// Package store owns the schema and every SQL query. All SQL is written with
// `?` placeholders and re-bound to `$n` when running on PostgreSQL.
package store

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"

	"oneblog/internal/db"
	"oneblog/internal/model"
	"oneblog/internal/render"
)

func renderHTML(md string) string { return render.Markdown(md) }

func readingMinutes(md string) int { return render.ReadingMinutes(md) }

var ErrNotFound = errors.New("not found")

type Store struct {
	db *db.DB
}

func New(d *db.DB) (*Store, error) {
	s := &Store{db: d}
	if err := s.migrate(); err != nil {
		return nil, err
	}
	return s, nil
}

// Ping 供 /api/health 探活数据库连接。
func (s *Store) Ping(ctx context.Context) error { return s.db.PingContext(ctx) }

func now() string { return time.Now().UTC().Format(time.RFC3339) }

func (s *Store) migrate() error {
	ai := s.db.AutoInc()
	stmts := []string{
		fmt.Sprintf(`CREATE TABLE IF NOT EXISTS posts (
			id              %s,
			kind            TEXT NOT NULL DEFAULT 'long',
			title           TEXT NOT NULL DEFAULT '',
			slug            TEXT NOT NULL,
			summary         TEXT NOT NULL DEFAULT '',
			cover_url       TEXT NOT NULL DEFAULT '',
			content_md      TEXT NOT NULL DEFAULT '',
			content_html    TEXT NOT NULL DEFAULT '',
			status          TEXT NOT NULL DEFAULT 'draft',
			published_at    TEXT NOT NULL,
			created_at      TEXT NOT NULL,
			updated_at      TEXT NOT NULL,
			reading_minutes INTEGER NOT NULL DEFAULT 1
		)`, ai),
		fmt.Sprintf(`CREATE TABLE IF NOT EXISTS tags (
			id    %s,
			name  TEXT NOT NULL,
			slug  TEXT NOT NULL,
			color TEXT NOT NULL DEFAULT ''
		)`, ai),
		`CREATE TABLE IF NOT EXISTS post_tags (
			post_id INTEGER NOT NULL,
			tag_id  INTEGER NOT NULL,
			PRIMARY KEY (post_id, tag_id)
		)`,
		`CREATE TABLE IF NOT EXISTS settings (
			key   TEXT PRIMARY KEY,
			value TEXT NOT NULL DEFAULT ''
		)`,
	}
	for _, q := range stmts {
		if _, err := s.db.Exec(s.db.Q(q)); err != nil {
			return fmt.Errorf("migrate: %w", err)
		}
	}

	// Lightweight column-add migrations for older databases. SQLite supports
	// ADD COLUMN; Postgres doesn't support IF NOT EXISTS on column add, so we
	// swallow "already exists" errors either way.
	columnAdds := []string{
		`ALTER TABLE posts ADD COLUMN cover_url TEXT NOT NULL DEFAULT ''`,
		`ALTER TABLE tags  ADD COLUMN color     TEXT NOT NULL DEFAULT ''`,
	}
	for _, q := range columnAdds {
		if _, err := s.db.Exec(s.db.Q(q)); err != nil && !strings.Contains(err.Error(), "already exists") &&
			!strings.Contains(err.Error(), "duplicate column") {
			return fmt.Errorf("migrate column: %w", err)
		}
	}

	// Indexes/unique constraints need dialect-specific "IF NOT EXISTS" support.
	indexes := []struct{ name, ddl string }{
		{"idx_posts_slug", `CREATE UNIQUE INDEX IF NOT EXISTS idx_posts_slug ON posts(slug)`},
		{"idx_posts_feed", `CREATE INDEX IF NOT EXISTS idx_posts_feed ON posts(status, published_at DESC)`},
		{"idx_tags_slug", `CREATE UNIQUE INDEX IF NOT EXISTS idx_tags_slug ON tags(slug)`},
		{"idx_post_tags_tag", `CREATE INDEX IF NOT EXISTS idx_post_tags_tag ON post_tags(tag_id)`},
	}
	for _, ix := range indexes {
		if _, err := s.db.Exec(s.db.Q(ix.ddl)); err != nil && !strings.Contains(err.Error(), "already exists") {
			return fmt.Errorf("migrate index %s: %w", ix.name, err)
		}
	}

	return s.seedSettings()
}

func (s *Store) seedSettings() error {
	defs := map[string]string{
		"site_title":     "ONE · 一个博客",
		"site_desc":      "长文与短文，同一种节奏。",
		"author_name":    "ONE",
		"author_bio":     "写点长的，也写点短的。",
		"footer_note":    "© ONE · 一个博客",
		"icp":            "",
		"posts_per_page": "10",
	}
	for k, v := range defs {
		if s.db.Dialect == db.Postgres {
			_, err := s.db.Exec(s.db.Q(`INSERT INTO settings(key,value) VALUES (?,?)
				ON CONFLICT (key) DO NOTHING`), k, v)
			if err != nil {
				return err
			}
			continue
		}
		if _, err := s.db.Exec(s.db.Q(`INSERT OR IGNORE INTO settings(key,value) VALUES (?,?)`), k, v); err != nil {
			return err
		}
	}
	return nil
}

