// Copyright 2019 The NATS Authors
// 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 server

import (
	"fmt"
	"io/ioutil"
	"math"
	"os"
	"path/filepath"
	"strings"
	"sync"

	"github.com/nats-io/nats-server/v2/server/sysmem"
)

// JetStreamConfig determines this server's configuration.
// MaxMemory and MaxStore are in bytes.
type JetStreamConfig struct {
	MaxMemory int64
	MaxStore  int64
	StoreDir  string
}

// This is for internal accounting for JetStream for this server.
type jetStream struct {
	mu            sync.RWMutex
	srv           *Server
	config        JetStreamConfig
	accounts      map[*Account]*jsAccount
	memReserved   int64
	storeReserved int64
}

// TODO(dlc) - decide on what these look like for single vs cluster vs supercluster.
// TODO(dlc) - need to track and rollup against server limits, etc.
type JetStreamAccountLimits struct {
	MaxMemory      int64
	MaxStore       int64
	MaxMsgSets     int
	MaxObservables int
}

// JetStreamAccountStats returns current statistics about the account's JetStream usage.
type JetStreamAccountStats struct {
	Memory  uint64
	Store   uint64
	MsgSets int
	Limits  JetStreamAccountLimits
}

const (
	// OK response
	OK = "+OK"

	// JetStreamEnabled allows a user to dynamically check if JetStream is enabled for an account.
	// Will return +OK on success, otherwise will timeout.
	JetStreamEnabled = "$JS.ENABLED"
	jsEnabledExport  = "$JS.*.ENABLED"

	// JetStreamInfo is for obtaining general information about JetStream for this account.
	// Will return JSON response.
	JetStreamInfo = "$JS.INFO"
	jsInfoExport  = "$JS.*.INFO"

	// JetStreamCreateObservable is the endpoint to create observers for a message set.
	// Will return +OK on success and -ERR on failure.
	JetStreamCreateObservable = "$JS.OB.CREATE"
	jsCreateObservableExport  = "$JS.*.OBS.CREATE"

	// JsObservableInfo is for obtaining general information about an observable.
	// Will return JSON response.
	JetStreamObservableInfo = "$JS.OBS.INFO"
	jsObservableInfoExport  = "$JS.*.OBS.INFO"

	// JetStreamCreateMsgSet is the endpoint to create message sets.
	// Will return +OK on success and -ERR on failure.
	JetStreamCreateMsgSet = "$JS.MSGSET.CREATE"
	jsCreateMsgSetExport  = "$JS.*.MSGSET.CREATE"

	// JetStreamMsgSetInfo is for obtaining general information about a named message set.
	// Will return JSON response.
	JetStreamMsgSetInfo = "$JS.MSGSET.INFO"
	jsMsgSetInfoExport  = "$JS.*.MSGSET.INFO"

	// JetStreamAckPre is the prefix for the ack stream coming back to an observable.
	JetStreamAckPre = "$JS.A"

	// JetStreamRequestNextPre is the prefix for the request next message(s) for an observable in worker/pull mode.
	JetStreamRequestNextPre = "$JS.RN"
)

// For easier handling of exports and imports.
var allJsExports = []string{jsEnabledExport, jsInfoExport, jsCreateObservableExport, jsObservableInfoExport, jsCreateMsgSetExport, jsMsgSetInfoExport}

// This represents a jetstream  enabled account.
// Worth noting that we include the js ptr, this is because
// in general we want to be very efficient when receiving messages on
// and internal sub for a msgSet, so we will direct link to the msgSet
// and walk backwards as needed vs multiple hash lookups and locks, etc.
type jsAccount struct {
	mu            sync.Mutex
	js            *jetStream
	account       *Account
	limits        JetStreamAccountLimits
	memReserved   int64
	memUsed       int64
	storeReserved int64
	storeUsed     int64
	msgSets       map[string]*MsgSet
}

