// Copyright 2024 Kelvin Clement Mwinuka
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package echovault

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"github.com/echovault/echovault/internal"
	"github.com/echovault/echovault/internal/aof"
	"github.com/echovault/echovault/internal/clock"
	"github.com/echovault/echovault/internal/config"
	"github.com/echovault/echovault/internal/constants"
	"github.com/echovault/echovault/internal/eviction"
	"github.com/echovault/echovault/internal/memberlist"
	"github.com/echovault/echovault/internal/modules/acl"
	"github.com/echovault/echovault/internal/modules/admin"
	"github.com/echovault/echovault/internal/modules/connection"
	"github.com/echovault/echovault/internal/modules/generic"
	"github.com/echovault/echovault/internal/modules/hash"
	"github.com/echovault/echovault/internal/modules/list"
	"github.com/echovault/echovault/internal/modules/pubsub"
	"github.com/echovault/echovault/internal/modules/set"
	"github.com/echovault/echovault/internal/modules/sorted_set"
	str "github.com/echovault/echovault/internal/modules/string"
	"github.com/echovault/echovault/internal/raft"
	"github.com/echovault/echovault/internal/snapshot"
	"io"
	"log"
	"net"
	"os"
	"sync"
	"sync/atomic"
	"time"
)

type EchoVault struct {
	// clock is an implementation of a time interface that allows mocking of time functions during testing.
	clock clock.Clock

	// config holds the echovault configuration variables.
	config config.Config

	// The current index for the latest connection id.
	// This number is incremented everytime there's a new connection and
	// the new number is the new connection's ID.
	connId atomic.Uint64

	// connInfo holds the connection information for embedded and TCP clients.
	// It keeps track of the protocol and database that each client is operating on.
	connInfo struct {
		mut        *sync.RWMutex                         // RWMutex for the connInfo object.
		tcpClients map[*net.Conn]internal.ConnectionInfo // Map that holds connection information for each TCP client.
		embedded   internal.ConnectionInfo               // Information for the embedded connection.
	}

	// Global read-write mutex for entire store.
	storeLock *sync.RWMutex
	// Data store to hold the keys and their associated data, expiry time, etc.
	// The int key on the outer map represents the database index.
	// Each database has a map that has a string key and the key data (value and expiry time).
	store map[int]map[string]internal.KeyData

	// Holds all the keys that are currently associated with an expiry.
	keysWithExpiry struct {
		// Mutex as only one process should be able to update this list at a time.
		rwMutex sync.RWMutex
		// A map holding a string slice of the volatile keys for each database.
		keys map[int][]string
	}
	// LFU cache used when eviction policy is allkeys-lfu or volatile-lfu.
	lfuCache struct {
		// Mutex as only one goroutine can edit the LFU cache at a time.
		mutex sync.Mutex
		// LFU cache for each database represented by a min heap.
		cache map[int]*eviction.CacheLFU
	}
	// LRU cache used when eviction policy is allkeys-lru or volatile-lru.
	lruCache struct {
		// Mutex as only one goroutine can edit the LRU at a time.
		mutex sync.Mutex
		// LRU cache represented by a max heap.
		cache map[int]*eviction.CacheLRU
	}

	// Holds the list of all commands supported by the echovault.
	commandsRWMut sync.RWMutex
	commands      []internal.Command

	raft       *raft.Raft             // The raft replication layer for the echovault.
	memberList *memberlist.MemberList // The memberlist layer for the echovault.

	context context.Context

	acl    *acl.ACL
	pubSub *pubsub.PubSub

	snapshotInProgress         atomic.Bool      // Atomic boolean that's true when actively taking a snapshot.
	rewriteAOFInProgress       atomic.Bool      // Atomic boolean that's true when actively rewriting AOF file is in progress.
	stateCopyInProgress        atomic.Bool      // Atomic boolean that's true when actively copying state for snapshotting or preamble generation.
	stateMutationInProgress    atomic.Bool      // Atomic boolean that is set to true when state mutation is in progress.
	latestSnapshotMilliseconds atomic.Int64     // Unix epoch in milliseconds.
	snapshotEngine             *snapshot.Engine // Snapshot engine for standalone mode.
	aofEngine                  *aof.Engine      // AOF engine for standalone mode.

	listener atomic.Value  // Holds the TCP listener.
	quit     chan struct{} // Channel that signals the closing of all client connections.
	stopTTL  chan struct{} // Channel that signals the TTL sampling goroutine to stop execution.
}

