package transport

import (
	"context"
	"net/http"
	"net/http/httptest"
	"testing"
)

func TestFetchBodyIfChangedPrefersETagAndTreats304AsUnchanged(t *testing.T) {
	t.Helper()

	var call int
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		call++
		switch call {
		case 1:
			if got := r.Header.Get("If-None-Match"); got != "" {
				t.Fatalf("first request If-None-Match = %q, want empty", got)
			}
			if got := r.Header.Get("If-Modified-Since"); got != "" {
				t.Fatalf("first request If-Modified-Since = %q, want empty", got)
			}
			w.Header().Set("ETag", `"v1"`)
			w.Header().Set("Last-Modified", "Mon, 02 Jan 2006 15:04:05 GMT")
			_, _ = w.Write([]byte(`{"ok":true}`))
		case 2:
			if got := r.Header.Get("If-None-Match"); got != `"v1"` {
				t.Fatalf("second request If-None-Match = %q, want %q", got, `"v1"`)
			}
			if got := r.Header.Get("If-Modified-Since"); got != "" {
				t.Fatalf("second request If-Modified-Since = %q, want empty when ETag is cached", got)
			}
			w.WriteHeader(http.StatusNotModified)
		default:
			t.Fatalf("unexpected call count %d", call)
		}
	}))
	defer srv.Close()

	validators := HTTPValidators{}
	body, changed, next, err := FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "application/json", true, validators)
	if err != nil {
		t.Fatalf("first FetchBodyIfChanged() error = %v", err)
	}
	if !changed {
		t.Fatalf("first FetchBodyIfChanged() changed = false, want true")
	}
	if got := string(body); got != `{"ok":true}` {
		t.Fatalf("first FetchBodyIfChanged() body = %q", got)
	}
	if got := next.ETag; got != `"v1"` {
		t.Fatalf("cached ETag = %q, want %q", got, `"v1"`)
	}
	if got := next.LastModified; got != "Mon, 02 Jan 2006 15:04:05 GMT" {
		t.Fatalf("cached Last-Modified = %q", got)
	}

	body, changed, next, err = FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "application/json", true, next)
	if err != nil {
		t.Fatalf("second FetchBodyIfChanged() error = %v", err)
	}
	if changed {
		t.Fatalf("second FetchBodyIfChanged() changed = true, want false")
	}
	if body != nil {
		t.Fatalf("second FetchBodyIfChanged() body = %q, want nil", string(body))
	}
	if got := next.ETag; got != `"v1"` {
		t.Fatalf("cached ETag after 304 = %q, want %q", got, `"v1"`)
	}
}

func TestFetchBodyIfChangedFallsBackToIfModifiedSince(t *testing.T) {
	t.Helper()

	var call int
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		call++
		switch call {
		case 1:
			w.Header().Set("Last-Modified", "Tue, 03 Jan 2006 15:04:05 GMT")
			_, _ = w.Write([]byte(`first`))
		case 2:
			if got := r.Header.Get("If-None-Match"); got != "" {
				t.Fatalf("second request If-None-Match = %q, want empty", got)
			}
			if got := r.Header.Get("If-Modified-Since"); got != "Tue, 03 Jan 2006 15:04:05 GMT" {
				t.Fatalf("second request If-Modified-Since = %q", got)
			}
			w.WriteHeader(http.StatusNotModified)
		default:
			t.Fatalf("unexpected call count %d", call)
		}
	}))
	defer srv.Close()

	_, changed, validators, err := FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", true, HTTPValidators{})
	if err != nil {
		t.Fatalf("first FetchBodyIfChanged() error = %v", err)
	}
	if !changed {
		t.Fatalf("first FetchBodyIfChanged() changed = false, want true")
	}
	if got := validators.LastModified; got != "Tue, 03 Jan 2006 15:04:05 GMT" {
		t.Fatalf("cached Last-Modified = %q", got)
	}