// EnableJetStream will enable JetStream support on this server with the given configuration.
// A nil configuration will dynamically choose the limits and temporary file storage directory.
// If this server is part of a cluster, a system account will need to be defined.
func (s *Server) EnableJetStream(config *JetStreamConfig) error {
	s.mu.Lock()
	if !s.standAloneMode() {
		s.mu.Unlock()
		return fmt.Errorf("jetstream restricted to single server mode")
	}
	if s.js != nil {
		s.mu.Unlock()
		return fmt.Errorf("jetstream already enabled")
	}
	s.Noticef("Starting JetStream")
	if config == nil {
		s.Debugf("JetStream creating dynamic configuration - 75%% system memory, %s disk", FriendlyBytes(JetStreamMaxStoreDefault))
		config = s.dynJetStreamConfig()
	}
	// Copy, don't change callers.
	cfg := *config
	if cfg.StoreDir == "" {
		cfg.StoreDir = filepath.Join(os.TempDir(), JetStreamStoreDir)
	}

	s.js = &jetStream{srv: s, config: cfg, accounts: make(map[*Account]*jsAccount)}
	s.mu.Unlock()

	if stat, err := os.Stat(cfg.StoreDir); os.IsNotExist(err) {
		if err := os.MkdirAll(cfg.StoreDir, 0755); err != nil {
			return fmt.Errorf("could not create storage directory - %v", err)
		}
	} else {
		// Make sure its a directory and that we can write to it.
		if stat == nil || !stat.IsDir() {
			return fmt.Errorf("storage directory is not a directory")
		}
		tmpfile, err := ioutil.TempFile(cfg.StoreDir, "_test_")
		if err != nil {
			return fmt.Errorf("storage directory is not writable")
		}
		os.Remove(tmpfile.Name())
		// TODO(dlc) - Recover state
	}

	// JetStream is an internal service so we need to make sure we have a system account.
	// This system account will export the JetStream service endpoints.
	if sacc := s.SystemAccount(); sacc == nil {
		s.SetDefaultSystemAccount()
	}

	// Setup our internal subscriptions.
	if _, err := s.sysSubscribe(jsEnabledExport, s.isJsEnabledRequest); err != nil {
		return fmt.Errorf("Error setting up internal jetstream subscriptions: %v", err)
	}

	s.Noticef("----------- JETSTREAM (Beta) -----------")
	s.Noticef("  Max Memory:      %s", FriendlyBytes(cfg.MaxMemory))
	s.Noticef("  Max Storage:     %s", FriendlyBytes(cfg.MaxStore))
	s.Noticef("  Store Directory: %q", cfg.StoreDir)

	// Setup our internal system exports.
	sacc := s.SystemAccount()
	// FIXME(dlc) - Should we lock these down?
	s.Debugf("  Exports:")
	for _, export := range allJsExports {
		s.Debugf("     %s", export)
		if err := sacc.AddServiceExport(export, nil); err != nil {
			return fmt.Errorf("Error setting up jetstream service exports: %v", err)
		}
	}
	s.Noticef("----------------------------------------")

	// If we have no configured accounts setup then setup imports on global account.
	if s.globalAccountOnly() {
		if err := s.GlobalAccount().EnableJetStream(nil); err != nil {
			return fmt.Errorf("Error enabling jetstream on the global account")
		}
	}

	return nil
}

// JetStreamEnabled reports if jetstream is enabled.
func (s *Server) JetStreamEnabled() bool {
	s.mu.Lock()
	enabled := s.js != nil
	s.mu.Unlock()
	return enabled
}

// JetStreamConfig will return the current config. Useful if the system
// created a dynamic configuration. A copy is returned.
func (s *Server) JetStreamConfig() *JetStreamConfig {
	var c *JetStreamConfig
	s.mu.Lock()
	if s.js != nil {
		copy := s.js.config
		c = &(copy)
	}
	s.mu.Unlock()
	return c
}

// JetStreamNumAccounts returns the number of enabled accounts this server is tracking.
func (s *Server) JetStreamNumAccounts() int {
	js := s.getJetStream()
	if js == nil {
		return 0
	}
	js.mu.Lock()
	defer js.mu.Unlock()
	return len(js.accounts)
}

