waterui_text/

styled.rs

use core::{fmt::Display, mem::take, ops::Add};

use crate::{
    font::{Font, FontWeight},
    text,
};
use alloc::{string::String, vec, vec::Vec};
use core::ops::AddAssign;
use nami::impl_constant;
use pulldown_cmark::{CodeBlockKind, Event, HeadingLevel, Options, Parser, Tag};
use waterui_color::Color;
use waterui_core::{Str, View};

/// A set of text attributes for rich text formatting.
#[derive(Debug, Clone, Default)]
pub struct Style {
    /// The font to use.
    pub font: Font,
    /// The foreground (text) color.
    pub foreground: Option<Color>,
    /// The background color.
    pub background: Option<Color>,
    /// Whether the text is italic.
    pub italic: bool,
    /// Whether the text has an underline.
    pub underline: bool,
    /// Whether the text has a strikethrough.
    pub strikethrough: bool,
}

impl Style {
    /// Creates a new default `Style`.
    #[must_use]
    pub fn new() -> Self {
        Self::default()
    }

    /// Sets the font.
    #[must_use]
    pub fn font(mut self, font: impl Into<Font>) -> Self {
        self.font = font.into();
        self
    }

    /// Sets the text color.
    #[must_use]
    pub fn foreground(mut self, color: impl Into<Color>) -> Self {
        self.foreground = Some(color.into());
        self
    }

    /// Sets the background color.
    #[must_use]
    pub fn background(mut self, color: impl Into<Color>) -> Self {
        self.background = Some(color.into());
        self
    }

    /// Sets the font weight.
    #[must_use]
    pub fn weight(mut self, weight: FontWeight) -> Self {
        self.font = self.font.weight(weight);
        self
    }

    /// Sets the bold style.
    /// Equal to calling `self.weight(FontWeight::Bold)`.
    #[must_use]
    pub fn bold(mut self) -> Self {
        self.font = self.font.bold();
        self
    }

    /// Sets the font size in points.
    #[must_use]
    pub fn size(mut self, size: f32) -> Self {
        self.font = self.font.size(size);
        self
    }

    /// Sets the italic style.
    #[must_use]
    pub const fn italic(mut self) -> Self {
        self.italic = true;
        self
    }

    /// Disables the italic style.
    #[must_use]
    pub const fn not_italic(mut self) -> Self {
        self.italic = false;
        self
    }

    /// Sets the underline style.
    #[must_use]
    pub const fn underline(mut self) -> Self {
        self.underline = true;
        self
    }

    /// Disables the underline style.
    #[must_use]
    pub const fn not_underline(mut self) -> Self {
        self.underline = false;
        self
    }

    /// Sets the strikethrough style.
    #[must_use]
    pub const fn strikethrough(mut self) -> Self {
        self.strikethrough = true;
        self
    }

    /// Disables the strikethrough style.
    #[must_use]
    pub const fn not_strikethrough(mut self) -> Self {
        self.strikethrough = false;
        self
    }
}

/// A string with associated text attributes for rich text formatting.
#[derive(Debug, Clone, Default)]
pub struct StyledStr {
    chunks: Vec<(Str, Style)>,
}

impl StyledStr {
    /// Creates a new empty `StyledStr`.
    #[must_use]
    pub const fn empty() -> Self {
        Self { chunks: Vec::new() }
    }

    /// Creates a styled string from a subset of Markdown.
    ///
    /// Supported features include headings, bold, and italic text. Other
    /// Markdown constructs are preserved as plain text.
    #[must_use]
    pub fn from_markdown(markdown: &str) -> Self {
        let options =
            Options::ENABLE_TABLES | Options::ENABLE_FOOTNOTES | Options::ENABLE_STRIKETHROUGH;
        let parser = Parser::new_ext(markdown, options);

        let mut builder = MarkdownInlineBuilder::new();
        let mut pending_block_break = false;

