// Package service — social bits of the BFF.
//
// `social_service.go` bundles three lightweight services (Post, Bookmark,
// Collection) because each is small (10–40 LOC of logic) and they share the
// same R2 + UserRepo dependencies. Keeping them together keeps `server.go`'s
// init-wiring tidy without sprawling into 4 separate files.
package service

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"path"
	"strings"
	"time"

	"github.com/prabhupadasays/spsays-bff/internal/model"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
)

// Sentinels surfaced to handlers.
var (
	ErrForbidden = errors.New("forbidden")
	ErrNotFound  = errors.New("not found")
)

// ---------------------------------------------------------------------------
// PostService
// ---------------------------------------------------------------------------

type PostService struct {
	posts *repository.PostRepo
	r2    *repository.R2
}

func NewPostService(posts *repository.PostRepo, r2 *repository.R2) *PostService {
	return &PostService{posts: posts, r2: r2}
}

// Create persists a new post. The caption is treated as opaque — we trust
// the frontend to send the exact text the user selected. Source URL must be
// a same-origin path (e.g. /books/bg/1/1?hl=…) — we strip the host if one
// was provided so links can't be hijacked.
func (s *PostService) Create(ctx context.Context, userID, caption, sourceURL, sourceTitle string, imageURLs []string) (*model.Post, error) {
	caption = strings.TrimSpace(caption)
	if caption == "" {
		return nil, errors.New("caption is required")
	}
	if len(caption) > 4000 {
		return nil, errors.New("caption too long (max 4000)")
	}
	sourceURL = stripHost(strings.TrimSpace(sourceURL))
	if sourceURL == "" || !strings.HasPrefix(sourceURL, "/") {
		return nil, errors.New("source_url must be an absolute path starting with /")
	}
	if len(imageURLs) > 5 {
		return nil, errors.New("a post can hold up to 5 images")
	}
	return s.posts.Create(ctx, userID, caption, sourceURL, sourceTitle, imageURLs)
}

// Get returns one post (public). `viewerID` is "" for anonymous callers;
// when set, the returned post carries the viewer's reshare state so the
// frontend can render the right action button without a second request.
func (s *PostService) Get(ctx context.Context, id, viewerID string) (*model.Post, error) {
	p, err := s.posts.FindByID(ctx, id)
	if err != nil {
		return nil, err
	}
	if err := s.hydrateReshareStates(ctx, viewerID, []*model.Post{p}); err != nil {
		return nil, err
	}
	return p, nil
}

// Reshare materialises a reshare as a brand-new posts row owned by the
// caller, with reshared_from_post_id pointing to the canonical original.
// Idempotent — calling it twice returns the same reshare row. Resharing
// one's own post (canonical or chained) is rejected at the repo layer.
//
// Returns the new post so the frontend can drop it into local state
// without a round-trip.
func (s *PostService) Reshare(ctx context.Context, postID, callerID string) (*model.Post, error) {
	return s.posts.Reshare(ctx, postID, callerID)
}

// Unreshare removes the caller's reshare of a canonical post by deleting
// their own reshare posts row. Idempotent — no-ops when nothing to delete.
func (s *PostService) Unreshare(ctx context.Context, postID, callerID string) error {
	return s.posts.Unreshare(ctx, postID, callerID)
}

// hydrateReshareStates fills in ViewerHasReshared on each post via one
// batched lookup. Skips the query when the viewer is anonymous (the
// answer is uniformly false) or the slice is empty.
func (s *PostService) hydrateReshareStates(ctx context.Context, viewerID string, posts []*model.Post) error {
	if viewerID == "" || len(posts) == 0 {
		return nil
	}
	ids := make([]string, 0, len(posts))
	for _, p := range posts {
		if p == nil {
			continue
		}
		ids = append(ids, p.ID)
	}
	if len(ids) == 0 {
		return nil
	}
	states, err := s.posts.ReshareStatesFor(ctx, viewerID, ids)
	if err != nil {
		return err
	}
	for _, p := range posts {
		if p == nil {
			continue
		}
		if states[p.ID] {
			p.ViewerHasReshared = true
		}
	}
	return nil
}

// hydrateReshareStatesSlice is the value-slice variant of
// hydrateReshareStates. Repository list methods return []model.Post
// (not pointers) — we wrap each element so the helper can mutate in
// place via a stable pointer.
func (s *PostService) hydrateReshareStatesSlice(ctx context.Context, viewerID string, posts []model.Post) error {
	if len(posts) == 0 {
		return nil
	}
	ptrs := make([]*model.Post, len(posts))
	for i := range posts {
		ptrs[i] = &posts[i]
	}
	return s.hydrateReshareStates(ctx, viewerID, ptrs)
}