// JetStreamReservedResources returns the reserved resources if JetStream is enabled.
func (s *Server) JetStreamReservedResources() (int64, int64, error) {
	js := s.getJetStream()
	if js == nil {
		return -1, -1, fmt.Errorf("jetstream not enabled")
	}
	js.mu.RLock()
	defer js.mu.RUnlock()
	return js.memReserved, js.storeReserved, nil
}

func (s *Server) getJetStream() *jetStream {
	s.mu.Lock()
	js := s.js
	s.mu.Unlock()
	return js
}

// EnableJetStream will enable JetStream on this account with the defined limits.
// This is a helper for JetStreamEnableAccount.
func (a *Account) EnableJetStream(limits *JetStreamAccountLimits) error {
	a.mu.RLock()
	s := a.srv
	a.mu.RUnlock()
	if s == nil {
		return fmt.Errorf("jetstream account not registered")
	}
	// FIXME(dlc) - cluster mode
	js := s.getJetStream()
	if js == nil {
		return fmt.Errorf("jetstream not enabled")
	}
	if a, err := s.LookupAccount(a.Name); err != nil || a == nil {
		return fmt.Errorf("jetstream unknown account")
	}

	// No limits means we dynamically set up limits.
	if limits == nil {
		limits = js.dynamicAccountLimits()
	}

	js.mu.Lock()
	// Check the limits against existing reservations.
	if err := js.sufficientResources(limits); err != nil {
		js.mu.Unlock()
		return err
	}
	if _, ok := js.accounts[a]; ok {
		js.mu.Unlock()
		return fmt.Errorf("jetstream already enabled for account")
	}
	jsa := &jsAccount{js: js, account: a, limits: *limits, msgSets: make(map[string]*MsgSet)}
	js.accounts[a] = jsa
	js.reserveResources(limits)
	js.mu.Unlock()

	// Stamp inside account as well.
	a.mu.Lock()
	a.js = jsa
	a.mu.Unlock()

	// Create the proper imports here.
	sys := s.SystemAccount()
	for _, export := range allJsExports {
		importTo := strings.Replace(export, "*", a.Name, -1)
		importFrom := strings.Replace(export, ".*.", tsep, -1)
		if err := a.AddServiceImport(sys, importFrom, importTo); err != nil {
			return fmt.Errorf("Error setting up jetstream service imports for account: %v", err)
		}
	}

	s.Debugf("Enabled JetStream for %q", a.Name)
	s.Debugf("  Max Memory:      %s", FriendlyBytes(limits.MaxMemory))
	s.Debugf("  Max Storage:     %s", FriendlyBytes(limits.MaxStore))

	return nil
}

// UpdateJetStreamLimits will update the account limits for a JetStream enabled account.
func (a *Account) UpdateJetStreamLimits(limits *JetStreamAccountLimits) error {
	a.mu.RLock()
	s := a.srv
	a.mu.RUnlock()
	if s == nil {
		return fmt.Errorf("jetstream account not registered")
	}

	js := s.getJetStream()
	if js == nil {
		return fmt.Errorf("jetstream not enabled")
	}

	jsa := js.lookupAccount(a)
	if jsa == nil {
		return fmt.Errorf("jetstream not enabled for account")
	}

	if limits == nil {
		limits = js.dynamicAccountLimits()
	}

	// Calculate the delta between what we have and what we want.
	jsa.mu.Lock()
	dl := diffCheckedLimits(&jsa.limits, limits)
	jsaLimits := jsa.limits
	jsa.mu.Unlock()

	js.mu.Lock()
	// Check the limits against existing reservations.
	if err := js.sufficientResources(&dl); err != nil {
		js.mu.Unlock()
		return err
	}
	// FIXME(dlc) - If we drop and are over the max on memory or store, do we delete??
	js.releaseResources(&jsaLimits)
	js.reserveResources(limits)
	js.mu.Unlock()

	// Update
	jsa.mu.Lock()
	jsa.limits = *limits
	jsa.mu.Unlock()

	return nil
}

func diffCheckedLimits(a, b *JetStreamAccountLimits) JetStreamAccountLimits {
	return JetStreamAccountLimits{
		MaxMemory: b.MaxMemory - a.MaxMemory,
		MaxStore:  b.MaxStore - a.MaxStore,
	}
}

