feat: render wml decks with paginated card sub-documents

wap/src/deck.rs

@@ -0,0 +1,447 @@
+//! Assembling cards into a WML deck.
+//!
+//! WML is the one output that paginates, because a WAP 1.x handset has a hard
+//! per-card byte budget and will refuse a deck that exceeds it. So a document
+//! becomes a sequence of cards, each card is packed to fit the budget, and
+//! navigation is wired between them.
+//!
+//! Two topologies: hub-and-spoke, where a menu card links to each of the others,
+//! and linear, where each card chains to the next. A single-section document is
+//! always linear — there is nothing for a menu to choose between.
+
+use itsybitsy_core::config::{MenuStyle, PageSettings};
+use itsybitsy_core::ir::{Block, Doc};
+use itsybitsy_core::render::{Part, RenderCtx, Rendered};
+
+use crate::escape;
+use crate::wml;
+
+const PROLOG: &str = "<?xml version=\"1.0\"?>\n";
+const DOCTYPE: &str = "<!DOCTYPE wml PUBLIC \"-//WAPFORUM//DTD WML 1.3//EN\" \
+                       \"http://www.wapforum.org/DTD/wml13.dtd\">\n";
+
+/// Bytes held back from the card budget for navigation markup. A template holds
+/// the shared part once, so only the per-card overrides have to be allowed for.
+const NAV_RESERVE: u32 = 160;
+const TEMPLATED_NAV_RESERVE: u32 = 24;
+
+/// Longest slug a card's own URL will carry.
+const MAX_SLUG: usize = 40;
+
+/// Content between dividers.
+struct Section {
+    title: Option<String>,
+    blocks: Vec<Block>,
+}
+
+/// How one deck is laid out.
+#[derive(Clone, Copy)]
+struct Shape {
+    /// The deck opens with a menu card linking to the others.
+    hub: bool,
+    /// Wire each card forward to the next. A deck holding one card has nowhere
+    /// to chain to.
+    chain: bool,
+    /// This deck is the page's front, so its opening card carries the page's
+    /// title and has nothing to go back to. A card's own deck is not the front:
+    /// the menu it came from is.
+    front: bool,
+}
+
+/// One card, already paginated to fit the byte budget.
+struct Card {
+    id: String,
+    title: Option<String>,
+    slug: String,
+    /// Markup per page; more than one means the card was over budget.
+    pages: Vec<String>,
+}
+
+pub fn render(doc: &Doc, ctx: &RenderCtx<'_>) -> Rendered {
+    let settings = ctx.settings;
+    let (intro, sections) = split_into_sections(doc, settings);
+
+    // A document with no divider at all is one card, so there is nothing for a
+    // menu to choose between; one divider is already enough, since the intro
+    // becomes the hub and the section becomes an entry on it.
+    let hub = settings.menu && !sections.is_empty();
+    let cards = build_cards(intro, sections, hub, settings);
+
+    if settings.deck_per_card && hub {
+        return per_card_decks(&cards, ctx);
+    }
+    Rendered::body(one_deck(&cards, hub, ctx).into_bytes())
+}
+
+// -- Sectioning ----------------------------------------------------------
+
+/// Split a document at its dividers.
+///
+/// Three things divide: an explicit `<!-- card -->`, a thematic break when
+/// `split_on_rule`, and a heading at `split_level`. All three apply together
+/// rather than by precedence, so a document that mixes them splits at every
+/// marker it carries. Content before the first divider is the intro.
+fn split_into_sections(doc: &Doc, settings: &PageSettings) -> (Vec<Block>, Vec<Section>) {
+    let mut intro = Vec::new();
+    let mut sections: Vec<Section> = Vec::new();
+
+    for block in &doc.blocks {
+        let divider = match block {
+            Block::CardBreak { title } => Some(title.clone()),
+            Block::Rule if settings.split_on_rule => Some(None),
+            Block::Heading { level, inline }
+                if settings.split_level > 0 && *level == settings.split_level =>
+            {
+                Some(Some(Doc::plain_text(inline)))
+            }
+            _ => None,
+        };
+
+        match divider {
+            Some(title) => sections.push(Section { title, blocks: Vec::new() }),
+            None => match sections.last_mut() {
+                Some(section) => section.blocks.push(block.clone()),
+                None => intro.push(block.clone()),
+            },
+        }
+    }
+
+    // A divider with nothing after it is not a card.
+    sections.retain(|section| !section.blocks.is_empty() || section.title.is_some());
+    (intro, sections)
+}
+
+/// A section's title: its divider's label, else its first heading.
+fn section_title(section: &Section) -> Option<String> {
+    if let Some(title) = &section.title {
+        return Some(title.clone());
+    }
+    section.blocks.iter().find_map(|block| match block {
+        Block::Heading { inline, .. } => Some(Doc::plain_text(inline)),
+        _ => None,
+    })
+}
+
+// -- Card construction ---------------------------------------------------
+
+fn build_cards(
+    intro: Vec<Block>,
+    sections: Vec<Section>,
+    hub: bool,
+    settings: &PageSettings,
+) -> Vec<Card> {
+    let mut cards = Vec::new();
+    let mut slugs: Vec<String> = Vec::new();
+
+    if hub {
+        // The menu card holds the intro and the links, which are added later once
+        // every card's id is known.
