helix-mods/helix-term/src/ui/markdown.rs

use crate::compositor::{Component, Context};
use tui::{
    buffer::Buffer as Surface,
    text::{Span, Spans, Text},
};

use std::sync::Arc;

use pulldown_cmark::{CodeBlockKind, Event, HeadingLevel, Options, Parser, Tag};

use helix_core::{
    syntax::{self, HighlightEvent, Syntax},
    Rope,
};
use helix_view::{
    graphics::{Margin, Rect, Style},
    Theme,
};

fn styled_multiline_text<'a>(text: String, style: Style) -> Text<'a> {
    let spans: Vec<_> = text
        .lines()
        .map(|line| Span::styled(line.to_string(), style))
        .map(Spans::from)
        .collect();
    Text::from(spans)
}

pub fn highlighted_code_block<'a>(
    text: String,
    language: &str,
    theme: Option<&Theme>,
    config_loader: Arc<syntax::Loader>,
    additional_highlight_spans: Option<Vec<(usize, std::ops::Range<usize>)>>,
) -> Text<'a> {
    let mut spans = Vec::new();
    let mut lines = Vec::new();

    let get_theme = |key: &str| -> Style { theme.map(|t| t.get(key)).unwrap_or_default() };
    let text_style = get_theme(Markdown::TEXT_STYLE);
    let code_style = get_theme(Markdown::BLOCK_STYLE);

    let theme = match theme {
        Some(t) => t,
        None => return styled_multiline_text(text, code_style),
    };

    let rope = Rope::from(text.as_ref());
    let syntax = config_loader
        .language_configuration_for_injection_string(language)
        .and_then(|config| config.highlight_config(theme.scopes()))
        .map(|config| Syntax::new(&rope, config, Arc::clone(&config_loader)));

    let syntax = match syntax {
        Some(s) => s,
        None => return styled_multiline_text(text, code_style),
    };

    let highlight_iter = syntax
        .highlight_iter(rope.slice(..), None, None)
        .map(|e| e.unwrap());
    let highlight_iter: Box<dyn Iterator<Item = HighlightEvent>> =
        if let Some(spans) = additional_highlight_spans {
            Box::new(helix_core::syntax::merge(highlight_iter, spans))
        } else {
            Box::new(highlight_iter)
        };

    let mut highlights = Vec::new();
    for event in highlight_iter {
        match event {
            HighlightEvent::HighlightStart(span) => {
                highlights.push(span);
            }
            HighlightEvent::HighlightEnd => {
                highlights.pop();
            }
            HighlightEvent::Source { start, end } => {
                let style = highlights
                    .iter()
                    .fold(text_style, |acc, span| acc.patch(theme.highlight(span.0)));

                let mut slice = &text[start..end];
                // TODO: do we need to handle all unicode line endings
                // here, or is just '\n' okay?
                while let Some(end) = slice.find('\n') {
                    // emit span up to newline
                    let text = &slice[..end];
                    let text = text.replace('\t', "    "); // replace tabs
                    let span = Span::styled(text, style);
                    spans.push(span);

                    // truncate slice to after newline
                    slice = &slice[end + 1..];

                    // make a new line
                    let spans = std::mem::take(&mut spans);
                    lines.push(Spans::from(spans));
                }

                // if there's anything left, emit it too
                if !slice.is_empty() {
                    let span = Span::styled(slice.replace('\t', "    "), style);
                    spans.push(span);
                }
            }
        }
    }

    if !spans.is_empty() {
        let spans = std::mem::take(&mut spans);
        lines.push(Spans::from(spans));
    }

    Text::from(lines)
}

pub struct Markdown {
    contents: String,

    config_loader: Arc<syntax::Loader>,
}

// TODO: pre-render and self reference via Pin
// better yet, just use Tendril + subtendril for references

impl Markdown {
    const TEXT_STYLE: &'static str = "ui.text";
    const BLOCK_STYLE: &'static str = "markup.raw.inline";
    const HEADING_STYLES: [&'static str; 6] = [
        "markup.heading.1",
        "markup.heading.2",
        "markup.heading.3",
        "markup.heading.4",
        "markup.heading.5",
        "markup.heading.6",
    ];

    pub fn new(contents: String, config_loader: Arc<syntax::Loader>) -> Self {
        Self {
            contents,
            config_loader,
        }
    }

