package repository

import (
	"context"
	"errors"
	"fmt"

	"github.com/jackc/pgx/v5"
	"github.com/prabhupadasays/spsays-bff/internal/model"
	"go.uber.org/zap"
)

var (
	// ErrCommentNotFound — no comment with that id (or not in the expected
	// scope, e.g. pinning a reply).
	ErrCommentNotFound = errors.New("comment not found")
	// ErrDuplicateComment — the same user re-posted identical text in the same
	// scope (caught by the dedup unique index).
	ErrDuplicateComment = errors.New("duplicate comment")
)

// CommentRepo handles post comments, replies, comment-likes, and pinning.
// Comment likes are far lower-volume than post likes, so likes_count is kept
// in sync transactionally rather than batched through Redis.
type CommentRepo struct {
	pg     *Postgres
	logger *zap.Logger
}

func NewCommentRepo(pg *Postgres, logger *zap.Logger) *CommentRepo {
	return &CommentRepo{pg: pg, logger: logger}
}

// nullUUIDArg returns nil for an empty id so a `$n::uuid` parameter binds to
// SQL NULL (anonymous viewer) instead of failing uuid parsing on "".
func nullUUIDArg(s string) *string {
	if s == "" {
		return nil
	}
	return &s
}

// commentSelect is the shared column list for reading a comment with its
// author, the reply-to handle, the viewer's like state, and the reply count.
// `vl` is a viewer-scoped LEFT JOIN on comment_likes; `ru` the reply-to user.
const commentSelect = `
	c.id, c.post_id, c.user_id, c.parent_id, c.body, c.likes_count,
	c.pinned_at, c.created_at, c.updated_at,
	u.name, u.handle, u.avatar_url,
	ru.handle,
	(vl.comment_id IS NOT NULL),
	(SELECT count(*) FROM post_comments rc WHERE rc.parent_id = c.id AND rc.deleted_at IS NULL)`

// The viewer id always rides in parameter slot $2 across the read queries
// below, so the shared viewer-scoped like join can hardcode it.
const commentFrom = `
	FROM post_comments c
	JOIN users u ON u.id = c.user_id
	LEFT JOIN users ru ON ru.id = c.reply_to_user_id
	LEFT JOIN comment_likes vl ON vl.comment_id = c.id AND vl.user_id = $2::uuid`

func scanComment(row pgx.Row, c *model.Comment) error {
	return row.Scan(&c.ID, &c.PostID, &c.UserID, &c.ParentID, &c.Body, &c.LikesCount,
		&c.PinnedAt, &c.CreatedAt, &c.UpdatedAt,
		&c.AuthorName, &c.AuthorHandle, &c.AuthorAvatarURL,
		&c.ReplyToHandle,
		&c.ViewerHasLiked, &c.ReplyCount)
}

func scanComments(rows pgx.Rows) ([]model.Comment, error) {
	defer rows.Close()
	out := []model.Comment{}
	for rows.Next() {
		var c model.Comment
		if err := scanComment(rows, &c); err != nil {
			return nil, fmt.Errorf("scan comment: %w", err)
		}
		out = append(out, c)
	}
	return out, rows.Err()
}

// PostAuthor returns the id of the user who owns the post, or ErrPostNotFound.
func (r *CommentRepo) PostAuthor(ctx context.Context, postID string) (string, error) {
	var uid string
	err := r.pg.Pool.QueryRow(ctx, `SELECT user_id FROM posts WHERE id = $1`, postID).Scan(&uid)
	if errors.Is(err, pgx.ErrNoRows) {
		return "", ErrPostNotFound
	}
	if err != nil {
		return "", fmt.Errorf("post author: %w", err)
	}
	return uid, nil
}

// Create inserts a comment. parentID is the thread root (nil for a top-level
// comment); replyToUserID is who a reply addresses (nil for top-level).
// Returns ErrDuplicateComment when the same user re-posts identical text in
// the same scope. The returned Comment carries author fields.
func (r *CommentRepo) Create(ctx context.Context, postID, userID string, parentID, replyToUserID *string, body string) (*model.Comment, error) {
	var id string
	err := r.pg.Pool.QueryRow(ctx, `
		INSERT INTO post_comments (post_id, user_id, parent_id, reply_to_user_id, body)
		VALUES ($1, $2, $3, $4, $5)
		ON CONFLICT (post_id, user_id, COALESCE(parent_id, '00000000-0000-0000-0000-000000000000'::uuid), md5(body))
		DO NOTHING
		RETURNING id`,
		postID, userID, parentID, replyToUserID, body,
	).Scan(&id)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrDuplicateComment
	}
	if err != nil {
		return nil, fmt.Errorf("insert comment: %w", err)
	}
	// The author hasn't liked their own brand-new comment, so viewer state is
	// resolved against userID (yields false) — fine for the create response.
	return r.Get(ctx, id, userID)
}

