crowbook/src/lib/html.rs

// Copyright (C) 2016-2023 Élisabeth HENRY.
//
// This file is part of Crowbook.
//
// Crowbook is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published
// by the Free Software Foundation, either version 2.1 of the License, or
// (at your option) any later version.
//
// Caribon is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Lesser General Public License for more details.
//
// You should have received ba copy of the GNU Lesser General Public License
// along with Crowbook.  If not, see <http://www.gnu.org/licenses/>.

use crate::book::Header;
use crate::book::HeaderData;
use crate::book::Book;
use crate::error::{Error, Result, Source};
use crate::lang;
use crate::number::Number;
use crate::parser::Parser;
use crate::renderer::Renderer;
use crate::resource_handler::ResourceHandler;
use crate::syntax::Syntax;
use crate::token::Data;
use crate::token::Token;
use crate::text_view;

use std::borrow::Cow;
use std::convert::{AsMut, AsRef};
use std::fmt::Write;

use crowbook_text_processing::escape;
use epub_builder::Toc;
use epub_builder::TocElement;
use numerals::roman::Roman;

#[derive(Debug, PartialEq, Copy, Clone)]
/// If/how to highlight code
pub enum Highlight {
    None,
    Js,
    Syntect,
}

/// Base structure for rendering HTML files
///
/// Used by EpubRenderer, HtmlSingleRenderer, HtmlDirRenderer
pub struct HtmlRenderer<'a> {
    table_head: bool,
    #[doc(hidden)]
    pub verbatim: bool,
    current_par: u32,
    #[doc(hidden)]
    pub first_letter: bool,
    first_paragraph: bool,
    footnotes: Vec<(String, String)>,
    filename: String,

    /// Book that must be rendered
    pub book: &'a Book<'a>,

    /// Proofread or not
    pub proofread: bool,

    /// Current part, chapter (and subsection, subsubsection and so on)
    #[doc(hidden)]
    pub current_chapter: [i32; 7],

    /// Current numbering level
    #[doc(hidden)]
    pub current_numbering: i32,

    /// Whether current chapter's title must be displayed
    #[doc(hidden)]
    pub current_hide: bool,

    /// Whether current chapter is actually a part
    #[doc(hidden)]
    pub current_part: bool,

    /// Resource handler
    #[doc(hidden)]
    pub handler: ResourceHandler,

    /// Current footnote number
    #[doc(hidden)]
    pub footnote_number: u32,

    /// Source for error messages
    #[doc(hidden)]
    pub source: Source,

    /// Table of contents
    #[doc(hidden)]
    pub toc: Toc,

    #[doc(hidden)]
    pub highlight: Highlight,

    /// Current link number
    #[doc(hidden)]
    pub link_number: u32,

    syntax: Option<Syntax>,

    part_template_html: upon::Template<'a, 'a>,
    chapter_template_html: upon::Template<'a, 'a>,
}

impl<'a> HtmlRenderer<'a> {
    fn get_highlight(book: &Book, theme: &str) -> (Highlight, Option<Syntax>) {
        match book.options.get_str("rendering.highlight").unwrap() {
            "syntect" => {
                // Don't init syntect if codeblocks are not used
                if book.features.codeblock {
                    (Highlight::Syntect, Some(Syntax::new(theme)))
                } else {
                    (Highlight::None, None)
                }
            }
            "none" => (Highlight::None, None),
            "highlight.js" => (Highlight::Js, None),
            value => {
                error!(
                    "{}",
                    lformat!("rendering.highlight set to '{}', not a valid value", value)
                );
                (Highlight::None, None)
            }
        }
    }

    /// Creates a new HTML renderer
    pub fn new(book: &'a Book, theme: &str) -> Result<HtmlRenderer<'a>> {
        let (highlight, syntax) = Self::get_highlight(book, theme);

        let mut html = HtmlRenderer {
            book,
            toc: Toc::new(),
            link_number: 0,
            current_chapter: [0, 0, 0, 0, 0, 0, 0],
            current_numbering: book.options.get_i32("rendering.num_depth").unwrap(),
            current_part: false,
            current_par: 0,
            current_hide: false,
            table_head: false,
            footnote_number: 0,
            footnotes: vec![],
            verbatim: false,
            filename: String::new(),
            handler: ResourceHandler::new(),
            source: Source::empty(),
            first_letter: false,
            first_paragraph: true,
            proofread: false,
            syntax,
            highlight,
            part_template_html: book.compile_str(
                book.options.get_str("html.part.template").unwrap(),
                Source::empty(),
                "html.part.template",
            )?,
            chapter_template_html: book.compile_str(
                book.options.get_str("html.chapter.template").unwrap(),
                Source::empty(),
                "html.chapter.template",
            )?,
        };
        html.handler.set_images_mapping(true);
        html.handler.set_base64(true);
        Ok(html)
    }

