package main

import (
	"database/sql"
	"errors"
	"slices"
	"strings"
	"time"
)

// dateLayout is how calendar days are stored and passed around in URLs.
const dateLayout = "2006-01-02"

// categoryFI maps the stored English category onto the Finnish key used for
// CSS custom properties and labels.
var categoryFI = map[string]string{
	"meat":       "liha",
	"chicken":    "kana",
	"fish":       "kala",
	"vegetarian": "kasvis",
}

type Dish struct {
	ID         int64
	Name       string
	HasSides   bool
	Categories []string
	TimesEaten int
}

// Rows flagged `special` in the database — Tähteet — are loggable but are not
// food. They carry no category, never appear in the catalog, and PRD §8
// excludes them from the suggester: cooldown, coverage and weighting all skip
// them. dishByID deliberately does not filter on the flag, because logging one
// has to work like logging anything else.

// CategoryKey picks the mark for a dish. One covering several categories
// (tortillas, build-your-own pizza) gets the mixed one; carrying none at all
// means it is not food, and Tähteet is not a mixture of anything.
func (d Dish) CategoryKey() string {
	switch len(d.Categories) {
	case 0:
		return "tahteet"
	case 1:
		return categoryFI[d.Categories[0]]
	default:
		return "sek"
	}
}

// Size buckets the dish by how often it has been eaten. The board draws
// favourites as bigger targets, so the likely answer is the easiest to hit.
func (d Dish) Size() string {
	switch {
	case d.TimesEaten >= 10:
		return "xl"
	case d.TimesEaten >= 6:
		return "lg"
	case d.TimesEaten >= 3:
		return "md"
	default:
		return "sm"
	}
}

type Side struct {
	ID   int64
	Name string
}

type Entry struct {
	Date  time.Time
	Main  Dish
	Sides []Side
}

func (e Entry) SidesLabel() string {
	if len(e.Sides) == 0 {
		return "Ei lisukkeita"
	}
	names := make([]string, len(e.Sides))
	for i, s := range e.Sides {
		names[i] = s.Name
	}
	return strings.Join(names, ", ")
}

// listDishes returns live mains ordered by how often they have been eaten.
// An empty search matches everything.
func listDishes(db *sql.DB, search string) ([]Dish, error) {
	return queryDishes(db, search, false)
}

// listSpecial returns the entries that are not food — Tähteet and anything
// like it. They are loggable but never suggested, and never appear in the
// catalog, so they are fetched deliberately rather than by accident.
func listSpecial(db *sql.DB, search string) ([]Dish, error) {
	return queryDishes(db, search, true)
}

func queryDishes(db *sql.DB, search string, special bool) ([]Dish, error) {
	rows, err := db.Query(`
		SELECT m.id, m.name, m.has_sides,
		       coalesce((SELECT group_concat(c.category)
		                 FROM main_dish_categories c
		                 WHERE c.main_dish_id = m.id), ''),
		       (SELECT count(*) FROM meal_log l WHERE l.main_dish_id = m.id)
		FROM main_dishes m
		WHERE m.deleted_at IS NULL
		  AND m.special = ?
		  AND (? = '' OR lower(m.name) LIKE '%' || lower(?) || '%')
		ORDER BY 5 DESC, m.name`, special, search, search)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var dishes []Dish
	for rows.Next() {
		var d Dish
		var cats string
		if err := rows.Scan(&d.ID, &d.Name, &d.HasSides, &cats, &d.TimesEaten); err != nil {
			return nil, err
		}
		if cats != "" {
			d.Categories = strings.Split(cats, ",")
		}
		dishes = append(dishes, d)
	}
	return dishes, rows.Err()
}

func dishByID(db *sql.DB, id int64) (*Dish, error) {
	var d Dish
	var cats string
	err := db.QueryRow(`
		SELECT m.id, m.name, m.has_sides,
		       coalesce((SELECT group_concat(c.category)
		                 FROM main_dish_categories c
		                 WHERE c.main_dish_id = m.id), ''),
		       (SELECT count(*) FROM meal_log l WHERE l.main_dish_id = m.id)
		FROM main_dishes m
		WHERE m.id = ? AND m.deleted_at IS NULL`, id,
	).Scan(&d.ID, &d.Name, &d.HasSides, &cats, &d.TimesEaten)
	if err != nil {
		return nil, err
	}
	if cats != "" {
		d.Categories = strings.Split(cats, ",")
	}
	return &d, nil
}

func listSides(db *sql.DB, search string) ([]Side, error) {
	rows, err := db.Query(`
		SELECT id, name FROM side_dishes
		WHERE deleted_at IS NULL
		  AND (? = '' OR lower(name) LIKE '%' || lower(?) || '%')
		ORDER BY name`, search, search)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var sides []Side
	for rows.Next() {
		var s Side
		if err := rows.Scan(&s.ID, &s.Name); err != nil {
			return nil, err
		}
		sides = append(sides, s)
	}
	return sides, rows.Err()
}

