// Copyright (C) 2017 Marius Schellenberger

package filter

import (
	"math/rand"
	"sync"
)

// QueryCache can be used to cache queries
type QueryCache struct {
	// protects m
	sync.RWMutex

	m   map[string]Query
	max int
}

// NewQueryCache returns a new QueryCache
func NewQueryCache(max int) *QueryCache {
	return &QueryCache{
		m:   make(map[string]Query),
		max: max,
	}
}

// NewQuery looks for the given query in the cache and returns it.
// If the query is not found it will be generated and inserted in the cache..
func (qc *QueryCache) NewQuery(s string) (q *Query, err error) {
	q = qc.Lookup(s)
	if q != nil {
		return
	}
	q, err = NewQuery(s)
	if err != nil {
		return
	}
	qc.Lock()
	defer qc.Unlock()
	if len(qc.m) == qc.max {
		qc.clean()
	}
	qc.m[s] = *q
	return
}

// Lookup looks for a given query string and returns the query object or nil.
func (qc *QueryCache) Lookup(s string) *Query {
	qc.RLock()
	defer qc.RUnlock()
	if q, ok := qc.m[s]; ok {
		return &q
	}
	return nil
}

func (qc *QueryCache) clean() {
	i := rand.Intn(len(qc.m))
	var k string
	for k = range qc.m {
		if i == 0 {
			break
		}
		i--
	}
	delete(qc.m, k)
}