“use strict”; var Buffer = require(“safer-buffer”).Buffer;

// Multibyte codec. In this scheme, a character is represented by 1 or more bytes. // Our codec supports UTF-16 surrogates, extensions for GB18030 and unicode sequences. // To save memory and loading time, we read table files only when requested.

exports._dbcs = DBCSCodec;

var UNASSIGNED = -1,

GB18030_CODE = -2,
SEQ_START  = -10,
NODE_START = -1000,
UNASSIGNED_NODE = new Array(0x100),
DEF_CHAR = -1;

for (var i = 0; i < 0x100; i++)

UNASSIGNED_NODE[i] = UNASSIGNED;

// Class DBCSCodec reads and initializes mapping tables. function DBCSCodec(codecOptions, iconv) {

this.encodingName = codecOptions.encodingName;
if (!codecOptions)
    throw new Error("DBCS codec is called without the data.")
if (!codecOptions.table)
    throw new Error("Encoding '" + this.encodingName + "' has no data.");

// Load tables.
var mappingTable = codecOptions.table();

// Decode tables: MBCS -> Unicode.

// decodeTables is a trie, encoded as an array of arrays of integers. Internal arrays are trie nodes and all have len = 256.
// Trie root is decodeTables[0].
// Values: >=  0 -> unicode character code. can be > 0xFFFF
//         == UNASSIGNED -> unknown/unassigned sequence.
//         == GB18030_CODE -> this is the end of a GB18030 4-byte sequence.
//         <= NODE_START -> index of the next node in our trie to process next byte.
//         <= SEQ_START  -> index of the start of a character code sequence, in decodeTableSeq.
this.decodeTables = [];
this.decodeTables[0] = UNASSIGNED_NODE.slice(0); // Create root node.

// Sometimes a MBCS char corresponds to a sequence of unicode chars. We store them as arrays of integers here. 
this.decodeTableSeq = [];

// Actual mapping tables consist of chunks. Use them to fill up decode tables.
for (var i = 0; i < mappingTable.length; i++)
    this._addDecodeChunk(mappingTable[i]);

this.defaultCharUnicode = iconv.defaultCharUnicode;

// Encode tables: Unicode -> DBCS.

// `encodeTable` is array mapping from unicode char to encoded char. All its values are integers for performance.
// Because it can be sparse, it is represented as array of buckets by 256 chars each. Bucket can be null.
// Values: >=  0 -> it is a normal char. Write the value (if <=256 then 1 byte, if <=65536 then 2 bytes, etc.).
//         == UNASSIGNED -> no conversion found. Output a default char.
//         <= SEQ_START  -> it's an index in encodeTableSeq, see below. The character starts a sequence.
this.encodeTable = [];

// `encodeTableSeq` is used when a sequence of unicode characters is encoded as a single code. We use a tree of
// objects where keys correspond to characters in sequence and leafs are the encoded dbcs values. A special DEF_CHAR key
// means end of sequence (needed when one sequence is a strict subsequence of another).
// Objects are kept separately from encodeTable to increase performance.
this.encodeTableSeq = [];

// Some chars can be decoded, but need not be encoded.
var skipEncodeChars = {};
if (codecOptions.encodeSkipVals)
    for (var i = 0; i < codecOptions.encodeSkipVals.length; i++) {
        var val = codecOptions.encodeSkipVals[i];
        if (typeof val === 'number')
            skipEncodeChars[val] = true;
        else
            for (var j = val.from; j <= val.to; j++)
                skipEncodeChars[j] = true;
    }

// Use decode trie to recursively fill out encode tables.
this._fillEncodeTable(0, 0, skipEncodeChars);

// Add more encoding pairs when needed.
if (codecOptions.encodeAdd) {
    for (var uChar in codecOptions.encodeAdd)
        if (Object.prototype.hasOwnProperty.call(codecOptions.encodeAdd, uChar))
            this._setEncodeChar(uChar.charCodeAt(0), codecOptions.encodeAdd[uChar]);
}

this.defCharSB  = this.encodeTable[0][iconv.defaultCharSingleByte.charCodeAt(0)];
if (this.defCharSB === UNASSIGNED) this.defCharSB = this.encodeTable[0]['?'];
if (this.defCharSB === UNASSIGNED) this.defCharSB = "?".charCodeAt(0);

// Load & create GB18030 tables when needed.
if (typeof codecOptions.gb18030 === 'function') {
    this.gb18030 = codecOptions.gb18030(); // Load GB18030 ranges.

