package main

import "mxl-player/internal/playback"

// videoDropTracker counts gaps only within one playback generation. Frame
// indices belong to their source and cannot be compared across feed changes.
type videoDropTracker struct {
	generation uint64
	source     playback.FeedConfig
	lastIndex  uint64
	hasIndex   bool
}

func (t *videoDropTracker) Observe(
	generation uint64,
	source playback.FeedConfig,
	index uint64,
) uint64 {
	if !t.hasIndex ||
		generation != t.generation ||
		!sameVideoSource(source, t.source) ||
		index <= t.lastIndex {
		t.generation = generation
		t.source = source
		t.lastIndex = index
		t.hasIndex = true
		return 0
	}

	dropped := index - t.lastIndex - 1
	t.lastIndex = index
	return dropped
}

func sameVideoSource(a, b playback.FeedConfig) bool {
	return a.Domain == b.Domain && a.UUID == b.UUID
}