const DEFAULT_COMIC_ART_ASPECT_RATIO = 16 / 9
const MIN_COMIC_ART_ASPECT_RATIO = 1.4
const MAX_COMIC_ART_ASPECT_RATIO = 3

function normalizeComicArtAspectRatio(page) {
  const requested = Number(page && page.artAspectRatio)
  if (
    Number.isFinite(requested)
    && requested >= MIN_COMIC_ART_ASPECT_RATIO
    && requested <= MAX_COMIC_ART_ASPECT_RATIO
  ) {
    return requested
  }
  return DEFAULT_COMIC_ART_ASPECT_RATIO
}

function getComicArtStageStyle(metrics, page) {
  const safeMetrics = metrics || {}
  const contentWidth = Math.max(
    1,
    Number(safeMetrics.windowWidth || 1)
      - Number(safeMetrics.safeLeft || 0)
      - Number(safeMetrics.safeRight || 0),
  )
  const contentHeight = Math.max(
    1,
    Number(safeMetrics.windowHeight || 1)
      - Number(safeMetrics.topbarHeight || 0)
      - Number(safeMetrics.safeBottom || 0),
  )
  const aspectRatio = normalizeComicArtAspectRatio(page)

  if (safeMetrics.compactHeight) {
    // A phone in landscape does not have enough height for a 16:9 picture
    // plus an elder-readable caption below it. Compact pages therefore open
    // like a two-page lianhuanhua spread: illustration on the left, caption
    // paper on the right. Keep these numbers in lockstep with chapter.wxss.
    const captionWidth = Math.max(190, contentWidth * 0.28)
    const artColumnWidth = Math.max(1, contentWidth - captionWidth)
    const artColumnPadding = 12
    const availableWidth = Math.max(1, artColumnWidth - artColumnPadding)
    const availableHeight = Math.max(1, contentHeight - artColumnPadding)
    const artWidth = Math.max(
      1,
      Math.min(availableWidth, availableHeight * aspectRatio),
    )
    const artHeight = artWidth / aspectRatio
    return [
      `width:${Math.round(artWidth)}px`,
      `height:${Math.round(artHeight)}px`,
    ].join(';')
  }

  // Keep this in lockstep with chapter.wxss:
  // regular: minmax(0, 3fr) minmax(190px, 1fr)
  // When the caption track reaches its minimum, the art receives the
  // remainder. Calculating that exact height prevents max-height from
  // compressing only the stage height and stretching a 16:9 illustration.
  const proportionalArtHeight = contentHeight * 0.75
  const captionMinimum = 190
  const artRowHeight = Math.max(
    1,
    Math.min(
      proportionalArtHeight,
      contentHeight - captionMinimum,
    ),
  )
  const artWidth = Math.max(
    1,
    Math.min(contentWidth, artRowHeight * aspectRatio),
  )
  const artHeight = artWidth / aspectRatio
  return [
    `width:${Math.round(artWidth)}px`,
    `height:${Math.round(artHeight)}px`,
  ].join(';')
}

module.exports = {
  DEFAULT_COMIC_ART_ASPECT_RATIO,
  normalizeComicArtAspectRatio,
  getComicArtStageStyle,
}