import { google } from "googleapis";
import { GmailConfig, EmailMessage, EmailAttachment } from "@/types";

export function createGmailClient(config: GmailConfig) {
  try {
    const oauth2Client = new google.auth.OAuth2(
      config.clientId,
      config.clientSecret,
      config.redirectUri
    );

    if (config.refreshToken) {
      oauth2Client.setCredentials({
        refresh_token: config.refreshToken,
      });
    }

    const gmail = google.gmail({ version: "v1", auth: oauth2Client });

    return { gmail, oauth2Client };
  } catch (e) {
    console.error("[gmail/client] createGmailClient:", e);
    throw new Error(`Failed to create Gmail client: ${e instanceof Error ? e.message : String(e)}`);
  }
}

export function getAuthUrl(config: GmailConfig): string {
  try {
    const oauth2Client = new google.auth.OAuth2(
      config.clientId,
      config.clientSecret,
      config.redirectUri
    );

    return oauth2Client.generateAuthUrl({
      access_type: "offline",
      scope: [
        "https://www.googleapis.com/auth/gmail.readonly",
        "https://www.googleapis.com/auth/gmail.modify",
      ],
      prompt: "consent",
    });
  } catch (e) {
    console.error("[gmail/client] getAuthUrl:", e);
    throw new Error(`Failed to generate auth URL: ${e instanceof Error ? e.message : String(e)}`);
  }
}

export async function exchangeCodeForTokens(
  config: GmailConfig,
  code: string
): Promise<{ refreshToken: string; accessToken: string }> {
  try {
    const oauth2Client = new google.auth.OAuth2(
      config.clientId,
      config.clientSecret,
      config.redirectUri
    );

    const { tokens } = await oauth2Client.getToken(code);
    return {
      refreshToken: tokens.refresh_token || "",
      accessToken: tokens.access_token || "",
    };
  } catch (e) {
    console.error("[gmail/client] exchangeCodeForTokens:", e);
    throw new Error(`Failed to exchange code for tokens: ${e instanceof Error ? e.message : String(e)}`);
  }
}

export async function fetchEmails(
  config: GmailConfig,
  maxResults: number = 100
): Promise<EmailMessage[]> {
  try {
    const { gmail } = createGmailClient(config);

    const listRes = await gmail.users.messages.list({
      userId: "me",
      maxResults,
      q: "has:attachment",
    });

    const messageIds = listRes.data.messages || [];
    const emails: EmailMessage[] = [];

    for (const msg of messageIds) {
      if (!msg.id) continue;
      const email = await fetchEmail(config, msg.id);
      if (email) emails.push(email);
    }

    return emails;
  } catch (e) {
    console.error("[gmail/client] fetchEmails:", e);
    throw new Error(`Failed to fetch emails: ${e instanceof Error ? e.message : String(e)}`);
  }
}

export async function fetchEmail(
  config: GmailConfig,
  messageId: string
): Promise<EmailMessage | null> {
  try {
    const { gmail } = createGmailClient(config);

    const res = await gmail.users.messages.get({
      userId: "me",
      id: messageId,
    });

    const msg = res.data;
    if (!msg) return null;

    const headers = msg.payload?.headers || [];
    const subject = headers.find((h) => h.name === "Subject")?.value || "";
    const from = headers.find((h) => h.name === "From")?.value || "";
    const date = headers.find((h) => h.name === "Date")?.value || "";

    const senderMatch = from.match(/^(.*?)\s*<(.*)>$/);
    const sender = senderMatch ? senderMatch[1].trim().replace(/"/g, "") : from;
    const senderEmail = senderMatch ? senderMatch[2] : from;

    const body = extractBody(msg.payload);
    const attachments = extractAttachments(msg.payload);

    return {
      id: messageId,
      subject,
      sender,
      senderEmail,
      receivedDate: date,
      bodyPreview: body.substring(0, 200),
      body,
      hasAttachments: attachments.length > 0,
      attachments,
      isRead: !msg.labelIds?.includes("UNREAD"),
      importance: "normal",
      categories: msg.labelIds || [],
      processed: false,
    };
  } catch (e) {
    console.error("[gmail/client] fetchEmail:", e);
    throw new Error(`Failed to fetch email ${messageId}: ${e instanceof Error ? e.message : String(e)}`);
  }
}

function extractBody(payload: any): string {
  if (!payload) return "";

  if (payload.body?.data) {
    return Buffer.from(payload.body.data, "base64").toString("utf-8");
  }

  if (payload.parts) {
    for (const part of payload.parts) {
      if (part.mimeType === "text/plain" && part.body?.data) {
        return Buffer.from(part.body.data, "base64").toString("utf-8");
      }
    }
    for (const part of payload.parts) {
      if (part.mimeType === "text/html" && part.body?.data) {
        return Buffer.from(part.body.data, "base64").toString("utf-8");
      }
    }
  }

  return "";
}

function extractAttachments(payload: any): EmailAttachment[] {
  const attachments: EmailAttachment[] = [];

  function walk(parts: any[]) {
    for (const part of parts) {
      if (part.filename && part.body?.attachmentId) {
        attachments.push({
          id: part.body.attachmentId,
          name: part.filename,
          contentType: part.mimeType || "application/octet-stream",
          size: part.body.size || 0,
        });
      }
      if (part.parts) {
        walk(part.parts);
      }
    }
  }

  if (payload?.parts) {
    walk(payload.parts);
  }

  return attachments;
}

export async function fetchAttachmentContent(
  config: GmailConfig,
  messageId: string,
  attachmentId: string
): Promise<Uint8Array> {
  try {
    const { gmail } = createGmailClient(config);

    const res = await gmail.users.messages.attachments.get({
      userId: "me",
      messageId,
      id: attachmentId,
    });

    const data = res.data.data || "";
    const buffer = Buffer.from(data, "base64");
    return new Uint8Array(buffer);
  } catch (e) {
    console.error("[gmail/client] fetchAttachmentContent:", e);
    throw new Error(`Failed to fetch attachment ${attachmentId}: ${e instanceof Error ? e.message : String(e)}`);
  }
}