// WithContext is an options that for the NewEchoVault function that allows you to
// configure a custom context object to be used in EchoVault.
// If you don't provide this option, EchoVault will create its own internal context object.
func WithContext(ctx context.Context) func(echovault *EchoVault) {
	return func(echovault *EchoVault) {
		echovault.context = ctx
	}
}

// WithConfig is an option for the NewEchoVault function that allows you to pass a
// custom configuration to EchoVault.
// If not specified, EchoVault will use the default configuration from config.DefaultConfig().
func WithConfig(config config.Config) func(echovault *EchoVault) {
	return func(echovault *EchoVault) {
		echovault.config = config
	}
}

// NewEchoVault creates a new EchoVault instance.
// This functions accepts the WithContext, WithConfig and WithCommands options.
func NewEchoVault(options ...func(echovault *EchoVault)) (*EchoVault, error) {
	echovault := &EchoVault{
		clock:   clock.NewClock(),
		context: context.Background(),
		config:  config.DefaultConfig(),
		connInfo: struct {
			mut        *sync.RWMutex
			tcpClients map[*net.Conn]internal.ConnectionInfo
			embedded   internal.ConnectionInfo
		}{
			mut:        &sync.RWMutex{},
			tcpClients: make(map[*net.Conn]internal.ConnectionInfo),
			embedded: internal.ConnectionInfo{
				Id:       0,
				Name:     "embedded",
				Protocol: 2,
				Database: 0,
			},
		},
		storeLock: &sync.RWMutex{},
		store:     make(map[int]map[string]internal.KeyData),
		keysWithExpiry: struct {
			rwMutex sync.RWMutex
			keys    map[int][]string
		}{
			rwMutex: sync.RWMutex{},
			keys:    make(map[int][]string),
		},
		commandsRWMut: sync.RWMutex{},
		commands: func() []internal.Command {
			var commands []internal.Command
			commands = append(commands, acl.Commands()...)
			commands = append(commands, admin.Commands()...)
			commands = append(commands, connection.Commands()...)
			commands = append(commands, generic.Commands()...)
			commands = append(commands, hash.Commands()...)
			commands = append(commands, list.Commands()...)
			commands = append(commands, pubsub.Commands()...)
			commands = append(commands, set.Commands()...)
			commands = append(commands, sorted_set.Commands()...)
			commands = append(commands, str.Commands()...)
			return commands
		}(),
		quit:    make(chan struct{}),
		stopTTL: make(chan struct{}),
	}

	for _, option := range options {
		option(echovault)
	}

	echovault.context = context.WithValue(
		echovault.context, "ServerID",
		internal.ContextServerID(echovault.config.ServerID),
	)

	// Load .so modules from config
	for _, path := range echovault.config.Modules {
		if err := echovault.LoadModule(path); err != nil {
			log.Printf("%s %v\n", path, err)
			continue
		}
		log.Printf("loaded plugin %s\n", path)
	}

	// Set up ACL module
	echovault.acl = acl.NewACL(echovault.config)

	// Set up Pub/Sub module
	echovault.pubSub = pubsub.NewPubSub()

