package platepdf

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

var svgAttrRE = regexp.MustCompile(`(?i)(\w+)\s*=\s*"([^"]*)"`)

func svgAttrValue(openTag, name string) string {
	for _, m := range svgAttrRE.FindAllStringSubmatch(openTag, -1) {
		if strings.EqualFold(m[1], name) {
			return m[2]
		}
	}
	return ""
}

// svgViewportMM reads width/height from the root <svg> element (supports mm suffix).
func svgViewportMM(data []byte) (widthMM, heightMM float64, err error) {
	s := string(data)
	open := strings.Index(s, "<svg")
	if open < 0 {
		return 0, 0, fmt.Errorf("invalid svg: missing root element")
	}
	tagEnd := strings.Index(s[open:], ">")
	if tagEnd < 0 {
		return 0, 0, fmt.Errorf("invalid svg: malformed root element")
	}
	tagEnd += open

	w, err := parseLengthMM(svgAttrValue(s[open:tagEnd], "width"))
	if err != nil {
		return 0, 0, err
	}
	h, err := parseLengthMM(svgAttrValue(s[open:tagEnd], "height"))
	if err != nil {
		return 0, 0, err
	}
	return w, h, nil
}

func parseLengthMM(s string) (float64, error) {
	s = strings.TrimSpace(s)
	if s == "" {
		return 0, fmt.Errorf("empty length")
	}
	if strings.HasSuffix(s, "mm") {
		return strconv.ParseFloat(strings.TrimSuffix(s, "mm"), 64)
	}
	return strconv.ParseFloat(s, 64)
}