    fn parse(&self, theme: Option<&Theme>) -> tui::text::Text<'_> {
        // // also 2021-03-04T16:33:58.553 helix_lsp::transport [INFO] <- {"contents":{"kind":"markdown","value":"\n```rust\ncore::num\n```\n\n```rust\npub const fn saturating_sub(self, rhs:Self) ->Self\n```\n\n---\n\n```rust\n```"},"range":{"end":{"character":61,"line":101},"start":{"character":47,"line":101}}}
        // let text = "\n```rust\ncore::iter::traits::iterator::Iterator\n```\n\n```rust\nfn collect<B: FromIterator<Self::Item>>(self) -> B\nwhere\n        Self: Sized,\n```\n\n---\n\nTransforms an iterator into a collection.\n\n`collect()` can take anything iterable, and turn it into a relevant\ncollection. This is one of the more powerful methods in the standard\nlibrary, used in a variety of contexts.\n\nThe most basic pattern in which `collect()` is used is to turn one\ncollection into another. You take a collection, call [`iter`](https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html) on it,\ndo a bunch of transformations, and then `collect()` at the end.\n\n`collect()` can also create instances of types that are not typical\ncollections. For example, a [`String`](https://doc.rust-lang.org/nightly/core/iter/std/string/struct.String.html) can be built from [`char`](type@char)s,\nand an iterator of [`Result<T, E>`](https://doc.rust-lang.org/nightly/core/result/enum.Result.html) items can be collected\ninto `Result<Collection<T>, E>`. See the examples below for more.\n\nBecause `collect()` is so general, it can cause problems with type\ninference. As such, `collect()` is one of the few times you'll see\nthe syntax affectionately known as the 'turbofish': `::<>`. This\nhelps the inference algorithm understand specifically which collection\nyou're trying to collect into.\n\n# Examples\n\nBasic usage:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled: Vec<i32> = a.iter()\n                         .map(|&x| x * 2)\n                         .collect();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nNote that we needed the `: Vec<i32>` on the left-hand side. This is because\nwe could collect into, for example, a [`VecDeque<T>`](https://doc.rust-lang.org/nightly/core/iter/std/collections/struct.VecDeque.html) instead:\n\n```rust\nuse std::collections::VecDeque;\n\nlet a = [1, 2, 3];\n\nlet doubled: VecDeque<i32> = a.iter().map(|&x| x * 2).collect();\n\nassert_eq!(2, doubled[0]);\nassert_eq!(4, doubled[1]);\nassert_eq!(6, doubled[2]);\n```\n\nUsing the 'turbofish' instead of annotating `doubled`:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled = a.iter().map(|x| x * 2).collect::<Vec<i32>>();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nBecause `collect()` only cares about what you're collecting into, you can\nstill use a partial type hint, `_`, with the turbofish:\n\n```rust\nlet a = [1, 2, 3];\n\nlet doubled = a.iter().map(|x| x * 2).collect::<Vec<_>>();\n\nassert_eq!(vec![2, 4, 6], doubled);\n```\n\nUsing `collect()` to make a [`String`](https://doc.rust-lang.org/nightly/core/iter/std/string/struct.String.html):\n\n```rust\nlet chars = ['g', 'd', 'k', 'k', 'n'];\n\nlet hello: String = chars.iter()\n    .map(|&x| x as u8)\n    .map(|x| (x + 1) as char)\n    .collect();\n\nassert_eq!(\"hello\", hello);\n```\n\nIf you have a list of [`Result<T, E>`](https://doc.rust-lang.org/nightly/core/result/enum.Result.html)s, you can use `collect()` to\nsee if any of them failed:\n\n```rust\nlet results = [Ok(1), Err(\"nope\"), Ok(3), Err(\"bad\")];\n\nlet result: Result<Vec<_>, &str> = results.iter().cloned().collect();\n\n// gives us the first error\nassert_eq!(Err(\"nope\"), result);\n\nlet results = [Ok(1), Ok(3)];\n\nlet result: Result<Vec<_>, &str> = results.iter().cloned().collect();\n\n// gives us the list of answers\nassert_eq!(Ok(vec![1, 3]), result);\n```";

        let mut options = Options::empty();
        options.insert(Options::ENABLE_STRIKETHROUGH);
        let parser = Parser::new_ext(&self.contents, options);

