/*
 * UTF7Encoding.cs - Implementation of the
 *		"System.Text.UTF7Encoding" class.
 *
 * Copyright (c) 2002  Southern Storm Software, Pty Ltd
 * Copyright (c) 2003, 2004, Novell, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 */

namespace System.Text
{

using System;

[Serializable]
[MonoTODO ("Fix serialization compatibility with MS.NET")]
#if ECMA_COMPAT
internal
#else
public
#endif
class UTF7Encoding : Encoding
{
	// Magic number used by Windows for UTF-7.
	internal const int UTF7_CODE_PAGE = 65000;

	// Internal state.
	private bool allowOptionals;

	// Encoding rule table for 0x00-0x7F.
	// 0 - full encode, 1 - direct, 2 - optional, 3 - encode plus.
	private static readonly byte[] encodingRules = {
		0, 0, 0, 0, 0, 0, 0, 0,   0, 1, 1, 0, 0, 1, 0, 0,	// 00
		0, 0, 0, 0, 0, 0, 0, 0,   0, 0, 0, 0, 0, 0, 0, 0,	// 10
		1, 2, 2, 2, 2, 2, 2, 1,   1, 1, 2, 3, 1, 1, 1, 1,	// 20
		1, 1, 1, 1, 1, 1, 1, 1,   1, 1, 1, 2, 2, 2, 2, 1,	// 30

		2, 1, 1, 1, 1, 1, 1, 1,   1, 1, 1, 1, 1, 1, 1, 1,	// 40
		1, 1, 1, 1, 1, 1, 1, 1,   1, 1, 1, 2, 0, 2, 2, 2,	// 50
		2, 1, 1, 1, 1, 1, 1, 1,   1, 1, 1, 1, 1, 1, 1, 1,	// 60
		1, 1, 1, 1, 1, 1, 1, 1,   1, 1, 1, 2, 2, 2, 0, 0,	// 70
	};

	// Characters to use to encode 6-bit values in base64.
	private const String base64Chars =
		"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

	// Map bytes in base64 to 6-bit values.
	private static readonly sbyte[] base64Values = {
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // 00
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // 10
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, 62, -1, -1, 63, // 20
		52, 53, 54, 55, 56, 57, 58, 59,   60, 61, -1, -1, -1, -1, -1, -1, // 30

		-1,  0,  1,  2,  3,  4,  5,  6,    7,  8,  9, 10, 11, 12, 13, 14, // 40
		15, 16, 17, 18, 19, 20, 21, 22,   23, 24, 25, -1, -1, -1, -1, -1, // 50
		-1, 26, 27, 28, 29, 30, 31, 32,   33, 34, 35, 36, 37, 38, 39, 40, // 60
		41, 42, 43, 44, 45, 46, 47, 48,   49, 50, 51, -1, -1, -1, -1, -1, // 70

		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // 80
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // 90
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // A0
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // B0

		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // C0
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // D0
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // E0
		-1, -1, -1, -1, -1, -1, -1, -1,   -1, -1, -1, -1, -1, -1, -1, -1, // F0
	};

	// Constructors.
	public UTF7Encoding ()
	: this (false)
	{
	}
	
	public UTF7Encoding (bool allowOptionals)
	: base (UTF7_CODE_PAGE)
	{
		this.allowOptionals = allowOptionals;
		
		body_name = "utf-7";
		encoding_name = "Unicode (UTF-7)";
		header_name = "utf-7";
		is_mail_news_display = true;
		is_mail_news_save = true;
		web_name = "utf-7";
		windows_code_page = UnicodeEncoding.UNICODE_CODE_PAGE;
	}

	// Internal version of "GetByteCount" that can handle
	// a rolling state between calls.
	private static int InternalGetByteCount
				(char[] chars, int index, int count, bool flush,
				 int leftOver, bool isInShifted, bool allowOptionals)
	{
		// Validate the parameters.
		if (chars == null) {
			throw new ArgumentNullException ("chars");
		}
		if (index < 0 || index > chars.Length) {
			throw new ArgumentOutOfRangeException ("index", _("ArgRange_Array"));
		}
		if (count < 0 || count > (chars.Length - index)) {
			throw new ArgumentOutOfRangeException ("count", _("ArgRange_Array"));
		}

