EdifactEncoder.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;

final class EdifactEncoder implements Encoder {

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

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

			int count = buffer.length();
			if (count >= 4) {
				context.writeCodewords(encodeToCodewords(buffer, 0));
				buffer.delete(0, 4);

				int newMode = HighLevelEncoder.lookAheadTest(
						context.getMessage(), context.pos, getEncodingMode());
				if (newMode != getEncodingMode()) {
					context.signalEncoderChange(HighLevelEncoder.ASCII_ENCODATION);
					break;
				}
			}
		}
		buffer.append((char) 31); // Unlatch
		handleEOD(context, buffer);
	}

	/**
	 * Handle "end of data" situations
	 * 
	 * @param context
	 *            the encoder context
	 * @param buffer
	 *            the buffer with the remaining encoded characters
	 */
	private static void handleEOD(EncoderContext context, CharSequence buffer) {
		try {
			int count = buffer.length();
			if (count == 0) {
				return; // Already finished
			}
			if (count == 1) {
				// Only an unlatch at the end
				context.updateSymbolInfo();
				int available = context.getSymbolInfo().getDataCapacity()
						- context.getCodewordCount();
				int remaining = context.getRemainingCharacters();
				if (remaining == 0 && available <= 2) {
					return; // No unlatch
				}
			}

			if (count > 4) {
				throw new IllegalStateException("Count must not exceed 4");
			}
			int restChars = count - 1;
			String encoded = encodeToCodewords(buffer, 0);
			boolean endOfSymbolReached = !context.hasMoreCharacters();
			boolean restInAscii = endOfSymbolReached && restChars <= 2;

			if (restChars <= 2) {
				context.updateSymbolInfo(context.getCodewordCount() + restChars);
				int available = context.getSymbolInfo().getDataCapacity()
						- context.getCodewordCount();
				if (available >= 3) {
					restInAscii = false;
					context.updateSymbolInfo(context.getCodewordCount()
							+ encoded.length());
					// available = context.symbolInfo.dataCapacity -
					// context.getCodewordCount();
				}
			}

			if (restInAscii) {
				context.resetSymbolInfo();
				context.pos -= restChars;
			} else {
				context.writeCodewords(encoded);
			}
		} finally {
			context.signalEncoderChange(HighLevelEncoder.ASCII_ENCODATION);
		}
	}

	private static void encodeChar(char c, StringBuilder sb) {
		if (c >= ' ' && c <= '?') {
			sb.append(c);
		} else if (c >= '@' && c <= '^') {
			sb.append((char) (c - 64));
		} else {
			HighLevelEncoder.illegalCharacter(c);
		}
	}

	private static String encodeToCodewords(CharSequence sb, int startPos) {
		int len = sb.length() - startPos;
		if (len == 0) {
			throw new IllegalStateException("StringBuilder must not be empty");
		}
		char c1 = sb.charAt(startPos);
		char c2 = len >= 2 ? sb.charAt(startPos + 1) : 0;
		char c3 = len >= 3 ? sb.charAt(startPos + 2) : 0;
		char c4 = len >= 4 ? sb.charAt(startPos + 3) : 0;

		int v = (c1 << 18) + (c2 << 12) + (c3 << 6) + c4;
		char cw1 = (char) ((v >> 16) & 255);
		char cw2 = (char) ((v >> 8) & 255);
		char cw3 = (char) (v & 255);
		StringBuilder res = new StringBuilder(3);
		res.append(cw1);
		if (len >= 2) {
			res.append(cw2);
		}
		if (len >= 3) {
			res.append(cw3);
		}
		return res.toString();
	}

}