js/core/lzstring.js

// Copyright (c) 2013 Pieroxy <pieroxy@pieroxy.net>
// This work is free. You can redistribute it and/or modify it
// under the terms of the WTFPL, Version 2
// For more information see LICENSE.txt or http://www.wtfpl.net/
//
// For more information, the home page:
// http://pieroxy.net/blog/pages/lz-string/testing.html
//
// LZ-based compression algorithm, version 1.4.4

const fromCharCode = String.fromCharCode;
const hasOwnProperty = Object.prototype.hasOwnProperty;

const keyStrUriSafe = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+-$";
const baseReverseDic = {};

function getBaseValue(alphabet, character) {
    if (!baseReverseDic[alphabet]) {
        baseReverseDic[alphabet] = {};
        for (let i = 0; i < alphabet.length; i++) {
            baseReverseDic[alphabet][alphabet.charAt(i)] = i;
        }
    }
    return baseReverseDic[alphabet][character];
}

//compress into uint8array (UCS-2 big endian format)
export function compressU8(uncompressed) {
    let compressed = compress(uncompressed);
    let buf = new Uint8Array(compressed.length * 2); // 2 bytes per character

    for (let i = 0, TotalLen = compressed.length; i < TotalLen; i++) {
        let current_value = compressed.charCodeAt(i);
        buf[i * 2] = current_value >>> 8;
        buf[i * 2 + 1] = current_value % 256;
    }
    return buf;
}

// Compreses with header
/**
 * @param {string} uncompressed
 * @param {number} header
 */
export function compressU8WHeader(uncompressed, header) {
    let compressed = compress(uncompressed);
    let buf = new Uint8Array(2 + compressed.length * 2); // 2 bytes per character

    buf[0] = header >>> 8;
    buf[1] = header % 256;
    for (let i = 0, TotalLen = compressed.length; i < TotalLen; i++) {
        let current_value = compressed.charCodeAt(i);
        buf[2 + i * 2] = current_value >>> 8;
        buf[2 + i * 2 + 1] = current_value % 256;
    }
    return buf;
}

//decompress from uint8array (UCS-2 big endian format)
/**
 *
 * @param {Uint8Array} compressed
 */
export function decompressU8WHeader(compressed) {
    // let buf = new Array(compressed.length / 2); // 2 bytes per character
    // for (let i = 0, TotalLen = buf.length; i < TotalLen; i++) {
    //     buf[i] = compressed[i * 2] * 256 + compressed[i * 2 + 1];
    // }

    // let result = [];
    // buf.forEach(function (c) {
    //     result.push(fromCharCode(c));
    // });
    let result = [];
    for (let i = 2, n = compressed.length; i < n; i += 2) {
        const code = compressed[i] * 256 + compressed[i + 1];
        result.push(fromCharCode(code));
    }
    return decompress(result.join(""));
}

//compress into a string that is already URI encoded
export function compressX64(input) {
    if (input == null) return "";
    return _compress(input, 6, function (a) {
        return keyStrUriSafe.charAt(a);
    });
}

//decompress from an output of compressToEncodedURIComponent
export function decompressX64(input) {
    if (input == null) return "";
    if (input == "") return null;
    input = input.replace(/ /g, "+");
    return _decompress(input.length, 32, function (index) {
        return getBaseValue(keyStrUriSafe, input.charAt(index));
    });
}

function compress(uncompressed) {
    return _compress(uncompressed, 16, function (a) {
        return fromCharCode(a);
    });
}

function _compress(uncompressed, bitsPerChar, getCharFromInt) {
    if (uncompressed == null) return "";
    let i,
        value,
        context_dictionary = {},
        context_dictionaryToCreate = {},
        context_c = "",
        context_wc = "",
        context_w = "",
        context_enlargeIn = 2, // Compensate for the first entry which should not count
        context_dictSize = 3,
        context_numBits = 2,
        context_data = [],
        context_data_val = 0,
        context_data_position = 0,
        ii;

    for (ii = 0; ii < uncompressed.length; ii += 1) {
        context_c = uncompressed.charAt(ii);
        if (!hasOwnProperty.call(context_dictionary, context_c)) {
            context_dictionary[context_c] = context_dictSize++;
            context_dictionaryToCreate[context_c] = true;
        }

