package network

import (
	"context"
	"errors"
	"io"
	"math"
	"net/http"
	"net/http/httptest"
	"os"
	"sync/atomic"
	"testing"
	"time"
)

func TestHexIP(t *testing.T) {
	// /proc/net/route prints each address as a host-order word: on a little-endian machine
	// 10.0.0.1 is written "0100000A". These cases are that machine, which is all of ours.
	for hex, want := range map[string]string{
		"0100000A": "10.0.0.1",
		"00000000": "0.0.0.0",
		"0101A8C0": "192.168.1.1",
	} {
		got, err := hexIP(hex)
		if err != nil || got != want {
			t.Errorf("hexIP(%q) = %q, %v; want %q", hex, got, err, want)
		}
	}
	if _, err := hexIP("nonsense"); err == nil {
		t.Error("hexIP accepted nonsense")
	}
}

func TestServerTimeIsNotLatency(t *testing.T) {
	h := http.Header{}
	h.Add("Server-Timing", "cfSpeedEdge;dur=7, cfSpeedWorker;dur=36")
	h.Add("Server-Timing", `cfL4;desc="?proto=TCP&rtt=3505&min_rtt=2856"`)
	if got := serverMs(h); got != 43 {
		t.Errorf("serverMs = %v, want 43 (7+36, and nothing from the cfL4 description)", got)
	}
	if got := serverMs(http.Header{}); got != 0 {
		t.Errorf("serverMs with no header = %v, want 0", got)
	}
	h2 := http.Header{"Cf-Ray": {"a41f6720f966a36c-SEA"}, "Cf-Meta-Ip": {"50.47.252.221"}}
	if m := readMeta(h2); m.Colo != "SEA" || m.IP != "50.47.252.221" {
		t.Errorf("readMeta = %+v, want the edge SEA and the address", m)
	}
}

func TestRates(t *testing.T) {
	// a gibibyte in eight seconds is 1073.7 Mbps
	if got := mbps(1<<30, 8); math.Abs(got-1073.7) > 0.1 {
		t.Errorf("mbps(1GiB, 8s) = %v, want ~1073.7", got)
	}
	if got := best([]float64{12.5, 9.2, 40, 9.9}); got != 9.2 {
		t.Errorf("best = %v, want 9.2 (the least of them)", got)
	}
	if got := jitter([]float64{10, 10, 10}); got != 0 {
		t.Errorf("jitter of a steady line = %v, want 0", got)
	}
	if got := jitter([]float64{10}); got != 0 {
		t.Errorf("jitter of one sample = %v, want 0", got)
	}
	if got := jitter([]float64{5, 50, 5, 50}); got != 45 {
		t.Errorf("jitter of a line alternating by 45 = %v, want 45", got)
	}
	// one slow probe among steady ones moves it a little, not enormously
	if got := jitter([]float64{10, 10, 10, 60, 10, 10}); got > 25 {
		t.Errorf("jitter with a single outlier = %v, want it not to run away", got)
	}
}

// The body an upload sends is a fixed size, counts itself, and costs nothing to make.
func TestZerosBodyCountsItself(t *testing.T) {
	var n atomic.Int64
	z := &zeros{left: 100, n: &n}
	buf := make([]byte, 30)
	total := 0
	for {
		got, err := z.Read(buf)
		total += got
		if err != nil {
			break
		}
	}
	if total != 100 || n.Load() != 100 {
		t.Errorf("read %d bytes and counted %d, want 100 and 100", total, n.Load())
	}
}

// Interfaces has to work on whatever machine this runs on, and always name a loopback.
func TestInterfacesHasLoopback(t *testing.T) {
	ifs := Interfaces()
	if len(ifs) == 0 {
		t.Fatal("no interfaces at all")
	}
	lo := false
	for _, f := range ifs {
		if f.Kind == "loopback" {
			lo = true
			if !f.Up || len(f.Addrs) == 0 {
				t.Errorf("loopback %s looks wrong: up=%v addrs=%v", f.Name, f.Up, f.Addrs)
			}
		}
		if f.Name == "" {
			t.Error("an interface with no name")
		}
	}
	if !lo {
		t.Error("no loopback among the interfaces")
	}
}