        for event in parser {
            match event {
                Event::Start(tag) => match tag {
                    Tag::Heading { level, .. } => {
                        if pending_block_break || !builder.is_empty() {
                            builder.push_text("\n\n");
                        }
                        pending_block_break = false;
                        builder.enter_with(move |_| heading_style(level));
                    }
                    Tag::Paragraph => {
                        if pending_block_break || !builder.is_empty() {
                            builder.push_text("\n\n");
                        }
                        pending_block_break = false;
                    }
                    Tag::Emphasis => builder.enter_emphasis(),
                    Tag::Strong => builder.enter_strong(),
                    Tag::CodeBlock(kind) => {
                        if pending_block_break || !builder.is_empty() {
                            builder.push_text("\n\n");
                        }
                        pending_block_break = false;
                        if let CodeBlockKind::Fenced(info) = kind
                            && !info.is_empty()
                        {
                            builder.push_text(info.as_ref());
                            builder.push_text(":\n");
                        }
                    }
                    Tag::List(_) | Tag::Item => {
                        if pending_block_break || !builder.is_empty() {
                            builder.push_text("\n");
                        }
                        pending_block_break = false;
                    }
                    _ => {}
                },
                Event::End(tag) => match tag {
                    pulldown_cmark::TagEnd::Heading(_) => {
                        builder.exit();
                        pending_block_break = true;
                    }
                    pulldown_cmark::TagEnd::Paragraph
                    | pulldown_cmark::TagEnd::CodeBlock
                    | pulldown_cmark::TagEnd::List(_) => {
                        pending_block_break = true;
                    }
                    pulldown_cmark::TagEnd::Emphasis | pulldown_cmark::TagEnd::Strong => {
                        builder.exit();
                    }
                    _ => {}
                },
                Event::Text(text)
                | Event::Code(text)
                | Event::Html(text)
                | Event::FootnoteReference(text)
                | Event::InlineMath(text)
                | Event::DisplayMath(text)
                | Event::InlineHtml(text) => {
                    if pending_block_break && !builder.is_empty() {
                        builder.push_text("\n\n");
                        pending_block_break = false;
                    }
                    builder.push_text(text.as_ref());
                }
                Event::SoftBreak => builder.push_soft_break(),
                Event::HardBreak => builder.push_hard_break(),
                Event::Rule => {
                    builder.push_text("\n\n——\n\n");
                    pending_block_break = false;
                }
                Event::TaskListMarker(checked) => {
                    if pending_block_break && !builder.is_empty() {
                        builder.push_text("\n");
                        pending_block_break = false;
                    }
                    builder.push_text(if checked { "[x] " } else { "[ ] " });
                }
            }
        }

        builder.finish()
    }

    /// Creates a plain attributed string with a single unstyled chunk.
    #[must_use]
    pub fn plain(text: impl Into<Str>) -> Self {
        let mut s = Self::empty();
        s.push(text.into(), Style::default());
        s
    }

    /// Adds a new text chunk with the specified style.
    pub fn push(&mut self, text: impl Into<Str>, style: Style) {
        let text = text.into();
        self.chunks.push((text, style));
    }

    /// Appends text to the last chunk, or creates a new chunk if empty.
    pub fn push_str(&mut self, text: impl Into<Str>) {
        let text = text.into();
        if let Some(last) = self.chunks.last_mut() {
            let (last_text, _) = last;
            last_text.add_assign(text);
        } else {
            self.chunks.push((text, Style::default()));
        }
    }

    /// Returns the total length of the attributed string.
    #[must_use]
    pub fn len(&self) -> usize {
        self.chunks.iter().map(|(text, _)| text.len()).sum()
    }

    /// Checks if the attributed string is empty.
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        self.chunks.is_empty()
    }

    /// Converts the attributed string into its plain representation.
    #[must_use]
    pub fn to_plain(&self) -> Str {
        if self.chunks.len() == 1 {
            return self.chunks[0].0.clone();
        }

        let mut result = String::new();
        for (text, _) in &self.chunks {
            result.push_str(text);
        }
        result.into()
    }

    /// Consumes the attributed string and returns its constituent chunks.
    #[must_use]
    pub fn into_chunks(self) -> Vec<(Str, Style)> {
        self.chunks
    }

