package db

import (
	"context"
	"database/sql"
	"fmt"
	"log/slog"
	"sort"
	"strconv"
	"strings"

	"github.com/jmoiron/sqlx"
	_ "modernc.org/sqlite"
)

// SQLiteImportStats summarizes a one-shot SQLite-to-Postgres import.
type SQLiteImportStats struct {
	SourceDSN      string
	TablesImported int
	TablesSkipped  int
	RowsImported   int64
}

type postgresColumn struct {
	Name     string `db:"column_name"`
	DataType string `db:"data_type"`
}

type importColumn struct {
	SourceName      string
	DestinationName string
	DestinationType string
}

// ImportSQLiteIntoPostgres imports all supported tables from a SQLite database into a configured Postgres database.
func ImportSQLiteIntoPostgres(ctx context.Context, logger *slog.Logger, destination *sqlx.DB, sqliteDSN string) (SQLiteImportStats, error) {
	stats := SQLiteImportStats{SourceDSN: strings.TrimSpace(sqliteDSN)}
	if ctx == nil {
		ctx = context.Background()
	}
	if logger == nil {
		logger = slog.Default()
	}
	if destination == nil {
		return stats, fmt.Errorf("destination database is nil")
	}
	driver := strings.ToLower(strings.TrimSpace(destination.DriverName()))
	if driver != "pgx" && driver != "postgres" {
		return stats, fmt.Errorf("sqlite import requires postgres destination; got %s", destination.DriverName())
	}
	if strings.TrimSpace(sqliteDSN) == "" {
		return stats, fmt.Errorf("sqlite source path/DSN is required")
	}

	source, err := sqlx.Open("sqlite", normalizeSqliteDSN(sqliteDSN))
	if err != nil {
		return stats, fmt.Errorf("failed to open sqlite source: %w", err)
	}
	defer source.Close()

	if err := source.PingContext(ctx); err != nil {
		return stats, fmt.Errorf("failed to connect to sqlite source: %w", err)
	}

	tables, err := listSQLiteUserTables(ctx, source)
	if err != nil {
		return stats, err
	}
	sort.Strings(tables)
	if len(tables) == 0 {
		logger.Warn("sqlite import source has no user tables")
		return stats, nil
	}

	importTables := make([]string, 0, len(tables))
	for _, tableName := range tables {
		if shouldSkipSQLiteImportTable(tableName) {
			stats.TablesSkipped++
			continue
		}
		if err := ensureDestinationImportTable(ctx, destination, tableName); err != nil {
			return stats, err
		}
		importTables = append(importTables, tableName)
	}
	if len(importTables) == 0 {
		logger.Warn("sqlite import found no tables to import after filtering")
		return stats, nil
	}

	tx, err := destination.BeginTxx(ctx, nil)
	if err != nil {
		return stats, fmt.Errorf("failed to start postgres import transaction: %w", err)
	}
	defer tx.Rollback()

	for _, tableName := range importTables {
		rowsCopied, err := copySQLiteTableIntoPostgres(ctx, source, tx, tableName)
		if err != nil {
			return stats, err
		}
		stats.TablesImported++
		stats.RowsImported += rowsCopied
		logger.Info("sqlite import copied table", "table", tableName, "rows", rowsCopied)
	}

	if err := tx.Commit(); err != nil {
		return stats, fmt.Errorf("failed to commit sqlite import transaction: %w", err)
	}

	return stats, nil
}

func listSQLiteUserTables(ctx context.Context, source *sqlx.DB) ([]string, error) {
	rows, err := source.QueryxContext(ctx, `
SELECT name
FROM sqlite_master
WHERE type = 'table'
ORDER BY name
`)
	if err != nil {
		return nil, fmt.Errorf("failed to list sqlite tables: %w", err)
	}
	defer rows.Close()

	var tables []string
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, fmt.Errorf("failed to scan sqlite table name: %w", err)
		}
		tables = append(tables, name)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("failed reading sqlite table names: %w", err)
	}

	return tables, nil
}

func shouldSkipSQLiteImportTable(tableName string) bool {
	normalized := strings.ToLower(strings.TrimSpace(tableName))
	if normalized == "" {
		return true
	}
	if strings.HasPrefix(normalized, "sqlite_") {
		return true
	}
	// Destination migration state is managed independently by goose.
	if normalized == "goose_db_version" {
		return true
	}
	return false
}

