// db-migrate copies all tables and data from a local SQLite database to a
// remote libsql database (e.g. Bunny Database, Turso). It reads the schema
// from sqlite_master, creates tables on the remote, and inserts all rows
// in batches. Generic — works with any SQLite DB (appview, hold, etc.).
//
// Usage:
//
//	go run ./cmd/db-migrate --local /path/to/local.db --remote "libsql://..." --token "..."
//	go run ./cmd/db-migrate --local /path/to/local.db --remote "libsql://..." --token "..." --skip-existing
package main

import (
	"database/sql"
	"flag"
	"fmt"
	"log"
	"os"
	"strings"
	"time"

	_ "github.com/tursodatabase/go-libsql"
)

func main() {
	localPath := flag.String("local", "", "Path to local SQLite database file")
	remoteURL := flag.String("remote", "", "Remote libsql URL (libsql://...)")
	authToken := flag.String("token", "", "Auth token for remote database")
	skipExisting := flag.Bool("skip-existing", false, "Skip tables that already have data on remote")
	batchSize := flag.Int("batch-size", 100, "Number of rows per INSERT batch")
	dryRun := flag.Bool("dry-run", false, "Show what would be migrated without writing")
	flag.Parse()

	if *localPath == "" || *remoteURL == "" || *authToken == "" {
		flag.Usage()
		os.Exit(1)
	}

	// Open local database read-only
	localDSN := *localPath
	if !strings.HasPrefix(localDSN, "file:") {
		localDSN = "file:" + localDSN
	}
	localDSN += "?mode=ro"

	localDB, err := sql.Open("libsql", localDSN)
	if err != nil {
		log.Fatalf("Failed to open local database: %v", err)
	}
	defer localDB.Close()

	if err := localDB.Ping(); err != nil {
		log.Fatalf("Failed to ping local database: %v", err)
	}

	// Open remote database
	remoteDSN := fmt.Sprintf("%s?authToken=%s", *remoteURL, *authToken)
	remoteDB, err := sql.Open("libsql", remoteDSN)
	if err != nil {
		log.Fatalf("Failed to open remote database: %v", err)
	}
	defer remoteDB.Close()

	if err := remoteDB.Ping(); err != nil {
		log.Fatalf("Failed to ping remote database: %v", err)
	}
	// Get all user tables from local
	tables, err := getTables(localDB)
	if err != nil {
		log.Fatalf("Failed to list tables: %v", err)
	}

	if len(tables) == 0 {
		log.Println("No tables found in local database")
		return
	}

	fmt.Printf("Found %d tables to migrate\n\n", len(tables))

	start := time.Now()

	if !*dryRun {
		// Phase 1: Create all tables first so FK references resolve
		fmt.Println("Creating tables...")
		for _, t := range tables {
			if err := createTable(remoteDB, t); err != nil {
				log.Fatalf("Failed to create table %s: %v", t.name, err)
			}
		}
		fmt.Println()
	}

	// Phase 2: Copy data
	fmt.Println("Migrating data...")
	totalRows := 0
	for _, t := range tables {
		count, err := migrateTable(localDB, remoteDB, t, *batchSize, *skipExisting, *dryRun)
		if err != nil {
			log.Fatalf("Failed to migrate table %s: %v", t.name, err)
		}
		totalRows += count
	}

	if !*dryRun {
		// Phase 3: Create indexes after data is loaded (faster than indexing during insert)
		fmt.Println("\nCreating indexes...")
		for _, t := range tables {
			if err := createIndexes(localDB, remoteDB, t.name); err != nil {
				log.Fatalf("Failed to create indexes for %s: %v", t.name, err)
			}
		}

