// Description of supported double byte encodings and aliases.
// Tables are not require()-d until they are needed to speed up library load.
// require()-s are direct to support Browserify.

module.exports = {
    
    // == Japanese/ShiftJIS ====================================================
    // All japanese encodings are based on JIS X set of standards:
    // JIS X 0201 - Single-byte encoding of ASCII + ¥ + Kana chars at 0xA1-0xDF.
    // JIS X 0208 - Main set of 6879 characters, placed in 94x94 plane, to be encoded by 2 bytes. 
    //              Has several variations in 1978, 1983, 1990 and 1997.
    // JIS X 0212 - Supplementary plane of 6067 chars in 94x94 plane. 1990. Effectively dead.
    // JIS X 0213 - Extension and modern replacement of 0208 and 0212. Total chars: 11233.
    //              2 planes, first is superset of 0208, second - revised 0212.
    //              Introduced in 2000, revised 2004. Some characters are in Unicode Plane 2 (0x2xxxx)

    // Byte encodings are:
    //  * Shift_JIS: Compatible with 0201, uses not defined chars in top half as lead bytes for double-byte
    //               encoding of 0208. Lead byte ranges: 0x81-0x9F, 0xE0-0xEF; Trail byte ranges: 0x40-0x7E, 0x80-0x9E, 0x9F-0xFC.
    //               Windows CP932 is a superset of Shift_JIS. Some companies added more chars, notably KDDI.
    //  * EUC-JP:    Up to 3 bytes per character. Used mostly on *nixes.
    //               0x00-0x7F       - lower part of 0201
    //               0x8E, 0xA1-0xDF - upper part of 0201
    //               (0xA1-0xFE)x2   - 0208 plane (94x94).
    //               0x8F, (0xA1-0xFE)x2 - 0212 plane (94x94).
    //  * JIS X 208: 7-bit, direct encoding of 0208. Byte ranges: 0x21-0x7E (94 values). Uncommon.
    //               Used as-is in ISO2022 family.
    //  * ISO2022-JP: Stateful encoding, with escape sequences to switch between ASCII, 
    //                0201-1976 Roman, 0208-1978, 0208-1983.
    //  * ISO2022-JP-1: Adds esc seq for 0212-1990.
    //  * ISO2022-JP-2: Adds esc seq for GB2313-1980, KSX1001-1992, ISO8859-1, ISO8859-7.
    //  * ISO2022-JP-3: Adds esc seq for 0201-1976 Kana set, 0213-2000 Planes 1, 2.
    //  * ISO2022-JP-2004: Adds 0213-2004 Plane 1.
    //
    // After JIS X 0213 appeared, Shift_JIS-2004, EUC-JISX0213 and ISO2022-JP-2004 followed, with just changing the planes.
    //
    // Overall, it seems that it's a mess :( http://www8.plala.or.jp/tkubota1/unicode-symbols-map2.html


    'shiftjis': {
        type: '_dbcs',
        table: function() { return require('./tables/shiftjis.json') },
        encodeAdd: {'\u00a5': 0x5C, '\u203E': 0x7E},
        encodeSkipVals: [{from: 0xED40, to: 0xF940}],
    },
    'csshiftjis': 'shiftjis',
    'mskanji': 'shiftjis',
    'sjis': 'shiftjis',
    'windows-31j': 'shiftjis',
    'x-sjis': 'shiftjis',
    'windows932': 'shiftjis',
    '932': 'shiftjis',
    'cp932': 'shiftjis',

    'eucjp': {
        type: '_dbcs',
        table: function() { return require('./tables/eucjp.json') },
        encodeAdd: {'\u00a5': 0x5C, '\u203E': 0x7E},
    },

    // TODO: KDDI extension to Shift_JIS
    // TODO: IBM CCSID 942 = CP932, but F0-F9 custom chars and other char changes.
    // TODO: IBM CCSID 943 = Shift_JIS = CP932 with original Shift_JIS lower 128 chars.