		// Determine the length of the output.
		int length = 0;
		int leftOverSize = (leftOver >> 8);
		byte[] rules = encodingRules;
		int ch, rule;
		while (count > 0) {
			ch = (int)(chars[index++]);
			--count;
			if (ch < 0x0080) {
				rule = rules[ch];
			} else {
				rule = 0;
			}
			switch (rule) {
			case 0:
				// Handle characters that must be fully encoded.
				if ( !isInShifted ) {
					++length;
				    leftOverSize = 0;
					isInShifted = true;
				}
				leftOverSize += 16;
				while (leftOverSize >= 6) {
					++length;
					leftOverSize -= 6;
				}
				break;
			case 1:
				// The character is encoded as itself.
				if (isInShifted) {
					if (leftOverSize != 0) {
						// Flush the previous encoded sequence.
						++length;
						leftOverSize = 0;
					}
					// Count the "-" (sequence terminator)
					++length;
					isInShifted = false;
				}
				++length;
				break;
			case 2:
				// The character may need to be encoded.
				if (allowOptionals) {
					goto case 1;
				} else {
					goto case 0;
				}
			// Not reached.
			case 3:
				// Encode the plus sign as "+-".
				if (isInShifted) {
					if (leftOverSize != 0) {
						// Flush the previous encoded sequence.
						++length;
						leftOverSize = 0;
					}
					// Count the "-" (sequence terminator)
					++length;
					isInShifted = false;
				}
				length += 2;
				break;
			}
		}
		if (isInShifted && flush) {
			if (leftOverSize != 0) 
			{
				// Flush the previous encoded sequence.
				++length;
			}
			// Count the "-" (sequence terminator)
			++length;
		}

		// Return the length to the caller.
		return length;
	}

	// Get the number of bytes needed to encode a character buffer.
	public override int GetByteCount (char[] chars, int index, int count)
	{
		return InternalGetByteCount (chars, index, count, true, 0, false, allowOptionals);
	}

	// Internal version of "GetBytes" that can handle a
	// rolling state between calls.
	private static int InternalGetBytes
				(char[] chars, int charIndex, int charCount,
				 byte[] bytes, int byteIndex, bool flush,
				 ref int leftOver, ref bool isInShifted, bool allowOptionals)
	{
		// Validate the parameters.
		if (chars == null) {
			throw new ArgumentNullException ("chars");
		}
		if (bytes == null) {
			throw new ArgumentNullException ("bytes");
		}
		if (charIndex < 0 || charIndex > chars.Length) {
			throw new ArgumentOutOfRangeException ("charIndex", _("ArgRange_Array"));
		}
		if (charCount < 0 || charCount > (chars.Length - charIndex)) {
			throw new ArgumentOutOfRangeException ("charCount", _("ArgRange_Array"));
		}
		if (byteIndex < 0 || byteIndex > bytes.Length) {
			throw new ArgumentOutOfRangeException ("byteIndex", _("ArgRange_Array"));
		}

