package model

import (
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/url"
	"strings"

	"gorm.io/gorm"
)

type databaseSchemaMigration struct {
	fromVersion int
	toVersion   int
	migrate     func(db *gorm.DB, backend string) error
	validate    func(db *gorm.DB, backend string) error
}

func autoMigrateSchemaMetadata(db *gorm.DB) error {
	for _, item := range schemaMetadataModels() {
		if err := db.AutoMigrate(item); err != nil {
			return err
		}
	}
	return nil
}

func migrateProxyRouteEnableHTTPSColumn(db *gorm.DB) error {
	if !db.Migrator().HasTable(&ProxyRoute{}) {
		return nil
	}
	if db.Migrator().HasColumn(&ProxyRoute{}, "enable_https") || !db.Migrator().HasColumn(&ProxyRoute{}, "enable_http_s") {
		return nil
	}
	return db.Migrator().RenameColumn(&ProxyRoute{}, "enable_http_s", "enable_https")
}

func migrateTextColumns(db *gorm.DB, backend string) error {
	if backend != "postgres" {
		return nil
	}
	type textColumn struct {
		model  any
		table  string
		column string
	}
	columns := []textColumn{
		{model: &Node{}, table: "nodes", column: "openresty_message"},
		{model: &Node{}, table: "nodes", column: "last_error"},
		{model: &ApplyLog{}, table: "apply_logs", column: "message"},
		{model: &NodeHealthEvent{}, table: "node_health_events", column: "message"},
	}
	for _, item := range columns {
		if !db.Migrator().HasTable(item.model) || !db.Migrator().HasColumn(item.model, item.column) {
			continue
		}
		sql := fmt.Sprintf(`ALTER TABLE "%s" ALTER COLUMN "%s" TYPE text`, item.table, item.column)
		if err := db.Exec(sql).Error; err != nil {
			return fmt.Errorf("migrate column %s.%s to text failed: %w", item.table, item.column, err)
		}
	}
	return nil
}

func migrateObservabilityLegacyColumns(db *gorm.DB) error {
	if db == nil {
		return nil
	}
	if !db.Migrator().HasTable(&NodeHealthEvent{}) || !db.Migrator().HasColumn(&NodeHealthEvent{}, "raw_json") {
		return nil
	}
	type legacyHealthEventRaw struct {
		ID           uint
		RawJSON      string
		MetadataJSON string
	}
	type legacyHealthEventPayload struct {
		Metadata map[string]string `json:"metadata"`
	}

	var rows []legacyHealthEventRaw
	if err := db.Model(&NodeHealthEvent{}).
		Select("id, raw_json, metadata_json").
		Where("raw_json <> '' AND (metadata_json IS NULL OR metadata_json = '')").
		Find(&rows).Error; err != nil {
		return fmt.Errorf("query legacy node health event raw_json failed: %w", err)
	}
	for _, row := range rows {
		var payload legacyHealthEventPayload
		if err := json.Unmarshal([]byte(row.RawJSON), &payload); err != nil {
			continue
		}
		if len(payload.Metadata) == 0 {
			continue
		}
		metadataJSON, err := json.Marshal(payload.Metadata)
		if err != nil {
			continue
		}
		if err := db.Model(&NodeHealthEvent{}).
			Where("id = ?", row.ID).
			Update("metadata_json", string(metadataJSON)).Error; err != nil {
			return fmt.Errorf("migrate node health event metadata_json failed: %w", err)
		}
	}
	return nil
}

func applyCurrentSchema(db *gorm.DB, backend string) error {
	if err := autoMigrateSchemaMetadata(db); err != nil {
		return err
	}
	if err := migrateProxyRouteEnableHTTPSColumn(db); err != nil {
		return err
	}
	if err := autoMigrateAll(db); err != nil {
		return err
	}
	if err := migrateTextColumns(db, backend); err != nil {
		return err
	}
	if err := migrateObservabilityLegacyColumns(db); err != nil {
		return err
	}
	return nil
}

func loadDatabaseSchemaVersion(db *gorm.DB) (int, bool, error) {
	if db == nil {
		return 0, false, nil
	}
	if !db.Migrator().HasTable(&DatabaseSchemaVersion{}) {
		return 0, false, nil
	}
	var state DatabaseSchemaVersion
	err := db.Where("id = ?", databaseSchemaVersionRowID).First(&state).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return 0, false, nil
	}
	if err != nil {
		return 0, false, err
	}
	return state.Version, true, nil
}

