package service

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"sort"
	"sync"
	"time"

	"github.com/google/uuid"

	"apskel-pos-be/internal/entities"
	"apskel-pos-be/internal/logger"
	"apskel-pos-be/internal/models"
	"apskel-pos-be/internal/repository"
)

const (
	defaultWalletReconciliationInterval = 6 * time.Hour
	// Per check, so one systematic bug cannot flood the log or the notification.
	walletReconciliationLimit = 50
)

type walletDiscrepancyFinder interface {
	FindDiscrepancies(ctx context.Context, limit int) ([]repository.WalletDiscrepancy, error)
}

type organizationUserLister interface {
	GetByOrganizationID(ctx context.Context, organizationID uuid.UUID) ([]*entities.User, error)
}

type notificationSender interface {
	Send(ctx context.Context, req *models.SendNotificationRequest) (*models.NotificationResponse, error)
}

// WalletReconciliationJob periodically runs the §7.5 checks of
// docs/prd-point-coin.md over every wallet (PC-108). It is silent while the data is
// consistent. When it finds a discrepancy it logs each one and notifies the admins,
// owners and managers of the organization concerned.
//
// An organization is notified again only when its set of discrepancies changes, so an
// unfixed problem does not page the same people every run. That memory is in-process:
// a restart notifies once more, and each running instance keeps its own.
type WalletReconciliationJob struct {
	finder   walletDiscrepancyFinder
	users    organizationUserLister
	notifier notificationSender

	mu       sync.Mutex
	notified map[uuid.UUID]string // organization -> fingerprint last notified
	stopCh   chan struct{}
	stopOnce sync.Once
}

func NewWalletReconciliationJob(finder walletDiscrepancyFinder, users organizationUserLister, notifier notificationSender) *WalletReconciliationJob {
	return &WalletReconciliationJob{
		finder:   finder,
		users:    users,
		notifier: notifier,
		notified: make(map[uuid.UUID]string),
		stopCh:   make(chan struct{}),
	}
}

// Start runs the checks once now and then every interval, in the background.
func (j *WalletReconciliationJob) Start(interval time.Duration) {
	if interval <= 0 {
		interval = defaultWalletReconciliationInterval
	}
	go func() {
		j.runLogged()
		ticker := time.NewTicker(interval)
		defer ticker.Stop()
		for {
			select {
			case <-ticker.C:
				j.runLogged()
			case <-j.stopCh:
				return
			}
		}
	}()
	logger.NonContext.Infof("Wallet reconciliation job started (interval: %s)", interval)
}

func (j *WalletReconciliationJob) Stop() {
	j.stopOnce.Do(func() { close(j.stopCh) })
}

func (j *WalletReconciliationJob) runLogged() {
	if _, err := j.RunOnce(context.Background()); err != nil {
		logger.NonContext.Error("Wallet reconciliation failed to run", err)
	}
}

// RunOnce runs every check, reports what it finds, and returns it.
func (j *WalletReconciliationJob) RunOnce(ctx context.Context) ([]repository.WalletDiscrepancy, error) {
	found, err := j.finder.FindDiscrepancies(ctx, walletReconciliationLimit)
	if err != nil {
		return nil, err
	}

	byOrg := make(map[uuid.UUID][]repository.WalletDiscrepancy)
	for _, d := range found {
		fields := map[string]interface{}{
			"check":           d.Check,
			"organization_id": d.OrganizationID.String(),
			"customer_id":     d.CustomerID.String(),
			"currency":        d.Currency,
			"expected":        d.Expected,
			"actual":          d.Actual,
		}
		if d.ObjectID != nil {
			fields["object_id"] = d.ObjectID.String()
		}
		logger.NonContext.WarnWithFields("Wallet reconciliation found a discrepancy", fields, nil)
		byOrg[d.OrganizationID] = append(byOrg[d.OrganizationID], d)
	}

	j.mu.Lock()
	defer j.mu.Unlock()
	// Organizations that are clean again are forgotten, so a later problem notifies.
	for org := range j.notified {
		if _, still := byOrg[org]; !still {
			delete(j.notified, org)
		}
	}
	for org, discrepancies := range byOrg {
		fingerprint := walletDiscrepancyFingerprint(discrepancies)
		if j.notified[org] == fingerprint {
			continue
		}
		if err := j.notify(ctx, org, discrepancies); err != nil {
			logger.NonContext.Error(fmt.Sprintf("Wallet reconciliation could not notify organization %s", org), err)
			continue
		}
		j.notified[org] = fingerprint
	}
	return found, nil
}

func (j *WalletReconciliationJob) notify(ctx context.Context, organizationID uuid.UUID, discrepancies []repository.WalletDiscrepancy) error {
	if organizationID == uuid.Nil {
		return fmt.Errorf("discrepancy without an organization")
	}
	users, err := j.users.GetByOrganizationID(ctx, organizationID)
	if err != nil {
		return err
	}
	var receivers []uuid.UUID
	for _, u := range users {
		switch u.Role {
		case entities.RoleAdmin, entities.RoleOwner, entities.RoleManager:
			receivers = append(receivers, u.ID)
		}
	}
	if len(receivers) == 0 {
		return nil
	}

	perCheck := map[string]int{}
	customers := map[string]bool{}
	for _, d := range discrepancies {
		perCheck[d.Check]++
		customers[d.CustomerID.String()] = true
	}
	customerIDs := make([]string, 0, len(customers))
	for id := range customers {
		customerIDs = append(customerIDs, id)
	}
	sort.Strings(customerIDs)

	_, err = j.notifier.Send(ctx, &models.SendNotificationRequest{
		Title: "Selisih saldo EnakPoint/EnakCoin terdeteksi",
		Body: fmt.Sprintf("Pemeriksaan rutin menemukan %d selisih pada saldo %d customer. Saldo belum dikoreksi otomatis; tim teknis perlu memeriksanya.",
			len(discrepancies), len(customerIDs)),
		Type:           "system",
		Category:       "wallet_reconciliation",
		Priority:       entities.NotificationPriorityHigh,
		NotifiableType: "organization",
		NotifiableID:   &organizationID,
		ReceiverIDs:    receivers,
		Data: map[string]interface{}{
			"organization_id": organizationID.String(),
			"discrepancies":   len(discrepancies),
			"per_check":       perCheck,
			"customer_ids":    customerIDs,
		},
	})
	return err
}

// walletDiscrepancyFingerprint identifies a set of discrepancies regardless of order.
func walletDiscrepancyFingerprint(discrepancies []repository.WalletDiscrepancy) string {
	keys := make([]string, 0, len(discrepancies))
	for _, d := range discrepancies {
		object := ""
		if d.ObjectID != nil {
			object = d.ObjectID.String()
		}
		keys = append(keys, fmt.Sprintf("%s|%s|%s|%s|%d|%d", d.Check, d.CustomerID, d.Currency, object, d.Expected, d.Actual))
	}
	sort.Strings(keys)
	h := sha256.New()
	for _, k := range keys {
		h.Write([]byte(k))
		h.Write([]byte{'\n'})
	}
	return hex.EncodeToString(h.Sum(nil))
}