package strategy

import (
	"sync"
	"testing"
	"time"

	"github.com/shopspring/decimal"
)

func d(i int64) decimal.Decimal { return decimal.NewFromInt(i) }

func TestSMA_WarmupAndSliding(t *testing.T) {
	type step struct {
		in      int64
		wantVal string // 用字串比對可避免浮點誤差（decimal 本就精準）
		ready   bool
	}
	tests := []struct {
		name   string
		window uint
		steps  []step
	}{
		{
			name:   "warmup_then_ready_and_slide",
			window: 3,
			steps: []step{
				{in: 1, wantVal: "1", ready: false},   // [1]     avg=1
				{in: 2, wantVal: "1.5", ready: false}, // [1,2]   avg=1.5
				{in: 3, wantVal: "2", ready: true},    // [1,2,3] avg=2
				{in: 4, wantVal: "3", ready: true},    // [2,3,4] avg=3
				{in: 5, wantVal: "4", ready: true},    // [3,4,5] avg=4
				{in: 6, wantVal: "5", ready: true},    // [4,5,6] avg=5
				{in: 7, wantVal: "6", ready: true},    // [5,6,7] avg=6
			},
		},
		{
			name:   "window_1_behaves_as_latest_value",
			window: 1,
			steps: []step{
				{in: 10, wantVal: "10", ready: true},
				{in: 11, wantVal: "11", ready: true},
				{in: 12, wantVal: "12", ready: true},
			},
		},
	}

	for _, tc := range tests {
		tc := tc
		t.Run(tc.name, func(t *testing.T) {
			s := NewSMA(tc.window)
			for i, st := range tc.steps {
				got := s.Update(d(st.in))
				if got.Value.String() != st.wantVal {
					t.Fatalf("step %d: got value %s, want %s", i, got.Value, st.wantVal)
				}
				if got.Ready != st.ready {
					t.Fatalf("step %d: ready mismatch, got %v, want %v", i, got.Ready, st.ready)
				}
				// Load() 應該等於最新快照
				ld := s.Load()
				if ld.Value.String() != st.wantVal || ld.Ready != st.ready {
					t.Fatalf("step %d: Load() not latest snapshot", i)
				}
			}
		})
	}
}

func TestSMA_NewZeroWindowShouldPanic(t *testing.T) {
	defer func() {
		if r := recover(); r == nil {
			t.Fatalf("expected panic when window=0")
		}
	}()
	_ = NewSMA(0)
}

func TestSMA_MultiReadersSingleWriter(t *testing.T) {
	s := NewSMA(3)

	var wg sync.WaitGroup
	stop := make(chan struct{})

	// 多 reader 併發讀取（零鎖）
	reader := func() {
		defer wg.Done()
		for {
			select {
			case <-stop:
				return
			default:
				_ = s.Load() // 不做判斷，重點是不得 panic
			}
		}
	}

	// 啟動多個讀者
	for i := 0; i < 8; i++ {
		wg.Add(1)
		go reader()
	}

	// 單 writer 更新
	prices := []int64{1, 2, 3, 4, 5, 6, 7}
	for _, p := range prices {
		s.Update(d(p))
		time.Sleep(1 * time.Millisecond)
	}

	// 停 reader
	close(stop)
	wg.Wait()

	// 最終應為 [5,6,7] 的平均=6，且 ready=true
	got := s.Load()
	if got.Value.String() != "6" || !got.Ready {
		t.Fatalf("final snapshot mismatch: got value=%s ready=%v", got.Value, got.Ready)
	}
}