    /// Add a footnote which will be renderer later on
    #[doc(hidden)]
    pub fn add_footnote(&mut self, number: String, content: String) {
        self.footnotes.push((number, content));
    }

    /// Configure the Renderer for this chapter
    #[doc(hidden)]
    pub fn chapter_config(&mut self, i: usize, n: Number, filename: String) {
        self.source = Source::new(self.book.chapters[i].filename.as_str());
        self.first_paragraph = true;
        self.current_hide = false;
        let book_numbering = self.book.options.get_i32("rendering.num_depth").unwrap();
        match n {
            Number::Unnumbered | Number::UnnumberedPart => self.current_numbering = 0,
            Number::Default | Number::DefaultPart => self.current_numbering = book_numbering,
            Number::Specified(n) => {
                self.current_numbering = book_numbering;
                self.current_chapter[1] = n - 1;
            }
            Number::SpecifiedPart(n) => {
                self.current_numbering = book_numbering;
                self.current_chapter[0] = n - 1;
            }
            Number::Hidden => {
                self.current_numbering = 0;
                self.current_hide = true;
            }
        } //          _ => panic!("Parts are not supported yet"),
        self.current_part = n.is_part();

        self.filename = filename;
    }

    /// Renders a chapter to HTML
    pub fn render_html<T>(this: &mut T, tokens: &[Token], render_end_notes: bool) -> Result<String>
    where
        T: AsMut<HtmlRenderer<'a>> + AsRef<HtmlRenderer<'a>> + Renderer,
    {
        let mut res = String::new();
        for token in tokens {
            res.push_str(&this.render_token(token)?);
            this.as_mut().render_side_notes(&mut res);
        }
        if render_end_notes {
            this.as_mut().render_end_notes(&mut res, "section", "");
        }
        Ok(res)
    }

    /// Renders a title (without `<h1>` tags), increasing header number beforehand
    #[doc(hidden)]
    pub fn render_title(&mut self, n: i32, vec: &[Token]) -> Result<HeaderData> {
        let n = if self.current_part { n - 1 } else { n };
        self.inc_header(n);

        let number = self.current_chapter[n as usize];
        let c_title = self.render_vec(vec)?;

        if n <= 1 && self.current_numbering >= 1 {
            let header = if n == 0 {
                Header::Part
            } else {
                Header::Chapter
            };
            self.book.get_header(header, number, c_title, |s| {
                let mut parser = Parser::from(self.book);
                self.render_vec(&parser.parse_inline(s)?)
            })
        } else if self.current_numbering >= n {
            let numbers = self.get_numbers();
            Ok(HeaderData {
                text: format!("{numbers} {c_title}"),
                number: numbers,
                header: String::new(),
                title: c_title,
            })
        } else {
            Ok(HeaderData {
                text: c_title.clone(),
                number: String::new(),
                header: String::new(),
                title: c_title,
            })
        }
    }

    /// Renders a title, including `<h1>` tags and appropriate links
    #[doc(hidden)]
    pub fn render_title_full(&mut self, n: i32, data: HeaderData) -> Result<String> {
        if n == 1 {
            if self.current_hide {
                Ok(format!("<h1 id = \"link-{}\"></h1>", self.link_number))
            } else {
                let template = if self.current_part {
                    &self.part_template_html
                } else {
                    &self.chapter_template_html
                };
                let has_number = !data.header.is_empty();
                let has_title = !data.title.is_empty();
                let data = upon::value!{
                    has_number: has_number,
                    has_title: has_title,
                    header: data.header,
                    number: data.number,
                    title: data.title,
                    link: format!("{}", self.link_number)
                };
                Ok(template.render(&data).to_string()?)
            }
        } else {
            Ok(format!(
                "<h{} id = \"link-{}\">{}</h{}>\n",
                n, self.link_number, data.text, n
            ))
        }
    }