	}

	fmt.Printf("\nDone. %d total rows across %d tables in %s\n", totalRows, len(tables), time.Since(start).Round(time.Millisecond))
	if *dryRun {
		fmt.Println("(dry run — nothing was written)")
	}
}

type tableInfo struct {
	name string
	ddl  string
}

func getTables(db *sql.DB) ([]tableInfo, error) {
	rows, err := db.Query(`
		SELECT name, sql FROM sqlite_master
		WHERE type = 'table'
		AND name NOT LIKE 'sqlite_%'
		AND name NOT LIKE '_litestream_%'
		AND name NOT LIKE 'libsql_%'
		ORDER BY name
	`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var tables []tableInfo
	for rows.Next() {
		var t tableInfo
		var ddl sql.NullString
		if err := rows.Scan(&t.name, &ddl); err != nil {
			return nil, err
		}
		if ddl.Valid {
			t.ddl = ddl.String
		}
		tables = append(tables, t)
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	// Sort tables so those referenced by foreign keys come first.
	// Tables with FK references depend on other tables existing and
	// having data, so we insert referenced tables first.
	return topoSortTables(db, tables)
}

// topoSortTables orders tables so that referenced (parent) tables come before
// tables that reference them via foreign keys.
func topoSortTables(db *sql.DB, tables []tableInfo) ([]tableInfo, error) {
	byName := make(map[string]tableInfo, len(tables))
	for _, t := range tables {
		byName[t.name] = t
	}

	// Build dependency graph: table -> tables it references
	deps := make(map[string][]string)
	for _, t := range tables {
		fkRows, err := db.Query(fmt.Sprintf("PRAGMA foreign_key_list([%s])", t.name))
		if err != nil {
			// PRAGMA might not return rows for tables without FKs
			continue
		}
		seen := make(map[string]bool)
		for fkRows.Next() {
			var id, seq int
			var table, from, to, onUpdate, onDelete, match string
			if err := fkRows.Scan(&id, &seq, &table, &from, &to, &onUpdate, &onDelete, &match); err != nil {
				fkRows.Close()
				return nil, err
			}
			if !seen[table] {
				deps[t.name] = append(deps[t.name], table)
				seen[table] = true
			}
		}
		fkRows.Close()
	}

	// Topological sort (Kahn's algorithm)
	visited := make(map[string]bool)
	var sorted []tableInfo
	var visit func(name string)
	visit = func(name string) {
		if visited[name] {
			return
		}
		visited[name] = true
		for _, dep := range deps[name] {
			visit(dep)
		}
		if t, ok := byName[name]; ok {
			sorted = append(sorted, t)
		}
	}
	for _, t := range tables {
		visit(t.name)
	}
	return sorted, nil
}

func getIndexes(db *sql.DB, tableName string) ([]string, error) {
	rows, err := db.Query(`
		SELECT sql FROM sqlite_master
		WHERE type = 'index'
		AND tbl_name = ?
		AND sql IS NOT NULL
	`, tableName)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

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

func createTable(remoteDB *sql.DB, t tableInfo) error {
	if t.ddl == "" {
		return nil
	}
	ddl := t.ddl
	if !strings.Contains(strings.ToUpper(ddl), "IF NOT EXISTS") {
		ddl = strings.Replace(ddl, "CREATE TABLE", "CREATE TABLE IF NOT EXISTS", 1)
	}
	if _, err := remoteDB.Exec(ddl); err != nil {
		return fmt.Errorf("create table %s: %w", t.name, err)
	}
	fmt.Printf("  %s\n", t.name)
	return nil
}

func createIndexes(localDB, remoteDB *sql.DB, tableName string) error {
	indexes, err := getIndexes(localDB, tableName)
	if err != nil {
		return err
	}
	for _, idx := range indexes {
		ddl := idx
		if !strings.Contains(strings.ToUpper(ddl), "IF NOT EXISTS") {
			ddl = strings.Replace(ddl, "CREATE INDEX", "CREATE INDEX IF NOT EXISTS", 1)
			ddl = strings.Replace(ddl, "CREATE UNIQUE INDEX", "CREATE UNIQUE INDEX IF NOT EXISTS", 1)
		}
		if _, err := remoteDB.Exec(ddl); err != nil {
			return fmt.Errorf("create index on %s: %w", tableName, err)
		}
	}
	if len(indexes) > 0 {
		fmt.Printf("  %s: %d indexes\n", tableName, len(indexes))
	}
	return nil
}

