package main

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

	"github.com/jackc/pgx/v4"
	_ "modernc.org/sqlite"
)

func main() {
	pgConn := flag.String("pg", "", "postgres connection string (e.g. postgres://user:pass@host:5432/kls?sslmode=verify-full)")
	out := flag.String("out", "kls.db", "output sqlite file path")
	flag.Parse()

	if *pgConn == "" {
		fmt.Fprintln(os.Stderr, "usage: pg2sqlite -pg <postgres-url> [-out kls.db]")
		os.Exit(1)
	}

	ctx := context.Background()

	// Connect to Postgres
	pg, err := pgx.Connect(ctx, *pgConn)
	if err != nil {
		log.Fatalf("postgres: %v", err)
	}
	defer pg.Close(ctx)

	// Open SQLite
	os.Remove(*out)
	lite, err := sql.Open("sqlite", *out)
	if err != nil {
		log.Fatalf("sqlite open: %v", err)
	}
	defer lite.Close()

	_, err = lite.ExecContext(ctx, `CREATE TABLE urls (
		id         TEXT PRIMARY KEY,
		url        TEXT NOT NULL,
		nurl       TEXT NOT NULL,
		short      TEXT NOT NULL UNIQUE,
		created_at TEXT NOT NULL
	)`)
	if err != nil {
		log.Fatalf("sqlite create table: %v", err)
	}

	// Read from Postgres
	rows, err := pg.Query(ctx, `SELECT id, url, nurl, short, created_at FROM urls ORDER BY created_at`)
	if err != nil {
		log.Fatalf("postgres query: %v", err)
	}
	defer rows.Close()

	tx, err := lite.BeginTx(ctx, nil)
	if err != nil {
		log.Fatalf("sqlite begin: %v", err)
	}

	stmt, err := tx.PrepareContext(ctx, `INSERT INTO urls (id, url, nurl, short, created_at) VALUES (?, ?, ?, ?, ?)`)
	if err != nil {
		log.Fatalf("sqlite prepare: %v", err)
	}
	defer stmt.Close()

	var n int
	for rows.Next() {
		var id, url, nurl, short string
		var createdAt time.Time
		if err := rows.Scan(&id, &url, &nurl, &short, &createdAt); err != nil {
			log.Fatalf("postgres scan: %v", err)
		}

		if _, err := stmt.ExecContext(ctx, id, url, nurl, short, createdAt.Format(time.RFC3339)); err != nil {
			log.Fatalf("sqlite insert: %v", err)
		}
		n++
	}
	if err := rows.Err(); err != nil {
		log.Fatalf("postgres rows: %v", err)
	}

	if err := tx.Commit(); err != nil {
		log.Fatalf("sqlite commit: %v", err)
	}

	log.Printf("migrated %d rows to %s", n, *out)
}