package localdb

import (
	"errors"
	"fmt"
	"log/slog"
	"strings"
	"time"

	"github.com/google/uuid"
	"gorm.io/gorm"
)

type LocalSchemaMigration struct {
	ID        string    `gorm:"primaryKey;size:128"`
	Name      string    `gorm:"not null;size:255"`
	AppliedAt time.Time `gorm:"not null"`
}

func (LocalSchemaMigration) TableName() string {
	return "local_schema_migrations"
}

type localMigration struct {
	id   string
	name string
	run  func(tx *gorm.DB) error
}

var localMigrations = []localMigration{
	{
		id:   "2026_02_04_versioning_backfill",
		name: "Ensure configuration versioning data and current pointers",
		run:  backfillConfigurationVersions,
	},
	{
		id:   "2026_02_04_is_active_backfill",
		name: "Ensure is_active defaults to true for existing configurations",
		run:  backfillConfigurationIsActive,
	},
	{
		id:   "2026_02_06_projects_backfill",
		name: "Create default projects and attach existing configurations",
		run:  backfillProjectsForConfigurations,
	},
	{
		id:   "2026_02_06_pricelist_backfill",
		name: "Attach existing configurations to latest local pricelist and recalc usage",
		run:  backfillConfigurationPricelists,
	},
	{
		id:   "2026_02_06_pricelist_index_fix",
		name: "Use unique server_id for local pricelists and allow duplicate versions",
		run:  fixLocalPricelistIndexes,
	},
	{
		id:   "2026_02_06_pricelist_source",
		name: "Backfill source for local pricelists and create source indexes",
		run:  backfillLocalPricelistSource,
	},
}

func runLocalMigrations(db *gorm.DB) error {
	if err := db.AutoMigrate(&LocalSchemaMigration{}); err != nil {
		return fmt.Errorf("migrate local schema migrations table: %w", err)
	}

	for _, migration := range localMigrations {
		var count int64
		if err := db.Model(&LocalSchemaMigration{}).Where("id = ?", migration.id).Count(&count).Error; err != nil {
			return fmt.Errorf("check local migration %s: %w", migration.id, err)
		}
		if count > 0 {
			continue
		}

		if err := db.Transaction(func(tx *gorm.DB) error {
			if err := migration.run(tx); err != nil {
				return fmt.Errorf("run migration %s: %w", migration.id, err)
			}

			record := &LocalSchemaMigration{
				ID:        migration.id,
				Name:      migration.name,
				AppliedAt: time.Now(),
			}
			if err := tx.Create(record).Error; err != nil {
				return fmt.Errorf("insert migration %s record: %w", migration.id, err)
			}
			return nil
		}); err != nil {
			return err
		}

		slog.Info("local migration applied", "id", migration.id, "name", migration.name)
	}

	return nil
}

func backfillConfigurationVersions(tx *gorm.DB) error {
	var configs []LocalConfiguration
	if err := tx.Find(&configs).Error; err != nil {
		return fmt.Errorf("load local configurations for backfill: %w", err)
	}

	for i := range configs {
		cfg := configs[i]
		var versionCount int64
		if err := tx.Model(&LocalConfigurationVersion{}).
			Where("configuration_uuid = ?", cfg.UUID).
			Count(&versionCount).Error; err != nil {
			return fmt.Errorf("count versions for %s: %w", cfg.UUID, err)
		}

		if versionCount == 0 {
			snapshot, err := BuildConfigurationSnapshot(&cfg)
			if err != nil {
				return fmt.Errorf("build initial snapshot for %s: %w", cfg.UUID, err)
			}
			note := "Initial snapshot backfill (v1)"
			version := LocalConfigurationVersion{
				ID:                uuid.NewString(),
				ConfigurationUUID: cfg.UUID,
				VersionNo:         1,
				Data:              snapshot,
				ChangeNote:        &note,
				AppVersion:        "backfill",
				CreatedAt:         chooseNonZeroTime(cfg.CreatedAt, time.Now()),
			}
			if err := tx.Create(&version).Error; err != nil {
				return fmt.Errorf("create v1 backfill for %s: %w", cfg.UUID, err)
			}
		}

		if cfg.CurrentVersionID == nil || *cfg.CurrentVersionID == "" {
			var latest LocalConfigurationVersion
			if err := tx.Where("configuration_uuid = ?", cfg.UUID).
				Order("version_no DESC").
				First(&latest).Error; err != nil {
				return fmt.Errorf("load latest version for %s: %w", cfg.UUID, err)
			}
			if err := tx.Model(&LocalConfiguration{}).
				Where("uuid = ?", cfg.UUID).
				Update("current_version_id", latest.ID).Error; err != nil {
				return fmt.Errorf("set current version for %s: %w", cfg.UUID, err)
			}
		}
	}

	return nil
}

func backfillConfigurationIsActive(tx *gorm.DB) error {
	return tx.Exec("UPDATE local_configurations SET is_active = 1 WHERE is_active IS NULL").Error
}

func backfillProjectsForConfigurations(tx *gorm.DB) error {
	var owners []string
	if err := tx.Model(&LocalConfiguration{}).
		Distinct("original_username").
		Pluck("original_username", &owners).Error; err != nil {
		return fmt.Errorf("load owners for projects backfill: %w", err)
	}