    /// Sets the style for all text in this styled text.
    #[must_use]
    pub fn set_style(self, style: &Style) -> Self {
        self.apply_style(|s| *s = style.clone())
    }

    fn apply_style(mut self, f: impl Fn(&mut Style)) -> Self {
        if self.chunks.is_empty() {
            return self;
        }
        let old_chunks = core::mem::take(&mut self.chunks);
        for (text, mut style) in old_chunks {
            f(&mut style);
            self.push(text, style);
        }
        self
    }

    /// Sets the font size for all chunks.
    #[must_use]
    pub fn size(self, size: f32) -> Self {
        self.apply_style(|s| *s = take(s).size(size))
    }

    /// Sets the font for all chunks.
    #[must_use]
    pub fn font(self, font: &Font) -> Self {
        self.apply_style(|s| s.font = font.clone())
    }

    /// Sets the foreground color for all chunks.
    #[must_use]
    pub fn foreground(self, color: impl Into<Color>) -> Self {
        let color = color.into();
        self.apply_style(|s| s.foreground = Some(color.clone()))
    }

    /// Sets the background color for all chunks.
    #[must_use]
    pub fn background_color(self, color: impl Into<Color>) -> Self {
        let color = color.into();
        self.apply_style(|s| s.background = Some(color.clone()))
    }

    /// Sets the font weight for all chunks.
    #[must_use]
    pub fn weight(self, weight: FontWeight) -> Self {
        self.apply_style(|s| {
            *s = take(s).weight(weight);
        })
    }

    /// Sets the font to bold for all chunks.
    #[must_use]
    pub fn bold(self) -> Self {
        self.weight(FontWeight::Bold)
    }

    /// Sets the italic style for all chunks.
    #[must_use]
    pub fn italic(self, italic: bool) -> Self {
        self.apply_style(|s| s.italic = italic)
    }

    /// Sets the underline style for all chunks.
    #[must_use]
    pub fn underline(self, underline: bool) -> Self {
        self.apply_style(|s| s.underline = underline)
    }

    /// Sets the strikethrough style for all chunks.
    #[must_use]
    pub fn strikethrough(self, strikethrough: bool) -> Self {
        self.apply_style(|s| s.strikethrough = strikethrough)
    }
}

/// Utility builder that incrementally constructs a [`StyledStr`] from Markdown
/// events. The builder keeps track of the active style stack and merges
/// contiguous text runs that share the same styling.
#[derive(Debug, Clone)]
pub struct MarkdownInlineBuilder {
    base_style: Style,
    stack: Vec<Style>,
    buffer: String,
    result: StyledStr,
}

impl Default for MarkdownInlineBuilder {
    fn default() -> Self {
        Self::new()
    }
}

impl MarkdownInlineBuilder {
    /// Creates a new builder using the default style.
    #[must_use]
    pub fn new() -> Self {
        Self::with_base_style(Style::default())
    }

    /// Creates a new builder with a custom base style.
    #[must_use]
    pub fn with_base_style(style: Style) -> Self {
        Self {
            base_style: style.clone(),
            stack: vec![style],
            buffer: String::new(),
            result: StyledStr::empty(),
        }
    }

    fn current_style(&self) -> Style {
        self.stack.last().cloned().unwrap_or_else(Style::default)
    }

    fn flush(&mut self) {
        if self.buffer.is_empty() {
            return;
        }

        let text = take(&mut self.buffer);
        self.result.push(text, self.current_style());
    }

    /// Appends raw text to the builder.
    pub fn push_text(&mut self, text: &str) {
        if !text.is_empty() {
            self.buffer.push_str(text);
        }
    }

    /// Appends a soft break (space) to the builder.
    pub fn push_soft_break(&mut self) {
        self.buffer.push(' ');
    }

    /// Appends a hard break (newline) to the builder.
    pub fn push_hard_break(&mut self) {
        self.buffer.push('\n');
    }

    /// Starts a new styled span using the closure to derive the child style.
    pub fn enter_with(&mut self, f: impl FnOnce(Style) -> Style) {
        self.flush();
        let style = self.current_style();
        self.stack.push(f(style));
    }