        // TODO: if possible, render links as terminal hyperlinks: https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda
        let mut tags = Vec::new();
        let mut spans = Vec::new();
        let mut lines = Vec::new();

        let get_theme = |key: &str| -> Style { theme.map(|t| t.get(key)).unwrap_or_default() };
        let text_style = get_theme(Self::TEXT_STYLE);
        let code_style = get_theme(Self::BLOCK_STYLE);
        let heading_styles: Vec<Style> = Self::HEADING_STYLES
            .iter()
            .map(|key| get_theme(key))
            .collect();

        let mut list_stack = Vec::new();

        for event in parser {
            match event {
                Event::Start(Tag::List(list)) => list_stack.push(list),
                Event::End(Tag::List(_)) => {
                    list_stack.pop();
                }
                Event::Start(Tag::Item) => {
                    tags.push(Tag::Item);
                    spans.push(Span::from("- "));
                }
                Event::Start(tag) => {
                    tags.push(tag);
                }
                Event::End(tag) => {
                    tags.pop();
                    match tag {
                        Tag::Heading(_, _, _)
                        | Tag::Paragraph
                        | Tag::CodeBlock(CodeBlockKind::Fenced(_))
                        | Tag::Item => {
                            // whenever code block or paragraph closes, new line
                            let spans = std::mem::take(&mut spans);
                            if !spans.is_empty() {
                                lines.push(Spans::from(spans));
                            }
                            lines.push(Spans::default());
                        }
                        _ => (),
                    }
                }
                Event::Text(text) => {
                    // TODO: temp workaround
                    if let Some(Tag::CodeBlock(CodeBlockKind::Fenced(language))) = tags.last() {
                        let tui_text = highlighted_code_block(
                            text.to_string(),
                            language,
                            theme,
                            Arc::clone(&self.config_loader),
                            None,
                        );
                        lines.extend(tui_text.lines.into_iter());
                    } else {
                        let style = if let Some(Tag::Heading(level, ..)) = tags.last() {
                            match level {
                                HeadingLevel::H1 => heading_styles[0],
                                HeadingLevel::H2 => heading_styles[1],
                                HeadingLevel::H3 => heading_styles[2],
                                HeadingLevel::H4 => heading_styles[3],
                                HeadingLevel::H5 => heading_styles[4],
                                HeadingLevel::H6 => heading_styles[5],
                            }
                        } else {
                            text_style
                        };
                        spans.push(Span::styled(text, style));
                    }
                }
                Event::Code(text) | Event::Html(text) => {
                    spans.push(Span::styled(text, code_style));
                }
                Event::SoftBreak | Event::HardBreak => {
                    // let spans = std::mem::replace(&mut spans, Vec::new());
                    // lines.push(Spans::from(spans));
                    spans.push(Span::raw(" "));
                }
                Event::Rule => {
                    lines.push(Spans::from(Span::styled("---", code_style)));
                    lines.push(Spans::default());
                }
                // TaskListMarker(bool) true if checked
                _ => {
                    log::warn!("unhandled markdown event {:?}", event);
                }
            }
            // build up a vec of Paragraph tui widgets
        }

        if !spans.is_empty() {
            lines.push(Spans::from(spans));
        }

        // if last line is empty, remove it
        if let Some(line) = lines.last() {
            if line.0.is_empty() {
                lines.pop();
            }
        }

        Text::from(lines)
    }
}

impl Component for Markdown {
    fn render(&mut self, area: Rect, surface: &mut Surface, cx: &mut Context) {
        use tui::widgets::{Paragraph, Widget, Wrap};

        let text = self.parse(Some(&cx.editor.theme));

        let par = Paragraph::new(text)
            .wrap(Wrap { trim: false })
            .scroll((cx.scroll.unwrap_or_default() as u16, 0));

        let margin = Margin {
            vertical: 1,
            horizontal: 1,
        };
        par.render(area.inner(&margin), surface);
    }

    fn required_size(&mut self, viewport: (u16, u16)) -> Option<(u16, u16)> {
        let padding = 2;
        if padding >= viewport.1 || padding >= viewport.0 {
            return None;
        }
        let contents = self.parse(None);

        // TODO: account for tab width
        let max_text_width = (viewport.0 - padding).min(120);
        let (width, height) = crate::ui::text::required_size(&contents, max_text_width);

        Some((width + padding, height + padding))
    }
}