bookhoard/internal/services/collection_service.go

package services

import (
	"bookhoard/internal/database"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgconn"
	"github.com/jackc/pgx/v5/pgtype"
)

// ErrCollectionNameTaken: the user already has a collection with this name.
var ErrCollectionNameTaken = errors.New("collection name already exists")

// Rule represents an auto-assign rule for collections
type Rule struct {
	ID       string `json:"id"`
	Field    string `json:"field"`    // "genre", "series", "author", "language", "publisher", "copyright_year", "tags"
	Operator string `json:"operator"` // "equals", "contains", "starts_with", "ends_with", "greater_than", "less_than"
	Value    string `json:"value"`
	Priority int    `json:"priority"` // 1-10, higher values take precedence
	// Enabled gates the rule in the LIVE evaluation used by smart
	// collections; absent (JSON omitempty) means enabled — rules written
	// before the field existed keep matching.
	Enabled *bool `json:"enabled,omitempty"`
}

// Known rule fields and operators — the rules builder UI and the
// persisted JSONB documents must agree with this vocabulary.
var ruleFields = map[string]bool{
	"genre": true, "series": true, "author": true, "language": true,
	"publisher": true, "copyright_year": true, "tags": true,
}

var ruleOperators = map[string]bool{
	"equals": true, "not_equals": true, "contains": true, "not_contains": true,
	"starts_with": true, "ends_with": true, "greater_than": true, "less_than": true,
}

// RuleValidationError reports a rule payload the evaluator could never
// honor (unknown field/operator, empty value).
type RuleValidationError struct{ Msg string }

func (e *RuleValidationError) Error() string { return e.Msg }

// RuleEvaluation represents the result of evaluating a rule
type RuleEvaluation struct {
	RuleID     string  `json:"rule_id"`
	Matches    bool    `json:"matches"`
	Confidence float64 `json:"confidence"`
}

// CollectionService handles collection management
type CollectionService struct {
	db *database.Queries
}

// NewCollectionService creates a new collection service
func NewCollectionService(db *database.Queries) *CollectionService {
	return &CollectionService{
		db: db,
	}
}

// CreateCollection creates a new collection
func (s *CollectionService) CreateCollection(ctx context.Context, userID uuid.UUID, name, description, color, icon string, autoAssignRules []Rule, viewSettings map[string]any) (database.Collections, error) {
	// Convert rules to JSONB ([]byte)
	var rulesJSON []byte
	if len(autoAssignRules) > 0 {
		var err error
		rulesJSON, err = json.Marshal(autoAssignRules)
		if err != nil {
			return database.Collections{}, fmt.Errorf("failed to marshal auto-assign rules: %v", err)
		}
	}

	// Convert view settings to JSONB ([]byte)
	var settingsJSON []byte
	if len(viewSettings) > 0 {
		var err error
		settingsJSON, err = json.Marshal(viewSettings)
		if err != nil {
			return database.Collections{}, fmt.Errorf("failed to marshal view settings: %v", err)
		}
	}

	collection, err := s.db.CreateCollection(ctx, database.CreateCollectionParams{
		UserID:          pgtype.UUID{Bytes: userID, Valid: true},
		Name:            name,
		Description:     pgtype.Text{String: description, Valid: description != ""},
		Color:           pgtype.Text{String: color, Valid: color != ""},
		Icon:            pgtype.Text{String: icon, Valid: icon != ""},
		AutoAssignRules: rulesJSON,
		ViewSettings:    settingsJSON,
	})

	if err != nil {
		// Duplicate name (UNIQUE(user_id, name)) is a client error, not a
		// server failure: surface it as 409 so callers can recover.
		var pgErr *pgconn.PgError
		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
			return database.Collections{}, ErrCollectionNameTaken
		}
		return database.Collections{}, fmt.Errorf("failed to create collection: %w", err)
	}

	return collection, nil
}

// GetCollection gets a collection by ID
func (s *CollectionService) GetCollection(ctx context.Context, collectionID uuid.UUID) (database.Collections, error) {
	collection, err := s.db.GetCollection(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		return database.Collections{}, fmt.Errorf("failed to get collection: %v", err)
	}