    // Add GB18030 decode tables.
    var thirdByteNodeIdx = this.decodeTables.length;
    var thirdByteNode = this.decodeTables[thirdByteNodeIdx] = UNASSIGNED_NODE.slice(0);

    var fourthByteNodeIdx = this.decodeTables.length;
    var fourthByteNode = this.decodeTables[fourthByteNodeIdx] = UNASSIGNED_NODE.slice(0);

    for (var i = 0x81; i <= 0xFE; i++) {
        var secondByteNodeIdx = NODE_START - this.decodeTables[0][i];
        var secondByteNode = this.decodeTables[secondByteNodeIdx];
        for (var j = 0x30; j <= 0x39; j++)
            secondByteNode[j] = NODE_START - thirdByteNodeIdx;
    }
    for (var i = 0x81; i <= 0xFE; i++)
        thirdByteNode[i] = NODE_START - fourthByteNodeIdx;
    for (var i = 0x30; i <= 0x39; i++)
        fourthByteNode[i] = GB18030_CODE
}

}

DBCSCodec.prototype.encoder = DBCSEncoder; DBCSCodec.prototype.decoder = DBCSDecoder;

// Decoder helpers DBCSCodec.prototype._getDecodeTrieNode = function(addr) {

var bytes = [];
for (; addr > 0; addr >>= 8)
    bytes.push(addr & 0xFF);
if (bytes.length == 0)
    bytes.push(0);

var node = this.decodeTables[0];
for (var i = bytes.length-1; i > 0; i--) { // Traverse nodes deeper into the trie.
    var val = node[bytes[i]];

    if (val == UNASSIGNED) { // Create new node.
        node[bytes[i]] = NODE_START - this.decodeTables.length;
        this.decodeTables.push(node = UNASSIGNED_NODE.slice(0));
    }
    else if (val <= NODE_START) { // Existing node.
        node = this.decodeTables[NODE_START - val];
    }
    else
        throw new Error("Overwrite byte in " + this.encodingName + ", addr: " + addr.toString(16));
}
return node;

}

DBCSCodec.prototype._addDecodeChunk = function(chunk) {

// First element of chunk is the hex mbcs code where we start.
var curAddr = parseInt(chunk[0], 16);

// Choose the decoding node where we'll write our chars.
var writeTable = this._getDecodeTrieNode(curAddr);
curAddr = curAddr & 0xFF;

// Write all other elements of the chunk to the table.
for (var k = 1; k < chunk.length; k++) {
    var part = chunk[k];
    if (typeof part === "string") { // String, write as-is.
        for (var l = 0; l < part.length;) {
            var code = part.charCodeAt(l++);
            if (0xD800 <= code && code < 0xDC00) { // Decode surrogate
                var codeTrail = part.charCodeAt(l++);
                if (0xDC00 <= codeTrail && codeTrail < 0xE000)
                    writeTable[curAddr++] = 0x10000 + (code - 0xD800) * 0x400 + (codeTrail - 0xDC00);
                else
                    throw new Error("Incorrect surrogate pair in "  + this.encodingName + " at chunk " + chunk[0]);
            }
            else if (0x0FF0 < code && code <= 0x0FFF) { // Character sequence (our own encoding used)
                var len = 0xFFF - code + 2;
                var seq = [];
                for (var m = 0; m < len; m++)
                    seq.push(part.charCodeAt(l++)); // Simple variation: don't support surrogates or subsequences in seq.

                writeTable[curAddr++] = SEQ_START - this.decodeTableSeq.length;
                this.decodeTableSeq.push(seq);
            }
            else
                writeTable[curAddr++] = code; // Basic char
        }
    } 
    else if (typeof part === "number") { // Integer, meaning increasing sequence starting with prev character.
        var charCode = writeTable[curAddr - 1] + 1;
        for (var l = 0; l < part; l++)
            writeTable[curAddr++] = charCode++;
    }
    else
        throw new Error("Incorrect type '" + typeof part + "' given in "  + this.encodingName + " at chunk " + chunk[0]);
}
if (curAddr > 0xFF)
    throw new Error("Incorrect chunk in "  + this.encodingName + " at addr " + chunk[0] + ": too long" + curAddr);

