export type Span = 2 | 3 | 4 | 6

/**
 * Column spans (out of 6) for `count` projects, so that every row is exactly full whatever the count:
 * rows of two or three, a feature row first, and never a lone project in the last row (a single project
 * spans the whole width). Two-project rows alternate 4+2 and 2+4 for rhythm.
 */
export function planSpans(count: number): Span[] {
  if (count <= 0) return []
  if (count === 1) return [6]

  const sizes: number[] = []
  const pattern = [2, 3, 3]
  let remaining = count
  for (let i = 0; remaining > 0; i++) {
    const size = Math.min(pattern[i % pattern.length], remaining)
    sizes.push(size)
    remaining -= size
  }

  const last = sizes.length - 1
  if (sizes[last] === 1) {
    if (sizes[last - 1] === 3) {
      sizes[last - 1] = 2
      sizes[last] = 2
    } else {
      sizes[last - 1] = 3
      sizes.pop()
    }
  }

  const spans: Span[] = []
  let pairs = 0
  for (const size of sizes) {
    if (size === 3) spans.push(2, 2, 2)
    else spans.push(...(pairs++ % 2 === 0 ? ([4, 2] as const) : ([2, 4] as const)))
  }
  return spans
}