/**
 * MotorSignal — Play Purchase Verification & Server Acknowledgement Module
 * Communicates with Google Play Developer API v3 (Android Publisher API)
 * to authoritatively verify and acknowledge subscriptions and one-time purchases.
 */

export interface PlayVerificationEnv {
  GOOGLE_SERVICE_ACCOUNT_EMAIL?: string;
  GOOGLE_SERVICE_ACCOUNT_PRIVATE_KEY?: string;
  GOOGLE_PLAY_PACKAGE_NAME?: string;
}

export const AUTHORITATIVE_PACKAGE_NAME = 'app.motorsignal.motorcycle';

export const ALLOWED_PRODUCTS = {
  PRO_MONTHLY: 'motorsignal_pro_monthly',
  PRO_LIFETIME: 'motorsignal_pro_lifetime',
} as const;

export interface VerifyPurchaseRequest {
  productId: string;
  purchaseToken: string;
}

export type AcknowledgementState = 'acknowledged' | 'pendingRetry' | 'notApplicable';

export interface VerificationResponse {
  schemaVersion: number;
  productId: string;
  plan: 'proMonthly' | 'proLifetime' | 'free';
  status:
    | 'proMonthlyActive'
    | 'proMonthlyGrace'
    | 'proMonthlyAccountHold'
    | 'proMonthlyPaused'
    | 'proMonthlyExpired'
    | 'proLifetime'
    | 'unknown'
    | 'syncPending';
  verificationStatus: 'verified' | 'unverified' | 'expired' | 'revoked';
  acknowledgementState: AcknowledgementState;
  verifiedAt: string;
  expiresAt: string | null;
  tokenHash: string;
  error?: string;
}

// In-memory token cache for short-lived Google OAuth access token
let cachedAccessToken: { token: string; expiresAtMs: number } | null = null;

/**
 * Derives SHA-256 fingerprint of purchase token for replay tracking / cache key.
 */
export async function computeTokenHash(token: string): Promise<string> {
  const enc = new TextEncoder().encode(token);
  const digest = await crypto.subtle.digest('SHA-256', enc);
  return Array.from(new Uint8Array(digest))
    .map((b) => b.toString(16).padStart(2, '0'))
    .join('');
}

/**
 * Generates an OAuth2 access token for Google APIs via a service account private key.
 */
export async function getGoogleAccessToken(
  clientEmail: string,
  privateKeyPem: string
): Promise<string> {
  const nowMs = Date.now();
  if (cachedAccessToken && cachedAccessToken.expiresAtMs > nowMs + 60000) {
    return cachedAccessToken.token;
  }

  const nowSec = Math.floor(nowMs / 1000);
  const expSec = nowSec + 3600;

  const header = {
    alg: 'RS256',
    typ: 'JWT',
  };

  const claimSet = {
    iss: clientEmail,
    scope: 'https://www.googleapis.com/auth/androidpublisher',
    aud: 'https://oauth2.googleapis.com/token',
    exp: expSec,
    iat: nowSec,
  };

  const encodedHeader = base64UrlEncode(JSON.stringify(header));
  const encodedClaimSet = base64UrlEncode(JSON.stringify(claimSet));
  const signingInput = `${encodedHeader}.${encodedClaimSet}`;

  const binaryKey = pemToBinary(privateKeyPem);
  const cryptoKey = await crypto.subtle.importKey(
    'pkcs8',
    binaryKey,
    {
      name: 'RSASSA-PKCS1-v1_5',
      hash: { name: 'SHA-256' },
    },
    false,
    ['sign']
  );

  const signature = await crypto.subtle.sign(
    'RSASSA-PKCS1-v1_5',
    cryptoKey,
    new TextEncoder().encode(signingInput)
  );

  const jwt = `${signingInput}.${base64UrlEncode(signature)}`;

  const tokenResp = await fetch('https://oauth2.googleapis.com/token', {
    method: 'POST',
    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
    body: new URLSearchParams({
      grant_type: 'urn:ietf:params:oauth:grant-type:jwt-bearer',
      assertion: jwt,
    }),
  });

  if (!tokenResp.ok) {
    const errText = await tokenResp.text().catch(() => '');
    throw new Error(`Google OAuth exchange failed (${tokenResp.status}): ${errText}`);
  }

