/*
   Copyright (c) 2016 VMware, Inc. All Rights Reserved.
   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package utils

import (
	"strings"
)

// Link : HTTP link header
type Link struct {
	// URL : url part of header
	URL string
	// Rel : prev or next
	Rel string
}

// Links : multiple link
type Links []*Link

// Prev returns the URL indicated by "prev" rel.
func (l Links) Prev() string {
	prev := ""
	for _, link := range l {
		if strings.ToLower(link.Rel) == "prev" {
			prev = link.URL
			break
		}
	}
	return prev
}

// Next returns the URL indicated by "next" rel.
func (l Links) Next() string {
	next := ""
	for _, link := range l {
		if link.Rel == "next" {
			next = link.URL
			break
		}
	}
	return next
}

// ParseLink parses the raw link header to Links
func ParseLink(raw string) Links {
	links := Links{}

	for _, l := range strings.Split(raw, ",") {
		link := parseSingleLink(l)
		if link != nil {
			links = append(links, link)
		}
	}

	return links
}

func parseSingleLink(raw string) *Link {
	link := &Link{}

	for _, str := range strings.Split(raw, ";") {
		str = strings.TrimSpace(str)
		if strings.HasPrefix(str, "<") && strings.HasSuffix(str, ">") {
			str = strings.Trim(str, "<>")
			link.URL = str
			continue
		}

		parts := strings.SplitN(str, "=", 2)
		if len(parts) != 2 || strings.ToLower(parts[0]) != "rel" {
			continue
		}

		link.Rel = strings.ToLower(strings.Trim(parts[1], "\""))
	}

	if len(link.URL) == 0 || len(link.Rel) == 0 {
		link = nil
	}

	return link
}