Allow a user template override

Cargo.toml

@@ -55,3 +55,4 @@ brotli = "6.0.0"
 lazy_static = "1.4.0"
 zeno = "0.3.1"
 homedir = "0.3.3"
+walkdir = "2.5.0"

src/bin/diffenator3.rs

@@ -58,6 +58,10 @@ struct Cli {
     #[clap(long = "output", default_value = "out", requires = "html")]
     output: String,
 
+    /// Directory for custom templates
+    #[clap(long = "templates", requires = "html")]
+    templates: Option<String>,
+
     /// Location in design space, in the form axis=123,other=456
     #[clap(long = "location")]
     location: Option<String>,
@@ -261,6 +265,7 @@ fn do_html(cli: &Cli, font_a: &DFont, font_b: &DFont, diff: Map<String, serde_js
         font_face_new,
         font_style_old,
         font_style_new,
+        cli.templates.as_ref(),
     )
     .unwrap_or_else(|err| die("rendering HTML", err));
 

src/html.rs

@@ -1,12 +1,11 @@
+use serde::Serialize;
+use serde_json::json;
 use std::{
     collections::HashMap,
     path::{Path, PathBuf},
 };
-
-use lazy_static::lazy_static;
-use serde::Serialize;
-use serde_json::json;
 use tera::{Context, Tera};
+use walkdir::WalkDir;
 
 use crate::dfont::DFont;
 
@@ -96,14 +95,12 @@ impl CSSFontStyle {
     }
 }
 
-lazy_static! {
-    pub static ref TEMPLATES: Tera = {
-        let homedir = create_user_home_templates_directory();
-        Tera::new(&format!("{}/*", homedir.to_str().unwrap())).unwrap_or_else(|e| {
-            println!("Problem parsing templates: {:?}", e);
-            std::process::exit(1)
-        })
-    };
+fn template_engine() -> Tera {
+    let homedir = create_user_home_templates_directory();
+    Tera::new(&format!("{}/*", homedir.to_str().unwrap())).unwrap_or_else(|e| {
+        println!("Problem parsing templates: {:?}", e);
+        std::process::exit(1)
+    })
 }
 
 pub fn create_user_home_templates_directory() -> PathBuf {
@@ -163,8 +160,29 @@ pub fn render_output(
     font_face_new: CSSFontFace,
     font_style_old: CSSFontStyle,
     font_style_new: CSSFontStyle,
+    user_templates: Option<&String>,
 ) -> Result<String, tera::Error> {
-    TEMPLATES.render(
+    let mut tera = template_engine();
+    if let Some(template_dir) = user_templates {
+        for entry in WalkDir::new(template_dir) {
+            if entry.as_ref().is_ok_and(|e| e.file_type().is_dir()) {
+                continue;
+            }
+            let path = entry.as_ref().unwrap().path();
+            if let Err(e) =
+                tera.add_template_file(path, path.strip_prefix(template_dir).unwrap().to_str())
+            {
+                println!("Problem adding template file: {:?}", e);
+                std::process::exit(1)
+            }
+        }
+        if let Err(e) = tera.build_inheritance_chains() {
+            println!("Problem building inheritance chains: {:?}", e);
+            std::process::exit(1)
+        }
+    }
+
+    tera.render(
         "diffenator.html",
         &Context::from_serialize(json!({
             "diff": {