import { countColumn } from "./misc"

// STRING STREAM

// Fed to the mode parsers, provides helper functions to make
// parsers more succinct.

class StringStream {
  constructor(string, tabSize, lineOracle) {
    this.pos = this.start = 0
    this.string = string
    this.tabSize = tabSize || 8
    this.lastColumnPos = this.lastColumnValue = 0
    this.lineStart = 0
    this.lineOracle = lineOracle
  }

  eol() {return this.pos >= this.string.length}
  sol() {return this.pos == this.lineStart}
  peek() {return this.string.charAt(this.pos) || undefined}
  next() {
    if (this.pos < this.string.length)
      return this.string.charAt(this.pos++)
  }
  eat(match) {
    let ch = this.string.charAt(this.pos)
    let ok
    if (typeof match == "string") ok = ch == match
    else ok = ch && (match.test ? match.test(ch) : match(ch))
    if (ok) {++this.pos; return ch}
  }
  eatWhile(match) {
    let start = this.pos
    while (this.eat(match)){}
    return this.pos > start
  }
  eatSpace() {
    let start = this.pos
    while (/[\s\u00a0]/.test(this.string.charAt(this.pos))) ++this.pos
    return this.pos > start
  }
  skipToEnd() {this.pos = this.string.length}
  skipTo(ch) {
    let found = this.string.indexOf(ch, this.pos)
    if (found > -1) {this.pos = found; return true}
  }
  backUp(n) {this.pos -= n}
  column() {
    if (this.lastColumnPos < this.start) {
      this.lastColumnValue = countColumn(this.string, this.start, this.tabSize, this.lastColumnPos, this.lastColumnValue)
      this.lastColumnPos = this.start
    }
    return this.lastColumnValue - (this.lineStart ? countColumn(this.string, this.lineStart, this.tabSize) : 0)
  }
  indentation() {
    return countColumn(this.string, null, this.tabSize) -
      (this.lineStart ? countColumn(this.string, this.lineStart, this.tabSize) : 0)
  }
  match(pattern, consume, caseInsensitive) {
    if (typeof pattern == "string") {
      let cased = str => caseInsensitive ? str.toLowerCase() : str
      let substr = this.string.substr(this.pos, pattern.length)
      if (cased(substr) == cased(pattern)) {
        if (consume !== false) this.pos += pattern.length
        return true
      }
    } else {
      let match = this.string.slice(this.pos).match(pattern)
      if (match && match.index > 0) return null
      if (match && consume !== false) this.pos += match[0].length
      return match
    }
  }
  current(){return this.string.slice(this.start, this.pos)}
  hideFirstChars(n, inner) {
    this.lineStart += n
    try { return inner() }
    finally { this.lineStart -= n }
  }
  lookAhead(n) {
    let oracle = this.lineOracle
    return oracle && oracle.lookAhead(n)
  }
}

export default StringStream
