// -=-=- StartHere -=-=-
//
// # Chapter XIV: A possible rewrite of Web Connectivity
//
// In this chapter we try to solve the exercise laid out in
// the previous chapter, using `measurex` primitives.
//
// (This file is auto-generated. Do not edit it directly! To apply
// changes you need to modify `./internal/tutorial/measurex/chapter14/main.go`.)
//
// ## main.go
//
// The beginning of the file is always pretty much the same.
//
// ```Go
package main

import (
	"context"
	"crypto/tls"
	"encoding/json"
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"time"

	"github.com/ooni/probe-cli/v3/internal/measurex"
	"github.com/ooni/probe-cli/v3/internal/netxlite"
	"github.com/ooni/probe-cli/v3/internal/runtimex"
)

func print(v interface{}) {
	data, err := json.Marshal(v)
	runtimex.PanicOnError(err, "json.Marshal failed")
	fmt.Printf("%s\n", string(data))
}

// ```
//
// ## measurement type
//
// We define a measurement type with the fields
// that a Web Connectivity measurement should have.
//
// ```Go

type measurement struct {
	Queries       []*measurex.DNSLookupEvent     `json:"queries"`
	TCPConnect    []*measurex.NetworkEvent       `json:"tcp_connect"`
	TLSHandshakes []*measurex.TLSHandshakeEvent  `json:"tls_handshakes"`
	Requests      []*measurex.HTTPRoundTripEvent `json:"requests"`
}

// ```
//
// ## WebConnectivity implementation
//
// We define a function that takes in input a context and a URL to
// measure and returns a measurement or an error.
//
// We will only error out in case the input does not allow us to
// proceed (i.e., invalid input URL).
//
// ```Go

func webConnectivity(ctx context.Context, URL string) (*measurement, error) {
	// ```
	//
	// We start by parsing the input URL. If we cannot parse it, of
	// course this is an hard error and we cannot continue.
	//
	// ```Go
	parsedURL, err := url.Parse(URL)
	if err != nil {
		return nil, err
	}

	// ```
	//
	// We create an empty measurement and a measurer with
	// default settings like we did in the previous chapters.
	//
	// ```Go
	m := &measurement{}
	mx := measurex.NewMeasurerWithDefaultSettings()

	// ```
	//
	// Now it's time to start measuring. We will address all
	// the points laid out in the previous chapter.
	//
	// ### 1. Enumerating IP addrs
	//
	// Let us enumerate all the IP addresses for
	// the input URL's domain using the system resolver.
	//
	// ```Go
	dns := mx.LookupHostSystem(ctx, parsedURL.Hostname())
	m.Queries = append(m.Queries, dns.LookupHost...)

	// ```
	//
	// This is code we have already seen in previous chapter.
	//
	//
	// ### 2. Building a list of endpoints
	//
	// ```Go
	epnts, err := measurex.AllHTTPEndpointsForURL(parsedURL, http.Header{}, dns)
	if err != nil {
		return nil, err
	}

	// ```
	//
	// This is also code we have seen in previous chapters. The only
	// difference is that we supply empty headers since we're not going
	// to actually use the headers inside the endpoints.
	//
	// ### 3 and 4. Measure each endpoint
	//
	// We will loop through the endpoints in the previous point
	// and issue the correct TCP or TLS primitive depending on
	// whether the input URL is HTTP or HTTPS.
	//
	// ```Go
	for _, epnt := range epnts {
		switch parsedURL.Scheme {
		case "http":
			tcp := mx.TCPConnect(ctx, epnt.Address)
			m.TCPConnect = append(m.TCPConnect, tcp.Connect...)
		case "https":
			config := &tls.Config{
				ServerName: parsedURL.Hostname(),
				NextProtos: []string{"h2", "http/1.1"},
				RootCAs:    netxlite.NewDefaultCertPool(),
			}
			tls := mx.TLSConnectAndHandshake(ctx, epnt.Address, config)
			m.TCPConnect = append(m.TCPConnect, tls.Connect...)
			m.TLSHandshakes = append(m.TLSHandshakes, tls.TLSHandshake...)
		}
	}

	// ```
	//
	// At this point we've addressed points 1-4. So let's
	// now focus on the last point:
	//
	// ### 5. HTTP measurement
	//
	// We need to manually build a `MeasurementDB`. This is a
	// "database" where networking code will store events.
	//
	// ```Go

	db := &measurex.MeasurementDB{}

	// ```
	//
	// Following the hint from the previous chapter we use the
	// `NewTracingHTTPTransportWithDefaultSettings` factory
	// to create an `http.Transport`-like object that will trace
	// HTTP round trip events writing them into `db`.
	//
	//
	// ```Go

	txp := measurex.NewTracingHTTPTransportWithDefaultSettings(mx.Begin, mx.Logger, db)

