package dht

import (
	"fmt"
	"time"

	ds "github.com/ipfs/go-datastore"
	dssync "github.com/ipfs/go-datastore/sync"
	"github.com/ipfs/go-ipns"
	"github.com/libp2p/go-libp2p-core/host"
	"github.com/libp2p/go-libp2p-core/network"
	"github.com/libp2p/go-libp2p-core/peer"
	"github.com/libp2p/go-libp2p-core/protocol"
	"github.com/libp2p/go-libp2p-kad-dht/providers"
	record "github.com/libp2p/go-libp2p-record"
)

// ModeOpt describes what mode the dht should operate in
type ModeOpt int

const (
	// ModeAuto utilizes EvtLocalReachabilityChanged events sent over the event bus to dynamically switch the DHT
	// between Client and Server modes based on network conditions
	ModeAuto ModeOpt = iota
	// ModeClient operates the DHT as a client only, it cannot respond to incoming queries
	ModeClient
	// ModeServer operates the DHT as a server, it can both send and respond to queries
	ModeServer
	// ModeAutoServer operates in the same way as ModeAuto, but acts as a server when reachability is unknown
	ModeAutoServer
)

// DefaultPrefix is the application specific prefix attached to all DHT protocols by default.
const DefaultPrefix protocol.ID = "/ipfs"

// Options is a structure containing all the options that can be used when constructing a DHT.
type config struct {
	datastore        ds.Batching
	validator        record.Validator
	validatorChanged bool // if true implies that the validator has been changed and that defaults should not be used
	mode             ModeOpt
	protocolPrefix   protocol.ID
	bucketSize       int
	concurrency      int
	resiliency       int
	maxRecordAge     time.Duration
	enableProviders  bool
	enableValues     bool
	providersOptions []providers.Option
	queryPeerFilter  QueryFilterFunc

	routingTable struct {
		refreshQueryTimeout time.Duration
		refreshInterval     time.Duration
		autoRefresh         bool
		latencyTolerance    time.Duration
		checkInterval       time.Duration
		peerFilter          RouteTableFilterFunc
	}

	// set to true if we're operating in v1 dht compatible mode
	v1CompatibleMode bool
}

func emptyQueryFilter(_ *IpfsDHT, ai peer.AddrInfo) bool  { return true }
func emptyRTFilter(_ *IpfsDHT, conns []network.Conn) bool { return true }

// apply applies the given options to this Option
func (c *config) apply(opts ...Option) error {
	for i, opt := range opts {
		if err := opt(c); err != nil {
			return fmt.Errorf("dht option %d failed: %s", i, err)
		}
	}
	return nil
}

// applyFallbacks sets default values that could not be applied during config creation since they are dependent
// on other configuration parameters (e.g. optA is by default 2x optB) and/or on the Host
func (c *config) applyFallbacks(h host.Host) error {
	if !c.validatorChanged {
		nsval, ok := c.validator.(record.NamespacedValidator)
		if ok {
			if _, pkFound := nsval["pk"]; !pkFound {
				nsval["pk"] = record.PublicKeyValidator{}
			}
			if _, ipnsFound := nsval["ipns"]; !ipnsFound {
				nsval["ipns"] = ipns.Validator{KeyBook: h.Peerstore()}
			}
		} else {
			return fmt.Errorf("the default validator was changed without being marked as changed")
		}
	}
	return nil
}

// Option DHT option type.
type Option func(*config) error

const defaultBucketSize = 20

// defaults are the default DHT options. This option will be automatically
// prepended to any options you pass to the DHT constructor.
var defaults = func(o *config) error {
	o.validator = record.NamespacedValidator{}
	o.datastore = dssync.MutexWrap(ds.NewMapDatastore())
	o.protocolPrefix = DefaultPrefix
	o.enableProviders = true
	o.enableValues = true
	o.queryPeerFilter = emptyQueryFilter

	o.routingTable.latencyTolerance = time.Minute
	o.routingTable.refreshQueryTimeout = 1 * time.Minute
	o.routingTable.refreshInterval = 10 * time.Minute
	o.routingTable.autoRefresh = true
	o.routingTable.peerFilter = emptyRTFilter
	o.maxRecordAge = time.Hour * 36