  const tokenData = (await tokenResp.json()) as {
    access_token: string;
    expires_in: number;
  };

  cachedAccessToken = {
    token: tokenData.access_token,
    expiresAtMs: nowMs + (tokenData.expires_in || 3600) * 1000,
  };

  return cachedAccessToken.token;
}

/**
 * Authoritatively verifies and acknowledges a Google Play purchase token.
 */
export async function verifyPlayPurchase(
  req: VerifyPurchaseRequest,
  env: PlayVerificationEnv
): Promise<{ status: number; body: VerificationResponse | { error: string; code: string } }> {
  const { productId, purchaseToken } = req;

  if (!productId || typeof productId !== 'string') {
    return { status: 400, body: { error: 'Invalid or missing productId', code: 'INVALID_PRODUCT' } };
  }

  if (!purchaseToken || typeof purchaseToken !== 'string' || purchaseToken.length < 10) {
    return { status: 400, body: { error: 'Invalid or missing purchaseToken', code: 'INVALID_PURCHASE' } };
  }

  if (
    productId !== ALLOWED_PRODUCTS.PRO_MONTHLY &&
    productId !== ALLOWED_PRODUCTS.PRO_LIFETIME
  ) {
    return {
      status: 400,
      body: { error: `Product '${productId}' is not recognized`, code: 'INVALID_PRODUCT' },
    };
  }

  const tokenHash = await computeTokenHash(purchaseToken);
  const packageName = env.GOOGLE_PLAY_PACKAGE_NAME || AUTHORITATIVE_PACKAGE_NAME;
  const clientEmail = env.GOOGLE_SERVICE_ACCOUNT_EMAIL;
  const privateKey = env.GOOGLE_SERVICE_ACCOUNT_PRIVATE_KEY;

  if (!clientEmail || !privateKey) {
    return {
      status: 503,
      body: {
        error: 'Google Play verification credentials not configured on server',
        code: 'GOOGLE_TEMPORARILY_UNAVAILABLE',
      },
    };
  }

  let accessToken: string;
  try {
    accessToken = await getGoogleAccessToken(clientEmail, privateKey);
  } catch (err: unknown) {
    const tokenPrefix = tokenHash.substring(0, 8);
    console.error(`[PlayVerification] [hash=${tokenPrefix}] OAuth token acquisition failed`, err);
    return {
      status: 502,
      body: {
        error: 'Failed to authenticate with Google Developer API',
        code: 'GOOGLE_TEMPORARILY_UNAVAILABLE',
      },
    };
  }

  if (productId === ALLOWED_PRODUCTS.PRO_MONTHLY) {
    return await verifySubscription(packageName, purchaseToken, tokenHash, accessToken);
  } else {
    return await verifyOneTimeProduct(packageName, productId, purchaseToken, tokenHash, accessToken);
  }
}

/**
 * Extracts latest valid expiration timestamp across all line items matching the target product.
 */
export function extractLatestExpiry(
  lineItems: Array<{ productId?: string; expiryTime?: string }> | undefined,
  targetProductId: string
): { expiryTimeIso: string | null; expiryTimeMs: number } {
  if (!lineItems || lineItems.length === 0) {
    return { expiryTimeIso: null, expiryTimeMs: NaN };
  }

  let latestMs = NaN;
  let latestIso: string | null = null;

  for (const item of lineItems) {
    if (item.productId && item.productId !== targetProductId) {
      continue;
    }
    if (item.expiryTime) {
      const ms = Date.parse(item.expiryTime);
      if (!isNaN(ms) && (isNaN(latestMs) || ms > latestMs)) {
        latestMs = ms;
        latestIso = new Date(ms).toISOString();
      }
    }
  }

  return { expiryTimeIso: latestIso, expiryTimeMs: latestMs };
}

/**
 * Acknowledges a subscription token server-side via purchases.subscriptions.acknowledge.
 */
export async function acknowledgeSubscription(
  packageName: string,
  subscriptionId: string,
  token: string,
  accessToken: string,
  tokenHash: string
): Promise<{ success: boolean; isRetryable: boolean }> {
  const endpoint = `https://androidpublisher.googleapis.com/androidpublisher/v3/applications/${encodeURIComponent(
    packageName
  )}/purchases/subscriptions/${encodeURIComponent(subscriptionId)}/tokens/${encodeURIComponent(
    token
  )}:acknowledge`;

  try {
    const res = await fetch(endpoint, {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${accessToken}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({}),
    });

    if (res.ok || res.status === 204) {
      return { success: true, isRetryable: false };
    }

    const tokenPrefix = tokenHash.substring(0, 8);
    const text = await res.text().catch(() => '');

