import type { ReactNode } from "react";
import { Resend } from "resend";

let resendClient: Resend | null = null;

type SendAppEmailInput = {
  to: string | string[];
  subject: string;
  react: ReactNode;
  from?: string;
  replyTo?: string | string[];
  idempotencyKey?: string;
};

type SendAppEmailResult =
  | { success: true; id?: string }
  | { success: false; error: string };

export function getAppEmailConfigError() {
  if (process.env.NODE_ENV === "development") {
    return null;
  }
  if (!process.env.RESEND_API_KEY) {
    return "E-Mail-Versand ist derzeit nicht verfügbar.";
  }

  if (!process.env.EMAIL_FROM) {
    return "E-Mail-Versand ist derzeit nicht verfügbar.";
  }

  return null;
}

export async function sendAppEmail({
  to,
  subject,
  react,
  from = process.env.EMAIL_FROM,
  replyTo,
  idempotencyKey,
}: SendAppEmailInput): Promise<SendAppEmailResult> {
  if (Array.isArray(to)) {
    let id: string | undefined;
    for (const recipient of new Set(to)) {
      const result = await sendAppEmail({ to: recipient, subject, react, from, replyTo });
      if (!result.success) return result;
      id = result.id;
    }
    return { success: true, id };
  }
  if (!process.env.RESEND_API_KEY) {
    if (process.env.NODE_ENV === "development") {
      console.log("\n✉️  [DEV EMAIL SIMULATION]");
      console.log(`From:    ${from || "not-configured"}`);
      console.log(`To:      ${Array.isArray(to) ? to.join(", ") : to}`);
      console.log(`Subject: ${subject}`);
      console.log("-----------------------------------------");
      console.log("Email body react element is rendered.");
      console.log("=========================================\n");
      return { success: true, id: "dev-simulated-id" };
    }
    return {
      success: false,
      error: "E-Mail-Versand ist derzeit nicht verfügbar.",
    };
  }

  if (!from) {
    return {
      success: false,
      error: "E-Mail-Versand ist derzeit nicht verfügbar.",
    };
  }

  try {
    resendClient ??= new Resend(process.env.RESEND_API_KEY);
    const { data, error } = await resendClient.emails.send(
      {
        from: from!,
        to,
        subject,
        react,
        replyTo,
      },
      { idempotencyKey },
    );

    if (error) {
      console.error("Resend konnte die E-Mail nicht versenden:", error);
      return {
        success: false,
        error: "E-Mail-Versand fehlgeschlagen.",
      };
    }

    return { success: true, id: data?.id };
  } catch (error) {
    console.error("Unerwarteter Fehler beim E-Mail-Versand:", error);
    return {
      success: false,
      error: "E-Mail-Versand fehlgeschlagen.",
    };
  }
}