1 files changed, 215 insertions, 0 deletions
diff --git a/crates/mdman/src/hbs.rs b/crates/mdman/src/hbs.rs
new file mode 100644
index 0000000..81ad7ee
--- /dev/null
+++ b/crates/mdman/src/hbs.rs
@@ -0,0 +1,215 @@
+//! Handlebars template processing.
+
+use crate::format::Formatter;
+use anyhow::Error;
+use handlebars::{
+    handlebars_helper, Context, Decorator, Handlebars, Helper, HelperDef, HelperResult, Output,
+    RenderContext, RenderError, Renderable,
+};
+use std::collections::HashMap;
+use std::path::Path;
+
+type FormatterRef<'a> = &'a (dyn Formatter + Send + Sync);
+
+/// Processes the handlebars template at the given file.
+pub fn expand(file: &Path, formatter: FormatterRef) -> Result<String, Error> {
+    let mut handlebars = Handlebars::new();
+    handlebars.set_strict_mode(true);
+    handlebars.register_helper("lower", Box::new(lower));
+    handlebars.register_helper("options", Box::new(OptionsHelper { formatter }));
+    handlebars.register_helper("option", Box::new(OptionHelper { formatter }));
+    handlebars.register_helper("man", Box::new(ManLinkHelper { formatter }));
+    handlebars.register_decorator("set", Box::new(set_decorator));
+    handlebars.register_template_file("template", file)?;
+    let includes = file.parent().unwrap().join("includes");
+    handlebars.register_templates_directory(".md", includes)?;
+    let man_name = file
+        .file_stem()
+        .expect("expected filename")
+        .to_str()
+        .expect("utf8 filename")
+        .to_string();
+    let data = HashMap::from([("man_name", man_name)]);
+    let expanded = handlebars.render("template", &data)?;
+    Ok(expanded)
+}
+
+/// Helper for `{{#options}}` block.
+struct OptionsHelper<'a> {
+    formatter: FormatterRef<'a>,
+}
+
+impl HelperDef for OptionsHelper<'_> {
+    fn call<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'reg, 'rc>,
+        r: &'reg Handlebars<'reg>,
+        ctx: &'rc Context,
+        rc: &mut RenderContext<'reg, 'rc>,
+        out: &mut dyn Output,
+    ) -> HelperResult {
+        if in_options(rc) {
+            return Err(RenderError::new("options blocks cannot be nested"));
+        }
+        // Prevent nested {{#options}}.
+        set_in_context(rc, "__MDMAN_IN_OPTIONS", serde_json::Value::Bool(true));
+        let s = self.formatter.render_options_start();
+        out.write(&s)?;
+        let t = match h.template() {
+            Some(t) => t,
+            None => return Err(RenderError::new("options block must not be empty")),
+        };
+        let block = t.renders(r, ctx, rc)?;
+        out.write(&block)?;
+
+        let s = self.formatter.render_options_end();
+        out.write(&s)?;
+        remove_from_context(rc, "__MDMAN_IN_OPTIONS");
+        Ok(())
+    }
+}
+
+/// Whether or not the context is currently inside a `{{#options}}` block.
+fn in_options(rc: &RenderContext<'_, '_>) -> bool {
+    rc.context()
+        .map_or(false, |ctx| ctx.data().get("__MDMAN_IN_OPTIONS").is_some())
+}
+
+/// Helper for `{{#option}}` block.
+struct OptionHelper<'a> {
+    formatter: FormatterRef<'a>,
+}
+
+impl HelperDef for OptionHelper<'_> {
+    fn call<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'reg, 'rc>,
+        r: &'reg Handlebars<'reg>,
+        ctx: &'rc Context,
+        rc: &mut RenderContext<'reg, 'rc>,
+        out: &mut dyn Output,
+    ) -> HelperResult {
+        if !in_options(rc) {
+            return Err(RenderError::new("option must be in options block"));
+        }
+        let params = h.params();
+        if params.is_empty() {
+            return Err(RenderError::new(
+                "option block must have at least one param",
+            ));
+        }
+        // Convert params to strings.