// The real thing, against the real endpoint: skipped by default, because `make test` must
// not need the internet. HAMLAB_NET_TEST=1 go test ./internal/network/ -run Live -v
func TestLiveSpeedTest(t *testing.T) {
	if os.Getenv("HAMLAB_NET_TEST") == "" {
		t.Skip("set HAMLAB_NET_TEST=1 to measure the actual line")
	}
	tr := NewTester(nil)
	if _, err := tr.Start(); err != nil {
		t.Fatal(err)
	}
	if _, err := tr.Start(); err == nil {
		t.Error("a second test started while the first was running")
	}
	deadline := time.Now().Add(90 * time.Second)
	for tr.Running() && time.Now().Before(deadline) {
		time.Sleep(250 * time.Millisecond)
	}
	st := tr.State()
	if st.Result == nil {
		t.Fatal("no result")
	}
	r := *st.Result
	t.Logf("down %s  up %s  latency %.1f ms  jitter %.1f ms  via %s  ip %s  %.0f MB moved in %.1fs",
		Mbits(r.DownMbps), Mbits(r.UpMbps), r.LatencyMs, r.JitterMs, r.Colo, r.IP,
		float64(r.DownBytes+r.UpBytes)/1e6, r.TookSec)
	if r.Error != "" {
		t.Fatalf("test failed: %s", r.Error)
	}
	if r.DownMbps <= 0 || r.UpMbps <= 0 || r.LatencyMs <= 0 {
		t.Errorf("a figure came back zero: %+v", r)
	}
	if r.IP == "" {
		t.Error("no public address reported")
	}
	if len(tr.History()) != 1 {
		t.Errorf("history has %d results, want 1", len(tr.History()))
	}
}

// A phase measured against a local server, at a rate the test controls. This is the part of
// the speed test with arithmetic in it — the window after the ramp, the byte cap that ends it
// early, and the rate that comes out — and none of it needs the internet to check.
func TestPhaseMeasuresTheWindow(t *testing.T) {
	const perTick = 1 << 20 // a mebibyte every 5 ms ≈ 1678 Mbps, whatever the machine is doing
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/up" {
			_, _ = io.Copy(io.Discard, r.Body)
			w.WriteHeader(204)
			return
		}
		buf := make([]byte, perTick)
		fl, _ := w.(http.Flusher)
		for {
			if _, err := w.Write(buf); err != nil {
				return
			}
			if fl != nil {
				fl.Flush()
			}
			select {
			case <-time.After(5 * time.Millisecond):
			case <-r.Context().Done():
				return
			}
		}
	}))
	defer srv.Close()

	defer func(up string, w, d, mw time.Duration, m int64) {
		upURL, warmUp, downFor, minWindow, measureBytes = up, w, d, mw, m
	}(upURL, warmUp, downFor, minWindow, measureBytes)
	upURL = srv.URL + "/up"
	warmUp, downFor, minWindow, measureBytes = 100*time.Millisecond, 3*time.Second, 200*time.Millisecond, 8<<20
	here := Source{"local", func(int) string { return srv.URL + "/down" }}

	tr := NewTester(nil)
	began := time.Now()
	mbps, moved, note, err := tr.phase(context.Background(), srv.Client(), "download", 2, downFor, 0, 1, here)
	took := time.Since(began)
	if err != nil {
		t.Fatalf("phase: %v", err)
	}
	if note != "" {
		t.Errorf("note = %q, want none — nothing went wrong", note)
	}
	// The cap must have ended it early rather than the clock: the phase was allowed three
	// seconds and should be done in well under one, having moved at least the cap.
	if moved < measureBytes {
		t.Errorf("moved %d bytes, want at least the %d-byte cap", moved, measureBytes)
	}
	if took > time.Second {
		t.Errorf("phase took %v of the %v it was allowed; the byte cap should have ended it", took.Round(time.Millisecond), downFor)
	}
	// The server hands out a mebibyte per 5 ms per stream, so the rate is in the hundreds of
	// Mbps. The point is that it is a real quotient of what moved over how long, not that it
	// hits a particular figure on a loaded test machine.
	if mbps < 50 || mbps > 20000 {
		t.Errorf("mbps = %v, which is not a believable quotient", mbps)
	}
	t.Logf("measured %.0f Mbps over %.1f MiB", mbps, float64(moved)/(1<<20))

