package imageproxy

import (
	"context"
	"database/sql"
	"errors"
	"testing"
	"time"

	"sneak.berlin/go/pixa/internal/imagerequest"
)

// pendingAccessTimesWait is how long a test waits for the database's
// connection, for a cache hit to be answered, for an access time to reach
// the database, or for a request to return past its deadline.
const pendingAccessTimesWait = 5 * time.Second

// holdDatabase takes the one connection of db, so that every other query
// waits for it, and returns the func that frees it.
func holdDatabase(t *testing.T, db *sql.DB) func() {
	t.Helper()

	ctx, cancel := context.WithTimeout(t.Context(), pendingAccessTimesWait)
	defer cancel()

	conn, err := db.Conn(ctx)
	if err != nil {
		t.Fatalf("failed to take the database connection: %v", err)
	}

	return func() { _ = conn.Close() }
}

// TestProxy_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy holds the
// database's one connection while a request whose fetch is held reaches its
// deadline. The request must return with the deadline's error while the
// connection is still held, as it waits for no database write past its
// deadline.
func TestProxy_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy(t *testing.T) {
	t.Parallel()

	svc, fixtures, fetcher := setupHeldFetchProxy(t)

	svc.cache.StartPendingAccessTimeWrites()
	defer func() { _ = svc.cache.StopPendingAccessTimeWrites(t.Context()) }()

	// Room for the request to reach its fetch on a busy host
	const timeout = 2 * time.Second

	ctx, cancel := context.WithTimeout(t.Context(), timeout)
	defer cancel()

	deadline, _ := ctx.Deadline()

	results := startGet(ctx, svc, photoVariant(fixtures, 85, imagerequest.FitCover))

	// The request has made its database reads by the time it fetches.
	select {
	case <-fetcher.started:
	case <-time.After(timeout):
		t.Fatal("request did not reach its fetch by its deadline")
	}

	releaseDatabase := holdDatabase(t, svc.db)
	defer releaseDatabase()

	select {
	case got := <-results:
		t.Logf("Get() returned %v after its deadline, error = %v",
			time.Since(deadline), got.err)

		if !errors.Is(got.err, context.DeadlineExceeded) {
			t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
		}
	case <-time.After(time.Until(deadline) + pendingAccessTimesWait):
		t.Fatal("request did not return while the database was busy")
	}
}