/// Parses a component with its coordinates.
func parseComponent<T: Collection>(_ bytes: T, _ start: Int, _ end: Int) -> Component?
where T.Element == UInt8, T.Index == Int {
  guard let (label, parenthesisIndex) = extractComponentLabel(bytes, start, end) else {
    return nil
  }

  guard
    let (coordinates, endIndex) = parseCoordinates(
      bytes, parenthesisIndex + 1, end)
  else {
    return nil
  }

  let shape = extractComponentShape(bytes, endIndex, end)

  return Component(label: label, coordinates: coordinates, shape: shape)
}

/// Looks for a component label by taking the string before the first open
/// parenthesis.
@inline(__always)
private func extractComponentLabel<T: Collection>(_ bytes: T, _ start: Int, _ end: Int) -> (
  String, Int
)?
where T.Element == UInt8, T.Index == Int {
  var index = start
  while index < end {
    if bytes[index] == kOpenParenthesis {
      guard index > start else { return nil }
      guard let label = extractTrimmedString(bytes, start, index) else { return nil }
      return (label, index)
    }
    index += 1
  }
  return nil
}

/// Extracts a shape by looking for a shape label in square brackets.
/// If missing, incomplete or invalid, it returns a circle
@inline(__always)
private func extractComponentShape<T: Collection>(_ bytes: T, _ start: Int, _ end: Int) -> Shape
where T.Element == UInt8, T.Index == Int {
  var index = skipWhitespace(bytes, end, start)

  guard index < end && bytes[index] == kOpenSquareBracket else { return .circle }

  index += 1
  let shapeStart = index
  while index < end && bytes[index] != kCloseSquareBracket { index += 1 }

  guard index > shapeStart && index < end else { return .circle }

  let shapeName = bytes[shapeStart..<index]
  return parseShapeFromBytes(shapeName)
}

/// Given the contents of a shape label, return the right type.
@inline(__always)
private func parseShapeFromBytes<T: Collection>(_ shapeName: T) -> Shape
where T.Element == UInt8, T.Index == Int {
  var trimStart = shapeName.startIndex
  var trimEnd = shapeName.endIndex

  trimStart = skipWhitespace(shapeName, trimEnd, trimStart)
  trimEnd = shaveWhitespace(shapeName, trimStart, trimEnd)

  let trimmedName = shapeName[trimStart..<trimEnd]

  // "x"
  if matchesKeyword(trimmedName, [120]) { return .xMark }
  // "square"
  if matchesKeyword(trimmedName, [115, 113, 117, 97, 114, 101]) { return .square }
  // "triangle"
  if matchesKeyword(trimmedName, [116, 114, 105, 97, 110, 103, 108, 101]) { return .triangle }

  return .circle
}