func saveDatabaseSchemaVersion(db *gorm.DB, version int) error {
	return db.Save(&DatabaseSchemaVersion{
		ID:      databaseSchemaVersionRowID,
		Version: version,
	}).Error
}

func validateDatabaseSchemaV2(db *gorm.DB, backend string) error {
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	if !db.Migrator().HasTable(&DatabaseSchemaVersion{}) {
		return fmt.Errorf("table %s is missing", (&DatabaseSchemaVersion{}).TableName())
	}
	models, err := buildDBModels()
	if err != nil {
		return err
	}
	for _, item := range models {
		if isShardedObservabilityTable(item.tableName) {
			for _, table := range observabilityShardTables(item.tableName) {
				if !db.Migrator().HasTable(table) {
					return fmt.Errorf("sharded table %s is missing", table)
				}
			}
			continue
		}
		if !db.Migrator().HasTable(item.value) {
			return fmt.Errorf("table %s is missing", item.tableName)
		}
	}
	if !db.Migrator().HasColumn(&NodeHealthEvent{}, "metadata_json") {
		return fmt.Errorf("column node_health_events.metadata_json is missing")
	}
	_ = backend
	return nil
}

func validateDatabaseSchemaV3(db *gorm.DB, backend string) error {
	if err := validateDatabaseSchemaV2(db, backend); err != nil {
		return err
	}
	for _, baseTable := range shardedObservabilityBaseTables() {
		for _, table := range observabilityShardTables(baseTable) {
			legacyTable := legacyObservabilityShardTableName(table)
			if db.Migrator().HasTable(legacyTable) {
				return fmt.Errorf("legacy sharded table %s still exists", legacyTable)
			}
		}
	}
	return nil
}

func validateDatabaseSchemaV4(db *gorm.DB, backend string) error {
	if err := validateDatabaseSchemaV3(db, backend); err != nil {
		return err
	}
	if !db.Migrator().HasTable(&Origin{}) {
		return fmt.Errorf("table origins is missing")
	}
	if !db.Migrator().HasColumn(&ProxyRoute{}, "origin_id") {
		return fmt.Errorf("column proxy_routes.origin_id is missing")
	}
	return nil
}

func renameLegacyObservabilityShardTables(db *gorm.DB) error {
	for _, baseTable := range shardedObservabilityBaseTables() {
		for _, table := range observabilityShardTables(baseTable) {
			legacyTable := legacyObservabilityShardTableName(table)
			if db.Migrator().HasTable(legacyTable) {
				return fmt.Errorf("legacy sharded table %s already exists", legacyTable)
			}
			if !db.Migrator().HasTable(table) {
				continue
			}
			if err := db.Migrator().RenameTable(table, legacyTable); err != nil {
				return fmt.Errorf("rename sharded table %s to %s failed: %w", table, legacyTable, err)
			}
			if err := dropLegacyObservabilitySecondaryIndexes(db, legacyTable); err != nil {
				return err
			}
		}
	}
	return nil
}

func dropLegacyObservabilitySecondaryIndexes(db *gorm.DB, table string) error {
	db = sessionIgnoringSharding(db)
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	backend := baseDialector(db).Name()
	indexes := make([]string, 0)
	switch backend {
	case "sqlite":
		if err := db.Raw(
			`SELECT name FROM sqlite_master WHERE type = 'index' AND tbl_name = ? AND name LIKE 'idx_%'`,
			table,
		).Scan(&indexes).Error; err != nil {
			return fmt.Errorf("list indexes for %s failed: %w", table, err)
		}
	case "postgres":
		if err := db.Raw(
			`SELECT indexname FROM pg_indexes WHERE schemaname = current_schema() AND tablename = ? AND indexname LIKE 'idx_%'`,
			table,
		).Scan(&indexes).Error; err != nil {
			return fmt.Errorf("list indexes for %s failed: %w", table, err)
		}
	default:
		return fmt.Errorf("unsupported database backend %s", backend)
	}
	for _, indexName := range indexes {
		if err := db.Exec(fmt.Sprintf(`DROP INDEX IF EXISTS "%s"`, indexName)).Error; err != nil {
			return fmt.Errorf("drop legacy index %s failed: %w", indexName, err)
		}
	}
	return nil
}

