import Token from './Token'
import GherkinLine from './GherkinLine'
import { messages } from 'cucumber-messages'

/**
 * The scanner reads a gherkin doc (typically read from a .feature file) and creates a token for each line.
 * The tokens are passed to the parser, which outputs an AST (Abstract Syntax Tree).
 *
 * If the scanner sees a `#` language header, it will reconfigure itself dynamically to look for
 * Gherkin keywords for the associated language. The keywords are defined in gherkin-languages.json.
 */
export default class TokenScanner {
  private lineNumber = 0
  private lines: string[]

  constructor(source: string) {
    this.lines = source.split(/\r?\n/)
    if (
      this.lines.length > 0 &&
      this.lines[this.lines.length - 1].trim() === ''
    ) {
      this.lines.pop()
    }
  }

  public read() {
    const line = this.lines[this.lineNumber++]
    const location = messages.Location.fromObject({
      line: this.lineNumber,
      column: 0,
    })
    return line == null
      ? new Token(null, location)
      : new Token(new GherkinLine(line, this.lineNumber), location)
  }
}