Add ability to specify a QR code version hint. (#637)

* Add ability to specify a QR code version hint.

* Checkstyle.

core/src/main/java/com/google/zxing/EncodeHintType.java

@@ -95,4 +95,10 @@ public enum EncodeHintType {
    * (Type {@link Integer}, or {@link String} representation of the integer value).
    */
    AZTEC_LAYERS,
+   
+   /**
+    * Specifies the exact version of QR code to be encoded. An integer. If the data specified
+    * cannot fit within the required version, a WriterException will be thrown.
+    */
+   QR_VERSION
 }

core/src/main/java/com/google/zxing/qrcode/encoder/Encoder.java

@@ -106,21 +106,18 @@ public final class Encoder {
     BitArray dataBits = new BitArray();
     appendBytes(content, mode, dataBits, encoding);
 
-    // Hard part: need to know version to know how many bits length takes. But need to know how many
-    // bits it takes to know version. First we take a guess at version by assuming version will be
-    // the minimum, 1:
-
-    int provisionalBitsNeeded = headerBits.getSize()
-        + mode.getCharacterCountBits(Version.getVersionForNumber(1))
-        + dataBits.getSize();
-    Version provisionalVersion = chooseVersion(provisionalBitsNeeded, ecLevel);
-
-    // Use that guess to calculate the right version. I am still not sure this works in 100% of cases.
-
-    int bitsNeeded = headerBits.getSize()
-        + mode.getCharacterCountBits(provisionalVersion)
-        + dataBits.getSize();
-    Version version = chooseVersion(bitsNeeded, ecLevel);
+    Version version = null;
+    if (hints != null && hints.containsKey(EncodeHintType.QR_VERSION)) {
+      Version requestedVersion = Version.getVersionForNumber((Integer) hints.get(EncodeHintType.QR_VERSION));
+      int bitsNeeded = calculateBitsNeeded(mode, headerBits, dataBits, requestedVersion);
+      if (willFit(bitsNeeded, requestedVersion, ecLevel)) {
+        version = requestedVersion;
+      } else {
+        throw new WriterException("Data too big for requested version");
+      }
+    } else {
+      version = recommendVersion(ecLevel, mode, headerBits, dataBits);
+    }
 
     BitArray headerAndDataBits = new BitArray();
     headerAndDataBits.appendBitArray(headerBits);
@@ -161,6 +158,36 @@ public final class Encoder {
     return qrCode;
   }
 
+  /**
+   * Decides the smallest version of QR code that will contain all of the provided data.
+   * @throws WriterException if the data cannot fit in any version
+   */
+  private static Version recommendVersion(ErrorCorrectionLevel ecLevel,
+                                          Mode mode,
+                                          BitArray headerBits,
+                                          BitArray dataBits) throws WriterException {
+    // Hard part: need to know version to know how many bits length takes. But need to know how many
+    // bits it takes to know version. First we take a guess at version by assuming version will be
+    // the minimum, 1:
+    int provisionalBitsNeeded = calculateBitsNeeded(mode, headerBits, dataBits, Version.getVersionForNumber(1));
+    Version provisionalVersion = chooseVersion(provisionalBitsNeeded, ecLevel);
+
+    // Use that guess to calculate the right version. I am still not sure this works in 100% of cases.
+    int bitsNeeded = calculateBitsNeeded(mode, headerBits, dataBits, provisionalVersion);
+    Version version = chooseVersion(bitsNeeded, ecLevel);
+    return version;
+  }
+
+  private static int calculateBitsNeeded(Mode mode,
+                                         BitArray headerBits,
+                                         BitArray dataBits,
+                                         Version version) {
+    int bitsNeeded = headerBits.getSize()
+                     + mode.getCharacterCountBits(version)
+                     + dataBits.getSize();
+    return bitsNeeded;
+  }
+
   /**
    * @return the code point of the table used in alphanumeric mode or
    *  -1 if there is no corresponding code in the table.
@@ -246,9 +273,21 @@ public final class Encoder {
   }
 
   private static Version chooseVersion(int numInputBits, ErrorCorrectionLevel ecLevel) throws WriterException {
-    // In the following comments, we use numbers of Version 7-H.
     for (int versionNum = 1; versionNum <= 40; versionNum++) {
       Version version = Version.getVersionForNumber(versionNum);
+      if (willFit(numInputBits, version, ecLevel)) {
+        return version;
+      }
+    }
+    throw new WriterException("Data too big");
+  }
+  
+  /**
+   * @return true if the number of input bits will fit in a code with the specified version and
+   * error correction level.
+   */
+  private static boolean willFit(int numInputBits, Version version, ErrorCorrectionLevel ecLevel) {
+      // In the following comments, we use numbers of Version 7-H.
       // numBytes = 196
       int numBytes = version.getTotalCodewords();
       // getNumECBytes = 130
@@ -257,11 +296,7 @@ public final class Encoder {
       // getNumDataBytes = 196 - 130 = 66
       int numDataBytes = numBytes - numEcBytes;
       int totalInputBytes = (numInputBits + 7) / 8;
-      if (numDataBytes >= totalInputBytes) {
-        return version;
-      }
-    }
-    throw new WriterException("Data too big");
+      return numDataBytes >= totalInputBytes;
   }
 
   /**

core/src/test/java/com/google/zxing/qrcode/encoder/EncoderTestCase.java

@@ -22,11 +22,13 @@ import com.google.zxing.common.BitArray;
 import com.google.zxing.qrcode.decoder.ErrorCorrectionLevel;
 import com.google.zxing.qrcode.decoder.Mode;
 import com.google.zxing.qrcode.decoder.Version;
+
 import org.junit.Assert;
 import org.junit.Test;
 
 import java.io.UnsupportedEncodingException;
 import java.util.EnumMap;
+import java.util.HashMap;
 import java.util.Map;
 
 /**
@@ -127,6 +129,26 @@ public final class EncoderTestCase extends Assert {
     assertEquals(expected, qrCode.toString());
   }
   
+  @Test
+  public void testEncodeWithVersion() throws WriterException {
+	  Map<EncodeHintType, Object> hints = new HashMap<>();
+	  hints.put(EncodeHintType.QR_VERSION, 7);
+	  QRCode qrCode = Encoder.encode("ABCDEF", ErrorCorrectionLevel.H, hints);
+	  assertTrue(qrCode.toString().contains(" version: 7\n"));
+  }
+  
+  @Test
+  public void testEncodeWithVersionTooSmall() throws WriterException {
+	  Map<EncodeHintType, Object> hints = new HashMap<>();
+	  hints.put(EncodeHintType.QR_VERSION, 3);
+	  try {
+		  Encoder.encode("THISMESSAGEISTOOLONGFORAQRCODEVERSION3", ErrorCorrectionLevel.H, hints);
+		  fail();
+	  } catch (WriterException e) {
+		  assertEquals("Data too big for requested version", e.getMessage());
+	  }
+  }
+
   @Test
   public void testSimpleUTF8ECI() throws WriterException {
     Map<EncodeHintType,Object> hints = new EnumMap<>(EncodeHintType.class);