export default function ApplesoftCompiler(mem)
{
    var _mem = mem;

    var LOMEM = 0x69;
    var ARRAY_START = 0x6B;
    var ARRAY_END = 0x6D;
    var PROGRAM_START = 0x801;

    var TOKENS = {
        'END': 0x80,
        'FOR': 0x81,
        'NEXT': 0x82,
        'DATA': 0x83,
        'INPUT': 0x84,
        'DEL': 0x85,
        'DIM': 0x86,
        'READ': 0x87,
        'GR': 0x88,
        'TEXT': 0x89,
        'PR#': 0x8a,
        'IN#': 0x8b,
        'CALL': 0x8c,
        'PLOT': 0x8d,
        'HLIN': 0x8e,
        'VLIN': 0x8f,
        'HGR2': 0x90,
        'HGR': 0x91,
        'HCOLOR=': 0x92,
        'HPLOT': 0x93,
        'DRAW': 0x94,
        'XDRAW': 0x95,
        'HTAB': 0x96,
        'HOME': 0x97,
        'ROT=': 0x98,
        'SCALE=': 0x99,
        'SHLOAD': 0x9a,
        'TRACE': 0x9b,
        'NOTRACE': 0x9c,
        'NORMAL': 0x9d,
        'INVERSE': 0x9e,
        'FLASH': 0x9f,
        'COLOR=': 0xa0,
        'POP=': 0xa1,
        'VTAB': 0xa2,
        'HIMEM:': 0xa3,
        'LOMEM:': 0xa4,
        'ONERR': 0xa5,
        'RESUME': 0xa6,
        'RECALL': 0xa7,
        'STORE': 0xa8,
        'SPEED=': 0xa9,
        'LET': 0xaa,
        'GOTO': 0xab,
        'RUN': 0xac,
        'IF': 0xad,
        'RESTORE': 0xae,
        '&': 0xaf,
        'GOSUB': 0xb0,
        'RETURN': 0xb1,
        'REM': 0xb2,
        'STOP': 0xb3,
        'ON': 0xb4,
        'WAIT': 0xb5,
        'LOAD': 0xb6,
        'SAVE': 0xb7,
        'DEF': 0xb8,
        'POKE': 0xb9,
        'PRINT': 0xba,
        'CONT': 0xbb,
        'LIST': 0xbc,
        'CLEAR': 0xbd,
        'GET': 0xbe,
        'NEW': 0xbf,
        'TAB(': 0xc0,
        'TO': 0xc1,
        'FN': 0xc2,
        'SPC(': 0xc3,
        'THEN': 0xc4,
        'AT': 0xc5,
        'NOT': 0xc6,
        'STEP': 0xc7,
        '+': 0xc8,
        '-': 0xc9,
        '*': 0xca,
        '/': 0xcb,
        '^': 0xcc,
        'AND': 0xcd,
        'OR': 0xce,
        '>': 0xcf,
        '=': 0xd0,
        '<': 0xd1,
        'SGN': 0xd2,
        'INT': 0xd3,
        'ABS': 0xd4,
        'USR': 0xd5,
        'FRE': 0xd6,
        'SCRN(': 0xd7,
        'PDL': 0xd8,
        'POS': 0xd9,
        'SQR': 0xda,
        'RND': 0xdb,
        'LOG': 0xdc,
        'EXP': 0xdd,
        'COS': 0xde,
        'SIN': 0xdf,
        'TAN': 0xe0,
        'ATN': 0xe1,
        'PEEK': 0xe2,
        'LEN': 0xe3,
        'STR$': 0xe4,
        'VAL': 0xe5,
        'ASC': 0xe6,
        'CHR$': 0xe7,
        'LEFT$': 0xe8,
        'RIGHT$': 0xe9,
        'MID$': 0xea
    };

    var STATES = {
        NORMAL: 0,
        STRING: 1,
        COMMENT: 2,
        DATA: 3
    };

    function writeByte(addr, val) {
        var page = addr >> 8,
            off = addr & 0xff;

        return _mem.write(page, off, val);
    }

    function writeWord(addr, val) {
        var lsb = val & 0xff;
        var msb = val >> 8;

