/**
 * Checkout Service - Domain layer for checkout operations
 * 
 * This module encapsulates all checkout business logic, making it:
 * - Testable: Pure functions with no UI dependencies
 * - Composable: Steps can be chained, mocked, or replaced
 * - Type-safe: All inputs/outputs are strictly typed
 * - Resilient: Clear contracts prevent ordering mistakes
 */

import { saleorClient } from "@/lib/saleor/client";
import type { Checkout, CheckoutLine } from "@/types/saleor";
import {
  CHECKOUT_SHIPPING_ADDRESS_UPDATE,
  CHECKOUT_BILLING_ADDRESS_UPDATE,
  CHECKOUT_COMPLETE,
  CHECKOUT_EMAIL_UPDATE,
  CHECKOUT_METADATA_UPDATE,
  CHECKOUT_SHIPPING_METHOD_UPDATE,
  CHECKOUT_LANGUAGE_CODE_UPDATE,
} from "@/lib/saleor/mutations/Checkout";

// ============================================================================
// GraphQL Response Types
// ============================================================================

interface GraphQLError {
  field?: string;
  message: string;
  code?: string;
}

interface CheckoutEmailUpdateResponse {
  checkoutEmailUpdate?: {
    checkout?: Checkout;
    errors?: GraphQLError[];
  };
}

interface CheckoutLanguageCodeUpdateResponse {
  checkoutLanguageCodeUpdate?: {
    checkout?: { id: string; languageCode: string };
    errors?: GraphQLError[];
  };
}

interface CheckoutShippingAddressUpdateResponse {
  checkoutShippingAddressUpdate?: {
    checkout?: Checkout;
    errors?: GraphQLError[];
  };
}

interface CheckoutBillingAddressUpdateResponse {
  checkoutBillingAddressUpdate?: {
    checkout?: Checkout;
    errors?: GraphQLError[];
  };
}

interface CheckoutShippingMethodUpdateResponse {
  checkoutShippingMethodUpdate?: {
    checkout?: Checkout;
    errors?: GraphQLError[];
  };
}

interface CheckoutMetadataUpdateResponse {
  updateMetadata?: {
    item?: {
      id: string;
      metadata?: Array<{ key: string; value: string }>;
    };
    errors?: GraphQLError[];
  };
}

interface CheckoutCompleteResponse {
  checkoutComplete?: {
    order?: {
      id: string;
      number: string;
      status: string;
      created: string;
      total?: {
        gross: {
          amount: number;
          currency: string;
        };
      };
    };
    errors?: GraphQLError[];
  };
}

// ============================================================================
// Domain Types
// ============================================================================

export interface Address {
  firstName: string;
  lastName: string;
  streetAddress1: string;
  streetAddress2?: string;
  city: string;
  postalCode: string;
  country: string;
  phone: string;
}

export interface CheckoutInput {
  checkoutId: string;
  email: string;
  shippingAddress: Address;
  billingAddress: Address;
  shippingMethodId: string;
  languageCode: string;
  metadata: Record<string, string>;
}

export interface CheckoutResult {
  success: boolean;
  order?: {
    id: string;
    number: string;
    languageCode: string;
  };
  error?: string;
}

export interface CheckoutStepResult<T = unknown> {
  success: boolean;
  data?: T;
  error?: string;
}

// ============================================================================
// Individual Checkout Steps (Composable Units)
// ============================================================================

/**
 * Step 1: Update checkout email
 * Isolated, testable unit that does one thing
 */
export async function updateCheckoutEmail(
  checkoutId: string,
  email: string
): Promise<CheckoutStepResult> {
  const { data } = await saleorClient.mutate<CheckoutEmailUpdateResponse>({
    mutation: CHECKOUT_EMAIL_UPDATE,
    variables: { checkoutId, email },
  });

  if (data?.checkoutEmailUpdate?.errors?.length) {
    const error = data.checkoutEmailUpdate.errors[0];
    if (error.message.includes("Couldn't resolve to a node")) {
      return { success: false, error: "CHECKOUT_EXPIRED" };
    }
    return { success: false, error: error.message };
  }

  return { success: true };
}

/**
 * Step 2: Update language code
 * CRITICAL: Must be called before checkoutComplete for correct email language
 */
export async function updateCheckoutLanguage(
  checkoutId: string,
  languageCode: string
): Promise<CheckoutStepResult> {
  const { data } = await saleorClient.mutate<CheckoutLanguageCodeUpdateResponse>({
    mutation: CHECKOUT_LANGUAGE_CODE_UPDATE,
    variables: { checkoutId, languageCode: languageCode.toUpperCase() },
  });

