feat(android): implement vector-based PDF header/footer rendering

Replace bitmap canvas rendering with PrintDocumentAdapter for vector quality.
Use PDFBox LayerUtility to merge header/footer PDFs while preserving vector graphics.
Add support for all page sizes with auto-adjusting pagination positioning.
Require explicit headerHeight/footerHeight values (removed auto-calculation).

Author: dhruvpatel374

android/src/main/java/android/print/PdfConverter.kt

@@ -178,29 +178,42 @@ class PdfConverter private constructor() : Runnable {
         if (htmlString == null) throw Exception("htmlString can't be null")
         if (file == null) throw Exception("file can't be null")
 
-        if (mIsCurrentlyConverting) {
-            Log.w(TAG, "PDF conversion already in progress, ignoring new request")
-            callback?.onFailure("Another PDF conversion is currently in progress")
-            return
-        }
+        synchronized(this) {
+            if (mIsCurrentlyConverting) {
+                Log.w(TAG, "PDF conversion already in progress, waiting...")
+                Thread {
+                    var waited = 0
+                    while (mIsCurrentlyConverting && waited < 30000) {
+                        Thread.sleep(100)
+                        waited += 100
+                    }
+                    if (mIsCurrentlyConverting) {
+                        callback?.onFailure("Previous conversion did not complete")
+                        return@Thread
+                    }
+                    convert(context, htmlString, file, shouldEncode, callback, baseURL)
+                }.start()
+                return
+            }
 
-        Log.d(TAG, "Starting PDF conversion for file: ${file.absolutePath}")
+            Log.d(TAG, "Starting PDF conversion for file: ${file.absolutePath}")
 
-        try {
-            mContext = context
-            mHtmlString = htmlString
-            mPdfFile = file
-            mIsCurrentlyConverting = true
-            mCallback = callback
-            mBaseURL = baseURL
-            
-            setupTimeout()
-            runOnUiThread(this)
-        } catch (e: Exception) {
-            Log.e(TAG, "Error setting up PDF conversion", e)
-            mIsCurrentlyConverting = false
-            cancelTimeout()
-            callback?.onFailure("Failed to setup PDF conversion: ${e.message}")
+            try {
+                mContext = context
+                mHtmlString = htmlString
+                mPdfFile = file
+                mIsCurrentlyConverting = true
+                mCallback = callback
+                mBaseURL = baseURL
+                
+                setupTimeout()
+                runOnUiThread(this)
+            } catch (e: Exception) {
+                Log.e(TAG, "Error setting up PDF conversion", e)
+                mIsCurrentlyConverting = false
+                cancelTimeout()
+                callback?.onFailure("Failed to setup PDF conversion: ${e.message}")
+            }
         }
     }
 

android/src/main/java/android/print/PdfPrintHelper.java

@@ -0,0 +1,88 @@
+package android.print;
+
+import android.os.Bundle;
+import android.os.CancellationSignal;
+import android.os.ParcelFileDescriptor;
+import android.util.Log;
+import android.webkit.WebView;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+
+public class PdfPrintHelper {
+    private static final String TAG = "PdfPrintHelper";
+
+    public interface PrintCallback {
+        void onSuccess();
+        void onFailure(String error);
+    }
+
+    public static void printWebViewToPdf(WebView webView, File outputFile, PrintAttributes printAttrs, PrintCallback callback) {
+        try {
+            Log.d(TAG, "Starting printWebViewToPdf for: " + outputFile.getName());
+            PrintDocumentAdapter adapter = webView.createPrintDocumentAdapter("doc");
+            ParcelFileDescriptor[] pipe = ParcelFileDescriptor.createPipe();
+            ParcelFileDescriptor readFd = pipe[0];
+            ParcelFileDescriptor writeFd = pipe[1];
+
+            adapter.onLayout(null, printAttrs, null, new PrintDocumentAdapter.LayoutResultCallback() {
+                @Override
+                public void onLayoutFinished(PrintDocumentInfo info, boolean changed) {
+                    Log.d(TAG, "Layout finished, pages: " + info.getPageCount());
+                    adapter.onWrite(new PageRange[]{PageRange.ALL_PAGES}, writeFd, new CancellationSignal(),
+                            new PrintDocumentAdapter.WriteResultCallback() {
+                                @Override
+                                public void onWriteFinished(PageRange[] pages) {
+                                    try {
+                                        Log.d(TAG, "Write finished, reading data...");
+                                        writeFd.close();
+                                        FileInputStream input = new FileInputStream(readFd.getFileDescriptor());
+                                        FileOutputStream output = new FileOutputStream(outputFile);
+                                        byte[] buffer = new byte[8192];
+                                        int bytesRead;
+                                        int totalBytes = 0;
+                                        while ((bytesRead = input.read(buffer)) != -1) {
+                                            output.write(buffer, 0, bytesRead);
+                                            totalBytes += bytesRead;
+                                        }
+                                        output.flush();
+                                        output.close();
+                                        input.close();
+                                        readFd.close();
+                                        Log.d(TAG, "PDF written successfully: " + totalBytes + " bytes to " + outputFile.getName());
+                                        callback.onSuccess();
+                                    } catch (Exception e) {
+                                        Log.e(TAG, "Error writing PDF", e);
+                                        callback.onFailure(e.getMessage());
+                                    }
+                                }
+
+                                @Override
+                                public void onWriteFailed(CharSequence error) {
+                                    Log.e(TAG, "Write failed: " + error);
+                                    try {
+                                        writeFd.close();
+                                        readFd.close();
+                                    } catch (Exception ignored) {}
+                                    callback.onFailure(error != null ? error.toString() : "Write failed");
+                                }
+                            });
+                }
+
+                @Override
+                public void onLayoutFailed(CharSequence error) {
+                    Log.e(TAG, "Layout failed: " + error);
+                    try {
+                        writeFd.close();
+                        readFd.close();
+                    } catch (Exception ignored) {}
+                    callback.onFailure(error != null ? error.toString() : "Layout failed");
+                }
+            }, new Bundle());
+        } catch (Exception e) {
+            Log.e(TAG, "Error in printWebViewToPdf", e);
+            callback.onFailure(e.getMessage());
+        }
+    }
+}