import invariant from 'tiny-invariant'

// given an array of items sorted by `comparator`, insert an item into its sort index and constrain the size to
// `maxSize` by removing the last item
export function sortedInsert<T>(items: T[], add: T, maxSize: number, comparator: (a: T, b: T) => number): T | null {
  invariant(maxSize > 0, 'MAX_SIZE_ZERO')
  // this is an invariant because the interface cannot return multiple removed items if items.length exceeds maxSize
  invariant(items.length <= maxSize, 'ITEMS_SIZE')

  // short circuit first item add
  if (items.length === 0) {
    items.push(add)
    return null
  } else {
    const isFull = items.length === maxSize
    // short circuit if full and the additional item does not come before the last item
    if (isFull && comparator(items[items.length - 1], add) <= 0) {
      return add
    }

    let lo = 0,
      hi = items.length

    while (lo < hi) {
      const mid = (lo + hi) >>> 1
      if (comparator(items[mid], add) <= 0) {
        lo = mid + 1
      } else {
        hi = mid
      }
    }
    items.splice(lo, 0, add)
    return isFull ? items.pop()! : null
  }
}