/**
 * Email sending utilities using Postmark
 * Implements Workstream G: Email Service (Backend)
 */

import type { OrgRole } from "@reviq/db-schema";
import { DurationFormat } from "@formatjs/intl-durationformat";
import { ServerClient } from "postmark";
import {
  BASE_URL,
  EMAIL_DEV_MODE,
  EMAIL_FROM,
  EMAIL_VERIFICATION_EXPIRY_HOURS,
  LOGIN_CONFIRMATION_EXPIRY_MINUTES,
  ORG_INVITE_EXPIRY_DAYS,
  PASSWORD_RESET_EXPIRY_HOURS,
  POSTMARK_API_KEY,
} from "../constants.js";

// ===== Types =====

/**
 * Email send result
 */
export interface EmailResult {
  success: boolean;
  messageId?: string;
  error?: string;
}

// ===== Postmark Client =====

let postmarkClient: ServerClient | null = null;

const getPostmarkClient = (): ServerClient => {
  if (!postmarkClient) {
    if (!POSTMARK_API_KEY) {
      throw new Error(
        "POSTMARK_API_KEY is required when EMAIL_DEV_MODE is false",
      );
    }
    postmarkClient = new ServerClient(POSTMARK_API_KEY);
  }
  return postmarkClient;
};

// ===== URL Helpers =====

/**
 * Build a URL with query parameters using the URL constructor
 */
const buildUrl = (path: string, params: Record<string, string>): string => {
  const url = new URL(path, BASE_URL);
  for (const [key, value] of Object.entries(params)) {
    url.searchParams.set(key, value);
  }
  return url.toString();
};

// ===== HTML Escaping =====

/**
 * Escape HTML special characters to prevent XSS
 */
const escapeHtml = (unsafe: string): string =>
  unsafe
    .replace(/&/g, "&amp;")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
    .replace(/"/g, "&quot;")
    .replace(/'/g, "&#039;");

// ===== Core Email Function =====

interface SendEmailParams {
  to: string;
  subject: string;
  htmlBody: string;
  textBody: string;
}

/**
 * Send an email via Postmark (or log in dev mode)
 */
const sendEmail = async (params: SendEmailParams): Promise<EmailResult> => {
  const { to, subject, htmlBody, textBody } = params;

  // Dev mode: log instead of sending
  if (EMAIL_DEV_MODE) {
    console.log("=== DEV MODE EMAIL ===");
    console.log(`To: ${to}`);
    console.log(`Subject: ${subject}`);
    console.log(`Body:\n${textBody}`);
    console.log("======================");
    return { success: true, messageId: "dev-mode" };
  }

  try {
    const client = getPostmarkClient();
    const result = await client.sendEmail({
      From: EMAIL_FROM,
      To: to,
      Subject: subject,
      HtmlBody: htmlBody,
      TextBody: textBody,
    });
    return { success: true, messageId: result.MessageID };
  } catch (error) {
    const message = error instanceof Error ? error.message : "Unknown error";
    console.error(`Failed to send email to ${to}:`, message);
    return { success: false, error: message };
  }
};

// ===== Template Helpers =====

const durationFormatter = new DurationFormat("en", { style: "long" });

const formatExpiryHours = (hours: number): string =>
  durationFormatter.format({ hours });

const formatExpiryMinutes = (minutes: number): string =>
  durationFormatter.format({ minutes });

const formatExpiryDays = (days: number): string =>
  durationFormatter.format({ days });

const roleLabels: Record<OrgRole, string> = {
  owner: "Owner",
  admin: "Admin",
  member: "Member",
};

const formatRoleDisplay = (role: OrgRole): string => roleLabels[role];

/**
 * Get the correct article (a/an) for a role
 */
const getArticleForRole = (role: OrgRole): string => {
  return role === "owner" || role === "admin" ? "an" : "a";
};

