[storage] Add FileIndex #59 (#60)

* Create file_index.rs

* Update storage.rs

* Update file_index.rs

* Update file_storage.rs

src/storage.rs

@@ -1 +1,2 @@
+mod file_index;
 mod file_storage;

src/storage/file_index.rs

@@ -0,0 +1,12 @@
+#[derive(Default)]
+pub(crate) struct FileIndex {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn file_index_can_be_default_constructed() {
+        let _index = FileIndex::default();
+    }
+}

src/storage/file_storage.rs

@@ -1,9 +1,11 @@
+use super::file_index::FileIndex;
 use std::fs::{File, OpenOptions};
 
 #[allow(dead_code)]
 pub(crate) struct FileStorage {
     filename: String,
     file: File,
+    index: FileIndex,
 }
 
 impl From<&str> for FileStorage {
@@ -14,14 +16,17 @@ impl From<&str> for FileStorage {
 
 impl From<String> for FileStorage {
     fn from(filename: String) -> Self {
+        let file = OpenOptions::new()
+            .write(true)
+            .create(true)
+            .read(true)
+            .open(&filename)
+            .unwrap();
+
         FileStorage {
-            file: OpenOptions::new()
-                .write(true)
-                .create(true)
-                .read(true)
-                .open(&filename)
-                .unwrap(),
             filename,
+            file,
+            index: FileIndex::default(),
         }
     }
 }