Function analyzeFillableSpaceGap

src/ink/screen.ts:770–831

(
  screen: Screen,
  y: number,
  startX: number,
  endX: number,
  currentStyleId: number,
  currentHyperlink: Hyperlink,
  defaultStyleId: number,
)

 * stats or materializing Cells.
 */
export function analyzeFillableSpaceGap(
  screen: Screen,
  y: number,
  startX: number,
  endX: number,
  currentStyleId: number,
  currentHyperlink: Hyperlink,
  defaultStyleId: number,
): FillableSpaceGapAnalysis {
  if (currentHyperlink !== undefined) {
    return { fillableCells: 0, blocker: 'active-hyperlink' }
  }

  if (endX <= startX || y < 0 || y >= screen.height) {
    return { fillableCells: 0, blocker: 'invalid-range' }
  }

  const rowContentEnd = screen.contentEnd[y] ?? 0
  if (rowContentEnd <= startX) {
    return { fillableCells: 0, blocker: 'content-end' }
  }

  const gapEnd = Math.min(endX, rowContentEnd)
  if (gapEnd <= startX) {
    return { fillableCells: 0, blocker: 'content-end' }
  }

  let fillableCells = 0
  for (let x = startX; x < gapEnd; x += 1) {
    const ci = (y * screen.width + x) << 1
    const charId = screen.cells[ci]!
    if (charId !== 0) {
      return { fillableCells, blocker: 'non-space-char' }
    }

    const word1 = screen.cells[ci + 1]!
    if ((word1 & 0x3fffc) !== 0) {
      return { fillableCells, blocker: 'space-metadata' }
    }

    const fgStyle = word1 >>> STYLE_SHIFT
    if (fgStyle === 0) {
      if (currentStyleId !== defaultStyleId) {
        return { fillableCells, blocker: 'default-style-mismatch' }
      }
      fillableCells += 1
      continue
    }

    if (fgStyle !== currentStyleId) {
      return { fillableCells, blocker: 'fg-style-mismatch' }
    }

    fillableCells += 1
  }

  if (gapEnd < endX) {
    return { fillableCells, blocker: 'content-end' }