// ===== Email Templates =====

// Common styles
const emailStyles = `font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; margin: 0; padding: 20px; background-color: #f5f5f5;`;
const containerStyles =
  "max-width: 600px; margin: 0 auto; background: white; border-radius: 8px; padding: 40px;";
const headingStyles = "margin: 0 0 24px; font-size: 24px; color: #1a1a1a;";
const paragraphStyles =
  "margin: 0 0 24px; font-size: 16px; color: #4a4a4a; line-height: 1.5;";
const buttonStyles =
  "display: inline-block; background-color: #0066cc; color: white; padding: 12px 24px; border-radius: 6px; text-decoration: none; font-weight: 500;";
const footerStyles = "margin: 24px 0 0; font-size: 14px; color: #6a6a6a;";

// Verification Email
const buildVerificationEmailHtml = (
  verifyUrl: string,
  expiresIn: string,
): string => `
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="${emailStyles}">
  <div style="${containerStyles}">
    <h1 style="${headingStyles}">Verify your email</h1>
    <p style="${paragraphStyles}">Please verify your email address by clicking the button below:</p>
    <a href="${verifyUrl}" style="${buttonStyles}">Verify Email</a>
    <p style="${footerStyles}">This link expires in ${expiresIn}.</p>
    <p style="${footerStyles}">If you didn't create an account, you can safely ignore this email.</p>
  </div>
</body>
</html>
`;

const buildVerificationEmailText = (
  verifyUrl: string,
  expiresIn: string,
): string =>
  `Verify your email

Please verify your email address by clicking the link below:

${verifyUrl}

This link expires in ${expiresIn}.

If you didn't create an account, you can safely ignore this email.
`;

// Password Reset Email
const buildPasswordResetEmailHtml = (
  resetUrl: string,
  expiresIn: string,
): string => `
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="${emailStyles}">
  <div style="${containerStyles}">
    <h1 style="${headingStyles}">Reset your password</h1>
    <p style="${paragraphStyles}">We received a request to reset your password. Click the button below to choose a new password:</p>
    <a href="${resetUrl}" style="${buttonStyles}">Reset Password</a>
    <p style="${footerStyles}">This link expires in ${expiresIn}.</p>
    <p style="${footerStyles}">If you didn't request a password reset, you can safely ignore this email. Your password will remain unchanged.</p>
  </div>
</body>
</html>
`;

const buildPasswordResetEmailText = (
  resetUrl: string,
  expiresIn: string,
): string =>
  `Reset your password

We received a request to reset your password. Click the link below to choose a new password:

${resetUrl}

This link expires in ${expiresIn}.

If you didn't request a password reset, you can safely ignore this email. Your password will remain unchanged.
`;

// Login Confirmation Email
const buildLoginConfirmationEmailHtml = (
  confirmUrl: string,
  expiresIn: string,
): string => `
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="${emailStyles}">
  <div style="${containerStyles}">
    <h1 style="${headingStyles}">Confirm your login</h1>
    <p style="${paragraphStyles}">Someone is trying to sign in to your account. If this was you, click the button below to confirm:</p>
    <a href="${confirmUrl}" style="${buttonStyles}">Confirm Login</a>
    <p style="${footerStyles}">This link expires in ${expiresIn}.</p>
    <p style="${footerStyles}">If you didn't try to sign in, you can safely ignore this email. Someone may have entered your email address by mistake.</p>
  </div>
</body>
</html>
`;

const buildLoginConfirmationEmailText = (
  confirmUrl: string,
  expiresIn: string,
): string =>
  `Confirm your login

Someone is trying to sign in to your account. If this was you, click the link below to confirm:

${confirmUrl}

This link expires in ${expiresIn}.

