package web

import (
	"fmt"
	"regexp"
	"strings"
	"unicode/utf8"

	qrcode "github.com/skip2/go-qrcode"
)

var validAccount = regexp.MustCompile(`^[A-Z]{2}\d{2,34}$|^\d{1,16}/\d{4}$`)

// BuildSPD builds a Czech QR Platba SPD string, matching Python's qr_code handler.
// Invalid account falls back to defaultAccount.
// Amount is clamped to [0, 10_000_000]; non-numeric input becomes "0.00".
// Message is truncated to 60 runes and stripped of '*' characters.
func BuildSPD(account, amount, message, defaultAccount string) string {
	if !validAccount.MatchString(account) {
		account = defaultAccount
	}

	var amtStr string
	var f float64
	if _, err := fmt.Sscanf(amount, "%f", &f); err != nil || f < 0 || f > 10_000_000 {
		amtStr = "0.00"
	} else {
		amtStr = fmt.Sprintf("%.2f", f)
	}

	if utf8.RuneCountInString(message) > 60 {
		runes := []rune(message)
		message = string(runes[:60])
	}
	message = strings.ReplaceAll(message, "*", "")

	var accStr string
	if parts := strings.SplitN(account, "/", 2); len(parts) == 2 {
		accStr = parts[0] + "*BC:" + parts[1]
	} else {
		accStr = account
	}

	return fmt.Sprintf("SPD*1.0*ACC:%s*AM:%s*CC:CZK*MSG:%s", accStr, amtStr, message)
}

// RenderQRCode encodes payload as a PNG QR code (256×256, error correction Medium).
func RenderQRCode(payload string) ([]byte, error) {
	return qrcode.Encode(payload, qrcode.Medium, 256)
}