Add Chunk utilities

src/org/kiwix/kiwixmobile/downloader/Chunk.java

@@ -0,0 +1,32 @@
+package org.kiwix.kiwixmobile.downloader;
+
+public class Chunk {
+
+  private String rangeHeader;
+  private String fileName;
+  private String url;
+  private long contentLength;
+
+  public Chunk(String rangeHeader, String fileName, String url, long contentLength) {
+    this.rangeHeader = rangeHeader;
+    this.fileName = fileName;
+    this.url = url;
+    this.contentLength = contentLength;
+  }
+
+  public String getRangeHeader() {
+    return rangeHeader;
+  }
+
+  public String getFileName() {
+    return fileName;
+  }
+
+  public long getContentLength() {
+    return contentLength;
+  }
+
+  public String getUrl() {
+    return url;
+  }
+}

src/org/kiwix/kiwixmobile/downloader/ChunkUtils.java

@@ -0,0 +1,59 @@
+package org.kiwix.kiwixmobile.downloader;
+
+import java.util.ArrayList;
+import java.util.List;
+import org.kiwix.kiwixmobile.utils.StorageUtils;
+
+public class ChunkUtils {
+
+  public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";
+  public static final String ZIM_EXTENSION = ".zim";
+  public static final long CHUNK_SIZE = 1024L * 1024L * 1024L * 2L;
+
+  public static List<Chunk> getChunks(String url, long contentLength) {
+    int fileCount = getZimChunkFileCount(contentLength);
+    String filename = StorageUtils.getFileNameFromUrl(url);
+    String[] fileNames = getZimChunkFileNames(filename, fileCount);
+    return generateChunks(contentLength, url, fileNames);
+  }
+
+  private static List<Chunk> generateChunks(long contentLength, String url, String[] fileNames) {
+    List<Chunk> chunks = new ArrayList<>();
+    long currentRange = 0;
+    for (String zim : fileNames) {
+      String range;
+      if (currentRange + CHUNK_SIZE >= contentLength) {
+        range = String.format("%d-", currentRange);
+      } else {
+        range = String.format("%d-%d", currentRange, currentRange + CHUNK_SIZE);
+      }
+      currentRange += CHUNK_SIZE + 1;
+      chunks.add(new Chunk(range, zim, url, contentLength));
+    }
+    return chunks;
+  }
+
+  private static int getZimChunkFileCount(long contentLength) {
+    int fits = (int) (contentLength / CHUNK_SIZE);
+    boolean hasRemainder = contentLength % CHUNK_SIZE > 0;
+    if (hasRemainder) return fits + 1;
+    return fits;
+  }
+
+  private static String[] getZimChunkFileNames(String fileName, int count) {
+    if (count == 1) {
+      return new String[] { fileName };
+    }
+    int position = fileName.lastIndexOf(".");
+    String baseName = position > 0 ? fileName.substring(0, position) : fileName;
+    String[] fileNames = new String[count];
+
+    for (int i = 0; i < count; i++) {
+      char first = ALPHABET.charAt(i / 26);
+      char second = ALPHABET.charAt(i % 26);
+      String chunkExtension = String.valueOf(first) + second;
+      fileNames[i] = baseName + ZIM_EXTENSION + chunkExtension;
+    }
+    return fileNames;
+  }
+}