// ---------- settings ----------

func (s *Store) GetSettings() (model.Settings, error) {
	rows, err := s.db.Query(s.db.Q(`SELECT key, value FROM settings`))
	if err != nil {
		return model.Settings{}, err
	}
	defer rows.Close()
	m := map[string]string{}
	for rows.Next() {
		var k, v string
		if err := rows.Scan(&k, &v); err != nil {
			return model.Settings{}, err
		}
		m[k] = v
	}
	return settingsFromMap(m), rows.Err()
}

func settingsFromMap(m map[string]string) model.Settings {
	st := model.Settings{
		SiteTitle:    m["site_title"],
		SiteDesc:     m["site_desc"],
		AuthorName:   m["author_name"],
		AuthorBio:    m["author_bio"],
		FooterNote:   m["footer_note"],
		ICPLicense:   m["icp"],
		PostsPerPage: 10,
	}
	// LightSkinID is the new canonical name; fall back to legacy theme_id
	// for clients that haven't been updated, and finally to "paper".
	st.LightSkinID = m["light_skin_id"]
	if st.LightSkinID == "" {
		st.LightSkinID = m["theme_id"]
	}
	if st.LightSkinID == "" {
		st.LightSkinID = "paper"
	}
	// Mirror the value into ThemeID so legacy API consumers still see it
	// in the JSON response.
	st.ThemeID = st.LightSkinID
	if n := atoi(m["posts_per_page"]); n > 0 {
		st.PostsPerPage = n
	}
	return st
}

func atoi(v string) int {
	n := 0
	for _, r := range v {
		if r < '0' || r > '9' {
			return 0
		}
		n = n*10 + int(r-'0')
	}
	return n
}

// ValidLightSkins is the whitelist of light-side skin ids the API accepts.
// Anything outside this set falls back to "paper" on write.
var ValidLightSkins = map[string]bool{
	"paper": true,
	"sage":  true,
	"rose":  true,
}

func (s *Store) UpdateSettings(st model.Settings) error {
	if st.PostsPerPage <= 0 {
		st.PostsPerPage = 10
	}
	if !ValidLightSkins[st.LightSkinID] {
		st.LightSkinID = "paper"
	}
	sets := map[string]string{
		"site_title":     st.SiteTitle,
		"site_desc":      st.SiteDesc,
		"author_name":    st.AuthorName,
		"author_bio":     st.AuthorBio,
		"footer_note":    st.FooterNote,
		"icp":            st.ICPLicense,
		"posts_per_page": fmt.Sprint(st.PostsPerPage),
		"light_skin_id":  st.LightSkinID,
		// Mirror to theme_id so any older client still sees something.
		"theme_id": st.LightSkinID,
	}
	for k, v := range sets {
		if s.db.Dialect == db.Postgres {
			if _, err := s.db.Exec(s.db.Q(`INSERT INTO settings(key,value) VALUES (?,?)
				ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value`), k, v); err != nil {
				return err
			}
			continue
		}
		if _, err := s.db.Exec(s.db.Q(`INSERT INTO settings(key,value) VALUES (?,?)
			ON CONFLICT(key) DO UPDATE SET value = excluded.value`), k, v); err != nil {
			return err
		}
	}
	return nil
}

// ---------- posts ----------

type ListOptions struct {
	Kind    string
	Tag     string
	Query   string
	Status  string // "" = published only (public), "any" = all (admin)
	Page    int
	Size    int
	OrderBy string
}

// OrderBy 来自查询参数，必须白名单校验后才能拼进 SQL。
var allowedOrder = map[string]bool{
	"published_at desc":    true,
	"published_at asc":     true,
	"updated_at desc":      true,
	"updated_at asc":       true,
	"created_at desc":      true,
	"reading_minutes desc": true,
	"reading_minutes asc":  true,
}

func sanitizeOrder(o string) string {
	key := strings.ToLower(strings.Join(strings.Fields(o), " "))
	if allowedOrder[key] {
		return key
	}
	return "published_at desc"
}

const postCols = `id, kind, title, slug, summary, cover_url, content_md, content_html, status,
	published_at, created_at, updated_at, reading_minutes, LENGTH(content_md)`