func autoMigrateObservabilityShardTables(db *gorm.DB) error {
	db = sessionIgnoringSharding(db)
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	dialector := baseDialector(db)
	if dialector == nil {
		return fmt.Errorf("database dialector is nil")
	}
	type shardedTable struct {
		model any
		base  string
	}
	tables := []shardedTable{
		{model: &NodeMetricSnapshot{}, base: "node_metric_snapshots"},
		{model: &NodeRequestReport{}, base: "node_request_reports"},
		{model: &NodeAccessLog{}, base: "node_access_logs"},
	}
	for _, item := range tables {
		for _, table := range observabilityShardTables(item.base) {
			tx := db.Table(table)
			if err := dialector.Migrator(tx).AutoMigrate(item.model); err != nil {
				return fmt.Errorf("auto migrate sharded table %s failed: %w", table, err)
			}
		}
	}
	return nil
}

func dropLegacyObservabilityShardTables(db *gorm.DB) error {
	db = sessionIgnoringSharding(db)
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	for _, baseTable := range shardedObservabilityBaseTables() {
		for _, table := range observabilityShardTables(baseTable) {
			legacyTable := legacyObservabilityShardTableName(table)
			if !db.Migrator().HasTable(legacyTable) {
				continue
			}
			if err := db.Exec(fmt.Sprintf(`DROP TABLE IF EXISTS "%s"`, legacyTable)).Error; err != nil {
				return fmt.Errorf("drop legacy sharded table %s failed: %w", legacyTable, err)
			}
		}
	}
	return nil
}

func migrateLegacyNodeMetricSnapshots(db *gorm.DB) error {
	for _, table := range observabilityShardTables("node_metric_snapshots") {
		legacyTable := legacyObservabilityShardTableName(table)
		if !db.Migrator().HasTable(legacyTable) {
			continue
		}
		var lastSeenID uint
		for {
			var rows []NodeMetricSnapshot
			query := db.Table(legacyTable).Order("id ASC").Limit(500)
			if lastSeenID > 0 {
				query = query.Where("id > ?", lastSeenID)
			}
			if err := query.Find(&rows).Error; err != nil {
				return fmt.Errorf("query legacy sharded table %s failed: %w", legacyTable, err)
			}
			if len(rows) == 0 {
				break
			}
			lastSeenID = rows[len(rows)-1].ID
			grouped := make(map[string][]NodeMetricSnapshot, observabilityShardCount)
			for index := range rows {
				rows[index].ID = 0
				if err := assignObservabilityID(&rows[index].ID); err != nil {
					return err
				}
				targetTable := observabilityShardTableForID("node_metric_snapshots", rows[index].ID)
				grouped[targetTable] = append(grouped[targetTable], rows[index])
			}
			for targetTable, batch := range grouped {
				if err := db.Table(targetTable).Create(&batch).Error; err != nil {
					return fmt.Errorf("write migrated rows into %s failed: %w", targetTable, err)
				}
			}
		}
	}
	return nil
}

func migrateLegacyNodeRequestReports(db *gorm.DB) error {
	for _, table := range observabilityShardTables("node_request_reports") {
		legacyTable := legacyObservabilityShardTableName(table)
		if !db.Migrator().HasTable(legacyTable) {
			continue
		}
		var lastSeenID uint
		for {
			var rows []NodeRequestReport
			query := db.Table(legacyTable).Order("id ASC").Limit(500)
			if lastSeenID > 0 {
				query = query.Where("id > ?", lastSeenID)
			}
			if err := query.Find(&rows).Error; err != nil {
				return fmt.Errorf("query legacy sharded table %s failed: %w", legacyTable, err)
			}
			if len(rows) == 0 {
				break
			}
			lastSeenID = rows[len(rows)-1].ID
			grouped := make(map[string][]NodeRequestReport, observabilityShardCount)
			for index := range rows {
				rows[index].ID = 0
				if err := assignObservabilityID(&rows[index].ID); err != nil {
					return err
				}
				targetTable := observabilityShardTableForID("node_request_reports", rows[index].ID)
				grouped[targetTable] = append(grouped[targetTable], rows[index])
			}
			for targetTable, batch := range grouped {
				if err := db.Table(targetTable).Create(&batch).Error; err != nil {
					return fmt.Errorf("write migrated rows into %s failed: %w", targetTable, err)
				}
			}
		}
	}
	return nil
}

