text: // Copyright 2012 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package present
  
  import (
  	"fmt"
  	"log"
  	"net/url"
  	"strings"
  )
  
  func init() {
  	Register("link", parseLink)
  }
  
  type Link struct {
  	URL   *url.URL
  	Label string
  }
  
  func (l Link) TemplateName() string { return "link" }
  
  func parseLink(ctx *Context, fileName string, lineno int, text string) (Elem, error) {
  	args := strings.Fields(text)
  	if len(args) < 2 {
  		return nil, fmt.Errorf("link element must have at least 2 arguments")
  	}
  	url, err := url.Parse(args[1])
  	if err != nil {
  		return nil, err
  	}
  	label := ""
  	if len(args) > 2 {
  		label = strings.Join(args[2:], " ")
  	} else {
  		scheme := url.Scheme + "://"
  		if url.Scheme == "mailto" {
  			scheme = "mailto:"
  		}
  		label = strings.Replace(url.String(), scheme, "", 1)
  	}
  	return Link{url, label}, nil
  }
  
  func renderLink(href, text string) string {
  	text = font(text)
  	if text == "" {
  		text = href
  	}
  	// Open links in new window only when their url is absolute.
  	target := "_blank"
  	if u, err := url.Parse(href); err != nil {
  		log.Println("renderLink parsing url:", err)
  	} else if !u.IsAbs() || u.Scheme == "javascript" {
  		target = "_self"
  	}
  
  	return fmt.Sprintf(`<a href="%s" target="%s">%s</a>`, href, target, text)
  }
  
  // parseInlineLink parses an inline link at the start of s, and returns
  // a rendered HTML link and the total length of the raw inline link.
  // If no inline link is present, it returns all zeroes.
  func parseInlineLink(s string) (link string, length int) {
  	if !strings.HasPrefix(s, "[[") {
  		return
  	}
  	end := strings.Index(s, "]]")
  	if end == -1 {
  		return
  	}
  	urlEnd := strings.Index(s, "]")
  	rawURL := s[2:urlEnd]
  	const badURLChars = `<>"{}|\^[] ` + "`" // per RFC2396 section 2.4.3
  	if strings.ContainsAny(rawURL, badURLChars) {
  		return
  	}
  	if urlEnd == end {
  		simpleUrl := ""
  		url, err := url.Parse(rawURL)
  		if err == nil {
  			// If the URL is http://foo.com, drop the http://
  			// In other words, render [[http://golang.org]] as:
  			//   <a href="http://golang.org">golang.org</a>
  			if strings.HasPrefix(rawURL, url.Scheme+"://") {
  				simpleUrl = strings.TrimPrefix(rawURL, url.Scheme+"://")
  			} else if strings.HasPrefix(rawURL, url.Scheme+":") {
  				simpleUrl = strings.TrimPrefix(rawURL, url.Scheme+":")
  			}
  		}
  		return renderLink(rawURL, simpleUrl), end + 2
  	}
  	if s[urlEnd:urlEnd+2] != "][" {
  		return
  	}
  	text := s[urlEnd+2 : end]
  	return renderLink(rawURL, text), end + 2
  }
  