func ensureDestinationImportTable(ctx context.Context, destination *sqlx.DB, tableName string) error {
	if TableExists(ctx, destination, tableName) {
		return nil
	}
	switch {
	case strings.HasPrefix(tableName, "inventory_hourly_"):
		return EnsureSnapshotTable(ctx, destination, tableName)
	case strings.HasPrefix(tableName, "inventory_daily_summary_"), strings.HasPrefix(tableName, "inventory_monthly_summary_"):
		return EnsureSummaryTable(ctx, destination, tableName)
	case tableName == "snapshot_runs":
		return EnsureSnapshotRunTable(ctx, destination)
	case tableName == "vm_hourly_stats":
		return EnsureVmHourlyStats(ctx, destination)
	case tableName == "vm_lifecycle_cache":
		return EnsureVmLifecycleCache(ctx, destination)
	case tableName == "vm_daily_rollup":
		return EnsureVmDailyRollup(ctx, destination)
	case tableName == "vm_identity", tableName == "vm_renames":
		return EnsureVmIdentityTables(ctx, destination)
	case tableName == "vcenter_totals":
		return EnsureVcenterTotalsTable(ctx, destination)
	case tableName == "vcenter_latest_totals":
		return EnsureVcenterLatestTotalsTable(ctx, destination)
	case tableName == "vcenter_aggregate_totals":
		return EnsureVcenterAggregateTotalsTable(ctx, destination)
	default:
		return fmt.Errorf("source table %q does not exist in postgres and cannot be auto-created", tableName)
	}
}

func copySQLiteTableIntoPostgres(ctx context.Context, source *sqlx.DB, destinationTX *sqlx.Tx, tableName string) (int64, error) {
	sourceColumns, err := listSQLiteTableColumns(ctx, source, tableName)
	if err != nil {
		return 0, err
	}
	destinationColumns, err := listPostgresTableColumns(ctx, destinationTX, tableName)
	if err != nil {
		return 0, err
	}
	columns := intersectImportColumns(sourceColumns, destinationColumns)
	if len(columns) == 0 {
		return 0, fmt.Errorf("no overlapping columns between sqlite and postgres table %q", tableName)
	}

	if _, err := destinationTX.ExecContext(ctx, fmt.Sprintf(`TRUNCATE TABLE %s RESTART IDENTITY CASCADE`, quoteIdentifier(tableName))); err != nil {
		return 0, fmt.Errorf("failed to truncate destination table %q: %w", tableName, err)
	}

	sourceColumnNames := make([]string, 0, len(columns))
	destinationColumnNames := make([]string, 0, len(columns))
	for _, col := range columns {
		sourceColumnNames = append(sourceColumnNames, col.SourceName)
		destinationColumnNames = append(destinationColumnNames, col.DestinationName)
	}

	selectSQL := fmt.Sprintf(
		`SELECT %s FROM %s`,
		joinQuotedIdentifiers(sourceColumnNames),
		quoteIdentifier(tableName),
	)
	rows, err := source.QueryxContext(ctx, selectSQL)
	if err != nil {
		return 0, fmt.Errorf("failed to query source table %q: %w", tableName, err)
	}
	defer rows.Close()

	insertSQL := fmt.Sprintf(
		`INSERT INTO %s (%s) VALUES (%s)`,
		quoteIdentifier(tableName),
		joinQuotedIdentifiers(destinationColumnNames),
		postgresPlaceholders(len(columns)),
	)
	stmt, err := destinationTX.PreparexContext(ctx, insertSQL)
	if err != nil {
		return 0, fmt.Errorf("failed to prepare insert for table %q: %w", tableName, err)
	}
	defer stmt.Close()

	var rowsCopied int64
	for rows.Next() {
		rawValues := make([]interface{}, len(columns))
		scanTargets := make([]interface{}, len(columns))
		for i := range rawValues {
			scanTargets[i] = &rawValues[i]
		}
		if err := rows.Scan(scanTargets...); err != nil {
			return rowsCopied, fmt.Errorf("failed to scan row from sqlite table %q: %w", tableName, err)
		}
		args := make([]interface{}, len(columns))
		for i, col := range columns {
			args[i] = coerceSQLiteValueForPostgres(rawValues[i], col.DestinationType)
		}
		if _, err := stmt.ExecContext(ctx, args...); err != nil {
			return rowsCopied, fmt.Errorf("failed to insert row into postgres table %q: %w", tableName, err)
		}
		rowsCopied++
	}
	if err := rows.Err(); err != nil {
		return rowsCopied, fmt.Errorf("failed to read rows from sqlite table %q: %w", tableName, err)
	}

	if err := resetPostgresSerialColumns(ctx, destinationTX, tableName); err != nil {
		return rowsCopied, fmt.Errorf("failed to reset postgres sequences for table %q: %w", tableName, err)
	}
	return rowsCopied, nil
}

func listSQLiteTableColumns(ctx context.Context, source *sqlx.DB, tableName string) ([]string, error) {
	rows, err := source.QueryxContext(ctx, fmt.Sprintf(`PRAGMA table_info(%s)`, quoteIdentifier(tableName)))
	if err != nil {
		return nil, fmt.Errorf("failed to inspect sqlite table %q: %w", tableName, err)
	}
	defer rows.Close()

	columns := make([]string, 0)
	for rows.Next() {
		var (
			cid        int
			name       string
			columnType string
			notNull    int
			defaultVal sql.NullString
			pk         int
		)
		if err := rows.Scan(&cid, &name, &columnType, &notNull, &defaultVal, &pk); err != nil {
			return nil, fmt.Errorf("failed to scan sqlite columns for %q: %w", tableName, err)
		}
		columns = append(columns, name)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("failed reading sqlite columns for %q: %w", tableName, err)
	}
	return columns, nil
}

