package handlers

import (
	"bookhoard/internal/database"
	"bookhoard/internal/services"
	wsync "bookhoard/internal/sync"
	"bookhoard/internal/utils"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

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

type CollectionHandler struct {
	db                *database.Queries
	collectionService *services.CollectionService
	libraryService    *services.LibraryService
	connManager       *wsync.ConnectionManager
}

func NewCollectionHandler(db *database.Queries, libraryService *services.LibraryService, connManager *wsync.ConnectionManager, search ...*services.SearchService) *CollectionHandler {
	return &CollectionHandler{
		db:                db,
		collectionService: services.NewCollectionService(db, search...),
		libraryService:    libraryService,
		connManager:       connManager,
	}
}

type CreateCollectionRequest struct {
	Name           string `form:"name" json:"name" validate:"required"`
	Description    string `form:"description" json:"description"`
	Color          string `form:"color" json:"color"`
	Icon           string `form:"icon" json:"icon"`
	CollectionType string `form:"collection_type" json:"collection_type"` // "static" (default) or "smart"
	// Custom-section builder payload (adapted 2026-10-31): the page
	// posts the legacy rules vocabulary — rules as a JSON-encoded array
	// (a string), a match_type select, hand-picked book ids, and the
	// dashboard pin. The server converts rules → filter tree at write
	// time and attaches the manual picks; storage stays tree-only.
	AutoAssignRules json.RawMessage        `json:"auto_assign_rules"`
	MatchType       string                 `json:"match_type"`
	ManualBookIDs   []string               `json:"manual_book_ids"`
	LibraryID       string                 `json:"library_id"` // selection context only — not stored
	ShowOnDashboard bool                   `json:"show_on_dashboard"`
	ViewSettings    map[string]interface{} `form:"view_settings" json:"view_settings"`
	// The unified filter tree (item 3.2): when present the collection's
	// smart membership runs through the qf engine. INVALID trees are a
	// 400 (ParseFilterTree at the handler); a tree supersedes
	// auto_assign_rules. Persisted as-is (any). RawMessage for
	// round-trip safety. JSON bodies bind FilterTree; FORM bodies
	// (the create modal's urlencoded hx-post) bind FilterTreeForm —
	// echo's binder cannot set an any-typed field from a form string
	// (the create-modal seed POST 400'd "invalid request" on it,
	// 2026-10-31).
	FilterTree any `json:"filter_tree"`
	// FilterTreeForm mirrors filter_tree for application/x-www-form-
	// urlencoded submissions: the raw JSON as a string, validated by
	// the same parseRequestFilterTree path.
	FilterTreeForm string `form:"filter_tree"`
}

// parseBuilderRules decodes the custom-section builder's rules payload:
// the page posts JSON.stringify(rules) — a JSON string CONTAINING the
// array (it has done so since the page was written, 2026-02-19) — while
// JSON clients may post the array directly. Null/empty = no rules.
func parseBuilderRules(raw json.RawMessage) ([]services.Rule, error) {
	if len(raw) == 0 || string(raw) == "null" {
		return nil, nil
	}
	var rules []services.Rule
	if raw[0] == '"' {
		var encoded string
		if err := json.Unmarshal(raw, &encoded); err != nil {
			return nil, err
		}
		if strings.TrimSpace(encoded) == "" {
			return nil, nil
		}
		return rules, json.Unmarshal([]byte(encoded), &rules)
	}
	return rules, json.Unmarshal(raw, &rules)
}

// treeFilterJSON returns the request's filter tree as JSON storage
// bytes (nil when none): object payloads marshal; strings (a legacy
// double-encoded client, the custom-section builder's known bug class)
// are written verbatim after object-attempt.
func treeFilterJSON(payload any) ([]byte, error) {
	switch v := payload.(type) {
	case nil:
		return nil, nil
	case map[string]interface{}:
		b, err := json.Marshal(v)
		if err != nil {
			return nil, err
		}
		return b, nil
	case string:
		return []byte(v), nil
	default:
		return nil, fmt.Errorf("filter_tree must be an object")
	}
}

// parseRequestFilterTree validates the request's tree against the
// engine grammar (ParseFilterTree) so an invalid tree is a 400, never
// a stored 500 at render time.
func parseRequestFilterTree(payload any) ([]byte, error) {
	b, err := treeFilterJSON(payload)
	if err != nil || b == nil {
		return b, err
	}
	if _, err := services.ParseFilterTree(string(b)); err != nil {
		return nil, fmt.Errorf("invalid filter_tree: %w", err)
	}
	return b, nil
}

// resolveTreePayload — the tree payload from either transport: JSON
// bodies carry the object in FilterTree, form bodies (the create
// modal's urlencoded hx-post) the raw JSON string in FilterTreeForm.
func resolveTreePayload(jsonTree any, formTree string) any {
	if formTree != "" {
		return formTree
	}
	return jsonTree
}

type UpdateCollectionRequest struct {
	Name string `form:"name" json:"name" validate:"required"`
	// The unified filter tree (item 3.2): when present the collection's
	// smart membership runs through the qf engine. INVALID trees are a
	// 400 (ParseFilterTree at the handler). JSON bodies bind FilterTree; form bodies bind
	// FilterTreeForm (echo's binder cannot set an any-typed field from
	// a form string — see CreateCollectionRequest).
	FilterTree     any                    `json:"filter_tree"`
	FilterTreeForm string                 `form:"filter_tree"`
	Description    string                 `form:"description" json:"description"`
	Color          string                 `form:"color" json:"color"`
	Icon           string                 `form:"icon" json:"icon"`
	ViewSettings   map[string]interface{} `form:"view_settings" json:"view_settings"`
	// A2c §3.3: playlist toggles — merged into view_settings server-side
	// (nil = untouched). []string because the form posts a hidden "false"
	// sibling next to the checkbox; the LAST value wins. JSON clients may
	// send a single-element array (or omit — untouched).
	HideFinished []string `form:"hide_finished" json:"hide_finished"`
	ShowUpNext   []string `form:"show_up_next" json:"show_up_next"`
}

