package moreser

// NormalizePage 规范化分页参数，限制单次请求数量避免大分页拖垮 MongoDB。
func NormalizePage(pageNum, pageSize, defaultPageSize, maxPageSize int64) (int64, int64) {
	if pageNum <= 0 {
		pageNum = 1
	}
	if pageSize <= 0 {
		pageSize = defaultPageSize
	}
	if pageSize > maxPageSize {
		pageSize = maxPageSize
	}
	return pageNum, pageSize
}

// InsertedAdsCount 计算实际可穿插的广告数量，每 interval 条内容后插入 1 条广告。
func InsertedAdsCount(contentTotal, adsTotal, interval int64) int64 {
	if contentTotal <= 0 || adsTotal <= 0 || interval <= 0 {
		return 0
	}
	insertSlots := contentTotal / interval
	if insertSlots > adsTotal {
		return adsTotal
	}
	return insertSlots
}

// ContentPosition 计算内容原始下标在混排列表中的全局位置。
func ContentPosition(contentIndex, adsTotal, interval int64) int64 {
	if interval <= 0 {
		return contentIndex
	}
	adsBefore := contentIndex / interval
	if adsBefore > adsTotal {
		adsBefore = adsTotal
	}
	return contentIndex + adsBefore
}

// FirstContentIndexAtOrAfter 找到指定混排位置之后第一条内容下标。
func FirstContentIndexAtOrAfter(pos, contentTotal, adsTotal, interval int64) int64 {
	left, right := int64(0), contentTotal
	for left < right {
		mid := left + (right-left)/2
		if ContentPosition(mid, adsTotal, interval) < pos {
			left = mid + 1
			continue
		}
		right = mid
	}
	return left
}

// ContentRange 计算当前混排分页需要读取的内容下标范围。
func ContentRange(start, end, contentTotal, adsTotal, interval int64) (int64, int64) {
	contentStart := FirstContentIndexAtOrAfter(start, contentTotal, adsTotal, interval)
	contentEnd := FirstContentIndexAtOrAfter(end, contentTotal, adsTotal, interval)
	if contentStart >= contentEnd {
		return 0, 0
	}
	return contentStart, contentEnd - contentStart
}

// ContentRangeWithoutTotal 计算当前混排分页需要读取的内容范围，不依赖内容总数。
// 适用于列表接口不返回 totalCount 的场景；广告位仍按“每 interval 条内容后插入 1 条广告”计算。
func ContentRangeWithoutTotal(start, end, adsTotal, interval int64) (int64, int64) {
	if start < 0 || end <= start {
		return 0, 0
	}
	contentStart := contentIndexAtMixedPosition(start, adsTotal, interval)
	contentEnd := contentIndexAtMixedPosition(end, adsTotal, interval)
	if contentStart >= contentEnd {
		return 0, 0
	}
	return contentStart, contentEnd - contentStart
}

// ContentIndexAtPositionWithoutTotal 计算混排位置对应的内容下标，不判断该位置是否为广告。
func ContentIndexAtPositionWithoutTotal(pos, adsTotal, interval int64) int64 {
	return contentIndexAtMixedPosition(pos, adsTotal, interval)
}

// AdIndexAtPositionWithoutTotal 计算混排位置对应的广告下标，返回 -1 表示该位置不是广告。
func AdIndexAtPositionWithoutTotal(pos, adsTotal, interval int64) int64 {
	if adsTotal <= 0 || interval <= 0 || pos < 0 {
		return -1
	}
	cycle := interval + 1
	if pos >= adsTotal*cycle {
		return -1
	}
	if pos%cycle != interval {
		return -1
	}
	return pos / cycle
}

// contentIndexAtMixedPosition 返回混排位置之前已经出现的内容数量。
func contentIndexAtMixedPosition(pos, adsTotal, interval int64) int64 {
	if pos <= 0 {
		return 0
	}
	if adsTotal <= 0 || interval <= 0 {
		return pos
	}
	adCycle := interval + 1
	adAreaSize := adsTotal * adCycle
	if pos >= adAreaSize {
		return pos - adsTotal
	}
	fullCycles := pos / adCycle
	remain := pos % adCycle
	return fullCycles*interval + minInt64(remain, interval)
}

func minInt64(a, b int64) int64 {
	if a < b {
		return a
	}
	return b
}

// AdIndexAtPosition 计算混排位置对应的广告下标，返回 -1 表示该位置不是广告。
func AdIndexAtPosition(pos, contentTotal, adsTotal, interval int64) int64 {
	if interval <= 0 {
		return -1
	}
	nextContent := FirstContentIndexAtOrAfter(pos+1, contentTotal, adsTotal, interval)
	prevContent := nextContent - 1
	if prevContent >= 0 && (prevContent+1)%interval == 0 && (prevContent+1)/interval-1 < adsTotal {
		if ContentPosition(prevContent, adsTotal, interval)+1 == pos {
			return (prevContent+1)/interval - 1
		}
	}
	return -1
}