+        cards.push(Card {
+            id: "menu".to_string(),
+            title: None,
+            slug: "menu".to_string(),
+            pages: vec![wml::content(&intro, settings)],
+        });
+    }
+
+    for (index, section) in sections.iter().enumerate() {
+        let title = section_title(section);
+        // In linear mode the intro belongs to the first card, since there is no
+        // menu card to hold it.
+        let mut blocks = Vec::new();
+        if !hub && index == 0 {
+            blocks.extend(intro.iter().cloned());
+        }
+        blocks.extend(section.blocks.iter().cloned());
+
+        let id = format!("card{}", index + 1);
+        let slug = unique_slug(title.as_deref().unwrap_or(&id), &mut slugs);
+        let pages = paginate(&blocks, &id, settings);
+        cards.push(Card { id, title, slug, pages });
+    }
+
+    // A document with no dividers at all still needs one card to live in.
+    if cards.is_empty() {
+        cards.push(Card {
+            id: "card1".to_string(),
+            title: None,
+            slug: "card1".to_string(),
+            pages: paginate(&intro, "card1", settings),
+        });
+    }
+    cards
+}
+
+/// Split a card's markup into pages that each fit the byte budget.
+///
+/// Blocks are kept whole: a paragraph split across a page boundary would read as
+/// two paragraphs. A single block larger than the whole budget becomes its own
+/// page, because the alternative is a deck a handset refuses outright.
+fn paginate(blocks: &[Block], id: &str, settings: &PageSettings) -> Vec<String> {
+    let markup: Vec<String> =
+        blocks.iter().map(|block| wml::content(std::slice::from_ref(block), settings)).collect();
+
+    if settings.max_card_bytes == 0 {
+        return vec![markup.concat()];
+    }
+    let reserve = if settings.template_nav { TEMPLATED_NAV_RESERVE } else { NAV_RESERVE };
+    let budget = settings.max_card_bytes.saturating_sub(reserve).max(1) as usize;
+
+    let mut pages = Vec::new();
+    let mut page = String::new();
+    for block in markup {
+        if block.len() > budget {
+            if !page.is_empty() {
+                pages.push(std::mem::take(&mut page));
+            }
+            log::warn!(
+                "card '{id}': a single block is {} bytes, over the {budget}-byte budget \
+                 (max_card_bytes {} less {reserve} reserved for navigation); \
+                 emitting it as its own page",
+                block.len(),
+                settings.max_card_bytes
+            );
+            pages.push(block);
+            continue;
+        }
+        if !page.is_empty() && page.len() + block.len() > budget {
+            pages.push(std::mem::take(&mut page));
+        }
+        page.push_str(&block);
+    }
+    if !page.is_empty() || pages.is_empty() {
+        pages.push(page);
+    }
+    pages
+}
+
+/// A URL-safe slug, unique within the deck.
+fn unique_slug(title: &str, taken: &mut Vec<String>) -> String {
+    let mut slug = String::new();
+    for ch in title.chars() {
+        if ch.is_ascii_alphanumeric() {
+            slug.push(ch.to_ascii_lowercase());
+        } else if !slug.ends_with('-') {
+            slug.push('-');
+        }
+    }
+    let base: String = slug.trim_matches('-').chars().take(MAX_SLUG).collect();
+    let base = if base.is_empty() { "card".to_string() } else { base };
+
+    let mut candidate = base.clone();
+    let mut suffix = 2;
+    while taken.contains(&candidate) {
+        candidate = format!("{base}-{suffix}");
+        suffix += 1;
+    }
+    taken.push(candidate.clone());
+    candidate
+}
+
+// -- Deck assembly -------------------------------------------------------
+
+/// Every card in one deck, with intra-deck links.
+fn one_deck(cards: &[Card], hub: bool, ctx: &RenderCtx<'_>) -> String {
+    let links = menu_links(cards, hub, ctx, None);
+    assemble(cards, Shape { hub, chain: true, front: true }, ctx, &links)
+}
+
+/// A deck per card, plus an index deck holding the menu.
+///
+/// The card decks are addressed under the page's own URL, which is the URL space
+/// a paginating format gets to claim.
+fn per_card_decks(cards: &[Card], ctx: &RenderCtx<'_>) -> Rendered {
+    let links = menu_links(cards, true, ctx, Some(ctx.url));
+    let index = assemble(&cards[..1], Shape { hub: true, chain: false, front: true }, ctx, &links);
+
+    let shape = Shape { hub: false, chain: false, front: false };
+    let parts = cards[1..]
+        .iter()
+        .map(|card| Part {
+            slug: card.slug.clone(),
+            body: assemble(std::slice::from_ref(card), shape, ctx, "").into_bytes(),
+        })
+        .collect();
+    Rendered { body: index.into_bytes(), parts }
+}
+
+/// The menu card's list of the cards it links to.
+///
+/// `base` makes each link point at a separate deck under that URL rather than at
+/// a card in this one.
+fn menu_links(cards: &[Card], hub: bool, ctx: &RenderCtx<'_>, base: Option<&str>) -> String {
+    if !hub {
+        return String::new();
+    }
+    let settings = ctx.settings;
+    let entries: Vec<(String, String)> = cards[1..]