type AddBooksRequest struct {
	BookIDs []string `json:"book_ids" validate:"required"`
}

type CreateDeviceMappingRequest struct {
	CollectionID    string `json:"collection_id" validate:"required"`
	DeviceShelfName string `json:"device_shelf_name" validate:"required"`
	SyncDirection   string `json:"sync_direction" validate:"required,oneof=bidirectional book_to_device device_to_book none"`
}

type UpdateDeviceMappingRequest struct {
	DeviceShelfName string `json:"device_shelf_name" validate:"required"`
	SyncDirection   string `json:"sync_direction" validate:"required,oneof=bidirectional book_to_device device_to_book none"`
}

// DeviceMappingSummary is one entry in GET /api/devices/:id/collections. Hoisted
// to package scope so the docs schema registry can pin the response shape.
type DeviceMappingSummary struct {
	ID              uuid.UUID `json:"id"`
	CollectionID    uuid.UUID `json:"collection_id"`
	CollectionName  string    `json:"collection_name"`
	DeviceShelfName string    `json:"device_shelf_name"`
	SyncDirection   string    `json:"sync_direction"`
	CreatedAt       string    `json:"created_at"`
}

// CollectionSummary is one entry in GET /api/collections. Package-level so
// the docs schema registry (internal/docs) can pin the response shape.
type CollectionSummary struct {
	ID          uuid.UUID `json:"id"`
	Name        string    `json:"name"`
	Description string    `json:"description"`
	Color       string    `json:"color"`
	Icon        string    `json:"icon"`
	CreatedAt   string    `json:"created_at"`
	BookCount   int       `json:"book_count"`
	IsSmart     bool      `json:"is_smart"`
}

// BookCollectionSummary is one entry in GET /api/collections/:id/books —
// the collections a book belongs to (list view: no rules/count fields).
type BookCollectionSummary struct {
	ID          uuid.UUID `json:"id"`
	Name        string    `json:"name"`
	Description string    `json:"description"`
	Color       string    `json:"color"`
	Icon        string    `json:"icon"`
}

type SectionData struct {
	ID           string     `json:"id"`
	CollectionID string     `json:"collection_id"`
	IsSystem     bool       `json:"is_system"`
	Title        string     `json:"title"`
	Description  string     `json:"description"`
	Icon         string     `json:"icon"`
	Items        []BookInfo `json:"items"`
	ViewAllURL   string     `json:"view_all_url"`
	Priority     int        `json:"priority"`
	// A2c: curated playlist marker (imported reading-order collection) and
	// the hide_finished completion state — dashboard.ts renders both.
	IsPlaylist bool `json:"is_playlist"`
	Complete   bool `json:"complete"`
}

func (h *CollectionHandler) CreateCollection(c *echo.Context) error {
	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)

	var req CreateCollectionRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	// Custom-section builder adapter: convert the posted rules to a
	// filter tree at WRITE time (the save-fix — the page's payload had
	// never once bound successfully before this).
	builderRules, rulesErr := parseBuilderRules(req.AutoAssignRules)
	if rulesErr != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "auto_assign_rules: " + rulesErr.Error()})
	}
	matchMode := req.MatchType
	if matchMode != services.RuleMatchAll && matchMode != services.RuleMatchAny {
		matchMode = services.RuleMatchAny
	}
	treeJSON, treeErr := parseRequestFilterTree(resolveTreePayload(req.FilterTree, req.FilterTreeForm))
	if treeErr != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": treeErr.Error()})
	}
	if treeJSON == nil && len(builderRules) > 0 {
		tree, cerr := services.RulesToFilterTree(builderRules, matchMode)
		if cerr != nil {
			return c.JSON(http.StatusBadRequest, map[string]string{"error": "section rule: " + cerr.Error()})
		}
		b, merr := json.Marshal(tree)
		if merr != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": merr.Error()})
		}
		// The strict-parse guarantee holds for converted trees too: an
		// invalid tree is a 400 at write, never a stored 500 at render.
		if _, verr := services.ParseFilterTree(string(b)); verr != nil {
			return c.JSON(http.StatusBadRequest, map[string]string{"error": "section rule: " + verr.Error()})
		}
		treeJSON = b
	}
	collection, err := h.collectionService.CreateCollection(
		c.Request().Context(),
		userUUID,
		req.Name,
		req.Description,
		req.Color,
		req.Icon,
		req.ViewSettings,
		req.ShowOnDashboard,
		treeJSON,
	)
	if err != nil {
		if errors.Is(err, services.ErrCollectionNameTaken) {
			return c.JSON(http.StatusConflict, map[string]string{"error": "a collection with this name already exists"})
		}
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	// Manual picks: a section = rules + hand-picked books. Attach after
	// create; unparsable ids are skipped (same leniency as AddBooks).
	for _, bookIDStr := range req.ManualBookIDs {
		bookID, perr := uuid.Parse(bookIDStr)
		if perr != nil {
			continue
		}
		_ = h.collectionService.AddBookToCollection(c.Request().Context(),
			uuid.UUID(collection.ID.Bytes), bookID, userUUID)
	}

	bookCount := int32(0)
	isSmart := req.CollectionType == "smart" || treeJSON != nil
	response := map[string]interface{}{
		"id":              uuid.UUID(collection.ID.Bytes).String(),
		"user_id":         uuid.UUID(collection.UserID.Bytes).String(),
		"name":            collection.Name,
		"description":     utils.PgTextString(collection.Description),
		"color":           utils.PgTextString(collection.Color),
		"icon":            utils.PgTextString(collection.Icon),
		"collection_type": map[bool]string{true: "smart", false: "static"}[isSmart],
		"view_settings":   collection.ViewSettings,
		"book_count":      bookCount,
		"created_at":      collection.CreatedAt.Time.String(),
	}