	// A phase whose server refuses outright fails, and says what it was told.
	bad := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) { w.WriteHeader(429) }))
	defer bad.Close()
	refuser := Source{"refuser", func(int) string { return bad.URL + "/down" }}
	_, _, _, err = tr.phase(context.Background(), bad.Client(), "download", 2, 300*time.Millisecond, 0, 1, refuser)
	if err == nil {
		t.Error("a phase against a server that refuses everything should fail")
	} else if !refused(err) {
		t.Errorf("error = %q, want the refusal that makes the fallback kick in", err)
	}
}

// Stopping a test mid-flight is reported as cancelled, not as whatever the streams said on
// their way out.
func TestCancelIsReportedAsCancelled(t *testing.T) {
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		buf := make([]byte, 1<<16)
		for {
			if _, err := w.Write(buf); err != nil {
				return
			}
			select {
			case <-time.After(time.Millisecond):
			case <-r.Context().Done():
				return
			}
		}
	}))
	defer srv.Close()
	defer func(w, d time.Duration) { warmUp, downFor = w, d }(warmUp, downFor)
	warmUp, downFor = 10*time.Millisecond, 10*time.Second
	here := Source{"local", func(int) string { return srv.URL + "/down" }}

	tr := NewTester(nil)
	ctx, cancel := context.WithCancel(context.Background())
	go func() { time.Sleep(200 * time.Millisecond); cancel() }()
	_, _, _, err := tr.phase(ctx, srv.Client(), "download", 1, downFor, 0, 1, here)
	// Cancelled after bytes moved: the figure stands, and the phase does not claim an error.
	if err != nil && !errors.Is(err, context.Canceled) {
		t.Errorf("err = %v, want nil or a cancellation", err)
	}
}

// When the first source refuses, the download is taken from the next one and the result says
// so. This is the whole reason there is more than one.
func TestDownloadFallsBackWhenRefused(t *testing.T) {
	serving := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/up" {
			_, _ = io.Copy(io.Discard, r.Body)
			w.WriteHeader(204)
			return
		}
		// paced, so the phase is governed by its window and not by a loopback moving a
		// gibibyte before the first tick
		buf := make([]byte, 1<<20)
		fl, _ := w.(http.Flusher)
		for i := 0; i < 64; i++ {
			if _, err := w.Write(buf); err != nil {
				return
			}
			if fl != nil {
				fl.Flush()
			}
			select {
			case <-time.After(2 * time.Millisecond):
			case <-r.Context().Done():
				return
			}
		}
	}))
	defer serving.Close()
	refusing := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) { w.WriteHeader(429) }))
	defer refusing.Close()

	defer func(srcs []Source, up string, w, d, mw time.Duration, m int64) {
		downSources, upURL, warmUp, downFor, minWindow, measureBytes = srcs, up, w, d, mw, m
	}(downSources, upURL, warmUp, downFor, minWindow, measureBytes)
	downSources = []Source{
		{"refuser", func(int) string { return refusing.URL + "/down" }},
		{"the-other-one", func(int) string { return serving.URL + "/down" }},
	}
	upURL = serving.URL + "/up"
	warmUp, downFor, upFor, minWindow, measureBytes = 50*time.Millisecond, time.Second, 300*time.Millisecond, 100*time.Millisecond, 4<<20

	tr := NewTester(nil)
	if _, err := tr.Start(); err != nil {
		t.Fatal(err)
	}
	deadline := time.Now().Add(30 * time.Second)
	for tr.Running() && time.Now().Before(deadline) {
		time.Sleep(50 * time.Millisecond)
	}
	res := tr.State().Result
	if res == nil {
		t.Fatal("no result")
	}
	if res.Source != "the-other-one" {
		t.Errorf("source = %q, want the second one — the first refused", res.Source)
	}
	if res.DownMbps <= 0 {
		t.Errorf("download = %v, want a figure from the source that did serve: %+v", res.DownMbps, res)
	}
}