	// ```
	//
	// We now build an `http.Client` using the transport
	// we've just created and a cookie jar (which we
	// use because otherwise some redirects will lead
	// to a redirect loop, as mentioned in previous chapters).
	//
	// ```Go

	clnt := &http.Client{
		Transport: txp,
		Jar:       measurex.NewCookieJar(),
	}

	// ```
	//
	// Now we use a method of the measurer that allows us to
	// perform an HTTP GET with an existing HTTP client
	// and a URL. This method will set a timeout and perform
	// the round trip. Reading a snapshot of the response
	// body is not implemented by this function but rather
	// is a property of the "tracing" HTTP transport we
	// created above (this type of transport is the one we
	// have been internally using in all the examples
	// presented so far.)
	//
	// ```Go

	resp, _ := mx.HTTPClientGET(ctx, clnt, parsedURL)

	// ```
	//
	// To be tidy, we also close the response body in case
	// we have a response. We don't really need to read
	// the body here. As mentioned previously, we're already
	// using an HTTP transport reading a body snapshot.
	//
	// ```Go

	if resp != nil {
		resp.Body.Close() // tidy
	}

	// ```
	//
	// Finally, we append the round trips we performed into
	// the right field and return the measurement.
	//
	// To this end, we're using the `db.AsMeasurement` method that
	// takes the current set of events into `db` and assembles
	// them into the `Measurement` struct we've been using in all
	// the chapters we have seen so far.
	//
	// ```Go

	m.Requests = append(m.Requests, db.AsMeasurement().HTTPRoundTrip...)
	return m, nil
}

// ```
//
// The rest of the program is pretty straightforward.
//
// ```Go

func main() {
	URL := flag.String("url", "https://www.google.com/", "URL to fetch")
	timeout := flag.Duration("timeout", 60*time.Second, "timeout to use")
	flag.Parse()
	ctx, cancel := context.WithTimeout(context.Background(), *timeout)
	defer cancel()
	m, err := webConnectivity(ctx, *URL)
	runtimex.PanicOnError(err, "invalid arguments to webConnectivity (wrong URL?)")
	print(m)
}

// ```
//
// ## Running the example program
//
// Let us perform a vanilla run first:
//
// ```bash
// go run -race ./internal/tutorial/measurex/chapter14
// ```
//
// Take a look at the JSON.
//
// Now try running the program with `http://gmail.com` as
// input. Take note of the redirect chain. See how the
// domain changes during the redirect. Take note of the
// fact that we are not measuring any TLS handshake. See
// how we're not trying QUIC endpoints. These are, in
// fact, some of the limitations of Web Connectivity that
// we were trying to address when we wrote `measurex`.
//
// Also, build the miniooni research client:
//
// ```
// go build -v ./internal/cmd/miniooni
// ```
//
// Run Web Connectivity with:
//
// ```
// ./miniooni -ni http://gmail.com web_connectivity
// ```
//
// This writes the report in a file named `report.jsonl`.
//
// Check the content of the file and match it with the
// output of this chapter. Are there other notable
// differences between the two outputs?
//
// ### Bonus question
//
// The solution we presented is true to the original
// spirit of Web Connectivity, where we first perform
// separate DNS, TCP/TLS steps, and then we also
// perform a separate HTTP step. Is there in `measurex`
// an API allowing you to invert the order of the
// operations, that is:
//
// 1. build a full-fledged HTTP client where we can
// trace _any_ operation;
//
// 2. use such client to measure the URL;
//
// 3. figure out what TCP endpoints we did not
// test for TCP/TLS during this process and run
// TCP/TLS testing only for them?
//
// If such an API exist, can you write a simple
// main.go client that implements points 1-3 above?
//
// ## Conclusion
//
// We have presented the solution to the exercise
// proposed in the previous chapter, i.e., how
// to rewrite Web Connectivity using `measurex` API.
//
// You have now been exposed to some complexity and
// APIs to perform OONI measurements. So you should now
// be read to help us write new and maitain existing
// network experiments.
//
// If you have further questions, please [contact us](
// https://ooni.org/about/).
//
// -=-=- StopHere -=-=-