import { stringToBase256 } from '../../common/typecast';

export default class TokenStream {
  buffer: string;
  index: number;

  constructor(buffer: string) {
    this.buffer = buffer;
    this.index = 0;
  }

  read() {
    let buffer = this.buffer;
    let length = buffer.length;
    let inComment = false;
    let inString = false;
    let inIdString = false;
    let token = '';

    while (this.index < length) {
      let c = buffer[this.index++];

      if (inComment) {
        if (c === '\n') {
          inComment = false;
          this.index--;
        }
      } else if (inString) {
        if (c === '\\') {
          token += c + buffer[this.index++];
        } else if (c === '\n') {
          token += '\\n';
        } else if (c === '\r') {
          token += '\\r';
        } else {
          token += c;
        }

        if (c === '"') {
          return token;
        }
      } else if (inIdString) {
        token += c;

        if (c === "'") {
          return token;
        }
      } else if (c === ' ' || c === '\t') {
        if (token.length) {
          return token;
        }
      } else if (c === '(' || c === ')' || c === '[' || c === ']' || c === '=' || c === '\r' || c === '\n' || c === ',' || c === '!' || c === '-' || c === '<' || c === '>' || c === '+' || c === '*' || c === '/') {
        if (token.length) {
          this.index--;
          return token;
        } else {
          let c2 = buffer[this.index];

          if (c === '=' && c2 === '=') {
            this.index++;
            return '==';
          } else if (c === '\r') {
            if (c2 === '\n') {
              this.index++;
            }

            return '\n';
          } else if (c === '!' && c2 === '=') {
            this.index++;
            return '!=';
          } else if (c === '/' && c2 === '/') {
            if (token.length) {
              this.index--;
              return token;
            } else {
              inComment = true;
            }
          } else {
            return c;
          }
        }
      } else if (c === '"') {
        if (token.length) {
          this.index--;
          return token;
        } else {
          token += c;
          inString = true;
        }
      } else if (c === "'") {
        if (token.length) {
          this.index--;
          return token;
        } else {
          token += c;
          inIdString = true;
        }
      } else {
        token += c;
      }

      if (this.index === length) {
        return token;
      }
    }
  }

  /**
   * Reads the next token without advancing the stream.
   */
  peek() {
    let index = this.index;
    let value = this.read();

    this.index = index;

    return value;
  }

  readSafe() {
    let token = this.read();

    if (token === undefined) {
      throw new Error('Premature end of stream reached');
    }

    if (token === 'null') {
      return 'nil';
    } else if (token === '!=') {
      return '~=';
    } else if (token[0] === "'") {
      return `${stringToBase256(token.slice(1, token.indexOf("'", 1)))}`;
    } else if (token === 'break' || token === 'do' || token === 'end' || token === 'for' || token === 'goto' || token === 'in' || token === 'nil' || token === 'repeat' || token === 'until' || token === 'while') { // Lua reserved keywords
      return token + '_';
    } else if (token === 'and' || token === 'or') {
      return ' ' + token + ' ';
    } else if (token[0] === '$') {
      return '0x' + token.slice(1);
    }

    return token;
  }

  readUntil(delimiter: string) {
    let tokens = '';
    let token;

    while ((token = this.readSafe()) !== delimiter) {
      tokens += token;
    }

    return tokens;
  }
}