package memory

import (
	"context"
	"math"
	"testing"
	"time"
)

func TestRetriever_DecayFactor_久未使用降权(t *testing.T) {
	t.Parallel()
	r := NewRetriever(newTestStore(t))
	now := time.Now().UTC()

	tests := []struct {
		name        string
		updatedAt   time.Time
		decayWeight float64
		want        float64
	}{
		{name: "fresh keeps full weight", updatedAt: now, decayWeight: 1.0, want: 1.0},
		// 默认半衰期为 30 天：60 天前 = 2 个半衰期 = 2^-2。
		{name: "two half-lives halves twice", updatedAt: now.Add(-60 * 24 * time.Hour), decayWeight: 1.0, want: 0.25},
		// 较低的基础 decay_weight 会整体压低曲线。
		{name: "low decay_weight scales down", updatedAt: now, decayWeight: 0.5, want: 0.5},
		{name: "low weight plus age compounds", updatedAt: now.Add(-60 * 24 * time.Hour), decayWeight: 0.5, want: 0.125},
		// 未来时间戳不得把得分抬到基础权重以上。
		{name: "future timestamp clamps to zero", updatedAt: now.Add(time.Hour), decayWeight: 1.0, want: 1.0},
	}
	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			got := r.decayFactor(MemoryItem{
				DecayWeight: tt.decayWeight,
				UpdatedAt:   tt.updatedAt,
			}, now)
			if math.Abs(got-tt.want) > 1e-9 {
				t.Fatalf("decayFactor = %v, want %v", got, tt.want)
			}
		})
	}
}

func TestRetriever_Retrieve_DecayWeight_降权(t *testing.T) {
	t.Parallel()
	ctx := context.Background()
	s := newTestStore(t)

	now := time.Now().UTC()
	// 一条新鲜但 decay_weight 近乎零的条目（design：用户可削弱某记忆）。
	addItem(t, s, MemoryItem{
		PersonaID: "persona.a", Content: "低权重但新鲜", UpdatedAt: now,
		DecayWeight: 0.1, Scope: ScopePersona, Kind: KindWorldEvent,
	})
	// 稍有历史、但 decay_weight 满额的条目。
	addItem(t, s, MemoryItem{
		PersonaID: "persona.a", Content: "权重高稍旧", UpdatedAt: now.Add(-time.Hour),
		DecayWeight: 1.0, Scope: ScopePersona, Kind: KindWorldEvent,
	})

	r := NewRetriever(s)
	// query 为空时无任何命中，因此排序完全由衰减因子
	// （decay_weight × 时间衰减）驱动：低权重的新条目必须
	// 排在满权重、稍旧的条目之后。
	results, err := r.Retrieve(ctx, "persona.a", "", 10)
	if err != nil {
		t.Fatalf("Retrieve: %v", err)
	}
	if len(results) != 2 {
		t.Fatalf("got %d results, want 2", len(results))
	}
	if got := results[0].Item.Content; got != "权重高稍旧" {
		t.Fatalf("top result = %q, want the full-decay-weight item", got)
	}
	if got := results[1].Item.Content; got != "低权重但新鲜" {
		t.Fatalf("second result = %q, want the low-decay-weight item", got)
	}
}