//! Inline markdown for descriptions: links on a short allow-list of
//! schemes, images gated and framed, with layout hints read from the
//! image title. Never raw HTML.

/// Descriptions are inline markdown: `[text](https://…)` links,
/// `*emphasis*`, `**strong**`, `` `code` ``. Block structure is
/// flattened (a description is one paragraph) and raw HTML in the
/// source is dropped, so content can link out without being able to
/// inject markup. Link targets are limited to https, mailto and
/// site-relative paths; anything else renders as plain text.
pub fn render_inline_markdown(text: &str) -> String {
    use pulldown_cmark::{html, Event, Options, Parser, Tag, TagEnd};
    let parser = Parser::new_ext(text, Options::empty());
    let mut in_link = 0usize;
    let mut in_dropped_image = 0usize;
    let filtered = parser.filter_map(|event| match event {
        Event::Html(_) | Event::InlineHtml(_) => None,
        Event::Start(Tag::Paragraph) | Event::End(TagEnd::Paragraph) => None,
        Event::SoftBreak => Some(Event::Text(" ".into())),
        Event::Start(Tag::Link { dest_url, .. })
            if !(dest_url.starts_with("https://")
                || dest_url.starts_with("mailto:")
                || dest_url.starts_with("tel:")
                || dest_url.starts_with('/')) =>
        {
            in_link += 1;
            None
        }
        Event::End(TagEnd::Link) if in_link > 0 => {
            in_link -= 1;
            None
        }
        // Images take the same gate as links: https or same-origin
        // only - no data:, no plain http. Unlike a dropped link (whose
        // label is real text worth keeping), a dropped image's alt
        // text is a caption for something that isn't there - swallow it.
        Event::Start(Tag::Image { dest_url, .. })
            if !(dest_url.starts_with("https://") || dest_url.starts_with('/')) =>
        {
            in_dropped_image += 1;
            None
        }
        Event::End(TagEnd::Image) if in_dropped_image > 0 => {
            in_dropped_image -= 1;
            None
        }
        Event::Text(_) if in_dropped_image > 0 => None,
        other => Some(other),
    });
    let mut out = String::new();
    html::push_html(&mut out, filtered);
    apply_image_hints(out.trim())
}

/// Translate a markdown image's title (`![alt](url "right 9rem")`)
/// into layout: `left`/`right` float via a class, a bare number
/// (optionally with `rem`) into a validated `max-width`. Unknown
/// tokens are ignored; the title attribute is dropped either way.
/// Only touches `<img>` tags in our own render output, and only ever
/// emits a numeric max-width - no arbitrary CSS reaches the page.
pub(crate) fn apply_image_hints(html: &str) -> String {
    let mut out = String::new();
    let mut rest = html;
    while let Some(pos) = rest.find("<img ") {
        out.push_str(&rest[..pos]);
        let after = &rest[pos..];
        let end = after.find('>').map(|e| e + 1).unwrap_or(after.len());
        out.push_str(&rewrite_img_tag(&after[..end]));
        rest = &after[end..];
    }
    out.push_str(rest);
    out
}

pub(crate) fn rewrite_img_tag(tag: &str) -> String {
    // Pull the title value, if any.
    let title = tag
        .find("title=\"")
        .map(|i| &tag[i + 7..])
        .and_then(|r| r.find('"').map(|e| &r[..e]))
        .unwrap_or("");

    let mut class = String::new();
    let mut max_rem: Option<f32> = None;
    for tok in title.split_whitespace() {
        match tok {
            "left" => class = "md-float-left".into(),
            "right" => class = "md-float-right".into(),
            other => {
                if let Ok(n) = other.trim_end_matches("rem").parse::<f32>() {
                    if n > 0.0 && n <= 60.0 {
                        max_rem = Some(n);
                    }
                }
            }
        }
    }

