// Command mockupstream is a local-only upstream used for manual gateway checks.
package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net/http"
	"time"
)

func main() {
	address := flag.String("address", "127.0.0.1:18080", "listen address")
	flag.Parse()
	mux := http.NewServeMux()
	mux.HandleFunc("POST /v1/chat/completions", openAI)
	mux.HandleFunc("POST /v1/messages", anthropic)
	server := &http.Server{Addr: *address, Handler: mux, ReadHeaderTimeout: 5 * time.Second}
	log.Printf("mock upstream listening on http://%s", *address)
	log.Fatal(server.ListenAndServe())
}

func openAI(w http.ResponseWriter, r *http.Request) {
	var request struct {
		Model  string `json:"model"`
		Stream bool   `json:"stream"`
	}
	if json.NewDecoder(r.Body).Decode(&request) != nil {
		http.Error(w, "invalid JSON", http.StatusBadRequest)
		return
	}
	if request.Stream {
		w.Header().Set("Content-Type", "text/event-stream")
		w.Header().Set("Cache-Control", "no-cache")
		fmt.Fprintf(w, "data: {\"id\":\"chatcmpl-local\",\"object\":\"chat.completion.chunk\",\"model\":%q,\"choices\":[{\"index\":0,\"delta\":{\"role\":\"assistant\",\"content\":\"hello from mock upstream\"},\"finish_reason\":null}]}\n\n", request.Model)
		w.(http.Flusher).Flush()
		time.Sleep(50 * time.Millisecond)
		fmt.Fprint(w, "data: {\"id\":\"chatcmpl-local\",\"object\":\"chat.completion.chunk\",\"choices\":[],\"usage\":{\"prompt_tokens\":4,\"completion_tokens\":4,\"total_tokens\":8}}\n\ndata: [DONE]\n\n")
		return
	}
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(map[string]any{
		"id": "chatcmpl-local", "object": "chat.completion", "model": request.Model,
		"choices": []any{map[string]any{"index": 0, "message": map[string]string{"role": "assistant", "content": "hello from mock upstream"}, "finish_reason": "stop"}},
		"usage":   map[string]int{"prompt_tokens": 4, "completion_tokens": 4, "total_tokens": 8},
	})
}

func anthropic(w http.ResponseWriter, r *http.Request) {
	var request struct {
		Model string `json:"model"`
	}
	if json.NewDecoder(r.Body).Decode(&request) != nil {
		http.Error(w, "invalid JSON", http.StatusBadRequest)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	_ = json.NewEncoder(w).Encode(map[string]any{
		"id": "msg_local", "type": "message", "role": "assistant", "model": request.Model,
		"content":     []any{map[string]string{"type": "text", "text": "hello from mock upstream"}},
		"stop_reason": "end_turn", "stop_sequence": nil,
		"usage": map[string]int{"input_tokens": 4, "output_tokens": 4},
	})
}