	if echovault.isInCluster() {
		echovault.raft = raft.NewRaft(raft.Opts{
			Config:                echovault.config,
			GetCommand:            echovault.getCommand,
			SetValues:             echovault.setValues,
			SetExpiry:             echovault.setExpiry,
			StartSnapshot:         echovault.startSnapshot,
			FinishSnapshot:        echovault.finishSnapshot,
			SetLatestSnapshotTime: echovault.setLatestSnapshot,
			GetHandlerFuncParams:  echovault.getHandlerFuncParams,
			DeleteKey: func(ctx context.Context, key string) error {
				echovault.storeLock.Lock()
				defer echovault.storeLock.Unlock()
				return echovault.deleteKey(ctx, key)
			},
			GetState: func() map[int]map[string]internal.KeyData {
				state := make(map[int]map[string]internal.KeyData)
				for database, store := range echovault.getState() {
					for k, v := range store {
						if data, ok := v.(internal.KeyData); ok {
							state[database][k] = data
						}
					}
				}
				return state
			},
		})
		echovault.memberList = memberlist.NewMemberList(memberlist.Opts{
			Config:           echovault.config,
			HasJoinedCluster: echovault.raft.HasJoinedCluster,
			AddVoter:         echovault.raft.AddVoter,
			RemoveRaftServer: echovault.raft.RemoveServer,
			IsRaftLeader:     echovault.raft.IsRaftLeader,
			ApplyMutate:      echovault.raftApplyCommand,
			ApplyDeleteKey:   echovault.raftApplyDeleteKey,
		})
	} else {
		// Set up standalone snapshot engine
		echovault.snapshotEngine = snapshot.NewSnapshotEngine(
			snapshot.WithClock(echovault.clock),
			snapshot.WithDirectory(echovault.config.DataDir),
			snapshot.WithThreshold(echovault.config.SnapShotThreshold),
			snapshot.WithInterval(echovault.config.SnapshotInterval),
			snapshot.WithStartSnapshotFunc(echovault.startSnapshot),
			snapshot.WithFinishSnapshotFunc(echovault.finishSnapshot),
			snapshot.WithSetLatestSnapshotTimeFunc(echovault.setLatestSnapshot),
			snapshot.WithGetLatestSnapshotTimeFunc(echovault.getLatestSnapshotTime),
			snapshot.WithGetStateFunc(func() map[int]map[string]internal.KeyData {
				state := make(map[int]map[string]internal.KeyData)
				for database, data := range echovault.getState() {
					state[database] = make(map[string]internal.KeyData)
					for key, value := range data {
						if keyData, ok := value.(internal.KeyData); ok {
							state[database][key] = keyData
						}
					}
				}
				return state
			}),
			snapshot.WithSetKeyDataFunc(func(database int, key string, data internal.KeyData) {
				ctx := context.WithValue(context.Background(), "Database", database)
				if err := echovault.setValues(ctx, map[string]interface{}{key: data.Value}); err != nil {
					log.Println(err)
				}
				echovault.setExpiry(ctx, key, data.ExpireAt, false)
			}),
		)

		// Set up standalone AOF engine
		aofEngine, err := aof.NewAOFEngine(
			aof.WithClock(echovault.clock),
			aof.WithDirectory(echovault.config.DataDir),
			aof.WithStrategy(echovault.config.AOFSyncStrategy),
			aof.WithStartRewriteFunc(echovault.startRewriteAOF),
			aof.WithFinishRewriteFunc(echovault.finishRewriteAOF),
			aof.WithGetStateFunc(func() map[int]map[string]internal.KeyData {
				state := make(map[int]map[string]internal.KeyData)
				for database, data := range echovault.getState() {
					state[database] = make(map[string]internal.KeyData)
					for key, value := range data {
						if keyData, ok := value.(internal.KeyData); ok {
							state[database][key] = keyData
						}
					}
				}
				return state
			}),
			aof.WithSetKeyDataFunc(func(database int, key string, value internal.KeyData) {
				ctx := context.WithValue(context.Background(), "Database", database)
				if err := echovault.setValues(ctx, map[string]interface{}{key: value.Value}); err != nil {
					log.Println(err)
				}
				echovault.setExpiry(ctx, key, value.ExpireAt, false)
			}),
			aof.WithHandleCommandFunc(func(database int, command []byte) {
				ctx := context.WithValue(context.Background(), "Protocol", 2)
				ctx = context.WithValue(ctx, "Database", database)
				_, err := echovault.handleCommand(ctx, command, nil, true, false)
				if err != nil {
					log.Println(err)
				}
			}),
		)
		if err != nil {
			return nil, err
		}
		echovault.aofEngine = aofEngine
	}

	// If eviction policy is not noeviction, start a goroutine to evict keys every 100 milliseconds.
	if echovault.config.EvictionPolicy != constants.NoEviction {
		go func() {
			ticker := time.NewTicker(echovault.config.EvictionInterval)
			defer func() {
				ticker.Stop()
			}()
			for {
				select {
				case <-ticker.C:
					// Run key eviction for each database that has volatile keys.
					wg := sync.WaitGroup{}
					for database, _ := range echovault.keysWithExpiry.keys {
						wg.Add(1)
						ctx := context.WithValue(context.Background(), "Database", database)
						go func(ctx context.Context, wg *sync.WaitGroup) {
							if err := echovault.evictKeysWithExpiredTTL(ctx); err != nil {
								log.Printf("evict with ttl: %v\n", err)
							}
							wg.Done()
						}(ctx, &wg)
					}
					wg.Wait()
				case <-echovault.stopTTL:
					break
				}
			}
		}()
	}

	if echovault.config.TLS && len(echovault.config.CertKeyPairs) <= 0 {
		return nil, errors.New("must provide certificate and key file paths for TLS mode")
	}

	if echovault.isInCluster() {
		// Initialise raft and memberlist
		echovault.raft.RaftInit(echovault.context)
		echovault.memberList.MemberListInit(echovault.context)
		// Initialise caches
		echovault.initialiseCaches()
	}

	if !echovault.isInCluster() {
		echovault.initialiseCaches()
		// Restore from AOF by default if it's enabled
		if echovault.config.RestoreAOF {
			err := echovault.aofEngine.Restore()
			if err != nil {
				log.Println(err)
			}
		}

