support build-time theme selection via build.rs

Cargo.toml

@@ -10,6 +10,10 @@ crate-type = ["cdylib", "rlib"]
 [features]
 default = ["console_error_panic_hook", "wee_alloc"]
 
+[build-dependencies]
+serde = "1.0"
+serde_json = "1.0"
+
 [dependencies]
 cfg-if = "0.1.2"
 chrono = "0.4"

build.rs

@@ -0,0 +1,19 @@
+extern crate serde_json;
+
+use std::io::prelude::*;
+
+fn main() {
+    println!("cargo:rerun-if-changed=config.json");
+    // Load theme name from config.json and output code to load the theme via include_dir!
+    let config: serde_json::Value = 
+        serde_json::from_str(&std::fs::read_to_string("./config.json").unwrap()).unwrap();
+    let theme_name = match config.get("theme") {
+        Some(name) => name,
+        None => panic!("Please define `theme` in `config.json`")
+    };
+    let theme_load_code = format!("const THEME_DIR: Dir = include_dir!(\"theme/{}\");", theme_name.as_str().unwrap());
+    let out_path = std::path::PathBuf::from(std::env::var("OUT_DIR").unwrap());
+    let mut out_file = std::fs::File::create(out_path.join("load_theme.rs")).unwrap();
+    out_file.write_all(theme_load_code.as_bytes()).unwrap();
+    out_file.sync_data().unwrap();
+}

src/render.rs

@@ -11,8 +11,9 @@ use serde::Serialize;
 use std::vec::Vec;
 use web_sys::*;
 
-// TODO: allow static configuration of which theme to use
-const THEME_DIR: Dir = include_dir!("theme/default");
+// Allows user-configurable theme at build-time
+// See build.rs
+include!(concat!(env!("OUT_DIR"), "/load_theme.rs"));
 
 pub fn build_routes(router: &mut Router) {
     router.add_route("/static/", &serve_static);