        writeByte(addr, lsb);
        writeByte(addr + 1, msb);
    }

    return {
        compile: function(program) {
            var lineNos = {};

            function compileLine(line, offset) {
                if (!line) {
                    return [];
                }

                var state = STATES.NORMAL;
                var result = [0, 0, 0, 0];
                var curChar = 0;
                var character;
                var lineNoStr = '';

                while (line.length) {
                    character = line.charAt(curChar);
                    if (/\d/.test(character)) {
                        lineNoStr += character;
                        curChar++;
                    } else {
                        break;
                    }
                }

                while (curChar < line.length) {
                    character = line.charAt(curChar).toUpperCase();
                    switch (state) {
                    case STATES.NORMAL:
                        if (character !== ' ') {
                            if (character === '"') {
                                result.push(character.charCodeAt(0));
                                state = STATES.STRING;
                                curChar++;
                            } else {
                                var foundToken = '';
                                for (var possibleToken in TOKENS) {
                                    if (possibleToken.charAt(0) == character) {
                                        var tokenIdx = curChar + 1;
                                        var idx = 1;
                                        while (idx < possibleToken.length) {
                                            if (line.charAt(tokenIdx) !== ' ') {
                                                if (line.charAt(tokenIdx).toUpperCase() !== possibleToken.charAt(idx)) {
                                                    break;
                                                }
                                                idx++;
                                            }
                                            tokenIdx++;
                                        }
                                        if (idx === possibleToken.length) {
                                            // Found a token
                                            if (possibleToken === 'AT') {
                                                var lookAhead = line.charAt(tokenIdx + 1).toUpperCase();
                                                // ATN takes precedence over AT
                                                if (lookAhead === 'N') {
                                                    foundToken = 'ATN';
                                                    tokenIdx++;
                                                }
                                                // TO takes precedence over AT
                                                if (lookAhead === 'O') {
                                                    result.push(lookAhead.charCodeAt(0));
                                                    foundToken = 'TO';
                                                    tokenIdx++;                                                    foundToken = 'TO';
                                                }
                                            }
                                            foundToken = possibleToken;
                                        }
                                    }
                                    if (foundToken) {
                                        break;
                                    }
                                }
                                if (foundToken) {
                                    result.push(TOKENS[foundToken]);
                                    curChar = tokenIdx;
                                    if (foundToken === 'REM') {
                                        state = STATES.COMMENT;
                                    }
                                } else {
                                    result.push(character.charCodeAt(0));
                                    curChar++;
                                }
                            }
                        } else {
                            curChar++;
                        }
                        break;
                    case STATES.COMMENT:
                        result.push(character.charCodeAt(0));
                        curChar++;
                        break;
                    case STATES.STRING:
                        result.push(character.charCodeAt(0));
                        if (character == '"') {
                            state = STATES.NORMAL;
                        }
                        curChar++;
                        break;
                    }
                }

                if (lineNoStr.length) {
                    var lineNo = parseInt(lineNoStr, 10);
                    if (lineNo < 0 || lineNo > 65535) {
                        throw new Error('Line number out of range');
                    }
                    if (lineNos[lineNoStr]) {
                        throw new Error('Duplicate line number');
                    }
                    lineNos[lineNoStr] = result;

                    // Next line pointer
                    result.push(0);
                    var nextLine = offset + result.length;
                    result[0] = nextLine & 0xff;
                    result[1] = nextLine >> 8;

                    // Line number
                    result[2] = lineNo & 0xff;
                    result[3] = lineNo >> 8;
                } else {
                    throw new Error('Missing line number');
                }

                return result;
            }

            var compiled = [];
            var lines = program.split(/[\r\n]+/g);

            while (lines.length) {
                var line = lines.shift();
                var compiledLine = compileLine(line, PROGRAM_START + compiled.length);
                compiled = compiled.concat(compiledLine);
            }
            compiled.push(0, 0);

            for (var idx = 0; idx < compiled.length; idx++) {
                writeByte(PROGRAM_START + idx, compiled[idx]);
            }
            writeWord(LOMEM, PROGRAM_START + compiled.length);
            writeWord(ARRAY_START, PROGRAM_START + compiled.length);
            writeWord(ARRAY_END, PROGRAM_START + compiled.length);
        }
    };
}