From 52e2cb785496f4a677f36650b27ee413069c69a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andi=20P=C3=A4tzold?= <github@andipaetzold.com>
Date: Sun, 19 Jul 2020 00:43:21 +0200
Subject: [PATCH] fix: implement usage maps type 1

---
 src/Table.ts     |  2 +-
 src/usage-map.ts | 42 +++++++++++++++++++++++++++++++++++-------
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/src/Table.ts b/src/Table.ts
index d395e34b..23773344 100644
--- a/src/Table.ts
+++ b/src/Table.ts
@@ -74,7 +74,7 @@ export default class Table {
         const usageMapBuffer = this.db.findPageRow(
             this.definitionBuffer.readUInt32LE(this.db.constants.tableDefinitionPage.usageMapOffset)
         );
-        this.dataPages = findMapPages(usageMapBuffer);
+        this.dataPages = findMapPages(usageMapBuffer, this.db);
     }
 
     /**
diff --git a/src/usage-map.ts b/src/usage-map.ts
index 108f72dc..aeb1cc1c 100644
--- a/src/usage-map.ts
+++ b/src/usage-map.ts
@@ -1,25 +1,57 @@
 import { getBitmapValue } from "./util";
+import Database from './Database';
+import PageType, { assertPageType } from './PageType';
 
 /**
  * @see https://github.com/brianb/mdbtools/blob/d6f5745d949f37db969d5f424e69b54f0da60b9b/HACKING#L556-L622
  */
-export function findMapPages(buffer: Buffer): number[] {
+export function findMapPages(buffer: Buffer, db: Database): number[] {
     switch (buffer[0]) {
         case 0x00:
             return findMapPages0(buffer);
         case 0x01:
-            return findMapPages1(buffer);
+            return findMapPages1(buffer, db);
         default:
             throw new Error("Unknown usage map type");
     }
 }
 
+/**
+ * @see https://github.com/brianb/mdbtools/blob/d6f5745d949f37db969d5f424e69b54f0da60b9b/src/libmdb/map.c#L25-L43
+ */
 function findMapPages0(buffer: Buffer): number[] {
     const pageStart = buffer.readUInt32LE(1);
+    const bitmap = buffer.slice(5);
+    return getPagesFromBitmap(bitmap, pageStart);
+}
+
+/**
+ * @see https://github.com/brianb/mdbtools/blob/d6f5745d949f37db969d5f424e69b54f0da60b9b/src/libmdb/map.c#L44-L84
+ */
+function findMapPages1(buffer: Buffer, db: Database): number[] {
+    const bitmapLength = (db.constants.pageSize - 4) * 8;
+    const mapCount = Math.floor((buffer.length - 1) / 4);
 
+    const pages: number[] = [];
+    for (let mapIndex = 0; mapIndex < mapCount; ++mapIndex) {
+        const page = buffer.readUInt32LE(1 + (mapIndex * 4));
+        if (page === 0) {
+            continue;
+        }
+
+        const pageBuffer = db.getPage(page);
+        assertPageType(pageBuffer, PageType.PageUsageBitmaps);
+
+        const bitmap = pageBuffer.slice(4);
+        pages.push(...getPagesFromBitmap(bitmap, mapIndex * bitmapLength));
+    }
+
+    return pages;
+}
+
+function getPagesFromBitmap(bitmap: Buffer, pageStart: number): number[] {
     const pages: number[] = [];
 
-    const bitmap = buffer.slice(5);
     for (let i = 0; i < bitmap.length * 8; i++) {
         if (getBitmapValue(bitmap, i)) {
             pages.push(pageStart + i);
@@ -28,7 +60,3 @@ function findMapPages0(buffer: Buffer): number[] {
 
     return pages;
 }
-
-function findMapPages1(_buffer: Buffer): number[] {
-    throw new Error("Not implemented yet");
-}