		// Convert the characters.
		int posn = byteIndex;
		int byteLength = bytes.Length;
		int leftOverSize = (leftOver >> 8);
		int leftOverBits = (leftOver & 0xFF);
		byte[] rules = encodingRules;
		String base64 = base64Chars;
		int ch, rule;
		while (charCount > 0) {
			ch = (int)(chars[charIndex++]);
			--charCount;
			if (ch < 0x0080) {
				rule = rules[ch];
			} else {
				rule = 0;
			}
			switch (rule) {
			case 0:
				// Handle characters that must be fully encoded.
				if (!isInShifted) {
					if (posn >= byteLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
					}
					// Start the sequence
					bytes[posn++] = (byte)'+';
					isInShifted = true;
					leftOverSize = 0;
				}
				leftOverBits = ((leftOverBits << 16) | ch);
				leftOverSize += 16;
				while (leftOverSize >= 6) {
					if (posn >= byteLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
					}
					leftOverSize -= 6;
					bytes[posn++] = (byte)(base64 [leftOverBits >> leftOverSize]);
					leftOverBits &= ((1 << leftOverSize) - 1);
				}
				break;
			case 1:
				// The character is encoded as itself.
				if (isInShifted) {
					if (leftOverSize != 0) {
						// Flush the previous encoded sequence.
						if ((posn + 1) > byteLength) {
							throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
						}
						bytes[posn++] = (byte)(base64 [leftOverBits << (6 - leftOverSize)]);
					}
					if ((posn + 1) > byteLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
					}
					// Terminate the sequence
					bytes[posn++] = (byte)'-';
					isInShifted = false;
					leftOverSize = 0;
					leftOverBits = 0;
				}
				if (posn >= byteLength) {
					throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
				}
				bytes[posn++] = (byte)ch;
				break;
			case 2:
				// The character may need to be encoded.
				if (allowOptionals) {
					goto case 1;
				} else {
					goto case 0;
				}
				// Not reached.
			case 3:
				// Encode the plus sign as "+-".
				if (isInShifted) {
					if (leftOverSize != 0) {
						// Flush the previous encoded sequence.
						if ((posn + 1) > byteLength) {
							throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
						}
						bytes[posn++] = (byte)(base64 [leftOverBits << (6 - leftOverSize)]);
					}
					if ((posn + 1) > byteLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
					}
					// Terminate the sequence
					bytes[posn++] = (byte)'-';
					isInShifted = false;
					leftOverSize = 0;
					leftOverBits = 0;
				}
				if ((posn + 2) > byteLength) {
					throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
				}
				bytes[posn++] = (byte)'+';
				bytes[posn++] = (byte)'-';
				break;
			}
		}
		if (isInShifted && flush) {
			// Flush the previous encoded sequence.
			if (leftOverSize != 0) {
				if ((posn + 1) > byteLength) {
					throw new ArgumentException (_("Arg_InsufficientSpace"), "bytes");
				}
				bytes[posn++] = (byte)(base64 [leftOverBits << (6 - leftOverSize)]);
			}
			// Terminate the sequence
			bytes[posn++] = (byte)'-';
			leftOverSize = 0;
			leftOverBits = 0;
			isInShifted = false;
		}
		leftOver = ((leftOverSize << 8) | leftOverBits);

		// Return the length to the caller.
		return posn - byteIndex;
	}

	// Get the bytes that result from encoding a character buffer.
	public override int GetBytes (char[] chars, int charIndex, int charCount,
								 byte[] bytes, int byteIndex)
	{
		int leftOver = 0;
		bool isInShifted = false;
		return InternalGetBytes (chars, charIndex, charCount, bytes, byteIndex, true,
								ref leftOver, ref isInShifted, allowOptionals);
	}

	// Internal version of "GetCharCount" that can handle
	// a rolling state between call.s
	private static int InternalGetCharCount
					(byte[] bytes, int index, int count, int leftOver)
	{
		// Validate the parameters.
		if (bytes == null) {
			throw new ArgumentNullException ("bytes");
		}
		if (index < 0 || index > bytes.Length) {
			throw new ArgumentOutOfRangeException ("index", _("ArgRange_Array"));
		}
		if (count < 0 || count > (bytes.Length - index)) {
			throw new ArgumentOutOfRangeException ("count", _("ArgRange_Array"));
		}

		// Determine the length of the result.
		int length = 0;
		int byteval;
		bool normal = ((leftOver & 0x01000000) == 0);
		bool prevIsPlus = ((leftOver & 0x02000000) != 0);
		int leftOverSize = ((leftOver >> 16) & 0xFF);
		sbyte[] base64 = base64Values;
		while (count > 0) {
			byteval = (int)(bytes[index++]);
			--count;
			if (normal) {
				if (byteval != '+') {
					// Directly-encoded character.
					++length;
				} else {
					// Start of a base64-encoded character.
					normal = false;
					prevIsPlus = true;
				}
			} else {
				// Process the next byte in a base64 sequence.
				if (byteval == (int)'-') {
					// End of a base64 sequence.
					if (prevIsPlus) {
						++length;
						leftOverSize = 0;
					}
					normal = true;
				} else if (base64 [byteval] != -1) {
					// Extra character in a base64 sequence.
					leftOverSize += 6;
					if (leftOverSize >= 16) {
						++length;
						leftOverSize -= 16;
					}
				} else {
					++length;
					normal = true;
					leftOverSize = 0;
				}
				prevIsPlus = false;
			}
		}

