// utf.d
// Written by Walter Bright
// Copyright (c) 2003 Digital Mars
// All Rights Reserved
// www.digitalmars.com

// Description of UTF-8 at:
// http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8

module std.utf;

//debug=utf;		// uncomment to turn on debugging printf's

class UtfError : Error
{
    uint idx;	// index in string of where error occurred

    this(char[] s, uint i)
    {
	idx = i;
	super("s");
    }
}


//alias uint dchar;

bit isValidDchar(dchar c)
{
    return c < 0xD800 ||
	(c > 0xDFFF && c <= 0x10FFFF && c != 0xFFFE && c != 0xFFFF);
}

unittest
{
    debug(utf) printf("utf.isValidDchar.unittest\n");
    assert(isValidDchar((dchar)'a') == true);
    assert(isValidDchar((dchar)0x1FFFFF) == false);
}

/* =================== Decode ======================= */

dchar decode(char[] s, inout uint idx)
    in
    {
	assert(idx >= 0 && idx < s.length);
    }
    out (result)
    {
	assert(isValidDchar(result));
    }
    body
    {
	uint len = s.length;
	dchar V;
	uint i = idx;
	char u = s[i];

	if (u & 0x80)
	{   uint n;
	    char u2;

	    /* The following encodings are valid, except for the 5 and 6 byte
	     * combinations:
	     *	0xxxxxxx
	     *	110xxxxx 10xxxxxx
	     *	1110xxxx 10xxxxxx 10xxxxxx
	     *	11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
	     *	111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
	     *	1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
	     */
	    for (n = 1; ; n++)
	    {
		if (n > 4)
		    goto Lerr;		// only do the first 4 of 6 encodings
		if (((u << n) & 0x80) == 0)
		{
		    if (n == 1)
			goto Lerr;
		    break;
		}
	    }

	    // Pick off (7 - n) significant bits of B from first byte of octet
	    V = cast(dchar)(u & ((1 << (7 - n)) - 1));

	    if (i + (n - 1) >= len)
		goto Lerr;			// off end of string

	    /* The following combinations are overlong, and illegal:
	     *	1100000x (10xxxxxx)
	     *	11100000 100xxxxx (10xxxxxx)
	     *	11110000 1000xxxx (10xxxxxx 10xxxxxx)
	     *	11111000 10000xxx (10xxxxxx 10xxxxxx 10xxxxxx)
	     *	11111100 100000xx (10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx)
	     */
	    u2 = s[i + 1];
	    if ((u & 0xFE) == 0xC0 ||
		(u == 0xE0 && (u2 & 0xE0) == 0x80) ||
		(u == 0xF0 && (u2 & 0xF0) == 0x80) ||
		(u == 0xF8 && (u2 & 0xF8) == 0x80) ||
		(u == 0xFC && (u2 & 0xFC) == 0x80))
		goto Lerr;			// overlong combination

	    for (uint j = 1; j != n; j++)
	    {
		u = s[i + j];
		if ((u & 0xC0) != 0x80)
		    goto Lerr;			// trailing bytes are 10xxxxxx
		V = (V << 6) | (u & 0x3F);
	    }
	    if (!isValidDchar(V))
		goto Lerr;
	    i += n;
	}
	else
	{
	    V = cast(dchar) u;
	    i++;
	}

	idx = i;
	return V;

      Lerr:
	throw new UtfError("invalid UTF-8 sequence", i);
    }

unittest
{   uint i;
    dchar c;

    debug(utf) printf("utf.decode.unittest\n");

    static char[] s1 = "abcd";
    i = 0;
    c = decode(s1, i);
    assert(c == (dchar)'a');
    assert(i == 1);
    c = decode(s1, i);
    assert(c == (dchar)'b');
    assert(i == 2);

    static char[] s2 = "\xC2\xA9";
    i = 0;
    c = decode(s2, i);
    assert(c == (dchar)'\u00A9');
    assert(i == 2);

    static char[] s3 = "\xE2\x89\xA0";
    i = 0;
    c = decode(s3, i);
    assert(c == (dchar)'\u2260');
    assert(i == 3);

    static char[][] s4 =
    [	"\xE2\x89",		// too short
	"\xC0\x8A",
	"\xE0\x80\x8A",
	"\xF0\x80\x80\x8A",
	"\xF8\x80\x80\x80\x8A",
	"\xFC\x80\x80\x80\x80\x8A",
    ];

    for (int j = 0; j < s4.length; j++)
    {
	try
	{
	    i = 0;
	    c = decode(s4[j], i);
	    assert(0);
	}
	catch (UtfError u)
	{
	    i = 23;
	}
	assert(i == 23);
    }
}

/********************************************************/

dchar decode(wchar[] s, inout uint idx)
    in
    {
	assert(idx >= 0 && idx < s.length);
    }
    out (result)
    {
	assert(isValidDchar(result));
    }
    body
    {
	char[] msg;
	dchar V;
	uint i = idx;
	uint u = s[i];

	if (u & ~0x7F)
	{   if (u >= 0xD800 && u <= 0xDBFF)
	    {   uint u2;

		if (i + 1 == s.length)
		{   msg = "surrogate UTF-16 high value past end of string";
		    goto Lerr;
		}
		u2 = s[i + 1];
		if (u2 < 0xDC00 || u2 > 0xDFFF)
		{   msg = "surrogate UTF-16 low value out of range";
		    goto Lerr;
		}
		u = ((u - 0xD7C0) << 10) + (u2 - 0xDC00);
		i += 2;
	    }
	    else if (u >= 0xDC00 && u <= 0xDFFF)
	    {   msg = "unpaired surrogate UTF-16 value";
		goto Lerr;
	    }
	    else if (u == 0xFFFE || u == 0xFFFF)
	    {   msg = "illegal UTF-16 value";
		goto Lerr;
	    }
	}
	else
	{
	    i++;
	}

	idx = i;
	return cast(dchar)u;