    // == Chinese/GBK ==========================================================
    // http://en.wikipedia.org/wiki/GBK

    // Oldest GB2312 (1981, ~7600 chars) is a subset of CP936
    'gb2312': 'cp936',
    'gb231280': 'cp936',
    'gb23121980': 'cp936',
    'csgb2312': 'cp936',
    'csiso58gb231280': 'cp936',
    'euccn': 'cp936',
    'isoir58': 'gbk',

    // Microsoft's CP936 is a subset and approximation of GBK.
    // TODO: Euro = 0x80 in cp936, but not in GBK (where it's valid but undefined)
    'windows936': 'cp936',
    '936': 'cp936',
    'cp936': {
        type: '_dbcs',
        table: function() { return require('./tables/cp936.json') },
    },

    // GBK (~22000 chars) is an extension of CP936 that added user-mapped chars and some other.
    'gbk': {
        type: '_dbcs',
        table: function() { return require('./tables/cp936.json').concat(require('./tables/gbk-added.json')) },
    },
    'xgbk': 'gbk',

    // GB18030 is an algorithmic extension of GBK.
    'gb18030': {
        type: '_dbcs',
        table: function() { return require('./tables/cp936.json').concat(require('./tables/gbk-added.json')) },
        gb18030: function() { return require('./tables/gb18030-ranges.json') },
    },

    'chinese': 'gb18030',

    // TODO: Support GB18030 (~27000 chars + whole unicode mapping, cp54936)
    // http://icu-project.org/docs/papers/gb18030.html
    // http://source.icu-project.org/repos/icu/data/trunk/charset/data/xml/gb-18030-2000.xml
    // http://www.khngai.com/chinese/charmap/tblgbk.php?page=0

    // == Korean ===============================================================
    // EUC-KR, KS_C_5601 and KS X 1001 are exactly the same.
    'windows949': 'cp949',
    '949': 'cp949',
    'cp949': {
        type: '_dbcs',
        table: function() { return require('./tables/cp949.json') },
    },

    'cseuckr': 'cp949',
    'csksc56011987': 'cp949',
    'euckr': 'cp949',
    'isoir149': 'cp949',
    'korean': 'cp949',
    'ksc56011987': 'cp949',
    'ksc56011989': 'cp949',
    'ksc5601': 'cp949',


    // == Big5/Taiwan/Hong Kong ================================================
    // There are lots of tables for Big5 and cp950. Please see the following links for history:
    // http://moztw.org/docs/big5/  http://www.haible.de/bruno/charsets/conversion-tables/Big5.html
    // Variations, in roughly number of defined chars:
    //  * Windows CP 950: Microsoft variant of Big5. Canonical: http://www.unicode.org/Public/MAPPINGS/VENDORS/MICSFT/WINDOWS/CP950.TXT
    //  * Windows CP 951: Microsoft variant of Big5-HKSCS-2001. Seems to be never public. http://me.abelcheung.org/articles/research/what-is-cp951/
    //  * Big5-2003 (Taiwan standard) almost superset of cp950.
    //  * Unicode-at-on (UAO) / Mozilla 1.8. Falling out of use on the Web. Not supported by other browsers.
    //  * Big5-HKSCS (-2001, -2004, -2008). Hong Kong standard. 
    //    many unicode code points moved from PUA to Supplementary plane (U+2XXXX) over the years.
    //    Plus, it has 4 combining sequences.
    //    Seems that Mozilla refused to support it for 10 yrs. https://bugzilla.mozilla.org/show_bug.cgi?id=162431 https://bugzilla.mozilla.org/show_bug.cgi?id=310299
    //    because big5-hkscs is the only encoding to include astral characters in non-algorithmic way.
    //    Implementations are not consistent within browsers; sometimes labeled as just big5.
    //    MS Internet Explorer switches from big5 to big5-hkscs when a patch applied.
    //    Great discussion & recap of what's going on https://bugzilla.mozilla.org/show_bug.cgi?id=912470#c31
    //    In the encoder, it might make sense to support encoding old PUA mappings to Big5 bytes seq-s.
    //    Official spec: http://www.ogcio.gov.hk/en/business/tech_promotion/ccli/terms/doc/2003cmp_2008.txt
    //                   http://www.ogcio.gov.hk/tc/business/tech_promotion/ccli/terms/doc/hkscs-2008-big5-iso.txt
    // 
    // Current understanding of how to deal with Big5(-HKSCS) is in the Encoding Standard, http://encoding.spec.whatwg.org/#big5-encoder
    // Unicode mapping (http://www.unicode.org/Public/MAPPINGS/OBSOLETE/EASTASIA/OTHER/BIG5.TXT) is said to be wrong.

    'windows950': 'cp950',
    '950': 'cp950',
    'cp950': {
        type: '_dbcs',
        table: function() { return require('./tables/cp950.json') },
    },

    // Big5 has many variations and is an extension of cp950. We use Encoding Standard's as a consensus.
    'big5': 'big5hkscs',
    'big5hkscs': {
        type: '_dbcs',
        table: function() { return require('./tables/cp950.json').concat(require('./tables/big5-added.json')) },
    },

    'cnbig5': 'big5hkscs',
    'csbig5': 'big5hkscs',
    'xxbig5': 'big5hkscs',

};