// Get returns one comment hydrated with author + viewer-like + reply count.
func (r *CommentRepo) Get(ctx context.Context, id, viewerID string) (*model.Comment, error) {
	q := `SELECT ` + commentSelect + commentFrom + ` WHERE c.id = $1 AND c.deleted_at IS NULL`
	c := &model.Comment{}
	err := scanComment(r.pg.Pool.QueryRow(ctx, q, id, nullUUIDArg(viewerID)), c)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrCommentNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("get comment: %w", err)
	}
	return c, nil
}

// ListTopLevel returns a page of a post's top-level comments — pinned first,
// then newest — plus the total top-level count.
func (r *CommentRepo) ListTopLevel(ctx context.Context, postID, viewerID string, limit, offset int) ([]model.Comment, int, error) {
	var total int
	if err := r.pg.Pool.QueryRow(ctx,
		`SELECT count(*) FROM post_comments WHERE post_id = $1 AND parent_id IS NULL AND deleted_at IS NULL`,
		postID).Scan(&total); err != nil {
		return nil, 0, fmt.Errorf("count comments: %w", err)
	}
	if total == 0 {
		return []model.Comment{}, 0, nil
	}
	q := `SELECT ` + commentSelect + commentFrom + `
		WHERE c.post_id = $1 AND c.parent_id IS NULL AND c.deleted_at IS NULL
		ORDER BY (c.pinned_at IS NOT NULL) DESC, c.pinned_at DESC NULLS LAST, c.created_at DESC
		LIMIT $3 OFFSET $4`
	rows, err := r.pg.Pool.Query(ctx, q, postID, nullUUIDArg(viewerID), limit, offset)
	if err != nil {
		return nil, 0, fmt.Errorf("list comments: %w", err)
	}
	out, err := scanComments(rows)
	return out, total, err
}

// ListReplies returns a page of a thread's replies (oldest first) + the total.
func (r *CommentRepo) ListReplies(ctx context.Context, parentID, viewerID string, limit, offset int) ([]model.Comment, int, error) {
	var total int
	if err := r.pg.Pool.QueryRow(ctx,
		`SELECT count(*) FROM post_comments WHERE parent_id = $1 AND deleted_at IS NULL`, parentID).Scan(&total); err != nil {
		return nil, 0, fmt.Errorf("count replies: %w", err)
	}
	if total == 0 {
		return []model.Comment{}, 0, nil
	}
	q := `SELECT ` + commentSelect + commentFrom + `
		WHERE c.parent_id = $1 AND c.deleted_at IS NULL
		ORDER BY c.created_at ASC
		LIMIT $3 OFFSET $4`
	rows, err := r.pg.Pool.Query(ctx, q, parentID, nullUUIDArg(viewerID), limit, offset)
	if err != nil {
		return nil, 0, fmt.Errorf("list replies: %w", err)
	}
	out, err := scanComments(rows)
	return out, total, err
}

// Hydrate fills each post's comment summary — its pinned comment (if any) and
// total comment count (top-level + replies) — in two batched queries for the
// page. Drives the card footer's pinned line and comment count.
func (r *CommentRepo) Hydrate(ctx context.Context, viewerID string, posts []*model.Post) error {
	ids := make([]string, 0, len(posts))
	for _, p := range posts {
		if p != nil {
			ids = append(ids, p.ID)
		}
	}
	if len(ids) == 0 {
		return nil
	}

	// Pinned comment per post.
	q := `SELECT ` + commentSelect + commentFrom + `
		WHERE c.post_id = ANY($1) AND c.pinned_at IS NOT NULL`
	rows, err := r.pg.Pool.Query(ctx, q, ids, nullUUIDArg(viewerID))
	if err != nil {
		return fmt.Errorf("hydrate pinned: %w", err)
	}
	list, err := scanComments(rows) // closes rows
	if err != nil {
		return err
	}
	pinnedByPost := make(map[string]*model.Comment, len(list))
	for i := range list {
		pinnedByPost[list[i].PostID] = &list[i]
	}

	// Total comment count per post (top-level + replies).
	counts := make(map[string]int, len(ids))
	crows, err := r.pg.Pool.Query(ctx,
		`SELECT post_id, count(*) FROM post_comments WHERE post_id = ANY($1) AND deleted_at IS NULL GROUP BY post_id`,
		ids)
	if err != nil {
		return fmt.Errorf("hydrate comment counts: %w", err)
	}
	defer crows.Close()
	for crows.Next() {
		var id string
		var n int
		if err := crows.Scan(&id, &n); err != nil {
			return fmt.Errorf("scan comment count: %w", err)
		}
		counts[id] = n
	}
	if err := crows.Err(); err != nil {
		return err
	}

	for _, p := range posts {
		if p == nil {
			continue
		}
		if c, ok := pinnedByPost[p.ID]; ok {
			p.PinnedComment = c
		}
		p.CommentsCount = counts[p.ID]
	}
	return nil
}