+        .iter()
+        .map(|card| {
+            let href = match base {
+                Some(base) => format!("{}#{}", join(base, &card.slug), card.id),
+                None => format!("#{}", card.id),
+            };
+            (href, card.title.clone().unwrap_or_else(|| "Untitled".to_string()))
+        })
+        .collect();
+
+    match settings.menu_style {
+        MenuStyle::Links => entries
+            .iter()
+            .map(|(href, label)| {
+                format!(
+                    "<p><a href=\"{}\">{}</a></p>\n",
+                    escape::wml_attr(href),
+                    escape::wml(label)
+                )
+            })
+            .collect(),
+        MenuStyle::Select => {
+            // One select a keypad can pick from, rather than a list of links.
+            let options: String = entries
+                .iter()
+                .map(|(href, label)| {
+                    format!(
+                        "<option onpick=\"{}\">{}</option>",
+                        escape::wml_attr(href),
+                        escape::wml(label)
+                    )
+                })
+                .collect();
+            format!("<p><select title=\"{}\">{options}</select></p>\n", escape::wml_attr(ctx.title))
+        }
+    }
+}
+
+/// Write out a deck: prolog, optional template, then the cards.
+fn assemble(cards: &[Card], shape: Shape, ctx: &RenderCtx<'_>, menu: &str) -> String {
+    let settings = ctx.settings;
+    let mut out = String::with_capacity(512);
+    out.push_str(PROLOG);
+    out.push_str(DOCTYPE);
+    out.push_str("<wml>\n");
+
+    if settings.template_nav {
+        out.push_str("<template>\n");
+        out.push_str(&format!(
+            "<do type=\"prev\" label=\"{}\"><prev/></do>\n",
+            escape::wml_attr(&settings.nav_back_label)
+        ));
+        if let Some(home) = &settings.home_label {
+            out.push_str(&format!(
+                "<do type=\"options\" label=\"{}\"><go href=\"#menu\"/></do>\n",
+                escape::wml_attr(home)
+            ));
+        }
+        out.push_str("</template>\n");
+    }
+
+    for (index, card) in cards.iter().enumerate() {
+        let first_card = index == 0;
+        for (page, markup) in card.pages.iter().enumerate() {
+            let first_page = page == 0;
+            // The page a card's second and later screens live on has no title of
+            // its own: it is a continuation, not a new section.
+            let id = page_id(card, page);
+            let title = if !first_page {
+                // A continuation page is not a new section, so it has no title.
+                None
+            } else if first_card && shape.front {
+                // The opening screen is the page's front and carries its title:
+                // the menu card has none of its own, and in linear mode the
+                // first section's title gives way to it.
+                Some(ctx.title.to_string())
+            } else {
+                card.title.clone()
+            };
+
+            match &title {
+                Some(title) => out.push_str(&format!(
+                    "<card id=\"{id}\" title=\"{}\">\n",
+                    escape::wml_attr(title)
+                )),
+                None => out.push_str(&format!("<card id=\"{id}\">\n")),
+            }
+            out.push_str(&card_nav(cards, card, index, page, shape, settings));
+            if first_page && shape.hub && first_card {
+                out.push_str(markup);
+                out.push_str(menu);
+            } else {
+                out.push_str(markup);
+            }
+            out.push_str("</card>\n");
+        }
+    }
+
+    out.push_str("</wml>\n");
+    out
+}
+
+/// The navigation for one page of one card.
+fn card_nav(
+    cards: &[Card],
+    card: &Card,
+    index: usize,
+    page: usize,
+    shape: Shape,
+    settings: &PageSettings,
+) -> String {
+    let mut out = String::new();
+    let first_page = page == 0;
+    let entry = shape.front && index == 0 && first_page;
+
+    if settings.template_nav {
+        if entry {
+            // Nothing to go back to from the first screen, so the template's
+            // softkey is cancelled rather than left pointing nowhere.
+            out.push_str("<do type=\"prev\"><noop/></do>\n");
+            if settings.home_label.is_some() {
+                out.push_str("<do type=\"options\"><noop/></do>\n");
+            }
+        } else if !first_page {
+            // A continuation page goes back a page, which is a different idea
+            // from going back a card, so it says so.
+            out.push_str(&format!(
+                "<do type=\"prev\" label=\"{}\"><prev/></do>\n",
+                escape::wml_attr(&settings.nav_prev_label)
+            ));
+        }
+    } else if !entry {
+        let label = if first_page { &settings.nav_back_label } else { &settings.nav_prev_label };
+        out.push_str(&format!(
+            "<do type=\"prev\" label=\"{}\"><prev/></do>\n",
+            escape::wml_attr(label)
+        ));
+        if settings.home_label.is_some() {
+            out.push_str(&format!(
+                "<do type=\"options\" label=\"{}\"><go href=\"#menu\"/></do>\n",
+                escape::wml_attr(settings.home_label.as_deref().unwrap_or_default())
+            ));
+        }
+    }
+
+    // Forward: the next page of this card, else the next card when chaining.
+    let next = if page + 1 < card.pages.len() {
+        Some(page_id(card, page + 1))
+    } else if shape.chain && !shape.hub {
+        cards.get(index + 1).map(|next| page_id(next, 0))
+    } else {
+        None
+    };
+    if let Some(next) = next {
+        out.push_str(&format!(
+            "<do type=\"accept\" label=\"{}\"><go href=\"#{next}\"/></do>\n",
+            escape::wml_attr(&settings.nav_next_label)
+        ));
+    }
+    out
+}
+
+fn page_id(card: &Card, page: usize) -> String {
+    if page == 0 { card.id.clone() } else { format!("{}-p{}", card.id, page + 1) }
+}
+
+/// Join a page URL and a slug, without doubling the separator at the root.
