package main

import (
	"database/sql"
	"encoding/hex"
	"flag"
	"fmt"
	"hr_receiver/config"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"
)

var defaultTables = []string{"users", "user_region_bindings", "kindergartens"}

func main() {
	var (
		tablesArg string
		outputArg string
		schemaArg string
	)

	flag.StringVar(&tablesArg, "tables", "", "Comma-separated table names to export. Default: users,user_region_bindings,kindergartens")
	flag.StringVar(&outputArg, "output", "", "Output .sql file path. Default: export_<timestamp>.sql")
	flag.StringVar(&schemaArg, "schema", "public", "Database schema name")
	flag.Parse()

	tables := resolveTables(tablesArg, flag.Args())
	if len(tables) == 0 {
		fmt.Fprintln(os.Stderr, "no tables specified")
		os.Exit(1)
	}

	config.InitConfig()
	config.ConnectDB()

	outputPath := outputArg
	if outputPath == "" {
		outputPath = fmt.Sprintf("export_%s.sql", time.Now().Format("20060102_150405"))
	}

	if err := os.MkdirAll(filepath.Dir(outputPath), 0o755); err != nil && filepath.Dir(outputPath) != "." {
		fmt.Fprintf(os.Stderr, "create output directory failed: %v\n", err)
		os.Exit(1)
	}

	file, err := os.Create(outputPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "create output file failed: %v\n", err)
		os.Exit(1)
	}
	defer file.Close()

	if err := exportTables(file, schemaArg, tables); err != nil {
		fmt.Fprintf(os.Stderr, "export failed: %v\n", err)
		os.Exit(1)
	}

	fmt.Printf("exported %d table(s) to %s\n", len(tables), outputPath)
}

func resolveTables(tablesArg string, positional []string) []string {
	if len(positional) > 0 {
		return dedupeNonEmpty(positional)
	}
	if strings.TrimSpace(tablesArg) == "" {
		return append([]string(nil), defaultTables...)
	}
	return dedupeNonEmpty(strings.Split(tablesArg, ","))
}

func dedupeNonEmpty(items []string) []string {
	result := make([]string, 0, len(items))
	seen := make(map[string]struct{}, len(items))
	for _, item := range items {
		value := strings.TrimSpace(item)
		if value == "" {
			continue
		}
		if _, ok := seen[value]; ok {
			continue
		}
		seen[value] = struct{}{}
		result = append(result, value)
	}
	return result
}

func exportTables(w io.Writer, schema string, tables []string) error {
	db, err := config.DB.DB()
	if err != nil {
		return err
	}

	header := []string{
		"-- Generated by cmd/export_sql",
		fmt.Sprintf("-- Time: %s", time.Now().Format(time.RFC3339)),
		fmt.Sprintf("-- Schema: %s", schema),
		fmt.Sprintf("-- Tables: %s", strings.Join(tables, ", ")),
		"",
	}
	if _, err := io.WriteString(w, strings.Join(header, "\n")); err != nil {
		return err
	}

	for _, table := range tables {
		columns, err := getColumns(db, schema, table)
		if err != nil {
			return fmt.Errorf("read columns for %s: %w", table, err)
		}
		if len(columns) == 0 {
			return fmt.Errorf("table %s not found or has no columns", table)
		}

		orderBy, err := getPrimaryKeyColumns(db, schema, table)
		if err != nil {
			return fmt.Errorf("read primary key for %s: %w", table, err)
		}

		if _, err := fmt.Fprintf(w, "-- Table: %s\n", table); err != nil {
			return err
		}

		if err := exportTableData(w, db, schema, table, columns, orderBy); err != nil {
			return err
		}

		if _, err := io.WriteString(w, "\n"); err != nil {
			return err
		}
	}

	return nil
}

func getColumns(db *sql.DB, schema, table string) ([]string, error) {
	const query = `
SELECT column_name
FROM information_schema.columns
WHERE table_schema = $1 AND table_name = $2
ORDER BY ordinal_position
`
	rows, err := db.Query(query, schema, table)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var columns []string
	for rows.Next() {
		var column string
		if err := rows.Scan(&column); err != nil {
			return nil, err
		}
		columns = append(columns, column)
	}
	return columns, rows.Err()
}