	for _, owner := range owners {
		project, err := ensureDefaultProjectTx(tx, owner)
		if err != nil {
			return err
		}

		if err := tx.Model(&LocalConfiguration{}).
			Where("original_username = ? AND (project_uuid IS NULL OR project_uuid = '')", owner).
			Update("project_uuid", project.UUID).Error; err != nil {
			return fmt.Errorf("assign default project for owner %s: %w", owner, err)
		}
	}

	return nil
}

func ensureDefaultProjectTx(tx *gorm.DB, ownerUsername string) (*LocalProject, error) {
	var project LocalProject
	err := tx.Where("owner_username = ? AND is_system = ? AND name = ?", ownerUsername, true, "Без проекта").
		First(&project).Error
	if err == nil {
		return &project, nil
	}
	if err != nil && !errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, fmt.Errorf("load system project for %s: %w", ownerUsername, err)
	}

	now := time.Now()
	project = LocalProject{
		UUID:          uuid.NewString(),
		OwnerUsername: ownerUsername,
		Name:          "Без проекта",
		IsActive:      true,
		IsSystem:      true,
		CreatedAt:     now,
		UpdatedAt:     now,
		SyncStatus:    "pending",
	}
	if err := tx.Create(&project).Error; err != nil {
		return nil, fmt.Errorf("create system project for %s: %w", ownerUsername, err)
	}

	return &project, nil
}

func backfillConfigurationPricelists(tx *gorm.DB) error {
	var latest LocalPricelist
	if err := tx.Where("source = ?", "estimate").Order("created_at DESC").First(&latest).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			return nil
		}
		return fmt.Errorf("load latest local pricelist: %w", err)
	}

	if err := tx.Model(&LocalConfiguration{}).
		Where("pricelist_id IS NULL").
		Update("pricelist_id", latest.ServerID).Error; err != nil {
		return fmt.Errorf("backfill configuration pricelist_id: %w", err)
	}

	if err := tx.Model(&LocalPricelist{}).Where("1 = 1").Update("is_used", false).Error; err != nil {
		return fmt.Errorf("reset local pricelist usage flags: %w", err)
	}

	if err := tx.Exec(`
		UPDATE local_pricelists
		SET is_used = 1
		WHERE server_id IN (
			SELECT DISTINCT pricelist_id
			FROM local_configurations
			WHERE pricelist_id IS NOT NULL AND is_active = 1
		)
	`).Error; err != nil {
		return fmt.Errorf("recalculate local pricelist usage flags: %w", err)
	}

	return nil
}

func chooseNonZeroTime(candidate time.Time, fallback time.Time) time.Time {
	if candidate.IsZero() {
		return fallback
	}
	return candidate
}

func fixLocalPricelistIndexes(tx *gorm.DB) error {
	type indexRow struct {
		Name   string `gorm:"column:name"`
		Unique int    `gorm:"column:unique"`
	}
	var indexes []indexRow
	if err := tx.Raw("PRAGMA index_list('local_pricelists')").Scan(&indexes).Error; err != nil {
		return fmt.Errorf("list local_pricelists indexes: %w", err)
	}

	for _, idx := range indexes {
		if idx.Unique == 0 {
			continue
		}

		type indexInfoRow struct {
			Name string `gorm:"column:name"`
		}
		var info []indexInfoRow
		if err := tx.Raw(fmt.Sprintf("PRAGMA index_info('%s')", strings.ReplaceAll(idx.Name, "'", "''"))).Scan(&info).Error; err != nil {
			return fmt.Errorf("load index info for %s: %w", idx.Name, err)
		}
		if len(info) != 1 || info[0].Name != "version" {
			continue
		}

		quoted := strings.ReplaceAll(idx.Name, `"`, `""`)
		if err := tx.Exec(fmt.Sprintf(`DROP INDEX IF EXISTS "%s"`, quoted)).Error; err != nil {
			return fmt.Errorf("drop unique version index %s: %w", idx.Name, err)
		}
	}

	if err := tx.Exec(`
		CREATE UNIQUE INDEX IF NOT EXISTS idx_local_pricelists_server_id
		ON local_pricelists(server_id)
	`).Error; err != nil {
		return fmt.Errorf("ensure unique index local_pricelists(server_id): %w", err)
	}

	if err := tx.Exec(`
		CREATE INDEX IF NOT EXISTS idx_local_pricelists_version
		ON local_pricelists(version)
	`).Error; err != nil {
		return fmt.Errorf("ensure index local_pricelists(version): %w", err)
	}

	return nil
}

func backfillLocalPricelistSource(tx *gorm.DB) error {
	if err := tx.Exec(`
		UPDATE local_pricelists
		SET source = 'estimate'
		WHERE source IS NULL OR source = ''
	`).Error; err != nil {
		return fmt.Errorf("backfill local_pricelists.source: %w", err)
	}

	if err := tx.Exec(`
		CREATE INDEX IF NOT EXISTS idx_local_pricelists_source_created_at
		ON local_pricelists(source, created_at DESC)
	`).Error; err != nil {
		return fmt.Errorf("ensure idx_local_pricelists_source_created_at: %w", err)
	}

	return nil
}