+fn join(base: &str, slug: &str) -> String {
+    if base.ends_with('/') { format!("{base}{slug}") } else { format!("{base}/{slug}") }
+}

wap/src/escape.rs

@@ -29,6 +29,21 @@ pub fn attr(value: &str) -> String {
     out
 }
 
+/// Escape text for WML element content.
+#[cfg(feature = "wml")]
+///
+/// WML reads `$` as the start of a variable reference, so a literal one has to be
+/// doubled; otherwise a handset would substitute something or fail to parse.
+pub fn wml(value: &str) -> String {
+    text(value).replace('$', "$$")
+}
+
+/// Escape text for a WML attribute value.
+#[cfg(feature = "wml")]
+pub fn wml_attr(value: &str) -> String {
+    attr(value).replace('$', "$$")
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -41,6 +56,17 @@ mod tests {
         assert_eq!(attr("say \"hi\" & bye"), "say "hi" & bye");
     }
 
+    #[test]
+    #[cfg(feature = "wml")]
+    fn wml_doubles_a_literal_dollar() {
+        assert_eq!(wml("Permit fee: $5"), "Permit fee: $$5");
+        assert_eq!(wml("a & $b"), "a & $$b");
+        assert_eq!(wml_attr("/x?a=1&b=$2"), "/x?a=1&b=$$2");
+        // The doubling runs after the markup escape, so an escaped entity is not
+        // itself rewritten.
+        assert_eq!(wml("<$>"), "&lt;$$&gt;");
+    }
+
     #[test]
     fn leaves_ordinary_text_alone() {
         assert_eq!(text("plain text 123"), "plain text 123");

wap/src/lib.rs

@@ -5,7 +5,11 @@
 //! is shared with nothing outside this family. Splitting them would duplicate the
 //! escaper and the markup builder.
 
+#[cfg(feature = "wml")]
+mod deck;
 mod escape;
+#[cfg(feature = "wml")]
+mod wml;
 mod xhtmlmp;
 
 use itsybitsy_core::Error;
@@ -46,6 +50,28 @@ impl Renderer for Html {
     }
 }
 
+/// WML 1.3 decks, for WAP 1.x handsets.
+///
+/// The only output that paginates: a handset has a hard per-card byte budget and
+/// refuses a deck that exceeds it, so a long page becomes a chain of screens.
+#[cfg(feature = "wml")]
+pub struct Wml;
+
+#[cfg(feature = "wml")]
+impl Renderer for Wml {
+    fn id(&self) -> &'static str {
+        "wml"
+    }
+
+    fn media_type(&self) -> &'static str {
+        "text/vnd.wap.wml; charset=utf-8"
+    }
+
+    fn render(&self, doc: &Doc, ctx: &RenderCtx<'_>) -> Result<Rendered, Error> {
+        Ok(deck::render(doc, ctx))
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use itsybitsy_core::config::PageSettings;
@@ -174,3 +200,283 @@ mod tests {
         assert!(out.contains("<body>\n</body>"), "{out}");
     }
 }
+
+#[cfg(all(test, feature = "wml"))]
+mod deck_tests {
+    use itsybitsy_core::config::{MenuStyle, PageSettings};
+    use itsybitsy_core::parse;
+
+    use super::*;
+
+    /// The fixture wapdown's output was captured from, so the assertions below
+    /// can be compared against it directly.
+    pub const TRAIL: &str = "Intro line.\n\n<!-- card Weather -->\n\n\
+                         Cold and clear. Permit fee: $5.\n\n\
+                         <!-- card Status -->\n\n- North: open\n";
+
+    fn render_with(settings: &PageSettings, markdown: &str) -> Rendered {
+        // Card dividers are comment directives, so the IR is built by hand here
+        // the way `parse::document` would produce it.
+        let doc = with_card_breaks(markdown);
+        let ctx = RenderCtx { url: "/trail", title: "Trail", settings, width: None };
+        Wml.render(&doc, &ctx).unwrap()
+    }
+
+    /// Parse, then turn `<!-- card X -->` comments into dividers, which is what
+    /// `directives::apply` does for a real request.
