import {
  MAX_SIZE_32
} from "./allocator";

import {
  String
} from "../string";

/** Size of a String header. */
export const HEADER_SIZE = (offsetof<String>() + 1) & ~1; // 2 byte aligned

/** Maximum length of a String. */
export const MAX_LENGTH = (<i32>MAX_SIZE_32 - HEADER_SIZE) >>> 1;

/** Singleton empty String. */
export const EMPTY = changetype<String>(""); // TODO: is this a bad idea with '===' in place?

/** Allocates a raw String with uninitialized contents. */
export function allocate(length: i32): String {
  assert(length > 0 && length <= MAX_LENGTH);
  var buffer = allocate_memory(HEADER_SIZE + (<usize>length << 1));
  store<i32>(buffer, length);
  return changetype<String>(buffer);
}

export function isWhiteSpaceOrLineTerminator(c: u16): bool {
  switch (c) {
    case 10:      // <LF>
    case 13:      // <CR>
    case 8232:    // <LS>
    case 8233:    // <PS>
    case 9:       // <TAB>
    case 11:      // <VT>
    case 12:      // <FF>
    case 32:      // <SP>
    case 160:     // <NBSP>
    case 65279: { // <ZWNBSP>
      return true;
    }
    default: return false;
  }
}

export const enum CharCode {
  PLUS = 0x2B,
  MINUS = 0x2D,
  DOT = 0x2E,
  _0 = 0x30,
  _1 = 0x31,
  _2 = 0x32,
  _3 = 0x33,
  _4 = 0x34,
  _5 = 0x35,
  _6 = 0x36,
  _7 = 0x37,
  _8 = 0x38,
  _9 = 0x39,
  A = 0x41,
  B = 0x42,
  E = 0x45,
  O = 0x4F,
  X = 0x58,
  Z = 0x5a,
  a = 0x61,
  b = 0x62,
  e = 0x65,
  o = 0x6F,
  x = 0x78,
  z = 0x7A
}

export function parse<T>(str: String, radix: i32 = 0): T {
  var len: i32 = str.length;
  if (!len) {
    return <T>NaN;
  }
  var ptr = changetype<usize>(str) /* + HEAD -> offset */;
  var code = <i32>load<u16>(ptr, HEADER_SIZE);

  // determine sign
  var sign: T;
  if (code == CharCode.MINUS) {
    if (!--len) {
      return <T>NaN;
    }
    code = <i32>load<u16>(ptr += 2, HEADER_SIZE);
    sign = -1;
  } else if (code == CharCode.PLUS) {
    if (!--len) {
      return <T>NaN;
    }
    code = <i32>load<u16>(ptr += 2, HEADER_SIZE);
    sign = 1;
  } else {
    sign = 1;
  }

  // determine radix
  if (!radix) {
    if (code == CharCode._0 && len > 2) {
      switch (<i32>load<u16>(ptr + 2, HEADER_SIZE)) {
        case CharCode.B:
        case CharCode.b: {
          ptr += 4; len -= 2;
          radix = 2;
          break;
        }
        case CharCode.O:
        case CharCode.o: {
          ptr += 4; len -= 2;
          radix = 8;
          break;
        }
        case CharCode.X:
        case CharCode.x: {
          ptr += 4; len -= 2;
          radix = 16;
          break;
        }
        default: {
          radix = 10;
        }
      }
    } else radix = 10;
  } else if (radix < 2 || radix > 36) {
    return <T>NaN;
  }

  // calculate value
  var num: T = 0;
  while (len--) {
    code = <i32>load<u16>(ptr, HEADER_SIZE);
    if (code >= CharCode._0 && code <= CharCode._9) {
      code -= CharCode._0;
    } else if (code >= CharCode.A && code <= CharCode.Z) {
      code -= CharCode.A - 10;
    } else if (code >= CharCode.a && code <= CharCode.z) {
      code -= CharCode.a - 10;
    } else {
      break;
    }
    if (code >= radix) {
      break;
    }
    num = (num * radix) + code;
    ptr += 2;
  }
  return sign * num;
}