Recreate bridgedb from file.

src/bin/bridgedb.rs

@@ -1,14 +1,25 @@
 use lox::BridgeDb;
 use std::fs::File;
 use std::io::Write;
+use std::path::Path;
 
 fn main() {
-    // create new bridgedb (implicitly generates keys)
-    let bridgedb = BridgeDb::new();
+    let bridgedb_outfile_name = "bridgedb.json";
+
+    // If bridgedb has already been created, recreate it from file.
+    // Otherwise, create new bridgedb.
+    let bridgedb = if Path::new(bridgedb_outfile_name).exists() {
+        // read in file
+        let bridgedb_infile = File::open(bridgedb_outfile_name).unwrap();
+        serde_json::from_reader(bridgedb_infile).unwrap()
+    } else {
+        // create new bridgedb (implicitly generates keys)
+        BridgeDb::new()
+    };
 
     // output full serialized bridgedb
     let mut bridgedb_outfile =
-        File::create("bridgedb.json").expect("Failed to create bridgedb.json");
+        File::create(bridgedb_outfile_name).expect("Failed to create bridgedb.json");
     let bridgedb_outfile_json = serde_json::to_string(&bridgedb).unwrap();
     write!(bridgedb_outfile, "{}", bridgedb_outfile_json)
         .expect("Failed to write to bridgedb.json");