+    pub fn with_card_breaks(markdown: &str) -> Doc {
+        let mut doc = parse::markdown(markdown);
+        doc.blocks = doc
+            .blocks
+            .into_iter()
+            .map(|block| match &block {
+                itsybitsy_core::ir::Block::Html(html) if html.contains("card") => {
+                    let title = html
+                        .trim()
+                        .trim_start_matches("<!--")
+                        .trim_end_matches("-->")
+                        .trim()
+                        .strip_prefix("card")
+                        .map(|rest| rest.trim().to_string())
+                        .filter(|title| !title.is_empty());
+                    itsybitsy_core::ir::Block::CardBreak { title }
+                }
+                _ => block,
+            })
+            .collect();
+        doc
+    }
+
+    fn body(rendered: &Rendered) -> String {
+        String::from_utf8(rendered.body.clone()).unwrap()
+    }
+
+    #[test]
+    fn a_deck_carries_the_wml_prolog_and_doctype() {
+        let out = body(&render_with(&PageSettings::default(), TRAIL));
+        assert!(out.starts_with("<?xml version=\"1.0\"?>\n<!DOCTYPE wml PUBLIC"), "{out}");
+        assert!(out.contains("wml13.dtd"), "{out}");
+        assert!(out.ends_with("</wml>\n"), "{out}");
+    }
+
+    #[test]
+    fn menu_mode_puts_the_intro_and_the_links_on_a_hub_card() {
+        let out = body(&render_with(&PageSettings::default(), TRAIL));
+        assert!(out.contains("<card id=\"menu\" title=\"Trail\">"), "{out}");
+        assert!(out.contains("<p>Intro line.</p>"), "{out}");
+        assert!(out.contains("<p><a href=\"#card1\">Weather</a></p>"), "{out}");
+        assert!(out.contains("<p><a href=\"#card2\">Status</a></p>"), "{out}");
+        assert!(out.contains("<card id=\"card1\" title=\"Weather\">"), "{out}");
+        assert!(out.contains("<card id=\"card2\" title=\"Status\">"), "{out}");
+    }
+
+    #[test]
+    fn a_literal_dollar_survives_into_the_card() {
+        // WML reads a single `$` as a variable reference.
+        let out = body(&render_with(&PageSettings::default(), TRAIL));
+        assert!(out.contains("Permit fee: $$5."), "{out}");
+    }
+
+    #[test]
+    fn shared_navigation_is_hoisted_into_a_template() {
+        let out = body(&render_with(&PageSettings::default(), TRAIL));
+        assert!(
+            out.contains("<template>\n<do type=\"prev\" label=\"Back\"><prev/></do>\n</template>"),
+            "{out}"
+        );
+        // The entry card has nothing to go back to, so it cancels the softkey.
+        assert!(out.contains("<do type=\"prev\"><noop/></do>"), "{out}");
+    }
+
+    #[test]
+    fn without_a_template_each_card_carries_its_own_navigation() {
+        let settings = PageSettings { template_nav: false, ..Default::default() };
+        let out = body(&render_with(&settings, TRAIL));
+        assert!(!out.contains("<template>"), "{out}");
+        assert!(!out.contains("<noop/>"), "{out}");
+        assert_eq!(out.matches("<do type=\"prev\" label=\"Back\">").count(), 2, "{out}");
+    }
+
+    #[test]
+    fn linear_mode_chains_the_cards_and_merges_the_intro() {
+        let settings = PageSettings { menu: false, ..Default::default() };
+        let out = body(&render_with(&settings, TRAIL));
+        assert!(!out.contains("id=\"menu\""), "{out}");
+        // The first card takes the page's title and the intro content.
+        assert!(out.contains("<card id=\"card1\" title=\"Trail\">"), "{out}");
+        assert!(out.contains("<p>Intro line.</p>"), "{out}");
+        assert!(
+            out.contains("<do type=\"accept\" label=\"More\"><go href=\"#card2\"/></do>"),
+            "{out}"
+        );
+    }
+
+    #[test]
+    fn a_select_menu_is_one_pickable_list() {
+        let settings = PageSettings { menu_style: MenuStyle::Select, ..Default::default() };
+        let out = body(&render_with(&settings, TRAIL));
+        assert!(out.contains("<select title=\"Trail\">"), "{out}");
+        assert!(out.contains("<option onpick=\"#card1\">Weather</option>"), "{out}");
+        assert!(!out.contains("<a href=\"#card1\">"), "{out}");
+    }
+
+    #[test]
+    fn a_home_label_adds_an_options_softkey() {
+        let settings = PageSettings { home_label: Some("Home".into()), ..Default::default() };
+        let out = body(&render_with(&settings, TRAIL));
+        assert!(
+            out.contains("<do type=\"options\" label=\"Home\"><go href=\"#menu\"/></do>"),
+            "{out}"
+        );
+        // Cancelled on the menu card, which is where it would point.
+        assert!(out.contains("<do type=\"options\"><noop/></do>"), "{out}");
+    }
+
+    #[test]
+    fn an_untitled_divider_still_gets_a_menu_entry() {
+        let out = body(&render_with(&PageSettings::default(), "A.\n\n---\n\nB.\n"));
+        assert!(out.contains("Untitled"), "{out}");
+    }
+
+    #[test]
+    fn a_document_with_no_divider_is_one_linear_card() {
+        let out = body(&render_with(&PageSettings::default(), "Just one paragraph.\n"));
+        assert!(!out.contains("id=\"menu\""), "{out}");
+        assert!(out.contains("<card id=\"card1\" title=\"Trail\">"), "{out}");
+    }
+
+    #[test]
+    fn headings_split_the_deck_when_asked_to() {
+        let settings = PageSettings { split_level: 2, ..Default::default() };
+        let out = body(&render_with(&settings, "Intro.\n\n## Alpha\n\nA.\n\n## Beta\n\nB.\n"));
+        assert!(out.contains("<card id=\"card1\" title=\"Alpha\">"), "{out}");
+        assert!(out.contains("<card id=\"card2\" title=\"Beta\">"), "{out}");
+    }
+
+    #[test]
+    fn a_rule_splits_the_deck_unless_turned_off() {
+        let source = "A.\n\n---\n\nB.\n";
+        let split = body(&render_with(&PageSettings::default(), source));
+        assert!(split.contains("id=\"menu\""), "{split}");
+        assert!(split.contains("id=\"card1\""), "{split}");
+
+        let settings = PageSettings { split_on_rule: false, ..Default::default() };
+        let whole = body(&render_with(&settings, source));
+        // One card, with the rule rendered as content instead of dividing.
