// Reading individual sales.
//
// The conversion report has aggregated `purchases` since it existed and
// nothing could read a row of it, so "revenue was 41,000 last week" could not
// be checked against a till. These are the reads that make that number
// falsifiable from outside.
package store

import (
	"context"
	"encoding/json"
	"errors"
	"time"

	"github.com/jackc/pgx/v5"

	"github.com/loyaly/behavision-server/internal/api"
)

const saleCols = `
	p.id::text, p.occurred_at, p.site_id::text, si.name, si.slug,
	p.amount, p.currency, p.visitor_id::text, v.number, v.label,
	p.visit_id::text, p.items, p.source, p.external_ref`

func scanSale(row pgx.Row) (api.Sale, error) {
	var s api.Sale
	var at time.Time
	// LEFT JOINed: a sale with no visitor is an ordinary walk-in nobody
	// identified, and it is still revenue.
	var visitorID, visitorLabel, visitID *string
	var number *int64
	var items []byte
	if err := row.Scan(&s.ID, &at, &s.SiteID, &s.Site, &s.SiteSlug,
		&s.Amount, &s.Currency, &visitorID, &number, &visitorLabel,
		&visitID, &items, &s.Source, &s.ExternalRef); err != nil {
		return api.Sale{}, err
	}
	s.OccurredAt = at.UTC().Format(time.RFC3339)
	if visitorID != nil {
		s.VisitorID = *visitorID
	}
	if visitorLabel != nil {
		s.VisitorLabel = *visitorLabel
	}
	if number != nil {
		s.VisitorRef = api.VisitorRef(*number)
	}
	if visitID != nil {
		s.VisitID = *visitID
	}
	// items is jsonb defaulting to '[]', but a null column would otherwise
	// unmarshal into a nil slice and serialise as null - and a client mapping
	// over it breaks on the first sale recorded without a basket.
	s.Items = []string{}
	if len(items) > 0 {
		_ = json.Unmarshal(items, &s.Items)
		if s.Items == nil {
			s.Items = []string{}
		}
	}
	return s, nil
}

// Sales lists purchases newest first, within one tenant.
//
// Bounded by `limit` and the date window rather than by a cursor. A keyset
// cursor needs a monotonic server-assigned column, and purchases has none -
// ordering by (occurred_at, id) with a random uuid tie-break is exactly the
// shape that silently dropped four simultaneous visits from the arrivals feed
// before `visits.seq` existed. Offering a cursor here would imply a delivery
// guarantee this table cannot make; narrowing the window is honest and is what
// a sales list is browsed by anyway.
func (s *Store) Sales(ctx context.Context, q api.SaleQuery) ([]api.Sale, error) {
	rows, err := s.pool.Query(ctx, `
		SELECT `+saleCols+`
		  FROM purchases p
		  JOIN sites si    ON si.id = p.site_id
		  LEFT JOIN visitors v ON v.id = p.visitor_id
		 WHERE p.client_id = $1::uuid
		   AND p.occurred_at >= $2 AND p.occurred_at < $3
		   AND ($4 = '' OR p.site_id = $4::uuid)
		   AND ($5 = '' OR p.visitor_id = $5::uuid)
		 ORDER BY p.occurred_at DESC, p.id
		 LIMIT $6`,
		q.ClientID, q.From, q.To, q.SiteID, q.VisitorID, q.Limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []api.Sale
	for rows.Next() {
		sale, err := scanSale(rows)
		if err != nil {
			return nil, err
		}
		out = append(out, sale)
	}
	return out, rows.Err()
}

// Sale is one purchase, scoped to the tenant. A row belonging to somebody else
// reads as absent, never as forbidden.
func (s *Store) Sale(ctx context.Context, clientID, id string) (api.Sale, error) {
	row := s.pool.QueryRow(ctx, `
		SELECT `+saleCols+`
		  FROM purchases p
		  JOIN sites si    ON si.id = p.site_id
		  LEFT JOIN visitors v ON v.id = p.visitor_id
		 WHERE p.client_id = $1::uuid AND p.id::text = $2`, clientID, id)
	sale, err := scanSale(row)
	if errors.Is(err, pgx.ErrNoRows) {
		return api.Sale{}, nil
	}
	return sale, err
}