If you didn't try to sign in, you can safely ignore this email. Someone may have entered your email address by mistake.
`;

// Org Invite Email
const buildOrgInviteEmailHtml = (
  email: string,
  orgName: string,
  inviterName: string,
  role: OrgRole,
  inviteUrl: string,
  expiresIn: string,
): string => {
  const safeOrgName = escapeHtml(orgName);
  const safeInviterName = escapeHtml(inviterName);
  const safeEmail = escapeHtml(email);
  const roleDisplay = formatRoleDisplay(role);
  const article = getArticleForRole(role);

  return `
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body style="${emailStyles}">
  <div style="${containerStyles}">
    <h1 style="${headingStyles}">You've been invited to join ${safeOrgName}</h1>
    <p style="${paragraphStyles}">${safeInviterName} has invited you to join <strong>${safeOrgName}</strong> as ${article} <strong>${roleDisplay}</strong>.</p>
    <a href="${inviteUrl}" style="${buttonStyles}">Accept Invitation</a>
    <p style="${footerStyles}">This invitation expires in ${expiresIn}.</p>
    <p style="${footerStyles}">This invitation was sent to ${safeEmail}. If you weren't expecting this invitation, you can safely ignore this email.</p>
  </div>
</body>
</html>
`;
};

const buildOrgInviteEmailText = (
  email: string,
  orgName: string,
  inviterName: string,
  role: OrgRole,
  inviteUrl: string,
  expiresIn: string,
): string => {
  const roleDisplay = formatRoleDisplay(role);
  const article = getArticleForRole(role);

  return `You've been invited to join ${orgName}

${inviterName} has invited you to join ${orgName} as ${article} ${roleDisplay}.

Click the link below to accept the invitation:

${inviteUrl}

This invitation expires in ${expiresIn}.

This invitation was sent to ${email}. If you weren't expecting this invitation, you can safely ignore this email.
`;
};

// ===== Email Helpers =====

/**
 * Send verification email to user
 */
export async function sendVerificationEmail(
  email: string,
  token: string,
): Promise<EmailResult> {
  const url = buildUrl("/auth/verify", { token });
  const expiresIn = formatExpiryHours(EMAIL_VERIFICATION_EXPIRY_HOURS);

  return sendEmail({
    to: email,
    subject: "Verify your email address",
    htmlBody: buildVerificationEmailHtml(url, expiresIn),
    textBody: buildVerificationEmailText(url, expiresIn),
  });
}

/**
 * Send login confirmation email (for untrusted device flow)
 */
export async function sendLoginConfirmationEmail(
  email: string,
  token: string,
): Promise<EmailResult> {
  const url = buildUrl("/auth/confirm", { token });
  const expiresIn = formatExpiryMinutes(LOGIN_CONFIRMATION_EXPIRY_MINUTES);

  return sendEmail({
    to: email,
    subject: "Confirm your login",
    htmlBody: buildLoginConfirmationEmailHtml(url, expiresIn),
    textBody: buildLoginConfirmationEmailText(url, expiresIn),
  });
}

/**
 * Send password reset email
 */
export async function sendPasswordResetEmail(
  email: string,
  token: string,
): Promise<EmailResult> {
  const url = buildUrl("/auth/reset-password", { token });
  const expiresIn = formatExpiryHours(PASSWORD_RESET_EXPIRY_HOURS);

  return sendEmail({
    to: email,
    subject: "Reset your password",
    htmlBody: buildPasswordResetEmailHtml(url, expiresIn),
    textBody: buildPasswordResetEmailText(url, expiresIn),
  });
}

/**
 * Send org invite email
 */
export async function sendOrgInviteEmail(
  email: string,
  token: string,
  orgName: string,
  inviterName: string,
  role: OrgRole,
): Promise<EmailResult> {
  const url = buildUrl("/invite/accept", { token });
  const expiresIn = formatExpiryDays(ORG_INVITE_EXPIRY_DAYS);

  return sendEmail({
    to: email,
    subject: `You've been invited to join ${orgName}`,
    htmlBody: buildOrgInviteEmailHtml(
      email,
      orgName,
      inviterName,
      role,
      url,
      expiresIn,
    ),
    textBody: buildOrgInviteEmailText(
      email,
      orgName,
      inviterName,
      role,
      url,
      expiresIn,
    ),
  });
}