+        assert!(!whole.contains("id=\"menu\""), "{whole}");
+        assert!(whole.contains("<p>---</p>"), "{whole}");
+    }
+
+    // -- Byte budget -------------------------------------------------------
+
+    fn long_page() -> String {
+        let para: String =
+            (0..60).map(|i| format!("word{i} ")).collect::<String>().trim_end().to_string();
+        format!("{para}\n\n{para}\n\n{para}\n")
+    }
+
+    #[test]
+    fn an_over_budget_card_is_split_into_pages() {
+        let settings = PageSettings { max_card_bytes: 400, ..Default::default() };
+        let out = body(&render_with(&settings, &long_page()));
+        // Continuation pages are numbered and carry no title of their own.
+        assert!(out.contains("<card id=\"card1-p2\">"), "{out}");
+        assert!(out.contains("<card id=\"card1-p3\">"), "{out}");
+        assert!(
+            out.contains("<do type=\"accept\" label=\"More\"><go href=\"#card1-p2\"/></do>"),
+            "{out}"
+        );
+        // Going back a page is a different idea from going back a card.
+        assert!(out.contains("<do type=\"prev\" label=\"Prev\"><prev/></do>"), "{out}");
+    }
+
+    #[test]
+    fn the_last_page_has_nowhere_further_to_go() {
+        let settings = PageSettings { max_card_bytes: 400, ..Default::default() };
+        let out = body(&render_with(&settings, &long_page()));
+        let last = out.rfind("<card id=\"card1-p3\">").unwrap();
+        assert!(!out[last..].contains("type=\"accept\""), "{}", &out[last..]);
+    }
+
+    #[test]
+    fn a_zero_budget_means_no_pagination() {
+        let settings = PageSettings { max_card_bytes: 0, ..Default::default() };
+        let out = body(&render_with(&settings, &long_page()));
+        assert!(!out.contains("-p2"), "{out}");
+    }
+
+    #[test]
+    fn each_page_stays_within_the_budget_where_a_block_allows_it() {
+        let settings = PageSettings { max_card_bytes: 1400, ..Default::default() };
+        let source: String = (0..40).map(|i| format!("Paragraph number {i}.\n\n")).collect();
+        let out = body(&render_with(&settings, &source));
+        for card in out.split("<card ").skip(1) {
+            let content = card.split_once('>').map(|(_, rest)| rest).unwrap_or("");
+            let body = content.split("</card>").next().unwrap_or("");
+            assert!(body.len() <= 1400, "a page is {} bytes:\n{body}", body.len());
+        }
+    }
+
+    // -- Deck per card -----------------------------------------------------
+
+    #[test]
+    fn deck_per_card_puts_each_card_in_its_own_deck() {
+        let settings = PageSettings { deck_per_card: true, ..Default::default() };
+        let rendered = render_with(&settings, TRAIL);
+        let index = body(&rendered);
+
+        // The index holds only the menu, linking out to each card's own URL.
+        assert!(index.contains("<card id=\"menu\" title=\"Trail\">"), "{index}");
+        assert!(!index.contains("id=\"card1\""), "{index}");
+        assert!(index.contains("<a href=\"/trail/weather#card1\">Weather</a>"), "{index}");
+
+        let slugs: Vec<&str> = rendered.parts.iter().map(|part| part.slug.as_str()).collect();
+        assert_eq!(slugs, ["weather", "status"]);
+        let weather = String::from_utf8(rendered.parts[0].body.clone()).unwrap();
+        assert!(weather.contains("<card id=\"card1\" title=\"Weather\">"), "{weather}");
+        assert!(weather.contains("Permit fee: $$5."), "{weather}");
+    }
+
+    #[test]
+    fn deck_per_card_is_ignored_without_a_menu_to_split() {
+        let settings = PageSettings { deck_per_card: true, menu: false, ..Default::default() };
+        assert!(render_with(&settings, TRAIL).parts.is_empty());
+    }
+
+    #[test]
+    fn slugs_are_url_safe_and_unique() {
+        let settings = PageSettings { deck_per_card: true, ..Default::default() };
+        let source = "Intro.\n\n<!-- card A & B! -->\n\nx\n\n<!-- card A & B! -->\n\ny\n";
+        let rendered = render_with(&settings, source);
+        let slugs: Vec<&str> = rendered.parts.iter().map(|part| part.slug.as_str()).collect();
+        assert_eq!(slugs, ["a-b", "a-b-2"]);
+    }
+}
+
+/// Writes this crate's WML output to `/tmp` so it can be diffed against the
+/// reference capture from wapdown. Run with `--ignored` when changing the deck.
