// 🤖 Tests for the global id allocator. Two harnesses:
//
//   - memCounter: an in-memory, CAS-correct fake of the counterStore interface
//     for the block/refill/retry LOGIC — deterministic, no HTTP.
//   - fakeCASS3: an httptest S3 fake that speaks conditional writes (If-Match /
//     If-None-Match → 412), driven by the REAL aws-sdk-go-v2 client via New's
//     Endpoint override — the same fake-endpoint pattern s3blobstore_test.go
//     uses, so the production S3 code path (conditional PutObject, ETag reads,
//     412 → retry) is exercised for real. The repo has no shared S3 fake with
//     conditional-write support, so this one is scoped to exactly the CAS
//     operations the allocator uses.
package idalloc

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"sync"
	"testing"
)

// --- in-memory CAS fake ------------------------------------------------------

// memCounter is a faithful compare-and-swap over one value: a swap succeeds only
// if its token matches the current version, exactly like S3's ETag conditional.
type memCounter struct {
	mu     sync.Mutex
	value  uint64
	exists bool
	ver    int // bumps on every successful swap; token is "v<ver>"
	loads  int
	swapOK int // successful swaps = blocks reserved
}

func (m *memCounter) tokenLocked() string {
	if !m.exists {
		return ""
	}
	return fmt.Sprintf("v%d", m.ver)
}

func (m *memCounter) load(ctx context.Context) (uint64, string, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	m.loads++
	return m.value, m.tokenLocked(), nil
}

func (m *memCounter) swap(ctx context.Context, token string, newValue uint64) (bool, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if token != m.tokenLocked() {
		return false, nil // stale token: a competitor moved the counter first
	}
	m.value = newValue
	m.exists = true
	m.ver++
	m.swapOK++
	return true, nil
}

// flakyStore wraps a memCounter and, for the first `conflicts` swaps, simulates a
// competitor slipping a block in between the caller's load and its swap: it
// advances the underlying counter and then reports the caller's write as lost.
// This drives the CAS-conflict retry branch deterministically.
type flakyStore struct {
	inner           *memCounter
	competitorBlock uint64

	mu        sync.Mutex
	conflicts int
	injected  int
}

func (f *flakyStore) load(ctx context.Context) (uint64, string, error) { return f.inner.load(ctx) }

func (f *flakyStore) swap(ctx context.Context, token string, newValue uint64) (bool, error) {
	f.mu.Lock()
	inject := f.conflicts > 0
	if inject {
		f.conflicts--
		f.injected++
	}
	f.mu.Unlock()
	if inject {
		cur, tok, _ := f.inner.load(ctx)
		if _, err := f.inner.swap(ctx, tok, cur+f.competitorBlock); err != nil {
			return false, err
		}
		return false, nil // caller's token is now stale
	}
	return f.inner.swap(ctx, token, newValue)
}

func TestAllocateBlockRefill(t *testing.T) {
	m := &memCounter{}
	a := newWithStore(m, 4) // small block so 10 ids span multiple reservations
	ctx := context.Background()

	var got []uint64
	for i := 0; i < 10; i++ {
		id, err := a.Allocate(ctx)
		if err != nil {
			t.Fatalf("allocate %d: %v", i, err)
		}
		got = append(got, id)
	}
	for i, id := range got {
		if want := uint64(i + 1); id != want {
			t.Fatalf("id[%d] = %d, want %d (ids must be 1-based and contiguous)", i, id, want)
		}
	}
	// ceil(10/4) = 3 blocks; each block is one S3 CAS. This is the whole point:
	// 10 ids cost 3 S3 writes, not 10.
	if m.swapOK != 3 {
		t.Fatalf("reservations = %d, want 3 (blocks of 4 covering 10 ids)", m.swapOK)
	}
	if m.value != 12 {
		t.Fatalf("high-water = %d, want 12 (3 blocks of 4)", m.value)
	}
}

func TestAllocatePersistsAcrossRestart(t *testing.T) {
	m := &memCounter{}
	ctx := context.Background()

	// A reserves a block of 100 but hands out only 3 ids, then "crashes".
	a := newWithStore(m, 100)
	for i := 0; i < 3; i++ {
		if _, err := a.Allocate(ctx); err != nil {
			t.Fatalf("A allocate: %v", err)
		}
	}
	if m.value != 100 {
		t.Fatalf("high-water after A = %d, want 100", m.value)
	}

