add OG usage

Author: kirjavascript

build.js

@@ -166,8 +166,9 @@ if (!fs.existsSync('clean.nes')) {
 } else {
     console.time('patch');
     const patcher = require('./tools/patch/create');
-    patcher('clean.nes', 'tetris.nes', 'tetris.bps');
+    const pct = patcher('clean.nes', 'tetris.nes', 'tetris.bps');
     console.timeEnd('patch');
+    console.log(`using ${pct}% of original file`);
 }
 
 // stats

tools/patch/bps.js

@@ -1,12 +1,26 @@
-const { MarcFile, createBPSFromFiles } = require('./bps.js');
+const { MarcFile, createBPSFromFiles, parseBPSFile } = require('./bps.js');
 const fs = require('fs');
 
+// https://github.com/blakesmith/rombp/blob/master/docs/bps_spec.md
+
 module.exports = function patch(original, modified, destination) {
     const patch = createBPSFromFiles(
         new MarcFile(original),
         new MarcFile(modified),
         true,
-    ).export('')._u8array;
+    ).export('');
+
+    fs.writeFileSync(destination, patch._u8array);
+
+    const bps = parseBPSFile(new MarcFile('tetris.bps'));
+
+    // count patch sizes
+    let source = 0;
+    bps.actions.forEach(action => {
+        if ([0, 2].includes(action.type)) {
+            source += action.length;
+        }
+    });
 
-    fs.writeFileSync(destination, patch);
+    return (source / bps.sourceSize) * 100 | 0;
 }