const { logMemory, num2hex } = require('./logging.js');
const {
  INITIAL_IP_ADDRESS,
  DISPLAY_ADDR,
  POINTER_TO_DISPLAY,
} = require('./machine.config.js');

// 1 = verbose
// 2 = what i'm currently focusing on
// 3 = always print
// 4 = silent
const DEBUG_LEVEL = 2;
let DEBUG; // Turn debugging on/off -- set by assemble()

/**
 * @param {string} assemblyCode
 * @param {Boolean} [debug = false]
 **/
exports.assemble = (assemblyCode, debug = false) => {
  DEBUG = debug;
  return decodeInstructions(assemblyCode);
}

// Configure pseudo-ops:
const ASM_IP_LABEL = '*';
const ASM_CONSTANT_PREFIX = '#';
const ASM_LABEL_PREFIX = '@';

const mnemonicsWithOptionalArgs = ['end', 'nop'];
const mnemonics2opcodes = {
  end: { direct: 0, indirect: 0 },
  sto: { direct: 1, indirect: 2 },
  lda: { direct: 3, indirect: 4 },
  add: { direct: 5, indirect: 6 },
  sub: { direct: 7, indirect: 8 },
  hop: { direct: 9, indirect: 10 },
  jmp: { direct: 11, indirect: 12 },
  ftg: { direct: 13, indirect: 13 },
  fhp: { direct: 14, indirect: 14 },
  nop: { direct: 15, indirect: 15 },
};


/**
 * @typedef {('code'|'comment'|'blank')} SourceLineType
 **/

/**
 * @typedef {Object} SourceLineInfo
 * @property {number} number - line number
 * @property {string} source - source text
 * @property {string} sanitized - source text, with comments and whitespace removed
 * @property {SourceLineType} type - line type
 * @property {string} [operation] - For code: the first non-whitespace chunk
 * @property {string} [argument] - For code: the second non-whitespace chunk, if there is one
 * @property {string} [extraArgument] - For code: the third non-whitespace chunk, if there is one
 **/

/**
 * @param {string} source
 * @returns {Array<SourceLineInfo>}
 **/
function preparseSourceCode(source) {
  let lines = source.split(/\n/); // returns an array of lines

  const isLineBlank = (l) => { return l.length === 0 ? true : false };
  const isLineComment = (l) => { return stripWhitespaceFromEnds(l).startsWith(';') };

  /**
   * @param {string} l
   * @returns {SourceLineType}
   **/
  const getLineType = (l) => {
    if (isLineBlank(l)) return 'blank';
    if (isLineComment(l)) return 'comment';
    return 'code';
  }

  return lines.map((line, index) => {
    dbg(1, `  in: ${line}`);
    let info = {
      number: index + 1,
      source: line,
      sanitized: stripWhitespaceFromEnds(stripComments(line)),
      type: getLineType(line),
    };
    dbg(1, `    → ${info.number} - ${info.type}: ${info.sanitized}`);
    dbg(1, ``);

    if (info.type === 'code') {
      const op_arg_array = info.sanitized.split(/\s+/); // split line into an array of [op, arg, extra_arg]
      if (op_arg_array[0] !== 'undefined') {
        info.operation = op_arg_array[0];
      }
      if (op_arg_array.length === 2) {
        info.argument = op_arg_array[1];
      }
      if (op_arg_array.length === 3) {
        info.argument = op_arg_array[1];
        info.extraArgument = op_arg_array[2];
      }
      // If there's too many arguments, throw an error
      // NB. there's a special case:
      // lines with the ASM_IP_LABEL can take an extra argument
      let maxArgs = 2;
      if (op_arg_array.length > 2 && op_arg_array[1].startsWith(ASM_IP_LABEL)) {
        maxArgs = 3;
      }
      if (op_arg_array.length > maxArgs) {
        console.error();
        console.error(`Error: Too many arguments`);
        console.error(` at line ${info.number}`);
        process.exit();
      }
    }
    return info;
  });
}



/**
 * @param {string} arg
 * @returns {number}
 **/
function decodeNumericOp(arg) {
  if (arg.startsWith("$")) return hex2num(arg.replace("$", ""));
  return parseInt(arg);
}


/**
 * @param {string} op
 * @param {object} labels // TODO document better
 * @param {number} IP
 * @returns {Array<string>} - array of labels
 **/
function handleLabelDefinition(op, IP, labels) {
  let label = op.substring(1); // strip label prefix

  if (label in labels) {
    labels[label].pointsToByte = IP;
  } else {
    labels[label] = {
      pointsToByte: IP,
      bytesToReplace: [],
    };
  }
  dbg(1, `  Label definition:`);
  dbg(1, `    Points to byte: ${labels[label].pointsToByte}`);
  dbg(1, `    Bytes to replace: ${labels[label].bytesToReplace}`);
  dbg(1, `    IP: $${num2hex(IP)}, new code: none`);
  dbgGroupEnd(1, 'Input line');
  return labels;
}