    // Strip the title attribute from the tag.
    let mut cleaned = tag.to_string();
    if let Some(i) = cleaned.find(" title=\"") {
        if let Some(e) = cleaned[i + 8..].find('"') {
            cleaned.replace_range(i..i + 8 + e + 1, "");
        }
    }

    // Inject class/style right after `<img`.
    let mut attrs = String::new();
    if !class.is_empty() {
        attrs.push_str(&format!(" class=\"{class}\""));
    }
    if let Some(n) = max_rem {
        attrs.push_str(&format!(" style=\"max-width:{n}rem\""));
    }
    if attrs.is_empty() {
        return cleaned;
    }
    cleaned.replacen("<img", &format!("<img{attrs}"), 1)
}


/// Markdown that a person wrote into a record - a bio on a card - as
/// opposed to the site's own content. Paragraphs, line breaks as they
/// were typed, lists, emphasis and links; no images (a picture has its
/// own field, and an image in text is a way to load something from
/// elsewhere into every visitor's page), no raw HTML, headings as plain
/// paragraphs. Links go to https, mailto or tel only, and say they are
/// the writer's, not the site's (`rel="nofollow ugc"`).
pub fn render_written_markdown(text: &str) -> String {
    use pulldown_cmark::{html, Event, Options, Parser, Tag, TagEnd};
    let parser = Parser::new_ext(text, Options::ENABLE_STRIKETHROUGH);
    let mut in_dropped_link = 0usize;
    let mut in_image = 0usize;
    let filtered = parser.filter_map(|event| match event {
        Event::Html(_) | Event::InlineHtml(_) => None,
        Event::Start(Tag::Image { .. }) => {
            in_image += 1;
            None
        }
        Event::End(TagEnd::Image) => {
            in_image = in_image.saturating_sub(1);
            None
        }
        _ if in_image > 0 => None,
        Event::Start(Tag::Heading { .. }) => Some(Event::Start(Tag::Paragraph)),
        Event::End(TagEnd::Heading(_)) => Some(Event::End(TagEnd::Paragraph)),
        // What someone typed on a new line is on a new line.
        Event::SoftBreak => Some(Event::HardBreak),
        Event::Start(Tag::Link { dest_url, .. })
            if !(dest_url.starts_with("https://") || dest_url.starts_with("mailto:") || dest_url.starts_with("tel:")) =>
        {
            in_dropped_link += 1;
            None
        }
        Event::End(TagEnd::Link) if in_dropped_link > 0 => {
            in_dropped_link -= 1;
            None
        }
        other => Some(other),
    });
    let mut out = String::new();
    html::push_html(&mut out, filtered);
    out.trim().replace("<a href=", "<a rel=\"nofollow ugc\" href=")
}

#[cfg(test)]
mod written_tests {
    use super::render_written_markdown as md;

    #[test]
    fn a_bio_keeps_what_a_person_would_write_and_nothing_that_reaches_out() {
        assert_eq!(md("Line one\nline two"), "<p>Line one<br />\nline two</p>");
        assert!(md("- NS 3424\n- NS 3423").contains("<ul>\n<li>NS 3424</li>"));
        assert!(md("**Sivilingeniør**, *NTNU*").contains("<strong>Sivilingeniør</strong>, <em>NTNU</em>"));
        assert_eq!(md("[Westra](https://westra.no)"), "<p><a rel=\"nofollow ugc\" href=\"https://westra.no\">Westra</a></p>");
        // Everything that would put something else in the page is gone.
        assert_eq!(md("<script>alert(1)</script>"), "");
        assert_eq!(md("hi <img src=x onerror=alert(1)>"), "<p>hi </p>");
        assert_eq!(md("[click](javascript:alert(1))"), "<p>click</p>");
        assert_eq!(md("[home](/kontor)"), "<p>home</p>", "a site path is the site's to link, not a bio's");
        assert_eq!(md("before ![pixel](https://tracker.example/p.gif) after"), "<p>before  after</p>");
        assert_eq!(md("# Shouting"), "<p>Shouting</p>");
    }
}