package database_test

import (
	"context"
	"fmt"
	"testing"
	"time"

	"github.com/google/uuid"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"gorm.io/gorm"
	"sneak.berlin/go/webhooker/internal/database"
)

// TestWebhookDBManager_OpenAddsEventTierIndexes verifies that opening a
// per-webhook database that predates these indexes creates them. It
// stands in for an older database file by dropping the indexes
// AutoMigrate just created, then reopening the same file.
func TestWebhookDBManager_OpenAddsEventTierIndexes(t *testing.T) {
	t.Parallel()

	indexes := []struct {
		model any
		name  string
	}{
		{&database.Delivery{}, "idx_deliveries_status"},
		{&database.Delivery{}, "idx_deliveries_event_id"},
		{&database.DeliveryResult{}, "idx_delivery_results_delivery_id"},
		{&database.Event{}, "idx_events_deleted_at_created_at"},
		{&database.Event{}, "idx_events_created_at"},
	}

	mgr, lc := setupTestWebhookDBManager(t)
	ctx := context.Background()
	require.NoError(t, lc.Start(ctx))

	defer func() { require.NoError(t, lc.Stop(ctx)) }()

	webhookID := uuid.New().String()

	db, err := mgr.GetDB(webhookID)
	require.NoError(t, err)

	// A fresh database has them.
	for _, ix := range indexes {
		require.True(t, db.Migrator().HasIndex(ix.model, ix.name))
	}

	// Stand in for a database file created before the indexes existed.
	for _, ix := range indexes {
		require.NoError(t, db.Migrator().DropIndex(ix.model, ix.name))
		require.False(t, db.Migrator().HasIndex(ix.model, ix.name))
	}

	// Drop the cached connection so the next open reopens the file and
	// runs AutoMigrate against it, as a restart would.
	require.NoError(t, mgr.CloseAll())

	db, err = mgr.GetDB(webhookID)
	require.NoError(t, err)

	for _, ix := range indexes {
		assert.True(t, db.Migrator().HasIndex(ix.model, ix.name),
			"opening the existing database should create %s", ix.name)
	}
}

// TestEventTierQueriesUseTheirIndexes verifies that the statements the
// indexes are for use them. GORM builds each statement in a dry run as
// the code named above it does, soft-delete condition included, and
// SQLite, which keeps no statistics on these tables, must plan to seek
// on each index listed by the columns in parentheses.
func TestEventTierQueriesUseTheirIndexes(t *testing.T) {
	t.Parallel()

	mgr, lc := setupTestWebhookDBManager(t)
	ctx := context.Background()
	require.NoError(t, lc.Start(ctx))

	defer func() { require.NoError(t, lc.Stop(ctx)) }()

	db, err := mgr.GetDB(uuid.New().String())
	require.NoError(t, err)

	dry := db.Session(&gorm.Session{DryRun: true})
	ids := []string{
		uuid.New().String(), uuid.New().String(), uuid.New().String(),
	}
	cutoff := time.Now()

	var (
		deliveries []database.Delivery
		results    []database.DeliveryResult
		depths     []struct{ Depth int }
	)

	byStatus := "idx_deliveries_status (status=? AND deleted_at=?)"
	byEvent := "idx_deliveries_event_id (event_id=? AND deleted_at=?)"
	byAge := "idx_events_deleted_at_created_at (deleted_at=? AND created_at<?)"

	// The delivery engine: recovery and the retry sweep, the sweep for
	// stranded pending deliveries, and the queue depth count.
	assertPlanUses(t, db, dry.Where(
		"status = ?", database.DeliveryStatusRetrying,
	).Find(&deliveries), byStatus)
	assertPlanUses(t, db, dry.Where(
		"status = ? AND updated_at < ?",
		database.DeliveryStatusPending, cutoff,
	).Limit(500).Find(&deliveries), byStatus)
	assertPlanUses(t, db, dry.Model(&database.Delivery{}).
		Select("target_id", "status", "count(*) as depth").
		Where("status IN ?", []database.DeliveryStatus{
			database.DeliveryStatusPending,
			database.DeliveryStatusRetrying,
		}).Group("target_id, status").Find(&depths), byStatus)

	// The event log: each event's deliveries, then their attempts
	// (loadEventsWithDeliveries, loadDeliveryResults).
	assertPlanUses(t, db, dry.Where("event_id = ?", ids[0]).
		Find(&deliveries), byEvent)
	assertPlanUses(t, db, dry.Where("delivery_id IN ?", ids).
		Order("attempt_num ASC").Find(&results),
		"idx_delivery_results_delivery_id (delivery_id=? AND deleted_at=?)")

