helix/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, CowStr, Event, Options, Parser, Tag};

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

pub struct Markdown {
    contents: String,

    config_loader: Arc<syntax::Loader>,

    text_style: String,
    block_style: String,
    heading_style: String,
}

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

impl Markdown {
    pub fn new(contents: String, config_loader: Arc<syntax::Loader>) -> Self {
        Self {
            contents,
            config_loader,
            text_style: "markup.normal".into(),
            block_style: "markup.raw.inline".into(),
            heading_style: "markup.heading".into(),
        }
    }

    pub fn style_group(mut self, suffix: &str) -> Self {
        self.text_style = format!("markup.normal.{}", suffix);
        self.block_style = format!("markup.raw.inline.{}", suffix);
        self.heading_style = format!("markup.heading.{}", suffix);
        self
    }

    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();

        fn to_span(text: pulldown_cmark::CowStr) -> Span {
            use std::ops::Deref;
            Span::raw::<std::borrow::Cow<_>>(match text {
                CowStr::Borrowed(s) => s.into(),
                CowStr::Boxed(s) => s.to_string().into(),
                CowStr::Inlined(s) => s.deref().to_owned().into(),
            })
        }

        macro_rules! get_theme {
            ($s1: expr) => {
                theme
                    .map(|theme| theme.try_get($s1.as_str()))
                    .flatten()
                    .unwrap_or_default()
            };
        }
        let text_style = get_theme!(self.text_style);
        let code_style = get_theme!(self.block_style);
        let heading_style = get_theme!(self.heading_style);

        for event in parser {
            match event {
                Event::Start(tag) => tags.push(tag),
                Event::End(tag) => {
                    tags.pop();
                    match tag {
                        Tag::Heading(_, _, _)
                        | Tag::Paragraph
                        | Tag::CodeBlock(CodeBlockKind::Fenced(_)) => {
                            // 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() {
                        if let Some(theme) = theme {
                            let rope = Rope::from(text.as_ref());
                            let syntax = self
                                .config_loader
                                .language_configuration_for_injection_string(language)
                                .and_then(|config| config.highlight_config(theme.scopes()))
                                .map(|config| {
                                    Syntax::new(&rope, config, self.config_loader.clone())
                                });

                            if let Some(syntax) = syntax {
                                // if we have a syntax available, highlight_iter and generate spans
                                let mut highlights = Vec::new();

                                for event in syntax.highlight_iter(rope.slice(..), None, None) {
                                    match event.unwrap() {
                                        HighlightEvent::HighlightStart(span) => {
                                            highlights.push(span);
                                        }
                                        HighlightEvent::HighlightEnd => {
                                            highlights.pop();
                                        }
                                        HighlightEvent::Source { start, end } => {
                                            let style = match highlights.first() {
                                                Some(span) => theme.get(&theme.scopes()[span.0]),
                                                None => text_style,
                                            };

                                            // TODO: replace tabs with indentation

                                            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);
                                            }
                                        }
                                    }
                                }
                            } else {
                                for line in text.lines() {
                                    let span = Span::styled(line.to_string(), code_style);
                                    lines.push(Spans::from(span));
                                }
                            }
                        } else {
                            for line in text.lines() {
                                let span = Span::styled(line.to_string(), code_style);
                                lines.push(Spans::from(span));
                            }
                        }
                    } else if let Some(Tag::Heading(_, _, _)) = tags.last() {
                        let mut span = to_span(text);
                        span.style = heading_style;
                        spans.push(span);
                    } else {
                        let mut span = to_span(text);
                        span.style = text_style;
                        spans.push(span);
                    }
                }
                Event::Code(text) | Event::Html(text) => {
                    let mut span = to_span(text);
                    span.style = code_style;
                    spans.push(span);
                }
                Event::SoftBreak | Event::HardBreak => {
                    // let spans = std::mem::replace(&mut spans, Vec::new());
                    // lines.push(Spans::from(spans));
                    spans.push(Span::raw(" "));
                }
                Event::Rule => {
                    let mut span = Span::raw("---");
                    span.style = code_style;
                    lines.push(Spans::from(span));
                    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 mut text_width = 0;
        let mut height = padding;
        for content in contents {
            height += 1;
            let content_width = content.width() as u16;
            if content_width > max_text_width {
                text_width = max_text_width;
                height += content_width / max_text_width;
            } else if content_width > text_width {
                text_width = content_width;
            }
        }

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