		// Restore from snapshot if snapshot restore is enabled and AOF restore is disabled
		if echovault.config.RestoreSnapshot && !echovault.config.RestoreAOF {
			err := echovault.snapshotEngine.Restore()
			if err != nil {
				log.Println(err)
			}
		}
	}

	return echovault, nil
}

func (server *EchoVault) startTCP() {
	conf := server.config

	listenConfig := net.ListenConfig{
		KeepAlive: 200 * time.Millisecond,
	}

	listener, err := listenConfig.Listen(
		server.context,
		"tcp",
		fmt.Sprintf("%s:%d", conf.BindAddr, conf.Port),
	)
	if err != nil {
		log.Printf("listener error: %v", err)
		return
	}

	if !conf.TLS {
		// TCP
		log.Printf("Starting TCP server at Address %s, Port %d...\n", conf.BindAddr, conf.Port)
	}

	if conf.TLS || conf.MTLS {
		// TLS
		if conf.MTLS {
			log.Printf("Starting mTLS server at Address %s, Port %d...\n", conf.BindAddr, conf.Port)
		} else {
			log.Printf("Starting TLS server at Address %s, Port %d...\n", conf.BindAddr, conf.Port)
		}

		var certificates []tls.Certificate
		for _, certKeyPair := range conf.CertKeyPairs {
			c, err := tls.LoadX509KeyPair(certKeyPair[0], certKeyPair[1])
			if err != nil {
				log.Printf("load cert key pair: %v\n", err)
				return
			}
			certificates = append(certificates, c)
		}

		clientAuth := tls.NoClientCert
		clientCerts := x509.NewCertPool()

		if conf.MTLS {
			clientAuth = tls.RequireAndVerifyClientCert
			for _, c := range conf.ClientCAs {
				ca, err := os.Open(c)
				if err != nil {
					log.Printf("client cert open: %v\n", err)
					return
				}
				certBytes, err := io.ReadAll(ca)
				if err != nil {
					log.Printf("client cert read: %v\n", err)
				}
				if ok := clientCerts.AppendCertsFromPEM(certBytes); !ok {
					log.Printf("client cert append: %v\n", err)
				}
			}
		}

		listener = tls.NewListener(listener, &tls.Config{
			Certificates: certificates,
			ClientAuth:   clientAuth,
			ClientCAs:    clientCerts,
		})
	}

	server.listener.Store(listener)

	// Listen to connection.
	for {
		select {
		case <-server.quit:
			return
		default:
			conn, err := listener.Accept()
			if err != nil {
				log.Printf("listener error: %v\n", err)
				return
			}
			// Read loop for connection
			go server.handleConnection(conn)
		}
	}
}

func (server *EchoVault) handleConnection(conn net.Conn) {
	// If ACL module is loaded, register the connection with the ACL
	if server.acl != nil {
		server.acl.RegisterConnection(&conn)
	}

	w, r := io.Writer(conn), io.Reader(conn)

	// Generate connection ID
	cid := server.connId.Add(1)
	ctx := context.WithValue(server.context, internal.ContextConnID("ConnectionID"),
		fmt.Sprintf("%s-%d", server.context.Value(internal.ContextServerID("ServerID")), cid))

