package web

import (
	"context"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/http/httptest"
	"strings"
	"sync/atomic"
	"testing"
	"time"

	"gitea.dooplex.hu/admin/felhom-hub/internal/gitea"
)

// artifactChoices fans the per-version sha lookups out concurrently (hub v0.100.0). The
// Configuration page took 26 SECONDS with two dropdowns because it made 42 sequential metadata
// round-trips. These tests pin the three things that must survive the change: the ORDER, the
// per-version failure isolation, and the concurrency itself.

// fakeGitea serves the two endpoints the client uses, with a controllable per-request delay so
// "concurrent" is measurable rather than asserted.
type fakeGitea struct {
	versions []string
	delay    time.Duration
	failVer  string // this version's /files call 500s

	inFlight  int32
	maxSeen   int32
	callCount int32
}

func (f *fakeGitea) start(t *testing.T) *gitea.Client {
	t.Helper()
	mux := http.NewServeMux()
	// BOTH patterns: the version list is GET /api/v1/packages/admin?... with NO trailing slash,
	// the per-version files call is /api/v1/packages/admin/generic/<pkg>/<ver>/files.
	handler := func(w http.ResponseWriter, r *http.Request) {
		n := atomic.AddInt32(&f.inFlight, 1)
		for {
			old := atomic.LoadInt32(&f.maxSeen)
			if n <= old || atomic.CompareAndSwapInt32(&f.maxSeen, old, n) {
				break
			}
		}
		defer atomic.AddInt32(&f.inFlight, -1)
		atomic.AddInt32(&f.callCount, 1)
		time.Sleep(f.delay)

		// .../generic/<pkg>/<version>/files  → the sha metadata
		if len(r.URL.Path) > 6 && r.URL.Path[len(r.URL.Path)-6:] == "/files" {
			for _, v := range f.versions {
				if f.failVer != "" && v == f.failVer && strings.Contains(r.URL.Path, "/"+v+"/") {
					http.Error(w, "boom", http.StatusInternalServerError)
					return
				}
			}
			ver := versionFromFilesPath(r.URL.Path)
			fmt.Fprintf(w, `[{"name":"felhom-agent","sha256":"sha-%s"}]`, ver)
			return
		}
		// the version list
		out := "["
		for i, v := range f.versions {
			if i > 0 {
				out += ","
			}
			out += fmt.Sprintf(`{"name":"felhom-agent","type":"generic","version":%q}`, v)
		}
		fmt.Fprint(w, out+"]")
	}
	mux.HandleFunc("/api/v1/packages/admin", handler)
	mux.HandleFunc("/api/v1/packages/admin/", handler)
	srv := httptest.NewServer(mux)
	t.Cleanup(srv.Close)
	return gitea.New(srv.URL, "admin", "u", "t")
}

func versionFromFilesPath(p string) string {
	// .../generic/<pkg>/<version>/files
	end := len(p) - len("/files")
	start := end - 1
	for start > 0 && p[start-1] != '/' {
		start--
	}
	return p[start:end]
}

func newTestWebServer(t *testing.T, c *gitea.Client) *Server {
	t.Helper()
	s := &Server{logger: log.New(io.Discard, "", 0)}
	s.SetGiteaClient(c)
	return s
}

// The dropdown is newest-first and the concurrent version must not scramble it.
func TestArtifactChoices_PreservesOrder(t *testing.T) {
	f := &fakeGitea{versions: []string{"0.9.0", "0.8.0", "0.7.0", "0.6.0", "0.5.0"}}
	s := newTestWebServer(t, f.start(t))

	got := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")

	if len(got) != 5 {
		t.Fatalf("got %d choices, want 5: %+v", len(got), got)
	}
	// ListVersions sorts newest-first; the fan-out must not disturb that, and each sha must belong
	// to ITS OWN version — a slot mix-up would show the operator a hash for a different artifact.
	for i, want := range []string{"0.9.0", "0.8.0", "0.7.0", "0.6.0", "0.5.0"} {
		if got[i].Version != want {
			t.Errorf("choice %d = %q, want %q — the concurrent fan-out scrambled the order", i, got[i].Version, want)
		}
		if got[i].SHA256 != "sha-"+want {
			t.Errorf("version %s carries sha %q — a sha was written into the wrong slot, which would show "+
				"the operator a hash belonging to a different artifact", got[i].Version, got[i].SHA256)
		}
	}
}

// A single failing version drops ITSELF and nothing else — unchanged from the serial version.
func TestArtifactChoices_OneFailureDropsOnlyThatVersion(t *testing.T) {
	f := &fakeGitea{versions: []string{"0.9.0", "0.8.0", "0.7.0"}, failVer: "0.8.0"}
	s := newTestWebServer(t, f.start(t))

	got := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")

	if len(got) != 2 {
		t.Fatalf("got %d choices, want 2 (the failing one dropped): %+v", len(got), got)
	}
	for _, c := range got {
		if c.Version == "0.8.0" {
			t.Error("the failing version was included")
		}
	}
	if got[0].Version != "0.9.0" || got[1].Version != "0.7.0" {
		t.Errorf("order broken around the dropped version: %+v", got)
	}
}