    /// Exits the most recently entered styled span.
    pub fn exit(&mut self) {
        self.flush();
        if self.stack.len() > 1 {
            self.stack.pop();
        }
    }

    /// Enters an italic styled span.
    pub fn enter_emphasis(&mut self) {
        self.enter_with(Style::italic);
    }

    /// Enters a bold styled span.
    pub fn enter_strong(&mut self) {
        self.enter_with(Style::bold);
    }

    /// Returns `true` if the builder has emitted no content yet.
    #[must_use]
    pub const fn is_empty(&self) -> bool {
        self.result.is_empty() && self.buffer.is_empty()
    }

    /// Returns the base style used by the builder.
    #[must_use]
    pub fn base_style(&self) -> Style {
        self.base_style.clone()
    }

    /// Takes the currently buffered content, resetting the builder to the base
    /// style. If no content has been emitted, `None` is returned.
    #[must_use]
    pub fn take(&mut self) -> Option<StyledStr> {
        self.flush();

        if self.result.is_empty() {
            return None;
        }

        let mut output = StyledStr::empty();
        core::mem::swap(&mut output, &mut self.result);
        self.stack.truncate(1);
        if let Some(first) = self.stack.first_mut() {
            *first = self.base_style.clone();
        }

        Some(output)
    }

    /// Consumes the builder and returns the final `StyledStr`.
    #[must_use]
    pub fn finish(mut self) -> StyledStr {
        self.flush();
        self.result
    }
}

/// Returns the default style applied to Markdown headings.
#[must_use]
pub fn heading_style(level: HeadingLevel) -> Style {
    use crate::font::{Body, Caption, Footnote, Headline, Subheadline, Title};

    let font: Font = match level {
        HeadingLevel::H1 => Headline.into(),
        HeadingLevel::H2 => Title.into(),
        HeadingLevel::H3 => Subheadline.into(),
        HeadingLevel::H4 => Body.into(),
        HeadingLevel::H5 => Caption.into(),
        HeadingLevel::H6 => Footnote.into(),
    };

    Style::default().font(font).bold()
}

impl View for StyledStr {
    fn body(self, _env: &waterui_core::Environment) -> impl waterui_core::View {
        text(self)
    }
}

impl Add for StyledStr {
    type Output = Self;

    fn add(mut self, rhs: Self) -> Self::Output {
        for (text, style) in rhs.chunks {
            self.push(text, style);
        }
        self
    }
}

impl Add<&'static str> for StyledStr {
    type Output = Self;

    fn add(mut self, rhs: &'static str) -> Self::Output {
        self.push(rhs, Style::default());
        self
    }
}

impl Extend<(Str, Style)> for StyledStr {
    fn extend<T: IntoIterator<Item = (Str, Style)>>(&mut self, iter: T) {
        for (text, style) in iter {
            self.push(text, style);
        }
    }
}

impl From<Str> for StyledStr {
    fn from(value: Str) -> Self {
        Self::plain(value)
    }
}

impl From<&'static str> for StyledStr {
    fn from(value: &'static str) -> Self {
        Self::plain(value)
    }
}

impl From<String> for StyledStr {
    fn from(value: String) -> Self {
        Self::plain(value)
    }
}

impl Display for StyledStr {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.write_str(&self.to_plain())
    }
}

impl_constant!(Style, StyledStr);

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

    #[test]
    fn parses_emphasis_markdown() {
        let styled = StyledStr::from_markdown("Hello *world*!");
        let chunks = styled.into_chunks();
        assert_eq!(chunks.len(), 3);
        assert_eq!(chunks[0].0.as_str(), "Hello ");
        assert_eq!(chunks[1].0.as_str(), "world");
        assert!(chunks[1].1.italic);
        assert_eq!(chunks[2].0.as_str(), "!");
    }

    #[test]
    fn parses_heading_markdown() {
        let styled = StyledStr::from_markdown("# Title");
        let chunks = styled.into_chunks();
        assert_eq!(chunks.len(), 1);
        assert_eq!(chunks[0].0.as_str(), "Title");
    }
}