// listCols 用于列表/时间线：不传 content_md（前端不用），
// 长文 content_html 只截 600 字符供无摘要时提取纯文本，短文保留全文渲染。
const listCols = `id, kind, title, slug, summary, cover_url,
	'' AS content_md,
	CASE WHEN kind = 'short' THEN content_html ELSE substr(content_html, 1, 600) END AS content_html,
	status, published_at, created_at, updated_at, reading_minutes, LENGTH(content_md)`

func scanPost(rows interface{ Scan(...any) error }) (model.Post, error) {
	var p model.Post
	err := rows.Scan(&p.ID, &p.Kind, &p.Title, &p.Slug, &p.Summary, &p.CoverURL,
		&p.ContentMd, &p.ContentHTML, &p.Status, &p.PublishedAt, &p.CreatedAt, &p.UpdatedAt,
		&p.ReadingMinutes, &p.ContentLen)
	p.Tags = []string{}
	return p, err
}

func (s *Store) List(o ListOptions) (model.Page, error) {
	if o.Page < 1 {
		o.Page = 1
	}
	if o.Size < 1 || o.Size > 100 {
		o.Size = 10
	}
	where := []string{}
	args := []any{}
	if o.Status == "any" {
		// admin: no status filter
	} else if o.Status != "" {
		where = append(where, "status = ?")
		args = append(args, o.Status)
	} else {
		where = append(where, "status = 'published'")
	}
	if o.Kind != "" {
		where = append(where, "kind = ?")
		args = append(args, o.Kind)
	}
	if o.Tag != "" {
		where = append(where, `id IN (SELECT pt.post_id FROM post_tags pt JOIN tags t ON t.id = pt.tag_id
			WHERE t.slug = ? OR t.name = ?)`)
		args = append(args, o.Tag, o.Tag)
	}
	if o.Query != "" {
		like := "%" + strings.ToLower(o.Query) + "%"
		where = append(where, `(lower(title) LIKE ? OR lower(summary) LIKE ? OR lower(content_md) LIKE ?)`)
		args = append(args, like, like, like)
	}
	w := ""
	if len(where) > 0 {
		w = "WHERE " + strings.Join(where, " AND ")
	}
	order := sanitizeOrder(o.OrderBy)

	var total int
	if err := s.db.QueryRow(s.db.Q(`SELECT COUNT(*) FROM posts `+w), args...).Scan(&total); err != nil {
		return model.Page{}, err
	}

	q := s.db.Q(fmt.Sprintf(`SELECT %s FROM posts %s ORDER BY %s LIMIT ? OFFSET ?`, listCols, w, order))
	rows, err := s.db.Query(q, append(args, o.Size, (o.Page-1)*o.Size)...)
	if err != nil {
		return model.Page{}, err
	}
	defer rows.Close()

	items := []model.Post{}
	for rows.Next() {
		p, err := scanPost(rows)
		if err != nil {
			return model.Page{}, err
		}
		items = append(items, p)
	}
	if err := rows.Err(); err != nil {
		return model.Page{}, err
	}
	if err := s.attachTags(items); err != nil {
		return model.Page{}, err
	}
	return model.Page{Items: items, Total: total, Page: o.Page, Size: o.Size}, nil
}

func (s *Store) attachTags(posts []model.Post) error {
	if len(posts) == 0 {
		return nil
	}
	ids := make([]any, 0, len(posts))
	idx := map[int64]int{}
	for i, p := range posts {
		ids = append(ids, p.ID)
		idx[p.ID] = i
	}
	ph := strings.TrimSuffix(strings.Repeat("?,", len(ids)), ",")
	q := s.db.Q(fmt.Sprintf(`SELECT pt.post_id, t.name FROM post_tags pt
		JOIN tags t ON t.id = pt.tag_id WHERE pt.post_id IN (%s) ORDER BY t.name`, ph))
	rows, err := s.db.Query(q, ids...)
	if err != nil {
		return err
	}
	defer rows.Close()
	for rows.Next() {
		var pid int64
		var name string
		if err := rows.Scan(&pid, &name); err != nil {
			return err
		}
		if i, ok := idx[pid]; ok {
			posts[i].Tags = append(posts[i].Tags, name)
		}
	}
	return rows.Err()
}

func (s *Store) Get(id int64) (model.Post, error) {
	var p model.Post
	row := s.db.QueryRow(s.db.Q(`SELECT `+postCols+` FROM posts WHERE id = ?`), id)
	if err := scanPostInto(row, &p); err != nil {
		return p, err
	}
	items := []model.Post{p}
	if err := s.attachTags(items); err != nil {
		return p, err
	}
	return items[0], nil
}