	_, changed, _, err = FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", true, validators)
	if err != nil {
		t.Fatalf("second FetchBodyIfChanged() error = %v", err)
	}
	if changed {
		t.Fatalf("second FetchBodyIfChanged() changed = true, want false")
	}
}

func TestFetchBodyIfChangedClearsValidatorsOn200WithoutValidators(t *testing.T) {
	t.Helper()

	var call int
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		call++
		switch call {
		case 1:
			w.Header().Set("ETag", `"v1"`)
			_, _ = w.Write([]byte(`first`))
		case 2:
			if got := r.Header.Get("If-None-Match"); got != `"v1"` {
				t.Fatalf("second request If-None-Match = %q", got)
			}
			_, _ = w.Write([]byte(`second`))
		case 3:
			if got := r.Header.Get("If-None-Match"); got != "" {
				t.Fatalf("third request If-None-Match = %q, want empty", got)
			}
			if got := r.Header.Get("If-Modified-Since"); got != "" {
				t.Fatalf("third request If-Modified-Since = %q, want empty", got)
			}
			_, _ = w.Write([]byte(`third`))
		default:
			t.Fatalf("unexpected call count %d", call)
		}
	}))
	defer srv.Close()

	_, _, validators, err := FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", true, HTTPValidators{})
	if err != nil {
		t.Fatalf("first FetchBodyIfChanged() error = %v", err)
	}
	_, _, validators, err = FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", true, validators)
	if err != nil {
		t.Fatalf("second FetchBodyIfChanged() error = %v", err)
	}
	if validators.ETag != "" || validators.LastModified != "" {
		t.Fatalf("validators after 200 without validators = %+v, want cleared", validators)
	}
	_, _, _, err = FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", true, validators)
	if err != nil {
		t.Fatalf("third FetchBodyIfChanged() error = %v", err)
	}
}

func TestFetchBodyIfChangedConditionalDisabledSkipsConditionalHeaders(t *testing.T) {
	t.Helper()

	var calls int
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		calls++
		if got := r.Header.Get("If-None-Match"); got != "" {
			t.Fatalf("request If-None-Match = %q, want empty", got)
		}
		if got := r.Header.Get("If-Modified-Since"); got != "" {
			t.Fatalf("request If-Modified-Since = %q, want empty", got)
		}
		_, _ = w.Write([]byte(`body`))
	}))
	defer srv.Close()

	validators := HTTPValidators{ETag: `"v1"`, LastModified: "Wed, 04 Jan 2006 15:04:05 GMT"}
	_, changed, next, err := FetchBodyIfChanged(context.Background(), srv.Client(), srv.URL, "test-agent", "", false, validators)
	if err != nil {
		t.Fatalf("FetchBodyIfChanged() error = %v", err)
	}
	if !changed {
		t.Fatalf("FetchBodyIfChanged() changed = false, want true")
	}
	if next != validators {
		t.Fatalf("validators changed when conditional disabled: got %+v want %+v", next, validators)
	}
	if calls != 1 {
		t.Fatalf("calls = %d, want 1", calls)
	}
}

func TestFetchBodyIfChangedAllowsEmpty304ButRejectsEmpty200(t *testing.T) {
	t.Helper()

	notModified := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusNotModified)
	}))
	defer notModified.Close()

	_, changed, _, err := FetchBodyIfChanged(
		context.Background(),
		notModified.Client(),
		notModified.URL,
		"test-agent",
		"",
		true,
		HTTPValidators{ETag: `"v1"`},
	)
	if err != nil {
		t.Fatalf("304 FetchBodyIfChanged() error = %v", err)
	}
	if changed {
		t.Fatalf("304 FetchBodyIfChanged() changed = true, want false")
	}

	emptyBody := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
	}))
	defer emptyBody.Close()

	_, _, _, err = FetchBodyIfChanged(context.Background(), emptyBody.Client(), emptyBody.URL, "test-agent", "", true, HTTPValidators{})
	if err == nil {
		t.Fatalf("empty 200 FetchBodyIfChanged() error = nil, want error")
	}
	if err.Error() != "empty response body" {
		t.Fatalf("empty 200 FetchBodyIfChanged() error = %q", err)
	}
}