// Delete checks ownership and removes the post.
func (s *PostService) Delete(ctx context.Context, postID, callerID string) error {
	return s.posts.Delete(ctx, postID, callerID)
}

// ReplaceImages swaps the image set on a post. Owner-only — every
// reshare is its own posts row, owned by the resharer, so this works
// uniformly for canonical posts and reshares.
func (s *PostService) ReplaceImages(ctx context.Context, postID, callerID string, imageURLs []string) (*model.Post, error) {
	if err := s.posts.ReplaceImages(ctx, postID, callerID, imageURLs); err != nil {
		return nil, err
	}
	return s.posts.FindByID(ctx, postID)
}

// ListByHandle is the public feed view. `viewerID` is "" for anonymous
// callers; when set, each returned post carries the viewer's reshare
// state.
func (s *PostService) ListByHandle(ctx context.Context, handle, viewerID string, limit, offset int) ([]model.Post, int, error) {
	if limit <= 0 || limit > 50 {
		limit = 20
	}
	if offset < 0 {
		offset = 0
	}
	posts, total, err := s.posts.ListByHandle(ctx, handle, limit, offset)
	if err != nil {
		return nil, 0, err
	}
	if err := s.hydrateReshareStatesSlice(ctx, viewerID, posts); err != nil {
		return nil, 0, err
	}
	return posts, total, nil
}

// ListMine is the owner's view of their own profile feed. Every post
// they own — authored or reshared — comes from posts.user_id, so the
// viewer is by construction the owner. ViewerHasReshared is true for
// reshare rows (the user IS the resharer) and false for canonical
// rows (you don't "reshare your own post").
func (s *PostService) ListMine(ctx context.Context, userID string, limit, offset int) ([]model.Post, int, error) {
	if limit <= 0 || limit > 50 {
		limit = 20
	}
	if offset < 0 {
		offset = 0
	}
	posts, total, err := s.posts.ListByUser(ctx, userID, limit, offset)
	if err != nil {
		return nil, 0, err
	}
	for i := range posts {
		if posts[i].ResharedFromPostID != nil {
			posts[i].ViewerHasReshared = true
		}
	}
	return posts, total, nil
}

// ImagePresign returns a one-shot R2 PUT URL for a post image.
// The key is namespaced under post-images/<user_id>/<random>.<ext>. We
// don't tie it to a post_id at presign time because the post might not
// exist yet — the user uploads images first, then submits the post with
// the public URLs.
func (s *PostService) ImagePresign(ctx context.Context, userID, contentType string) (uploadURL, publicURL string, err error) {
	return presignImage(ctx, s.r2, "post-images", userID, contentType)
}

// ---------------------------------------------------------------------------
// BookmarkService
// ---------------------------------------------------------------------------

type BookmarkService struct {
	users     *repository.UserRepo
	bookmarks *repository.BookmarkRepo
}

func NewBookmarkService(users *repository.UserRepo, bookmarks *repository.BookmarkRepo) *BookmarkService {
	return &BookmarkService{users: users, bookmarks: bookmarks}
}

// Create enforces the plan cap and inserts a new bookmark.
//
// If the same URL is already bookmarked (UNIQUE constraint), we return the
// existing row as a 200 idempotent response instead of an error — clicking
// "Bookmark" twice on the same passage should feel like a no-op.
func (s *BookmarkService) Create(ctx context.Context, userID, sourceURL, sourceTitle string, excerpt, note *string) (*model.Bookmark, error) {
	u, err := s.users.FindByID(ctx, userID)
	if err != nil {
		return nil, err
	}

	current, err := s.bookmarks.CountByUser(ctx, userID)
	if err != nil {
		return nil, err
	}
	if err := EnforceBookmarkLimit(u.Plan, current); err != nil {
		return nil, err
	}

	b, err := s.bookmarks.Create(ctx, userID, stripHost(sourceURL), sourceTitle, excerpt, note)
	if err == nil {
		return b, nil
	}
	if errors.Is(err, repository.ErrBookmarkExists) {
		// Idempotent: return whatever is already there.
		list, lerr := s.bookmarks.ListByUser(ctx, userID)
		if lerr != nil {
			return nil, lerr
		}
		for _, existing := range list {
			if existing.SourceURL == stripHost(sourceURL) {
				return &existing, nil
			}
		}
	}
	return nil, err
}