	// Add redirect header for HTMX requests
	if c.Request().Header.Get("HX-Request") == "true" {
		// A smart collection starts with an empty ruleset; the builder is
		// where it becomes real. Static collections head back to the grid.
		if isSmart {
			c.Response().Header().Set("HX-Redirect", "/collections/"+uuid.UUID(collection.ID.Bytes).String()+"/rules")
		} else {
			c.Response().Header().Set("HX-Redirect", "/collections")
		}
	}

	return c.JSON(http.StatusCreated, response)
}

func (h *CollectionHandler) GetCollections(c *echo.Context) error {
	includeAuto := c.QueryParam("include_auto") == "true"
	sortBy := c.QueryParam("sort_by")
	libraryID := c.QueryParam("library_id")

	collections, err := h.GetCollectionsData(c)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	response := make([]CollectionSummary, 0, len(collections))
	for _, col := range collections {
		isSmart := services.IsCollectionSmart(col)
		if !includeAuto && isSmart {
			// Legacy default for API clients (the Android app pre-dates
			// smart collections): rule-driven collections stay opt-in so
			// their membership could never be stale for old readers.
			continue
		}

		bookCount := 0
		var libUUID pgtype.UUID
		if libraryID != "" {
			if libParsed, libErr := uuid.Parse(libraryID); libErr == nil {
				libUUID = pgtype.UUID{Bytes: libParsed, Valid: true}
			}
		}
		if isSmart {
			visibleIDs, visErr := h.userVisibleLibraryIDs(c)
			if visErr == nil {
				matches, evalErr := h.collectionService.EvaluateSmartMembership(c.Request().Context(), col, services.SmartEvalOptions{
					LibraryID:    libUUID,
					VisibleIDs:   visibleIDs,
					ViewerUserID: MustGetAuthenticatedUser(c).ID,
				})
				if evalErr == nil {
					bookCount = len(matches)
				}
			}
		} else {
			count, countErr := h.db.CountCollectionLiveItems(c.Request().Context(), database.CountCollectionLiveItemsParams{
				CollectionID: pgtype.UUID{Bytes: col.ID.Bytes, Valid: true},
				LibraryID:    libUUID,
			})
			if countErr == nil {
				bookCount = int(count)
			}
		}

		response = append(response, CollectionSummary{
			ID:          col.ID.Bytes,
			Name:        col.Name,
			Description: utils.PgTextString(col.Description),
			Color:       utils.PgTextString(col.Color),
			Icon:        utils.PgTextString(col.Icon),
			CreatedAt:   col.CreatedAt.Time.String(),
			BookCount:   bookCount,
			IsSmart:     isSmart,
		})
	}

	if sortBy == "name" {
		for i := 0; i < len(response); i++ {
			for j := i + 1; j < len(response); j++ {
				if response[i].Name > response[j].Name {
					response[i], response[j] = response[j], response[i]
				}
			}
		}
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"collections": response,
		"total":       len(response),
	})
}

func (h *CollectionHandler) GetCollection(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	collection, err := h.GetCollectionData(c, collectionID)
	if err != nil {
		return c.JSON(http.StatusNotFound, map[string]string{"error": "collection not found"})
	}

	libraryID := c.QueryParam("library_id")
	var bookList []BookInfo

	var libUUID pgtype.UUID
	if libraryID != "" {
		parsed, parseErr := uuid.Parse(libraryID)
		if parseErr != nil {
			return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid library_id"})
		}
		libUUID = pgtype.UUID{Bytes: parsed, Valid: true}
	}

