feat: added file loader

src/error.rs

@@ -6,6 +6,9 @@ pub enum EnvError {
 
     /// An environment variable was expected, but it was not found.
     MissingVar(String),
+
+    /// A file was expected to be found, but it was not found or could not be read.
+    FileError { path: String, message: String }
 }
 
 impl EnvError {
@@ -28,4 +31,12 @@ impl EnvError {
     where T: Into<String> {
         Self::MissingVar(key.into())
     }
+
+    /// Creates a new `EnvError::FileMissing` with the given path and message.
+    pub fn file_error<P: Into<String>, M: Into<String>>(path: P, message: M) -> Self {
+        Self::FileError {
+            path: path.into(),
+            message: message.into()
+        }
+    }
 }

src/lib.rs

@@ -49,6 +49,35 @@ impl FromEnv for String {
 pub struct EnvLoader;
 
 impl EnvLoader {
+    /// Creates a new `EnvLoader`.
+    pub fn new() -> Self {
+        Self
+    }
+
+    /// Loads environment variables from a file. The file should have one variable per line, in the format `KEY=VALUE`. Lines starting with `#` are treated as comments and ignored.
+    pub fn load_file(&self, path: &str) -> Result<(), EnvError> {
+        // Load the file
+        let contents = std::fs::read_to_string(path).map_err(|e| EnvError::file_error(path, e.to_string()))?;
+
+        // Parse the file
+        for line in contents.lines() {
+            let line = line.trim();
+            if line.is_empty() || line.starts_with("#") { continue }
+            let parts: Vec<&str> = line.splitn(2, '=').collect();
+            if parts.len() != 2 {
+                return Err(EnvError::file_error(path, format!("Invalid line: {}", line)));
+            }
+
+            // Trim the key and value
+            let key = parts[0].trim();
+            let value = parts[1].trim();
+
+            // Set the environment variable
+            unsafe { std::env::set_var(key, value) }
+        }
+        Ok(())
+    }
+
     /// Creates a new `EnvLoader` with the given prefix.
     pub fn with_prefix<P: Into<String>>(&self, prefix: P) -> PrefixedEnvLoader {
         PrefixedEnvLoader {