+#[cfg(all(test, feature = "wml"))]
+mod oracle_dump {
+    use itsybitsy_core::config::{MenuStyle, PageSettings};
+
+    use super::deck_tests::*;
+    use super::*;
+
+    #[test]
+    #[ignore = "writes files for manual comparison against the reference capture"]
+    fn dump_for_comparison() {
+        let cases: Vec<(&str, PageSettings)> = vec![
+            ("default", PageSettings::default()),
+            ("linear", PageSettings { menu: false, ..Default::default() }),
+            ("select", PageSettings { menu_style: MenuStyle::Select, ..Default::default() }),
+            ("notemplate", PageSettings { template_nav: false, ..Default::default() }),
+            ("home", PageSettings { home_label: Some("Home".into()), ..Default::default() }),
+        ];
+        for (name, settings) in cases {
+            let doc = with_card_breaks(TRAIL);
+            let ctx = RenderCtx { url: "/trail", title: "Trail", settings: &settings, width: None };
+            let out = Wml.render(&doc, &ctx).unwrap();
+            std::fs::write(format!("/tmp/mine-{name}.wml"), out.body).unwrap();
+        }
+    }
+}

wap/src/wml.rs

@@ -0,0 +1,240 @@
+//! WML 1.3 markup for one card's content.
+//!
+//! WML is much narrower than XHTML: there are no list elements at all, and `$`
+//! introduces a variable reference, so a literal one has to be doubled. Both
+//! constraints shape what the blocks below turn into.
+
+use itsybitsy_core::config::{Images, PageSettings};
+use itsybitsy_core::ir::{Block, Doc, Inline};
+
+use crate::escape;
+
+/// Render blocks as the inside of a `<card>`.
+pub fn content(blocks: &[Block], settings: &PageSettings) -> String {
+    let mut out = String::new();
+    for block in blocks {
+        block_markup(block, settings, &mut out);
+    }
+    out
+}
+
+fn block_markup(block: &Block, settings: &PageSettings, out: &mut String) {
+    match block {
+        // WML has no heading elements, so a heading is a paragraph set in bold.
+        // Level is not expressible; the text is what survives.
+        Block::Heading { inline, .. } => {
+            out.push_str(&format!("<p><b>{}</b></p>\n", inlines(inline, settings)));
+        }
+        Block::Paragraph(inline) => {
+            let markup = inlines(inline, settings);
+            if !markup.trim().is_empty() {
+                out.push_str(&format!("<p>{markup}</p>\n"));
+            }
+        }
+        // No preformatted element either: `<br/>` keeps the line structure, which
+        // is the part of a code block that carries meaning.
+        Block::CodeBlock { lines, .. } | Block::Art { lines, .. } => {
+            let body = lines.iter().map(|line| escape::wml(line)).collect::<Vec<_>>().join("<br/>");
+            out.push_str(&format!("<p>{body}</p>\n"));
+        }
+        // A quote is marked with a prefix, since there is nothing to indent with.
+        Block::BlockQuote(inner) => {
+            let mut quoted = String::new();
+            for block in inner {
+                block_markup(block, settings, &mut quoted);
+            }
+            out.push_str(&quoted.replace("<p>", "<p>| "));
+        }
+        Block::List { ordered, start, items } => {
+            let mut lines = Vec::new();
+            for (index, item) in items.iter().enumerate() {
+                let marker =
+                    if *ordered { format!("{}. ", start + index as u64) } else { "- ".to_string() };
+                lines.push(format!("{marker}{}", item_markup(item, settings)));
+            }
+            if !lines.is_empty() {
+                out.push_str(&format!("<p>{}</p>\n", lines.join("<br/>")));
+            }
+        }
+        Block::Table { head, rows, .. } => {
+            let columns = head.len().max(rows.iter().map(Vec::len).max().unwrap_or(0));
+            if columns == 0 {
+                return;
+            }
+            out.push_str(&format!("<table columns=\"{columns}\">\n"));
+            for row in std::iter::once(head).filter(|head| !head.is_empty()).chain(rows) {
+                out.push_str("<tr>");
+                for index in 0..columns {
+                    let cell =
+                        row.get(index).map(|cell| inlines(cell, settings)).unwrap_or_default();
+                    out.push_str(&format!("<td>{cell}</td>"));
+                }
+                out.push_str("</tr>\n");
+            }
+            out.push_str("</table>\n");
+        }
+        // WML has no horizontal rule.
+        Block::Rule => out.push_str("<p>---</p>\n"),
+        // Alignment is a fixed-width concern; a handset lays out its own screen.
+        Block::Aligned { block, .. } => block_markup(block, settings, out),
+        // Pagination here is the deck's own job, driven by the byte budget.
+        Block::CardBreak { .. } => {}
+        // Raw HTML is not WML and would not parse on a handset.
+        Block::Html(_) => {}
+    }
+}
+
+/// A list item flattened onto one line: WML cannot nest block content in a list.
+fn item_markup(blocks: &[Block], settings: &PageSettings) -> String {
+    let mut parts = Vec::new();
+    for block in blocks {
+        match block {
+            Block::Paragraph(inline) | Block::Heading { inline, .. } => {
+                parts.push(inlines(inline, settings))
+            }
+            Block::List { items, .. } => {
+                // A nested list is flattened with its own markers rather than
+                // dropped, since there is no nesting to express it with.