  if (data?.checkoutLanguageCodeUpdate?.errors?.length) {
    return { success: false, error: data.checkoutLanguageCodeUpdate.errors[0].message };
  }

  return { success: true };
}

/**
 * Step 3: Update shipping address
 */
export async function updateShippingAddress(
  checkoutId: string,
  address: Address
): Promise<CheckoutStepResult> {
  const { data } = await saleorClient.mutate<CheckoutShippingAddressUpdateResponse>({
    mutation: CHECKOUT_SHIPPING_ADDRESS_UPDATE,
    variables: {
      checkoutId,
      shippingAddress: {
        firstName: address.firstName,
        lastName: address.lastName,
        streetAddress1: address.streetAddress1,
        streetAddress2: address.streetAddress2 || "",
        city: address.city,
        postalCode: address.postalCode,
        country: address.country,
        phone: address.phone,
      },
    },
  });

  if (data?.checkoutShippingAddressUpdate?.errors?.length) {
    return { success: false, error: data.checkoutShippingAddressUpdate.errors[0].message };
  }

  return { success: true };
}

/**
 * Step 4: Update billing address
 */
export async function updateBillingAddress(
  checkoutId: string,
  address: Address
): Promise<CheckoutStepResult> {
  const { data } = await saleorClient.mutate<CheckoutBillingAddressUpdateResponse>({
    mutation: CHECKOUT_BILLING_ADDRESS_UPDATE,
    variables: {
      checkoutId,
      billingAddress: {
        firstName: address.firstName,
        lastName: address.lastName,
        streetAddress1: address.streetAddress1,
        streetAddress2: address.streetAddress2 || "",
        city: address.city,
        postalCode: address.postalCode,
        country: address.country,
        phone: address.phone,
      },
    },
  });

  if (data?.checkoutBillingAddressUpdate?.errors?.length) {
    return { success: false, error: data.checkoutBillingAddressUpdate.errors[0].message };
  }

  return { success: true };
}

/**
 * Step 5: Update shipping method
 */
export async function updateShippingMethod(
  checkoutId: string,
  shippingMethodId: string
): Promise<CheckoutStepResult> {
  const { data } = await saleorClient.mutate<CheckoutShippingMethodUpdateResponse>({
    mutation: CHECKOUT_SHIPPING_METHOD_UPDATE,
    variables: { checkoutId, shippingMethodId },
  });

  if (data?.checkoutShippingMethodUpdate?.errors?.length) {
    return { success: false, error: data.checkoutShippingMethodUpdate.errors[0].message };
  }

  return { success: true };
}

/**
 * Step 6: Update metadata
 * Non-critical - failures are logged but don't stop checkout
 */
export async function updateCheckoutMetadata(
  checkoutId: string,
  metadata: Record<string, string>
): Promise<CheckoutStepResult> {
  const metadataArray = Object.entries(metadata).map(([key, value]) => ({ key, value }));

  const { data } = await saleorClient.mutate<CheckoutMetadataUpdateResponse>({
    mutation: CHECKOUT_METADATA_UPDATE,
    variables: { checkoutId, metadata: metadataArray },
  });

  if (data?.updateMetadata?.errors?.length) {
    // Metadata is non-critical, log but don't fail
    console.warn("Failed to save checkout metadata:", data.updateMetadata.errors);
    return { success: true }; // Still return success
  }

  return { success: true };
}

/**
 * Final Step: Complete checkout
 * Returns the created order
 */
export async function completeCheckout(
  checkoutId: string
): Promise<CheckoutStepResult<{ id: string; number: string; languageCode: string }>> {
  const { data } = await saleorClient.mutate<CheckoutCompleteResponse>({
    mutation: CHECKOUT_COMPLETE,
    variables: { checkoutId },
  });

  if (data?.checkoutComplete?.errors?.length) {
    return { success: false, error: data.checkoutComplete.errors[0].message };
  }

  const order = data?.checkoutComplete?.order;
  if (!order) {
    return { success: false, error: "Order creation failed - no order returned" };
  }

  return {
    success: true,
    data: {
      id: order.id,
      number: order.number,
      languageCode: "EN", // Default fallback since checkoutComplete doesn't return languageCode directly
    },
  };
}

// ============================================================================
// Checkout Pipeline (Composed Steps)
// ============================================================================

/**
 * Execute full checkout pipeline with proper ordering
 * 
 * This function enforces the correct sequence of operations:
 * 1. Email (identifies customer)
 * 2. Language (MUST be before complete for email language!)
 * 3. Addresses
 * 4. Shipping method
 * 5. Metadata
 * 6. Complete
 * 
 * If any step fails, the pipeline stops and returns the error.
 * This prevents partial checkouts and ensures data consistency.
 */
export async function executeCheckoutPipeline(
  input: CheckoutInput
): Promise<CheckoutResult> {
  const { checkoutId, email, shippingAddress, billingAddress, shippingMethodId, languageCode, metadata } = input;

