package services

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"time"

	"go.uber.org/zap"
)

// CaptchaService verifies CAPTCHA tokens.
// F027/F029: ORIGIN_FEATURES_REGISTRY.md — CAPTCHA anti-bot.
// Supports Cloudflare Turnstile (preferred over reCAPTCHA per ORIGIN spec).
type CaptchaService struct {
	secretKey  string
	verifyURL  string
	enabled    bool
	httpClient *http.Client
	logger     *zap.Logger
}

// CaptchaConfig holds configuration for the CAPTCHA service.
type CaptchaConfig struct {
	Enabled   bool
	SecretKey string
	// Provider: "turnstile" (default) or "hcaptcha"
	Provider string
}

// turnstileResponse is the response from Cloudflare Turnstile verification API.
type turnstileResponse struct {
	Success    bool     `json:"success"`
	ErrorCodes []string `json:"error-codes"`
}

// NewCaptchaService creates a new CAPTCHA verification service.
func NewCaptchaService(config CaptchaConfig, logger *zap.Logger) *CaptchaService {
	verifyURL := "https://challenges.cloudflare.com/turnstile/v0/siteverify"
	if config.Provider == "hcaptcha" {
		verifyURL = "https://hcaptcha.com/siteverify"
	}

	return &CaptchaService{
		secretKey: config.SecretKey,
		verifyURL: verifyURL,
		enabled:   config.Enabled,
		httpClient: &http.Client{
			Timeout: 10 * time.Second,
		},
		logger: logger,
	}
}

// Verify validates a CAPTCHA response token.
// Returns nil if valid, error if invalid or verification failed.
func (s *CaptchaService) Verify(ctx context.Context, token, remoteIP string) error {
	if !s.enabled {
		return nil
	}
	if token == "" {
		return fmt.Errorf("captcha token required")
	}

	form := url.Values{
		"secret":   {s.secretKey},
		"response": {token},
	}
	if remoteIP != "" {
		form.Set("remoteip", remoteIP)
	}

	resp, err := s.httpClient.PostForm(s.verifyURL, form)
	if err != nil {
		s.logger.Warn("captcha verification request failed", zap.Error(err))
		// Fail open: if CAPTCHA service is down, allow the request
		return nil
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		s.logger.Warn("failed to read captcha response", zap.Error(err))
		return nil
	}

	var result turnstileResponse
	if err := json.Unmarshal(body, &result); err != nil {
		s.logger.Warn("failed to parse captcha response", zap.Error(err))
		return nil
	}

	if !result.Success {
		return fmt.Errorf("captcha verification failed: %v", result.ErrorCodes)
	}

	return nil
}

// IsEnabled returns whether CAPTCHA verification is active.
func (s *CaptchaService) IsEnabled() bool {
	return s.enabled
}