package gateway

import (
	"testing"

	"llmsproxy/internal/types"
)

// TestMergeUsageKeepsZeroCacheDetails locks the streaming counterpart of the
// "distinguish missed from not reported" contract: a usage chunk that reports
// prompt_tokens_details with 0 cached tokens must survive the merge, otherwise
// streaming rows lose cache_reported and the UI shows "—" instead of 0%.
func TestMergeUsageKeepsZeroCacheDetails(t *testing.T) {
	t.Run("zero-hit details survive merge", func(t *testing.T) {
		prev := &types.TokenUsage{Prompt: 10, Completion: 1, Total: 11}
		cur := &types.TokenUsage{
			Prompt: 10, Completion: 5, Total: 15,
			PromptTokensDetails: &types.PromptTokensDetails{CachedTokens: 0},
		}
		got := mergeUsage(prev, cur)
		if got.PromptTokensDetails == nil {
			t.Fatal("zero-hit prompt_tokens_details was dropped by mergeUsage")
		}
		if got.PromptTokensDetails.CachedTokens != 0 {
			t.Fatalf("cached_tokens = %d, want 0", got.PromptTokensDetails.CachedTokens)
		}
	})

	t.Run("non-zero hit still wins", func(t *testing.T) {
		prev := &types.TokenUsage{Prompt: 10, Completion: 1, Total: 11}
		cur := &types.TokenUsage{
			Prompt: 10, Completion: 5, Total: 15,
			PromptTokensDetails: &types.PromptTokensDetails{CachedTokens: 64},
		}
		got := mergeUsage(prev, cur)
		if got.PromptTokensDetails == nil || got.PromptTokensDetails.CachedTokens != 64 {
			t.Fatalf("cached_tokens lost: %+v", got.PromptTokensDetails)
		}
	})

	t.Run("absent details do not overwrite an earlier report", func(t *testing.T) {
		prev := &types.TokenUsage{
			Prompt: 10, Completion: 1, Total: 11,
			PromptTokensDetails: &types.PromptTokensDetails{CachedTokens: 32},
		}
		cur := &types.TokenUsage{Prompt: 10, Completion: 5, Total: 15}
		got := mergeUsage(prev, cur)
		if got.PromptTokensDetails == nil || got.PromptTokensDetails.CachedTokens != 32 {
			t.Fatalf("earlier cache report clobbered by a later chunk without details: %+v",
				got.PromptTokensDetails)
		}
	})

	t.Run("no cache data anywhere stays nil", func(t *testing.T) {
		prev := &types.TokenUsage{Prompt: 10, Completion: 1, Total: 11}
		cur := &types.TokenUsage{Prompt: 10, Completion: 5, Total: 15}
		got := mergeUsage(prev, cur)
		if got.PromptTokensDetails != nil {
			t.Fatalf("fabricated cache details: %+v", got.PromptTokensDetails)
		}
	})
}