      Lerr:
	throw new UtfError(msg, i);
    }

/********************************************************/

dchar decode(dchar[] s, inout uint idx)
    in
    {
	assert(idx >= 0 && idx < s.length);
    }
    body
    {
	uint i = idx;
	dchar c = s[i];

	if (!isValidDchar(c))
	    goto Lerr;
	idx = i + 1;
	return c;

      Lerr:
	throw new UtfError("invalid UTF-32 value", i);
    }


/* =================== Encode ======================= */

void encode(inout char[] s, dchar c)
    in
    {
	assert(isValidDchar(c));
    }
    body
    {
	char[] r = s;

	if (c <= 0x7F)
	{
	    r ~= cast(char) c;
	}
	else
	{
	    char[4] buf;
	    uint L;

	    if (c <= 0x7FF)
	    {
		buf[0] = cast(char)(0xC0 | (c >> 6));
		buf[1] = cast(char)(0x80 | (c & 0x3F));
		L = 2;
	    }
	    else if (c <= 0xFFFF)
	    {
		buf[0] = cast(char)(0xE0 | (c >> 12));
		buf[1] = cast(char)(0x80 | ((c >> 6) & 0x3F));
		buf[2] = cast(char)(0x80 | (c & 0x3F));
		L = 3;
	    }
	    else if (c <= 0x10FFFF)
	    {
		buf[0] = cast(char)(0xF0 | (c >> 18));
		buf[1] = cast(char)(0x80 | ((c >> 12) & 0x3F));
		buf[2] = cast(char)(0x80 | ((c >> 6) & 0x3F));
		buf[3] = cast(char)(0x80 | (c & 0x3F));
		L = 4;
	    }
	    else
	    {
		assert(0);
	    }
	    r ~= buf[0 .. L];
	}
	s = r;
    }

unittest
{
    debug(utf) printf("utf.encode.unittest\n");

    char[] s = "abcd";
    encode(s, (dchar)'a');
    assert(s.length == 5);
    assert(s == "abcda");

    encode(s, (dchar)'\u00A9');
    assert(s.length == 7);
    assert(s == "abcda\xC2\xA9");
    //assert(s == "abcda\u00A9");	// BUG: fix compiler

    encode(s, (dchar)'\u2260');
    assert(s.length == 10);
    assert(s == "abcda\xC2\xA9\xE2\x89\xA0");
}

/********************************************************/

void encode(inout wchar[] s, dchar c)
    in
    {
	assert(isValidDchar(c));
    }
    body
    {
	wchar[] r = s;

	if (c <= 0xFFFF)
	{
	    r ~= cast(wchar) c;
	}
	else
	{
	    wchar[2] buf;

	    buf[0] = (((c - 0x10000) >> 10) & 0x3FF) + 0xD800;
	    buf[1] = ((c - 0x10000) & 0x3FF) + 0xDC00;
	    r ~= buf;
	}
	s = r;
    }

void encode(inout dchar[] s, dchar c)
    in
    {
	assert(isValidDchar(c));
    }
    body
    {
	s ~= c;
    }

/* =================== Validation ======================= */

void validate(char[] s)
{
    uint len = s.length;
    uint i;

    for (i = 0; i < len; )
    {
	decode(s, i);
    }
}

void validate(wchar[] s)
{
    uint len = s.length;
    uint i;

    for (i = 0; i < len; )
    {
	decode(s, i);
    }
}

void validate(dchar[] s)
{
    uint len = s.length;
    uint i;

    for (i = 0; i < len; )
    {
	decode(s, i);
    }
}

/* =================== Conversion to UTF8 ======================= */


char[] toUTF8(char[] s)
    in
    {
	validate(s);
    }
    body
    {
	return s;
    }

char[] toUTF8(wchar[] s)
{
    char[] r;

    for (int i = 0; i < s.length; i++)
    {
	encode(r, cast(dchar)s[i]);
    }
    return r;
}

char[] toUTF8(dchar[] s)
{
    char[] r;

    for (int i = 0; i < s.length; i++)
    {
	encode(r, s[i]);
    }
    return r;
}

/* =================== Conversion to UTF16 ======================= */

wchar[] toUTF16(char[] s)
{
    wchar[] r;

    for (uint i = 0; i < s.length; )
    {
	dchar c = decode(s, i);
	encode(r, c);
    }
    return r;
}

wchar[] toUTF16(wchar[] s)
    in
    {
	validate(s);
    }
    body
    {
	return s;
    }

wchar[] toUTF16(dchar[] s)
{
    wchar[] r;

    for (uint i = 0; i < s.length; i++)
    {
	encode(r, s[i]);
    }
    return r;
}

/* =================== Conversion to UTF32 ======================= */

dchar[] toUTF32(char[] s)
{
    dchar[] r;

    for (uint i = 0; i < s.length; )
    {
	dchar c = decode(s, i);
	r ~= c;
    }
    return r;
}

dchar[] toUTF32(wchar[] s)
{
    dchar[] r;

    for (uint i = 0; i < s.length; )
    {
	dchar c = decode(s, i);
	r ~= c;
    }
    return r;
}

dchar[] toUTF32(dchar[] s)
    in
    {
	validate(s);
    }
    body
    {
	return s;
    }