package main

import (
	"fmt"
	"strings"
)

type linkParseError struct {
	msg string
}

func (e linkParseError) Error() string {
	return "link parse error: " + e.msg
}

type link struct {
	Title string
	URL   string
	Rel   string
}

func (l link) String() string {
	return fmt.Sprintf("Title: %s, URL: %s, Rel: %s", l.Title, l.URL, l.Rel)
}

type links []link

func (l *links) Set(value string) error {
	linkAttributes := strings.Split(value, ",")

	lenLinkAttributes := len(linkAttributes)
	if lenLinkAttributes != 2 && lenLinkAttributes != 3 {
		return linkParseError{msg: fmt.Sprintf("unexpected number of attributes found %s, want 2 or 3, got %d", value, lenLinkAttributes)}
	}

	var thisLink link

	for _, attr := range linkAttributes {
		split := strings.Split(attr, "=")
		switch strings.ToLower(split[0]) {
		case "title":
			thisLink.Title = split[1]
		case "url":
			thisLink.URL = split[1]
		case "rel":
			thisLink.Rel = split[1]
		}
	}

	if thisLink.Title == "" {
		return linkParseError{msg: fmt.Sprintf("the title attribute is missing from %s", value)}
	}

	if thisLink.URL == "" {
		return linkParseError{msg: fmt.Sprintf("the URL attribute is missing from %s", value)}
	}

	*l = append(*l, thisLink)

	return nil
}

func (l *links) String() string {
	if len(*l) == 0 {
		return ""
	}

	var builder strings.Builder

	for _, link := range *l {
		fmt.Fprintln(&builder, link)
	}

	return builder.String()
}