// WebAuthn helpers for passkey registration/authentication against the
// MyAccount Hamsoo API. Implements the real WebAuthn ceremony (the backend
// performs cryptographic attestation/assertion verification).

const BASE = process.env.NEXT_PUBLIC_API_URL || "http://localhost:8000/api/v1";

function bufToBase64url(buf: ArrayBuffer): string {
  const bytes = new Uint8Array(buf);
  let str = "";
  for (let i = 0; i < bytes.length; i++) str += String.fromCharCode(bytes[i]);
  return btoa(str).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
}

function base64urlToBuf(b64: string): ArrayBuffer {
  const pad = b64.length % 4 ? 4 - (b64.length % 4) : 0;
  const b = atob(b64.replace(/-/g, "+").replace(/_/g, "/") + "====".slice(0, pad));
  const bytes = new Uint8Array(b.length);
  for (let i = 0; i < b.length; i++) bytes[i] = b.charCodeAt(i);
  return bytes.buffer;
}

function prepareCreationOptions(publicKey: any) {
  publicKey.challenge = base64urlToBuf(publicKey.challenge);
  if (publicKey.user) publicKey.user.id = base64urlToBuf(publicKey.user.id);
  if (Array.isArray(publicKey.excludeCredentials)) {
    publicKey.excludeCredentials = publicKey.excludeCredentials.map((c: any) => ({
      ...c,
      id: base64urlToBuf(c.id),
    }));
  }
  return publicKey;
}

export async function registerPasskey(token: string, name: string) {
  const beginRes = await fetch(`${BASE}/auth/passkeys/register/begin/`, {
    method: "POST",
    headers: { Authorization: `Bearer ${token}` },
    credentials: "include",
  });
  if (!beginRes.ok) throw new Error("Failed to begin passkey registration");
  const options = await beginRes.json();

  const cred = (await navigator.credentials.create({
    publicKey: prepareCreationOptions(options.publicKey),
  })) as any;

  const payload = {
    id: cred.id,
    rawId: bufToBase64url(cred.rawId),
    response: {
      clientDataJSON: bufToBase64url(cred.response.clientDataJSON),
      attestationObject: bufToBase64url(cred.response.attestationObject),
    },
    type: cred.type,
    clientExtensionResults: cred.getClientExtensionResults
      ? cred.getClientExtensionResults()
      : {},
    name,
  };

  const finishRes = await fetch(`${BASE}/auth/passkeys/register/finish/`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${token}`,
    },
    credentials: "include",
    body: JSON.stringify(payload),
  });
  if (!finishRes.ok) {
    const err = await finishRes.json().catch(() => ({}));
    throw new Error(err.detail || "Passkey registration failed");
  }
  return finishRes.json();
}

export async function authenticatePasskey(token: string | null, email: string) {
  const headers: Record<string, string> = {};
  if (token) headers.Authorization = `Bearer ${token}`;
  const beginRes = await fetch(`${BASE}/auth/passkeys/authenticate/begin/`, {
    method: "POST",
    headers: { "Content-Type": "application/json", ...headers },
    credentials: "include",
    body: JSON.stringify({ email }),
  });
  if (!beginRes.ok) throw new Error("Failed to begin passkey authentication");
  const options = await beginRes.json();

  const requestOptions = options.publicKey;
  requestOptions.challenge = base64urlToBuf(requestOptions.challenge);
  if (Array.isArray(requestOptions.allowCredentials)) {
    requestOptions.allowCredentials = requestOptions.allowCredentials.map(
      (c: any) => ({ ...c, id: base64urlToBuf(c.id) }),
    );
  }

  const assertion = (await navigator.credentials.get({
    publicKey: requestOptions,
  })) as any;

  const payload = {
    id: assertion.id,
    rawId: bufToBase64url(assertion.rawId),
    response: {
      clientDataJSON: bufToBase64url(assertion.response.clientDataJSON),
      authenticatorData: bufToBase64url(assertion.response.authenticatorData),
      signature: bufToBase64url(assertion.response.signature),
      userHandle: assertion.response.userHandle
        ? bufToBase64url(assertion.response.userHandle)
        : undefined,
    },
    type: assertion.type,
    clientExtensionResults: assertion.getClientExtensionResults
      ? assertion.getClientExtensionResults()
      : {},
  };

  const finishRes = await fetch(`${BASE}/auth/passkeys/authenticate/finish/`, {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    credentials: "include",
    body: JSON.stringify(payload),
  });
  if (!finishRes.ok) {
    const err = await finishRes.json().catch(() => ({}));
    throw new Error(err.detail || "Passkey authentication failed");
  }
  return finishRes.json();
}