package link.roadio.riff.userstate

/** Immutable indexed records retain their backing snapshot and only a bounded decoded working set. */
class BoundedReadList<T>(
    override val size: Int,
    private val read: (Int) -> T,
) : AbstractList<T>(),
    java.util.RandomAccess {
    init {
        require(size >= 0)
    }

    private val cache =
        object : LinkedHashMap<Int, T>(128, 0.75f, true) {
            override fun removeEldestEntry(eldest: MutableMap.MutableEntry<Int, T>): Boolean = size > 128
        }

    @Synchronized
    override fun get(index: Int): T {
        if (index !in indices) throw IndexOutOfBoundsException("Record $index outside $size")
        return cache.getOrPut(index) { read(index) }
    }
}