package trakr

import (
	"fmt"
	"time"

	"github.com/jzelinskie/trakr/bittorrent"
	"github.com/jzelinskie/trakr/stopper"
)

// ErrResourceDoesNotExist is the error returned by all delete methods in the
// store if the requested resource does not exist.
var ErrResourceDoesNotExist = bittorrent.ClientError(errors.New("resource does not exist"))

// PeerStore is an interface that abstracts the interactions of storing and
// manipulating Peers such that it can be implemented for various data stores.
type PeerStore interface {
	// PutSeeder adds a Seeder to the Swarm identified by the provided infoHash.
	PutSeeder(infoHash bittorrent.InfoHash, p bittorrent.Peer) error

	// DeleteSeeder removes a Seeder from the Swarm identified by the provided
	// infoHash.
	//
	// If the Swarm or Peer does not exist, this function should return
	// ErrResourceDoesNotExist.
	DeleteSeeder(infoHash bittorrent.InfoHash, p bittorrent.Peer) error

	// PutLeecher adds a Leecher to the Swarm identified by the provided
	// infoHash.
	PutLeecher(infoHash bittorrent.InfoHash, p bittorrent.Peer) error

	// DeleteLeecher removes a Leecher from the Swarm identified by the provided
	// infoHash.
	//
	// If the Swarm or Peer does not exist, this function should return
	// ErrResourceDoesNotExist.
	DeleteLeecher(infoHash bittorrent.InfoHash, p bittorrent.Peer) error

	// GraduateLeecher promotes a Leecher to a Seeder in the Swarm identified by
	// the provided infoHash.
	//
	// If the given Peer is not present as a Leecher, add the Peer as a Seeder
	// and return no error.
	GraduateLeecher(infoHash bittorrent.InfoHash, p bittorrent.Peer) error

	// AnnouncePeers is a best effort attempt to return Peers from the Swarm
	// identified by the provided infoHash. The returned Peers are required to be
	// either all IPv4 or all IPv6.
	//
	// The returned Peers should strive be:
	// - as close to length equal to numWant as possible without going over
	// - all IPv4 or all IPv6 depending on the provided ipv6 boolean
	// - if seeder is true, should ideally return more leechers than seeders
	// - if seeder is false, should ideally return more seeders than leechers
	AnnouncePeers(infoHash bittorrent.InfoHash, seeder bool, numWant int, ipv6 bool) (peers []bittorrent.Peer, err error)

	// CollectGarbage deletes all Peers from the PeerStore which are older than
	// the cutoff time. This function must be able to execute while other methods
	// on this interface are being executed in parallel.
	CollectGarbage(cutoff time.Time) error

	// Stopper is an interface that expects a Stop method to stops the PeerStore.
	// For more details see the documentation in the stopper package.
	stopper.Stopper
}

// PeerStoreConstructor is a function used to create a new instance of a
// PeerStore.
type PeerStoreConstructor func(interface{}) (PeerStore, error)

var peerStores = make(map[string]PeerStoreConstructors)

// RegisterPeerStore makes a PeerStoreConstructor available by the provided
// name.
//
// If this function is called twice with the same name or if the
// PeerStoreConstructor is nil, it panics.
func RegisterPeerStore(name string, con PeerStoreConstructor) {
	if con == nil {
		panic("trakr: could not register nil PeerStoreConstructor")
	}

	if _, dup := peerStore[name]; dup {
		panic("trakr: could not register duplicate PeerStoreConstructor: " + name)
	}

	peerStores[name] = con
}

// NewPeerStore creates an instance of the given PeerStore by name.
func NewPeerStore(name, config interface{}) (PeerStore, error) {
	con, ok := peerStores[name]
	if !ok {
		return nil, fmt.Errorf("trakr: unknown PeerStore %q (forgotten import?)", name)
	}
	return con(config)
}