// Package bimap provides a threadsafe bidirectional map
package bimap

import "sync"

// BiMap is a bi-directional hashmap that is thread safe and supports immutability
type BiMap struct {
	s         sync.RWMutex
	immutable bool
	forward   map[interface{}]interface{}
	inverse   map[interface{}]interface{}
}

// NewBiMap returns a an empty, mutable, biMap
func NewBiMap() *BiMap {
	return &BiMap{forward: make(map[interface{}]interface{}), inverse: make(map[interface{}]interface{}), immutable: false}
}

// Insert puts a key and value into the BiMap, provided its mutable. Also creates the reverse mapping from value to key.
func (b *BiMap) Insert(k interface{}, v interface{}) {
	b.s.RLock()
	if b.immutable {
		panic("Cannot modify immutable map")
	}
	b.s.RUnlock()

	b.s.Lock()
	defer b.s.Unlock()
	b.forward[k] = v
	b.inverse[v] = k
}

// Exists checks whether or not a key exists in the BiMap
func (b *BiMap) Exists(k interface{}) bool {
	b.s.RLock()
	defer b.s.RUnlock()
	_, ok := b.forward[k]
	return ok
}

// ExistsInverse checks whether or not a value exists in the BiMap
func (b *BiMap) ExistsInverse(k interface{}) bool {
	b.s.RLock()
	defer b.s.RUnlock()

	_, ok := b.inverse[k]
	return ok
}

// Get returns the value for a given key in the BiMap and whether or not the element was present.
func (b *BiMap) Get(k interface{}) (interface{}, bool) {
	if !b.Exists(k) {
		return "", false
	}
	b.s.RLock()
	defer b.s.RUnlock()
	return b.forward[k], true

}

// GetInverse returns the key for a given value in the BiMap and whether or not the element was present.
func (b *BiMap) GetInverse(v interface{}) (interface{}, bool) {
	if !b.ExistsInverse(v) {
		return "", false
	}
	b.s.RLock()
	defer b.s.RUnlock()
	return b.inverse[v], true

}

// Delete removes a key-value pair from the BiMap for a given key. Returns if the key doesn't exist
func (b *BiMap) Delete(k interface{}) {
	b.s.RLock()
	if b.immutable {
		panic("Cannot modify immutable map")
	}
	b.s.RUnlock()

	if !b.Exists(k) {
		return
	}
	val, _ := b.Get(k)
	b.s.Lock()
	defer b.s.Unlock()
	delete(b.forward, k)
	delete(b.inverse, val)
}

// DeleteInverse emoves a key-value pair from the BiMap for a given value. Returns if the value doesn't exist
func (b *BiMap) DeleteInverse(v interface{}) {
	b.s.RLock()
	if b.immutable {
		panic("Cannot modify immutable map")
	}
	b.s.RUnlock()

	if !b.ExistsInverse(v) {
		return
	}

	key, _ := b.GetInverse(v)
	b.s.Lock()
	defer b.s.Unlock()
	delete(b.inverse, v)
	delete(b.forward, key)

}

// Size returns the number of elements in the bimap
func (b *BiMap) Size() int {
	b.s.RLock()
	defer b.s.RUnlock()
	return len(b.forward)
}

// MakeImmutable freezes the BiMap preventing any further write actions from taking place
func (b *BiMap) MakeImmutable() {
	b.s.Lock()
	defer b.s.Unlock()
	b.immutable = true
}

// GetInverseMap returns a regular go map mapping from the BiMap's values to its keys
func (b *BiMap) GetInverseMap() map[interface{}]interface{} {
	return b.inverse
}

// GetForwardMap returns a regular go map mapping from the BiMap's keys to its values
func (b *BiMap) GetForwardMap() map[interface{}]interface{} {
	return b.forward
}

// Lock manually locks the BiMap's mutex
func (b *BiMap) Lock() {
	b.s.Lock()
}

// Unlock manually unlocks the BiMap's mutex
func (b *BiMap) Unlock() {
	b.s.Unlock()
}