package repository

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/prabhupadasays/spsays-bff/internal/model"
)

// ErrPostNotFound is returned by lookup methods when no row matches.
var ErrPostNotFound = errors.New("post not found")

// PostRepo wraps Postgres access for posts + post_images.
//
// Reshare model: a reshare is a real `posts` row owned by the resharer
// with `reshared_from_post_id` pointing at the canonical original. Likes
// and comments (future) will hang off post.id, so they diverge between
// original and reshare for free. Backgrounds are per-row in post_images,
// same story. The only thing the original and its reshares share is the
// caption / source_url / source_title at the moment of reshare.
type PostRepo struct{ pg *Postgres }

func NewPostRepo(pg *Postgres) *PostRepo { return &PostRepo{pg: pg} }

// postSelectColumns is the canonical column list used by every reader so
// every Post payload carries the same shape — including reshare
// attribution. The LEFT JOINs to `original_post` + `original_user` are
// always present; for canonical (non-reshare) rows they just yield NULL.
const postSelectColumns = `
	p.id, p.user_id, p.caption, p.source_url, COALESCE(p.source_title, ''),
	p.created_at, p.updated_at,
	u.name, u.handle, u.avatar_url,
	p.reshared_from_post_id,
	ou.name AS original_author_name,
	ou.handle AS original_author_handle,
	ou.avatar_url AS original_author_avatar
`

const postSelectFrom = `
	FROM posts p
	JOIN users u ON u.id = p.user_id
	LEFT JOIN posts op ON op.id = p.reshared_from_post_id
	LEFT JOIN users ou ON ou.id = op.user_id
`

// scanPost decodes one row produced by `postSelectColumns` into the
// destination Post. Single source of truth for the column → struct
// mapping, used by every reader.
func scanPost(row interface {
	Scan(dest ...any) error
}, p *model.Post) error {
	return row.Scan(
		&p.ID, &p.UserID, &p.Caption, &p.SourceURL, &p.SourceTitle,
		&p.CreatedAt, &p.UpdatedAt,
		&p.AuthorName, &p.AuthorHandle, &p.AuthorAvatarURL,
		&p.ResharedFromPostID,
		&p.OriginalAuthorName, &p.OriginalAuthorHandle, &p.OriginalAuthorAvatar,
	)
}

// Create inserts a post + its images in a single transaction so we never
// end up with orphan images.
func (r *PostRepo) Create(ctx context.Context, userID, caption, sourceURL, sourceTitle string, imageURLs []string) (*model.Post, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin tx: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	p := &model.Post{}
	err = tx.QueryRow(ctx, `
		INSERT INTO posts (user_id, caption, source_url, source_title)
		VALUES ($1, $2, $3, $4)
		RETURNING id, user_id, caption, source_url, COALESCE(source_title, ''), created_at, updated_at`,
		userID, caption, sourceURL, sourceTitle,
	).Scan(&p.ID, &p.UserID, &p.Caption, &p.SourceURL, &p.SourceTitle, &p.CreatedAt, &p.UpdatedAt)
	if err != nil {
		return nil, fmt.Errorf("insert post: %w", err)
	}

	for i, url := range imageURLs {
		var img model.PostImage
		err = tx.QueryRow(ctx, `
			INSERT INTO post_images (post_id, url, position)
			VALUES ($1, $2, $3)
			RETURNING id, url, position`,
			p.ID, url, i,
		).Scan(&img.ID, &img.URL, &img.Position)
		if err != nil {
			return nil, fmt.Errorf("insert post image %d: %w", i, err)
		}
		p.Images = append(p.Images, img)
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit: %w", err)
	}
	return p, nil
}

// ReplaceImages atomically swaps a post's image set. Owner-only — every
// reshare is its own posts row now, so the resharer is the owner of
// their reshare and edits it just like any other post they made.
func (r *PostRepo) ReplaceImages(ctx context.Context, postID, userID string, imageURLs []string) error {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin tx: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	var owner string
	if err := tx.QueryRow(ctx, `SELECT user_id FROM posts WHERE id = $1 FOR UPDATE`, postID).Scan(&owner); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return ErrPostNotFound
		}
		return fmt.Errorf("lock post: %w", err)
	}
	if owner != userID {
		return ErrPostNotFound
	}

	if _, err := tx.Exec(ctx, `DELETE FROM post_images WHERE post_id = $1`, postID); err != nil {
		return fmt.Errorf("delete images: %w", err)
	}
	for i, url := range imageURLs {
		if _, err := tx.Exec(ctx, `
			INSERT INTO post_images (post_id, url, position)
			VALUES ($1, $2, $3)`, postID, url, i,
		); err != nil {
			return fmt.Errorf("insert image %d: %w", i, err)
		}
	}
	if _, err := tx.Exec(ctx, `UPDATE posts SET updated_at = now() WHERE id = $1`, postID); err != nil {
		return fmt.Errorf("touch post: %w", err)
	}
	return tx.Commit(ctx)
}

