feat: implement AI gateway phase one runtime

apps/api/internal/clients/simulation.go

@@ -0,0 +1,119 @@
+package clients
+
+import (
+	"context"
+	"fmt"
+	"strings"
+)
+
+type SimulationClient struct{}
+
+func (c SimulationClient) Run(ctx context.Context, request Request) (Response, error) {
+	_ = ctx
+	profile := simulationProfile(request)
+	if profile == "retryable_failure" {
+		return Response{}, &ClientError{Code: "server_error", Message: "simulated retryable failure", Retryable: true}
+	}
+	if profile == "fatal_failure" || profile == "non_retryable_failure" {
+		return Response{}, &ClientError{Code: "bad_request", Message: "simulated non-retryable failure", Retryable: false}
+	}
+	return Response{
+		Result:   simulatedResult(request),
+		Usage:    simulatedUsage(request),
+		Progress: simulatedProgress(request),
+	}, nil
+}
+
+func simulationProfile(request Request) string {
+	if value := stringValue(request.Candidate.Credentials, "simulationFailure"); value != "" {
+		return value
+	}
+	if value := stringValue(request.Candidate.PlatformConfig, "simulationFailure"); value != "" {
+		return value
+	}
+	if value := stringValue(request.Body, "simulationProfile"); value != "" {
+		return value
+	}
+	if value := stringValue(request.Body, "testProfile"); value != "" {
+		return value
+	}
+	return "success"
+}
+
+func simulatedResult(request Request) map[string]any {
+	switch request.Kind {
+	case "chat.completions":
+		return map[string]any{
+			"id":      "chatcmpl-simulated",
+			"object":  "chat.completion",
+			"created": nowUnix(),
+			"model":   request.Model,
+			"choices": []any{map[string]any{
+				"index":         0,
+				"finish_reason": "stop",
+				"message": map[string]any{
+					"role":    "assistant",
+					"content": fmt.Sprintf("simulation response from %s", request.Candidate.Provider),
+				},
+			}},
+			"usage": map[string]any{"prompt_tokens": 12, "completion_tokens": 8, "total_tokens": 20},
+		}
+	case "responses":
+		return map[string]any{
+			"id":          "resp-simulated",
+			"object":      "response",
+			"created_at":  nowUnix(),
+			"model":       request.Model,
+			"output_text": fmt.Sprintf("simulation response from %s", request.Candidate.Provider),
+			"usage":       map[string]any{"input_tokens": 12, "output_tokens": 8, "total_tokens": 20},
+		}
+	case "images.edits":
+		return map[string]any{
+			"id":      "img-edit-simulated",
+			"created": nowUnix(),
+			"model":   request.Model,
+			"data": []any{map[string]any{
+				"url":            "/static/simulation/image-edit.png",
+				"revised_prompt": firstNonEmptyPrompt(request.Body, "simulation image edit"),
+			}},
+		}
+	default:
+		return map[string]any{
+			"id":      "img-simulated",
+			"created": nowUnix(),
+			"model":   request.Model,
+			"data": []any{map[string]any{
+				"url":            "/static/simulation/image.png",
+				"revised_prompt": firstNonEmptyPrompt(request.Body, "simulation image"),
+			}},
+		}
+	}
+}
+
+func simulatedUsage(request Request) Usage {
+	if request.ModelType == "chat" || request.Kind == "responses" {
+		return Usage{InputTokens: 12, OutputTokens: 8, TotalTokens: 20}
+	}
+	return Usage{}
+}
+
+func simulatedProgress(request Request) []Progress {
+	provider := request.Candidate.Provider
+	if provider == "" {
+		provider = "simulation"
+	}
+	return []Progress{
+		{Phase: "normalizing", Progress: 0.2, Message: "request normalized", Payload: map[string]any{"provider": provider}},
+		{Phase: "submitting", Progress: 0.55, Message: "simulation client submitted", Payload: map[string]any{"clientId": request.Candidate.ClientID}},
+		{Phase: "fetching_result", Progress: 0.85, Message: "simulation result ready", Payload: map[string]any{"kind": request.Kind}},
+	}
+}
+
+func firstNonEmptyPrompt(body map[string]any, fallback string) string {
+	for _, key := range []string{"prompt", "input"} {
+		if value := strings.TrimSpace(stringValue(body, key)); value != "" {
+			return value
+		}
+	}
+	return fallback
+}