	// A fresh allocator over the same backing store must continue PAST the stored
	// high-water — skipping the unused tail of A's block (ids 4..100 are burned).
	b := newWithStore(m, 100)
	id, err := b.Allocate(ctx)
	if err != nil {
		t.Fatalf("B allocate: %v", err)
	}
	if id != 101 {
		t.Fatalf("restarted allocator handed out %d, want 101 (must not reuse A's block)", id)
	}
}

func TestAllocateRetriesOnCASConflict(t *testing.T) {
	inner := &memCounter{}
	f := &flakyStore{inner: inner, competitorBlock: 7, conflicts: 1}
	a := newWithStore(f, 100)

	id, err := a.Allocate(context.Background())
	if err != nil {
		t.Fatalf("allocate: %v", err)
	}
	if f.injected != 1 {
		t.Fatalf("injected conflicts = %d, want 1 (the retry path must have fired)", f.injected)
	}
	// The competitor took ids [1,7]; our retry must start strictly after it.
	if id != 8 {
		t.Fatalf("id after conflict = %d, want 8 (must skip the competitor's block)", id)
	}
	if inner.value != 107 {
		t.Fatalf("high-water = %d, want 107 (competitor's 7 + our block of 100)", inner.value)
	}
}

func TestAllocateConcurrentUniqueAcrossAllocators(t *testing.T) {
	// Two independent allocators over ONE shared counter — the production shape:
	// two region clouds minting at once must never collide.
	shared := &memCounter{}
	a1 := newWithStore(shared, 10)
	a2 := newWithStore(shared, 10)
	ctx := context.Background()

	const goroutines = 8
	const perGoroutine = 200 // > blockSize, so every goroutine forces refills

	var mu sync.Mutex
	seen := map[uint64]bool{}
	var wg sync.WaitGroup

	run := func(a *Allocator) {
		defer wg.Done()
		for i := 0; i < perGoroutine; i++ {
			id, err := a.Allocate(ctx)
			if err != nil {
				t.Errorf("allocate: %v", err)
				return
			}
			mu.Lock()
			if seen[id] {
				t.Errorf("duplicate id handed out: %d", id)
			}
			seen[id] = true
			mu.Unlock()
		}
	}
	for i := 0; i < goroutines; i++ {
		wg.Add(2)
		go run(a1)
		go run(a2)
	}
	wg.Wait()

	want := goroutines * 2 * perGoroutine
	if len(seen) != want {
		t.Fatalf("unique ids = %d, want %d (concurrent allocators overlapped)", len(seen), want)
	}
	for id := range seen {
		if id == 0 {
			t.Fatalf("handed out id 0 (ids must be 1-based)")
		}
	}
}

// --- httptest S3 fake (real SDK path) ---------------------------------------

type fakeObj struct {
	body []byte
	etag string // includes the surrounding quotes, as S3 returns them
}

// fakeCASS3 is just enough S3 for the counter: path-style GET / conditional PUT
// over an in-memory map, honouring If-Match / If-None-Match with a real 412.
type fakeCASS3 struct {
	mu      sync.Mutex
	objects map[string]fakeObj
	etagSeq int
	gets    int
	putOK   int
	put412  int
	// forceConflicts makes the next N PUTs answer 412 regardless of the
	// precondition — S3's ConditionalRequestConflict, letting a single-threaded
	// test drive the retry loop over the real wire deterministically.
	forceConflicts int
}

func (f *fakeCASS3) precondition412(w http.ResponseWriter) {
	f.put412++
	w.Header().Set("Content-Type", "application/xml")
	w.WriteHeader(http.StatusPreconditionFailed)
	io.WriteString(w, `<Error><Code>PreconditionFailed</Code><Message>At least one of the preconditions you specified did not hold.</Message></Error>`)
}

func (f *fakeCASS3) handler(w http.ResponseWriter, r *http.Request) {
	f.mu.Lock()
	defer f.mu.Unlock()
	key := r.URL.Path
	switch r.Method {
	case http.MethodGet:
		f.gets++
		obj, ok := f.objects[key]
		if !ok {
			w.Header().Set("Content-Type", "application/xml")
			w.WriteHeader(http.StatusNotFound)
			io.WriteString(w, `<Error><Code>NoSuchKey</Code><Message>The specified key does not exist.</Message></Error>`)
			return
		}
		w.Header().Set("ETag", obj.etag)
		w.WriteHeader(http.StatusOK)
		w.Write(obj.body)
	case http.MethodPut:
		if f.forceConflicts > 0 {
			f.forceConflicts--
			f.precondition412(w)
			return
		}
		body, _ := io.ReadAll(r.Body)
		obj, exists := f.objects[key]
		if r.Header.Get("If-None-Match") == "*" && exists {
			f.precondition412(w) // create-only, but it already exists
			return
		}
		if m := r.Header.Get("If-Match"); m != "" && (!exists || m != obj.etag) {
			f.precondition412(w) // replace-only, but the object moved on
			return
		}
		f.etagSeq++
		etag := fmt.Sprintf("\"e%d\"", f.etagSeq)
		f.objects[key] = fakeObj{body: body, etag: etag}
		f.putOK++
		w.Header().Set("ETag", etag)
		w.WriteHeader(http.StatusOK)
	default:
		w.WriteHeader(http.StatusNotImplemented)
	}
}

