package store

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

const (
	MaxListSize         = 65535
	RecommendedListSize = 100
	SoftListSizeWarning = 1000
)

type List struct {
	ID          int64  `json:"id"`
	Slug        string `json:"slug"`
	Title       string `json:"title"`
	Category    string `json:"category"`
	Description string `json:"description"`
	MaxItems    int    `json:"maxItems"`
	Position    int    `json:"position"`
	Visible     bool   `json:"visible"`
	Layout      string `json:"layout"` // a ListStyles key, e.g. "podium"
	Art         string `json:"art"`    // "", "poster" or "square"; "" = category default
	ItemCount   int    `json:"itemCount"`
	UpdatedAt   int64  `json:"updatedAt"`
}

const listColumns = `l.id, l.slug, l.title, l.category, l.description, l.max_items, l.position, l.visible, l.layout, l.art, l.updated_at,
	(SELECT COUNT(*) FROM items i WHERE i.list_id = l.id)`

func scanList(row interface{ Scan(...any) error }) (List, error) {
	var l List
	err := row.Scan(&l.ID, &l.Slug, &l.Title, &l.Category, &l.Description, &l.MaxItems, &l.Position, &l.Visible, &l.Layout, &l.Art, &l.UpdatedAt, &l.ItemCount)
	if errors.Is(err, sql.ErrNoRows) {
		return l, ErrNotFound
	}
	return l, err
}

func (s *Store) Lists(ctx context.Context, includeHidden bool) ([]List, error) {
	q := `SELECT ` + listColumns + ` FROM lists l`
	if !includeHidden {
		q += ` WHERE l.visible = 1`
	}
	q += ` ORDER BY l.position, l.id`
	rows, err := s.db.QueryContext(ctx, q)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []List
	for rows.Next() {
		l, err := scanList(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, l)
	}
	return out, rows.Err()
}

func (s *Store) ListByID(ctx context.Context, id int64) (List, error) {
	return scanList(s.db.QueryRowContext(ctx, `SELECT `+listColumns+` FROM lists l WHERE l.id = ?`, id))
}

func (s *Store) ListBySlug(ctx context.Context, slug string) (List, error) {
	return scanList(s.db.QueryRowContext(ctx, `SELECT `+listColumns+` FROM lists l WHERE l.slug = ?`, slug))
}

// ValidationError is returned for bad user input; its message is safe to
// show to the user.
type ValidationError struct{ Msg string }

func (e ValidationError) Error() string { return e.Msg }

func invalid(format string, args ...any) error {
	return ValidationError{Msg: fmt.Sprintf(format, args...)}
}

func (l *List) normalize() error {
	l.Title = strings.TrimSpace(l.Title)
	l.Description = strings.TrimSpace(l.Description)
	if l.Title == "" {
		return invalid("Title is required")
	}
	if len(l.Title) > 200 {
		return invalid("Title is too long")
	}
	if _, ok := CategoryByKey(l.Category); !ok {
		return invalid("Unknown category %q", l.Category)
	}
	if l.MaxItems < 1 || l.MaxItems > MaxListSize {
		return invalid("List size must be between 1 and %d", MaxListSize)
	}
	if _, ok := StyleByKey(l.Layout); !ok {
		l.Layout = DefaultStyle
	}
	if l.Art != "poster" && l.Art != "square" {
		l.Art = ""
	}
	return nil
}

var slugStrip = regexp.MustCompile(`[^a-z0-9]+`)

func slugify(s string) string {
	s = slugStrip.ReplaceAllString(strings.ToLower(s), "-")
	s = strings.Trim(s, "-")
	if len(s) > 60 {
		s = strings.Trim(s[:60], "-")
	}
	if s == "" {
		s = "list"
	}
	return s
}

func (s *Store) uniqueSlug(ctx context.Context, base string, exceptID int64) (string, error) {
	slug := base
	for i := 2; ; i++ {
		var n int
		if err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM lists WHERE slug = ? AND id != ?`, slug, exceptID).Scan(&n); err != nil {
			return "", err
		}
		if n == 0 {
			return slug, nil
		}
		slug = fmt.Sprintf("%s-%d", base, i)
	}
}

