feat: implement advanced condition-based heuristic model routing

Upgrades the routing engine to support tag, token limit, multimodal, reasoning, and tool calling conditions. Adds unit tests for the new routing features.

internal/providers/helpers_test.go

@@ -0,0 +1,127 @@
+package providers
+
+import (
+	"encoding/json"
+	"testing"
+
+	"gophergate/internal/models"
+)
+
+func TestSanitizeFunctionName(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"google-search", "google-search"},
+		{"google.search", "google_search"},
+		{"google search", "google_search"},
+		{"web_search(query)", "web_search_query_"},
+		{"", "function"},
+		{"123_abc-XYZ", "123_abc-XYZ"},
+		{"invalid.name.with.dots", "invalid_name_with_dots"},
+	}
+
+	for _, tc := range tests {
+		actual := sanitizeFunctionName(tc.input)
+		if actual != tc.expected {
+			t.Errorf("sanitizeFunctionName(%q) = %q; expected %q", tc.input, actual, tc.expected)
+		}
+	}
+}
+
+func TestMessagesToOpenAIJSON_SanitizeToolCalls(t *testing.T) {
+	messages := []models.UnifiedMessage{
+		{
+			Role: "assistant",
+			Content: []models.UnifiedContentPart{
+				{Type: "text", Text: "I will use search."},
+			},
+			ToolCalls: []models.ToolCall{
+				{
+					ID:   "call_1",
+					Type: "function",
+					Function: models.FunctionCall{
+						Name:      "google.search",
+						Arguments: `{"query": "hello"}`,
+					},
+				},
+			},
+		},
+		{
+			Role: "tool",
+			Content: []models.UnifiedContentPart{
+				{Type: "text", Text: `{"result": "success"}`},
+			},
+			ToolCallID: stringPtr("call_1"),
+			Name:       stringPtr("google.search"),
+		},
+	}
+
+	res, err := MessagesToOpenAIJSON(messages)
+	if err != nil {
+		t.Fatalf("MessagesToOpenAIJSON failed: %v", err)
+	}
+
+	if len(res) != 2 {
+		t.Fatalf("expected 2 messages, got %d", len(res))
+	}
+
+	// Verify assistant message
+	msg1 := res[0].(map[string]interface{})
+	if msg1["role"] != "assistant" {
+		t.Errorf("expected role assistant, got %v", msg1["role"])
+	}
+	calls := msg1["tool_calls"].([]models.ToolCall)
+	if len(calls) != 1 {
+		t.Fatalf("expected 1 tool call, got %d", len(calls))
+	}
+	if calls[0].Function.Name != "google_search" {
+		t.Errorf("expected function name google_search, got %q", calls[0].Function.Name)
+	}
+
+	// Verify tool response message
+	msg2 := res[1].(map[string]interface{})
+	if msg2["role"] != "tool" {
+		t.Errorf("expected role tool, got %v", msg2["role"])
+	}
+	if msg2["name"] != "google_search" {
+		t.Errorf("expected tool name google_search, got %v", msg2["name"])
+	}
+}
+
+func TestBuildOpenAIBody_SanitizeToolsAndChoice(t *testing.T) {
+	req := &models.UnifiedRequest{
+		Model: "gpt-4o",
+		Tools: []models.Tool{
+			{
+				Type: "function",
+				Function: models.FunctionDef{
+					Name: "google.search",
+				},
+			},
+		},
+		ToolChoice: json.RawMessage(`{"type": "function", "function": {"name": "google.search"}}`),
+	}
+
+	body := BuildOpenAIBody(req, nil, false)
+
+	// Verify tools
+	tools := body["tools"].([]models.Tool)
+	if len(tools) != 1 {
+		t.Fatalf("expected 1 tool, got %d", len(tools))
+	}
+	if tools[0].Function.Name != "google_search" {
+		t.Errorf("expected tool function name google_search, got %q", tools[0].Function.Name)
+	}
+
+	// Verify tool_choice
+	toolChoice := body["tool_choice"].(map[string]interface{})
+	funcObj := toolChoice["function"].(map[string]interface{})
+	if funcObj["name"] != "google_search" {
+		t.Errorf("expected tool_choice function name google_search, got %q", funcObj["name"])
+	}
+}
+
+func stringPtr(s string) *string {
+	return &s
+}