// Package pushserver turns events into notifications: it keeps each user's
// push rules and pushers, evaluates every event against the rules of every
// local member of its room, records what notified whom with per-room unread
// counts, and pushes to the push gateways of the users' devices.
//
// It is PLAN.md Phase 8. The rule language is internal/pushrules; this
// package is everything around it that needs storage, rooms or a network.
//
// It hangs off the roomserver's emit stage like the federation queue does,
// and like the queue it does no work there: the emit stage runs with the
// room's write lock held, and evaluating an event needs the room's members,
// their display names, the power levels and a ruleset per member. So an
// event is put on a list and a worker of this package's own takes it from
// there. What that costs is a moment in which a sync can show a message
// whose notification has not been counted yet; the counts are a stream of
// their own in the sync token (see storage.PushStore), so the sync that
// follows the worker's write carries the corrected count.
package pushserver

import (
	"context"
	"errors"
	"log/slog"
	"net/http"
	"sync"
	"time"

	"github.com/dariuszjaniak/warp/server/internal/pushrules"
	"github.com/dariuszjaniak/warp/server/internal/roomserver"
	"github.com/dariuszjaniak/warp/server/internal/storage"
)

// Errors callers have to tell apart. The rule-language sentinels are
// re-exported so that a handler needs only this package.
var (
	ErrNoSuchRule   = pushrules.ErrNoSuchRule
	ErrNoSuchAnchor = pushrules.ErrNoSuchAnchor
	ErrInvalidRule  = pushrules.ErrInvalidRule

	// ErrInvalidPusher is a pusher a client may not register.
	ErrInvalidPusher = errors.New("invalid pusher")

	// ErrMissingPusherField is a pusher missing a field the spec requires.
	ErrMissingPusherField = errors.New("missing pusher field")
)

// Accounts is the part of the userapi this package needs: push rules are
// the m.push_rules account data. *userapi.API satisfies it.
type Accounts interface {
	AccountData(ctx context.Context, localpart, roomID, dataType string) ([]byte, error)
	SetAccountData(ctx context.Context, localpart, roomID, dataType string, content []byte) error
}

// Rooms is the part of the roomserver this package reads. *roomserver.API
// satisfies it.
type Rooms interface {
	PushRoomFor(ctx context.Context, roomID string) (roomserver.PushRoom, error)
	Event(ctx context.Context, roomID, userID, eventID string) (roomserver.ClientEvent, error)
	EventPosition(ctx context.Context, roomID, userID, eventID string) (int64, error)
}

// Notifier wakes a user's blocked syncs. *syncapi.Notifier satisfies it.
type Notifier interface {
	NotifyUser(userID string)
	NotifyUsers(userIDs []string)
}

// API is the push server.
type API struct {
	serverName string
	store      storage.PushStore
	accounts   Accounts
	rooms      Rooms
	notifier   Notifier
	gateway    *gateway
	log        *slog.Logger
	now        func() time.Time

	// pushEnabled sends pushes to gateways. Notifications are counted
	// either way: the counts are what a client shows, and are no less
	// right on a server that does not push.
	pushEnabled bool

	// retention is how long a read notification is kept for GET
	// /notifications before it is pruned.
	retention time.Duration

	// rules caches each user's merged ruleset. Every event is evaluated
	// against the rules of every local member of its room, and reading
	// and merging them from account data each time would put a query per
	// member in front of every message. Every write goes through this
	// package, which is what makes the cache safe in one process.
	rulesMu    sync.Mutex
	rulesCache map[string]pushrules.Ruleset
	writeLocks sync.Map // localpart -> *sync.Mutex

	// The event list the emit stage appends to and the worker drains.
	mu       sync.Mutex
	incoming []roomserver.Notification
	busy     bool
	wake     chan struct{}
	idle     *sync.Cond

	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup
}

// Options configure the component.
type Options struct {
	ServerName string
	Store      storage.PushStore
	Accounts   Accounts
	Rooms      Rooms

	// Notifier wakes the syncs a count change concerns. Nil wakes
	// nobody, which only a test wants.
	Notifier Notifier