func (s *Store) GetBySlug(slug string) (model.Post, error) {
	var p model.Post
	row := s.db.QueryRow(s.db.Q(`SELECT `+postCols+` FROM posts WHERE slug = ?`), slug)
	if err := scanPostInto(row, &p); err != nil {
		return p, err
	}
	items := []model.Post{p}
	if err := s.attachTags(items); err != nil {
		return p, err
	}
	return items[0], nil
}

func scanPostInto(row *sql.Row, p *model.Post) error {
	err := row.Scan(&p.ID, &p.Kind, &p.Title, &p.Slug, &p.Summary, &p.CoverURL,
		&p.ContentMd, &p.ContentHTML, &p.Status, &p.PublishedAt, &p.CreatedAt, &p.UpdatedAt,
		&p.ReadingMinutes, &p.ContentLen)
	if err == sql.ErrNoRows {
		return ErrNotFound
	}
	if err != nil {
		return err
	}
	p.Tags = []string{}
	return nil
}

// ---------- slug ----------

var slugSep = regexp.MustCompile(`[^\p{L}\p{N}]+`)

func Slugify(s string) string {
	s = strings.TrimSpace(strings.ToLower(s))
	s = slugSep.ReplaceAllString(s, "-")
	s = strings.Trim(s, "-")
	return s
}

func (s *Store) uniqueSlug(base string, excludeID int64) string {
	base = Slugify(base)
	if base == "" {
		base = "post"
	}
	candidate := base
	for i := 2; ; i++ {
		var id int64
		err := s.db.QueryRow(s.db.Q(`SELECT id FROM posts WHERE slug = ? AND id <> ?`), candidate, excludeID).Scan(&id)
		if err == sql.ErrNoRows {
			return candidate
		}
		if err != nil {
			return fmt.Sprintf("%s-%d", base, time.Now().Unix())
		}
		candidate = fmt.Sprintf("%s-%d", base, i)
	}
}

// ---------- write ----------

func (s *Store) Create(in model.PostInput) (model.Post, error) {
	p := model.Post{
		Kind:     in.Kind,
		Title:    strings.TrimSpace(in.Title),
		Slug:     in.Slug,
		Status:   in.Status,
		CoverURL: strings.TrimSpace(in.CoverURL),
		Tags:     []string{},
	}
	if p.Kind == "" {
		p.Kind = model.KindLong
	}
	if p.Status == "" {
		p.Status = model.StatusDraft
	}
	if p.Slug == "" {
		p.Slug = Slugify(p.Title)
	}
	if p.Slug == "" {
		// Titles without any latin characters (typical for short notes) get a
		// date-based slug instead of colliding on "post", "post-2", ...
		p.Slug = "s-" + time.Now().UTC().Format("20060102-150405")
	}
	p.Slug = s.uniqueSlug(p.Slug, 0)
	// Short posts have no visible title, but archive and tag listings still
	// need something to index them by.
	if p.Kind == model.KindShort && p.Title == "" {
		p.Title = render.TitleFromMarkdown(in.ContentMd)
	}
	p.Summary = strings.TrimSpace(in.Summary)
	p.ContentMd = in.ContentMd
	p.ContentHTML = renderHTML(in.ContentMd)
	p.PublishedAt = in.PublishedAt
	p.CreatedAt = now()
	p.UpdatedAt = p.CreatedAt
	if p.PublishedAt == "" {
		p.PublishedAt = p.CreatedAt
	}
	if in.ReadingMinutes != nil && *in.ReadingMinutes > 0 {
		p.ReadingMinutes = *in.ReadingMinutes
	} else {
		p.ReadingMinutes = readingMinutes(in.ContentMd)
	}

	var id int64
	q := s.db.Q(`INSERT INTO posts (kind,title,slug,summary,cover_url,content_md,content_html,status,
		published_at,created_at,updated_at,reading_minutes)
		VALUES (?,?,?,?,?,?,?,?,?,?,?,?)`)
	if s.db.Dialect == db.Postgres {
		err := s.db.QueryRow(q, p.Kind, p.Title, p.Slug, p.Summary, p.CoverURL, p.ContentMd, p.ContentHTML,
			p.Status, p.PublishedAt, p.CreatedAt, p.UpdatedAt, p.ReadingMinutes).Scan(&id)
		if err != nil {
			return p, err
		}
	} else {
		res, err := s.db.Exec(q, p.Kind, p.Title, p.Slug, p.Summary, p.CoverURL, p.ContentMd, p.ContentHTML,
			p.Status, p.PublishedAt, p.CreatedAt, p.UpdatedAt, p.ReadingMinutes)
		if err != nil {
			return p, err
		}
		id, err = res.LastInsertId()
		if err != nil {
			return p, err
		}
	}
	p.ID = id
	if err := s.setTags(id, in.Tags); err != nil {
		return p, err
	}
	return s.Get(id)
}