	return collection, nil
}

// GetCollectionWithBookCount gets a collection with book count
func (s *CollectionService) GetCollectionWithBookCount(ctx context.Context, collectionID uuid.UUID) (map[string]any, error) {
	collection, err := s.db.GetCollectionWithBookCount(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		return nil, fmt.Errorf("failed to get collection: %v", err)
	}

	return map[string]any{
		"id":                uuid.UUID(collection.ID.Bytes).String(),
		"user_id":           uuid.UUID(collection.UserID.Bytes).String(),
		"name":              collection.Name,
		"description":       collection.Description.String,
		"color":             collection.Color.String,
		"icon":              collection.Icon.String,
		"auto_assign_rules": collection.AutoAssignRules,
		"view_settings":     collection.ViewSettings,
		"created_at":        collection.CreatedAt.Time.String(),
		"book_count":        collection.BookCount,
	}, nil
}

// GetUserCollections gets all collections for a user
func (s *CollectionService) GetUserCollections(ctx context.Context, userID uuid.UUID) ([]database.Collections, error) {
	collections, err := s.db.GetCollectionsByUser(ctx, pgtype.UUID{Bytes: userID, Valid: true})
	if err != nil {
		return nil, fmt.Errorf("failed to get user collections: %v", err)
	}

	return collections, nil
}

// UpdateCollection updates a collection
func (s *CollectionService) UpdateCollection(ctx context.Context, collectionID uuid.UUID, name, description, color, icon string, autoAssignRules []Rule, viewSettings map[string]any) (database.Collections, error) {
	// Convert rules to JSONB ([]byte)
	var rulesJSON []byte
	if len(autoAssignRules) > 0 {
		var err error
		rulesJSON, err = json.Marshal(autoAssignRules)
		if err != nil {
			return database.Collections{}, fmt.Errorf("failed to marshal auto-assign rules: %v", err)
		}
	}

	// Convert view settings to JSONB ([]byte)
	var settingsJSON []byte
	if len(viewSettings) > 0 {
		var err error
		settingsJSON, err = json.Marshal(viewSettings)
		if err != nil {
			return database.Collections{}, fmt.Errorf("failed to marshal view settings: %v", err)
		}
	}

	collection, err := s.db.UpdateCollection(ctx, database.UpdateCollectionParams{
		ID:              pgtype.UUID{Bytes: collectionID, Valid: true},
		Name:            name,
		Description:     pgtype.Text{String: description, Valid: description != ""},
		Color:           pgtype.Text{String: color, Valid: color != ""},
		Icon:            pgtype.Text{String: icon, Valid: icon != ""},
		AutoAssignRules: rulesJSON,
		ViewSettings:    settingsJSON,
	})

	if err != nil {
		return database.Collections{}, fmt.Errorf("failed to update collection: %v", err)
	}

	return collection, nil
}

// DeleteCollection deletes a collection
func (s *CollectionService) DeleteCollection(ctx context.Context, collectionID uuid.UUID) error {
	// System collections (the 5 dashboard sections) are PERMANENT: a
	// delete tombstones the row (invisible everywhere, restorable with
	// the same id) instead of destroying it and every reference to it.
	row, err := s.db.GetCollection(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil // already gone: keep delete idempotent
		}
		return fmt.Errorf("failed to fetch collection: %w", err)
	}

	if row.IsSystemCollection.Bool {
		return s.db.TombstoneSystemCollection(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	}

	err = s.db.DeleteCollection(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		return fmt.Errorf("failed to delete collection: %w", err)
	}

	return nil
}

// AddBookToCollection adds a book to a collection
func (s *CollectionService) AddBookToCollection(ctx context.Context, collectionID, mediaItemID, userID uuid.UUID) error {
	_, err := s.db.AddBookToCollection(ctx, database.AddBookToCollectionParams{
		CollectionID:  pgtype.UUID{Bytes: collectionID, Valid: true},
		MediaItemID:   pgtype.UUID{Bytes: mediaItemID, Valid: true},
		AddedByUserID: pgtype.UUID{Bytes: userID, Valid: true},
	})

	if err != nil {
		return fmt.Errorf("failed to add book to collection: %v", err)
	}

