package verification

import (
	"context"
	"errors"
	"time"

	verificationmodel "git.sendico.io/tech/sxchnge/product/verification/model"
	"git.sendico.io/tech/sxchnge/shared/database/repository"
	"git.sendico.io/tech/sxchnge/shared/database/repository/builder"
	"git.sendico.io/tech/sxchnge/shared/errors"
)

type CreateResult struct {
	VerificationToken string
	Created           bool
	ExpiresAt         time.Time
}

func activeContextFilter(request *Request, now time.Time) builder.Query {
	filters := []builder.Query{
		repository.Filter("accountRef", request.AccountRef),
		repository.Filter("purpose", request.Purpose),
		targetFilter(request.Target),
		repository.Filter("usedAt", nil),
		repository.Query().Comparison(repository.Field("expiresAt"), builder.Gt, now),
	}
	filters = appendContextRefFilter(filters, request.Purpose, request.ContextRef)
	return repository.Query().And(filters...)
}

func cooldownActiveContextFilter(request *Request, now, cutoff time.Time) builder.Query {
	filters := []builder.Query{
		repository.Filter("accountRef", request.AccountRef),
		repository.Filter("purpose", request.Purpose),
		targetFilter(request.Target),
		repository.Filter("usedAt", nil),
		repository.Query().Comparison(repository.Field("expiresAt"), builder.Gt, now),
		repository.Query().Comparison(repository.Field("createdAt"), builder.Gt, cutoff),
	}
	filters = appendContextRefFilter(filters, request.Purpose, request.ContextRef)
	return repository.Query().And(filters...)
}

func hashFilter(hash string) builder.Query {
	return repository.Filter("verifyTokenHash", hash)
}

func storedVerificationInstant(value time.Time) time.Time {
	return value.UTC().Truncate(time.Millisecond)
}

func newVerificationToken(
	request *Request,
	idempotencyKey string,
	hasIdempotency bool,
) (*verificationmodel.VerificationToken, string, error) {

	now := storedVerificationInstant(time.Now())

	var (
		raw  string
		hash string
		salt *string
		err  error
	)

	switch request.Kind {
	case TokenKindOTP:
		if hasIdempotency {
			var saltValue string
			raw, saltValue, hash = generateDeterministicOTP(idempotencySeed(request, idempotencyKey))
			salt = &saltValue
		} else {
			var s string
			raw, s, hash, err = generateOTP()
			if err != nil {
				return nil, "", err
			}
			salt = &s
		}

	default: // Magic token
		if hasIdempotency {
			raw, hash = generateDeterministicMagic(idempotencySeed(request, idempotencyKey))
		} else {
			raw, hash, err = generateMagic()
			if err != nil {
				return nil, "", err
			}
		}
	}

	token := &verificationmodel.VerificationToken{
		AccountRef:      request.AccountRef,
		Purpose:         request.Purpose,
		Target:          request.Target,
		ContextRef:      request.ContextRef,
		IdempotencyKey:  nil,
		VerifyTokenHash: hash,
		Salt:            salt,
		UsedAt:          nil,
		ExpiresAt:       storedVerificationInstant(now.Add(request.Ttl)),
		MaxRetries:      request.MaxRetries,
	}
	if hasIdempotency {
		token.IdempotencyKey = &idempotencyKey
	}

	return token, raw, nil
}

func (db *verificationDB) Create(
	ctx context.Context,
	request *Request,
) (string, error) {
	result, err := db.CreateWithResult(ctx, request)
	if err != nil {
		return "", err
	}
	return result.VerificationToken, nil
}

func (db *verificationDB) CreateWithResult(
	ctx context.Context,
	request *Request,
) (CreateResult, error) {

	if request == nil {
		return CreateResult{}, merrors.Internal("nil request")
	}
	contextRef, err := normalizeContextRef(request.Purpose, request.ContextRef)
	if err != nil {
		return CreateResult{}, err
	}
	request.ContextRef = contextRef