/**
 * @param {string} op
 * @param {string} arg
 * @param {number} IP
 * @returns {Array<string>} - array of constants
 **/
function handleConstantDefinitions(op, arg, IP, constants) {
  let constantName = op.substring(1); // strip '>'
  let constantValue = arg;
  if (constantValue === ASM_IP_LABEL) {
    constantValue = IP.toString();
  }
  constants[constantName] = constantValue;
  dbg(1, '');
  dbg(1, `Constants:`);
  dbg(1, constants);
  dbg(1, '');
  return constants;
}


/**
 * Assemble source code.
 * 
 * If the source doesn't explicitly set an address to assemble to,
 * it will be assembled to the default intial value of the IP,
 * as specified in `machine.config.js`.
 * @param {string} source - Assembly source to decode
 * @return {{ debugInfo: Object, machineCode: Uint8Array }};
 **/
function decodeInstructions(source) {
  dbg(1, 'Pre-parsing...');
  let lines = preparseSourceCode(source);
  dbg(1, '');
  dbg(1, 'Done pre-parsing.');
  dbg(1, '');
  dbg(1, 'Assembling...');

  // Figure out where to start assembly...

  /** @type {number} IP - Destination addr for the next line **/
  let IP;

  // Check if the source code explicitly sets an address to assemble at
  // by including a `* [addr]` as the first (non-blank, non-comment) line
  let idOfFirstLineWithCode = lines.findIndex((el) => el.type === 'code');
  if (lines[idOfFirstLineWithCode].operation.startsWith(ASM_IP_LABEL)) {
    IP = parseInt(lines[idOfFirstLineWithCode].argument);
  } else {
    IP = INITIAL_IP_ADDRESS;
  }

  // Initialize arrays to collect assembled code

  /** @type {Array<number>} - Assembled source code, as an array of bytes **/
  let machineCode = new Array(IP).fill(0);
  
  let debugInfo = {};

  // Initialize memory-mapped IO -- TODO this should probably be in the CPU, not here
  machineCode[POINTER_TO_DISPLAY] = DISPLAY_ADDR;

  // Initialize arrays that collect code references that
  // have to be revisited after our first pass through the source
  let labels = {};
  let constants = {};


  // Decode line by line...
  for (let i = 0; i < lines.length; i++) {
    let line = lines[i];
    // dbg(2, `line info:`);
    // dbg(2, line);
    if (line.type === 'code') {
      const op = line.operation;

      if (typeof line.argument === 'undefined') {
        // If this isn't a label definition,
        // or one of the ops with optional arguments,
        //  then it's an error
        if (!line.operation.startsWith('@')) {
          if (mnemonicsWithOptionalArgs.indexOf(line.operation.toLowerCase()) < 0) {
            console.error('');
            console.error(`Error: Missing operand ${line.source}`);
            console.error(`  at line ${line.number}`);
            process.exit();
          } else {
            // It *is* one of the special optional-arg ops
            // So let's fill in the implicit operand with $00
            line.argument = '0';
          }
        }
      }


      // *** Decode special operations ***

      // Opcodes - Handle label definitions
      if (op.startsWith(ASM_LABEL_PREFIX)) {
        labels = handleLabelDefinition(op, IP, labels);
        continue;
      }

      // Opcodes - Handle constant definitions
      if (op.startsWith(ASM_CONSTANT_PREFIX)) {
        constants = handleConstantDefinitions(op, line.argument, IP, constants);
        continue;
      }

      // Opcodes - Handle setting value of IP
      if (op.startsWith(ASM_IP_LABEL)) {
        IP = parseInt(line.argument);
        continue;
      }

      // *** Decode regular operations ***

      /** @type {number|null} decodedOp **/
      let decodedOp = null;

      /** @type {number|null} decodedArg **/
      let decodedArg = null;

      /** @typedef {'direct'|'indirect'} AddressingMode **/
      let addressingMode = 'direct';

      // Now that it can't be a label or a constant, normalize the opcode
      line.operation = line.operation.toLowerCase();

      // Operands - Handle references to labels
      if (line.argument.startsWith(ASM_LABEL_PREFIX)) {
        let label = line.argument.substring(1); // strip label prefix
        if (label in labels) {
          dbg(1, `'${label}' already in labels object`);
          labels[label].bytesToReplace.push(IP + 1);
        } else {
          dbg(1, `'${label}' NOT in labels object`);
          labels[label] = {
            bytesToReplace: [IP + 1],
          };
        }
        dbg(1, `Label reference:`);
        dbg(1, `  Points to byte: ${labels[label].pointsToByte}`);
        dbg(1, `  Bytes to replace: ${labels[label].bytesToReplace}`);
        decodedArg = 0; // Return 0 for operand for now -- we'll replace it later
      }
      