	o.bucketSize = defaultBucketSize
	o.concurrency = 3
	o.resiliency = 3

	o.v1CompatibleMode = true

	return nil
}

func (c *config) validate() error {
	if c.protocolPrefix != DefaultPrefix {
		return nil
	}
	if c.bucketSize != defaultBucketSize {
		return fmt.Errorf("protocol prefix %s must use bucket size %d", DefaultPrefix, defaultBucketSize)
	}
	if !c.enableProviders {
		return fmt.Errorf("protocol prefix %s must have providers enabled", DefaultPrefix)
	}
	if !c.enableValues {
		return fmt.Errorf("protocol prefix %s must have values enabled", DefaultPrefix)
	}

	nsval, isNSVal := c.validator.(record.NamespacedValidator)
	if !isNSVal {
		return fmt.Errorf("protocol prefix %s must use a namespaced validator", DefaultPrefix)
	}

	if len(nsval) != 2 {
		return fmt.Errorf("protocol prefix %s must have exactly two namespaced validators - /pk and /ipns", DefaultPrefix)
	}

	if pkVal, pkValFound := nsval["pk"]; !pkValFound {
		return fmt.Errorf("protocol prefix %s must support the /pk namespaced validator", DefaultPrefix)
	} else if _, ok := pkVal.(record.PublicKeyValidator); !ok {
		return fmt.Errorf("protocol prefix %s must use the record.PublicKeyValidator for the /pk namespace", DefaultPrefix)
	}

	if ipnsVal, ipnsValFound := nsval["ipns"]; !ipnsValFound {
		return fmt.Errorf("protocol prefix %s must support the /ipns namespaced validator", DefaultPrefix)
	} else if _, ok := ipnsVal.(ipns.Validator); !ok {
		return fmt.Errorf("protocol prefix %s must use ipns.Validator for the /ipns namespace", DefaultPrefix)
	}
	return nil
}

// RoutingTableLatencyTolerance sets the maximum acceptable latency for peers
// in the routing table's cluster.
func RoutingTableLatencyTolerance(latency time.Duration) Option {
	return func(c *config) error {
		c.routingTable.latencyTolerance = latency
		return nil
	}
}

// RoutingTableRefreshQueryTimeout sets the timeout for routing table refresh
// queries.
func RoutingTableRefreshQueryTimeout(timeout time.Duration) Option {
	return func(c *config) error {
		c.routingTable.refreshQueryTimeout = timeout
		return nil
	}
}

// RoutingTableRefreshPeriod sets the period for refreshing buckets in the
// routing table. The DHT will refresh buckets every period by:
//
// 1. First searching for nearby peers to figure out how many buckets we should try to fill.
// 1. Then searching for a random key in each bucket that hasn't been queried in
//    the last refresh period.
func RoutingTableRefreshPeriod(period time.Duration) Option {
	return func(c *config) error {
		c.routingTable.refreshInterval = period
		return nil
	}
}

// Datastore configures the DHT to use the specified datastore.
//
// Defaults to an in-memory (temporary) map.
func Datastore(ds ds.Batching) Option {
	return func(c *config) error {
		c.datastore = ds
		return nil
	}
}

// Mode configures which mode the DHT operates in (Client, Server, Auto).
//
// Defaults to ModeAuto.
func Mode(m ModeOpt) Option {
	return func(c *config) error {
		c.mode = m
		return nil
	}
}

// Validator configures the DHT to use the specified validator.
//
// Defaults to a namespaced validator that can validate both public key (under the "pk"
// namespace) and IPNS records (under the "ipns" namespace). Setting the validator
// implies that the user wants to control the validators and therefore the default
// public key and IPNS validators will not be added.
func Validator(v record.Validator) Option {
	return func(c *config) error {
		c.validator = v
		c.validatorChanged = true
		return nil
	}
}

// NamespacedValidator adds a validator namespaced under `ns`. This option fails
// if the DHT is not using a `record.NamespacedValidator` as its validator (it
// uses one by default but this can be overridden with the `Validator` option).
// Adding a namespaced validator without changing the `Validator` will result in
// adding a new validator in addition to the default public key and IPNS validators.
// The "pk" and "ipns" namespaces cannot be overridden here unless a new `Validator`
// has been set first.
//
// Example: Given a validator registered as `NamespacedValidator("ipns",
// myValidator)`, all records with keys starting with `/ipns/` will be validated
// with `myValidator`.
func NamespacedValidator(ns string, v record.Validator) Option {
	return func(c *config) error {
		nsval, ok := c.validator.(record.NamespacedValidator)
		if !ok {
			return fmt.Errorf("can only add namespaced validators to a NamespacedValidator")
		}
		nsval[ns] = v
		return nil
	}
}

