package admin

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"strings"

	"github.com/google/uuid"

	"github.com/yuxingu/digital-psychology/apps/api/internal/repository"
)

var (
	ErrBadBatchQty   = errString("quantity must be 1..100")
	ErrCodeDisable   = errString("code not unused")
	ErrBatchNotFound = errString("batch not found")
)

// CreateRedemptionBatch generates codes for a membership plan.
func (s *Service) CreateRedemptionBatch(
	ctx context.Context, adminID uuid.UUID, label, planCode string, qty int,
) (*repository.RedemptionBatch, []repository.RedemptionCodeRow, error) {
	label = strings.TrimSpace(label)
	planCode = strings.TrimSpace(planCode)
	if label == "" || qty < 1 || qty > 100 {
		return nil, nil, ErrBadBatchQty
	}
	if _, err := s.GetMembershipPlan(ctx, planCode); err != nil {
		return nil, nil, err
	}
	codes := make([]string, 0, qty)
	seen := map[string]struct{}{}
	for len(codes) < qty {
		c, err := newRedemptionCode()
		if err != nil {
			return nil, nil, err
		}
		if _, ok := seen[c]; ok {
			continue
		}
		seen[c] = struct{}{}
		codes = append(codes, c)
	}
	meta, _ := json.Marshal(map[string]any{"label": label, "plan": planCode, "quantity": qty})
	return s.Repo.CreateRedemptionBatchWithCodes(ctx, adminID, label, planCode, codes, meta)
}

// ListRedemptionBatches lists recent batches.
func (s *Service) ListRedemptionBatches(ctx context.Context, limit int) ([]repository.RedemptionBatch, error) {
	items, err := s.Repo.ListRedemptionBatches(ctx, limit)
	if err != nil {
		return nil, err
	}
	if items == nil {
		items = []repository.RedemptionBatch{}
	}
	return items, nil
}

// ListRedemptionCodes lists codes in a batch.
func (s *Service) ListRedemptionCodes(ctx context.Context, batchID uuid.UUID) ([]repository.RedemptionCodeRow, error) {
	ok, err := s.Repo.BatchExists(ctx, batchID)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, ErrBatchNotFound
	}
	items, err := s.Repo.ListRedemptionCodesByBatch(ctx, batchID)
	if err != nil {
		return nil, err
	}
	if items == nil {
		items = []repository.RedemptionCodeRow{}
	}
	return items, nil
}

// DisableRedemptionCode voids an unused code.
func (s *Service) DisableRedemptionCode(ctx context.Context, adminID, codeID uuid.UUID) error {
	err := s.Repo.DisableRedemptionCode(ctx, adminID, codeID)
	if err != nil && err.Error() == "code not unused" {
		return ErrCodeDisable
	}
	return err
}

func newRedemptionCode() (string, error) {
	b := make([]byte, 6)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return "YXG-" + strings.ToUpper(hex.EncodeToString(b)), nil
}