    // Idempotency: If already acknowledged, Google may respond with 400 'Purchase already acknowledged' or similar
    if (res.status === 400 && text.toLowerCase().includes('already acknowledged')) {
      return { success: true, isRetryable: false };
    }

    console.error(
      `[PlayVerification] [hash=${tokenPrefix}] Subscription acknowledge failed: status=${res.status} body=${text}`
    );

    const isRetryable = res.status === 429 || res.status >= 500;
    return { success: false, isRetryable };
  } catch (e) {
    const tokenPrefix = tokenHash.substring(0, 8);
    console.error(`[PlayVerification] [hash=${tokenPrefix}] Subscription acknowledge network exception:`, e);
    return { success: false, isRetryable: true };
  }
}

/**
 * Acknowledges a one-time product token server-side via purchases.products.acknowledge.
 */
export async function acknowledgeOneTimeProduct(
  packageName: string,
  productId: string,
  token: string,
  accessToken: string,
  tokenHash: string
): Promise<{ success: boolean; isRetryable: boolean }> {
  const endpoint = `https://androidpublisher.googleapis.com/androidpublisher/v3/applications/${encodeURIComponent(
    packageName
  )}/purchases/products/${encodeURIComponent(productId)}/tokens/${encodeURIComponent(
    token
  )}:acknowledge`;

  try {
    const res = await fetch(endpoint, {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${accessToken}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({}),
    });

    if (res.ok || res.status === 204) {
      return { success: true, isRetryable: false };
    }

    const tokenPrefix = tokenHash.substring(0, 8);
    const text = await res.text().catch(() => '');

    // Idempotency check for product acknowledgement
    if (res.status === 400 && text.toLowerCase().includes('already acknowledged')) {
      return { success: true, isRetryable: false };
    }

    console.error(
      `[PlayVerification] [hash=${tokenPrefix}] Product acknowledge failed: status=${res.status} body=${text}`
    );

    const isRetryable = res.status === 429 || res.status >= 500;
    return { success: false, isRetryable };
  } catch (e) {
    const tokenPrefix = tokenHash.substring(0, 8);
    console.error(`[PlayVerification] [hash=${tokenPrefix}] Product acknowledge network exception:`, e);
    return { success: false, isRetryable: true };
  }
}

/**
 * Verifies subscription using purchases.subscriptionsv2.get
 */
async function verifySubscription(
  packageName: string,
  token: string,
  tokenHash: string,
  accessToken: string
): Promise<{ status: number; body: VerificationResponse | { error: string; code: string } }> {
  const endpoint = `https://androidpublisher.googleapis.com/androidpublisher/v3/applications/${encodeURIComponent(
    packageName
  )}/purchases/subscriptionsv2/tokens/${encodeURIComponent(token)}`;

  const res = await fetch(endpoint, {
    method: 'GET',
    headers: {
      Authorization: `Bearer ${accessToken}`,
      Accept: 'application/json',
    },
  });

  if (res.status === 404) {
    return {
      status: 404,
      body: { error: 'Purchase token not found in Google Play', code: 'INVALID_PURCHASE' },
    };
  }

  if (res.status === 401 || res.status === 403) {
    const tokenPrefix = tokenHash.substring(0, 8);
    console.error(`[PlayVerification] [hash=${tokenPrefix}] Google returned status ${res.status}`);
    return {
      status: 502,
      body: { error: 'Google API authorization failure', code: 'GOOGLE_TEMPORARILY_UNAVAILABLE' },
    };
  }

  if (res.status === 429) {
    return {
      status: 429,
      body: { error: 'Google Developer API rate limited', code: 'RATE_LIMITED' },
    };
  }