	isSmart := services.IsCollectionSmart(collection)
	libTypes := LibraryTypeMap(c.Request().Context(), h.db)
	if isSmart {
		visibleIDs, err := h.userVisibleLibraryIDs(c)
		if err != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
		}
		matches, evalErr := h.collectionService.EvaluateSmartMembership(c.Request().Context(), collection, services.SmartEvalOptions{
			LibraryID:    libUUID,
			VisibleIDs:   visibleIDs,
			ViewerUserID: MustGetAuthenticatedUser(c).ID,
		})
		if evalErr != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": evalErr.Error()})
		}
		bookList = BookCardsFromMediaItems(matches, libTypes)
	} else if collection.IsSystemCollection.Bool && collection.QueryType.Valid && collection.QueryType.String != "" && collection.QueryType.String != "filter" {
		user := c.Get("user").(database.Users)
		userUUID := uuid.UUID(user.ID.Bytes)
		dashboardSvc := services.NewDashboardService(h.db, h.collectionService.Search())
		sections, secErr := dashboardSvc.GetDashboardSections(c.Request().Context(), userUUID, libUUID, 1000, []string{}, []string{})
		if secErr != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": secErr.Error()})
		}
		for _, section := range sections {
			if section.CollectionID == collectionID {
				bookList = BookCardsFromMediaItems(section.Items, libTypes)
				break
			}
		}
	} else if libUUID.Valid {
		// A2c §3.3: the detail page honors the same per-collection
		// hide_finished as the dashboard section, against the viewer's
		// progress. The viewer_percentage rides along for card graying.
		hideFinished := false
		if len(collection.ViewSettings) > 0 {
			var vs map[string]interface{}
			if json.Unmarshal(collection.ViewSettings, &vs) == nil {
				if b, ok := vs["hide_finished"].(bool); ok {
					hideFinished = b
				}
			}
		}
		var viewerID pgtype.UUID
		if u, ok := c.Get("user").(database.Users); ok {
			viewerID = u.ID
		}
		collItems, collErr := h.db.GetCollectionItemsForDashboard(c.Request().Context(),
			database.GetCollectionItemsForDashboardParams{
				CollectionID: pgtype.UUID{Bytes: collectionID, Valid: true},
				LibraryID:    libUUID,
				ViewerUserID: viewerID,
				HideFinished: pgtype.Bool{Bool: hideFinished, Valid: hideFinished},
				Limit:        pgtype.Int4{Int32: 10000, Valid: true},
			})
		if collErr != nil {
			bookList = BookCardsFromCollectionDashRows(nil, libTypes)
		} else {
			// The query filters excluded rows in SQL; cards build straight
			// from the embedded media rows.
			bookList = BookCardsFromCollectionDashRows(collItems, libTypes)
		}
	} else {
		books, booksErr := h.GetCollectionBooksData(c, collectionID)
		if booksErr != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": booksErr.Error()})
		}
		bookList = BookCardsFromCollectionItemRows(books, libTypes)
	}

	if u, ok := c.Get("user").(database.Users); ok {
		bookList = MarkActiveConflicts(c.Request().Context(), h.db, u.ID, bookList)
	}

	var viewSettings map[string]interface{}
	if len(collection.ViewSettings) > 0 {
		err := json.Unmarshal(collection.ViewSettings, &viewSettings)
		if err != nil {
			return err
		}
	}

	// A2c §3.4: the collection's reading queue for the Up Next strip.
	// Library visibility enforced — a hidden library's books never surface
	// here even if they sit in a visible collection.
	upNext := []map[string]interface{}{}
	if !isSmart {
		hideFinished := false
		if b, ok := viewSettings["hide_finished"].(bool); ok {
			hideFinished = b
		}
		_ = hideFinished
		visibleIDs, visErr := h.userVisibleLibraryIDs(c)
		if visErr == nil {
			user := c.Get("user").(database.Users)
			rows, upErr := h.db.GetCollectionUpNext(c.Request().Context(), database.GetCollectionUpNextParams{
				CollectionID:      pgtype.UUID{Bytes: collectionID, Valid: true},
				ViewerUserID:      pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
				VisibleLibraryIds: visibleIDs,
				Limit:             pgtype.Int4{Int32: 10, Valid: true},
			})
			if upErr == nil {
				for _, row := range rows {
					upNext = append(upNext, map[string]interface{}{
						"id":       uuid.UUID(row.MediaItems.ID.Bytes).String(),
						"title":    row.MediaItems.Title,
						"author":   utils.PgTextString(row.MediaItems.Author),
						"cover":    utils.PgTextString(row.MediaItems.CoverImagePath),
						"format":   row.MediaItems.FormatGroup,
						"progress": row.ViewerPercentage,
					})
				}
			}
		}
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"id":            uuid.UUID(collection.ID.Bytes).String(),
		"user_id":       uuid.UUID(collection.UserID.Bytes).String(),
		"name":          collection.Name,
		"description":   utils.PgTextString(collection.Description),
		"color":         utils.PgTextString(collection.Color),
		"icon":          utils.PgTextString(collection.Icon),
		"view_settings": viewSettings,
		"filter_tree":   treeEnvelope(collection.FilterTree),
		"books":         bookList,
		"book_count":    len(bookList),
		"is_smart":      isSmart,
		"up_next":       upNext,
		"created_at":    collection.CreatedAt.Time.String(),
	})
}

func (h *CollectionHandler) UpdateCollection(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	var req UpdateCollectionRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	// A2c §3.3: playlist toggles ride the edit form as top-level fields and
	// merge into view_settings server-side (the form can't bind a map).
	// The form posts a hidden "false" sibling before the checkbox, so the
	// LAST value is the checkbox state.
	if v := optionalFlag(req.HideFinished); v != nil {
		if req.ViewSettings == nil {
			req.ViewSettings = map[string]interface{}{}
		}
		req.ViewSettings["hide_finished"] = *v
	}
	if v := optionalFlag(req.ShowUpNext); v != nil {
		if req.ViewSettings == nil {
			req.ViewSettings = map[string]interface{}{}
		}
		req.ViewSettings["show_up_next"] = *v
	}

	treeJSON, treeErr := parseRequestFilterTree(resolveTreePayload(req.FilterTree, req.FilterTreeForm))
	if treeErr != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": treeErr.Error()})
	}
	collection, err := h.collectionService.UpdateCollection(
		c.Request().Context(),
		collectionID,
		req.Name,
		req.Description,
		req.Color,
		req.Icon,
		req.ViewSettings,
		treeJSON,
	)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			// Collections RLS: another user's collection is INVISIBLE —
			// the update touched no rows. Answer 404, not a 500 that
			// reads like a bug (2026-10-31 collections RLS).
			return c.JSON(http.StatusNotFound, map[string]string{"error": "collection not found"})
		}
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	response := map[string]interface{}{
		"id":            uuid.UUID(collection.ID.Bytes).String(),
		"user_id":       uuid.UUID(collection.UserID.Bytes).String(),
		"name":          collection.Name,
		"description":   utils.PgTextString(collection.Description),
		"color":         utils.PgTextString(collection.Color),
		"icon":          utils.PgTextString(collection.Icon),
		"view_settings": json.RawMessage(collection.ViewSettings),
		"created_at":    collection.CreatedAt.Time.String(),
	}