// entryFor returns the meal logged on a date, or nil when nothing is. Dishes
// are resolved even if they have since been soft-deleted, so history keeps
// displaying its names (PRD §6).
func entryFor(db *sql.DB, date time.Time) (*Entry, error) {
	e := &Entry{Date: date}
	var logID int64
	var cats string

	err := db.QueryRow(`
		SELECT l.id, m.id, m.name, m.has_sides,
		       coalesce((SELECT group_concat(c.category)
		                 FROM main_dish_categories c
		                 WHERE c.main_dish_id = m.id), '')
		FROM meal_log l
		JOIN main_dishes m ON m.id = l.main_dish_id
		WHERE l.date = ?`, date.Format(dateLayout),
	).Scan(&logID, &e.Main.ID, &e.Main.Name, &e.Main.HasSides, &cats)
	if err == sql.ErrNoRows {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	if cats != "" {
		e.Main.Categories = strings.Split(cats, ",")
	}

	rows, err := db.Query(`
		SELECT s.id, s.name
		FROM meal_log_sides ls
		JOIN side_dishes s ON s.id = ls.side_dish_id
		WHERE ls.meal_log_id = ?
		ORDER BY s.name`, logID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		var s Side
		if err := rows.Scan(&s.ID, &s.Name); err != nil {
			return nil, err
		}
		e.Sides = append(e.Sides, s)
	}
	return e, rows.Err()
}

// saveEntry records what was eaten, replacing whatever was there. The unique
// constraint allows one entry per date, so editing is delete-then-insert; the
// old sides go with it through ON DELETE CASCADE.
func saveEntry(db *sql.DB, date time.Time, mainID int64, sideIDs []int64) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	day := date.Format(dateLayout)
	if _, err := tx.Exec(`DELETE FROM meal_log WHERE date = ?`, day); err != nil {
		return err
	}
	res, err := tx.Exec(
		`INSERT INTO meal_log (date, main_dish_id) VALUES (?, ?)`, day, mainID)
	if err != nil {
		return err
	}
	logID, err := res.LastInsertId()
	if err != nil {
		return err
	}
	for _, id := range sideIDs {
		if _, err := tx.Exec(
			`INSERT OR IGNORE INTO meal_log_sides (meal_log_id, side_dish_id) VALUES (?, ?)`,
			logID, id,
		); err != nil {
			return err
		}
	}
	return tx.Commit()
}

func deleteEntry(db *sql.DB, date time.Time) error {
	_, err := db.Exec(`DELETE FROM meal_log WHERE date = ?`, date.Format(dateLayout))
	return err
}

// errNameTaken is returned when a name collides with a live dish. The
// comparison is case-insensitive and ignores soft-deleted rows (PRD §7.3).
var errNameTaken = errors.New("nimi on jo listalla")

func taken(err error) error {
	// ponytail: string match rather than a driver-specific error type, so
	// this survives swapping the driver.
	if err != nil && strings.Contains(err.Error(), "UNIQUE constraint failed") {
		return errNameTaken
	}
	return err
}

// createMain inserts a main dish and its categories in one transaction.
func createMain(db *sql.DB, name string, categories []string, hasSides bool) (int64, error) {
	tx, err := db.Begin()
	if err != nil {
		return 0, err
	}
	defer tx.Rollback()

	res, err := tx.Exec(
		`INSERT INTO main_dishes (name, has_sides) VALUES (?, ?)`, name, hasSides)
	if err != nil {
		return 0, taken(err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return 0, err
	}
	if err := setCategories(tx, id, categories); err != nil {
		return 0, err
	}
	return id, tx.Commit()
}

// updateMain rewrites a main dish, replacing its category set wholesale.
func updateMain(db *sql.DB, id int64, name string, categories []string, hasSides bool) error {
	tx, err := db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	if _, err := tx.Exec(
		`UPDATE main_dishes SET name = ?, has_sides = ? WHERE id = ? AND deleted_at IS NULL`,
		name, hasSides, id,
	); err != nil {
		return taken(err)
	}
	if _, err := tx.Exec(
		`DELETE FROM main_dish_categories WHERE main_dish_id = ?`, id); err != nil {
		return err
	}
	if err := setCategories(tx, id, categories); err != nil {
		return err
	}
	return tx.Commit()
}

func setCategories(tx *sql.Tx, mainID int64, categories []string) error {
	for _, c := range categories {
		if _, err := tx.Exec(
			`INSERT OR IGNORE INTO main_dish_categories (main_dish_id, category) VALUES (?, ?)`,
			mainID, c,
		); err != nil {
			return err
		}
	}
	return nil
}

func createSide(db *sql.DB, name string) error {
	_, err := db.Exec(`INSERT INTO side_dishes (name) VALUES (?)`, name)
	return taken(err)
}

func updateSide(db *sql.DB, id int64, name string) error {
	_, err := db.Exec(
		`UPDATE side_dishes SET name = ? WHERE id = ? AND deleted_at IS NULL`, name, id)
	return taken(err)
}

