from typing import TypedDict

class LineData(TypedDict):
  line: str
  indent: str
  level: int
  offsetHead: int
  offsetTail: int

def createLineData(line: str = '', indent: str = ' ') -> LineData:
  return { "line": line, "indent": indent, "level": 0, "offsetHead": 0, "offsetTail": 0 }

def 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`)

  level = 0

  # Repeat previous level for blank lines.
  if len(lineData['line']) == 0:
    lineData['level'] = lineData['level']
    lineData['offsetHead'] = 0
    lineData['offsetTail'] = 0
  else:
    while level < len(lineData['line']) and lineData['line'][level] == lineData['indent'] and level <= lineData['level'] + 1:
      level += 1
    lineData['level'] = level
    lineData['offsetHead'] = level
    lineData['offsetTail'] = level

    while lineData['offsetTail'] < len(lineData['line']) and lineData['line'][lineData['offsetTail']] != ' ':
      lineData['offsetTail'] += 1

  return lineData