refactor backend API structure

internal/httpapi/gemini/convert_request.go

@@ -0,0 +1,48 @@
+package gemini
+
+import (
+	"fmt"
+	"strings"
+
+	"ds2api/internal/config"
+	"ds2api/internal/promptcompat"
+	"ds2api/internal/util"
+)
+
+//nolint:unused // kept for native Gemini adapter route compatibility.
+func normalizeGeminiRequest(store ConfigReader, routeModel string, req map[string]any, stream bool) (promptcompat.StandardRequest, error) {
+	requestedModel := strings.TrimSpace(routeModel)
+	if requestedModel == "" {
+		return promptcompat.StandardRequest{}, fmt.Errorf("model is required in request path")
+	}
+
+	resolvedModel, ok := config.ResolveModel(store, requestedModel)
+	if !ok {
+		return promptcompat.StandardRequest{}, fmt.Errorf("model %q is not available", requestedModel)
+	}
+	defaultThinkingEnabled, searchEnabled, _ := config.GetModelConfig(resolvedModel)
+	thinkingEnabled := util.ResolveThinkingEnabled(req, defaultThinkingEnabled)
+
+	messagesRaw := geminiMessagesFromRequest(req)
+	if len(messagesRaw) == 0 {
+		return promptcompat.StandardRequest{}, fmt.Errorf("request must include non-empty contents")
+	}
+
+	toolsRaw := convertGeminiTools(req["tools"])
+	finalPrompt, toolNames := promptcompat.BuildOpenAIPromptForAdapter(messagesRaw, toolsRaw, "", thinkingEnabled)
+	passThrough := collectGeminiPassThrough(req)
+
+	return promptcompat.StandardRequest{
+		Surface:        "google_gemini",
+		RequestedModel: requestedModel,
+		ResolvedModel:  resolvedModel,
+		ResponseModel:  requestedModel,
+		Messages:       messagesRaw,
+		FinalPrompt:    finalPrompt,
+		ToolNames:      toolNames,
+		Stream:         stream,
+		Thinking:       thinkingEnabled,
+		Search:         searchEnabled,
+		PassThrough:    passThrough,
+	}, nil
+}