// Copyright 2025 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cache

import (
	"fmt"
	"testing"

	"github.com/google/go-cmp/cmp"

	"go.etcd.io/etcd/api/v3/mvccpb"
	clientv3 "go.etcd.io/etcd/client/v3"
)

func TestPeekLatestAndOldest(t *testing.T) {
	tests := []struct {
		name          string
		capacity      int
		revs          []int64
		wantLatestRev int64
		wantOldestRev int64
	}{
		{
			name:          "empty_buffer",
			capacity:      4,
			revs:          nil,
			wantLatestRev: 0,
			wantOldestRev: 0,
		},
		{
			name:          "single_element",
			capacity:      8,
			revs:          []int64{1},
			wantLatestRev: 1,
			wantOldestRev: 1,
		},
		{
			name:          "ascending_fill",
			capacity:      4,
			revs:          []int64{1, 2, 3, 4},
			wantLatestRev: 4,
			wantOldestRev: 1,
		},
		{
			name:          "overwrite_when_full",
			capacity:      3,
			revs:          []int64{5, 6, 7, 8},
			wantLatestRev: 8,
			wantOldestRev: 6,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			rb := newRingBuffer(tt.capacity, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })
			for _, r := range tt.revs {
				batch, err := makeEventBatch(r, "k", 1)
				if err != nil {
					t.Fatalf("makeEventBatch(%d, k, 1) failed: %v", r, err)
				}
				rb.Append(batch)
			}

			latestRev := rb.PeekLatest()
			oldestRev := rb.PeekOldest()

			gotLatestRev := latestRev
			gotOldestRev := oldestRev

			if tt.wantLatestRev != gotLatestRev {
				t.Fatalf("PeekLatest()=%d, want=%d", gotLatestRev, tt.wantLatestRev)
			}
			if tt.wantOldestRev != gotOldestRev {
				t.Fatalf("PeekOldest()=%d, want=%d", gotOldestRev, tt.wantOldestRev)
			}
		})
	}
}

func TestIterationMethods(t *testing.T) {
	type iterTestCase struct {
		method            iterMethod
		pivot             int64
		wantIterRevisions []int64
	}
	tests := []struct {
		name           string
		capacity       int
		setupRevisions []int64
		cases          []iterTestCase
	}{
		{
			name:           "empty_buffer",
			capacity:       4,
			setupRevisions: nil,
			cases: []iterTestCase{
				{ascendGTE, 0, []int64{}},
				{ascendLT, 10, []int64{}},
				{descendGT, 0, []int64{}},
				{descendLTE, 10, []int64{}},
			},
		},
		{
			name:           "basic_filtering",
			capacity:       5,
			setupRevisions: []int64{1, 2, 3},
			cases: []iterTestCase{
				{ascendGTE, 0, []int64{1, 2, 3}},
				{ascendGTE, 2, []int64{2, 3}},
				{ascendGTE, 100, []int64{}},
				{ascendLT, 3, []int64{1, 2}},
				{ascendLT, 1, []int64{}},
				{ascendLT, 100, []int64{1, 2, 3}},
				{descendGT, 1, []int64{3, 2}},
				{descendGT, 3, []int64{}},
				{descendGT, 0, []int64{3, 2, 1}},
				{descendLTE, 2, []int64{2, 1}},
				{descendLTE, 3, []int64{3, 2, 1}},
				{descendLTE, 0, []int64{}},
			},
		},
		{
			name:           "overflowed stores only entries within capacity",
			capacity:       3,
			setupRevisions: []int64{20, 21, 22, 23, 24}, // stored: 22, 23, 24
			cases: []iterTestCase{
				{ascendGTE, 23, []int64{23, 24}},
				{ascendGTE, 0, []int64{22, 23, 24}},
				{ascendLT, 23, []int64{22}},
				{ascendLT, 25, []int64{22, 23, 24}},
				{descendGT, 22, []int64{24, 23}},
				{descendGT, 25, []int64{}},
				{descendLTE, 23, []int64{23, 22}},
				{descendLTE, 24, []int64{24, 23, 22}},
			},
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			rb := setupRingBuffer(t, tt.capacity, tt.setupRevisions)