// THE POINT OF THE CHANGE. With a per-request delay, a serial implementation takes
// len(versions) * delay; the concurrent one takes about ceil(n/8) * delay. Asserting the wall-clock
// is what makes this a test of the fix rather than of the plumbing — and the in-flight counter
// proves requests genuinely overlapped rather than the timing being luck.
func TestArtifactChoices_IsConcurrent(t *testing.T) {
	const n = 16
	vers := make([]string, n)
	for i := range vers {
		vers[i] = fmt.Sprintf("0.%d.0", 100-i) // already newest-first
	}
	f := &fakeGitea{versions: vers, delay: 50 * time.Millisecond}
	s := newTestWebServer(t, f.start(t))

	start := time.Now()
	got := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")
	elapsed := time.Since(start)

	if len(got) != n {
		t.Fatalf("got %d choices, want %d", len(got), n)
	}
	serial := time.Duration(n) * 50 * time.Millisecond // 800ms
	if elapsed > serial/2 {
		t.Errorf("took %v; a serial implementation would take ~%v and the concurrent one should be far "+
			"under half of that. This is the 26-second Configuration page.", elapsed, serial)
	}
	if max := atomic.LoadInt32(&f.maxSeen); max < 2 {
		t.Errorf("max concurrent in-flight requests was %d — the lookups did not actually overlap, so a "+
			"fast wall-clock here would be luck rather than concurrency", max)
	}
	// and it must respect the bound rather than opening one connection per version
	if max := atomic.LoadInt32(&f.maxSeen); max > 8 {
		t.Errorf("max concurrent in-flight was %d, above the bound of 8 — a large package list would "+
			"stampede Gitea", max)
	}
}

// The cap is unchanged: at most 20 versions are offered however many exist.
func TestArtifactChoices_StillCapsAtTwenty(t *testing.T) {
	vers := make([]string, 30)
	for i := range vers {
		vers[i] = fmt.Sprintf("0.%d.0", 200-i)
	}
	f := &fakeGitea{versions: vers}
	s := newTestWebServer(t, f.start(t))

	got := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")
	if len(got) != 20 {
		t.Errorf("got %d choices, want the 20 cap", len(got))
	}
	if atomic.LoadInt32(&f.callCount) > 21 { // 1 version list + 20 sha lookups
		t.Errorf("made %d requests; the cap must limit the FAN-OUT too, not just the rendered list",
			atomic.LoadInt32(&f.callCount))
	}
}

// R-267: the dropdown is memoised for artifactChoicesTTL. A second load inside the window must make
// NO further Gitea calls; a failed resolve must NOT be cached, or a blip would pin an empty list in
// front of the operator for a minute.
func TestArtifactChoices_CachedWithinTTL(t *testing.T) {
	f := &fakeGitea{versions: []string{"0.9.0", "0.8.0"}}
	s := newTestWebServer(t, f.start(t))

	first := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")
	after := atomic.LoadInt32(&f.callCount)
	if after == 0 {
		t.Fatal("the first resolve made no calls")
	}
	second := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")

	if atomic.LoadInt32(&f.callCount) != after {
		t.Errorf("a second load inside the TTL hit Gitea again (%d -> %d calls) — the cache is not "+
			"in the path", after, atomic.LoadInt32(&f.callCount))
	}
	if len(second) != len(first) || second[0].Version != first[0].Version || second[0].SHA256 != first[0].SHA256 {
		t.Errorf("cached result differs from the fresh one: %+v vs %+v", second, first)
	}
}

func TestArtifactChoices_FailureIsNotCached(t *testing.T) {
	// every version fails → an empty list, which must NOT be remembered
	f := &fakeGitea{versions: []string{"0.9.0"}, failVer: "0.9.0"}
	s := newTestWebServer(t, f.start(t))

	if got := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent"); len(got) != 0 {
		t.Fatalf("precondition: expected an empty list, got %+v", got)
	}
	before := atomic.LoadInt32(&f.callCount)
	_ = s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")
	if atomic.LoadInt32(&f.callCount) == before {
		t.Error("an empty/failed resolve was cached — a Gitea blip would then show the operator an " +
			"empty dropdown for a full minute with no way to retry")
	}
}

// Two packages must not share a cache slot.
func TestArtifactChoices_CacheIsPerPackage(t *testing.T) {
	f := &fakeGitea{versions: []string{"0.9.0"}}
	s := newTestWebServer(t, f.start(t))
	a := s.artifactChoices(context.Background(), "felhom-agent", "felhom-agent")
	before := atomic.LoadInt32(&f.callCount)
	_ = s.artifactChoices(context.Background(), "felhom-golden", "golden.tar.zst")
	if atomic.LoadInt32(&f.callCount) == before {
		t.Error("a different package was served from the first package's cache entry")
	}
	if len(a) == 0 {
		t.Error("precondition")
	}
}