apex/up

// Package inject provides script and style injection utilities.
package inject

import (
    "encoding/json"
    "html"
    "io/ioutil"
    "strings"

    "github.com/apex/log"
    "github.com/apex/up/internal/validate"
    "github.com/pkg/errors"
)

// TODO: template support
// TODO: move config to "config" pkg

// locations valid.
var locations = []string{
    "head",
    "body",
}

// types valid.
var types = []string{
    "literal",
    "comment",
    "style",
    "script",
    "inline style",
    "inline script",
    "google analytics",
    "segment",
}

// Rules is a set of rules mapped by location.
type Rules map[string][]*Rule

// Default rules.
func (r Rules) Default() error {
    for pos, rules := range r {
        for i, rule := range rules {
            if err := rule.Default(); err != nil {
                return errors.Wrapf(err, "%s rule #%d", pos, i+1)
            }
        }
    }

    return nil
}

// Validate rules.
func (r Rules) Validate() error {
    for pos, rules := range r {
        if err := validate.List(pos, locations); err != nil {
            return errors.Wrap(err, "invalid location")
        }

        for i, rule := range rules {
            if err := rule.Validate(); err != nil {
                return errors.Wrapf(err, "%s rule #%d", pos, i+1)
            }
        }
    }

    return nil
}

// Apply rules to html.
func (r Rules) Apply(html string) string {
    for pos, rules := range r {
        log.Debugf("injecting %s rules", pos)
        for _, rule := range rules {
            log.Debugf("  inject %s %q", rule.Type, rule.Value)
            switch pos {
            case "head":
                html = Head(html, rule.Apply(html))
            case "body":
                html = Body(html, rule.Apply(html))
            }
        }
    }

    return html
}

// Rule is an injection rule.
type Rule struct {
    // Type of injection, defaults to "literal" unless File is used,
    // or Value contains .js or .css extensions.
    Type string `json:"type"`

    // Value is the literal, inline string, or src/href of the injected tag.
    Value string `json:"value"`

    // File is used to load source from disk instead of providing Value. Note
    // that if Type is not explicitly provided, then it will default to
    // "inline script" or "inline style" for .js and .css files respectively.
    File string `json:"file"`
}

// Apply rule to html.
func (r *Rule) Apply(html string) string {
    switch r.Type {
    case "literal":
        return r.Value
    case "script":
        return Script(r.Value)
    case "style":
        return Style(r.Value)
    case "inline script":
        return ScriptInline(r.Value)
    case "inline style":
        return StyleInline(r.Value)
    case "comment":
        return Comment(r.Value)
    case "segment":
        return Segment(r.Value)
    case "google analytics":
        return GoogleAnalytics(r.Value)
    default:
        return ""
    }
}

// Default applies defaults.
func (r *Rule) Default() error {
    if r.Type == "" {
        r.Type = "literal"
    }

    if r.File != "" {
        if err := r.defaultFile(r.File); err != nil {
            return err
        }
    }

    return nil
}

// Validate returns an error if incorrect.
func (r *Rule) Validate() error {
    if err := validate.List(r.Type, types); err != nil {
        return errors.Wrap(err, "invalid .type")
    }

    if strings.TrimSpace(r.Value) == "" {
        return errors.Errorf(`.value is required`)
    }

    return nil
}

// defaultFile defaults value" from the given path.
func (r *Rule) defaultFile(path string) error {
    b, err := ioutil.ReadFile(path)
    if err != nil {
        return err
    }

    r.Value = string(b)
    return nil
}

// Head injects a string before the closing head tag.
func Head(html, s string) string {
    return strings.Replace(html, "</head>", "  "+s+"\n  </head>", 1)
}

// Body injects a string before the closing body tag.
func Body(html, s string) string {
    return strings.Replace(html, "</body>", "  "+s+"\n  </body>", 1)
}

// Script returns an script.
func Script(src string) string {
    return `<script src="` + html.EscapeString(src) + `"></script>`
}

// ScriptInline returns an inline script.
func ScriptInline(s string) string {
    return `<script>` + s + `</script>`
}

// Style returns an style.
func Style(href string) string {
    return `<link rel="stylesheet" href="` + html.EscapeString(href) + `">`
}

// StyleInline returns an inline style.
func StyleInline(s string) string {
    return `<style>` + s + `</style>`
}

// Comment returns an html comment.
func Comment(s string) string {
    return "<!-- " + html.EscapeString(s) + " -->"
}

// Segment inline script with key.
func Segment(key string) string {
    return ScriptInline(`
  !function(){var analytics=window.analytics=window.analytics||[];if(!analytics.initialize)if(analytics.invoked)window.console&&console.error&&console.error("Segment snippet included twice.");else{analytics.invoked=!0;analytics.methods=["trackSubmit","trackClick","trackLink","trackForm","pageview","identify","reset","group","track","ready","alias","debug","page","once","off","on"];analytics.factory=function(t){return function(){var e=Array.prototype.slice.call(arguments);e.unshift(t);analytics.push(e);return analytics}};for(var t=0;t<analytics.methods.length;t++){var e=analytics.methods[t];analytics[e]=analytics.factory(e)}analytics.load=function(t){var e=document.createElement("script");e.type="text/javascript";e.async=!0;e.src=("https:"===document.location.protocol?"https://":"http://")+"cdn.segment.com/analytics.js/v1/"+t+"/analytics.min.js";var n=document.getElementsByTagName("script")[0];n.parentNode.insertBefore(e,n)};analytics.SNIPPET_VERSION="4.0.0";
  analytics.load("` + key + `");
  analytics.page();
  }}();
`)
}

// GoogleAnalytics inline script with tracking key.
func GoogleAnalytics(trackingID string) string {
    return ScriptInline(`
  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');

  ga('create', '` + trackingID + `', 'auto');
  ga('send', 'pageview');
`)
}

// Var injection.
func Var(kind, name string, v interface{}) string {
    b, _ := json.Marshal(v)
    return ScriptInline(kind + ` ` + name + ` = ` + string(b))
}