}

// Encoder helpers DBCSCodec.prototype._getEncodeBucket = function(uCode) {

var high = uCode >> 8; // This could be > 0xFF because of astral characters.
if (this.encodeTable[high] === undefined)
    this.encodeTable[high] = UNASSIGNED_NODE.slice(0); // Create bucket on demand.
return this.encodeTable[high];

}

DBCSCodec.prototype._setEncodeChar = function(uCode, dbcsCode) {

var bucket = this._getEncodeBucket(uCode);
var low = uCode & 0xFF;
if (bucket[low] <= SEQ_START)
    this.encodeTableSeq[SEQ_START-bucket[low]][DEF_CHAR] = dbcsCode; // There's already a sequence, set a single-char subsequence of it.
else if (bucket[low] == UNASSIGNED)
    bucket[low] = dbcsCode;

}

DBCSCodec.prototype._setEncodeSequence = function(seq, dbcsCode) {

// Get the root of character tree according to first character of the sequence.
var uCode = seq[0];
var bucket = this._getEncodeBucket(uCode);
var low = uCode & 0xFF;

var node;
if (bucket[low] <= SEQ_START) {
    // There's already a sequence with  - use it.
    node = this.encodeTableSeq[SEQ_START-bucket[low]];
}
else {
    // There was no sequence object - allocate a new one.
    node = {};
    if (bucket[low] !== UNASSIGNED) node[DEF_CHAR] = bucket[low]; // If a char was set before - make it a single-char subsequence.
    bucket[low] = SEQ_START - this.encodeTableSeq.length;
    this.encodeTableSeq.push(node);
}

// Traverse the character tree, allocating new nodes as needed.
for (var j = 1; j < seq.length-1; j++) {
    var oldVal = node[uCode];
    if (typeof oldVal === 'object')
        node = oldVal;
    else {
        node = node[uCode] = {}
        if (oldVal !== undefined)
            node[DEF_CHAR] = oldVal
    }
}

// Set the leaf to given dbcsCode.
uCode = seq[seq.length-1];
node[uCode] = dbcsCode;

}

DBCSCodec.prototype._fillEncodeTable = function(nodeIdx, prefix, skipEncodeChars) {

var node = this.decodeTables[nodeIdx];
for (var i = 0; i < 0x100; i++) {
    var uCode = node[i];
    var mbCode = prefix + i;
    if (skipEncodeChars[mbCode])
        continue;

    if (uCode >= 0)
        this._setEncodeChar(uCode, mbCode);
    else if (uCode <= NODE_START)
        this._fillEncodeTable(NODE_START - uCode, mbCode << 8, skipEncodeChars);
    else if (uCode <= SEQ_START)
        this._setEncodeSequence(this.decodeTableSeq[SEQ_START - uCode], mbCode);
}

}

// == Encoder ==================================================================

function DBCSEncoder(options, codec) {

// Encoder state
this.leadSurrogate = -1;
this.seqObj = undefined;

// Static data
this.encodeTable = codec.encodeTable;
this.encodeTableSeq = codec.encodeTableSeq;
this.defaultCharSingleByte = codec.defCharSB;
this.gb18030 = codec.gb18030;

}

DBCSEncoder.prototype.write = function(str) {

var newBuf = Buffer.alloc(str.length * (this.gb18030 ? 4 : 3)),
    leadSurrogate = this.leadSurrogate,
    seqObj = this.seqObj, nextChar = -1,
    i = 0, j = 0;

while (true) {
    // 0. Get next character.
    if (nextChar === -1) {
        if (i == str.length) break;
        var uCode = str.charCodeAt(i++);
    }
    else {
        var uCode = nextChar;
        nextChar = -1;    
    }

    // 1. Handle surrogates.
    if (0xD800 <= uCode && uCode < 0xE000) { // Char is one of surrogates.
        if (uCode < 0xDC00) { // We've got lead surrogate.
            if (leadSurrogate === -1) {
                leadSurrogate = uCode;
                continue;
            } else {
                leadSurrogate = uCode;
                // Double lead surrogate found.
                uCode = UNASSIGNED;
            }
        } else { // We've got trail surrogate.
            if (leadSurrogate !== -1) {
                uCode = 0x10000 + (leadSurrogate - 0xD800) * 0x400 + (uCode - 0xDC00);
                leadSurrogate = -1;
            } else {
                // Incomplete surrogate pair - only trail surrogate found.
                uCode = UNASSIGNED;
            }

        }
    }
    else if (leadSurrogate !== -1) {
        // Incomplete surrogate pair - only lead surrogate found.
        nextChar = uCode; uCode = UNASSIGNED; // Write an error, then current char.
        leadSurrogate = -1;
    }

    // 2. Convert uCode character.
    var dbcsCode = UNASSIGNED;
    if (seqObj !== undefined && uCode != UNASSIGNED) { // We are in the middle of the sequence
        var resCode = seqObj[uCode];
        if (typeof resCode === 'object') { // Sequence continues.
            seqObj = resCode;
            continue;

        } else if (typeof resCode == 'number') { // Sequence finished. Write it.
            dbcsCode = resCode;

        } else if (resCode == undefined) { // Current character is not part of the sequence.