	return nil
}

// RemoveBookFromCollection removes a book from a collection
func (s *CollectionService) RemoveBookFromCollection(ctx context.Context, collectionID, mediaItemID uuid.UUID) error {
	err := s.db.RemoveBookFromCollection(ctx, database.RemoveBookFromCollectionParams{
		CollectionID: pgtype.UUID{Bytes: collectionID, Valid: true},
		MediaItemID:  pgtype.UUID{Bytes: mediaItemID, Valid: true},
	})

	if err != nil {
		return fmt.Errorf("failed to remove book from collection: %v", err)
	}

	return nil
}

// GetCollectionBooks gets all books in a collection
func (s *CollectionService) GetCollectionBooks(ctx context.Context, collectionID uuid.UUID) ([]database.GetCollectionItemsRow, error) {
	books, err := s.db.GetCollectionItems(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		return nil, fmt.Errorf("failed to get collection books: %v", err)
	}

	return books, nil
}

// GetBookCollections gets all collections that contain a specific book
func (s *CollectionService) GetBookCollections(ctx context.Context, mediaItemID uuid.UUID) ([]database.Collections, error) {
	collections, err := s.db.GetCollectionsForBook(ctx, pgtype.UUID{Bytes: mediaItemID, Valid: true})
	if err != nil {
		return nil, fmt.Errorf("failed to get book collections: %v", err)
	}

	return collections, nil
}

// ParseRules decodes a collection's auto_assign_rules JSONB into typed
// rules. "null", empty, and malformed docs mean "no rules".
func (s *CollectionService) ParseRules(raw []byte) []Rule {
	if len(raw) == 0 {
		return nil
	}
	var rules []Rule
	if err := json.Unmarshal(raw, &rules); err != nil {
		return nil
	}
	return rules
}

// IsSmartCollection derives the collection type: a non-empty ruleset
// makes it SMART (live-matched), an empty/absent ruleset makes it STATIC
// (stored collection_items links).
func (s *CollectionService) IsSmartCollection(raw []byte) bool {
	return len(s.ParseRules(raw)) > 0
}

// EnabledRules filters a ruleset down to the rules that participate in
// live evaluation (absent enabled = enabled for backward compatibility).
func (s *CollectionService) EnabledRules(rules []Rule) []Rule {
	enabled := make([]Rule, 0, len(rules))
	for _, rule := range rules {
		if rule.Enabled == nil || *rule.Enabled {
			enabled = append(enabled, rule)
		}
	}
	return enabled
}

// validateRule checks a rule payload the evaluator will have to honor.
func (s *CollectionService) validateRule(rule Rule) error {
	if !ruleFields[rule.Field] {
		return &RuleValidationError{Msg: "unknown rule field: " + rule.Field}
	}
	if !ruleOperators[rule.Operator] {
		return &RuleValidationError{Msg: "unknown rule operator: " + rule.Operator}
	}
	if strings.TrimSpace(rule.Value) == "" {
		return &RuleValidationError{Msg: "rule value is required"}
	}
	if rule.Priority < 0 || rule.Priority > 10 {
		return &RuleValidationError{Msg: "priority must be between 0 and 10"}
	}
	return nil
}

// AddRule appends a rule to the collection's ruleset, generating an id
// when the caller did not supply one. Adding the first rule CONVERTS a
// static collection to smart (type is derived from rules presence).
func (s *CollectionService) AddRule(ctx context.Context, collectionID uuid.UUID, rule Rule) (database.Collections, Rule, error) {
	if err := s.validateRule(rule); err != nil {
		return database.Collections{}, Rule{}, err
	}

	collection, err := s.GetCollection(ctx, collectionID)
	if err != nil {
		return database.Collections{}, Rule{}, err
	}

	rules := s.ParseRules(collection.AutoAssignRules)
	if rule.ID == "" {
		rule.ID = uuid.NewString()
	}
	rules = append(rules, rule)

	rulesJSON, marshalErr := json.Marshal(rules)
	if marshalErr != nil {
		return database.Collections{}, Rule{}, fmt.Errorf("failed to marshal rules: %w", marshalErr)
	}

	updated, err := s.db.UpdateCollectionRulesJSON(ctx, database.UpdateCollectionRulesJSONParams{
		ID:              pgtype.UUID{Bytes: collectionID, Valid: true},
		AutoAssignRules: rulesJSON,
	})
	if err != nil {
		return database.Collections{}, Rule{}, fmt.Errorf("failed to save rules: %w", err)
	}
	return updated, rule, nil
}