// ProtocolPrefix sets an application specific prefix to be attached to all DHT protocols. For example,
// /myapp/kad/1.0.0 instead of /ipfs/kad/1.0.0. Prefix should be of the form /myapp.
//
// Defaults to dht.DefaultPrefix
func ProtocolPrefix(prefix protocol.ID) Option {
	return func(c *config) error {
		c.protocolPrefix = prefix
		return nil
	}
}

// ProtocolExtension adds an application specific protocol to the DHT protocol. For example,
// /ipfs/lan/kad/1.0.0 instead of /ipfs/kad/1.0.0. extension should be of the form /lan.
func ProtocolExtension(ext protocol.ID) Option {
	return func(c *config) error {
		c.protocolPrefix += ext
		return nil
	}
}

// BucketSize configures the bucket size (k in the Kademlia paper) of the routing table.
//
// The default value is 20.
func BucketSize(bucketSize int) Option {
	return func(c *config) error {
		c.bucketSize = bucketSize
		return nil
	}
}

// Concurrency configures the number of concurrent requests (alpha in the Kademlia paper) for a given query path.
//
// The default value is 3.
func Concurrency(alpha int) Option {
	return func(c *config) error {
		c.concurrency = alpha
		return nil
	}
}

// Resiliency configures the number of peers closest to a target that must have responded in order for a given query
// path to complete.
//
// The default value is 3.
func Resiliency(beta int) Option {
	return func(c *config) error {
		c.resiliency = beta
		return nil
	}
}

// MaxRecordAge specifies the maximum time that any node will hold onto a record ("PutValue record")
// from the time its received. This does not apply to any other forms of validity that
// the record may contain.
// For example, a record may contain an ipns entry with an EOL saying its valid
// until the year 2020 (a great time in the future). For that record to stick around
// it must be rebroadcasted more frequently than once every 'MaxRecordAge'
func MaxRecordAge(maxAge time.Duration) Option {
	return func(c *config) error {
		c.maxRecordAge = maxAge
		return nil
	}
}

// DisableAutoRefresh completely disables 'auto-refresh' on the DHT routing
// table. This means that we will neither refresh the routing table periodically
// nor when the routing table size goes below the minimum threshold.
func DisableAutoRefresh() Option {
	return func(c *config) error {
		c.routingTable.autoRefresh = false
		return nil
	}
}

// DisableProviders disables storing and retrieving provider records.
//
// Defaults to enabled.
//
// WARNING: do not change this unless you're using a forked DHT (i.e., a private
// network and/or distinct DHT protocols with the `Protocols` option).
func DisableProviders() Option {
	return func(c *config) error {
		c.enableProviders = false
		return nil
	}
}

// DisableValues disables storing and retrieving value records (including
// public keys).
//
// Defaults to enabled.
//
// WARNING: do not change this unless you're using a forked DHT (i.e., a private
// network and/or distinct DHT protocols with the `Protocols` option).
func DisableValues() Option {
	return func(c *config) error {
		c.enableValues = false
		return nil
	}
}

// ProvidersOptions are options passed directly to the provider manager.
//
// The provider manager adds and gets provider records from the datastore, cahing
// them in between. These options are passed to the provider manager allowing
// customisation of things like the GC interval and cache implementation.
func ProvidersOptions(opts []providers.Option) Option {
	return func(c *config) error {
		c.providersOptions = opts
		return nil
	}
}

// QueryFilter sets a function that approves which peers may be dialed in a query
func QueryFilter(filter QueryFilterFunc) Option {
	return func(c *config) error {
		c.queryPeerFilter = filter
		return nil
	}
}

// RoutingTableFilter sets a function that approves which peers may be added to the routing table. The host should
// already have at least one connection to the peer under consideration.
func RoutingTableFilter(filter RouteTableFilterFunc) Option {
	return func(c *config) error {
		c.routingTable.peerFilter = filter
		return nil
	}
}

// V1CompatibleMode sets the DHT to operate in V1 compatible mode. In this mode,
// the DHT node will act like a V1 DHT node (use the V1 protocol names) but will
// use the V2 query and routing table logic.
//
// For now, this option defaults to true for backwards compatibility. In the
// near future, it will switch to false.
//
// This option is perma-unstable and may be removed in the future.
func V1CompatibleMode(enable bool) Option {
	return func(c *config) error {
		c.v1CompatibleMode = enable
		return nil
	}
}