            // Try default character for this sequence
            resCode = seqObj[DEF_CHAR];
            if (resCode !== undefined) {
                dbcsCode = resCode; // Found. Write it.
                nextChar = uCode; // Current character will be written too in the next iteration.

            } else {
                // TODO: What if we have no default? (resCode == undefined)
                // Then, we should write first char of the sequence as-is and try the rest recursively.
                // Didn't do it for now because no encoding has this situation yet.
                // Currently, just skip the sequence and write current char.
            }
        }
        seqObj = undefined;
    }
    else if (uCode >= 0) {  // Regular character
        var subtable = this.encodeTable[uCode >> 8];
        if (subtable !== undefined)
            dbcsCode = subtable[uCode & 0xFF];

        if (dbcsCode <= SEQ_START) { // Sequence start
            seqObj = this.encodeTableSeq[SEQ_START-dbcsCode];
            continue;
        }

        if (dbcsCode == UNASSIGNED && this.gb18030) {
            // Use GB18030 algorithm to find character(s) to write.
            var idx = findIdx(this.gb18030.uChars, uCode);
            if (idx != -1) {
                var dbcsCode = this.gb18030.gbChars[idx] + (uCode - this.gb18030.uChars[idx]);
                newBuf[j++] = 0x81 + Math.floor(dbcsCode / 12600); dbcsCode = dbcsCode % 12600;
                newBuf[j++] = 0x30 + Math.floor(dbcsCode / 1260); dbcsCode = dbcsCode % 1260;
                newBuf[j++] = 0x81 + Math.floor(dbcsCode / 10); dbcsCode = dbcsCode % 10;
                newBuf[j++] = 0x30 + dbcsCode;
                continue;
            }
        }
    }

    // 3. Write dbcsCode character.
    if (dbcsCode === UNASSIGNED)
        dbcsCode = this.defaultCharSingleByte;

    if (dbcsCode < 0x100) {
        newBuf[j++] = dbcsCode;
    }
    else if (dbcsCode < 0x10000) {
        newBuf[j++] = dbcsCode >> 8;   // high byte
        newBuf[j++] = dbcsCode & 0xFF; // low byte
    }
    else {
        newBuf[j++] = dbcsCode >> 16;
        newBuf[j++] = (dbcsCode >> 8) & 0xFF;
        newBuf[j++] = dbcsCode & 0xFF;
    }
}

this.seqObj = seqObj;
this.leadSurrogate = leadSurrogate;
return newBuf.slice(0, j);

}

DBCSEncoder.prototype.end = function() {

if (this.leadSurrogate === -1 && this.seqObj === undefined)
    return; // All clean. Most often case.

var newBuf = Buffer.alloc(10), j = 0;

if (this.seqObj) { // We're in the sequence.
    var dbcsCode = this.seqObj[DEF_CHAR];
    if (dbcsCode !== undefined) { // Write beginning of the sequence.
        if (dbcsCode < 0x100) {
            newBuf[j++] = dbcsCode;
        }
        else {
            newBuf[j++] = dbcsCode >> 8;   // high byte
            newBuf[j++] = dbcsCode & 0xFF; // low byte
        }
    } else {
        // See todo above.
    }
    this.seqObj = undefined;
}

if (this.leadSurrogate !== -1) {
    // Incomplete surrogate pair - only lead surrogate found.
    newBuf[j++] = this.defaultCharSingleByte;
    this.leadSurrogate = -1;
}

return newBuf.slice(0, j);

}

// Export for testing DBCSEncoder.prototype.findIdx = findIdx;

// == Decoder ==================================================================

function DBCSDecoder(options, codec) {

// Decoder state
this.nodeIdx = 0;
this.prevBuf = Buffer.alloc(0);