	// Set the default connection information
	server.connInfo.mut.Lock()
	server.connInfo.tcpClients[&conn] = internal.ConnectionInfo{
		Id:       cid,
		Name:     "",
		Protocol: 2,
		Database: 0,
	}
	server.connInfo.mut.Unlock()

	defer func() {
		log.Printf("closing connection %d...", cid)
		if err := conn.Close(); err != nil {
			log.Println(err)
		}
	}()

	for {
		message, err := internal.ReadMessage(r)

		if err != nil && errors.Is(err, io.EOF) {
			// Connection closed
			log.Println(err)
			break
		}

		if err != nil {
			log.Println(err)
			break
		}

		res, err := server.handleCommand(ctx, message, &conn, false, false)
		if err != nil && errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			if _, err = w.Write([]byte(fmt.Sprintf("-Error %s\r\n", err.Error()))); err != nil {
				log.Println(err)
			}
			continue
		}

		chunkSize := 1024

		// If the length of the response is 0, return nothing to the client.
		if len(res) == 0 {
			continue
		}

		if len(res) <= chunkSize {
			_, _ = w.Write(res)
			continue
		}

		// If the response is large, send it in chunks.
		startIndex := 0
		for {
			// If the current start index is less than chunkSize from length, return the remaining bytes.
			if len(res)-1-startIndex < chunkSize {
				_, err = w.Write(res[startIndex:])
				if err != nil {
					log.Println(err)
				}
				break
			}
			n, _ := w.Write(res[startIndex : startIndex+chunkSize])
			if n < chunkSize {
				break
			}
			startIndex += chunkSize
		}
	}
}

// Start starts the EchoVault instance's TCP listener.
// This allows the instance to accept connections handle client commands over TCP.
//
// You can still use command functions like echovault.Set if you're embedding EchoVault in your application.
// However, if you'd like to also accept TCP request on the same instance, you must call this function.
func (server *EchoVault) Start() {
	server.startTCP()
}

// takeSnapshot triggers a snapshot when called.
func (server *EchoVault) takeSnapshot() error {
	if server.snapshotInProgress.Load() {
		return errors.New("snapshot already in progress")
	}

	go func() {
		if server.isInCluster() {
			// Handle snapshot in cluster mode
			if err := server.raft.TakeSnapshot(); err != nil {
				log.Println(err)
			}
			return
		}
		// Handle snapshot in standalone mode
		if err := server.snapshotEngine.TakeSnapshot(); err != nil {
			log.Println(err)
		}
	}()

	return nil
}

func (server *EchoVault) startSnapshot() {
	server.snapshotInProgress.Store(true)
}

func (server *EchoVault) finishSnapshot() {
	server.snapshotInProgress.Store(false)
}

func (server *EchoVault) setLatestSnapshot(msec int64) {
	server.latestSnapshotMilliseconds.Store(msec)
}

// getLatestSnapshotTime returns the latest snapshot time in unix epoch milliseconds.
func (server *EchoVault) getLatestSnapshotTime() int64 {
	return server.latestSnapshotMilliseconds.Load()
}

func (server *EchoVault) startRewriteAOF() {
	server.rewriteAOFInProgress.Store(true)
}

func (server *EchoVault) finishRewriteAOF() {
	server.rewriteAOFInProgress.Store(false)
}

// rewriteAOF triggers an AOF compaction when running in standalone mode.
func (server *EchoVault) rewriteAOF() error {
	if server.rewriteAOFInProgress.Load() {
		return errors.New("aof rewrite in progress")
	}
	if err := server.aofEngine.RewriteLog(); err != nil {
		return err
	}
	return nil
}

// ShutDown gracefully shuts down the EchoVault instance.
// This function shuts down the memberlist and raft layers.
func (server *EchoVault) ShutDown() {
	if server.listener.Load() != nil {
		go func() { server.quit <- struct{}{} }()
		go func() { server.stopTTL <- struct{}{} }()
		log.Println("closing tcp listener...")
		if err := server.listener.Load().(net.Listener).Close(); err != nil {
			log.Printf("listener close: %v\n", err)
		}
	}
	if server.isInCluster() {
		server.raft.RaftShutdown()
		server.memberList.MemberListShutdown()
	}
}

func (server *EchoVault) initialiseCaches() {
	// Set up LFU cache.
	server.lfuCache = struct {
		mutex sync.Mutex
		cache map[int]*eviction.CacheLFU
	}{
		mutex: sync.Mutex{},
		cache: make(map[int]*eviction.CacheLFU),
	}
	// set up LRU cache.
	server.lruCache = struct {
		mutex sync.Mutex
		cache map[int]*eviction.CacheLRU
	}{
		mutex: sync.Mutex{},
		cache: make(map[int]*eviction.CacheLRU),
	}
	// Initialise caches for each preloaded database.
	for database, _ := range server.store {
		server.lfuCache.cache[database] = eviction.NewCacheLFU()
		server.lruCache.cache[database] = eviction.NewCacheLRU()
	}
}