const PACK = {
    u8(value) {
        return new Uint8Array([ value & 0xFF ]);
    },
    u16(value) {
        return new Uint8Array([ (value >> 8) & 0xFF, value & 0xFF ]);
    },
    u32(value) {
        return new Uint8Array([
            (value >> 24) & 0xFF,
            (value >> 16) & 0xFF,
            (value >> 8) & 0xFF,
            value & 0xFF
        ]);
    },
};

const UNPACK = {
    u8(data, index) {
        let result = 0;
        if(index + 1 <= data.length) {
            result = data[index];
            index += 1;
        }
        return { data: result, index: index };
    },
    u16(data, index) {
        let result = 0;
        if(index + 2 <= data.length) {
            result = (data[index] << 8) + data[index + 1];
            index += 2;
        }
        return { data: result, index: index };
    },
    u32(data, index) {
        let result = 0;
        if(index + 4 <= data.length) {
            result = (data[index] << 24)
                + (data[index + 1] << 16)
                + (data[index + 1] << 8)
                + data[index + 1];
            index += 4;
        }
        return { data: result, index: index };
    },
    string(data, index) {
        let result = UNPACK.u16(data, index);
        index = result.index;
        let length = result.data;

        let dec = new TextDecoder();

        let result_str = "";
        if(index + length <= data.length) {
            let bytes = new Uint8Array(length);
            for(let i = 0; i < length; ++i) {
                bytes[i] = data[index + i];
            }
            index += length;

            result_str = dec.decode(bytes);
        }

        return { data: result_str, index: index };
    },
    move(bytes) {
        function piece_by_id(id) {
            switch(id) {
                case 0: return "";
                case 1: return "M";
                case 2: return "N";
                case 3: return "L";
                case 4: return "T";
                case 5: return "C";
                case 6: return "D";
                case 7: return "K";
            }
        }

        /*
        ** From  [6]
        ** To    [6]
        ** Piece [3]
        ** Take  [3]
        ** 
        */

        let from = (bytes[0] & 0xFC) >> 2;
        let to = ((bytes[0] & 0x03) << 4) | ((bytes[1] & 0xC0) >> 6);
        let piece = piece_by_id((bytes[1] & 0x38) >> 3);
        let take = piece_by_id(bytes[1] & 0x07);
        let source = (bytes[2] & 0x80) >> 7;
        switch((bytes[2] & 0x60) >> 5) {
            case 0: state = "";
            case 1: state = "◇"; break;
            case 2: state = "◈"; break;
            case 3: state = "◆"; break;
        }

        let str = "";
        if(state.length > 0) {
            if(source == 1) {
                str = "" + piece + " " + state + " " + to;
            } else {
                str = "" + from + " " + piece + " " + state + " " + to + " " + take;
            }
            if(take != "") { str += " " + take; }
        }
        return str;
    }
};

const BITWISE = {
    lsb(x) {
        return x & -x;
    },

    ffs(x) {
        return 31 - Math.clz32(x & -x);
    },

    count(mask) {
    // source: https://graphics.stanford.edu/~seander/bithacks.html
        mask = mask|0;
        mask = mask - ((mask >> 1) & 0x55555555);
        mask = (mask & 0x33333333) + ((mask >> 2) & 0x33333333);
        return ((mask + (mask >> 4) & 0xF0F0F0F) * 0x1010101) >> 24;
    }
};

const MATH = {
    sign(a)
    {
        return 1 - ((a < 0) << 1);
    },

    mod(a, b)
    {
        return ((a % b) + b) % b
    },
};