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

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

export function parseLine(lineData: LineData): LineData {
  if ((typeof lineData !== 'object' || !lineData) || typeof lineData.level !== 'number') throw new Error(`'lineData' must be an object with string line and numeric level 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 level = 0

  // Repeat previous level for blank lines.
  if (!lineData.line.length) {
    lineData.level = lineData.level
    lineData.offsetHead = 0
    lineData.offsetTail = 0
  } else {
    while (lineData.line[level] === lineData.indent && level <= lineData.level + 1) ++level
    lineData.level = level
    lineData.offsetHead = level
    lineData.offsetTail = level

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

  return lineData
}