// SetRuleEnabled flips a single rule's enabled flag in place.
func (s *CollectionService) SetRuleEnabled(ctx context.Context, collectionID uuid.UUID, ruleID string, enabled bool) (database.Collections, error) {
	collection, err := s.GetCollection(ctx, collectionID)
	if err != nil {
		return database.Collections{}, err
	}
	rules := s.ParseRules(collection.AutoAssignRules)
	found := false
	for i := range rules {
		if rules[i].ID == ruleID {
			rules[i].Enabled = &enabled
			found = true
			break
		}
	}
	if !found {
		return database.Collections{}, fmt.Errorf("rule not found: %s", ruleID)
	}

	rulesJSON, marshalErr := json.Marshal(rules)
	if marshalErr != nil {
		return database.Collections{}, fmt.Errorf("failed to marshal rules: %w", marshalErr)
	}

	updated, err := s.db.UpdateCollectionRulesJSON(ctx, database.UpdateCollectionRulesJSONParams{
		ID:              pgtype.UUID{Bytes: collectionID, Valid: true},
		AutoAssignRules: rulesJSON,
	})
	if err != nil {
		return database.Collections{}, fmt.Errorf("failed to save rules: %w", err)
	}
	return updated, nil
}

// RemoveRule deletes a single rule from the ruleset. Removing the LAST
// rule converts the collection back to static (type is derived).
func (s *CollectionService) RemoveRule(ctx context.Context, collectionID uuid.UUID, ruleID string) (database.Collections, error) {
	collection, err := s.GetCollection(ctx, collectionID)
	if err != nil {
		return database.Collections{}, err
	}
	rules := s.ParseRules(collection.AutoAssignRules)
	kept := make([]Rule, 0, len(rules))
	found := false
	for _, rule := range rules {
		if rule.ID == ruleID {
			found = true
			continue
		}
		kept = append(kept, rule)
	}
	if !found {
		return database.Collections{}, fmt.Errorf("rule not found: %s", ruleID)
	}

	rulesJSON, marshalErr := json.Marshal(kept)
	if marshalErr != nil {
		return database.Collections{}, fmt.Errorf("failed to marshal rules: %w", marshalErr)
	}

	updated, err := s.db.UpdateCollectionRulesJSON(ctx, database.UpdateCollectionRulesJSONParams{
		ID:              pgtype.UUID{Bytes: collectionID, Valid: true},
		AutoAssignRules: rulesJSON,
	})
	if err != nil {
		return database.Collections{}, fmt.Errorf("failed to save rules: %w", err)
	}
	return updated, nil
}

// SmartEvalOptions scopes a smart collection's live evaluation.
type SmartEvalOptions struct {
	// LibraryID, when valid, restricts matching to one library (the
	// detail page's library switcher).
	LibraryID pgtype.UUID
	// VisibleIDs is the requesting user's visible-library set (family
	// lens). Empty means no visible-library filter.
	VisibleIDs []pgtype.UUID
}

// EvaluateSmartCollection resolves a smart collection's membership LIVE:
// every visible live book matched by at least one enabled rule is in.
// No stored links are consulted — "truly dynamic," always current.
func (s *CollectionService) EvaluateSmartCollection(ctx context.Context, rules []Rule, opts SmartEvalOptions) ([]database.MediaItems, error) {
	enabled := s.EnabledRules(rules)
	if len(enabled) == 0 {
		return []database.MediaItems{}, nil
	}

	var visibleArg []pgtype.UUID
	if len(opts.VisibleIDs) > 0 {
		visibleArg = opts.VisibleIDs
	}
	items, err := s.db.GetVisibleLiveMediaForRules(ctx, database.GetVisibleLiveMediaForRulesParams{
		LibraryID:         opts.LibraryID,
		VisibleLibraryIds: visibleArg,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to load candidate books: %w", err)
	}

