/*
 * P2PFaaS - A framework for FaaS Load Balancing
 * Copyright (c) 2019 - 2022. Gabriele Proietti Mattia <pm.gabriele@outlook.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

// Package hashtable creates a ValueHashtable data structure for the Item type
package hashtable

import (
	"fmt"
	"sync"

	"github.com/cheekybits/genny/generic"
)

// Key the key of the dictionary
type Key generic.Type

// Value the content of the dictionary
type Value generic.Type

// ValueHashtable the set of Items
type ValueHashtable struct {
	items map[int]Value
	lock  sync.RWMutex
}

// the hash() private function uses the famous Horner's method
// to generate a hash of a string with O(n) complexity
func hash(k Key) int {
	key := fmt.Sprintf("%s", k)
	h := 0
	for i := 0; i < len(key); i++ {
		h = 31*h + int(key[i])
	}
	return h
}

// Put item with value v and key k into the hashtable
func (ht *ValueHashtable) Put(k Key, v Value) {
	ht.lock.Lock()
	defer ht.lock.Unlock()
	i := hash(k)
	if ht.items == nil {
		ht.items = make(map[int]Value)
	}
	ht.items[i] = v
}

// Remove item with key k from hashtable
func (ht *ValueHashtable) Remove(k Key) {
	ht.lock.Lock()
	defer ht.lock.Unlock()
	i := hash(k)
	delete(ht.items, i)
}

// Get item with key k from the hashtable
func (ht *ValueHashtable) Get(k Key) Value {
	ht.lock.RLock()
	defer ht.lock.RUnlock()
	i := hash(k)
	return ht.items[i]
}

// Size returns the number of the hashtable elements
func (ht *ValueHashtable) Size() int {
	ht.lock.RLock()
	defer ht.lock.RUnlock()
	return len(ht.items)
}