  // Step 1: Email
  const emailResult = await updateCheckoutEmail(checkoutId, email);
  if (!emailResult.success) {
    return { success: false, error: emailResult.error };
  }

  // Step 2: Language (CRITICAL for email language)
  const languageResult = await updateCheckoutLanguage(checkoutId, languageCode);
  if (!languageResult.success) {
    return { success: false, error: languageResult.error };
  }

  // Step 3: Shipping Address
  const shippingResult = await updateShippingAddress(checkoutId, shippingAddress);
  if (!shippingResult.success) {
    return { success: false, error: shippingResult.error };
  }

  // Step 4: Billing Address
  const billingResult = await updateBillingAddress(checkoutId, billingAddress);
  if (!billingResult.success) {
    return { success: false, error: billingResult.error };
  }

  // Step 5: Shipping Method
  const methodResult = await updateShippingMethod(checkoutId, shippingMethodId);
  if (!methodResult.success) {
    return { success: false, error: methodResult.error };
  }

  // Step 6: Metadata (non-critical, continues on failure)
  await updateCheckoutMetadata(checkoutId, metadata);

  // Step 7: Complete checkout
  const completeResult = await completeCheckout(checkoutId);
  if (!completeResult.success || !completeResult.data) {
    return { success: false, error: completeResult.error };
  }

  return {
    success: true,
    order: completeResult.data,
  };
}

// ============================================================================
// Validation Helpers
// ============================================================================

export function validateAddress(address: Partial<Address>): string | null {
  if (!address.firstName?.trim()) return "First name is required";
  if (!address.lastName?.trim()) return "Last name is required";
  if (!address.streetAddress1?.trim()) return "Street address is required";
  if (!address.city?.trim()) return "City is required";
  if (!address.postalCode?.trim()) return "Postal code is required";
  if (!address.country?.trim()) return "Country is required";
  if (!address.phone?.trim() || address.phone.length < 8) return "Valid phone number is required";
  return null;
}

export function validateEmail(email: string): string | null {
  if (!email?.trim()) return "Email is required";
  if (!email.includes("@")) return "Invalid email format";
  return null;
}

export function validateCheckoutInput(input: CheckoutInput): string | null {
  const emailError = validateEmail(input.email);
  if (emailError) return emailError;

  const shippingError = validateAddress(input.shippingAddress);
  if (shippingError) return `Shipping ${shippingError}`;

  const billingError = validateAddress(input.billingAddress);
  if (billingError) return `Billing ${billingError}`;

  if (!input.shippingMethodId) return "Shipping method is required";
  if (!input.checkoutId) return "Checkout ID is required";

  return null;
}

// ============================================================================
// Checkout Service Class (High-level API)
// ============================================================================

export class CheckoutService {
  constructor(private checkoutId: string) {}

  async updateEmail(email: string): Promise<CheckoutStepResult> {
    return updateCheckoutEmail(this.checkoutId, email);
  }

  async updateLanguage(languageCode: string): Promise<CheckoutStepResult> {
    return updateCheckoutLanguage(this.checkoutId, languageCode);
  }

  async updateShippingAddress(address: Address): Promise<CheckoutStepResult> {
    return updateShippingAddress(this.checkoutId, address);
  }

  async updateBillingAddress(address: Address): Promise<CheckoutStepResult> {
    return updateBillingAddress(this.checkoutId, address);
  }

  async updateShippingMethod(shippingMethodId: string): Promise<CheckoutStepResult> {
    return updateShippingMethod(this.checkoutId, shippingMethodId);
  }

  async updateMetadata(metadata: Record<string, string>): Promise<CheckoutStepResult> {
    return updateCheckoutMetadata(this.checkoutId, metadata);
  }

  async complete(): Promise<CheckoutStepResult<{ id: string; number: string; languageCode: string }>> {
    return completeCheckout(this.checkoutId);
  }

  /**
   * Execute full checkout with validation
   */
  async execute(input: Omit<CheckoutInput, "checkoutId">): Promise<CheckoutResult> {
    const fullInput: CheckoutInput = {
      ...input,
      checkoutId: this.checkoutId,
    };

    const validationError = validateCheckoutInput(fullInput);
    if (validationError) {
      return { success: false, error: validationError };
    }

    return executeCheckoutPipeline(fullInput);
  }
}

// Factory function for creating checkout service
export function createCheckoutService(checkoutId: string): CheckoutService {
  return new CheckoutService(checkoutId);
}