			for _, tc := range tt.cases {
				tc := tc
				t.Run(fmt.Sprintf("%s_pivot_%d", tc.method, tc.pivot), func(t *testing.T) {
					got := collectRevisions(rb, tc.method, tc.pivot)
					if diff := cmp.Diff(tc.wantIterRevisions, got); diff != "" {
						t.Fatalf("%s(%d) mismatch (-want +got):\n%s", tc.method, tc.pivot, diff)
					}
				})
			}
		})
	}
}

func TestIterationWithBatching(t *testing.T) {
	rb := newRingBuffer(6, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })
	batchA := []*clientv3.Event{
		{Kv: &mvccpb.KeyValue{Key: []byte("key-a"), ModRevision: 5}},
	}
	batchB := []*clientv3.Event{
		{Kv: &mvccpb.KeyValue{Key: []byte("key-b-1"), ModRevision: 10}},
		{Kv: &mvccpb.KeyValue{Key: []byte("key-b-2"), ModRevision: 10}},
		{Kv: &mvccpb.KeyValue{Key: []byte("key-b-3"), ModRevision: 10}},
	}
	batchC := []*clientv3.Event{
		{Kv: &mvccpb.KeyValue{Key: []byte("key-c"), ModRevision: 12}},
	}
	rb.Append(batchA)
	rb.Append(batchB)
	rb.Append(batchC)

	tests := []struct {
		name   string
		method iterMethod
		pivot  int64
		want   [][]*clientv3.Event
	}{
		{
			name:   "ascending_gte_includes_batched_revision",
			method: ascendGTE,
			pivot:  10,
			want: [][]*clientv3.Event{
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-1"), ModRevision: 10}},
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-2"), ModRevision: 10}},
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-3"), ModRevision: 10}},
				},
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-c"), ModRevision: 12}},
				},
			},
		},
		{
			name:   "ascending_lt_stops_before_batched_revision",
			method: ascendLT,
			pivot:  10,
			want: [][]*clientv3.Event{
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-a"), ModRevision: 5}},
				},
			},
		},
		{
			name:   "all_revisions_with_proper_batch_sizes",
			method: ascendGTE,
			pivot:  0,
			want: [][]*clientv3.Event{
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-a"), ModRevision: 5}},
				},
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-1"), ModRevision: 10}},
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-2"), ModRevision: 10}},
					{Kv: &mvccpb.KeyValue{Key: []byte("key-b-3"), ModRevision: 10}},
				},
				{
					{Kv: &mvccpb.KeyValue{Key: []byte("key-c"), ModRevision: 12}},
				},
			},
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			var got [][]*clientv3.Event

			rb.iterate(tt.method, tt.pivot, func(rev int64, events []*clientv3.Event) bool {
				got = append(got, events)
				return true
			})

			if diff := cmp.Diff(tt.want, got); diff != "" {
				t.Fatalf("Events mismatch (-want +got):\n%s", diff)
			}
		})
	}
}

func TestIterationEarlyStop(t *testing.T) {
	rb := setupRingBuffer(t, 5, []int64{5, 10, 15, 20})
	tests := []struct {
		name      string
		method    iterMethod
		pivot     int64
		stopAfter int
		want      []int64
	}{
		{
			name:      "find_first_match_ascending",
			method:    ascendGTE,
			pivot:     10,
			stopAfter: 1,
			want:      []int64{10},
		},
		{
			name:      "find_first_two_ascending_lt",
			method:    ascendLT,
			pivot:     20,
			stopAfter: 2,
			want:      []int64{5, 10},
		},
		{
			name:      "find_first_two_descending_gt",
			method:    descendGT,
			pivot:     5,
			stopAfter: 2,
			want:      []int64{20, 15},
		},
		{
			name:      "find_first_match_descending_lte",
			method:    descendLTE,
			pivot:     15,
			stopAfter: 1,
			want:      []int64{15},
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			var collected []int64
			callCount := 0