func getPrimaryKeyColumns(db *sql.DB, schema, table string) ([]string, error) {
	const query = `
SELECT a.attname
FROM pg_index i
JOIN pg_class c ON c.oid = i.indrelid
JOIN pg_namespace n ON n.oid = c.relnamespace
JOIN pg_attribute a ON a.attrelid = c.oid AND a.attnum = ANY(i.indkey)
WHERE i.indisprimary
  AND n.nspname = $1
  AND c.relname = $2
ORDER BY array_position(i.indkey, a.attnum)
`
	rows, err := db.Query(query, schema, table)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var columns []string
	for rows.Next() {
		var column string
		if err := rows.Scan(&column); err != nil {
			return nil, err
		}
		columns = append(columns, column)
	}
	return columns, rows.Err()
}

func exportTableData(w io.Writer, db *sql.DB, schema, table string, columns, orderBy []string) error {
	query := fmt.Sprintf(
		`SELECT %s FROM %s.%s`,
		joinIdentifiers(columns),
		quoteIdentifier(schema),
		quoteIdentifier(table),
	)
	if len(orderBy) > 0 {
		query += " ORDER BY " + joinIdentifiers(orderBy)
	}

	rows, err := db.Query(query)
	if err != nil {
		return fmt.Errorf("query rows for %s: %w", table, err)
	}
	defer rows.Close()

	values := make([]any, len(columns))
	scanTargets := make([]any, len(columns))
	for i := range values {
		scanTargets[i] = &values[i]
	}

	rowCount := 0
	for rows.Next() {
		clear(values)
		if err := rows.Scan(scanTargets...); err != nil {
			return fmt.Errorf("scan row for %s: %w", table, err)
		}

		literals := make([]string, len(columns))
		for i, value := range values {
			literals[i] = toSQLLiteral(value)
		}

		stmt := fmt.Sprintf(
			"INSERT INTO %s.%s (%s) VALUES (%s);\n",
			quoteIdentifier(schema),
			quoteIdentifier(table),
			joinIdentifiers(columns),
			strings.Join(literals, ", "),
		)
		if _, err := io.WriteString(w, stmt); err != nil {
			return err
		}
		rowCount++
	}
	if err := rows.Err(); err != nil {
		return err
	}

	if rowCount == 0 {
		_, err := io.WriteString(w, "-- no rows\n")
		return err
	}

	return nil
}

func joinIdentifiers(columns []string) string {
	quoted := make([]string, len(columns))
	for i, column := range columns {
		quoted[i] = quoteIdentifier(column)
	}
	return strings.Join(quoted, ", ")
}

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

func toSQLLiteral(value any) string {
	switch v := value.(type) {
	case nil:
		return "NULL"
	case string:
		return quoteString(v)
	case []byte:
		if len(v) == 0 {
			return quoteString("")
		}
		if isPrintableUTF8(v) {
			return quoteString(string(v))
		}
		return quoteString(`\x` + hex.EncodeToString(v))
	case bool:
		if v {
			return "TRUE"
		}
		return "FALSE"
	case int:
		return fmt.Sprintf("%d", v)
	case int8:
		return fmt.Sprintf("%d", v)
	case int16:
		return fmt.Sprintf("%d", v)
	case int32:
		return fmt.Sprintf("%d", v)
	case int64:
		return fmt.Sprintf("%d", v)
	case uint:
		return fmt.Sprintf("%d", v)
	case uint8:
		return fmt.Sprintf("%d", v)
	case uint16:
		return fmt.Sprintf("%d", v)
	case uint32:
		return fmt.Sprintf("%d", v)
	case uint64:
		return fmt.Sprintf("%d", v)
	case float32:
		return fmt.Sprintf("%g", v)
	case float64:
		return fmt.Sprintf("%g", v)
	case time.Time:
		return quoteString(v.Format(time.RFC3339Nano))
	default:
		return quoteString(fmt.Sprint(v))
	}
}

func quoteString(value string) string {
	return "'" + strings.ReplaceAll(value, "'", "''") + "'"
}

func isPrintableUTF8(data []byte) bool {
	for _, b := range data {
		if b == 0 {
			return false
		}
	}
	return true
}