 0xee)));
    }

    #[test]
    fn parsing_color_from_style_with_terminal_semicolon() {
        let mut color_spec = ColorSpec::new();
        TextReadingState::parse_color_from_style(
            &mut color_spec,
            b"color: #fed; background: #c0ffee;",
        )
        .unwrap();

        assert_eq!(color_spec.fg(), Some(&Color::Rgb(0xff, 0xee, 0xdd)));
        assert_eq!(color_spec.bg(), Some(&Color::Rgb(0xc0, 0xff, 0xee)));
    }
}