func migrateTable(localDB, remoteDB *sql.DB, t tableInfo, batchSize int, skipExisting, dryRun bool) (int, error) {
	var localCount int
	if err := localDB.QueryRow(fmt.Sprintf("SELECT COUNT(*) FROM [%s]", t.name)).Scan(&localCount); err != nil {
		return 0, fmt.Errorf("count local rows: %w", err)
	}

	if localCount == 0 {
		fmt.Printf("  %-30s %6d rows (empty)\n", t.name, 0)
		return 0, nil
	}

	if dryRun {
		fmt.Printf("  %-30s %6d rows (would migrate)\n", t.name, localCount)
		return localCount, nil
	}

	if skipExisting {
		var remoteCount int
		if err := remoteDB.QueryRow(fmt.Sprintf("SELECT COUNT(*) FROM [%s]", t.name)).Scan(&remoteCount); err != nil {
			return 0, fmt.Errorf("count remote rows: %w", err)
		}
		if remoteCount > 0 {
			fmt.Printf("  %-30s %6d rows (skipped, %d on remote)\n", t.name, localCount, remoteCount)
			return 0, nil
		}
	}

	rows, err := localDB.Query(fmt.Sprintf("SELECT * FROM [%s]", t.name))
	if err != nil {
		return 0, fmt.Errorf("select: %w", err)
	}
	defer rows.Close()

	cols, err := rows.Columns()
	if err != nil {
		return 0, fmt.Errorf("columns: %w", err)
	}

	placeholders := make([]string, len(cols))
	quotedCols := make([]string, len(cols))
	for i, c := range cols {
		placeholders[i] = "?"
		quotedCols[i] = fmt.Sprintf("[%s]", c)
	}
	insertPrefix := fmt.Sprintf("INSERT INTO [%s] (%s) VALUES ", t.name, strings.Join(quotedCols, ", "))
	rowPlaceholder := "(" + strings.Join(placeholders, ", ") + ")"

	inserted := 0
	batch := make([][]any, 0, batchSize)

	for rows.Next() {
		vals := make([]any, len(cols))
		ptrs := make([]any, len(cols))
		for i := range vals {
			ptrs[i] = &vals[i]
		}
		if err := rows.Scan(ptrs...); err != nil {
			return 0, fmt.Errorf("scan: %w", err)
		}
		batch = append(batch, vals)

		if len(batch) >= batchSize {
			if err := insertBatch(remoteDB, insertPrefix, rowPlaceholder, batch); err != nil {
				return 0, fmt.Errorf("insert batch at row %d: %w", inserted, err)
			}
			inserted += len(batch)
			batch = batch[:0]
		}
	}

	if len(batch) > 0 {
		if err := insertBatch(remoteDB, insertPrefix, rowPlaceholder, batch); err != nil {
			return 0, fmt.Errorf("insert final batch: %w", err)
		}
		inserted += len(batch)
	}

	if err := rows.Err(); err != nil {
		return 0, fmt.Errorf("rows iteration: %w", err)
	}

	fmt.Printf("  %-30s %6d rows migrated\n", t.name, inserted)
	return inserted, nil
}

func insertBatch(db *sql.DB, prefix, rowPlaceholder string, batch [][]any) error {
	if len(batch) == 0 {
		return nil
	}

	placeholders := make([]string, len(batch))
	var args []any
	for i, row := range batch {
		placeholders[i] = rowPlaceholder
		args = append(args, row...)
	}

	query := prefix + strings.Join(placeholders, ", ")
	_, err := db.Exec(query, args...)
	return err
}