[feat] add models_dir_path helper and implement dynamic models directory resolution

src/models.rs

@@ -340,8 +340,17 @@ fn compute_file_sha256_hex(path: &Path) -> Result<String> {
     Ok(to_hex_lower(&hasher.finalize()))
 }
 
+fn models_dir_path() -> std::path::PathBuf {
+    if let Ok(p) = env::var("POLYSCRIBE_MODELS_DIR") {
+        let pb = std::path::PathBuf::from(p);
+        if !pb.as_os_str().is_empty() { return pb; }
+    }
+    std::path::PathBuf::from("models")
+}
+
 pub fn run_interactive_model_downloader() -> Result<()> {
-    let models_dir = Path::new("models");
+    let models_dir_buf = models_dir_path();
+    let models_dir = models_dir_buf.as_path();
     if !models_dir.exists() { create_dir_all(models_dir).context("Failed to create models directory")?; }
     let client = Client::builder()
         .user_agent("PolyScribe/0.1 (+https://github.com/)")
@@ -504,7 +513,8 @@ pub fn download_one_model(client: &Client, models_dir: &Path, entry: &ModelEntry
 }
 
 pub fn update_local_models() -> Result<()> {
-    let models_dir = Path::new("models");
+    let models_dir_buf = models_dir_path();
+    let models_dir = models_dir_buf.as_path();
     if !models_dir.exists() {
         create_dir_all(models_dir).context("Failed to create models directory")?;
     }
@@ -591,3 +601,69 @@ pub fn update_local_models() -> Result<()> {
 
     Ok(())
 }
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+    use std::fs;
+    use std::io::Write;
+
+    fn sha256_hex(data: &[u8]) -> String {
+        use sha2::{Digest, Sha256};
+        let mut hasher = Sha256::new();
+        hasher.update(data);
+        let out = hasher.finalize();
+        let mut s = String::new();
+        for b in out { s.push_str(&format!("{:02x}", b)); }
+        s
+    }
+
+    #[test]
+    fn test_update_local_models_offline_copy_and_manifest() {
+        let tmp_models = tempdir().unwrap();
+        let tmp_base = tempdir().unwrap();
+        let tmp_manifest = tempdir().unwrap();
+
+        // Prepare source model file content and hash
+        let model_name = "tiny.en-q5_1";
+        let src_path = tmp_base.path().join(format!("ggml-{}.bin", model_name));
+        let new_content = b"new model content";
+        fs::write(&src_path, new_content).unwrap();
+        let expected_sha = sha256_hex(new_content);
+        let expected_size = new_content.len() as u64;
+
+        // Write a wrong existing local file to trigger update
+        let local_path = tmp_models.path().join(format!("ggml-{}.bin", model_name));
+        fs::write(&local_path, b"old content").unwrap();
+
+        // Write manifest JSON
+        let manifest_path = tmp_manifest.path().join("manifest.json");
+        let manifest = serde_json::json!([
+            {
+                "name": model_name,
+                "base": "tiny",
+                "subtype": "en-q5_1",
+                "size": expected_size,
+                "sha256": expected_sha,
+                "repo": "ggerganov/whisper.cpp"
+            }
+        ]);
+        fs::write(&manifest_path, serde_json::to_string_pretty(&manifest).unwrap()).unwrap();
+
+        // Set env vars to force offline behavior and directories
+        unsafe {
+            std::env::set_var("POLYSCRIBE_MODELS_MANIFEST", &manifest_path);
+            std::env::set_var("POLYSCRIBE_MODELS_BASE_COPY_DIR", tmp_base.path());
+            std::env::set_var("POLYSCRIBE_MODELS_DIR", tmp_models.path());
+        }
+
+        // Run update
+        update_local_models().unwrap();
+
+        // Verify local file equals source content
+        let got = fs::read(&local_path).unwrap();
+        assert_eq!(got, new_content);
+    }
+}