// List returns the caller's bookmarks.
func (s *BookmarkService) List(ctx context.Context, userID string) ([]model.Bookmark, error) {
	return s.bookmarks.ListByUser(ctx, userID)
}

// Delete removes a bookmark belonging to the caller.
func (s *BookmarkService) Delete(ctx context.Context, id, userID string) error {
	return s.bookmarks.Delete(ctx, id, userID)
}

// ---------------------------------------------------------------------------
// CollectionService
// ---------------------------------------------------------------------------

type CollectionService struct {
	users       *repository.UserRepo
	collections *repository.CollectionRepo
	posts       *repository.PostRepo
	r2          *repository.R2
}

func NewCollectionService(users *repository.UserRepo, collections *repository.CollectionRepo, posts *repository.PostRepo, r2 *repository.R2) *CollectionService {
	return &CollectionService{users: users, collections: collections, posts: posts, r2: r2}
}

// Create enforces per-visibility plan caps and inserts.
func (s *CollectionService) Create(ctx context.Context, userID, title string, description, coverURL *string, isPublic bool) (*model.CollectionRecord, error) {
	if title = strings.TrimSpace(title); title == "" {
		return nil, errors.New("title is required")
	}
	if len(title) > 120 {
		return nil, errors.New("title too long (max 120)")
	}
	u, err := s.users.FindByID(ctx, userID)
	if err != nil {
		return nil, err
	}
	current, err := s.collections.CountByUserAndVisibility(ctx, userID, isPublic)
	if err != nil {
		return nil, err
	}
	if err := EnforceCollectionLimit(u.Plan, isPublic, current); err != nil {
		return nil, err
	}
	return s.collections.Create(ctx, userID, title, description, coverURL, isPublic)
}

// Update — only the owner may edit. Visibility changes that would exceed
// the plan cap are blocked.
func (s *CollectionService) Update(ctx context.Context, id, userID string, title, description, coverURL *string, isPublic *bool) (*model.CollectionRecord, error) {
	c, err := s.collections.FindByID(ctx, id)
	if err != nil {
		return nil, err
	}
	if c.UserID != userID {
		return nil, ErrForbidden
	}
	// If the caller is flipping visibility, make sure they wouldn't blow the cap.
	if isPublic != nil && *isPublic != c.IsPublic {
		u, err := s.users.FindByID(ctx, userID)
		if err != nil {
			return nil, err
		}
		current, err := s.collections.CountByUserAndVisibility(ctx, userID, *isPublic)
		if err != nil {
			return nil, err
		}
		if err := EnforceCollectionLimit(u.Plan, *isPublic, current); err != nil {
			return nil, err
		}
	}
	return s.collections.Update(ctx, id, userID, title, description, coverURL, isPublic)
}

// Delete — only the owner may delete.
func (s *CollectionService) Delete(ctx context.Context, id, userID string) error {
	c, err := s.collections.FindByID(ctx, id)
	if err != nil {
		return err
	}
	if c.UserID != userID {
		return ErrForbidden
	}
	return s.collections.Delete(ctx, id, userID)
}

// ListMine returns the caller's collections (both public and private).
func (s *CollectionService) ListMine(ctx context.Context, userID string) ([]model.CollectionRecord, error) {
	return s.collections.ListByUser(ctx, userID)
}

// AddItem inserts a post into a collection. Caller must own the collection.
// We don't require ownership of the *post* — collections can curate other
// users' public posts in a future iteration; for v1 the toolbar always
// creates a fresh post owned by the caller before calling this.
func (s *CollectionService) AddItem(ctx context.Context, collectionID, postID, callerID string) error {
	c, err := s.collections.FindByID(ctx, collectionID)
	if err != nil {
		return err
	}
	if c.UserID != callerID {
		return ErrForbidden
	}
	if _, err := s.posts.FindByID(ctx, postID); err != nil {
		return err
	}
	return s.collections.AddItem(ctx, collectionID, postID)
}

// SetItemOrder updates positions for the given post ids so the new order
// matches the input array. Owner-only.
func (s *CollectionService) SetItemOrder(ctx context.Context, collectionID, callerID string, postIDs []string) error {
	c, err := s.collections.FindByID(ctx, collectionID)
	if err != nil {
		return err
	}
	if c.UserID != callerID {
		return ErrForbidden
	}
	return s.collections.SetItemOrder(ctx, collectionID, postIDs)
}