// FindByID returns one post with its images and author info (plus original
// author info if this row is a reshare).
func (r *PostRepo) FindByID(ctx context.Context, id string) (*model.Post, error) {
	q := `SELECT ` + postSelectColumns + postSelectFrom + `WHERE p.id = $1`
	p := &model.Post{}
	if err := scanPost(r.pg.Pool.QueryRow(ctx, q, id), p); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrPostNotFound
		}
		return nil, fmt.Errorf("find post: %w", err)
	}
	imgs, err := r.ImagesFor(ctx, []string{p.ID})
	if err != nil {
		return nil, err
	}
	p.Images = imgs[p.ID]
	return p, nil
}

// ListByHandle returns the profile feed for a user. Unknown handle →
// empty page (matches pre-existing behaviour).
func (r *PostRepo) ListByHandle(ctx context.Context, handle string, limit, offset int) ([]model.Post, int, error) {
	var userID string
	if err := r.pg.Pool.QueryRow(ctx, `SELECT id FROM users WHERE handle = $1`, handle).Scan(&userID); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return []model.Post{}, 0, nil
		}
		return nil, 0, fmt.Errorf("lookup user by handle: %w", err)
	}
	return r.ListByUser(ctx, userID, limit, offset)
}

// ListByUser returns the user's profile feed — every post they own,
// authored or reshared. Reshares are interleaved naturally because
// they're stored as real rows; sort by created_at gets the right order
// without any UNION gymnastics.
func (r *PostRepo) ListByUser(ctx context.Context, userID string, limit, offset int) ([]model.Post, int, error) {
	total, err := r.CountByUser(ctx, userID)
	if err != nil {
		return nil, 0, err
	}
	q := `SELECT ` + postSelectColumns + postSelectFrom + `
		WHERE p.user_id = $1
		ORDER BY p.created_at DESC, p.id
		LIMIT $2 OFFSET $3`
	return r.collectPosts(ctx, total, q, userID, limit, offset)
}

// Delete removes a post only if it belongs to the caller. Cascades:
//   - the post's images (post_images.post_id FK)
//   - any reshares of this post made by other users (posts.reshared_from_post_id FK)
//   - those reshares' images (post_images.post_id FK on each reshare)
func (r *PostRepo) Delete(ctx context.Context, postID, userID string) error {
	tag, err := r.pg.Pool.Exec(ctx,
		`DELETE FROM posts WHERE id = $1 AND user_id = $2`, postID, userID)
	if err != nil {
		return fmt.Errorf("delete post: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrPostNotFound
	}
	return nil
}

// CountByUser returns the user's total post count (authored + reshared).
// Now just a single COUNT against posts.user_id.
func (r *PostRepo) CountByUser(ctx context.Context, userID string) (int, error) {
	var n int
	err := r.pg.Pool.QueryRow(ctx,
		`SELECT COUNT(*) FROM posts WHERE user_id = $1`, userID,
	).Scan(&n)
	if err != nil {
		return 0, fmt.Errorf("count posts: %w", err)
	}
	return n, nil
}

// PostedDates returns the set of UTC calendar days, on or after `since`,
// on which the user created at least one post. Used by the sādhana streak
// to detect the "posted a quote today" discipline (and to score past days
// of the streak) without loading whole posts. Keys are "YYYY-MM-DD".
func (r *PostRepo) PostedDates(ctx context.Context, userID string, since time.Time) (map[string]bool, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT DISTINCT (created_at AT TIME ZONE 'UTC')::date AS d
		FROM posts
		WHERE user_id = $1 AND created_at >= $2`,
		userID, since,
	)
	if err != nil {
		return nil, fmt.Errorf("posted dates: %w", err)
	}
	defer rows.Close()

	out := make(map[string]bool)
	for rows.Next() {
		var d time.Time
		if err := rows.Scan(&d); err != nil {
			return nil, fmt.Errorf("scan posted date: %w", err)
		}
		out[d.Format("2006-01-02")] = true
	}
	return out, rows.Err()
}