// JetStreamUsage reports on JetStream usage and limits for an account.
func (a *Account) JetStreamUsage() JetStreamAccountStats {
	a.mu.RLock()
	jsa := a.js
	a.mu.RUnlock()

	var stats JetStreamAccountStats
	if jsa != nil {
		jsa.mu.Lock()
		stats.Memory = uint64(jsa.memUsed)
		stats.Store = uint64(jsa.storeUsed)
		stats.MsgSets = len(jsa.msgSets)
		stats.Limits = jsa.limits
		jsa.mu.Unlock()
	}
	return stats
}

// DisableJetStream will disable JetStream for this account.
func (a *Account) DisableJetStream() error {
	a.mu.RLock()
	s := a.srv
	a.mu.RUnlock()
	if s == nil {
		return fmt.Errorf("jetstream account not registered")
	}

	js := s.getJetStream()
	if js == nil {
		return fmt.Errorf("jetstream not enabled")
	}

	jsa := js.lookupAccount(a)
	if jsa == nil {
		return fmt.Errorf("jetstream not enabled for account")
	}

	// Remove service imports.
	for _, export := range allJsExports {
		from := strings.Replace(export, ".*.", tsep, -1)
		a.removeServiceImport(from)
	}

	js.mu.Lock()
	if jsa, ok := js.accounts[a]; !ok {
		js.mu.Unlock()
		return fmt.Errorf("jetstream not enabled for account")
	} else {
		delete(js.accounts, a)
		js.releaseResources(&jsa.limits)
	}
	js.mu.Unlock()

	a.mu.Lock()
	a.js = nil
	a.mu.Unlock()

	jsa.delete()

	return nil
}

// JetStreamEnabled is a helper to determine if jetstream is enabled for an account.
func (a *Account) JetStreamEnabled() bool {
	if a == nil {
		return false
	}
	a.mu.RLock()
	enabled := a.js != nil
	a.mu.RUnlock()
	return enabled
}

// Updates accounting on in use memory and storage.
func (jsa *jsAccount) updateUsage(storeType StorageType, delta int64) {
	// TODO(dlc) - atomics? snapshot limits?
	jsa.mu.Lock()
	if storeType == MemoryStorage {
		jsa.memUsed += delta
	} else {
		jsa.storeUsed += delta
	}
	jsa.mu.Unlock()
}

func (jsa *jsAccount) limitsExceeded(storeType StorageType) bool {
	var exceeded bool
	jsa.mu.Lock()
	if storeType == MemoryStorage {
		if jsa.memUsed > jsa.limits.MaxMemory {
			exceeded = true
		}
	} else {
		if jsa.storeUsed > jsa.limits.MaxStore {
			exceeded = true
		}
	}
	jsa.mu.Unlock()
	return exceeded
}

// Check if a new proposed msg set while exceed our account limits.
// Lock should be held.
func (jsa *jsAccount) checkLimits(config *MsgSetConfig) error {
	if jsa.limits.MaxMsgSets > 0 && len(jsa.msgSets) >= jsa.limits.MaxMsgSets {
		return fmt.Errorf("maximum number of message sets reached")
	}
	// FIXME(dlc) - Add check here for replicas based on clustering.
	if config.Replicas != 1 {
		return fmt.Errorf("replicas setting of %d not allowed", config.Replicas)
	}
	// Check MaxObservables
	if config.MaxObservables > 0 && config.MaxObservables > jsa.limits.MaxObservables {
		return fmt.Errorf("maximum observables exceeds account limit")
	} else {
		config.MaxObservables = jsa.limits.MaxObservables
	}
	// Check storage, memory or disk.
	if config.MaxBytes > 0 {
		mb := config.MaxBytes * int64(config.Replicas)
		switch config.Storage {
		case MemoryStorage:
			if jsa.memReserved+mb > jsa.limits.MaxMemory {
				return fmt.Errorf("insufficient memory resources available")
			}
		case FileStorage:
			if jsa.storeReserved+mb > jsa.limits.MaxStore {
				return fmt.Errorf("insufficient storage resources available")
			}
		}
	}
	return nil
}