	// Add redirect header for HTMX requests
	if c.Request().Header.Get("HX-Request") == "true" {
		c.Response().Header().Set("HX-Redirect", "/collections")
	}

	return c.JSON(http.StatusCreated, response)
}

// ValidChainOrders — the collection chain's listening-order vocabulary
// (plan §10 R2: a collection's playback order is CURATED on the
// collection, not a player-side knob). Mirrors OrderEpisodes' orders;
// "" means native (the pre-chain-order default).
var ValidChainOrders = map[string]bool{"": true, "native": true, "newest": true, "oldest": true, "reverse": true}

// CollectionChainOrder resolves a collection row's curated chain order
// from its view_settings JSONB — "" (native) when absent/unknown. The
// episode chain producer routes OrderEpisodes through this; the
// view-settings PUT writes the key (SetCollectionChainOrder).
func CollectionChainOrder(viewSettings []byte) string {
	if len(viewSettings) == 0 {
		return ""
	}
	var vs map[string]interface{}
	if json.Unmarshal(viewSettings, &vs) != nil {
		return ""
	}
	if s, ok := vs["chain_order"].(string); ok && ValidChainOrders[s] {
		return s
	}
	return ""
}

// SetCollectionChainOrder — PUT /api/collections/:id/view-settings with
// {"chain_order": "..."}: merges the key into the collection's stored
// view_settings (the playlist toggles share that JSONB — a blind write
// would clobber them). The episode chain producer
// (buildSmartCollectionSequenceContext) honors it.
func (h *CollectionHandler) SetCollectionChainOrder(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	var req struct {
		ChainOrder string `json:"chain_order"`
	}
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if !ValidChainOrders[req.ChainOrder] {
		return c.JSON(http.StatusBadRequest, map[string]string{
			"error": "chain_order must be one of: native, newest, oldest, reverse"})
	}

	collection, err := h.collectionService.GetCollection(c.Request().Context(), collectionID)
	if err != nil {
		return c.JSON(http.StatusNotFound, map[string]string{"error": "collection not found"})
	}
	// Same owner gate as the sibling config mutation (ReorderItems) —
	// my endpoint writes the row, so it must not let a non-owner flip
	// someone else's chain order.
	if u, ok := c.Get("user").(database.Users); ok {
		owns, err := h.collectionService.UserOwnsCollection(c.Request().Context(), collectionID, uuid.UUID(u.ID.Bytes))
		if err != nil || !owns {
			return c.JSON(http.StatusForbidden, map[string]string{"error": "only the collection owner can change it"})
		}
	} else {
		return c.JSON(http.StatusUnauthorized, map[string]string{"error": "no user in context"})
	}

	settings := map[string]interface{}{}
	if len(collection.ViewSettings) > 0 {
		if uerr := json.Unmarshal(collection.ViewSettings, &settings); uerr != nil {
			return c.JSON(http.StatusInternalServerError, map[string]string{"error": "corrupt view_settings"})
		}
	}
	if req.ChainOrder == "" || req.ChainOrder == "native" {
		// Both spellings mean the default — drop the key entirely so the
		// stored doc stays clean.
		delete(settings, "chain_order")
	} else {
		settings["chain_order"] = req.ChainOrder
	}
	blob, err := json.Marshal(settings)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}
	if err := h.db.UpdateCollectionViewSettings(c.Request().Context(), database.UpdateCollectionViewSettingsParams{
		ID:           pgtype.UUID{Bytes: collectionID, Valid: true},
		ViewSettings: blob,
	}); err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"id":            uuid.UUID(collection.ID.Bytes).String(),
		"chain_order":   req.ChainOrder,
		"view_settings": settings,
	})
}

func (h *CollectionHandler) DeleteCollection(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	err = h.collectionService.DeleteCollection(c.Request().Context(), collectionID)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	if c.Request().Header.Get("HX-Request") == "true" {
		// CSP: no inline scripts in partials — auth_forms.ts navigates.
		html := `<div class="text-green-500" data-redirect="/collections">Collection deleted! Redirecting...</div>`
		return c.HTML(http.StatusOK, html)
	}

	return c.NoContent(http.StatusNoContent)
}

func (h *CollectionHandler) AddBooks(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	if guardErr := h.rejectSmartMutation(c, collectionID); guardErr != nil {
		return guardErr
	}

	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)

	var req AddBooksRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	addedCount := 0
	var addedBookIDs []string
	for _, bookIDStr := range req.BookIDs {
		bookID, err := uuid.Parse(bookIDStr)
		if err != nil {
			continue
		}
		err = h.collectionService.AddBookToCollection(c.Request().Context(), collectionID, bookID, userUUID)
		if err == nil {
			addedCount++
			addedBookIDs = append(addedBookIDs, bookID.String())
		}
	}

	if addedCount > 0 && h.connManager != nil {
		h.connManager.BroadcastToUser(userUUID.String(), wsync.BroadcastMessage{
			Type:      "collection_updated",
			Timestamp: time.Now().Format(time.RFC3339),
			Data: map[string]interface{}{
				"collection_id": collectionID.String(),
				"action":        "books_added",
				"book_ids":      addedBookIDs,
				"count":         addedCount,
			},
		})
	}

	return c.NoContent(http.StatusNoContent)
}

func (h *CollectionHandler) RemoveBook(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	if guardErr := h.rejectSmartMutation(c, collectionID); guardErr != nil {
		return guardErr
	}

	bookID, err := uuid.Parse(c.Param("bookId"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid book id"})
	}