		// Return the final length to the caller.
		return length;
	}

	// Get the number of characters needed to decode a byte buffer.
	public override int GetCharCount (byte[] bytes, int index, int count)
	{
		return InternalGetCharCount (bytes, index, count, 0);
	}

	// Internal version of "GetChars" that can handle a
	// rolling state between calls.
	private static int InternalGetChars (byte[] bytes, int byteIndex, int byteCount,
				 char[] chars, int charIndex, ref int leftOver)
	{
		// Validate the parameters.
		if (bytes == null) {
			throw new ArgumentNullException ("bytes");
		}
		if (chars == null) {
			throw new ArgumentNullException ("chars");
		}
		if (byteIndex < 0 || byteIndex > bytes.Length) {
			throw new ArgumentOutOfRangeException ("byteIndex", _("ArgRange_Array"));
		}
		if (byteCount < 0 || byteCount > (bytes.Length - byteIndex)) {
			throw new ArgumentOutOfRangeException ("byteCount", _("ArgRange_Array"));
		}
		if (charIndex < 0 || charIndex > chars.Length) {
			throw new ArgumentOutOfRangeException ("charIndex", _("ArgRange_Array"));
		}

		// Convert the bytes into characters.
		int posn = charIndex;
		int charLength = chars.Length;
		int byteval, b64value;
		bool normal = ((leftOver & 0x01000000) == 0);
		bool prevIsPlus = ((leftOver & 0x02000000) != 0);
		bool afterHighSurrogate = ((leftOver & 0x04000000) != 0);
		int leftOverSize = ((leftOver >> 16) & 0xFF);
		int leftOverBits = (leftOver & 0xFFFF);
		sbyte[] base64 = base64Values;
		while (byteCount > 0) {
			byteval = (int)(bytes[byteIndex++]);
			--byteCount;
			if (normal) {
				if (byteval != '+') {
					// Directly-encoded character.
					if (posn >= charLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "chars");
					}
					if (afterHighSurrogate) {
						throw new ArgumentException (_("Arg_InvalidUTF7"), "chars");
					}
					chars[posn++] = (char)byteval;
				} else {
					// Start of a base64-encoded character.
					normal = false;
					prevIsPlus = true;
				}
			} else {
				// Process the next byte in a base64 sequence.
				if (byteval == (int)'-') {
					// End of a base64 sequence.
					if (prevIsPlus) {
						if (posn >= charLength) {
							throw new ArgumentException (_("Arg_InsufficientSpace"), "chars");
						}
						if (afterHighSurrogate) {
							throw new ArgumentException (_("Arg_InvalidUTF7"), "chars");
						}
						chars[posn++] = '+';
					}
					// RFC1642 Rule #2
					// When decoding, any bits at the end of the Modified Base64 sequence that 
					// do not constitute a complete 16-bit Unicode character are discarded. 
					// If such discarded bits are non-zero the sequence is ill-formed.
					normal = true;
					leftOverSize = 0;
					leftOverBits = 0;
				} 
				else if ((b64value = base64[byteval]) != -1) 
				{
					// Extra character in a base64 sequence.
					leftOverBits = (leftOverBits << 6) | b64value;
					leftOverSize += 6;
					if (leftOverSize >= 16) {
						if (posn >= charLength) {
							throw new ArgumentException (_("Arg_InsufficientSpace"), "chars");
						}
						leftOverSize -= 16;
						char nextChar = (char)(leftOverBits >> leftOverSize);
						if ((nextChar & 0xFC00) == 0xD800) {
						  afterHighSurrogate = true;
						}
						else if ((nextChar & 0xFC00) == 0xDC00) {
							if (!afterHighSurrogate) {
								throw new ArgumentException (_("Arg_InvalidUTF7"), "chars");
							}
							afterHighSurrogate = false;
						}
						chars[posn++] = nextChar;
						leftOverBits &= ((1 << leftOverSize) - 1);
					}
				} else {
					if (posn >= charLength) {
						throw new ArgumentException (_("Arg_InsufficientSpace"), "chars");
					}
					if (afterHighSurrogate) {
						throw new ArgumentException (_("Arg_InvalidUTF7"), "chars");
					}
					chars[posn++] = (char)byteval;
					normal = true;
					leftOverSize = 0;
					leftOverBits = 0;
				}
				prevIsPlus = false;
			}
		}
		leftOver = (leftOverBits | (leftOverSize << 16) |
				    (normal ? 0 : 0x01000000) |
				    (prevIsPlus ? 0x02000000 : 0) |
				    (afterHighSurrogate ? 0x04000000 : 0));