	matches := make([]database.MediaItems, 0, len(items))
	for _, item := range items {
		if s.mediaItemMatchesAnyRule(item, enabled) {
			matches = append(matches, item)
		}
	}
	return matches, nil
}

func (s *CollectionService) mediaItemMatchesAnyRule(item database.MediaItems, rules []Rule) bool {
	for _, rule := range rules {
		if s.mediaItemMatchesRule(item, rule) {
			return true
		}
	}
	return false
}

func (s *CollectionService) mediaItemMatchesRule(item database.MediaItems, rule Rule) bool {
	if rule.Enabled != nil && !*rule.Enabled {
		return false
	}

	var fieldValue string
	switch rule.Field {
	case "genre":
		if item.Genre.Valid {
			fieldValue = item.Genre.String
		}
	case "series":
		if item.Series.Valid {
			fieldValue = item.Series.String
		}
	case "author":
		if item.Author.Valid {
			fieldValue = item.Author.String
		}
	case "language":
		if item.Language.Valid {
			fieldValue = item.Language.String
		}
	case "publisher":
		if item.Publisher.Valid {
			fieldValue = item.Publisher.String
		}
	case "copyright_year":
		if item.CopyrightYear.Valid {
			fieldValue = fmt.Sprintf("%d", item.CopyrightYear.Int32)
		}
	case "tags":
		if len(item.Tags) > 0 {
			fieldValue = strings.Join(item.Tags, ", ")
		}
	}

	return s.evaluateRule(fieldValue, rule.Operator, rule.Value)
}

// EvaluateRules evaluates auto-assign rules for a media item
func (s *CollectionService) EvaluateRules(mediaItem database.MediaItems, rules []Rule) []RuleEvaluation {
	var evaluations []RuleEvaluation

	// Sort rules by priority (higher priority first)
	sortedRules := make([]Rule, len(rules))
	copy(sortedRules, rules)
	for i := range len(sortedRules) {
		for j := i + 1; j < len(sortedRules); j++ {
			if sortedRules[i].Priority < sortedRules[j].Priority {
				sortedRules[i], sortedRules[j] = sortedRules[j], sortedRules[i]
			}
		}
	}

	for _, rule := range sortedRules {
		// Disabled rules never match (kept for context in the UI only).
		if rule.Enabled != nil && !*rule.Enabled {
			evaluations = append(evaluations, RuleEvaluation{RuleID: rule.ID, Matches: false})
			continue
		}
		eval := RuleEvaluation{
			RuleID:  rule.ID,
			Matches: false,
		}

		switch rule.Field {
		case "genre":
			if mediaItem.Genre.Valid {
				eval.Matches = s.evaluateRule(mediaItem.Genre.String, rule.Operator, rule.Value)
			}
		case "series":
			if mediaItem.Series.Valid {
				eval.Matches = s.evaluateRule(mediaItem.Series.String, rule.Operator, rule.Value)
			}
		case "author":
			if mediaItem.Author.Valid {
				eval.Matches = s.evaluateRule(mediaItem.Author.String, rule.Operator, rule.Value)
			}
		case "language":
			if mediaItem.Language.Valid {
				eval.Matches = s.evaluateRule(mediaItem.Language.String, rule.Operator, rule.Value)
			}
		case "publisher":
			if mediaItem.Publisher.Valid {
				eval.Matches = s.evaluateRule(mediaItem.Publisher.String, rule.Operator, rule.Value)
			}
		case "copyright_year":
			if mediaItem.CopyrightYear.Valid {
				yearStr := fmt.Sprintf("%d", mediaItem.CopyrightYear.Int32)
				eval.Matches = s.evaluateRule(yearStr, rule.Operator, rule.Value)
			}
		case "tags":
			if len(mediaItem.Tags) > 0 {
				tagsStr := strings.Join(mediaItem.Tags, ", ")
				eval.Matches = s.evaluateRule(tagsStr, rule.Operator, rule.Value)
			}
		}