func (s *Store) Update(id int64, in model.PostInput) (model.Post, error) {
	cur, err := s.Get(id)
	if err != nil {
		return cur, err
	}
	p := cur
	if in.Kind != "" {
		p.Kind = in.Kind
	}
	if in.Title != "" || in.Kind == model.KindShort {
		p.Title = strings.TrimSpace(in.Title)
	}
	if in.Summary != "" {
		p.Summary = strings.TrimSpace(in.Summary)
	}
	if in.ContentMd != "" {
		p.ContentMd = in.ContentMd
		p.ContentHTML = renderHTML(in.ContentMd)
	}
	if in.Status != "" {
		p.Status = in.Status
	}
	if in.Slug != "" && in.Slug != cur.Slug {
		p.Slug = s.uniqueSlug(in.Slug, id)
	}
	if in.PublishedAt != "" {
		p.PublishedAt = in.PublishedAt
	}
	// CoverURL is taken verbatim from input. The frontend always sends the
	// current value (empty string included), so any update round-trips with
	// whatever the user last saved.
	p.CoverURL = strings.TrimSpace(in.CoverURL)
	p.UpdatedAt = now()
	if in.ReadingMinutes != nil && *in.ReadingMinutes > 0 {
		p.ReadingMinutes = *in.ReadingMinutes
	} else if in.ContentMd != "" {
		p.ReadingMinutes = readingMinutes(in.ContentMd)
	}

	if _, err := s.db.Exec(s.db.Q(`UPDATE posts SET kind=?,title=?,slug=?,summary=?,cover_url=?,content_md=?,
		content_html=?,status=?,published_at=?,updated_at=?,reading_minutes=? WHERE id=?`),
		p.Kind, p.Title, p.Slug, p.Summary, p.CoverURL, p.ContentMd, p.ContentHTML, p.Status,
		p.PublishedAt, p.UpdatedAt, p.ReadingMinutes, id); err != nil {
		return p, err
	}
	if in.Tags != nil {
		if err := s.setTags(id, in.Tags); err != nil {
			return p, err
		}
	}
	return s.Get(id)
}

// BulkUpdateStatus flips the status of many posts in a single transaction.
func (s *Store) BulkUpdateStatus(ids []int64, status string) (int, error) {
	if len(ids) == 0 {
		return 0, nil
	}
	status = NormalizeStatus(status)
	placeholders := strings.TrimSuffix(strings.Repeat("?,", len(ids)), ",")
	args := []any{status, now()}
	for _, id := range ids {
		args = append(args, id)
	}
	q := s.db.Q(`UPDATE posts SET status=?, updated_at=? WHERE id IN (` + placeholders + `)`)
	res, err := s.db.Exec(q, args...)
	if err != nil {
		return 0, err
	}
	n, _ := res.RowsAffected()
	return int(n), nil
}

// NormalizeStatus coerces an arbitrary input string into a known post status
// value, defaulting to draft when nothing matches.
func NormalizeStatus(s string) string {
	switch strings.ToLower(strings.TrimSpace(s)) {
	case model.StatusDraft, model.StatusPublished:
		return strings.ToLower(strings.TrimSpace(s))
	default:
		return model.StatusDraft
	}
}

func (s *Store) Delete(id int64) error {
	return s.tx(func(tx *sql.Tx) error {
		if _, err := tx.Exec(s.db.Q(`DELETE FROM post_tags WHERE post_id = ?`), id); err != nil {
			return err
		}
		res, err := tx.Exec(s.db.Q(`DELETE FROM posts WHERE id = ?`), id)
		if err != nil {
			return err
		}
		if n, err := res.RowsAffected(); err == nil && n == 0 {
			return ErrNotFound
		}
		return nil
	})
}

// tx 把多语句写包进一个事务：中途失败整体回滚，不留半截状态。
func (s *Store) tx(fn func(tx *sql.Tx) error) error {
	tx, err := s.db.Begin()
	if err != nil {
		return err
	}
	if err := fn(tx); err != nil {
		_ = tx.Rollback()
		return err
	}
	return tx.Commit()
}

