package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"
)

type Proxy struct {
	client  *http.Client
	cfg     Config
	metrics *Metrics
}

func NewProxy(cfg Config, metrics *Metrics) *Proxy {
	return &Proxy{
		client:  &http.Client{Timeout: cfg.RequestTimeout},
		cfg:     cfg,
		metrics: metrics,
	}
}

type pushResponse struct {
	Status string `json:"status"`
}

func (p *Proxy) Forward(w http.ResponseWriter, r *http.Request, backendURL, path string, body []byte, platform string) {
	start := time.Now()
	target := backendURL + path

	req, err := http.NewRequestWithContext(r.Context(), http.MethodPost, target, bytes.NewReader(body))
	if err != nil {
		p.metrics.observeUpstream(platform, "error", time.Since(start))
		writePushError(w, fmt.Sprintf("failed to create upstream request: %v", err))
		return
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := p.client.Do(req)
	if err != nil {
		p.metrics.observeUpstream(platform, "error", time.Since(start))
		writePushError(w, fmt.Sprintf("upstream request failed: %v", err))
		return
	}
	defer func() { _ = resp.Body.Close() }()

	respBody, err := io.ReadAll(resp.Body)
	if err != nil {
		p.metrics.observeUpstream(platform, "error", time.Since(start))
		writePushError(w, fmt.Sprintf("failed to read upstream response: %v", err))
		return
	}

	p.metrics.observeUpstream(platform, upstreamOutcome(resp.StatusCode, respBody), time.Since(start))

	for k, vals := range resp.Header {
		for _, v := range vals {
			w.Header().Add(k, v)
		}
	}
	if w.Header().Get("Content-Type") == "" {
		w.Header().Set("Content-Type", "application/json")
	}
	w.WriteHeader(resp.StatusCode)
	_, _ = w.Write(respBody)
}

func upstreamOutcome(statusCode int, body []byte) string {
	var resp pushResponse
	if err := json.Unmarshal(body, &resp); err == nil {
		switch resp.Status {
		case "OK":
			return "success"
		case "FAIL":
			return "fail"
		}
	}

	if statusCode >= 400 {
		return "fail"
	}

	return "success"
}

func writePushError(w http.ResponseWriter, message string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusOK)
	payload, _ := json.Marshal(map[string]string{
		"status": "FAIL",
		"error":  message,
	})
	_, _ = w.Write(payload)
}