		// Calculate confidence based on rule type and priority
		if eval.Matches {
			baseConfidence := 0.7
			switch rule.Field {
			case "genre", "series":
				baseConfidence = 0.9
			case "author", "publisher":
				baseConfidence = 0.8
			}
			// Add priority boost (0.01 per priority point, max 0.1)
			priorityBoost := float64(rule.Priority) * 0.01
			if priorityBoost > 0.1 {
				priorityBoost = 0.1
			}
			eval.Confidence = baseConfidence + priorityBoost
			if eval.Confidence > 1.0 {
				eval.Confidence = 1.0
			}
		}

		evaluations = append(evaluations, eval)
	}

	return evaluations
}

// evaluateRule evaluates a single rule
func (s *CollectionService) evaluateRule(fieldValue, operator, ruleValue string) bool {
	switch operator {
	case "equals":
		return containsIgnoreCase(fieldValue, ruleValue) && len(fieldValue) == len(ruleValue)
	case "contains":
		return containsIgnoreCase(fieldValue, ruleValue)
	case "starts_with":
		return hasPrefixIgnoreCase(fieldValue, ruleValue)
	case "ends_with":
		return hasSuffixIgnoreCase(fieldValue, ruleValue)
	case "greater_than":
		return compareNumbers(fieldValue, ruleValue, ">")
	case "less_than":
		return compareNumbers(fieldValue, ruleValue, "<")
	default:
		return false
	}
}

// containsIgnoreCase checks if a string contains another (case-insensitive)
func containsIgnoreCase(s, substr string) bool {
	s = toLower(s)
	substr = toLower(substr)
	return contains(s, substr)
}

// hasPrefixIgnoreCase checks if a string starts with a prefix (case-insensitive)
func hasPrefixIgnoreCase(s, prefix string) bool {
	s = toLower(s)
	prefix = toLower(prefix)
	return hasPrefix(s, prefix)
}

// hasSuffixIgnoreCase checks if a string ends with a suffix (case-insensitive)
func hasSuffixIgnoreCase(s, suffix string) bool {
	s = toLower(s)
	suffix = toLower(suffix)
	return hasSuffix(s, suffix)
}

// compareNumbers compares two numeric strings
func compareNumbers(a, b, op string) bool {
	aFloat, errA := parseFloat(a)
	bFloat, errB := parseFloat(b)

	if errA != nil || errB != nil {
		return false
	}

	switch op {
	case ">":
		return aFloat > bFloat
	case "<":
		return aFloat < bFloat
	case ">=":
		return aFloat >= bFloat
	case "<=":
		return aFloat <= bFloat
	default:
		return false
	}
}

// CreateDeviceShelfMapping creates a shelf mapping for a device
func (s *CollectionService) CreateDeviceShelfMapping(ctx context.Context, collectionID, deviceID uuid.UUID, deviceShelfName, syncDirection string) (database.DeviceShelfMappings, error) {
	mapping, err := s.db.CreateDeviceShelfMapping(ctx, database.CreateDeviceShelfMappingParams{
		CollectionID:    pgtype.UUID{Bytes: collectionID, Valid: true},
		DeviceID:        pgtype.UUID{Bytes: deviceID, Valid: true},
		DeviceShelfName: pgtype.Text{String: deviceShelfName, Valid: deviceShelfName != ""},
		SyncDirection:   pgtype.Text{String: syncDirection, Valid: syncDirection != ""},
	})

	if err != nil {
		return database.DeviceShelfMappings{}, fmt.Errorf("failed to create shelf mapping: %v", err)
	}

	return mapping, nil
}

// GetDeviceShelfMappings gets all shelf mappings for a device
func (s *CollectionService) GetDeviceShelfMappings(ctx context.Context, deviceID uuid.UUID) ([]database.GetDeviceShelfMappingsRow, error) {
	mappings, err := s.db.GetDeviceShelfMappings(ctx, pgtype.UUID{Bytes: deviceID, Valid: true})
	if err != nil {
		return nil, fmt.Errorf("failed to get shelf mappings: %v", err)
	}