	// PushEnabled sends pushes to the pushers' gateways.
	PushEnabled bool

	// IncludeContent puts the event's content into a push. Off, a push
	// carries only who sent what kind of event where, for operators who
	// would rather not have message text pass through a third-party push
	// service.
	IncludeContent bool

	// GatewayTimeout bounds one request to a push gateway.
	GatewayTimeout time.Duration

	// HTTPClient sends pushes; nil builds one. Tests pass their own.
	HTTPClient *http.Client

	// NotificationRetention is how long a read notification is kept.
	NotificationRetention time.Duration

	Logger *slog.Logger
	Now    func() time.Time
}

// Defaults.
const (
	DefaultGatewayTimeout        = 10 * time.Second
	DefaultNotificationRetention = 30 * 24 * time.Hour

	// pruneInterval is how often read notifications past their retention
	// are deleted.
	pruneInterval = time.Hour
)

// New builds the component and starts its worker. Close stops it.
func New(opts Options) (*API, error) {
	switch {
	case opts.ServerName == "":
		return nil, errors.New("pushserver: ServerName must not be empty")
	case opts.Store == nil:
		return nil, errors.New("pushserver: Store must not be nil")
	case opts.Accounts == nil:
		return nil, errors.New("pushserver: Accounts must not be nil")
	case opts.Rooms == nil:
		return nil, errors.New("pushserver: Rooms must not be nil")
	}
	if opts.Logger == nil {
		opts.Logger = slog.Default()
	}
	if opts.Now == nil {
		opts.Now = time.Now
	}
	if opts.GatewayTimeout <= 0 {
		opts.GatewayTimeout = DefaultGatewayTimeout
	}
	if opts.NotificationRetention <= 0 {
		opts.NotificationRetention = DefaultNotificationRetention
	}
	if opts.HTTPClient == nil {
		opts.HTTPClient = &http.Client{Timeout: opts.GatewayTimeout}
	}

	ctx, cancel := context.WithCancel(context.Background())
	a := &API{
		serverName:  opts.ServerName,
		store:       opts.Store,
		accounts:    opts.Accounts,
		rooms:       opts.Rooms,
		notifier:    opts.Notifier,
		log:         opts.Logger,
		now:         opts.Now,
		pushEnabled: opts.PushEnabled,
		retention:   opts.NotificationRetention,
		rulesCache:  map[string]pushrules.Ruleset{},
		wake:        make(chan struct{}, 1),
		ctx:         ctx,
		cancel:      cancel,
	}
	a.idle = sync.NewCond(&a.mu)
	a.gateway = newGateway(gatewayOptions{
		client:         opts.HTTPClient,
		includeContent: opts.IncludeContent,
		rejected:       a.pushKeyRejected,
		log:            opts.Logger,
	})

	a.wg.Add(2)
	go a.work()
	go a.prune()
	a.gateway.start(ctx)
	return a, nil
}

// Close stops the worker and the gateway senders. Events not yet
// evaluated are dropped: the emit stage is not durable, and a
// notification is not worth holding up a shutdown for.
func (a *API) Close() {
	a.cancel()
	a.mu.Lock()
	a.idle.Broadcast()
	a.mu.Unlock()
	a.wg.Wait()
	a.gateway.wait()
}

// notifyUsers wakes syncs, if there is anybody to wake them.
func (a *API) notifyUsers(userIDs ...string) {
	if a.notifier == nil || len(userIDs) == 0 {
		return
	}
	a.notifier.NotifyUsers(userIDs)
}

// prune deletes read notifications past their retention, hourly.
func (a *API) prune() {
	defer a.wg.Done()
	ticker := time.NewTicker(pruneInterval)
	defer ticker.Stop()
	for {
		select {
		case <-a.ctx.Done():
			return
		case <-ticker.C:
		}
		cutoff := a.now().Add(-a.retention).UnixMilli()
		n, err := a.store.PruneNotifications(a.ctx, cutoff)
		switch {
		case err != nil && a.ctx.Err() == nil:
			a.log.Warn("pruning read notifications failed", "error", err)
		case n > 0:
			a.log.Debug("pruned read notifications", "count", n)
		}
	}
}