// Like / Unlike toggle the viewer's like on a comment and return the new
// likes_count. Idempotent; the membership change and counter update happen in
// one transaction so concurrent likes stay consistent.
func (r *CommentRepo) Like(ctx context.Context, commentID, userID string) (int, error) {
	return r.setLike(ctx, commentID, userID, true)
}

func (r *CommentRepo) Unlike(ctx context.Context, commentID, userID string) (int, error) {
	return r.setLike(ctx, commentID, userID, false)
}

func (r *CommentRepo) setLike(ctx context.Context, commentID, userID string, like bool) (int, error) {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return 0, fmt.Errorf("begin like txn: %w", err)
	}
	defer tx.Rollback(ctx)

	// Lock the comment row up front: this validates existence (clean 404
	// instead of a leaked FK violation) and serializes concurrent likes so
	// the counter stays exact.
	var count int
	if err := tx.QueryRow(ctx,
		`SELECT likes_count FROM post_comments WHERE id = $1 FOR UPDATE`, commentID).Scan(&count); err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return 0, ErrCommentNotFound
		}
		return 0, fmt.Errorf("read comment likes_count: %w", err)
	}

	if like {
		tag, err := tx.Exec(ctx,
			`INSERT INTO comment_likes (comment_id, user_id) VALUES ($1, $2) ON CONFLICT DO NOTHING`,
			commentID, userID)
		if err != nil {
			return 0, fmt.Errorf("insert comment like: %w", err)
		}
		if tag.RowsAffected() > 0 {
			count++
			if _, err := tx.Exec(ctx,
				`UPDATE post_comments SET likes_count = $2 WHERE id = $1`, commentID, count); err != nil {
				return 0, fmt.Errorf("bump comment likes: %w", err)
			}
		}
	} else {
		tag, err := tx.Exec(ctx,
			`DELETE FROM comment_likes WHERE comment_id = $1 AND user_id = $2`, commentID, userID)
		if err != nil {
			return 0, fmt.Errorf("delete comment like: %w", err)
		}
		if tag.RowsAffected() > 0 {
			if count > 0 {
				count--
			}
			if _, err := tx.Exec(ctx,
				`UPDATE post_comments SET likes_count = $2 WHERE id = $1`, commentID, count); err != nil {
				return 0, fmt.Errorf("drop comment likes: %w", err)
			}
		}
	}

	if err := tx.Commit(ctx); err != nil {
		return 0, fmt.Errorf("commit like txn: %w", err)
	}
	return count, nil
}

// Pin makes commentID the post's single pinned comment (top-level only),
// unpinning any previously pinned comment in the same transaction. Returns
// ErrCommentNotFound when the comment isn't a top-level comment of postID.
func (r *CommentRepo) Pin(ctx context.Context, postID, commentID string) error {
	tx, err := r.pg.Pool.Begin(ctx)
	if err != nil {
		return fmt.Errorf("begin pin txn: %w", err)
	}
	defer tx.Rollback(ctx)

	if _, err := tx.Exec(ctx,
		`UPDATE post_comments SET pinned_at = NULL WHERE post_id = $1 AND pinned_at IS NOT NULL`,
		postID); err != nil {
		return fmt.Errorf("unpin existing: %w", err)
	}
	tag, err := tx.Exec(ctx,
		`UPDATE post_comments SET pinned_at = now(), updated_at = now()
		 WHERE id = $1 AND post_id = $2 AND parent_id IS NULL`,
		commentID, postID)
	if err != nil {
		return fmt.Errorf("pin comment: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrCommentNotFound
	}
	return tx.Commit(ctx)
}

// Unpin clears the pin on commentID for postID.
func (r *CommentRepo) Unpin(ctx context.Context, postID, commentID string) error {
	tag, err := r.pg.Pool.Exec(ctx,
		`UPDATE post_comments SET pinned_at = NULL WHERE id = $1 AND post_id = $2`,
		commentID, postID)
	if err != nil {
		return fmt.Errorf("unpin comment: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrCommentNotFound
	}
	return nil
}

// Delete removes the comment. For a thread root this cascades to its replies
// (and all comment_likes) via ON DELETE CASCADE. Authorization is the caller's
// responsibility.
func (r *CommentRepo) Delete(ctx context.Context, commentID string) error {
	tag, err := r.pg.Pool.Exec(ctx, `DELETE FROM post_comments WHERE id = $1`, commentID)
	if err != nil {
		return fmt.Errorf("delete comment: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrCommentNotFound
	}
	return nil
}

// CreateReport files a report against a comment.
func (r *CommentRepo) CreateReport(ctx context.Context, reporterID, commentID, category, reason string) error {
	if _, err := r.pg.Pool.Exec(ctx,
		`INSERT INTO comment_reports (reporter_id, comment_id, category, reason)
		 VALUES ($1, $2, $3, $4)`,
		reporterID, commentID, category, reason,
	); err != nil {
		return fmt.Errorf("create comment report: %w", err)
	}
	return nil
}