	// Get user from context for WebSocket broadcast
	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)

	err = h.collectionService.RemoveBookFromCollection(c.Request().Context(), collectionID, bookID)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	// Broadcast to user's other devices via WebSocket
	if h.connManager != nil {
		h.connManager.BroadcastToUser(userUUID.String(), wsync.BroadcastMessage{
			Type:      "collection_updated",
			Timestamp: time.Now().Format(time.RFC3339),
			Data: map[string]interface{}{
				"collection_id": collectionID.String(),
				"action":        "book_removed",
				"book_id":       bookID.String(),
			},
		})
	}

	return c.NoContent(http.StatusNoContent)
}

type BulkRemoveBooksRequest struct {
	BookIDs []string `json:"book_ids" validate:"required"`
}

func (h *CollectionHandler) BulkRemoveBooks(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	if guardErr := h.rejectSmartMutation(c, collectionID); guardErr != nil {
		return guardErr
	}

	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)

	var req BulkRemoveBooksRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	removedCount := 0
	var removedBookIDs []string
	for _, bookIDStr := range req.BookIDs {
		bookID, err := uuid.Parse(bookIDStr)
		if err != nil {
			continue
		}

		err = h.collectionService.RemoveBookFromCollection(c.Request().Context(), collectionID, bookID)
		if err == nil {
			removedCount++
			removedBookIDs = append(removedBookIDs, bookID.String())
		}
	}

	if removedCount > 0 && h.connManager != nil {
		h.connManager.BroadcastToUser(userUUID.String(), wsync.BroadcastMessage{
			Type:      "collection_updated",
			Timestamp: time.Now().Format(time.RFC3339),
			Data: map[string]interface{}{
				"collection_id": collectionID.String(),
				"action":        "books_removed",
				"book_ids":      removedBookIDs,
				"count":         removedCount,
			},
		})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"removed": removedCount,
		"total":   len(req.BookIDs),
	})
}

func (h *CollectionHandler) GetDeviceMappings(c *echo.Context) error {
	deviceID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid device id"})
	}

	mappings, err := h.collectionService.GetDeviceShelfMappings(c.Request().Context(), deviceID)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	response := make([]DeviceMappingSummary, 0, len(mappings))
	for _, m := range mappings {
		response = append(response, DeviceMappingSummary{
			ID:              m.ID.Bytes,
			CollectionID:    m.CollectionID.Bytes,
			CollectionName:  m.CollectionName,
			DeviceShelfName: utils.PgTextString(m.DeviceShelfName),
			SyncDirection:   utils.PgTextString(m.SyncDirection),
			CreatedAt:       m.CreatedAt.Time.String(),
		})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"device_id": deviceID.String(),
		"mappings":  response,
		"total":     len(response),
	})
}

func (h *CollectionHandler) CreateDeviceMapping(c *echo.Context) error {
	deviceID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid device id"})
	}

	var req CreateDeviceMappingRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	collectionID, err := uuid.Parse(req.CollectionID)
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}

	mapping, err := h.collectionService.CreateDeviceShelfMapping(
		c.Request().Context(),
		collectionID,
		deviceID,
		req.DeviceShelfName,
		req.SyncDirection,
	)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	return c.JSON(http.StatusCreated, map[string]interface{}{
		"id":                uuid.UUID(mapping.ID.Bytes).String(),
		"collection_id":     uuid.UUID(mapping.CollectionID.Bytes).String(),
		"device_id":         uuid.UUID(mapping.DeviceID.Bytes).String(),
		"device_shelf_name": utils.PgTextString(mapping.DeviceShelfName),
		"sync_direction":    utils.PgTextString(mapping.SyncDirection),
		"created_at":        mapping.CreatedAt.Time.String(),
	})
}

func (h *CollectionHandler) UpdateDeviceMapping(c *echo.Context) error {
	mappingID, err := uuid.Parse(c.Param("mappingId"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid mapping id"})
	}

	var req UpdateDeviceMappingRequest
	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid request"})
	}
	if err := c.Validate(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": err.Error()})
	}

	mapping, err := h.collectionService.UpdateDeviceShelfMapping(
		c.Request().Context(),
		mappingID,
		req.DeviceShelfName,
		req.SyncDirection,
	)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"id":                uuid.UUID(mapping.ID.Bytes).String(),
		"collection_id":     uuid.UUID(mapping.CollectionID.Bytes).String(),
		"device_id":         uuid.UUID(mapping.DeviceID.Bytes).String(),
		"device_shelf_name": utils.PgTextString(mapping.DeviceShelfName),
		"sync_direction":    utils.PgTextString(mapping.SyncDirection),
		"created_at":        mapping.CreatedAt.Time.String(),
	})
}

func (h *CollectionHandler) DeleteDeviceMapping(c *echo.Context) error {
	mappingID, err := uuid.Parse(c.Param("mappingId"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid mapping id"})
	}

	err = h.collectionService.DeleteDeviceShelfMapping(c.Request().Context(), mappingID)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	return c.NoContent(http.StatusNoContent)
}

