package db

import (
	"context"
	"embed"
	"fmt"

	"github.com/golang-migrate/migrate/v4"
	_ "github.com/golang-migrate/migrate/v4/database/postgres"
	"github.com/golang-migrate/migrate/v4/source/iofs"
	"github.com/jackc/pgx/v5/pgxpool"
)

//go:embed migrations/*.sql
var migrationsFS embed.FS

func Connect(ctx context.Context, dsn string) (*pgxpool.Pool, error) {
	pool, err := pgxpool.New(ctx, dsn)
	if err != nil {
		return nil, fmt.Errorf("create pool: %w", err)
	}
	if err := pool.Ping(ctx); err != nil {
		return nil, fmt.Errorf("ping db: %w", err)
	}
	return pool, nil
}

func Migrate(dsn string) error {
	src, err := iofs.New(migrationsFS, "migrations")
	if err != nil {
		return fmt.Errorf("load migrations: %w", err)
	}
	// convert pgx DSN → lib/pq DSN format for migrate
	m, err := migrate.NewWithSourceInstance("iofs", src, "postgres://"+dsnToURL(dsn))
	if err != nil {
		return fmt.Errorf("init migrate: %w", err)
	}
	if err := m.Up(); err != nil && err != migrate.ErrNoChange {
		return fmt.Errorf("run migrations: %w", err)
	}
	return nil
}

// dsnToURL converts "host=... port=... dbname=... user=... password=... sslmode=..."
// to a postgres:// URL for golang-migrate.
func dsnToURL(dsn string) string {
	// pgxpool DSN is already accepted by migrate if we prefix with postgres://
	// Actually golang-migrate accepts the postgres:// URL format.
	// Since our DSN is key=value, we need to convert it.
	// Simplest approach: parse key=value pairs.
	params := map[string]string{}
	for _, part := range splitDSN(dsn) {
		if len(part) == 0 {
			continue
		}
		idx := indexByte(part, '=')
		if idx < 0 {
			continue
		}
		params[part[:idx]] = part[idx+1:]
	}
	host := params["host"]
	port := params["port"]
	if port == "" {
		port = "5432"
	}
	return fmt.Sprintf("%s:%s@%s:%s/%s?sslmode=%s",
		params["user"], params["password"],
		host, port, params["dbname"],
		orDefault(params["sslmode"], "disable"),
	)
}

func splitDSN(dsn string) []string {
	var parts []string
	cur := ""
	for _, r := range dsn {
		if r == ' ' {
			if cur != "" {
				parts = append(parts, cur)
				cur = ""
			}
		} else {
			cur += string(r)
		}
	}
	if cur != "" {
		parts = append(parts, cur)
	}
	return parts
}

func indexByte(s string, b byte) int {
	for i := 0; i < len(s); i++ {
		if s[i] == b {
			return i
		}
	}
	return -1
}

func orDefault(s, def string) string {
	if s == "" {
		return def
	}
	return s
}