// PostCountsByDate returns, for each UTC calendar day on or after `since`,
// how many posts the user created that day. Keys are "YYYY-MM-DD"; days
// with no posts are absent (so a missing key reads as zero). The sādhana
// vine uses this both for the "posted a quote today" discipline and to
// annotate each day's fold with the number of quotes shared.
func (r *PostRepo) PostCountsByDate(ctx context.Context, userID string, since time.Time) (map[string]int, error) {
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT (created_at AT TIME ZONE 'UTC')::date AS d, count(*) AS n
		FROM posts
		WHERE user_id = $1 AND created_at >= $2
		GROUP BY d`,
		userID, since,
	)
	if err != nil {
		return nil, fmt.Errorf("post counts by date: %w", err)
	}
	defer rows.Close()

	out := make(map[string]int)
	for rows.Next() {
		var (
			d time.Time
			n int
		)
		if err := rows.Scan(&d, &n); err != nil {
			return nil, fmt.Errorf("scan post count: %w", err)
		}
		out[d.Format("2006-01-02")] = n
	}
	return out, rows.Err()
}

// Reshare creates a new posts row owned by `resharerID` that points at
// the canonical original via `reshared_from_post_id`. Copies the
// original's caption / source_url / source_title and its current images
// so the resharer's view renders identically at the moment of reshare;
// after that the two diverge — edits to either side never touch the
// other.
//
// If the post being reshared is itself a reshare we point at *its*
// canonical (transitive ancestor), so every reshare always references
// the true original.
//
// Idempotent: a user already resharing a canonical post returns the
// existing reshare row instead of creating a second one.
//
// Service-layer rule (caller can't reshare their own canonical) is
// enforced above this method.
func (r *PostRepo) Reshare(ctx context.Context, originalPostID, resharerID string) (*model.Post, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin tx: %w", err)
	}
	defer func() { _ = tx.Rollback(ctx) }()

	// Load the post being reshared. Walk one level back to canonical
	// in case the caller is resharing someone else's reshare.
	var (
		canonicalID   string
		caption       string
		sourceURL     string
		sourceTitle   string
		canonicalUser string
	)
	if err := tx.QueryRow(ctx, `
		SELECT
		    COALESCE(p.reshared_from_post_id, p.id),
		    p.caption, p.source_url, COALESCE(p.source_title, ''),
		    COALESCE(op.user_id, p.user_id)
		FROM posts p
		LEFT JOIN posts op ON op.id = p.reshared_from_post_id
		WHERE p.id = $1`, originalPostID,
	).Scan(&canonicalID, &caption, &sourceURL, &sourceTitle, &canonicalUser); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrPostNotFound
		}
		return nil, fmt.Errorf("load canonical: %w", err)
	}
	if canonicalUser == resharerID {
		return nil, errors.New("cannot reshare your own post")
	}

	// Idempotency: existing reshare by this user of this canonical?
	var existingID string
	switch err := tx.QueryRow(ctx, `
		SELECT id FROM posts
		WHERE user_id = $1 AND reshared_from_post_id = $2
		LIMIT 1`, resharerID, canonicalID,
	).Scan(&existingID); {
	case err == nil:
		// Already exists — commit the no-op tx and return the existing row.
		if err := tx.Commit(ctx); err != nil {
			return nil, fmt.Errorf("commit: %w", err)
		}
		return r.FindByID(ctx, existingID)
	case errors.Is(err, pgx.ErrNoRows):
		// Fresh reshare path below.
	default:
		return nil, fmt.Errorf("check existing reshare: %w", err)
	}

	var newID string
	if err := tx.QueryRow(ctx, `
		INSERT INTO posts (user_id, caption, source_url, source_title, reshared_from_post_id)
		VALUES ($1, $2, $3, $4, $5)
		RETURNING id`,
		resharerID, caption, sourceURL, sourceTitle, canonicalID,
	).Scan(&newID); err != nil {
		return nil, fmt.Errorf("insert reshare post: %w", err)
	}