			rb.iterate(tt.method, tt.pivot, func(rev int64, events []*clientv3.Event) bool {
				collected = append(collected, rev)
				callCount++

				shouldContinue := callCount < tt.stopAfter

				if !shouldContinue {
					t.Logf("Stopping early after %d items (callback returned false)", callCount)
				}

				return shouldContinue
			})

			if diff := cmp.Diff(tt.want, collected); diff != "" {
				t.Fatalf("Early stop failed.\nExpected: \nDiff (-want +got):\n%s", diff)
			}

			if callCount != tt.stopAfter {
				t.Fatalf("Expected exactly %d callback calls, got %d", tt.stopAfter, callCount)
			}

			t.Logf("Successfully stopped early: collected %v after %d callbacks",
				collected, callCount)
		})
	}
}

type iterMethod string

const (
	ascendGTE  iterMethod = "AscendGreaterOrEqual"
	ascendLT   iterMethod = "AscendLessThan"
	descendGT  iterMethod = "DescendGreaterThan"
	descendLTE iterMethod = "DescendLessOrEqual"
)

func (r *ringBuffer[T]) iterate(method iterMethod, pivot int64, fn IterFunc[T]) {
	switch method {
	case ascendGTE:
		r.AscendGreaterOrEqual(pivot, fn)
	case ascendLT:
		r.AscendLessThan(pivot, fn)
	case descendGT:
		r.DescendGreaterThan(pivot, fn)
	case descendLTE:
		r.DescendLessOrEqual(pivot, fn)
	default:
		panic(fmt.Sprintf("unknown iteration method: %s", method))
	}
}

func TestAtomicOrdered(t *testing.T) {
	tests := []struct {
		name     string
		capacity int
		inputs   []struct {
			rev  int64
			key  string
			size int
		}
		wantRev  []int64
		wantSize []int
	}{
		{
			name:     "unfiltered",
			capacity: 5,
			inputs: []struct {
				rev  int64
				key  string
				size int
			}{
				{5, "a", 1},
				{10, "b", 3},
				{15, "c", 7},
				{20, "d", 11},
			},
			wantRev:  []int64{5, 10, 15, 20},
			wantSize: []int{1, 3, 7, 11},
		},
		{
			name:     "across_wrap",
			capacity: 3,
			inputs: []struct {
				rev  int64
				key  string
				size int
			}{
				{1, "a", 2},
				{2, "b", 1},
				{3, "c", 3},
				{4, "d", 7},
			},
			wantRev:  []int64{2, 3, 4},
			wantSize: []int{1, 3, 7},
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			rb := newRingBuffer(tt.capacity, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })
			for _, in := range tt.inputs {
				batch, err := makeEventBatch(in.rev, in.key, in.size)
				if err != nil {
					t.Fatalf("makeEventBatch(%d, k, 1) failed: %v", in.rev, err)
				}
				rb.Append(batch)
			}

			gotRevs := []int64{}
			var gotSizes []int
			rb.AscendGreaterOrEqual(0, func(rev int64, events []*clientv3.Event) bool {
				gotRevs = append(gotRevs, rev)
				gotSizes = append(gotSizes, len(events))
				return true
			})

			if len(gotRevs) != len(tt.wantRev) {
				t.Fatalf("len(got) = %d, want %d", len(gotRevs), len(tt.wantRev))
			}
			for i := range gotRevs {
				if gotRevs[i] != tt.wantRev[i] {
					t.Errorf("at idx %d: rev = %d, want %d", i, gotRevs[i], tt.wantRev[i])
				}
				if gotSizes[i] != tt.wantSize[i] {
					t.Errorf("at rev %d: events.len = %d, want %d", gotRevs[i], gotSizes[i], tt.wantSize[i])
				}
			}
		})
	}
}