// delete the JetStream resources.
func (jsa *jsAccount) delete() {
	var msgSets []*MsgSet
	jsa.mu.Lock()
	for _, ms := range jsa.msgSets {
		msgSets = append(msgSets, ms)
	}
	jsa.mu.Unlock()
	for _, ms := range msgSets {
		ms.Delete()
	}
}

func (js *jetStream) lookupAccount(a *Account) *jsAccount {
	js.mu.RLock()
	jsa := js.accounts[a]
	js.mu.RUnlock()
	return jsa
}

// Will dynamically create limits for this account.
func (js *jetStream) dynamicAccountLimits() *JetStreamAccountLimits {
	js.mu.RLock()
	// For now used all resources. Mostly meant for $G in non-account mode.
	limits := &JetStreamAccountLimits{js.config.MaxMemory, js.config.MaxStore, -1, -1}
	js.mu.RUnlock()
	return limits
}

// Check to see if we have enough system resources for this account.
// Lock should be held.
func (js *jetStream) sufficientResources(limits *JetStreamAccountLimits) error {
	if limits == nil {
		return nil
	}
	if js.memReserved+limits.MaxMemory > js.config.MaxMemory {
		return fmt.Errorf("insufficient memory resources available")
	}
	if js.storeReserved+limits.MaxStore > js.config.MaxStore {
		return fmt.Errorf("insufficient storage resources available")
	}
	return nil
}

// This will (blindly) reserve the respources requested.
// Lock should be held.
func (js *jetStream) reserveResources(limits *JetStreamAccountLimits) error {
	if limits == nil {
		return nil
	}
	if limits.MaxMemory > 0 {
		js.memReserved += limits.MaxMemory
	}
	if limits.MaxStore > 0 {
		js.storeReserved += limits.MaxStore
	}
	return nil
}

func (js *jetStream) releaseResources(limits *JetStreamAccountLimits) error {
	if limits == nil {
		return nil
	}
	if limits.MaxMemory > 0 {
		js.memReserved -= limits.MaxMemory
	}
	if limits.MaxStore > 0 {
		js.storeReserved -= limits.MaxStore
	}
	return nil
}

// Request to check if jetstream is enabled.
func (s *Server) isJsEnabledRequest(sub *subscription, c *client, subject, reply string, msg []byte) {
	if c != nil && c.acc != nil && c.acc.JetStreamEnabled() {
		s.sendInternalAccountMsg(c.acc, reply, OK)
	}
}

const (
	// JetStreamStoreDir is the prefix we use.
	JetStreamStoreDir = "jetstream"
	// JetStreamMaxStoreDefault is the default disk storage limit. 1TB
	JetStreamMaxStoreDefault = 1024 * 1024 * 1024 * 1024
	// JetStreamMaxMemDefault is only used when we can't determine system memory. 256MB
	JetStreamMaxMemDefault = 1024 * 1024 * 256
)

// Dynamically create a config with a tmp based directory (repeatable) and 75% of system memory.
func (s *Server) dynJetStreamConfig() *JetStreamConfig {
	jsc := &JetStreamConfig{}
	jsc.StoreDir = filepath.Join(os.TempDir(), JetStreamStoreDir)
	jsc.MaxStore = JetStreamMaxStoreDefault
	// Estimate to 75% of total memory if we can determine system memory.
	if sysMem := sysmem.Memory(); sysMem > 0 {
		jsc.MaxMemory = sysMem / 4 * 3
	} else {
		jsc.MaxMemory = JetStreamMaxMemDefault
	}
	return jsc
}

// friendlyBytes returns a string with the given bytes int64
// represented as a size, such as 1KB, 10MB, etc...
func FriendlyBytes(bytes int64) string {
	fbytes := float64(bytes)
	base := 1024
	pre := []string{"K", "M", "G", "T", "P", "E"}
	if fbytes < float64(base) {
		return fmt.Sprintf("%v B", fbytes)
	}
	exp := int(math.Log(fbytes) / math.Log(float64(base)))
	index := exp - 1
	return fmt.Sprintf("%.2f %sB", fbytes/math.Pow(float64(base), float64(exp)), pre[index])
}

func isValidName(name string) bool {
	if name == "" {
		return false
	}
	return !strings.ContainsAny(name, ".*>")
}