C40Encoder.java

/*
 * Copyright 2006-2007 Jeremias Maerki.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.zxing.datamatrix.encoder;

class C40Encoder implements Encoder {

	@Override
	public int getEncodingMode() {
		return HighLevelEncoder.C40_ENCODATION;
	}

	@Override
	public void encode(EncoderContext context) {
		// step C
		StringBuilder buffer = new StringBuilder();
		while (context.hasMoreCharacters()) {
			char c = context.getCurrentChar();
			context.pos++;

			int lastCharSize = encodeChar(c, buffer);

			int unwritten = (buffer.length() / 3) * 2;

			int curCodewordCount = context.getCodewordCount() + unwritten;
			context.updateSymbolInfo(curCodewordCount);
			int available = context.getSymbolInfo().getDataCapacity()
					- curCodewordCount;

			if (!context.hasMoreCharacters()) {
				// Avoid having a single C40 value in the last triplet
				StringBuilder removed = new StringBuilder();
				if ((buffer.length() % 3) == 2) {
					if (available < 2 || available > 2) {
						lastCharSize = backtrackOneCharacter(context, buffer,
								removed, lastCharSize);
					}
				}
				while ((buffer.length() % 3) == 1
						&& ((lastCharSize <= 3 && available != 1) || lastCharSize > 3)) {
					lastCharSize = backtrackOneCharacter(context, buffer,
							removed, lastCharSize);
				}
				break;
			}

			int count = buffer.length();
			if ((count % 3) == 0) {
				int newMode = HighLevelEncoder.lookAheadTest(
						context.getMessage(), context.pos, getEncodingMode());
				if (newMode != getEncodingMode()) {
					context.signalEncoderChange(newMode);
					break;
				}
			}
		}
		handleEOD(context, buffer);
	}

	private int backtrackOneCharacter(EncoderContext context,
			StringBuilder buffer, StringBuilder removed, int lastCharSize) {
		int count = buffer.length();
		buffer.delete(count - lastCharSize, count);
		context.pos--;
		char c = context.getCurrentChar();
		lastCharSize = encodeChar(c, removed);
		context.resetSymbolInfo(); // Deal with possible reduction in symbol
									// size
		return lastCharSize;
	}

	static void writeNextTriplet(EncoderContext context, StringBuilder buffer) {
		context.writeCodewords(encodeToCodewords(buffer, 0));
		buffer.delete(0, 3);
	}

	/**
	 * Handle "end of data" situations
	 * 
	 * @param context
	 *            the encoder context
	 * @param buffer
	 *            the buffer with the remaining encoded characters
	 */
	void handleEOD(EncoderContext context, StringBuilder buffer) {
		int unwritten = (buffer.length() / 3) * 2;
		int rest = buffer.length() % 3;

		int curCodewordCount = context.getCodewordCount() + unwritten;
		context.updateSymbolInfo(curCodewordCount);
		int available = context.getSymbolInfo().getDataCapacity()
				- curCodewordCount;

		if (rest == 2) {
			buffer.append('\0'); // Shift 1
			while (buffer.length() >= 3) {
				writeNextTriplet(context, buffer);
			}
			if (context.hasMoreCharacters()) {
				context.writeCodeword(HighLevelEncoder.C40_UNLATCH);
			}
		} else if (available == 1 && rest == 1) {
			while (buffer.length() >= 3) {
				writeNextTriplet(context, buffer);
			}
			if (context.hasMoreCharacters()) {
				context.writeCodeword(HighLevelEncoder.C40_UNLATCH);
			}
			// else no unlatch
			context.pos--;
		} else if (rest == 0) {
			while (buffer.length() >= 3) {
				writeNextTriplet(context, buffer);
			}
			if (available > 0 || context.hasMoreCharacters()) {
				context.writeCodeword(HighLevelEncoder.C40_UNLATCH);
			}
		} else {
			throw new IllegalStateException("Unexpected case. Please report!");
		}
		context.signalEncoderChange(HighLevelEncoder.ASCII_ENCODATION);
	}

	int encodeChar(char c, StringBuilder sb) {
		if (c == ' ') {
			sb.append('\3');
			return 1;
		} else if (c >= '0' && c <= '9') {
			sb.append((char) (c - 48 + 4));
			return 1;
		} else if (c >= 'A' && c <= 'Z') {
			sb.append((char) (c - 65 + 14));
			return 1;
		} else if (c >= '\0' && c <= '\u001f') {
			sb.append('\0'); // Shift 1 Set
			sb.append(c);
			return 2;
		} else if (c >= '!' && c <= '/') {
			sb.append('\1'); // Shift 2 Set
			sb.append((char) (c - 33));
			return 2;
		} else if (c >= ':' && c <= '@') {
			sb.append('\1'); // Shift 2 Set
			sb.append((char) (c - 58 + 15));
			return 2;
		} else if (c >= '[' && c <= '_') {
			sb.append('\1'); // Shift 2 Set
			sb.append((char) (c - 91 + 22));
			return 2;
		} else if (c >= '\u0060' && c <= '\u007f') {
			sb.append('\2'); // Shift 3 Set
			sb.append((char) (c - 96));
			return 2;
		} else if (c >= '\u0080') {
			sb.append("\1\u001e"); // Shift 2, Upper Shift
			int len = 2;
			len += encodeChar((char) (c - 128), sb);
			return len;
		} else {
			throw new IllegalArgumentException("Illegal character: " + c);
		}
	}

	private static String encodeToCodewords(CharSequence sb, int startPos) {
		char c1 = sb.charAt(startPos);
		char c2 = sb.charAt(startPos + 1);
		char c3 = sb.charAt(startPos + 2);
		int v = (1600 * c1) + (40 * c2) + c3 + 1;
		char cw1 = (char) (v / 256);
		char cw2 = (char) (v % 256);
		return new String(new char[] { cw1, cw2 });
	}

}