  if (!res.ok) {
    return {
      status: 502,
      body: { error: `Google API returned error status ${res.status}`, code: 'GOOGLE_TEMPORARILY_UNAVAILABLE' },
    };
  }

  const sub = (await res.json()) as {
    subscriptionState?: string;
    acknowledgementState?: string;
    lineItems?: Array<{
      productId?: string;
      expiryTime?: string;
    }>;
  };

  const { expiryTimeIso, expiryTimeMs } = extractLatestExpiry(
    sub.lineItems,
    ALLOWED_PRODUCTS.PRO_MONTHLY
  );
  const nowMs = Date.now();

  const state = sub.subscriptionState || 'SUBSCRIPTION_STATE_UNSPECIFIED';
  let plan: 'proMonthly' | 'free' = 'proMonthly';
  let status: VerificationResponse['status'] = 'proMonthlyActive';
  let verificationStatus: VerificationResponse['verificationStatus'] = 'verified';

  switch (state) {
    case 'SUBSCRIPTION_STATE_ACTIVE':
      status = 'proMonthlyActive';
      verificationStatus = 'verified';
      break;

    case 'SUBSCRIPTION_STATE_IN_GRACE_PERIOD':
      status = 'proMonthlyGrace';
      verificationStatus = 'verified';
      break;

    case 'SUBSCRIPTION_STATE_ON_HOLD':
      status = 'proMonthlyAccountHold';
      verificationStatus = 'verified'; // Hold is confirmed verified, but entitlement state will deny pro
      break;

    case 'SUBSCRIPTION_STATE_PAUSED':
      status = 'proMonthlyPaused';
      verificationStatus = 'verified'; // Explicit Paused state; denies Pro access
      break;

    case 'SUBSCRIPTION_STATE_CANCELED':
      // Canceled: user keeps entitlement until paid period expires
      if (!isNaN(expiryTimeMs) && expiryTimeMs > nowMs) {
        status = 'proMonthlyActive';
        verificationStatus = 'verified';
      } else {
        status = 'proMonthlyExpired';
        verificationStatus = 'expired';
      }
      break;

    case 'SUBSCRIPTION_STATE_EXPIRED':
      status = 'proMonthlyExpired';
      verificationStatus = 'expired';
      break;

    case 'SUBSCRIPTION_STATE_PENDING':
      status = 'syncPending';
      verificationStatus = 'unverified';
      break;

    default:
      status = 'unknown';
      verificationStatus = 'unverified';
      break;
  }

  // Server-Side Acknowledgement
  // Only acknowledge if purchase is in active/entitled state and not already acknowledged.
  let ackState: AcknowledgementState = 'notApplicable';
  const isAlreadyAcknowledged =
    sub.acknowledgementState === 'ACKNOWLEDGEMENT_STATE_ACKNOWLEDGED';

  const shouldAcknowledge =
    (status === 'proMonthlyActive' ||
      status === 'proMonthlyGrace' ||
      status === 'proMonthlyAccountHold') &&
    verificationStatus === 'verified';

  if (shouldAcknowledge) {
    if (isAlreadyAcknowledged) {
      ackState = 'acknowledged';
    } else {
      const ackResult = await acknowledgeSubscription(
        packageName,
        ALLOWED_PRODUCTS.PRO_MONTHLY,
        token,
        accessToken,
        tokenHash
      );
      if (ackResult.success) {
        ackState = 'acknowledged';
      } else {
        // Verification succeeded, but acknowledgement requires retry
        ackState = 'pendingRetry';
      }
    }
  }

  return {
    status: 200,
    body: {
      schemaVersion: 1,
      productId: ALLOWED_PRODUCTS.PRO_MONTHLY,
      plan,
      status,
      verificationStatus,
      acknowledgementState: ackState,
      verifiedAt: new Date().toISOString(),
      expiresAt: expiryTimeIso,
      tokenHash,
    },
  };
}