func (s *Store) CreateList(ctx context.Context, l List) (List, error) {
	if err := l.normalize(); err != nil {
		return l, err
	}
	// Default to the category name so the address stays sensible if the
	// list's size (and so its "Top N" title) changes later.
	base := slugify(l.Slug)
	if strings.TrimSpace(l.Slug) == "" {
		c, _ := CategoryByKey(l.Category)
		base = slugify(c.Label)
		if c.Key == "custom" {
			base = slugify(l.Title)
		}
	}
	slug, err := s.uniqueSlug(ctx, base, 0)
	if err != nil {
		return l, err
	}
	res, err := s.db.ExecContext(ctx, `INSERT INTO lists (slug, title, category, description, max_items, position, visible, layout, art)
		VALUES (?, ?, ?, ?, ?, (SELECT COALESCE(MAX(position), 0) + 1 FROM lists), ?, ?, ?)`,
		slug, l.Title, l.Category, l.Description, l.MaxItems, l.Visible, l.Layout, l.Art)
	if err != nil {
		return l, err
	}
	id, _ := res.LastInsertId()
	return s.ListByID(ctx, id)
}

func (s *Store) UpdateList(ctx context.Context, l List) (List, error) {
	if err := l.normalize(); err != nil {
		return l, err
	}
	cur, err := s.ListByID(ctx, l.ID)
	if err != nil {
		return l, err
	}
	if l.MaxItems < cur.ItemCount {
		return l, invalid("This list already has %d items; remove some before shrinking it to %d", cur.ItemCount, l.MaxItems)
	}
	if l.Category != cur.Category && cur.ItemCount > 0 {
		return l, invalid("Can't change the category of a list that has items")
	}
	slug := cur.Slug
	if strings.TrimSpace(l.Slug) != "" && slugify(l.Slug) != cur.Slug {
		if slug, err = s.uniqueSlug(ctx, slugify(l.Slug), l.ID); err != nil {
			return l, err
		}
	}
	_, err = s.db.ExecContext(ctx, `UPDATE lists SET slug=?, title=?, category=?, description=?, max_items=?, visible=?, layout=?, art=?, updated_at=unixepoch() WHERE id=?`,
		slug, l.Title, l.Category, l.Description, l.MaxItems, l.Visible, l.Layout, l.Art, l.ID)
	if err != nil {
		return l, err
	}
	return s.ListByID(ctx, l.ID)
}

func (s *Store) DeleteList(ctx context.Context, id int64) error {
	res, err := s.db.ExecContext(ctx, `DELETE FROM lists WHERE id = ?`, id)
	if err != nil {
		return err
	}
	if n, _ := res.RowsAffected(); n == 0 {
		return ErrNotFound
	}
	return nil
}

// ReorderLists sets list positions to match the order of ids.
func (s *Store) ReorderLists(ctx context.Context, ids []int64) error {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}
	defer tx.Rollback()
	for i, id := range ids {
		if _, err := tx.ExecContext(ctx, `UPDATE lists SET position = ? WHERE id = ?`, i+1, id); err != nil {
			return err
		}
	}
	return tx.Commit()
}

// ListCovers returns up to n image file names per list, from the top ranks.
func (s *Store) ListCovers(ctx context.Context, n int) (map[int64][]string, error) {
	rows, err := s.db.QueryContext(ctx, `SELECT list_id, image FROM (
		SELECT list_id, image, ROW_NUMBER() OVER (PARTITION BY list_id ORDER BY rank) AS rn
		FROM items WHERE image != '') WHERE rn <= ? ORDER BY list_id, rn`, n)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := map[int64][]string{}
	for rows.Next() {
		var id int64
		var img string
		if err := rows.Scan(&id, &img); err != nil {
			return nil, err
		}
		out[id] = append(out[id], "/images/"+img)
	}
	return out, rows.Err()
}

// Aspect is the list's artwork shape: its own choice, or the category's.
func (l List) Aspect() string {
	if l.Art != "" {
		return l.Art
	}
	c, _ := CategoryByKey(l.Category)
	return c.Aspect
}

// ListStyle is a way of presenting a ranked list.
type ListStyle struct {
	Key         string `json:"key"`
	Label       string `json:"label"`
	Icon        string `json:"icon"`
	Description string `json:"description"`
}

var ListStyles = []ListStyle{
	{"podium", "Podium", "podium", "Top 3 on a medal podium, the rest behind “Show more”."},
	{"spotlight", "Spotlight", "spotlight", "#1 as a big feature, the rest as a ranked list."},
	{"grid", "Grid", "grid", "Every entry as artwork in a grid."},
	{"rows", "List", "rows", "A compact numbered list with notes."},
}

const DefaultStyle = "podium"

func StyleByKey(key string) (ListStyle, bool) {
	for _, s := range ListStyles {
		if s.Key == key {
			return s, true
		}
	}
	return ListStyle{}, false
}