package cuckoo

import (
	"hash/maphash"
)

// A Hash function maps any data to a fixed-length value (in this case, a
// [uint64]).
//
// It is used by the [Table] to evenly distribute values
// amongst its slots. A good hash function is uniform, [chaotic], and
// deterministic. [Table] uses [NewDefaultHash] by default, which is built on
// [maphash.Comparable].
//
// [chaotic]: https://en.wikipedia.org/wiki/Avalanche_effect
type Hash[K any] = func(key K) (digest uint64)

// NewDefaultHash returns a new [Hash] which uses [maphash.Comparable].
//
// Each hash has a random seed, so calling this function again will return a new
// hash. Do not use this for testing.
func NewDefaultHash[K comparable]() Hash[K] {
	seed := maphash.MakeSeed()
	return func(key K) (digest uint64) {
		return maphash.Comparable(seed, key)
	}
}