	// Copy the canonical's current images as the resharer's starting set.
	if _, err := tx.Exec(ctx, `
		INSERT INTO post_images (post_id, url, position)
		SELECT $1, url, position
		FROM post_images
		WHERE post_id = $2`, newID, canonicalID,
	); err != nil {
		return nil, fmt.Errorf("copy images: %w", err)
	}

	if err := tx.Commit(ctx); err != nil {
		return nil, fmt.Errorf("commit: %w", err)
	}
	return r.FindByID(ctx, newID)
}

// Unreshare removes the caller's reshare of a canonical post. The
// caller passes the canonical post id (what the UI knows); we look up
// the caller's reshare-row and delete it. Idempotent — no reshare to
// delete is a no-op.
func (r *PostRepo) Unreshare(ctx context.Context, canonicalPostID, resharerID string) error {
	if _, err := r.pg.Pool.Exec(ctx, `
		DELETE FROM posts
		WHERE user_id = $1 AND reshared_from_post_id = $2`,
		resharerID, canonicalPostID,
	); err != nil {
		return fmt.Errorf("unreshare: %w", err)
	}
	return nil
}

// ReshareStatesFor returns the set of post IDs from the supplied list
// that the viewer has reshared. Used by feed renderers to flip the
// post-card "Reshare ↔ Send" toggle.
//
// `postIDs` may carry either canonical posts or reshare rows; the query
// resolves each id to its canonical first, then asks "does the viewer
// have a row whose reshared_from_post_id equals that canonical?". The
// returned map keys are the supplied ids — callers don't need to know
// the canonical relationship.
func (r *PostRepo) ReshareStatesFor(ctx context.Context, viewerID string, postIDs []string) (map[string]bool, error) {
	out := make(map[string]bool, len(postIDs))
	if viewerID == "" || len(postIDs) == 0 {
		return out, nil
	}
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT p.id
		FROM posts p
		WHERE p.id = ANY($2)
		  AND EXISTS (
		      SELECT 1 FROM posts r
		      WHERE r.user_id = $1
		        AND r.reshared_from_post_id = COALESCE(p.reshared_from_post_id, p.id)
		  )`, viewerID, postIDs,
	)
	if err != nil {
		return nil, fmt.Errorf("query reshare states: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, fmt.Errorf("scan reshare state: %w", err)
		}
		out[id] = true
	}
	return out, rows.Err()
}

// --- internal helpers ---

func (r *PostRepo) collectPosts(ctx context.Context, total int, query string, args ...any) ([]model.Post, int, error) {
	rows, err := r.pg.Pool.Query(ctx, query, args...)
	if err != nil {
		return nil, 0, fmt.Errorf("query posts: %w", err)
	}
	defer rows.Close()

	posts := []model.Post{}
	ids := []string{}
	for rows.Next() {
		var p model.Post
		if err := scanPost(rows, &p); err != nil {
			return nil, 0, fmt.Errorf("scan post: %w", err)
		}
		posts = append(posts, p)
		ids = append(ids, p.ID)
	}
	if err := rows.Err(); err != nil {
		return nil, 0, fmt.Errorf("iterate posts: %w", err)
	}

	if len(ids) > 0 {
		imgs, err := r.ImagesFor(ctx, ids)
		if err != nil {
			return nil, 0, err
		}
		for i := range posts {
			posts[i].Images = imgs[posts[i].ID]
		}
	}
	return posts, total, nil
}

// ImagesFor returns a map post_id → [images...] for a batch of post IDs in
// a single query so we don't N+1 the feed endpoint. Exported because the
// CollectionService needs to hydrate images onto posts that come back
// from CollectionRepo.PostsIn (which only joins posts/users — not
// post_images — to keep that query focused).
func (r *PostRepo) ImagesFor(ctx context.Context, postIDs []string) (map[string][]model.PostImage, error) {
	out := make(map[string][]model.PostImage, len(postIDs))
	if len(postIDs) == 0 {
		return out, nil
	}
	rows, err := r.pg.Pool.Query(ctx, `
		SELECT post_id, id, url, position
		FROM post_images
		WHERE post_id = ANY($1)
		ORDER BY post_id, position`, postIDs,
	)
	if err != nil {
		return nil, fmt.Errorf("query post images: %w", err)
	}
	defer rows.Close()
	for rows.Next() {
		var postID string
		var img model.PostImage
		if err := rows.Scan(&postID, &img.ID, &img.URL, &img.Position); err != nil {
			return nil, fmt.Errorf("scan post image: %w", err)
		}
		out[postID] = append(out[postID], img)
	}
	return out, rows.Err()
}