package instanceid

import (
	"sync"
	"testing"

	"github.com/google/uuid"
	"github.com/stretchr/testify/require"
	"gorm.io/gorm"

	"github.com/pocket-id/pocket-id/backend/internal/model"
	testutils "github.com/pocket-id/pocket-id/backend/internal/utils/testing"
)

// readInstanceID returns the value stored in the kv table under the "instance_id" key, together with the number of rows that match (to detect duplicates)
func readInstanceID(t *testing.T, db *gorm.DB) (value string, count int) {
	t.Helper()
	var rows []model.KV
	err := db.Where("key = ?", "instance_id").Find(&rows).Error
	require.NoError(t, err)
	if len(rows) == 0 {
		return "", 0
	}
	require.NotNil(t, rows[0].Value, "instance_id value should not be NULL")
	return *rows[0].Value, len(rows)
}

func TestLoad(t *testing.T) {
	t.Run("generates and persists a new instance ID when none exists", func(t *testing.T) {
		db := testutils.NewDatabaseForTest(t)

		id, err := Load(t.Context(), db)
		require.NoError(t, err)
		require.NotEmpty(t, id)

		// The generated ID should be a valid UUID
		_, err = uuid.Parse(id)
		require.NoError(t, err, "generated instance ID should be a valid UUID")

		// The value should have been persisted in the kv table
		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, id, stored)
	})

	t.Run("returns the existing instance ID on subsequent calls", func(t *testing.T) {
		db := testutils.NewDatabaseForTest(t)

		first, err := Load(t.Context(), db)
		require.NoError(t, err)
		require.NotEmpty(t, first)

		// A second call must return the same ID and must not create a duplicate row
		second, err := Load(t.Context(), db)
		require.NoError(t, err)
		require.Equal(t, first, second)

		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, first, stored)
	})

	t.Run("returns an instance ID that was already stored", func(t *testing.T) {
		db := testutils.NewDatabaseForTest(t)

		// Seed an instance ID directly in the database, e.g. as written by the migration that moved it out of the app config table
		existing := "existing-instance-id"
		err := db.Create(&model.KV{Key: "instance_id", Value: &existing}).Error
		require.NoError(t, err)

		id, err := Load(t.Context(), db)
		require.NoError(t, err)
		require.Equal(t, existing, id)

		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, existing, stored)
	})

	t.Run("concurrent calls without an existing instance ID converge on a single value", func(t *testing.T) {
		// This needs a database that allows concurrent access, so the goroutines race
		db := testutils.NewConcurrentDatabaseForTest(t)

		const parallel = 25

		// Each goroutine writes to its own index, so no locking is needed to collect the results
		ids := make([]string, parallel)
		loadErrs := make([]error, parallel)

		// The start channel is a barrier so all goroutines race their Load call at once
		start := make(chan struct{})

		var wg sync.WaitGroup
		wg.Add(parallel)
		for i := range parallel {
			go func() {
				defer wg.Done()
				<-start
				ids[i], loadErrs[i] = Load(t.Context(), db)
			}()
		}
		close(start)
		wg.Wait()

		// No concurrent call should have failed
		for i, err := range loadErrs {
			require.NoErrorf(t, err, "goroutine %d errored", i)
		}

		// Every goroutine must have observed the same, non-empty instance ID, meaning only one of them actually generated and persisted a value
		first := ids[0]
		require.NotEmpty(t, first)
		for _, id := range ids {
			require.Equal(t, first, id)
		}

		// Only a single row must have been persisted, and it must match the shared value
		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, first, stored)
	})
}

// TestMigrateFromAppConfig validates the database migration that moves the instance ID out of the legacy app_config_variables table and into the kv table
// The value used to be stored as an app config variable under the "instanceId" key
func TestMigrateFromAppConfig(t *testing.T) {
	// Version of the migration right before "20260708130000_move_instance_id_to_kv", which performs the move
	// We seed the legacy table right after this version, so the following migration has data to operate on
	const versionBeforeMove uint = 20260708120000

	// seedAppConfigInstanceID inserts a legacy "instanceId" row into the app_config_variables table
	seedAppConfigInstanceID := func(value string) func(t *testing.T, db *gorm.DB) {
		return func(t *testing.T, db *gorm.DB) {
			t.Helper()
			err := db.Exec(`INSERT INTO app_config_variables ("key", "value") VALUES ('instanceId', ?)`, value).Error
			require.NoError(t, err)
		}
	}

	// countLegacyInstanceID returns the number of "instanceId" rows left in the app_config_variables table
	countLegacyInstanceID := func(t *testing.T, db *gorm.DB) int64 {
		t.Helper()
		var count int64
		err := db.Table("app_config_variables").Where(`"key" = ?`, "instanceId").Count(&count).Error
		require.NoError(t, err)
		return count
	}

	t.Run("moves an existing instance ID from app_config_variables into the kv table", func(t *testing.T) {
		legacyID := uuid.NewString()
		db := testutils.NewDatabaseForTestWithMigrationSeed(t, versionBeforeMove, seedAppConfigInstanceID(legacyID))

		// The migration should have copied the value into the kv table under the "instance_id" key
		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, legacyID, stored)

		// The legacy row must have been removed from app_config_variables
		require.Zero(t, countLegacyInstanceID(t, db))

		// Load must return the migrated value without generating a new one
		id, err := Load(t.Context(), db)
		require.NoError(t, err)
		require.Equal(t, legacyID, id)

		stored, count = readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, legacyID, stored)
	})

	t.Run("keeps the existing kv value when both tables have an instance ID", func(t *testing.T) {
		legacyID := uuid.NewString()
		db := testutils.NewDatabaseForTestWithMigrationSeed(t, versionBeforeMove, func(t *testing.T, db *gorm.DB) {
			t.Helper()
			// An instance ID is already present in the kv table before the move runs
			err := db.Exec(`INSERT INTO kv ("key", "value") VALUES ('instance_id', ?)`, "kv-instance-id").Error
			require.NoError(t, err)
			// And a different value lingers in the legacy app_config_variables table
			seedAppConfigInstanceID(legacyID)(t, db)
		})

		// The migration must not clobber the value already stored in the kv table
		stored, count := readInstanceID(t, db)
		require.Equal(t, 1, count)
		require.Equal(t, "kv-instance-id", stored)

		// The legacy row must still be removed regardless of the conflict
		require.Zero(t, countLegacyInstanceID(t, db))
	})
}