package proxy

import (
	"bytes"
	"io"
	"net/http"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
)

const maxResponseBytes = 10 << 20 // 10 MiB MVP safety cap

type Handler struct {
	BaseClient *http.Client
}

func NewHandler() *Handler {
	return &Handler{BaseClient: &http.Client{Timeout: 30 * time.Second}}
}

func normalizeMethod(raw string) string {
	m := strings.ToUpper(strings.TrimSpace(raw))
	switch m {
	case http.MethodGet, http.MethodPost, http.MethodPut, http.MethodPatch,
		http.MethodDelete, http.MethodHead, http.MethodOptions:
		return m
	default:
		return http.MethodGet
	}
}

func (h *Handler) ProxyHTTP(c *gin.Context) {
	var spec HttpSpec
	if err := c.ShouldBindJSON(&spec); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid HttpSpec", "detail": err.Error()})
		return
	}

	method := normalizeMethod(spec.Method)

	u, err := ValidateURL(spec.URL)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}
	query := u.Query()
	for key, value := range spec.Query {
		query.Set(key, value)
	}
	u.RawQuery = query.Encode()

	var body io.Reader
	if spec.Body != nil && spec.Body.Mode != "none" && method != http.MethodGet && method != http.MethodHead {
		body = bytes.NewBufferString(spec.Body.Raw)
	}

	req, err := http.NewRequestWithContext(c.Request.Context(), method, u.String(), body)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "cannot create request", "detail": err.Error()})
		return
	}
	for key, value := range spec.Headers {
		// Hop-by-hop headers are managed by net/http.
		if !isHopByHop(key) {
			req.Header.Set(key, value)
		}
	}
	if spec.Body != nil && spec.Body.Mode == "json" && req.Header.Get("Content-Type") == "" {
		req.Header.Set("Content-Type", "application/json")
	}

	client := h.BaseClient
	if spec.TimeoutMS > 0 {
		client = &http.Client{Timeout: time.Duration(spec.TimeoutMS) * time.Millisecond}
	}
	started := time.Now()
	res, err := client.Do(req)
	if err != nil {
		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream request failed", "detail": err.Error()})
		return
	}
	defer res.Body.Close()

	payload, err := io.ReadAll(io.LimitReader(res.Body, maxResponseBytes+1))
	if err != nil {
		c.JSON(http.StatusBadGateway, gin.H{"error": "cannot read upstream response", "detail": err.Error()})
		return
	}
	if len(payload) > maxResponseBytes {
		c.JSON(http.StatusBadGateway, gin.H{"error": "upstream response exceeds 10 MiB limit"})
		return
	}

	headers := make(map[string]string, len(res.Header))
	for key, values := range res.Header {
		headers[strings.ToLower(key)] = strings.Join(values, ", ")
	}
	c.JSON(http.StatusOK, HttpResult{
		Status:  res.StatusCode,
		Headers: headers,
		Body:    string(payload),
		TimeMS:  time.Since(started).Milliseconds(),
		Size:    len(payload),
	})
}

func isHopByHop(name string) bool {
	switch strings.ToLower(name) {
	case "connection", "keep-alive", "proxy-authenticate", "proxy-authorization", "te", "trailer", "transfer-encoding", "upgrade", "host", "content-length":
		return true
	default:
		return false
	}
}