// CollectionsContaining returns the ids of the caller's collections
// that already include the given post. Used by the save-to-collection
// drawer to disable rows the post is already in.
func (s *CollectionService) CollectionsContaining(ctx context.Context, postID, callerID string) ([]string, error) {
	return s.collections.CollectionsContaining(ctx, postID, callerID)
}

// RemoveItem detaches a post from a collection (owner only).
func (s *CollectionService) RemoveItem(ctx context.Context, collectionID, postID, callerID string) error {
	c, err := s.collections.FindByID(ctx, collectionID)
	if err != nil {
		return err
	}
	if c.UserID != callerID {
		return ErrForbidden
	}
	return s.collections.RemoveItem(ctx, collectionID, postID)
}

// Get returns one collection. Visibility is enforced by the caller —
// `viewerID` is the calling user id ("" if anonymous). If the collection is
// private and the viewer isn't the owner, returns ErrForbidden.
func (s *CollectionService) Get(ctx context.Context, id, viewerID string) (*model.CollectionRecord, []model.Post, error) {
	c, err := s.collections.FindByID(ctx, id)
	if err != nil {
		return nil, nil, err
	}
	if !c.IsPublic && c.UserID != viewerID {
		return nil, nil, ErrForbidden
	}
	posts, err := s.collections.PostsIn(ctx, id)
	if err != nil {
		return nil, nil, err
	}
	// PostsIn returns posts without images (single-table boundary). Hydrate
	// them in one batched query so callers — and the post cards rendered
	// inside collection carousels — can show the post's first image as
	// background instead of falling back to the empty quote panel.
	if len(posts) > 0 {
		ids := make([]string, len(posts))
		for i := range posts {
			ids[i] = posts[i].ID
		}
		imgs, err := s.posts.ImagesFor(ctx, ids)
		if err != nil {
			return nil, nil, err
		}
		for i := range posts {
			posts[i].Images = imgs[posts[i].ID]
		}
		// Same batched approach for reshare states so the action footer
		// on each card swaps Reshare↔Send correctly. Anonymous viewers
		// (viewerID == "") get all-false at zero cost.
		if viewerID != "" {
			states, err := s.posts.ReshareStatesFor(ctx, viewerID, ids)
			if err != nil {
				return nil, nil, err
			}
			for i := range posts {
				if states[posts[i].ID] {
					posts[i].ViewerHasReshared = true
				}
			}
		}
	}
	return c, posts, nil
}

// CoverPresign returns a one-shot R2 PUT URL for a collection cover image.
func (s *CollectionService) CoverPresign(ctx context.Context, userID, contentType string) (uploadURL, publicURL string, err error) {
	return presignImage(ctx, s.r2, "collection-covers", userID, contentType)
}

// ---------------------------------------------------------------------------
// shared helpers
// ---------------------------------------------------------------------------

// presignImage builds an R2 presign for a user-scoped media key under the
// given prefix. The random suffix invalidates browser caches when the image
// is replaced.
func presignImage(ctx context.Context, r2 *repository.R2, prefix, userID, contentType string) (uploadURL, publicURL string, err error) {
	if r2 == nil {
		return "", "", errors.New("media uploads are not configured")
	}
	ext, ok := imageExtensionFor(contentType)
	if !ok {
		return "", "", fmt.Errorf("unsupported content type: %s", contentType)
	}
	suffix := make([]byte, 8)
	if _, err := rand.Read(suffix); err != nil {
		return "", "", err
	}
	key := path.Join(prefix, userID, hex.EncodeToString(suffix)+ext)
	return r2.PresignPut(ctx, key, contentType, 5*time.Minute)
}

func imageExtensionFor(ct string) (string, bool) {
	switch ct {
	case "image/png":
		return ".png", true
	case "image/jpeg":
		return ".jpg", true
	case "image/webp":
		return ".webp", true
	case "image/gif":
		return ".gif", true
	default:
		return "", false
	}
}

// stripHost reduces "https://prabhupadasays.org/books/bg/1/1?hl=x" to
// "/books/bg/1/1?hl=x" so we never store arbitrary external URLs.
// Anything that doesn't parse cleanly is returned unchanged (and rejected
// later by the prefix-check in the service).
func stripHost(u string) string {
	u = strings.TrimSpace(u)
	if u == "" {
		return u
	}
	if strings.HasPrefix(u, "/") {
		return u
	}
	for _, prefix := range []string{"http://", "https://"} {
		if strings.HasPrefix(u, prefix) {
			rest := u[len(prefix):]
			if i := strings.IndexByte(rest, '/'); i >= 0 {
				return rest[i:]
			}
			return "/"
		}
	}
	return u
}