package repositories

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"strings"

	"agent-desk/internal/models"
	"agent-desk/internal/pkg/enums"
	"gorm.io/gorm"
)

// ErrAmbiguousCustomerIdentity requires deliberate operator reconciliation. Never
// choose the first row: the historical unique index also includes customer_id.
var ErrAmbiguousCustomerIdentity = errors.New("ambiguous customer identity")

// GetUniqueBy includes disabled rows when detecting conflicts. A disabled mapping
// must not let a caller create a replacement customer and reacquire the identity.
func (r *customerIdentityRepository) GetUniqueBy(db *gorm.DB, scope string, source enums.ExternalSource, externalID string) (*models.CustomerIdentity, error) {
	if strings.TrimSpace(string(source)) == "" || strings.TrimSpace(externalID) == "" {
		return nil, errors.New("invalid customer identity")
	}
	var identities []models.CustomerIdentity
	query := db.Where("identity_scope = ? AND external_source = ? AND external_id = ?", scope, source, strings.TrimSpace(externalID))
	if key := ScopedCustomerIdentityKey(scope, source, externalID); key != nil {
		// Digest comparison is independent of MySQL's external_id collation. The
		// NULL branch also detects manually migrated/inconsistent scoped mappings.
		query = db.Where("scoped_key = ? OR (scoped_key IS NULL AND identity_scope = ? AND external_source = ? AND external_id = ?)", *key, scope, source, strings.TrimSpace(externalID))
	}
	err := query.Limit(2).Find(&identities).Error
	if err != nil {
		return nil, err
	}
	if len(identities) > 1 {
		return nil, ErrAmbiguousCustomerIdentity
	}
	if len(identities) == 0 {
		return nil, nil
	}
	if identities[0].IdentityScope != scope || identities[0].ExternalSource != source || identities[0].ExternalID != strings.TrimSpace(externalID) {
		return nil, ErrAmbiguousCustomerIdentity
	}
	if identities[0].Status != enums.StatusOk {
		return nil, errors.New("inactive customer identity")
	}
	return &identities[0], nil
}

// ScopedCustomerIdentityKey gives new scoped registrations a database-enforced
// claim without imposing a new unique constraint on dirty legacy data. Both
// SQLite and MySQL permit multiple NULL values in a unique index. Encoding an
// array avoids delimiter collisions and hashing avoids collation ambiguity.
func ScopedCustomerIdentityKey(scope string, source enums.ExternalSource, externalID string) *string {
	if scope == "" {
		return nil
	}
	encoded, _ := json.Marshal([]string{scope, string(source), strings.TrimSpace(externalID)})
	digest := sha256.Sum256(encoded)
	key := hex.EncodeToString(digest[:])
	return &key
}