+        let params = params
+            .iter()
+            .map(|param| {
+                param
+                    .value()
+                    .as_str()
+                    .ok_or_else(|| RenderError::new("option params must be strings"))
+            })
+            .collect::<Result<Vec<&str>, RenderError>>()?;
+        let t = match h.template() {
+            Some(t) => t,
+            None => return Err(RenderError::new("option block must not be empty")),
+        };
+        // Render the block.
+        let block = t.renders(r, ctx, rc)?;
+
+        // Get the name of this page.
+        let man_name = ctx
+            .data()
+            .get("man_name")
+            .expect("expected man_name in context")
+            .as_str()
+            .expect("expect man_name str");
+
+        // Ask the formatter to convert this option to its format.
+        let option = self
+            .formatter
+            .render_option(&params, &block, man_name)
+            .map_err(|e| RenderError::new(format!("option render failed: {}", e)))?;
+        out.write(&option)?;
+        Ok(())
+    }
+}
+
+/// Helper for `{{man name section}}` expression.
+struct ManLinkHelper<'a> {
+    formatter: FormatterRef<'a>,
+}
+
+impl HelperDef for ManLinkHelper<'_> {
+    fn call<'reg: 'rc, 'rc>(
+        &self,
+        h: &Helper<'reg, 'rc>,
+        _r: &'reg Handlebars<'reg>,
+        _ctx: &'rc Context,
+        _rc: &mut RenderContext<'reg, 'rc>,
+        out: &mut dyn Output,
+    ) -> HelperResult {
+        let params = h.params();
+        if params.len() != 2 {
+            return Err(RenderError::new("{{man}} must have two arguments"));
+        }
+        let name = params[0]
+            .value()
+            .as_str()
+            .ok_or_else(|| RenderError::new("man link name must be a string"))?;
+        let section = params[1]
+            .value()
+            .as_u64()
+            .ok_or_else(|| RenderError::new("man link section must be an integer"))?;
+        let section =
+            u8::try_from(section).map_err(|_e| RenderError::new("section number too large"))?;
+        let link = self
+            .formatter
+            .linkify_man_to_md(name, section)
+            .map_err(|e| RenderError::new(format!("failed to linkify man: {}", e)))?;
+        out.write(&link)?;
+        Ok(())
+    }
+}
+
+/// `{{*set var=value}}` decorator.
+///
+/// This sets a variable to a value within the template context.
+fn set_decorator(
+    d: &Decorator,
+    _: &Handlebars,
+    _ctx: &Context,
+    rc: &mut RenderContext,
+) -> Result<(), RenderError> {
+    let data_to_set = d.hash();
+    for (k, v) in data_to_set {
+        set_in_context(rc, k, v.value().clone());
+    }
+    Ok(())
+}
+
+/// Sets a variable to a value within the context.
+fn set_in_context(rc: &mut RenderContext, key: &str, value: serde_json::Value) {
+    let mut ctx = match rc.context() {
+        Some(c) => (*c).clone(),
+        None => Context::wraps(serde_json::Value::Object(serde_json::Map::new())).unwrap(),
+    };
+    if let serde_json::Value::Object(m) = ctx.data_mut() {
+        m.insert(key.to_string(), value);
+        rc.set_context(ctx);
+    } else {
+        panic!("expected object in context");
+    }
+}
+
+/// Removes a variable from the context.
+fn remove_from_context(rc: &mut RenderContext, key: &str) {
+    let ctx = rc.context().expect("cannot remove from null context");
+    let mut ctx = (*ctx).clone();
+    if let serde_json::Value::Object(m) = ctx.data_mut() {
+        m.remove(key);
+        rc.set_context(ctx);
+    } else {
+        panic!("expected object in context");
+    }
+}
+
+handlebars_helper!(lower: |s: str| s.to_lowercase());