    /// Increases a header if it needs to be
    ///
    /// Also sets up first_paragraph, link stuff and so on
    fn inc_header(&mut self, n: i32) {
        if n <= 1 {
            self.first_paragraph = true;
        }
        if self.current_numbering >= n {
            assert!(n >= 0);
            let n = n as usize;
            assert!(n < self.current_chapter.len());
            self.current_chapter[n] += 1;
            let begin = if n == 0
                && !self
                    .book
                    .options
                    .get_bool("rendering.part.reset_counter")
                    .unwrap()
            {
                n + 2
            } else {
                n + 1
            };
            for i in begin..self.current_chapter.len() {
                self.current_chapter[i] = 0;
            }
        }
        self.link_number += 1;
    }

    /// Returns a "x.y.z" corresponding to current chapter/section/...
    fn get_numbers(&self) -> String {
        let mut output = String::new();
        for i in 1..self.current_chapter.len() {
            if self.current_chapter[i] == 0 {
                if i == self.current_chapter.len() - 1 {
                    break;
                }
                if !self.current_chapter[i + 1..]
                    .iter()
                    .map(|x| *x != 0)
                    .any(|x| x)
                {
                    break;
                }
            }
            if i != 1
                || !self
                    .book
                    .options
                    .get_bool("rendering.chapter.roman_numerals")
                    .unwrap()
            {
                write!(output, "{}.", self.current_chapter[i]).unwrap(); //todo
            } else if self.current_chapter[i] >= 1 {
                write!(output, "{:X}.", Roman::from(self.current_chapter[i] as i16)).unwrap();
            } else {
                error!(
                    "{}",
                    lformat!(
                        "can not use roman numerals with zero or negative chapter numbers ({n})",
                        n = self.current_chapter[i]
                    )
                );
            }
        }
        output
    }

    /// Display side notes if option is to true
    #[doc(hidden)]
    pub fn render_side_notes(&mut self, res: &mut String) {
        if self.book.options.get_bool("html.side_notes").unwrap() {
            for (note_number, footnote) in self.footnotes.drain(..) {
                write!(
                    res,
                    "<div class = \"sidenote\">\n{note_number} {footnote}\n</div>\n",
                )
                .unwrap();
            }
        }
    }

    /// Display end notes, if side_notes option is set to false
    ///
    /// * res: string to write to
    /// * section_tag: should be section for HTML5, id for XHTML
    /// * option: can be "", useful for EPUB3
    #[doc(hidden)]
    pub fn render_end_notes(&mut self, res: &mut String, section_tag: &str, option: &str) {
        if !self.footnotes.is_empty() {
            write!(
                res,
                "<{section_tag} class = \"notes\" {option}>
 <h2 class = \"notes\">{}</h2>\n",
                lang::get_str(self.book.options.get_str("lang").unwrap(), "notes")
            )
            .unwrap();
            res.push_str("<table class = \"notes\">\n");
            for (note_number, footnote) in self.footnotes.drain(..) {
                write!(
                    res,
                    "<tr class = \"notes\">
 <td class = \"note-number\">
  {note_number}
 </td>
 <td class = \"note\">
  {footnote}
  </td>
</tr>\n"
                )
                .unwrap();
            }
            res.push_str("</table>\n");
            res.push_str(&format!("</{section_tag}>\n"));
        }
    }

    /// Renders a token
    ///
    /// Used by render_token implementation of Renderer trait. Separate function
    /// because we need to be able to call it from other renderers.
    ///
    /// See http://lise-henry.github.io/articles/rust_inheritance.html
    #[doc(hidden)]
    pub fn static_render_token<T>(this: &mut T, token: &Token) -> Result<String>
    where
        T: AsMut<HtmlRenderer<'a>> + AsRef<HtmlRenderer<'a>> + Renderer,
    {
        match *token {
            Token::Annotation(ref annotation, ref v) => {
                let content = this.as_mut().render_vec(v)?;
                if this.as_ref().proofread {
                    match *annotation {
                        Data::GrammarError(ref s) => Ok(format!(
                            "<span title = \"{}\" class = \"grammar-error\">{}</span>",
                            html_escape::encode_double_quoted_attribute(s.as_str()),
                            content
                        )),
                        Data::Repetition(ref colour) => {
                            if !this.as_ref().verbatim {
                                Ok(format!(
                                    "<span class = \"repetition\" \
                                            style = \"text-decoration-line: underline; \
                                            text-decoration-style: wavy; \
                                            text-decoration-color: {colour}\">{content}</span>"
                                ))
                            } else {
                                Ok(content)
                            }
                        }
                    }
                } else {
                    Ok(content)
                }
            }
            Token::Str(ref text) => {
                let mut content = if this.as_ref().verbatim {
                    Cow::Borrowed(text.as_ref())
                } else {
                    escape::html(this.as_ref()
                                      .book.clean(text.as_str())
                    )
                };
                if this.as_ref().first_letter {
                    this.as_mut().first_letter = false;
                }

