package link.roadio.riff.player.playback

import link.roadio.riff.player.storage.PlaybackQueueOccurrence

/** Primitive index for a validated immutable queue; preserves zero and every signed occurrence ID. */
internal class QueueOccurrenceIndex(
    occurrences: List<PlaybackQueueOccurrence>,
) {
    private val capacity = Integer.highestOneBit(maxOf(2, Math.multiplyExact(occurrences.size, 2) - 1)) shl 1
    private val keys = LongArray(capacity)
    private val ordinals = IntArray(capacity) { -1 }

    init {
        occurrences.forEach { occurrence ->
            var slot = slot(occurrence.occurrenceId)
            while (ordinals[slot] != -1) {
                require(keys[slot] != occurrence.occurrenceId)
                slot = (slot + 1) and (capacity - 1)
            }
            keys[slot] = occurrence.occurrenceId
            ordinals[slot] = occurrence.ordinal
        }
    }

    private fun slot(key: Long): Int = java.lang.Long.hashCode(key) and (capacity - 1)

    operator fun get(key: Long): Int? {
        var slot = slot(key)
        while (ordinals[slot] != -1) {
            if (keys[slot] == key) return ordinals[slot]
            slot = (slot + 1) and (capacity - 1)
        }
        return null
    }
}