/**
 * Verifies one-time lifetime purchase using purchases.products.get
 */
async function verifyOneTimeProduct(
  packageName: string,
  productId: string,
  token: string,
  tokenHash: string,
  accessToken: string
): Promise<{ status: number; body: VerificationResponse | { error: string; code: string } }> {
  const endpoint = `https://androidpublisher.googleapis.com/androidpublisher/v3/applications/${encodeURIComponent(
    packageName
  )}/purchases/products/${encodeURIComponent(productId)}/tokens/${encodeURIComponent(token)}`;

  const res = await fetch(endpoint, {
    method: 'GET',
    headers: {
      Authorization: `Bearer ${accessToken}`,
      Accept: 'application/json',
    },
  });

  if (res.status === 404) {
    return {
      status: 404,
      body: { error: 'Purchase token not found in Google Play', code: 'INVALID_PURCHASE' },
    };
  }

  if (res.status === 401 || res.status === 403) {
    const tokenPrefix = tokenHash.substring(0, 8);
    console.error(`[PlayVerification] [hash=${tokenPrefix}] Google returned status ${res.status}`);
    return {
      status: 502,
      body: { error: 'Google API authorization failure', code: 'GOOGLE_TEMPORARILY_UNAVAILABLE' },
    };
  }

  if (res.status === 429) {
    return {
      status: 429,
      body: { error: 'Google Developer API rate limited', code: 'RATE_LIMITED' },
    };
  }

  if (!res.ok) {
    return {
      status: 502,
      body: { error: `Google API returned error status ${res.status}`, code: 'GOOGLE_TEMPORARILY_UNAVAILABLE' },
    };
  }

  const prod = (await res.json()) as {
    purchaseState?: number; // 0 = Purchased, 1 = Canceled/Refunded, 2 = Pending
    consumptionState?: number;
    acknowledgementState?: number; // 0 = Yet to be acknowledged, 1 = Acknowledged
  };

  const purchaseState = prod.purchaseState ?? 0;
  let status: VerificationResponse['status'] = 'proLifetime';
  let verificationStatus: VerificationResponse['verificationStatus'] = 'verified';

  if (purchaseState === 0) {
    // Purchased & valid
    status = 'proLifetime';
    verificationStatus = 'verified';
  } else if (purchaseState === 1) {
    // Canceled / refunded
    status = 'unknown';
    verificationStatus = 'revoked';
  } else if (purchaseState === 2) {
    // Pending
    status = 'syncPending';
    verificationStatus = 'unverified';
  }

  // Server-Side Acknowledgement for Lifetime
  let ackState: AcknowledgementState = 'notApplicable';
  const isAlreadyAcknowledged = prod.acknowledgementState === 1;

  if (purchaseState === 0 && verificationStatus === 'verified') {
    if (isAlreadyAcknowledged) {
      ackState = 'acknowledged';
    } else {
      const ackResult = await acknowledgeOneTimeProduct(
        packageName,
        productId,
        token,
        accessToken,
        tokenHash
      );
      if (ackResult.success) {
        ackState = 'acknowledged';
      } else {
        ackState = 'pendingRetry';
      }
    }
  }

  return {
    status: 200,
    body: {
      schemaVersion: 1,
      productId: ALLOWED_PRODUCTS.PRO_LIFETIME,
      plan: 'proLifetime',
      status,
      verificationStatus,
      acknowledgementState: ackState,
      verifiedAt: new Date().toISOString(),
      expiresAt: null,
      tokenHash,
    },
  };
}

// Helpers for PKCS#8 PEM decoding and Base64URL
function pemToBinary(pem: string): ArrayBuffer {
  const cleanPem = pem
    .replace(/-----BEGIN[ A-Z0-9_-]+-----/g, '')
    .replace(/-----END[ A-Z0-9_-]+-----/g, '')
    .replace(/\s+/g, '');
  const raw = atob(cleanPem);
  const bytes = new Uint8Array(raw.length);
  for (let i = 0; i < raw.length; i++) {
    bytes[i] = raw.charCodeAt(i);
  }
  return bytes.buffer;
}

function base64UrlEncode(input: string | ArrayBuffer): string {
  let base64: string;
  if (typeof input === 'string') {
    base64 = btoa(input);
  } else {
    const bytes = new Uint8Array(input);
    let binary = '';
    for (let i = 0; i < bytes.byteLength; i++) {
      binary += String.fromCharCode(bytes[i]);
    }
    base64 = btoa(binary);
  }
  return base64.replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}