        context_wc = context_w + context_c;
        if (hasOwnProperty.call(context_dictionary, context_wc)) {
            context_w = context_wc;
        } else {
            if (hasOwnProperty.call(context_dictionaryToCreate, context_w)) {
                if (context_w.charCodeAt(0) < 256) {
                    for (i = 0; i < context_numBits; i++) {
                        context_data_val = context_data_val << 1;
                        if (context_data_position == bitsPerChar - 1) {
                            context_data_position = 0;
                            context_data.push(getCharFromInt(context_data_val));
                            context_data_val = 0;
                        } else {
                            context_data_position++;
                        }
                    }
                    value = context_w.charCodeAt(0);
                    for (i = 0; i < 8; i++) {
                        context_data_val = (context_data_val << 1) | (value & 1);
                        if (context_data_position == bitsPerChar - 1) {
                            context_data_position = 0;
                            context_data.push(getCharFromInt(context_data_val));
                            context_data_val = 0;
                        } else {
                            context_data_position++;
                        }
                        value = value >> 1;
                    }
                } else {
                    value = 1;
                    for (i = 0; i < context_numBits; i++) {
                        context_data_val = (context_data_val << 1) | value;
                        if (context_data_position == bitsPerChar - 1) {
                            context_data_position = 0;
                            context_data.push(getCharFromInt(context_data_val));
                            context_data_val = 0;
                        } else {
                            context_data_position++;
                        }
                        value = 0;
                    }
                    value = context_w.charCodeAt(0);
                    for (i = 0; i < 16; i++) {
                        context_data_val = (context_data_val << 1) | (value & 1);
                        if (context_data_position == bitsPerChar - 1) {
                            context_data_position = 0;
                            context_data.push(getCharFromInt(context_data_val));
                            context_data_val = 0;
                        } else {
                            context_data_position++;
                        }
                        value = value >> 1;
                    }
                }
                context_enlargeIn--;
                if (context_enlargeIn == 0) {
                    context_enlargeIn = Math.pow(2, context_numBits);
                    context_numBits++;
                }
                delete context_dictionaryToCreate[context_w];
            } else {
                value = context_dictionary[context_w];
                for (i = 0; i < context_numBits; i++) {
                    context_data_val = (context_data_val << 1) | (value & 1);
                    if (context_data_position == bitsPerChar - 1) {
                        context_data_position = 0;
                        context_data.push(getCharFromInt(context_data_val));
                        context_data_val = 0;
                    } else {
                        context_data_position++;
                    }
                    value = value >> 1;
                }
            }
            context_enlargeIn--;
            if (context_enlargeIn == 0) {
                context_enlargeIn = Math.pow(2, context_numBits);
                context_numBits++;
            }
            // Add wc to the dictionary.
            context_dictionary[context_wc] = context_dictSize++;
            context_w = String(context_c);
        }
    }

    // Output the code for w.
    if (context_w !== "") {
        if (hasOwnProperty.call(context_dictionaryToCreate, context_w)) {
            if (context_w.charCodeAt(0) < 256) {
                for (i = 0; i < context_numBits; i++) {
                    context_data_val = context_data_val << 1;
                    if (context_data_position == bitsPerChar - 1) {
                        context_data_position = 0;
                        context_data.push(getCharFromInt(context_data_val));
                        context_data_val = 0;
                    } else {
                        context_data_position++;
                    }
                }
                value = context_w.charCodeAt(0);
                for (i = 0; i < 8; i++) {
                    context_data_val = (context_data_val << 1) | (value & 1);
                    if (context_data_position == bitsPerChar - 1) {
                        context_data_position = 0;
                        context_data.push(getCharFromInt(context_data_val));
                        context_data_val = 0;
                    } else {
                        context_data_position++;
                    }
                    value = value >> 1;
                }
            } else {
                value = 1;
                for (i = 0; i < context_numBits; i++) {
                    context_data_val = (context_data_val << 1) | value;
                    if (context_data_position == bitsPerChar - 1) {
                        context_data_position = 0;
                        context_data.push(getCharFromInt(context_data_val));
                        context_data_val = 0;
                    } else {
                        context_data_position++;
                    }
                    value = 0;
                }
                value = context_w.charCodeAt(0);
                for (i = 0; i < 16; i++) {
                    context_data_val = (context_data_val << 1) | (value & 1);
                    if (context_data_position == bitsPerChar - 1) {
                        context_data_position = 0;
                        context_data.push(getCharFromInt(context_data_val));
                        context_data_val = 0;
                    } else {
                        context_data_position++;
                    }
                    value = value >> 1;
                }
            }
            context_enlargeIn--;
            if (context_enlargeIn == 0) {
                context_enlargeIn = Math.pow(2, context_numBits);
                context_numBits++;
            }
            delete context_dictionaryToCreate[context_w];
        } else {
            value = context_dictionary[context_w];
            for (i = 0; i < context_numBits; i++) {
                context_data_val = (context_data_val << 1) | (value & 1);
                if (context_data_position == bitsPerChar - 1) {
                    context_data_position = 0;
                    context_data.push(getCharFromInt(context_data_val));
                    context_data_val = 0;
                } else {
                    context_data_position++;
                }
                value = value >> 1;
            }
        }
        context_enlargeIn--;
        if (context_enlargeIn == 0) {
            context_enlargeIn = Math.pow(2, context_numBits);
            context_numBits++;
        }
    }

