1 files changed, 109 insertions, 0 deletions

diff --git a/crates/teraron/src/lib.rs b/crates/teraron/src/lib.rs
new file mode 100644
index 000000000..e464ea080
--- /dev/null
+++ b/crates/teraron/src/lib.rs
@@ -0,0 +1,109 @@
+//! A simple tool to generate rust code by passing a ron value
+//! to a tera template
+
+#[macro_use]
+extern crate failure;
+extern crate tera;
+extern crate ron;
+extern crate heck;
+
+use std::{
+    fs,
+    collections::HashMap,
+    path::Path,
+};
+
+use heck::{CamelCase, ShoutySnakeCase, SnakeCase};
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum Mode {
+    Overwrite,
+    Verify,
+}
+
+pub use Mode::*;
+
+/// A helper to update file on disk if it has changed.
+/// With verify = false,
+pub fn update(path: &Path, contents: &str, mode: Mode) -> Result<(), failure::Error> {
+    match fs::read_to_string(path) {
+        Ok(ref old_contents) if old_contents == contents => {
+            return Ok(());
+        }
+        _ => (),
+    }
+    if mode == Verify {
+        bail!("`{}` is not up-to-date", path.display());
+    }
+    eprintln!("updating {}", path.display());
+    fs::write(path, contents)?;
+    Ok(())
+}
+
+pub fn generate(
+    template: &Path,
+    src: &Path,
+    mode: Mode,
+) -> Result<(), failure::Error> {
+    assert_eq!(
+        template.extension().and_then(|it| it.to_str()), Some("tera"),
+        "template file must have .rs.tera extension",
+    );
+    let file_name = template.file_stem().unwrap().to_str().unwrap();
+    assert!(
+        file_name.ends_with(".rs"),
+        "template file must have .rs.tera extension",
+    );
+    let tgt = template.with_file_name(file_name);
+    let template = fs::read_to_string(template)?;
+    let src: ron::Value = {
+        let text = fs::read_to_string(src)?;
+        ron::de::from_str(&text)?
+    };
+    let content = render(&template, src)?;
+    update(
+        &tgt,
+        &content,
+        mode,
+    )
+}
+
+pub fn render(
+    template: &str,
+    src: ron::Value,
+) -> Result<String, failure::Error> {
+    let mut tera = mk_tera();
+    tera.add_raw_template("_src", template)
+        .map_err(|e| format_err!("template parsing error: {:?}", e))?;
+    let res = tera.render("_src", &src)
+        .map_err(|e| format_err!("template rendering error: {:?}", e))?;
+    return Ok(res);
+}
+
+fn mk_tera() -> tera::Tera {
+    let mut res = tera::Tera::default();
+    res.register_filter("camel", |arg, _| {
+        Ok(arg.as_str().unwrap().to_camel_case().into())
+    });
+    res.register_filter("snake", |arg, _| {
+        Ok(arg.as_str().unwrap().to_snake_case().into())
+    });
+    res.register_filter("SCREAM", |arg, _| {
+        Ok(arg.as_str().unwrap().to_shouty_snake_case().into())
+    });
+    res.register_function("concat", Box::new(concat));
+    res
+}
+
+fn concat(args: HashMap<String, tera::Value>) -> tera::Result<tera::Value> {
+    let mut elements = Vec::new();
+    for &key in ["a", "b", "c"].iter() {
+        let val = match args.get(key) {
+            Some(val) => val,
+            None => continue,
+        };
+        let val = val.as_array().unwrap();
+        elements.extend(val.iter().cloned());
+    }
+    Ok(tera::Value::Array(elements))
+}