	idempotencyKey, hasIdempotency := normalizedIdempotencyKey(request.IdempotencyKey)
	if !hasIdempotency {
		// Always store an idempotency key. Client keys enable replay; generated
		// keys avoid null-key collisions on older Mongo indexes and keep
		// transaction retries deterministic.
		idempotencyKey, err = syntheticIdempotencyKey()
		if err != nil {
			return CreateResult{}, err
		}
		hasIdempotency = true
	}

	token, raw, err := newVerificationToken(request, idempotencyKey, hasIdempotency)
	if err != nil {
		return CreateResult{}, err
	}

	result, err := db.tf.CreateTransaction().Execute(ctx, func(tx context.Context) (any, error) {
		now := time.Now().UTC()

		activeFilter := activeContextFilter(request, now)

		// Idempotency and transaction-retry support.
		if hasIdempotency {
			replayedToken, replayed, err := db.lookupIdempotencyReplay(tx, request, idempotencyKey)
			if err != nil {
				return nil, err
			}
			if replayed {
				return CreateResult{Created: false, ExpiresAt: replayedToken.ExpiresAt}, nil
			}

			var sameToken verificationmodel.VerificationToken
			err = db.FindOne(tx, hashFilter(token.VerifyTokenHash), &sameToken)
			switch {
			case err == nil:
				// Same hash means the same Create operation already succeeded.
				return CreateResult{Created: true, ExpiresAt: sameToken.ExpiresAt}, nil
			case errors.Is(err, merrors.ErrNoData):
			default:
				return nil, err
			}
		}

		// 1) Cooldown: if there exists ANY active token created after cutoff → block
		if request.Cooldown != nil {
			cutoff := now.Add(-*request.Cooldown)

			var recent verificationmodel.VerificationToken
			err := db.FindOne(tx, cooldownActiveContextFilter(request, now, cutoff), &recent)
			switch {
			case err == nil:
				retryAfter := recent.CreatedAt.Add(*request.Cooldown).Sub(now)
				return nil, ErrorCooldownActiveFor(retryAfter)
			case errors.Is(err, merrors.ErrNoData):
			default:
				return nil, err
			}
		}

		// Reserve every abuse-control scope in the same transaction as token
		// creation. A denied request rolls back all reservations and cannot race
		// another instance into publishing an extra code.
		if err := db.reserveIssuance(tx, request, now); err != nil {
			return nil, err
		}

		// 2) Invalidate active tokens for this context
		if _, err := db.PatchMany(
			tx,
			activeFilter,
			repository.Patch().Set(repository.Field("usedAt"), now),
		); err != nil {
			return nil, err
		}

		// 3) Create new token only after cooldown/idempotency checks pass.
		if err := db.DBImp.Create(tx, token); err != nil {
			if hasIdempotency && errors.Is(err, merrors.ErrDataConflict) {
				replayedToken, replayed, replayErr := db.lookupIdempotencyReplay(tx, request, idempotencyKey)
				if replayErr != nil {
					return nil, replayErr
				}
				if replayed {
					return CreateResult{Created: false, ExpiresAt: replayedToken.ExpiresAt}, nil
				}

				var sameToken verificationmodel.VerificationToken
				findErr := db.FindOne(tx, hashFilter(token.VerifyTokenHash), &sameToken)
				switch {
				case findErr == nil:
					return CreateResult{Created: true, ExpiresAt: sameToken.ExpiresAt}, nil
				case errors.Is(findErr, merrors.ErrNoData):
				default:
					return nil, findErr
				}
			}
			return nil, err
		}
		return CreateResult{Created: true, ExpiresAt: token.ExpiresAt}, nil
	})

	if err != nil {
		return CreateResult{}, err
	}

	createResult, ok := result.(CreateResult)
	if !ok {
		return CreateResult{}, merrors.Internal("unexpected verification create result")
	}

	createResult.VerificationToken = raw
	return createResult, nil
}

// Older records omit an empty target; Mongo does not equate a missing field
// with the empty string. Match both forms for cooldown, invalidation and replay.
func targetFilter(target string) builder.Query {
	if target != "" {
		return repository.Filter("target", target)
	}
	return repository.Query().Or(repository.Filter("target", ""), repository.Filter("target", nil))
}