package shopify

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

	"github.com/descrybe/descrybe-v2/apps/api/internal/security"
)

const (
	authModeLegacyToken       = "legacy_token"
	authModeClientCredentials = "client_credentials"
	tokenRefreshSkew          = 2 * time.Minute
	maxTokenBodyBytes         = 1 << 20
)

var (
	ErrInvalidClientCredentials = errors.New("shopify client id and secret are required together")
	ErrTokenExchangeFailed      = errors.New("shopify token exchange failed")
)

// AccessTokenResult is the Admin API token from client_credentials grant.
type AccessTokenResult struct {
	AccessToken string
	Scope       string
	ExpiresIn   int
	ExpiresAt   time.Time
}

type tokenExchangeResponse struct {
	AccessToken string `json:"access_token"`
	Scope       string `json:"scope"`
	ExpiresIn   int    `json:"expires_in"`
	Error       string `json:"error"`
	ErrorDesc   string `json:"error_description"`
}

// ExchangeClientCredentials requests a short-lived Admin API token (≈24h).
// shopHost must be a normalized *.myshopify.com host. Uses SSRF-safe dialing via httpClient.
func ExchangeClientCredentials(ctx context.Context, httpClient *http.Client, shopHost, clientID, clientSecret string) (AccessTokenResult, error) {
	clientID = strings.TrimSpace(clientID)
	clientSecret = strings.TrimSpace(clientSecret)
	if clientID == "" || clientSecret == "" {
		return AccessTokenResult{}, ErrInvalidClientCredentials
	}
	shopHost = strings.TrimSpace(strings.ToLower(shopHost))
	shopHost = strings.TrimPrefix(shopHost, "https://")
	shopHost = strings.TrimPrefix(shopHost, "http://")
	tokenURL := AdminBaseURL(shopHost) + "/admin/oauth/access_token"
	if err := GuardAdminURL(tokenURL, shopHost); err != nil {
		return AccessTokenResult{}, err
	}
	if httpClient == nil {
		httpClient = security.SafeHTTPClient(defaultTimeout, false)
	}

	form := url.Values{}
	form.Set("grant_type", "client_credentials")
	form.Set("client_id", clientID)
	form.Set("client_secret", clientSecret)

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenURL, strings.NewReader(form.Encode()))
	if err != nil {
		return AccessTokenResult{}, err
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	req.Header.Set("Accept", "application/json")
	req.Header.Set("User-Agent", "Descrybe-Shopify/2.0")

	res, err := httpClient.Do(req)
	if err != nil {
		return AccessTokenResult{}, err
	}
	defer res.Body.Close()

	limited := io.LimitReader(res.Body, maxTokenBodyBytes+1)
	raw, err := io.ReadAll(limited)
	if err != nil {
		return AccessTokenResult{}, err
	}
	if len(raw) > maxTokenBodyBytes {
		return AccessTokenResult{}, fmt.Errorf("%w: response too large", ErrTokenExchangeFailed)
	}

	parsed, err := parseAccessTokenResponse(raw)
	if err != nil {
		return AccessTokenResult{}, err
	}
	if res.StatusCode < 200 || res.StatusCode >= 300 {
		detail := firstNonEmpty(parsed.ErrorDesc, parsed.Error, strings.TrimSpace(string(raw)))
		if len(detail) > 400 {
			detail = detail[:400] + "…"
		}
		return AccessTokenResult{}, fmt.Errorf("%w: HTTP %d: %s", ErrTokenExchangeFailed, res.StatusCode, detail)
	}
	if parsed.AccessToken == "" {
		return AccessTokenResult{}, fmt.Errorf("%w: empty access_token", ErrTokenExchangeFailed)
	}
	expiresIn := parsed.ExpiresIn
	if expiresIn <= 0 {
		expiresIn = 86399
	}
	now := time.Now().UTC()
	return AccessTokenResult{
		AccessToken: parsed.AccessToken,
		Scope:       parsed.Scope,
		ExpiresIn:   expiresIn,
		ExpiresAt:   now.Add(time.Duration(expiresIn) * time.Second),
	}, nil
}

func parseAccessTokenResponse(raw []byte) (tokenExchangeResponse, error) {
	var parsed tokenExchangeResponse
	if len(raw) == 0 {
		return parsed, fmt.Errorf("%w: empty body", ErrTokenExchangeFailed)
	}
	if err := json.Unmarshal(raw, &parsed); err != nil {
		return parsed, fmt.Errorf("%w: invalid json", ErrTokenExchangeFailed)
	}
	return parsed, nil
}

func tokenNeedsRefresh(expiresAt *time.Time, now time.Time) bool {
	if expiresAt == nil {
		return true
	}
	return !expiresAt.After(now.Add(tokenRefreshSkew))
}