package human

import (
	"net/url"
	"strings"
)

// GetURLFromHTML returns the [url.URL] extracted from the raw HTML.
// Base is the URL containing the HTML.
//
// Returns nil if nothing is found.
func GetURLFromHTML(b []byte, base *url.URL) (*url.URL, error) {
	content := string(b)
	i := strings.Index(content, `<link `)
	for i >= 0 {
		if i+6 >= len(content) {
			return nil, nil
		}
		args := parseArgs(string([]rune(content)[i+6:]))
		if args["rel"] == "human-json" {
			href, ok := args["href"]
			if ok {
				u, err := url.Parse(href)
				if err != nil {
					return nil, err
				}
				if u.Host != "" {
					return u, nil
				}
				path := u.Path
				*u = *base
				if strings.HasPrefix(path, "/") {
					u.Path = path
				} else {
					u = u.JoinPath(path)
				}
				return u, nil
			}
		}
		i = strings.IndexAny(content[i:], `<link `)
	}
	return nil, nil
}

func parseArgs(base string) map[string]string {
	content := []rune(base)
	i := 0
	res := map[string]string{}

	var sep bool
	var key strings.Builder
	var value strings.Builder
	var quote bool
	for i < len(content) && content[i] != '>' && (i+1 == len(content) || string(content[i:i+2]) != "/>") {
		curr := content[i]
		if !sep {
			switch curr {
			case '=':
				sep = true
			case ' ':
				sep = false
				if key.Len() > 0 {
					res[key.String()] = ""
				}
				key.Reset()
			default:
				key.WriteRune(curr)
			}
		} else {
			if value.Len() == 0 && curr == '"' {
				quote = true
			} else if (curr == '"' && quote) || curr == ' ' && !quote {
				quote = false
				sep = false
				res[key.String()] = value.String()
				key.Reset()
				value.Reset()
			} else {
				value.WriteRune(curr)
			}
		}
		i++
	}
	if key.Len() > 0 {
		res[key.String()] = value.String()
	}
	return res
}