func newFakeS3Allocator(t *testing.T, blockSize uint64) (*Allocator, *fakeCASS3) {
	t.Helper()
	fake := &fakeCASS3{objects: map[string]fakeObj{}}
	srv := httptest.NewServer(http.HandlerFunc(fake.handler))
	t.Cleanup(srv.Close)

	// Static creds + region so the SDK's signer is satisfied offline (same as
	// s3blobstore_test.go).
	t.Setenv("AWS_ACCESS_KEY_ID", "test")
	t.Setenv("AWS_SECRET_ACCESS_KEY", "test")
	t.Setenv("AWS_REGION", "auto")

	a, err := New(context.Background(), Config{
		Bucket:    "idbucket",
		Prefix:    "pfx",
		Endpoint:  srv.URL,
		BlockSize: blockSize,
	})
	if err != nil {
		t.Fatalf("New: %v", err)
	}
	return a, fake
}

func TestS3AllocatorRoundTrip(t *testing.T) {
	a, fake := newFakeS3Allocator(t, 100)
	ctx := context.Background()

	for i := 0; i < 5; i++ {
		id, err := a.Allocate(ctx)
		if err != nil {
			t.Fatalf("allocate %d: %v", i, err)
		}
		if want := uint64(i + 1); id != want {
			t.Fatalf("id[%d] = %d, want %d", i, id, want)
		}
	}
	// 5 ids, one block: exactly one successful PUT.
	if fake.putOK != 1 {
		t.Fatalf("successful PUTs = %d, want 1 (one block for 5 ids)", fake.putOK)
	}
	obj := fake.objects["/idbucket/pfx/mesh/id-sequence"]
	if string(obj.body) != "100" {
		t.Fatalf("counter object = %q, want \"100\"", obj.body)
	}
}

func TestS3AllocatorRetriesReal412(t *testing.T) {
	a, fake := newFakeS3Allocator(t, 100)
	fake.forceConflicts = 2 // the first two PUTs come back 412 over the real SDK

	id, err := a.Allocate(context.Background())
	if err != nil {
		t.Fatalf("allocate: %v", err)
	}
	if id != 1 {
		t.Fatalf("id = %d, want 1", id)
	}
	if fake.put412 != 2 {
		t.Fatalf("412 responses = %d, want 2 (the SDK must have retried each)", fake.put412)
	}
	if fake.putOK != 1 {
		t.Fatalf("successful PUTs = %d, want 1", fake.putOK)
	}
}

func TestS3AllocatorConcurrentUnique(t *testing.T) {
	// Two allocators, one fake bucket, blockSize 1 → maximum CAS contention over
	// the real conditional-PUT path. Uniqueness can only hold if 412s are being
	// retried correctly.
	fake := &fakeCASS3{objects: map[string]fakeObj{}}
	srv := httptest.NewServer(http.HandlerFunc(fake.handler))
	t.Cleanup(srv.Close)
	t.Setenv("AWS_ACCESS_KEY_ID", "test")
	t.Setenv("AWS_SECRET_ACCESS_KEY", "test")
	t.Setenv("AWS_REGION", "auto")

	newA := func() *Allocator {
		a, err := New(context.Background(), Config{Bucket: "idbucket", Endpoint: srv.URL, BlockSize: 1})
		if err != nil {
			t.Fatalf("New: %v", err)
		}
		return a
	}
	a1, a2 := newA(), newA()
	ctx := context.Background()

	const goroutines = 6
	const perGoroutine = 40

	var mu sync.Mutex
	seen := map[uint64]bool{}
	var wg sync.WaitGroup
	run := func(a *Allocator) {
		defer wg.Done()
		for i := 0; i < perGoroutine; i++ {
			id, err := a.Allocate(ctx)
			if err != nil {
				t.Errorf("allocate: %v", err)
				return
			}
			mu.Lock()
			if seen[id] {
				t.Errorf("duplicate id: %d", id)
			}
			seen[id] = true
			mu.Unlock()
		}
	}
	for i := 0; i < goroutines; i++ {
		wg.Add(2)
		go run(a1)
		go run(a2)
	}
	wg.Wait()

	if want := goroutines * 2 * perGoroutine; len(seen) != want {
		t.Fatalf("unique ids = %d, want %d", len(seen), want)
	}
}