func migrateLegacyNodeAccessLogs(db *gorm.DB) error {
	for _, table := range observabilityShardTables("node_access_logs") {
		legacyTable := legacyObservabilityShardTableName(table)
		if !db.Migrator().HasTable(legacyTable) {
			continue
		}
		var lastSeenID uint
		for {
			var rows []NodeAccessLog
			query := db.Table(legacyTable).Order("id ASC").Limit(500)
			if lastSeenID > 0 {
				query = query.Where("id > ?", lastSeenID)
			}
			if err := query.Find(&rows).Error; err != nil {
				return fmt.Errorf("query legacy sharded table %s failed: %w", legacyTable, err)
			}
			if len(rows) == 0 {
				break
			}
			lastSeenID = rows[len(rows)-1].ID
			grouped := make(map[string][]NodeAccessLog, observabilityShardCount)
			for index := range rows {
				rows[index].ID = 0
				if err := assignObservabilityID(&rows[index].ID); err != nil {
					return err
				}
				targetTable := observabilityShardTableForID("node_access_logs", rows[index].ID)
				grouped[targetTable] = append(grouped[targetTable], rows[index])
			}
			for targetTable, batch := range grouped {
				if err := db.Table(targetTable).Create(&batch).Error; err != nil {
					return fmt.Errorf("write migrated rows into %s failed: %w", targetTable, err)
				}
			}
		}
	}
	return nil
}

func normalizeOriginAddressForMigration(raw string) string {
	return strings.ToLower(strings.TrimSpace(raw))
}

func extractOriginAddressForMigration(rawURL string) string {
	parsed, err := url.ParseRequestURI(strings.TrimSpace(rawURL))
	if err != nil {
		return ""
	}
	return normalizeOriginAddressForMigration(parsed.Hostname())
}

func backfillOriginsFromProxyRoutes(db *gorm.DB) error {
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	if !db.Migrator().HasTable(&Origin{}) || !db.Migrator().HasTable(&ProxyRoute{}) {
		return nil
	}

	var routes []ProxyRoute
	if err := db.Order("id asc").Find(&routes).Error; err != nil {
		return fmt.Errorf("list proxy routes for origin backfill failed: %w", err)
	}

	type originSeed struct {
		ID      uint
		Address string
	}

	originByAddress := make(map[string]originSeed)
	var origins []Origin
	if err := db.Order("id asc").Find(&origins).Error; err != nil {
		return fmt.Errorf("list origins for backfill failed: %w", err)
	}
	for _, origin := range origins {
		address := normalizeOriginAddressForMigration(origin.Address)
		if address == "" {
			continue
		}
		originByAddress[address] = originSeed{ID: origin.ID, Address: address}
	}

	for _, route := range routes {
		address := extractOriginAddressForMigration(route.OriginURL)
		if address == "" {
			continue
		}
		origin, ok := originByAddress[address]
		if !ok {
			name := address
			if ip := net.ParseIP(address); ip != nil {
				name = ip.String()
			}
			record := Origin{
				Name:    name,
				Address: address,
				Remark:  "",
			}
			if err := db.Create(&record).Error; err != nil {
				return fmt.Errorf("create origin for address %s failed: %w", address, err)
			}
			origin = originSeed{ID: record.ID, Address: address}
			originByAddress[address] = origin
		}
		if route.OriginID != nil && *route.OriginID == origin.ID {
			continue
		}
		if err := db.Model(&ProxyRoute{}).
			Where("id = ?", route.ID).
			Update("origin_id", origin.ID).Error; err != nil {
			return fmt.Errorf("backfill proxy route %d origin_id failed: %w", route.ID, err)
		}
	}

	return nil
}

// migrateV2 upgrades the legacy schema to the first versioned schema by
// creating schema metadata, applying the current tables, and backfilling
// compatibility columns.
func migrateV2(db *gorm.DB, backend string) error {
	return applyCurrentSchema(db, backend)
}

// migrateV3 upgrades observability shard tables from legacy ID layout to the
// current ID-sharded layout and migrates existing shard data into the new tables.
func migrateV3(db *gorm.DB, backend string) error {
	if db == nil {
		return fmt.Errorf("database handle is nil")
	}
	_ = backend
	if err := renameLegacyObservabilityShardTables(db); err != nil {
		return err
	}
	if err := autoMigrateObservabilityShardTables(db); err != nil {
		return err
	}
	if err := migrateLegacyNodeMetricSnapshots(db); err != nil {
		return err
	}
	if err := migrateLegacyNodeRequestReports(db); err != nil {
		return err
	}
	if err := migrateLegacyNodeAccessLogs(db); err != nil {
		return err
	}
	return dropLegacyObservabilityShardTables(db)
}