// ---------- tags ----------

func (s *Store) setTags(postID int64, names []string) error {
	return s.tx(func(tx *sql.Tx) error {
		if _, err := tx.Exec(s.db.Q(`DELETE FROM post_tags WHERE post_id = ?`), postID); err != nil {
			return err
		}
		seen := map[string]bool{}
		for _, raw := range names {
			name := strings.TrimSpace(raw)
			if name == "" || seen[name] {
				continue
			}
			seen[name] = true
			tagID, err := s.upsertTagOn(tx, name)
			if err != nil {
				return err
			}
			if _, err := tx.Exec(s.db.Q(`INSERT INTO post_tags(post_id, tag_id) VALUES (?,?)`), postID, tagID); err != nil {
				return err
			}
		}
		return nil
	})
}

// execer 让 upsertTag 在普通连接和事务里都能跑。
type execer interface {
	Exec(query string, args ...any) (sql.Result, error)
	QueryRow(query string, args ...any) *sql.Row
}

func (s *Store) upsertTag(name string) (int64, error) {
	return s.upsertTagOn(s.db, name)
}

func (s *Store) upsertTagOn(x execer, name string) (int64, error) {
	slug := Slugify(name)
	if slug == "" {
		slug = "tag"
	}
	var id int64
	err := x.QueryRow(s.db.Q(`SELECT id FROM tags WHERE slug = ?`), slug).Scan(&id)
	if err == nil {
		return id, nil
	}
	if err != sql.ErrNoRows {
		return 0, err
	}
	if s.db.Dialect == db.Postgres {
		err = x.QueryRow(s.db.Q(`INSERT INTO tags(name,slug) VALUES (?,?) RETURNING id`), name, slug).Scan(&id)
		return id, err
	}
	res, err := x.Exec(s.db.Q(`INSERT INTO tags(name,slug) VALUES (?,?)`), name, slug)
	if err != nil {
		return 0, err
	}
	return res.LastInsertId()
}

func (s *Store) ListTags() ([]model.Tag, error) {
	q := s.db.Q(`SELECT t.id, t.name, t.slug, t.color, COUNT(pt.post_id) AS c
		FROM tags t LEFT JOIN post_tags pt ON pt.tag_id = t.id
		GROUP BY t.id, t.name, t.slug, t.color ORDER BY c DESC, t.name`)
	rows, err := s.db.Query(q)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []model.Tag{}
	for rows.Next() {
		var t model.Tag
		if err := rows.Scan(&t.ID, &t.Name, &t.Slug, &t.Color, &t.Count); err != nil {
			return nil, err
		}
		out = append(out, t)
	}
	return out, rows.Err()
}

func (s *Store) CreateTag(name string) (model.Tag, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return model.Tag{}, errors.New("tag name required")
	}
	id, err := s.upsertTag(name)
	if err != nil {
		return model.Tag{}, err
	}
	return model.Tag{ID: id, Name: name, Slug: Slugify(name)}, nil
}

// CreateTagFull is used by the admin API when color is supplied.
func (s *Store) CreateTagFull(name, color string) (model.Tag, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return model.Tag{}, errors.New("tag name required")
	}
	slug := Slugify(name)
	if slug == "" {
		return model.Tag{}, errors.New("tag slug required")
	}
	var id int64
	err := s.db.QueryRow(s.db.Q(`SELECT id FROM tags WHERE slug = ?`), slug).Scan(&id)
	if err != nil && err != sql.ErrNoRows {
		return model.Tag{}, err
	}
	if err == nil {
		// already exists — update color and return
		if _, err := s.db.Exec(s.db.Q(`UPDATE tags SET color=? WHERE id=?`), color, id); err != nil {
			return model.Tag{}, err
		}
		return s.getTag(id)
	}
	color = strings.TrimSpace(color)
	if s.db.Dialect == db.Postgres {
		err := s.db.QueryRow(s.db.Q(`INSERT INTO tags(name,slug,color) VALUES (?,?,?) RETURNING id`),
			name, slug, color).Scan(&id)
		if err != nil {
			return model.Tag{}, err
		}
	} else {
		res, err := s.db.Exec(s.db.Q(`INSERT INTO tags(name,slug,color) VALUES (?,?,?)`), name, slug, color)
		if err != nil {
			return model.Tag{}, err
		}
		id, err = res.LastInsertId()
		if err != nil {
			return model.Tag{}, err
		}
	}
	return s.getTag(id)
}