	return mappings, nil
}

// UpdateDeviceShelfMapping updates a shelf mapping
func (s *CollectionService) UpdateDeviceShelfMapping(ctx context.Context, mappingID uuid.UUID, deviceShelfName, syncDirection string) (database.DeviceShelfMappings, error) {
	mapping, err := s.db.UpdateDeviceShelfMapping(ctx, database.UpdateDeviceShelfMappingParams{
		ID:              pgtype.UUID{Bytes: mappingID, Valid: true},
		DeviceShelfName: pgtype.Text{String: deviceShelfName, Valid: deviceShelfName != ""},
		SyncDirection:   pgtype.Text{String: syncDirection, Valid: syncDirection != ""},
	})

	if err != nil {
		return database.DeviceShelfMappings{}, fmt.Errorf("failed to update shelf mapping: %v", err)
	}

	return mapping, nil
}

// DeleteDeviceShelfMapping deletes a shelf mapping
func (s *CollectionService) DeleteDeviceShelfMapping(ctx context.Context, mappingID uuid.UUID) error {
	err := s.db.DeleteDeviceShelfMapping(ctx, pgtype.UUID{Bytes: mappingID, Valid: true})
	if err != nil {
		return fmt.Errorf("failed to delete shelf mapping: %v", err)
	}

	return nil
}

func toLower(s string) string {
	if len(s) == 0 {
		return s
	}

	result := make([]byte, len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		if c >= 'A' && c <= 'Z' {
			result[i] = c + 32
		} else {
			result[i] = c
		}
	}
	return string(result)
}

func contains(s, substr string) bool {
	return len(s) >= len(substr) && indexOf(s, substr) >= 0
}

func hasPrefix(s, prefix string) bool {
	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
}

func hasSuffix(s, suffix string) bool {
	return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
}

func indexOf(s, substr string) int {
	for i := 0; i <= len(s)-len(substr); i++ {
		if s[i:i+len(substr)] == substr {
			return i
		}
	}
	return -1
}

func parseFloat(s string) (float64, error) {
	var result float64
	var sign float64 = 1
	var divisor float64 = 1
	var decimalPlaces = 0
	var seenDecimal bool

	// Skip leading whitespace
	start := 0
	for start < len(s) && (s[start] == ' ' || s[start] == '\t' || s[start] == '\n') {
		start++
	}

	// Handle sign
	if start < len(s) && s[start] == '-' {
		sign = -1
		start++
	} else if start < len(s) && s[start] == '+' {
		start++
	}

	// Parse digits
	for i := start; i < len(s); i++ {
		c := s[i]
		if c >= '0' && c <= '9' {
			result = result*10 + float64(c-'0')
			if seenDecimal {
				decimalPlaces++
				divisor *= 10
			}
		} else if c == '.' && !seenDecimal {
			seenDecimal = true
		} else {
			break
		}
	}

	return sign * result / divisor, nil
}

// UserOwnsCollection gates playlist-ordering writes (A2c §3.2): the
// collection row's owner is the only user whose drag actions rewrite
// positions.
func (s *CollectionService) UserOwnsCollection(ctx context.Context, collectionID, userID uuid.UUID) (bool, error) {
	collection, err := s.db.GetCollection(ctx, pgtype.UUID{Bytes: collectionID, Valid: true})
	if err != nil {
		return false, err
	}
	return uuid.UUID(collection.UserID.Bytes) == userID, nil
}

// ReorderItems applies a full playlist order (A2c §3.2): the payload is the
// complete ordered id list; positions become 1..n in payload order. Ids
// not in the payload keep their relative order after — the SQL only
// touches the given ids, and NULL positions sort last. Never deletes.
func (s *CollectionService) ReorderItems(ctx context.Context, collectionID uuid.UUID, orderedIDs []uuid.UUID) error {
	if len(orderedIDs) == 0 {
		return nil
	}
	ids := make([]pgtype.UUID, 0, len(orderedIDs))
	for _, id := range orderedIDs {
		ids = append(ids, pgtype.UUID{Bytes: id, Valid: true})
	}
	if err := s.db.ReorderCollectionItems(ctx, database.ReorderCollectionItemsParams{
		CollectionID: pgtype.UUID{Bytes: collectionID, Valid: true},
		MediaItemIds: ids,
	}); err != nil {
		return fmt.Errorf("failed to reorder collection items: %v", err)
	}
	return nil
}