func TestRebaseHistory(t *testing.T) {
	tests := []struct {
		name string
		revs []int64
	}{
		{
			name: "rebase_empty_buffer",
			revs: nil,
		},
		{
			name: "rebase_after_data",
			revs: []int64{7, 8, 9},
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			rb := newRingBuffer(4, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })
			for _, r := range tt.revs {
				batch, err := makeEventBatch(r, "k", 1)
				if err != nil {
					t.Fatalf("makeEventBatch(%d, k, 1) failed: %v", r, err)
				}
				rb.Append(batch)
			}

			rb.RebaseHistory()

			oldestRev := rb.PeekOldest()
			latestRev := rb.PeekLatest()

			if oldestRev != 0 {
				t.Fatalf("PeekOldest()=%d, want=%d", oldestRev, 0)
			}
			if latestRev != 0 {
				t.Fatalf("PeekLatest()=%d, want=%d", latestRev, 0)
			}

			gotRevs := []int64{}
			rb.AscendGreaterOrEqual(0, func(rev int64, events []*clientv3.Event) bool {
				gotRevs = append(gotRevs, rev)
				return true
			})

			if len(gotRevs) != 0 {
				t.Fatalf("AscendGreaterOrEqual() len(events)=%d, want=%d", len(gotRevs), 0)
			}
		})
	}
}

func TestFull(t *testing.T) {
	tests := []struct {
		name         string
		capacity     int
		numAppends   int
		expectedFull bool
	}{
		{
			name:         "empty_buffer",
			capacity:     3,
			numAppends:   0,
			expectedFull: false,
		},
		{
			name:         "partially_filled",
			capacity:     5,
			numAppends:   3,
			expectedFull: false,
		},
		{
			name:         "exactly_at_capacity",
			capacity:     3,
			numAppends:   3,
			expectedFull: true,
		},
		{
			name:         "beyond_capacity_wrapping",
			capacity:     3,
			numAppends:   5,
			expectedFull: true,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			rb := newRingBuffer(tt.capacity, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })

			for i := 1; i <= tt.numAppends; i++ {
				batch, err := makeEventBatch(int64(i), "k", 1)
				if err != nil {
					t.Fatalf("makeEventBatch(%d, k, 1) failed: %v", i, err)
				}
				rb.Append(batch)
			}

			if got := rb.full(); got != tt.expectedFull {
				t.Fatalf("full()=%t, want=%t (capacity=%d, appends=%d)",
					got, tt.expectedFull, tt.capacity, tt.numAppends)
			}
		})
	}
}

func setupRingBuffer(t *testing.T, capacity int, revs []int64) *ringBuffer[[]*clientv3.Event] {
	rb := newRingBuffer(capacity, func(batch []*clientv3.Event) int64 { return batch[0].Kv.ModRevision })
	for _, r := range revs {
		batch, err := makeEventBatch(r, "key", 1)
		if err != nil {
			t.Fatalf("makeEventBatch(%d, %s, %d) failed: %v", r, "key", 1, err)
		}
		rb.Append(batch)
	}
	return rb
}

func collectRevisions(rb *ringBuffer[[]*clientv3.Event], method iterMethod, pivot int64) []int64 {
	revs := []int64{}
	rb.iterate(method, pivot, func(rev int64, events []*clientv3.Event) bool {
		revs = append(revs, rev)
		return true
	})
	return revs
}

func makeEventBatch(rev int64, key string, batchSize int) ([]*clientv3.Event, error) {
	if batchSize < 0 {
		return nil, fmt.Errorf("invalid batchSize %d", batchSize)
	}
	events := make([]*clientv3.Event, batchSize)
	for i := range events {
		events[i] = &clientv3.Event{
			Kv: &mvccpb.KeyValue{
				Key:         []byte(fmt.Sprintf("%s-%d", key, i)),
				ModRevision: rev,
			},
		}
	}
	return events, nil
}