                if this
                    .as_ref()
                    .book
                    .options
                    .get_bool("html.escape_nb_spaces")
                    .unwrap()
                {
                    content = escape::nb_spaces_html(content);
                }
                Ok(content.into_owned())
            }
            Token::Paragraph(ref vec) => {
                if this.as_ref().first_paragraph {
                    this.as_mut().first_paragraph = false;
                    if !vec.is_empty() && vec[0].is_str() {
                        // Only use initials if first element is a Token::str
                        this.as_mut().first_letter = true;
                    }
                }
                let class = if this.as_ref().first_letter
                    && this
                        .as_ref()
                        .book
                        .options
                        .get_bool("rendering.initials")
                        .unwrap()
                {
                    " class = \"first-para\""
                } else {
                    ""
                };
                let content = this.render_vec(vec)?;
                this.as_mut().current_par += 1;
                let par = this.as_ref().current_par;
                Ok(format!("<p id = \"para-{par}\"{class}>{content}</p>\n"))
            }
            Token::Header(n, ref vec) => {
                let data = this.as_mut().render_title(n, vec)?;
                if n <= this
                    .as_ref()
                    .book
                    .options
                    .get_i32("rendering.num_depth")
                    .unwrap()
                {
                    let url = format!(
                        "{}#link-{}",
                        this.as_ref().filename,
                        this.as_ref().link_number
                    );
                    if !this.as_ref().current_part {
                        this.as_mut()
                            .toc
                            .add(TocElement::new(url, data.text.clone())
                                 .level(n)
                                 .raw_title(escape::html(text_view::view_as_text(vec)))
                                            // TODO: should use proper text renderer
                            );
                    } else {
                        this.as_mut()
                            .toc
                            .add(TocElement::new(url, data.text.clone())
                                 .level(n - 1)
                                 .raw_title(escape::html(text_view::view_as_text(vec)))
                                            // TODO: same
                            );
                    
                    }
                }
                Ok(this.as_mut().render_title_full(n, data)?)
            }
            Token::TaskItem(checked, ref vec) => Ok(format!(
                "<input type = \"checkbox\" disabled = \"\" {}/>{}",
                if checked { "checked = \"\"" } else { "" },
                this.render_vec(vec)?
            )),
            Token::Emphasis(ref vec) => Ok(format!("<em>{}</em>", this.render_vec(vec)?)),
            Token::Strong(ref vec) => Ok(format!("<b>{}</b>", this.render_vec(vec)?)),
            Token::Strikethrough(ref vec) => Ok(format!("<del>{}</del>", this.render_vec(vec)?)),
            Token::Code(ref s) => Ok(format!("<code>{}</code>", escape::html(s))),
            Token::Subscript(ref vec) => Ok(format!("<sub>{}</sub>", this.render_vec(vec)?)),
            Token::Superscript(ref vec) => Ok(format!("<sup>{}</sup>", this.render_vec(vec)?)),
            Token::BlockQuote(ref vec) => Ok(format!(
                "<blockquote>{}</blockquote>\n",
                this.render_vec(vec)?
            )),
            Token::CodeBlock(ref language, ref s) => {
                let output = if let Some(ref syntax) = this.as_ref().syntax {
                    syntax.to_html(s, language)?
                } else if language.is_empty() {
                    format!("<pre><code>{s}</code></pre>\n")
                } else {
                    format!(
                        "<pre><code class = \"language-{language}\">{}</code></pre>\n",
                        escape::html(s)
                    )
                };
                Ok(output)
            }
            Token::Rule => Ok(String::from("<p class = \"rule\">***</p>\n")),
            Token::SoftBreak => Ok(String::from(" ")),
            Token::HardBreak => Ok(String::from("<br />\n")),
            Token::List(ref vec) => Ok(format!("<ul>\n{}</ul>\n", this.render_vec(vec)?)),
            Token::OrderedList(n, ref vec) => Ok(format!(
                "<ol{}>\n{}</ol>\n",
                if n == 1 {
                    String::new()
                } else {
                    format!(" start = \"{n}\"")
                },
                this.render_vec(vec)?
            )),
            Token::Item(ref vec) => Ok(format!("<li>{}</li>\n", this.render_vec(vec)?)),
            Token::DescriptionList(ref v) => Ok(format!(
                "<dl>
{}
</dl>",
                this.render_vec(v)?
            )),
            Token::DescriptionItem(ref v) => Ok(this.render_vec(v)?),
            Token::DescriptionTerm(ref v) => Ok(format!("<dt>{}</dt>\n", this.render_vec(v)?)),
            Token::DescriptionDetails(ref v) => Ok(format!("<dd>{}</dd>\n", this.render_vec(v)?)),
            Token::Link(ref url, ref title, ref vec) => {
                let url = html_escape::encode_double_quoted_attribute(url.as_str());
                let url = if ResourceHandler::is_local(&url) {
                    Cow::Owned(this.as_ref().handler.get_link(&url).to_owned())
                } else {
                    url
                };