// Soft delete: the row stays so historical log entries keep resolving their
// names, but it disappears from the catalog and every picker (PRD §6).
func softDeleteMain(db *sql.DB, id int64) error {
	_, err := db.Exec(
		`UPDATE main_dishes SET deleted_at = datetime('now') WHERE id = ?`, id)
	return err
}

func softDeleteSide(db *sql.DB, id int64) error {
	_, err := db.Exec(
		`UPDATE side_dishes SET deleted_at = datetime('now') WHERE id = ?`, id)
	return err
}

func sideByID(db *sql.DB, id int64) (*Side, error) {
	var s Side
	err := db.QueryRow(
		`SELECT id, name FROM side_dishes WHERE id = ? AND deleted_at IS NULL`, id,
	).Scan(&s.ID, &s.Name)
	if err != nil {
		return nil, err
	}
	return &s, nil
}

// DishGroup is one category's worth of dishes for the catalog listing.
type DishGroup struct {
	Key    string
	Label  string
	Dishes []Dish
}

// groupOrder fixes the order the catalog lists categories in. Sekalaiset is a
// display grouping for dishes covering more than one category, not a fifth
// category: the stored set is what PRD §8.1 counts for coverage, and one
// Tortillat still satisfies meat, chicken, fish and vegetarian at once.
var groupOrder = []DishGroup{
	{Key: "liha", Label: "Liha"},
	{Key: "kana", Label: "Kana"},
	{Key: "kala", Label: "Kala"},
	{Key: "kasvis", Label: "Kasvis"},
	{Key: "sek", Label: "Sekalaiset"},
}

// groupDishes buckets dishes by category, keeping whatever order they arrived
// in. The caller decides that order: the log board hands over listDishes'
// frequency-then-name ordering, the catalog sorts by name first.
func groupDishes(dishes []Dish) []DishGroup {
	byKey := make(map[string][]Dish, len(groupOrder))
	for _, d := range dishes {
		key := d.CategoryKey()
		byKey[key] = append(byKey[key], d)
	}

	var groups []DishGroup
	for _, g := range groupOrder {
		in := byKey[g.Key]
		if len(in) == 0 {
			continue
		}
		groups = append(groups, DishGroup{Key: g.Key, Label: g.Label, Dishes: in})
	}
	return groups
}

// sortByName orders dishes alphabetically, case-insensitively.
func sortByName(dishes []Dish) {
	slices.SortFunc(dishes, func(a, b Dish) int {
		return strings.Compare(strings.ToLower(a.Name), strings.ToLower(b.Name))
	})
}

// HistoryRow is one calendar day: either what was eaten or an unfilled gap.
type HistoryRow struct {
	Date  time.Time
	Entry *Entry
}

// HistoryPage is one window of history plus where to continue from. After a
// few years of daily entries the whole log is far too much to render at once.
type HistoryPage struct {
	Rows []HistoryRow
	More bool      // older entries exist beyond this window
	Next time.Time // the day the next window starts at
}

// history walks back day by day from a given day, so a day nobody wrote down
// shows up as an explicit gap rather than silently missing. It stops at the
// first entry ever recorded — before that there is no history to be missing.
func history(db *sql.DB, loc *time.Location, from time.Time, days int) (HistoryPage, error) {
	var first sql.NullString
	if err := db.QueryRow(`SELECT min(date) FROM meal_log`).Scan(&first); err != nil {
		if err == sql.ErrNoRows {
			return HistoryPage{}, nil
		}
		return HistoryPage{}, err
	}
	if !first.Valid || first.String == "" {
		return HistoryPage{}, nil
	}
	firstDate, err := time.ParseInLocation(dateLayout, first.String, loc)
	if err != nil {
		return HistoryPage{}, err
	}
	if from.Before(firstDate) {
		return HistoryPage{}, nil
	}

	oldest := from.AddDate(0, 0, -days+1)
	page := HistoryPage{More: true}
	if !firstDate.Before(oldest) {
		oldest = firstDate
		page.More = false
	}
	page.Next = oldest.AddDate(0, 0, -1)

	for d := from; !d.Before(oldest); d = d.AddDate(0, 0, -1) {
		entry, err := entryFor(db, d)
		if err != nil {
			return HistoryPage{}, err
		}
		page.Rows = append(page.Rows, HistoryRow{Date: d, Entry: entry})
	}
	return page, nil
}