	// Retention's deletes (deleteExpired), whose subqueries are built
	// afresh for each statement as it builds them.
	expiredEventIDs := func() *gorm.DB {
		return dry.Model(&database.Event{}).Select("id").
			Where("created_at < ?", cutoff)
	}

	assertPlanUses(t, db, dry.Unscoped().Where(
		"delivery_id IN (?)", dry.Model(&database.Delivery{}).
			Select("id").Where("event_id IN (?)", expiredEventIDs()),
	).Delete(&database.DeliveryResult{}),
		"idx_delivery_results_delivery_id (delivery_id=?)", byEvent, byAge)
	var failed struct{ Count int64 }

	assertPlanUses(t, db, dry.Unscoped().Model(&database.Delivery{}).
		Select("count(CASE WHEN status = ? THEN 1 END) AS count",
			database.DeliveryStatusFailed).
		Where("event_id IN (?)", expiredEventIDs()).
		Take(&failed),
		"idx_deliveries_event_id (event_id=?)", byAge)
	assertPlanUses(t, db, dry.Unscoped().Where(
		"event_id IN (?)", expiredEventIDs(),
	).Delete(&database.Delivery{}),
		"idx_deliveries_event_id (event_id=?)", byAge)
	assertPlanUses(t, db, dry.Unscoped().Where(
		"created_at < ?", cutoff,
	).Delete(&database.Event{}), "idx_events_created_at (created_at<?)")

	// The webhook page's statistics (readEventStats in the handlers):
	// deliveries in progress, deliveries finished and events received
	// since a time, and the newest event, which must come straight
	// off an index rather than from sorting every event.
	var (
		count  int64
		newest []time.Time
	)

	assertPlanUses(t, db, dry.Model(&database.Delivery{}).
		Where("status IN ?", []database.DeliveryStatus{
			database.DeliveryStatusPending,
			database.DeliveryStatusRetrying,
		}).Count(&count), byStatus)
	assertPlanUses(t, db, dry.Model(&database.Delivery{}).
		Where("status = ? AND finished_at >= ?",
			database.DeliveryStatusFailed, cutoff).Count(&count),
		"idx_deliveries_status "+
			"(status=? AND deleted_at=? AND finished_at>?)")
	assertPlanUses(t, db, dry.Model(&database.Event{}).
		Where("created_at >= ?", cutoff).Count(&count),
		"idx_events_deleted_at_created_at "+
			"(deleted_at=? AND created_at>?)")

	newestEvent := dry.Model(&database.Event{}).
		Order("created_at DESC").Limit(1).Pluck("created_at", &newest)
	assertPlanUses(t, db, newestEvent,
		"idx_events_deleted_at_created_at (deleted_at=?)")
	assert.NotContains(t, queryPlan(t, db, newestEvent), "TEMP B-TREE")
}

// assertPlanUses asserts that SQLite's plan for a statement GORM built
// in a dry run, run with the same SQL and arguments GORM would send,
// names each of the given indexes.
func assertPlanUses(
	t *testing.T, db, built *gorm.DB, indexes ...string,
) {
	t.Helper()

	plan := queryPlan(t, db, built)

	for _, index := range indexes {
		assert.Contains(t, plan, index, built.Statement.SQL.String())
	}
}

// queryPlan returns SQLite's plan for a statement GORM built in a dry
// run, run with the same SQL and arguments GORM would send.
func queryPlan(t *testing.T, db, built *gorm.DB) string {
	t.Helper()

	var plan []struct{ Detail string }

	require.NoError(t, db.Raw(
		"EXPLAIN QUERY PLAN "+built.Statement.SQL.String(),
		built.Statement.Vars...,
	).Scan(&plan).Error)

	return fmt.Sprint(plan)
}