// Package google provides a function to do Google searches using the Google Web
// Search API. See https://developers.google.com/web-search/docs/
//
// This package is an example to accompany https://blog.golang.org/context.
// It is not intended for use by others.
//
// Google has since disabled its search API,
// and so this package is no longer useful.
package google

import (
"context"
"encoding/json"
"net/http"

"golang.org/x/blog/content/context/userip"

)

// Results is an ordered list of search results.
type Results []Result

// A Result contains the title and URL of a search result.
type Result struct {
Title, URL string
}

// Search sends query to Google search and returns the results.
func Search(ctx context.Context, query string) (Results, error) {
// Prepare the Google Search API request.
req, err := http.NewRequest("GET", "https://ajax.googleapis.com/ajax/services/search/web?v=1.0", nil)
if err != nil {
return nil, err
}
q := req.URL.Query()
q.Set("q", query)

// If ctx is carrying the user IP address, forward it to the server.
// Google APIs use the user IP to distinguish server-initiated requests
// from end-user requests.
if userIP, ok := userip.FromContext(ctx); ok {
	q.Set("userip", userIP.String())
}
req.URL.RawQuery = q.Encode()

// Issue the HTTP request and handle the response. The httpDo function
// cancels the request if ctx.Done is closed.
var results Results
err = httpDo(ctx, req, func(resp *http.Response, err error) error {
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	// Parse the JSON search result.
	// https://developers.google.com/web-search/docs/#fonje
	var data struct {
		ResponseData struct {
			Results []struct {
				TitleNoFormatting string
				URL               string
			}
		}
	}
	if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
		return err
	}
	for _, res := range data.ResponseData.Results {
		results = append(results, Result{Title: res.TitleNoFormatting, URL: res.URL})
	}
	return nil
})
// httpDo waits for the closure we provided to return, so it's safe to
// read results here.
return results, err

}

// httpDo issues the HTTP request and calls f with the response. If ctx.Done is
// closed while the request or f is running, httpDo cancels the request, waits
// for f to exit, and returns ctx.Err. Otherwise, httpDo returns f's error.
func httpDo(ctx context.Context, req *http.Request, f func(*http.Response, error) error) error {
// Run the HTTP request in a goroutine and pass the response to f.
c := make(chan error, 1)
req = req.WithContext(ctx)
go func() { c <- f(http.DefaultClient.Do(req)) }()
select {
case <-ctx.Done():
<-c // Wait for f to return.
return ctx.Err()
case err := <-c:
return err
}
}