func (s *Store) getTag(id int64) (model.Tag, error) {
	var t model.Tag
	err := s.db.QueryRow(s.db.Q(`SELECT t.id, t.name, t.slug, t.color, COUNT(pt.post_id)
		FROM tags t LEFT JOIN post_tags pt ON pt.tag_id = t.id
		WHERE t.id = ? GROUP BY t.id`), id).Scan(&t.ID, &t.Name, &t.Slug, &t.Color, &t.Count)
	if err == sql.ErrNoRows {
		return t, ErrNotFound
	}
	return t, err
}

func (s *Store) RenameTag(id int64, name string) (model.Tag, error) {
	name = strings.TrimSpace(name)
	slug := Slugify(name)
	if name == "" {
		return model.Tag{}, errors.New("tag name required")
	}
	if _, err := s.db.Exec(s.db.Q(`UPDATE tags SET name=?, slug=? WHERE id=?`), name, slug, id); err != nil {
		return model.Tag{}, err
	}
	return s.getTag(id)
}

// UpdateTag is the combined rename + recolor used by the admin UI.
func (s *Store) UpdateTag(id int64, name, color string) (model.Tag, error) {
	name = strings.TrimSpace(name)
	slug := Slugify(name)
	if name == "" {
		return model.Tag{}, errors.New("tag name required")
	}
	color = strings.TrimSpace(color)
	if _, err := s.db.Exec(s.db.Q(`UPDATE tags SET name=?, slug=?, color=? WHERE id=?`), name, slug, color, id); err != nil {
		return model.Tag{}, err
	}
	return s.getTag(id)
}

// MergeTags moves every post from fromID to toID, then deletes fromID. It is a
// no-op if the ids are equal or either doesn't exist.
func (s *Store) MergeTags(fromID, toID int64) (model.Tag, error) {
	if fromID == toID {
		return model.Tag{}, errors.New("source and target are the same tag")
	}
	if _, err := s.getTag(fromID); err != nil {
		return model.Tag{}, err
	}
	if _, err := s.getTag(toID); err != nil {
		return model.Tag{}, err
	}
	// De-duplicate before the move so we don't end up with two rows pointing
	// at the same post.
	if err := s.tx(func(tx *sql.Tx) error {
		if _, err := tx.Exec(s.db.Q(`DELETE FROM post_tags
			WHERE post_id IN (SELECT post_id FROM post_tags WHERE tag_id = ?)
			AND tag_id = ?`), toID, toID); err != nil {
			return err
		}
		if _, err := tx.Exec(s.db.Q(`UPDATE post_tags SET tag_id=? WHERE tag_id=?`), toID, fromID); err != nil {
			return err
		}
		_, err := tx.Exec(s.db.Q(`DELETE FROM tags WHERE id=?`), fromID)
		return err
	}); err != nil {
		return model.Tag{}, err
	}
	return s.getTag(toID)
}

func (s *Store) DeleteTag(id int64) error {
	return s.tx(func(tx *sql.Tx) error {
		if _, err := tx.Exec(s.db.Q(`DELETE FROM post_tags WHERE tag_id = ?`), id); err != nil {
			return err
		}
		_, err := tx.Exec(s.db.Q(`DELETE FROM tags WHERE id = ?`), id)
		return err
	})
}

// ---------- archive ----------

func (s *Store) Archive() ([]model.ArchiveYear, error) {
	var items []model.Post
	if err := s.scanPostsInto(s.db.Q(`SELECT `+listCols+` FROM posts
		WHERE status = ? ORDER BY published_at DESC`), []any{model.StatusPublished}, &items); err != nil {
		return nil, err
	}
	years := []model.ArchiveYear{}
	yearIdx := map[string]int{}
	monthIdx := map[string]int{}
	for _, p := range items {
		y, m := splitDate(p.PublishedAt)
		if y == "" {
			continue
		}
		yi, ok := yearIdx[y]
		if !ok {
			years = append(years, model.ArchiveYear{Year: y, Months: []model.ArchiveMonth{}})
			yi = len(years) - 1
			yearIdx[y] = yi
		}
		key := y + "-" + m
		mi, ok := monthIdx[key]
		if !ok {
			years[yi].Months = append(years[yi].Months, model.ArchiveMonth{Month: m, Posts: []model.Post{}})
			mi = len(years[yi].Months) - 1
			monthIdx[key] = mi
		}
		years[yi].Count++
		years[yi].Months[mi].Posts = append(years[yi].Months[mi].Posts, p)
	}
	return years, nil
}

func splitDate(rfc3339 string) (string, string) {
	if len(rfc3339) < 7 {
		return "", ""
	}
	return rfc3339[0:4], rfc3339[5:7]
}

