package db

import (
	"context"
	"fmt"

	"github.com/jackc/pgx/v5/pgtype"
)

// All queries in this file are hand-written and intentionally NOT defined in
// `db/queries/*.sql`, so they are not regenerated by sqlc.

// TrendingWindow is the trailing time-window over which visits are summed
// to compute "trending". Values are expressed in days so they map to exact
// row ranges in the daily-bucket location_page_visits table.
type TrendingWindow string

const (
	TrendingWindowWeek     TrendingWindow = "week"     // 7 days
	TrendingWindowMonth    TrendingWindow = "month"    // 30 days
	TrendingWindow3Month   TrendingWindow = "3month"   // 90 days
	TrendingWindowSemester TrendingWindow = "semester" // 180 days
	TrendingWindowYear     TrendingWindow = "year"     // 365 days
)

// Days returns the trailing window length in days. Returns (0, false) for
// unknown values.
func (w TrendingWindow) Days() (int, bool) {
	switch w {
	case TrendingWindowWeek:
		return 7, true
	case TrendingWindowMonth:
		return 30, true
	case TrendingWindow3Month:
		return 90, true
	case TrendingWindowSemester:
		return 180, true
	case TrendingWindowYear:
		return 365, true
	default:
		return 0, false
	}
}

// ParseTrendingWindow returns the typed window for a string, or false if
// the string isn't recognised.
func ParseTrendingWindow(s string) (TrendingWindow, bool) {
	w := TrendingWindow(s)
	if _, ok := w.Days(); !ok {
		return "", false
	}
	return w, true
}

// RecordLocationVisit increments today's visit bucket for the given location,
// creating the row if it does not yet exist. Idempotent within Postgres
// transactions; the (location_id, day) UNIQUE constraint guarantees a single
// row per location per day.
func (q *Queries) RecordLocationVisit(ctx context.Context, locationID int32) error {
	const query = `
		INSERT INTO location_page_visits (location_id, day, visit_count, updated_at)
		VALUES ($1, CURRENT_DATE, 1, now())
		ON CONFLICT (location_id, day)
		DO UPDATE SET
			visit_count = location_page_visits.visit_count + 1,
			updated_at = now()
	`
	_, err := q.db.Exec(ctx, query, locationID)
	return err
}

// GetLocationLifetimeVisits returns the all-time sum of visit_count for a
// single location. Cheap because the (location_id, day) index covers it.
func (q *Queries) GetLocationLifetimeVisits(ctx context.Context, locationID int32) (int64, error) {
	const query = `
		SELECT COALESCE(SUM(visit_count), 0)::bigint AS total
		FROM location_page_visits
		WHERE location_id = $1
	`
	row := q.db.QueryRow(ctx, query, locationID)
	var total int64
	err := row.Scan(&total)
	return total, err
}

type GetTrendingLocationsParams struct {
	Window TrendingWindow `json:"window"`
	Limit  int32          `json:"limit"`
	Offset int32          `json:"offset"`
}

type GetTrendingLocationsRow struct {
	RowNumber      int32       `json:"row_number"`
	ID             int32       `json:"id"`
	Name           string      `json:"name"`
	Address        string      `json:"address"`
	LocationType   string      `json:"location_type"`
	GoogleMapsLink pgtype.Text `json:"google_maps_link"`
	Thumbnail      pgtype.Text `json:"thumbnail"`
	RegencyName    string      `json:"regency_name"`
	ProvinceName   string      `json:"province_name"`
	RegionName     string      `json:"region_name"`
	WindowVisits   int64       `json:"window_visits"`
}

// GetTrendingLocations ranks approved, non-deleted locations by total page
// visits over the trailing window. The query is keyed off the
// idx_location_page_visits_day_count index (day, visit_count DESC).
//
// The bound day count is bound as a parameter; the planner still treats it as
// a constant for the row (current_date - $1::int), so the index range scan is
// effective.
func (q *Queries) GetTrendingLocations(ctx context.Context, arg GetTrendingLocationsParams) ([]GetTrendingLocationsRow, error) {
	days, ok := arg.Window.Days()
	if !ok {
		return nil, fmt.Errorf("invalid trending window %q", arg.Window)
	}

	const query = `
		SELECT
			row_number() OVER (ORDER BY window_visits DESC, l.id ASC) AS row_number,
			l.id,
			l.name,
			l.address,
			l.location_type::text AS location_type,
			l.google_maps_link,
			l.thumbnail,
			COALESCE(re.regency_name, '')   AS regency_name,
			COALESCE(prov.province_name, '') AS province_name,
			COALESCE(reg.region_name, '')   AS region_name,
			window_visits
		FROM (
			SELECT v.location_id, SUM(v.visit_count)::bigint AS window_visits
			FROM location_page_visits v
			WHERE v.day >= (CURRENT_DATE - $1::int)
			GROUP BY v.location_id
		) agg
		JOIN locations l    ON l.id = agg.location_id
		JOIN regencies re   ON re.id = l.regency_id
		JOIN provinces prov ON prov.id = re.province_id
		JOIN regions reg    ON reg.id = prov.region_id
		WHERE l.is_deleted = false
		  AND l.approved_by IS NOT NULL
		ORDER BY window_visits DESC, l.id ASC
		LIMIT $2 OFFSET $3
	`

	rows, err := q.db.Query(ctx, query, days, arg.Limit, arg.Offset)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	items := []GetTrendingLocationsRow{}
	for rows.Next() {
		var i GetTrendingLocationsRow
		if err := rows.Scan(
			&i.RowNumber,
			&i.ID,
			&i.Name,
			&i.Address,
			&i.LocationType,
			&i.GoogleMapsLink,
			&i.Thumbnail,
			&i.RegencyName,
			&i.ProvinceName,
			&i.RegionName,
			&i.WindowVisits,
		); err != nil {
			return nil, err
		}
		items = append(items, i)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return items, nil
}