#
mdman/
hbs.rs

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    //! Handlebars template processing.

    use std::collections::HashMap;
    use std::path::Path;

    use anyhow::Error;
    use handlebars::{
        handlebars_helper, Context, Decorator, DirectorySourceOptions, Handlebars, Helper, HelperDef,
        HelperResult, Output, RenderContext, RenderError, RenderErrorReason, Renderable,
    };

    use crate::format::Formatter;

    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");
        let mut options = DirectorySourceOptions::default();
        options.tpl_extension = ".md".to_string();
        handlebars.register_templates_directory(includes, options)?;
        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<'rc>,
            r: &'reg Handlebars<'reg>,
            ctx: &'rc Context,
            rc: &mut RenderContext<'reg, 'rc>,
            out: &mut dyn Output,
        ) -> HelperResult {
            if in_options(rc) {
                return Err(
                    RenderErrorReason::Other("options blocks cannot be nested".to_string()).into(),
                );
            }
            // 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(RenderErrorReason::Other(
                        "options block must not be empty".to_string(),
                    )
                    .into());
                }
            };
            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<'rc>,
            r: &'reg Handlebars<'reg>,
            gctx: &'rc Context,
            rc: &mut RenderContext<'reg, 'rc>,
            out: &mut dyn Output,
        ) -> HelperResult {
            if !in_options(rc) {
                return Err(
                    RenderErrorReason::Other("option must be in options block".to_string()).into(),
                );
            }
            let params = h.params();
            if params.is_empty() {
                return Err(RenderErrorReason::Other(
                    "option block must have at least one param".to_string(),
                )
                .into());
            }
            // Convert params to strings.
            let params = params
                .iter()
                .map(|param| {
                    param
                        .value()
                        .as_str()
                        .ok_or_else(|| {
                            RenderErrorReason::Other("option params must be strings".to_string())
                        })
                        .into()
                })
                .collect::<Result<Vec<&str>, RenderErrorReason>>()?;
            let t = match h.template() {
                Some(t) => t,
                None => {
                    return Err(
                        RenderErrorReason::Other("option block must not be empty".to_string()).into(),
                    );
                }
            };
            // Render the block.
            let block = t.renders(r, gctx, rc)?;

            // Windows newlines can break some rendering, so normalize.
            let block = block.replace("\r\n", "\n");

            // Get the name of this page.
            let man_name = gctx
                .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| RenderErrorReason::Other(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<'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(
                    RenderErrorReason::Other("{{man}} must have two arguments".to_string()).into(),
                );
            }
            let name = params[0].value().as_str().ok_or_else(|| {
                RenderErrorReason::Other("man link name must be a string".to_string())
            })?;
            let section = params[1].value().as_u64().ok_or_else(|| {
                RenderErrorReason::Other("man link section must be an integer".to_string())
            })?;
            let section = u8::try_from(section)
                .map_err(|_e| RenderErrorReason::Other("section number too large".to_string()))?;
            let link = self
                .formatter
                .linkify_man_to_md(name, section)
                .map_err(|e| RenderErrorReason::Other(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 gctx = 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) = gctx.data_mut() {
            m.insert(key.to_string(), value);
            rc.set_context(gctx);
        } else {
            panic!("expected object in context");
        }
    }

    /// Removes a variable from the context.
    fn remove_from_context(rc: &mut RenderContext<'_, '_>, key: &str) {
        let gctx = rc.context().expect("cannot remove from null context");
        let mut gctx = (*gctx).clone();
        if let serde_json::Value::Object(m) = gctx.data_mut() {
            m.remove(key);
            rc.set_context(gctx);
        } else {
            panic!("expected object in context");
        }
    }

    handlebars_helper!(lower: |s: str| s.to_lowercase());