		// Return the final length to the caller.
		return posn - charIndex;
	}

	// Get the characters that result from decoding a byte buffer.
	public override int GetChars (byte[] bytes, int byteIndex, int byteCount,
								 char[] chars, int charIndex)
	{
		int leftOver = 0;
		int amount = InternalGetChars (bytes, byteIndex, byteCount, chars, charIndex, ref leftOver);
		if ((leftOver & 0x04000000) != 0) {
			throw new ArgumentException (_("Arg_InvalidUTF7"), "chars");
		}
		return amount;
	}

	// Get the maximum number of bytes needed to encode a
	// specified number of characters.
	public override int GetMaxByteCount (int charCount)
	{
		if (charCount < 0) {
			throw new ArgumentOutOfRangeException ("charCount", _("ArgRange_NonNegative"));
		}
		if (charCount == 0)
			return 0;
		return 8 * (int) (charCount / 3) + (charCount % 3) * 3 + 2;
	}

	// Get the maximum number of characters needed to decode a
	// specified number of bytes.
	public override int GetMaxCharCount (int byteCount)
	{
		if (byteCount < 0) {
			throw new ArgumentOutOfRangeException ("byteCount", _("ArgRange_NonNegative"));
		}
		return byteCount;
	}

	// Get a UTF7-specific decoder that is attached to this instance.
	public override Decoder GetDecoder ()
	{
		return new UTF7Decoder ();
	}

	// Get a UTF7-specific encoder that is attached to this instance.
	public override Encoder GetEncoder ()
	{
		return new UTF7Encoder (allowOptionals);
	}

	// UTF-7 decoder implementation.
	private sealed class UTF7Decoder : Decoder
	{
		// Internal state.
		private int leftOver;

		// Constructor.
		public UTF7Decoder ()
		{
			leftOver = 0;
		}

		// Override inherited methods.
		public override int GetCharCount (byte[] bytes, int index, int count)
		{
			return InternalGetCharCount (bytes, index, count, leftOver);
		}
		public override int GetChars (byte[] bytes, int byteIndex,
									 int byteCount, char[] chars,
									 int charIndex)
		{
			return InternalGetChars (bytes, byteIndex, byteCount, chars, charIndex, ref leftOver);
		}

	} // class UTF7Decoder

	// UTF-7 encoder implementation.
	private sealed class UTF7Encoder : Encoder
	{
		private bool allowOptionals;
		private int leftOver = 0;
		private bool isInShifted = false;

		// Constructor.
		public UTF7Encoder (bool allowOptionals)
		{
			this.allowOptionals = allowOptionals;
		}

		// Override inherited methods.
		public override int GetByteCount (char[] chars, int index,
										 int count, bool flush)
		{
			return InternalGetByteCount
				(chars, index, count, flush, leftOver, isInShifted, allowOptionals);
		}
		public override int GetBytes (char[] chars, int charIndex,
									 int charCount, byte[] bytes,
									 int byteIndex, bool flush)
		{
			return InternalGetBytes (chars, charIndex, charCount,
									bytes, byteIndex, flush,
									ref leftOver, ref isInShifted, allowOptionals);
		}

	} // class UTF7Encoder

}; // class UTF7Encoding

}; // namespace System.Text