+                for item in items {
+                    parts.push(format!("- {}", item_markup(item, settings)));
+                }
+            }
+            Block::Aligned { block, .. } => {
+                parts.push(item_markup(std::slice::from_ref(block), settings))
+            }
+            _ => {}
+        }
+    }
+    parts.join(" ")
+}
+
+pub fn inlines(inline: &[Inline], settings: &PageSettings) -> String {
+    let mut out = String::new();
+    for item in inline {
+        match item {
+            Inline::Text(text) => out.push_str(&escape::wml(text)),
+            // No `<code>` in WML; monospace is not available either.
+            Inline::Code(code) => out.push_str(&escape::wml(code)),
+            Inline::Emph(inner) => out.push_str(&format!("<em>{}</em>", inlines(inner, settings))),
+            Inline::Strong(inner) => {
+                out.push_str(&format!("<strong>{}</strong>", inlines(inner, settings)))
+            }
+            // No strikethrough element; the words survive without it.
+            Inline::Strike(inner) => out.push_str(&inlines(inner, settings)),
+            Inline::Link { href, label, .. } => {
+                out.push_str(&format!(
+                    "<a href=\"{}\">{}</a>",
+                    escape::wml_attr(href),
+                    inlines(label, settings)
+                ));
+            }
+            Inline::Image { src, alt, .. } => {
+                let alt_text = escape::wml_attr(&Doc::plain_text(alt));
+                match settings.images {
+                    Images::Keep => out.push_str(&format!(
+                        "<img src=\"{}\" alt=\"{alt_text}\"/>",
+                        escape::wml_attr(src)
+                    )),
+                    Images::Alt => out.push_str(&escape::wml(&Doc::plain_text(alt))),
+                    Images::Drop => {}
+                }
+            }
+            Inline::SoftBreak => out.push(' '),
+            Inline::HardBreak => out.push_str("<br/>"),
+            Inline::Html(_) => {}
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use itsybitsy_core::parse;
+
+    use super::*;
+
+    fn render(markdown: &str) -> String {
+        let doc = parse::markdown(markdown);
+        content(&doc.blocks, &PageSettings::default())
+    }
+
+    #[test]
+    fn a_literal_dollar_is_doubled_because_wml_reads_it_as_a_variable() {
+        assert_eq!(render("Permit fee: $5.\n"), "<p>Permit fee: $$5.</p>\n");
+    }
+
+    #[test]
+    fn headings_become_bold_paragraphs_since_wml_has_none() {
+        assert_eq!(render("# Title\n"), "<p><b>Title</b></p>\n");
+        assert_eq!(render("###### Deep\n"), "<p><b>Deep</b></p>\n");
+    }
+
+    #[test]
+    fn lists_become_one_paragraph_of_marked_lines() {
+        // WML has no list element at all.
+        assert_eq!(render("- a\n- b\n"), "<p>- a<br/>- b</p>\n");
+        assert_eq!(render("3. a\n4. b\n"), "<p>3. a<br/>4. b</p>\n");
+    }
+
+    #[test]
+    fn a_nested_list_is_flattened_rather_than_dropped() {
+        let out = render("- a\n  - b\n");
+        assert!(out.contains("- a - b"), "{out}");
+    }
+
+    #[test]
+    fn tables_are_rendered_because_wml_has_them() {
+        // wapdown's own parser produces no tables, so this is new output.
+        assert_eq!(
+            render("| a | b |\n| --- | --- |\n| 1 | 2 |\n"),
+            "<table columns=\"2\">\n<tr><td>a</td><td>b</td></tr>\n<tr><td>1</td><td>2</td></tr>\n</table>\n"
+        );
+    }
+
+    #[test]
+    fn code_keeps_its_line_structure_through_breaks() {
+        assert_eq!(
+            render("```\nlet x = 1;\nlet y = 2;\n```\n"),
+            "<p>let x = 1;<br/>let y = 2;</p>\n"
+        );
+    }
+
+    #[test]
+    fn a_quote_is_marked_with_a_prefix() {
+        assert_eq!(render("> quoted\n"), "<p>| quoted</p>\n");
+    }
+
+    #[test]
+    fn inline_markup_uses_the_elements_wml_has() {
+        assert_eq!(render("a *b* **c**\n"), "<p>a <em>b</em> <strong>c</strong></p>\n");
+        // No element for these, so the words survive unmarked.
+        assert_eq!(render("~~gone~~\n"), "<p>gone</p>\n");
+        assert_eq!(render("`code`\n"), "<p>code</p>\n");
+    }
+
+    #[test]
+    fn links_are_escaped_in_both_text_and_attribute() {
+        assert_eq!(
+            render("[a $ b](/x?y=1&z=$2)\n"),
+            "<p><a href=\"/x?y=1&amp;z=$$2\">a $$ b</a></p>\n"
+        );
+    }
+
+    #[test]
+    fn images_follow_the_configured_policy() {
+        let doc = parse::markdown("![a photo](/i.png)\n");
+        for (policy, expected) in [
+            (Images::Keep, "<p><img src=\"/i.png\" alt=\"a photo\"/></p>\n"),
+            (Images::Alt, "<p>a photo</p>\n"),
+            (Images::Drop, ""),
+        ] {
+            let settings = PageSettings { images: policy, ..Default::default() };
+            assert_eq!(content(&doc.blocks, &settings), expected, "{policy:?}");
+        }
+    }
+
+    #[test]
+    fn raw_html_is_left_out_because_it_is_not_wml() {
+        assert_eq!(render("<div>x</div>\n"), "");
+    }
+}