      // Operands - Handle references to the Instruction Pointer
      if (line.argument === ASM_IP_LABEL) {
        dbg(1, `  References current IP - ${IP}`);
        if (typeof line.extraArgument === 'undefined') {
          decodedArg = IP;
        } else {
          decodedArg = IP + decodeNumericOp(line.extraArgument);
        }
      }

      // Operands - Handle references to constants
      if (line.argument.startsWith(ASM_CONSTANT_PREFIX)) {
        dbg(1, `References '${line.argument}'`);
        if (typeof constants[line.argument.substring(1)] === 'undefined') {
          console.error();
          console.error(`Error: Undefined constant '${line.argument}'`);
          console.error(`  at line ${line.number}`);
          process.exit();
        }
        decodedArg = decodeNumericOp(constants[line.argument.substring(1)]); // substring(1) strips '>'
      }

      // Operands - Handle references to constants in indirect mode
      if (line.argument.startsWith(`(${ASM_CONSTANT_PREFIX}`)) {
        addressingMode = "indirect";
        dbg(1, `(Indirectly) References '${line.argument}'`);
        let constName = line.argument.replace(`(${ASM_CONSTANT_PREFIX}`, "");
        constName = constName.replace(")", "");
        decodedArg = decodeNumericOp(constants[constName]);
      }

      // Operands - Handle indirect expressions
      if (decodedArg === null && line.argument.startsWith("(")) {
        addressingMode = "indirect";
        let indyTemp = line.argument.replace("(", "").replace(")", "");
        decodedArg = decodeNumericOp(indyTemp);
      }

      // Decode regular opcodes
      if (decodedOp === null) {
        decodedOp = mnemonics2opcodes[line.operation][addressingMode];
      }

      // Decode regular operands
      if (decodedArg === null) {
        decodedArg = decodeNumericOp(line.argument);
      }

      machineCode[IP] = decodedOp;
      machineCode[IP + 1] = decodedArg;

      debugInfo[IP] = {
        lineNumber: line.number,
        source: line.source,
        address: IP,
        machine: [decodedOp, decodedArg]
      };


      dbg(3, ``);
      dbg(3, `Line ${line.number}: ${line.source}`);
      if (line.argument) {
        dbg(3, `  Asm operation: ${line.operation.toUpperCase()} ${line.argument}`);
      } else if (line.operation) {
        dbg(3, `  Asm operation: ${line.operation.toUpperCase()}`);
      }

      dbg(3, `  Machine code:  $${num2hex(decodedOp)} $${num2hex(decodedArg)}`);
      dbg(3, `  IP: $${num2hex(IP)}`);
      IP += 2;
    };
  }

  dbg(1, '');
  dbgGroup(1, 'Memory before filling in label constants');
  dbgExec(1, () => logMemory(new Uint8Array(machineCode)));
  dbgGroupEnd(1);

  // Backfill label references
  for (let k of Object.keys(labels)) {
    dbgGroup(1, `${ASM_LABEL_PREFIX}${k}`);
    let label = labels[k];
    dbg(1, `Points to byte: ${label.pointsToByte}`);
    dbg(1, `Bytes to replace: ${label.bytesToReplace}`);
    dbgGroupEnd(1);
    for (let j = 0; j < label.bytesToReplace.length; j++) {
      machineCode[label.bytesToReplace[j]] = label.pointsToByte;
    }
  }

  return { 'debugInfo': debugInfo, 'machineCode': new Uint8Array(machineCode) };
}


/**
 * @param {string} line
 * @returns {string}
 **/
function stripComments(line) {
  return line.replace(/;.+/,"");
}

/**
 * @param {string} line
 * @returns {string}
 **/
function stripWhitespaceFromEnds(line) {
  line = line.replace(/^\s+/,"");
  line = line.replace(/\s+$/,"");
  return line;
}

function hex2num(hex) { return parseInt(hex, 16) };

// Debug helpers
const dbg = (lvl, s) => { if (DEBUG && (lvl >= DEBUG_LEVEL)) console.log(s) };
const dbgGroup = (lvl, s) => { if (DEBUG && (lvl >= DEBUG_LEVEL)) console.group(s) };
const dbgGroupEnd = (lvl, s) => { if (DEBUG && (lvl >= DEBUG_LEVEL)) console.groupEnd() };
const dbgExec = (lvl, func) => { if (DEBUG && (lvl >= DEBUG_LEVEL)) func(); }