                Ok(format!(
                    "<a href = \"{url}\"{}>{}</a>",
                    if title.is_empty() {
                        String::new()
                    } else {
                        format!(" title = \"{title}\"")
                    },
                    this.render_vec(vec)?
                ))
            }
            Token::Image(ref url, ref title, ref alt)
            | Token::StandaloneImage(ref url, ref title, ref alt) => {
                let content = this.render_vec(alt)?;
                let html: &mut HtmlRenderer = this.as_mut();
                let url = html.handler.map_image(&html.source, url.as_str())?;

                if token.is_image() {
                    Ok(format!(
                        "<img src = \"{url}\" title = \"{title}\" alt = \"{content}\" />",
                    ))
                } else {
                    Ok(format!(
                        "<div class = \"image\">
  <img src = \"{url}\" title = \"{title}\" alt = \
                                \"{content}\" />
</div>",
                    ))
                }
            }
            Token::Table(_, ref vec) => Ok(format!(
                "<div class = \"table\">
    <table>\n{}
    </table>
</div>\n",
                this.render_vec(vec)?
            )),
            Token::TableRow(ref vec) => Ok(format!("<tr>\n{}</tr>\n", this.render_vec(vec)?)),
            Token::TableCell(ref vec) => {
                let tag = if this.as_ref().table_head { "th" } else { "td" };
                Ok(format!("<{tag}>{}</{tag}>", this.render_vec(vec)?))
            }
            Token::TableHead(ref vec) => {
                this.as_mut().table_head = true;
                let s = this.render_vec(vec)?;
                this.as_mut().table_head = false;
                Ok(format!("<tr>\n{s}</tr>\n"))
            }
            Token::FootnoteReference(ref reference) => Ok(format!(
                "<a href = \"#note-dest-{reference}\"><sup id = \
                            \"note-source-{reference}\">[{reference}]</sup></a>",
            )),
            Token::FootnoteDefinition(ref reference, ref vec) => {
                let note_number = format!(
                    "<p class = \"note-number\">
  <a href = \"#note-source-{reference}\">[{reference}]</a>
</p>\n",
                );

                let inner = format!(
                    "<aside id = \"note-dest-{}\">{}</aside>",
                    reference,
                    this.render_vec(vec)?
                );
                this.as_mut().footnotes.push((note_number, inner));
                Ok(String::new())
            }
        }
    }

    /// Consider the html as a template
    fn templatize(&mut self, s: &str) -> Result<String> {
        let data = self.book.get_metadata(|s| Ok(s.to_owned()))?;
        let template = self.book.compile_str(s, &self.book.source, "")?;
        Ok(template.render(&data).to_string()?)
    }

    /// Renders the toc name
    #[doc(hidden)]
    pub fn get_toc_name(&mut self) -> Result<String> {
        let data = self
            .book
            .get_metadata(|s| self.render_vec(&Parser::new().parse_inline(s)?))?;
        let template = self
            .book
            .options
            .get_str("rendering.inline_toc.name")
            .unwrap();
        let template = self.book.compile_str(template, &self.book.source, "rendering.inline_toc.name")?;
        Ok(template.render(&data).to_string()?)
    }