// migrateV4 introduces the origins schema and backfills proxy route origin
// references from existing origin_url values.
func migrateV4(db *gorm.DB, backend string) error {
	if err := applyCurrentSchema(db, backend); err != nil {
		return err
	}
	return backfillOriginsFromProxyRoutes(db)
}

func databaseSchemaMigrations() []databaseSchemaMigration {
	return []databaseSchemaMigration{
		{fromVersion: 1, toVersion: 2, migrate: migrateV2, validate: validateDatabaseSchemaV2},
		{fromVersion: 2, toVersion: 3, migrate: migrateV3, validate: validateDatabaseSchemaV3},
		{fromVersion: 3, toVersion: 4, migrate: migrateV4, validate: validateDatabaseSchemaV4},
	}
}

func databaseSchemaMigrationMap() map[int]databaseSchemaMigration {
	migrations := make(map[int]databaseSchemaMigration, len(databaseSchemaMigrations()))
	for _, item := range databaseSchemaMigrations() {
		migrations[item.fromVersion] = item
	}
	return migrations
}

func runDatabaseSchemaMigration(db *gorm.DB, backend string, migration databaseSchemaMigration) error {
	if backend == "sqlite" {
		if err := migration.migrate(db, backend); err != nil {
			return fmt.Errorf("migrate database schema from v%d to v%d failed: %w", migration.fromVersion, migration.toVersion, err)
		}
		if err := migration.validate(db, backend); err != nil {
			return fmt.Errorf("validate database schema v%d failed: %w", migration.toVersion, err)
		}
		if err := saveDatabaseSchemaVersion(db, migration.toVersion); err != nil {
			return fmt.Errorf("persist database schema version v%d failed: %w", migration.toVersion, err)
		}
		return nil
	}

	return db.Transaction(func(tx *gorm.DB) error {
		if err := migration.migrate(tx, backend); err != nil {
			return fmt.Errorf("migrate database schema from v%d to v%d failed: %w", migration.fromVersion, migration.toVersion, err)
		}
		if err := migration.validate(tx, backend); err != nil {
			return fmt.Errorf("validate database schema v%d failed: %w", migration.toVersion, err)
		}
		if err := saveDatabaseSchemaVersion(tx, migration.toVersion); err != nil {
			return fmt.Errorf("persist database schema version v%d failed: %w", migration.toVersion, err)
		}
		return nil
	})
}

func upgradeDatabaseSchema(db *gorm.DB, backend string, version int) error {
	if version > currentDatabaseSchemaVersion {
		return fmt.Errorf("database schema version %d is newer than application version %d", version, currentDatabaseSchemaVersion)
	}
	if version == currentDatabaseSchemaVersion {
		return nil
	}
	migrationMap := databaseSchemaMigrationMap()
	for version < currentDatabaseSchemaVersion {
		migration, ok := migrationMap[version]
		if !ok {
			return fmt.Errorf("database schema migration from v%d is not defined", version)
		}
		if err := runDatabaseSchemaMigration(db, backend, migration); err != nil {
			return err
		}
		version = migration.toVersion
	}
	return nil
}

func initializeFreshDatabaseSchema(db *gorm.DB, backend string) error {
	if err := applyCurrentSchema(db, backend); err != nil {
		return err
	}
	if err := backfillOriginsFromProxyRoutes(db); err != nil {
		return err
	}
	if err := migrateSQLiteDataIfNeeded(db, backend); err != nil {
		return err
	}
	if err := validateDatabaseSchemaV4(db, backend); err != nil {
		return err
	}
	return saveDatabaseSchemaVersion(db, currentDatabaseSchemaVersion)
}

func ensureDatabaseSchemaUpToDate(db *gorm.DB, backend string) error {
	version, exists, err := loadDatabaseSchemaVersion(db)
	if err != nil {
		return err
	}
	if exists {
		return upgradeDatabaseSchema(db, backend, version)
	}
	empty, err := isDatabaseEmpty(db)
	if err != nil {
		return err
	}
	if empty {
		return initializeFreshDatabaseSchema(db, backend)
	}
	if err := autoMigrateSchemaMetadata(db); err != nil {
		return err
	}
	return upgradeDatabaseSchema(db, backend, legacyDatabaseSchemaVersion)
}