enum LineType {
  BLANK,
  NORMAL,
}

export type LineData = {
  line: string;
  indent: string;
  type: number;
  level: number;
  offsetHead: number;
  offsetTail: number;
}

export function createLineData(line: string = '', indent: string = ' '): LineData {
  return { line, indent, type: 0, level: 0, offsetHead: 0, offsetTail: 0 }
}

export function parseLine(lineData: LineData): LineData {
  if ((typeof lineData !== 'object' || !lineData) || typeof lineData.type !== 'number' || typeof lineData.level !== 'number') throw new Error(`'lineData' must be an object with 'line' string, and 'type' and 'level' integer properties`)
  if (typeof lineData.indent !== 'string' || lineData.indent.length === 0 || lineData.indent.length > 1) throw new Error(`'lineData.indent' must be a single-character string`)
  if (typeof lineData.line !== 'string') throw new Error(`'lineData.line' must be a string`)

  let type = LineType.BLANK
  let level = 0

  if (!lineData.line.length) {
    // TODO: Not sure if this is necessary. If the previous line was a normal line, it makes the blank line a child of the normal line.
    // If the previous line was a blank line, the blank line retains the same level.
    if (lineData.type === LineType.NORMAL) level = lineData.level + 1
    if (lineData.type === LineType.BLANK) level = lineData.level

    lineData.type = type
    lineData.level = level
    lineData.offsetHead = 0
    lineData.offsetTail = 0
  } else {
    type = LineType.NORMAL

    while (lineData.line[level] === lineData.indent && level <= lineData.level + 1) ++level
    lineData.type = type
    lineData.level = level
    lineData.offsetHead = level
    lineData.offsetTail = level

    while (lineData.line[lineData.offsetTail] && lineData.line[lineData.offsetTail] !== ' ') ++lineData.offsetTail
  }

  return lineData
}