    // Mark the end of the stream
    value = 2;
    for (i = 0; i < context_numBits; i++) {
        context_data_val = (context_data_val << 1) | (value & 1);
        if (context_data_position == bitsPerChar - 1) {
            context_data_position = 0;
            context_data.push(getCharFromInt(context_data_val));
            context_data_val = 0;
        } else {
            context_data_position++;
        }
        value = value >> 1;
    }

    // Flush the last char
    // eslint-disable-next-line no-constant-condition
    while (true) {
        context_data_val = context_data_val << 1;
        if (context_data_position == bitsPerChar - 1) {
            context_data.push(getCharFromInt(context_data_val));
            break;
        } else context_data_position++;
    }
    return context_data.join("");
}

function decompress(compressed) {
    if (compressed == null) return "";
    if (compressed == "") return null;
    return _decompress(compressed.length, 32768, function (index) {
        return compressed.charCodeAt(index);
    });
}

function _decompress(length, resetValue, getNextValue) {
    let dictionary = [],
        next,
        enlargeIn = 4,
        dictSize = 4,
        numBits = 3,
        entry = "",
        result = [],
        i,
        w,
        bits,
        resb,
        maxpower,
        power,
        c,
        data = { val: getNextValue(0), position: resetValue, index: 1 };

    for (i = 0; i < 3; i += 1) {
        dictionary[i] = i;
    }

    bits = 0;
    maxpower = Math.pow(2, 2);
    power = 1;
    while (power != maxpower) {
        resb = data.val & data.position;
        data.position >>= 1;
        if (data.position == 0) {
            data.position = resetValue;
            data.val = getNextValue(data.index++);
        }
        bits |= (resb > 0 ? 1 : 0) * power;
        power <<= 1;
    }

    switch ((next = bits)) {
        case 0:
            bits = 0;
            maxpower = Math.pow(2, 8);
            power = 1;
            while (power != maxpower) {
                resb = data.val & data.position;
                data.position >>= 1;
                if (data.position == 0) {
                    data.position = resetValue;
                    data.val = getNextValue(data.index++);
                }
                bits |= (resb > 0 ? 1 : 0) * power;
                power <<= 1;
            }
            c = fromCharCode(bits);
            break;
        case 1:
            bits = 0;
            maxpower = Math.pow(2, 16);
            power = 1;
            while (power != maxpower) {
                resb = data.val & data.position;
                data.position >>= 1;
                if (data.position == 0) {
                    data.position = resetValue;
                    data.val = getNextValue(data.index++);
                }
                bits |= (resb > 0 ? 1 : 0) * power;
                power <<= 1;
            }
            c = fromCharCode(bits);
            break;
        case 2:
            return "";
    }
    dictionary[3] = c;
    w = c;
    result.push(c);

    // eslint-disable-next-line no-constant-condition
    while (true) {
        if (data.index > length) {
            return "";
        }

        bits = 0;
        maxpower = Math.pow(2, numBits);
        power = 1;
        while (power != maxpower) {
            resb = data.val & data.position;
            data.position >>= 1;
            if (data.position == 0) {
                data.position = resetValue;
                data.val = getNextValue(data.index++);
            }
            bits |= (resb > 0 ? 1 : 0) * power;
            power <<= 1;
        }

        switch ((c = bits)) {
            case 0:
                bits = 0;
                maxpower = Math.pow(2, 8);
                power = 1;
                while (power != maxpower) {
                    resb = data.val & data.position;
                    data.position >>= 1;
                    if (data.position == 0) {
                        data.position = resetValue;
                        data.val = getNextValue(data.index++);
                    }
                    bits |= (resb > 0 ? 1 : 0) * power;
                    power <<= 1;
                }

                dictionary[dictSize++] = fromCharCode(bits);
                c = dictSize - 1;
                enlargeIn--;
                break;
            case 1:
                bits = 0;
                maxpower = Math.pow(2, 16);
                power = 1;
                while (power != maxpower) {
                    resb = data.val & data.position;
                    data.position >>= 1;
                    if (data.position == 0) {
                        data.position = resetValue;
                        data.val = getNextValue(data.index++);
                    }
                    bits |= (resb > 0 ? 1 : 0) * power;
                    power <<= 1;
                }
                dictionary[dictSize++] = fromCharCode(bits);
                c = dictSize - 1;
                enlargeIn--;
                break;
            case 2:
                return result.join("");
        }

        if (enlargeIn == 0) {
            enlargeIn = Math.pow(2, numBits);
            numBits++;
        }

        if (dictionary[c]) {
            // @ts-ignore
            entry = dictionary[c];
        } else {
            if (c === dictSize) {
                entry = w + w.charAt(0);
            } else {
                return null;
            }
        }
        result.push(entry);

        // Add w+entry[0] to the dictionary.
        dictionary[dictSize++] = w + entry.charAt(0);
        enlargeIn--;

        w = entry;

        if (enlargeIn == 0) {
            enlargeIn = Math.pow(2, numBits);
            numBits++;
        }
    }
}