func listPostgresTableColumns(ctx context.Context, destinationTX *sqlx.Tx, tableName string) ([]postgresColumn, error) {
	var columns []postgresColumn
	if err := destinationTX.SelectContext(ctx, &columns, `
SELECT column_name, data_type
FROM information_schema.columns
WHERE table_schema = 'public' AND table_name = $1
ORDER BY ordinal_position
`, tableName); err != nil {
		return nil, fmt.Errorf("failed to inspect postgres columns for %q: %w", tableName, err)
	}
	if len(columns) == 0 {
		return nil, fmt.Errorf("postgres table %q has no columns", tableName)
	}
	return columns, nil
}

func intersectImportColumns(sourceColumns []string, destinationColumns []postgresColumn) []importColumn {
	sourceByLower := make(map[string]string, len(sourceColumns))
	for _, sourceColumn := range sourceColumns {
		sourceByLower[strings.ToLower(sourceColumn)] = sourceColumn
	}

	columns := make([]importColumn, 0, len(destinationColumns))
	for _, destinationColumn := range destinationColumns {
		sourceColumn, exists := sourceByLower[strings.ToLower(destinationColumn.Name)]
		if !exists {
			continue
		}
		columns = append(columns, importColumn{
			SourceName:      sourceColumn,
			DestinationName: destinationColumn.Name,
			DestinationType: destinationColumn.DataType,
		})
	}
	return columns
}

func resetPostgresSerialColumns(ctx context.Context, destinationTX *sqlx.Tx, tableName string) error {
	type serialColumn struct {
		Name string `db:"column_name"`
	}
	var columns []serialColumn
	if err := destinationTX.SelectContext(ctx, &columns, `
SELECT column_name
FROM information_schema.columns
WHERE table_schema = 'public'
  AND table_name = $1
  AND column_default LIKE 'nextval(%'
ORDER BY ordinal_position
`, tableName); err != nil {
		return err
	}

	tableRef := fmt.Sprintf("public.%s", quoteIdentifier(tableName))
	for _, column := range columns {
		var sequence sql.NullString
		if err := destinationTX.GetContext(ctx, &sequence, `SELECT pg_get_serial_sequence($1, $2)`, tableRef, column.Name); err != nil {
			return err
		}
		if !sequence.Valid || strings.TrimSpace(sequence.String) == "" {
			continue
		}
		setvalSQL := fmt.Sprintf(
			`SELECT setval($1, COALESCE((SELECT MAX(%s) FROM %s), 0) + 1, false)`,
			quoteIdentifier(column.Name),
			quoteIdentifier(tableName),
		)
		if _, err := destinationTX.ExecContext(ctx, setvalSQL, sequence.String); err != nil {
			return err
		}
	}
	return nil
}

func coerceSQLiteValueForPostgres(value interface{}, destinationType string) interface{} {
	if value == nil {
		return nil
	}
	destinationType = strings.ToLower(strings.TrimSpace(destinationType))

	if bytesValue, ok := value.([]byte); ok && destinationType != "bytea" {
		value = string(bytesValue)
	}

	if destinationType == "boolean" {
		if boolValue, ok := coerceBoolValue(value); ok {
			return boolValue
		}
	}

	return value
}

func coerceBoolValue(value interface{}) (bool, bool) {
	switch v := value.(type) {
	case bool:
		return v, true
	case int64:
		return v != 0, true
	case int:
		return v != 0, true
	case float64:
		return v != 0, true
	case string:
		return parseBoolString(v)
	case []byte:
		return parseBoolString(string(v))
	default:
		return false, false
	}
}

func parseBoolString(raw string) (bool, bool) {
	normalized := strings.ToLower(strings.TrimSpace(raw))
	switch normalized {
	case "1", "t", "true", "y", "yes", "on":
		return true, true
	case "0", "f", "false", "n", "no", "off":
		return false, true
	}
	if parsedInt, err := strconv.ParseInt(normalized, 10, 64); err == nil {
		return parsedInt != 0, true
	}
	return false, false
}

func quoteIdentifier(identifier string) string {
	return `"` + strings.ReplaceAll(identifier, `"`, `""`) + `"`
}

func joinQuotedIdentifiers(identifiers []string) string {
	if len(identifiers) == 0 {
		return ""
	}
	quoted := make([]string, 0, len(identifiers))
	for _, identifier := range identifiers {
		quoted = append(quoted, quoteIdentifier(identifier))
	}
	return strings.Join(quoted, ", ")
}

func postgresPlaceholders(count int) string {
	if count <= 0 {
		return ""
	}
	placeholders := make([]string, 0, count)
	for i := 1; i <= count; i++ {
		placeholders = append(placeholders, fmt.Sprintf("$%d", i))
	}
	return strings.Join(placeholders, ", ")
}