// Static data
this.decodeTables = codec.decodeTables;
this.decodeTableSeq = codec.decodeTableSeq;
this.defaultCharUnicode = codec.defaultCharUnicode;
this.gb18030 = codec.gb18030;

}

DBCSDecoder.prototype.write = function(buf) {

var newBuf = Buffer.alloc(buf.length*2),
    nodeIdx = this.nodeIdx, 
    prevBuf = this.prevBuf, prevBufOffset = this.prevBuf.length,
    seqStart = -this.prevBuf.length, // idx of the start of current parsed sequence.
    uCode;

if (prevBufOffset > 0) // Make prev buf overlap a little to make it easier to slice later.
    prevBuf = Buffer.concat([prevBuf, buf.slice(0, 10)]);

for (var i = 0, j = 0; i < buf.length; i++) {
    var curByte = (i >= 0) ? buf[i] : prevBuf[i + prevBufOffset];

    // Lookup in current trie node.
    var uCode = this.decodeTables[nodeIdx][curByte];

    if (uCode >= 0) { 
        // Normal character, just use it.
    }
    else if (uCode === UNASSIGNED) { // Unknown char.
        // TODO: Callback with seq.
        //var curSeq = (seqStart >= 0) ? buf.slice(seqStart, i+1) : prevBuf.slice(seqStart + prevBufOffset, i+1 + prevBufOffset);
        i = seqStart; // Try to parse again, after skipping first byte of the sequence ('i' will be incremented by 'for' cycle).
        uCode = this.defaultCharUnicode.charCodeAt(0);
    }
    else if (uCode === GB18030_CODE) {
        var curSeq = (seqStart >= 0) ? buf.slice(seqStart, i+1) : prevBuf.slice(seqStart + prevBufOffset, i+1 + prevBufOffset);
        var ptr = (curSeq[0]-0x81)*12600 + (curSeq[1]-0x30)*1260 + (curSeq[2]-0x81)*10 + (curSeq[3]-0x30);
        var idx = findIdx(this.gb18030.gbChars, ptr);
        uCode = this.gb18030.uChars[idx] + ptr - this.gb18030.gbChars[idx];
    }
    else if (uCode <= NODE_START) { // Go to next trie node.
        nodeIdx = NODE_START - uCode;
        continue;
    }
    else if (uCode <= SEQ_START) { // Output a sequence of chars.
        var seq = this.decodeTableSeq[SEQ_START - uCode];
        for (var k = 0; k < seq.length - 1; k++) {
            uCode = seq[k];
            newBuf[j++] = uCode & 0xFF;
            newBuf[j++] = uCode >> 8;
        }
        uCode = seq[seq.length-1];
    }
    else
        throw new Error("iconv-lite internal error: invalid decoding table value " + uCode + " at " + nodeIdx + "/" + curByte);

    // Write the character to buffer, handling higher planes using surrogate pair.
    if (uCode > 0xFFFF) { 
        uCode -= 0x10000;
        var uCodeLead = 0xD800 + Math.floor(uCode / 0x400);
        newBuf[j++] = uCodeLead & 0xFF;
        newBuf[j++] = uCodeLead >> 8;

        uCode = 0xDC00 + uCode % 0x400;
    }
    newBuf[j++] = uCode & 0xFF;
    newBuf[j++] = uCode >> 8;

    // Reset trie node.
    nodeIdx = 0; seqStart = i+1;
}

this.nodeIdx = nodeIdx;
this.prevBuf = (seqStart >= 0) ? buf.slice(seqStart) : prevBuf.slice(seqStart + prevBufOffset);
return newBuf.slice(0, j).toString('ucs2');

}

DBCSDecoder.prototype.end = function() {

var ret = '';

// Try to parse all remaining chars.
while (this.prevBuf.length > 0) {
    // Skip 1 character in the buffer.
    ret += this.defaultCharUnicode;
    var buf = this.prevBuf.slice(1);

    // Parse remaining as usual.
    this.prevBuf = Buffer.alloc(0);
    this.nodeIdx = 0;
    if (buf.length > 0)
        ret += this.write(buf);
}

this.nodeIdx = 0;
return ret;

}

// Binary search for GB18030. Returns largest i such that table <= val. function findIdx(table, val) {

if (table[0] > val)
    return -1;

var l = 0, r = table.length;
while (l < r-1) { // always table[l] <= val < table[r]
    var mid = l + Math.floor((r-l+1)/2);
    if (table[mid] <= val)
        l = mid;
    else
        r = mid;
}
return l;

}