    /// Render a section containing schema.org JSON-LD code
    pub fn get_json_ld(&mut self) -> Result<String> {
        let json = r#"
<script type = 'application/ld+json'>
{
    "@context": "http://schema.org/",
    "@type": "Book",
    "author": "{{{author}}}",
    "name": "{{{title}}}",
    {{#has_version}}"version": "{{{version}}}",{{/has_version}}
    {{#has_subtitle}}"alternateName": "{{{subtitle}}}",{{/has_subtitle}}
    {{#has_subject}}"keywords": "{{{subject}}}",{{/has_subject}}
    {{#has_license}}"license": "{{{license}}}",{{/has_license}}
    {{#has_description}}"about": "{{{description}}}",{{/has_description}}
    "inLanguage": "{{{lang}}}"




}
</script>"#;
        self.templatize(json)
    }

    /// Renders a footer, which can include a "Generated by Crowboook" link
    /// or a customized text
    #[doc(hidden)]
    pub fn get_footer<T>(this: &mut T) -> Result<String>
    where
        T: AsMut<HtmlRenderer<'a>> + AsRef<HtmlRenderer<'a>> + Renderer,
    {
        let content = if let Ok(footer) = this.as_ref().book.options.get_str("html.footer") {
            match this.as_mut().templatize(footer) {
                Ok(content) => content,
                Err(err) => {
                    return Err(Error::render(
                        &this.as_ref().book.source,
                        lformat!(
                            "rendering 'html.footer' \
                                                       template:\n{error}",
                            error = err
                        ),
                    ))
                }
            }
        } else {
            String::new()
        };
        if content.is_empty() {
            Ok(content)
        } else {
            let tokens = Parser::from(this.as_ref().book).parse(&content, None)?;
            let content = this.render_vec(&tokens)?;
            Ok(format!("<footer id = \"footer\">{content}</footer>"))
        }
    }

    /// Renders a header
    #[doc(hidden)]
    pub fn get_header<T>(this: &mut T) -> Result<String>
    where
        T: AsMut<HtmlRenderer<'a>> + AsRef<HtmlRenderer<'a>> + Renderer,
    {
        if let Ok(top) = this.as_ref().book.options.get_str("html.header") {
            match this.as_mut().templatize(top) {
                Ok(content) => {
                    let tokens = Parser::from(this.as_ref().book).parse(&content, None)?;
                    Ok(format!(
                        "<div id = \"top\">{}</div>",
                        this.render_vec(&tokens)?
                    ))
                }
                Err(err) => Err(Error::render(
                    &this.as_ref().book.source,
                    lformat!("rendering 'html.header' template:\n{error}", error = err),
                )),
            }
        } else {
            Ok(String::new())
        }
    }
}

impl<'a> AsMut<HtmlRenderer<'a>> for HtmlRenderer<'a> {
    fn as_mut(&mut self) -> &mut HtmlRenderer<'a> {
        self
    }
}

impl<'a> AsRef<HtmlRenderer<'a>> for HtmlRenderer<'a> {
    fn as_ref(&self) -> &HtmlRenderer<'a> {
        self
    }
}

impl<'a> Renderer for HtmlRenderer<'a> {
    fn render_token(&mut self, token: &Token) -> Result<String> {
        HtmlRenderer::static_render_token(self, token)
    }
}

/// This macro automatically generates AsRef and AsMut implementations
/// for a type, to itself and to HtmlRenderer. Type must have a .html element
/// and use a <'a> lifetime parameter.
///
/// # Example
///
/// ```
/// #[macro_use]
/// extern crate crowbook;
/// use crowbook::{HtmlRenderer, Renderer, Token, Result};
/// struct Foo<'a> {
///     html: HtmlRenderer<'a>,
/// }
///
/// derive_html!{Foo<'a>, HtmlRenderer::static_render_token}
/// fn main() {}
/// ```
macro_rules! derive_html {
    {$t:ty, $f:path} => (
        impl<'a> AsRef<HtmlRenderer<'a>> for $t {
            fn as_ref(&self) -> &HtmlRenderer<'a> {
                &self.html
            }
        }

        impl<'a> AsMut<HtmlRenderer<'a>> for $t {
            fn as_mut(&mut self) -> &mut HtmlRenderer<'a> {
                &mut self.html
            }
        }

        impl<'a> AsRef<$t> for $t {
            fn as_ref(&self) -> &$t {
                self
            }
        }

        impl<'a> AsMut<$t> for $t {
            fn as_mut(&mut self) -> &mut $t {
                self
            }
        }

        impl<'a> Renderer for $t {
            fn render_token(&mut self, token: &Token) -> Result<String> {
                $f(self, token)
            }
        }

    );
}