func (h *CollectionHandler) GetBookCollections(c *echo.Context) error {
	bookID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid book id"})
	}

	collections, err := h.collectionService.GetBookCollections(c.Request().Context(), bookID)
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	response := make([]BookCollectionSummary, 0, len(collections))
	for _, col := range collections {
		response = append(response, BookCollectionSummary{
			ID:          col.ID.Bytes,
			Name:        col.Name,
			Description: utils.PgTextString(col.Description),
			Color:       utils.PgTextString(col.Color),
			Icon:        utils.PgTextString(col.Icon),
		})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"book_id":     bookID.String(),
		"collections": response,
		"total":       len(response),
	})
}

func (h *CollectionHandler) GetCollectionsData(c *echo.Context) ([]database.Collections, error) {
	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)
	return h.collectionService.GetUserCollections(c.Request().Context(), userUUID)
}

func (h *CollectionHandler) GetCollectionData(c *echo.Context, collectionID uuid.UUID) (database.Collections, error) {
	return h.collectionService.GetCollection(c.Request().Context(), collectionID)
}

func (h *CollectionHandler) GetCollectionBooksData(c *echo.Context, collectionID uuid.UUID) ([]database.GetCollectionItemsRow, error) {
	return h.collectionService.GetCollectionBooks(c.Request().Context(), collectionID)
}

// userVisibleLibraryIDs loads the requester's visible-library set (the
// family lens). Smart-collection evaluation funnels every book candidate
// through it so hidden libraries contribute nothing.
// userVisibleLibraryIDs adapts the collection endpoints' identity
// source to the canonical resolver (H4.5).
func (h *CollectionHandler) userVisibleLibraryIDs(c *echo.Context) ([]pgtype.UUID, error) {
	user, ok := c.Get("user").(database.Users)
	if !ok {
		return nil, echo.NewHTTPError(http.StatusUnauthorized, "invalid user")
	}
	_, ids, err := h.libraryService.VisibleLibrarySet(c.Request().Context(), user.ID)
	return ids, err
}

// UserVisibleLibraryIDs is the exported entry point for the router's
// frontend page handlers, which resolve the visible-library set before
// evaluating smart-collection rule matches.
func (h *CollectionHandler) UserVisibleLibraryIDs(c *echo.Context) ([]pgtype.UUID, error) {
	return h.userVisibleLibraryIDs(c)
}

// CollectionService returns the underlying service so the router's
// frontend handlers can share the exact same evaluation the API uses.
func (h *CollectionHandler) CollectionService() *services.CollectionService {
	return h.collectionService
}

// rejectSmartMutation returns a 400 for smart collections: membership is
// derived live from rules, so stored link mutations have nothing to act
// on. v1 has no hybrid mode — add/remove with both rules and hand-picked
// books is deliberately unsupported (collection_items.excluded awaits it).
func (h *CollectionHandler) rejectSmartMutation(c *echo.Context, collectionID uuid.UUID) *echo.HTTPError {
	collection, err := h.GetCollectionData(c, collectionID)
	if err != nil {
		return echo.NewHTTPError(http.StatusNotFound, "collection not found")
	}
	if services.IsCollectionSmart(collection) {
		return echo.NewHTTPError(http.StatusBadRequest, "smart collections are tree-based — membership is managed by the collection's filter tree, not by hand")
	}
	return nil
}

// treeEnvelope renders the stored filter tree for the envelope: nil
// (static collections) serializes as null, trees as the object.
func treeEnvelope(t []byte) any {
	if len(t) == 0 {
		return nil
	}
	var v interface{}
	if json.Unmarshal(t, &v) == nil {
		return v
	}
	return nil
}

func (h *CollectionHandler) HandleBulkAddBooks(c *echo.Context) error {
	user := c.Get("user").(database.Users)
	userUUID := uuid.UUID(user.ID.Bytes)

	var req struct {
		Operations []struct {
			CollectionID string   `json:"collection_id" validate:"required"`
			BookIDs      []string `json:"book_ids" validate:"required"`
		} `json:"operations" validate:"required"`
	}

	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid request"})
	}

	if len(req.Operations) == 0 {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "operations required"})
	}

	// Smart collections are rejected up front per operation so the
	// caller sees a clean, actionable error instead of silent no-ops.
	for _, op := range req.Operations {
		if colUUID, err := uuid.Parse(op.CollectionID); err == nil {
			if guardErr := h.rejectSmartMutation(c, colUUID); guardErr != nil {
				return guardErr
			}
		}
	}

	results := make([]map[string]interface{}, 0)
	successCount := 0
	failedCount := 0

	for _, op := range req.Operations {
		collectionID, err := uuid.Parse(op.CollectionID)
		if err != nil {
			results = append(results, map[string]interface{}{
				"collection_id": op.CollectionID,
				"status":        "error",
				"error":         "Invalid collection UUID",
			})
			failedCount++
			continue
		}

		for _, bookIDStr := range op.BookIDs {
			bookID, err := uuid.Parse(bookIDStr)
			if err != nil {
				results = append(results, map[string]interface{}{
					"collection_id": op.CollectionID,
					"book_id":       bookIDStr,
					"status":        "error",
					"error":         "Invalid book UUID",
				})
				failedCount++
				continue
			}

			collectionUUID := pgtype.UUID{Bytes: collectionID, Valid: true}
			bookUUID := pgtype.UUID{Bytes: bookID, Valid: true}