// ---------- dashboard ----------

// Dashboard produces the snapshot rendered on the admin home page.
func (s *Store) Dashboard() (model.Dashboard, error) {
	d := model.Dashboard{
		RecentPosts:      []model.Post{},
		RecentDrafts:     []model.Post{},
		TopTags:          []model.Tag{},
		PublishedByMonth: []model.MonthBucket{},
	}

	// status / kind counts --------------------------------------------------
	rows, err := s.db.Query(s.db.Q(`SELECT status, kind, COUNT(*) FROM posts GROUP BY status, kind`))
	if err != nil {
		return d, err
	}
	for rows.Next() {
		var status, kind string
		var n int
		if err := rows.Scan(&status, &kind, &n); err != nil {
			rows.Close()
			return d, err
		}
		d.TotalPosts += n
		switch status {
		case model.StatusPublished:
			d.PublishedPosts += n
		case model.StatusDraft:
			d.DraftPosts += n
		}
		switch kind {
		case model.KindShort:
			d.ShortPosts += n
		case model.KindLong:
			d.LongPosts += n
		}
	}
	rows.Close()

	// total tag count -------------------------------------------------------
	if err := s.db.QueryRow(s.db.Q(`SELECT COUNT(*) FROM tags`)).Scan(&d.TotalTags); err != nil {
		return d, err
	}

	// total word count: sum of content_md length ----------------------------
	if err := s.db.QueryRow(s.db.Q(`SELECT COALESCE(SUM(LENGTH(content_md)),0) FROM posts`)).Scan(&d.TotalWords); err != nil {
		return d, err
	}

	// recent published posts (5) --------------------------------------------
	if err := s.scanPostsInto(s.db.Q(`SELECT `+listCols+` FROM posts
		WHERE status=? ORDER BY published_at DESC LIMIT 5`), []any{model.StatusPublished}, &d.RecentPosts); err != nil {
		return d, err
	}

	// recent drafts (5) -----------------------------------------------------
	if err := s.scanPostsInto(s.db.Q(`SELECT `+listCols+` FROM posts
		WHERE status=? ORDER BY updated_at DESC LIMIT 5`), []any{model.StatusDraft}, &d.RecentDrafts); err != nil {
		return d, err
	}

	// top tags (10) ---------------------------------------------------------
	if err := s.db.QueryRow(s.db.Q(`SELECT COUNT(*) FROM tags`)).Scan(&d.TotalTags); err != nil {
		return d, err
	}
	tagRows, err := s.db.Query(s.db.Q(`SELECT t.id, t.name, t.slug, t.color, COUNT(pt.post_id) AS c
		FROM tags t LEFT JOIN post_tags pt ON pt.tag_id = t.id
		GROUP BY t.id, t.name, t.slug, t.color ORDER BY c DESC, t.name LIMIT 10`))
	if err != nil {
		return d, err
	}
	for tagRows.Next() {
		var t model.Tag
		if err := tagRows.Scan(&t.ID, &t.Name, &t.Slug, &t.Color, &t.Count); err != nil {
			tagRows.Close()
			return d, err
		}
		d.TopTags = append(d.TopTags, t)
	}
	tagRows.Close()

	// published_by_month — last 12 months -----------------------------------
	monthRows, err := s.db.Query(s.db.Q(`SELECT substr(published_at,1,7) AS m, COUNT(*) AS c
		FROM posts WHERE status=? AND length(published_at) >= 7
		GROUP BY m ORDER BY m DESC LIMIT 12`), model.StatusPublished)
	if err != nil {
		return d, err
	}
	defer monthRows.Close()
	for monthRows.Next() {
		var b model.MonthBucket
		if err := monthRows.Scan(&b.Month, &b.Count); err != nil {
			return d, err
		}
		d.PublishedByMonth = append(d.PublishedByMonth, b)
	}
	// reverse so we can render left-to-right on the chart
	for i, j := 0, len(d.PublishedByMonth)-1; i < j; i, j = i+1, j-1 {
		d.PublishedByMonth[i], d.PublishedByMonth[j] = d.PublishedByMonth[j], d.PublishedByMonth[i]
	}

	return d, nil
}

// scanPostsInto is a small helper that runs a query and scans rows into the
// given slice, attaching tags at the end.
func (s *Store) scanPostsInto(query string, args []any, dst *[]model.Post) error {
	rows, err := s.db.Query(query, args...)
	if err != nil {
		return err
	}
	defer rows.Close()
	out := []model.Post{}
	for rows.Next() {
		p, err := scanPost(rows)
		if err != nil {
			return err
		}
		out = append(out, p)
	}
	if err := rows.Err(); err != nil {
		return err
	}
	if err := s.attachTags(out); err != nil {
		return err
	}
	*dst = out
	return nil
}