			_, err = h.db.AddBookToCollection(c.Request().Context(), database.AddBookToCollectionParams{
				CollectionID:  collectionUUID,
				MediaItemID:   bookUUID,
				AddedByUserID: pgtype.UUID{Bytes: user.ID.Bytes, Valid: true},
			})

			if err != nil {
				results = append(results, map[string]interface{}{
					"collection_id": op.CollectionID,
					"book_id":       bookIDStr,
					"status":        "error",
					"error":         err.Error(),
				})
				failedCount++
				continue
			}

			results = append(results, map[string]interface{}{
				"collection_id": op.CollectionID,
				"book_id":       bookIDStr,
				"status":        "success",
			})
			successCount++
		}
	}

	if successCount > 0 && h.connManager != nil {
		h.connManager.BroadcastToUser(userUUID.String(), wsync.BroadcastMessage{
			Type:      "collection_updated",
			Timestamp: time.Now().Format(time.RFC3339),
			Data: map[string]interface{}{
				"action": "books_added_bulk",
				"count":  successCount,
			},
		})
	}

	return c.JSON(http.StatusOK, map[string]interface{}{
		"results": results,
		"total":   len(results),
		"added":   successCount,
		"failed":  failedCount,
	})
}

func (h *CollectionHandler) PreviewCollection(c *echo.Context) error {
	user := c.Get("user")
	if user == nil {
		return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
	}

	var req struct {
		LibraryID     string          `json:"library_id"`
		Rules         []services.Rule `json:"rules"`
		ManualBookIDs []string        `json:"manual_book_ids"`
		Limit         int             `json:"limit"`
	}

	if err := c.Bind(&req); err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "Invalid request"})
	}

	libUUID, err := uuid.Parse(req.LibraryID)
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid library_id"})
	}

	_, err = h.db.GetLibrary(c.Request().Context(), pgtype.UUID{Bytes: libUUID, Valid: true})
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return c.JSON(http.StatusBadRequest, map[string]string{"error": "library not found"})
		}
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}

	if req.Limit <= 0 || req.Limit > 100 {
		req.Limit = 20
	}

	allItems, err := h.db.GetLibraryItems(c.Request().Context(), pgtype.UUID{Bytes: libUUID, Valid: true})
	if err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "Failed to load library items"})
	}

	// Book-scope preview (the rules page remains books-first until the
	// filter-unification pass); no viewer progress loaded here, so
	// played/unplayed rules preview at the no-progress default.
	var matchedItems []database.MediaItems
	for _, item := range allItems {
		evaluations := h.collectionService.EvaluateRules(item, 0, req.Rules)
		for _, eval := range evaluations {
			if eval.Matches {
				matchedItems = append(matchedItems, item)
				break
			}
		}
	}

	for _, bookID := range req.ManualBookIDs {
		bookUUID, err := uuid.Parse(bookID)
		if err != nil {
			continue
		}

		for _, item := range allItems {
			itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
			if itemUUID == bookUUID {
				alreadyAdded := false
				for _, added := range matchedItems {
					addedUUID, _ := uuid.FromBytes(added.ID.Bytes[0:16])
					if addedUUID == bookUUID {
						alreadyAdded = true
						break
					}
				}
				if !alreadyAdded {
					matchedItems = append(matchedItems, item)
				}
				break
			}
		}
	}

	if len(matchedItems) > req.Limit {
		matchedItems = matchedItems[:req.Limit]
	}

	bookCards := BookCardsFromMediaItems(matchedItems, LibraryTypeMap(c.Request().Context(), h.db))
	if u, ok := c.Get("user").(database.Users); ok {
		bookCards = MarkActiveConflicts(c.Request().Context(), h.db, u.ID, bookCards)
	}

	return c.JSON(http.StatusOK, map[string]interface{}{"items": bookCards})
}

// ReorderItems applies a static collection's manual playlist order
// (A2c §3.2). Owner-only; the payload is the COMPLETE ordered id list —
// ids omitted keep their relative order appended after (the service never
// deletes membership).
func (h *CollectionHandler) ReorderItems(c *echo.Context) error {
	collectionID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid collection id"})
	}
	user, ok := c.Get("user").(database.Users)
	if !ok {
		return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
	}

	var req struct {
		ItemIDs []string `json:"item_ids"`
	}
	if err := c.Bind(&req); err != nil || len(req.ItemIDs) == 0 {
		return c.JSON(http.StatusBadRequest, map[string]string{"error": "item_ids must be a non-empty ordered id list"})
	}

	owns, err := h.collectionService.UserOwnsCollection(c.Request().Context(), collectionID, uuid.UUID(user.ID.Bytes))
	if err != nil || !owns {
		return c.JSON(http.StatusForbidden, map[string]string{"error": "only the collection owner can reorder it"})
	}

	ordered := make([]uuid.UUID, 0, len(req.ItemIDs))
	for _, raw := range req.ItemIDs {
		id, parseErr := uuid.Parse(raw)
		if parseErr != nil {
			return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid media item id: " + raw})
		}
		ordered = append(ordered, id)
	}

	if err := h.collectionService.ReorderItems(c.Request().Context(), collectionID, ordered); err != nil {
		return c.JSON(http.StatusInternalServerError, map[string]string{"error": err.Error()})
	}
	return c.JSON(http.StatusOK, map[string]string{"status": "reordered"})
}

// optionalFlag interprets a multi-valued form flag: last value wins
// (hidden-false sibling precedes the checkbox), absent → nil (untouched).
func optionalFlag(values []string) *bool {
	if len(values) == 0 {
		return nil
	}
	v := strings.EqualFold(values[len(values)-1], "true")
	return &v
}