import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import {
  DynamoDBDocumentClient,
  GetCommand,
  PutCommand,
  ScanCommand,
  BatchWriteCommand,
} from "@aws-sdk/lib-dynamodb";
import { SQSClient, SendMessageCommand } from "@aws-sdk/client-sqs";
import { SSMClient, GetParameterCommand } from "@aws-sdk/client-ssm";
import { simpleParser } from "mailparser";

const s3 = new S3Client();
const ddb = DynamoDBDocumentClient.from(new DynamoDBClient());
const sqs = new SQSClient();
const ssm = new SSMClient();

const TABLE_NAME = process.env.TABLE_NAME;
const CHANNEL_ID = process.env.PAYROLL_CHANNEL_ID;
const QUEUE_URL = process.env.CONTRACTOR_BATCH_QUEUE_URL;

let cachedToken;
async function getSlackToken() {
  if (cachedToken) return cachedToken;
  const { Parameter } = await ssm.send(
    new GetParameterCommand({
      Name: process.env.SLACK_BOT_TOKEN_PARAM,
      WithDecryption: true,
    })
  );
  cachedToken = Parameter.Value;
  return cachedToken;
}

const formatCurrency = (v) =>
  new Intl.NumberFormat("en-US", {
    style: "currency",
    currency: "USD",
  }).format(Number(v || 0));

function classifyEmail(from, subject, text) {
  const fromAddr = (from?.text || from || "").toLowerCase();
  const subj = (subject || "").toLowerCase();

  if (
    fromAddr.includes("automated@gusto.com") &&
    subj.includes("payroll confirmation")
  ) {
    return "employee";
  }
  if (
    fromAddr.includes("gustonoreply@gusto.com") &&
    subj.includes("payment confirmation")
  ) {
    return "contractor";
  }

  const strippedSubj = subj.replace(/^fwd?:\s*/i, "");
  const body = (text || "").toLowerCase();
  const bodyMentionsGusto = body.includes("gusto.com");

  if (bodyMentionsGusto && strippedSubj.includes("payroll confirmation")) {
    return "employee";
  }
  if (bodyMentionsGusto && strippedSubj.includes("payment confirmation")) {
    return "contractor";
  }

  return null;
}

function parseDateFromSubject(subject) {
  const m = subject.match(/:\s*(\w+,\s*\w+\s+\d+)\s+(?:payroll|payment)\s+confirmation/i);
  if (!m) return null;
  const raw = m[1].trim();
  const year = new Date().getFullYear();
  const d = new Date(`${raw}, ${year}`);
  if (isNaN(d)) return null;
  return {
    display: raw,
    iso: d.toISOString().slice(0, 10),
  };
}

function parseEmployeePayroll(subject, text) {
  const checkDate = parseDateFromSubject(subject);
  if (!checkDate) return null;

  const norm = text.replace(/\n/g, " ").replace(/\s+/g, " ");

  const debitMatch = norm.match(
    /we.ll debit \$([\d,]+\.\d{2}) from the bank account ending in (\d+)/i
  );
  if (!debitMatch) return null;

  const totalDebit = parseFloat(debitMatch[1].replace(/,/g, ""));
  const bankSuffix = debitMatch[2];

  const payPeriodMatch = norm.match(/payroll for the (.+?)\s+pay period/i);
  const netPayMatch = norm.match(
    /\$([\d,]+\.\d{2}) will be for your employee net pay/i
  );
  const taxesMatch = norm.match(/\$([\d,]+\.\d{2}) will be for taxes/i);
  const reimbursementsMatch = norm.match(
    /\$([\d,]+\.\d{2}) will be for reimbursements/i
  );

  return {
    checkDate: checkDate.display,
    dateKey: checkDate.iso,
    totalDebit,
    bankSuffix,
    payPeriod: payPeriodMatch ? payPeriodMatch[1].trim() : null,
    netPay: netPayMatch ? parseFloat(netPayMatch[1].replace(/,/g, "")) : null,
    taxes: taxesMatch ? parseFloat(taxesMatch[1].replace(/,/g, "")) : null,
    reimbursements: reimbursementsMatch
      ? parseFloat(reimbursementsMatch[1].replace(/,/g, ""))
      : null,
  };
}

function parseContractorPayment(subject, text) {
  const checkDate = parseDateFromSubject(subject);
  if (!checkDate) return null;

  const norm = text.replace(/\n/g, " ").replace(/\s+/g, " ");

  const debitMatch = norm.match(
    /we.ll debit \$([\d,]+\.\d{2}) from the bank account ending in (\d+)/i
  );
  if (!debitMatch) return null;

  const totalDebit = parseFloat(debitMatch[1].replace(/,/g, ""));
  const bankSuffix = debitMatch[2];

  const nameMatch = norm.match(/at that time for (.+?) to be paid on/i);
  const contractorName = nameMatch ? nameMatch[1].trim() : "Unknown contractor";

  return {
    checkDate: checkDate.display,
    dateKey: checkDate.iso,
    totalDebit,
    bankSuffix,
    contractorName,
  };
}

function buildCombinedBlocks(dateDisplay, employee, contractors) {
  const blocks = [
    {
      type: "header",
      text: {
        type: "plain_text",
        text: `Payroll Processed — ${dateDisplay}`,
      },
    },
  ];

  if (employee) {
    const topFields = [
      { type: "mrkdwn", text: `*Check Date*\n${employee.checkDate}` },
    ];
    if (employee.payPeriod) {
      topFields.unshift({
        type: "mrkdwn",
        text: `*Pay Period*\n${employee.payPeriod}`,
      });
    }
    blocks.push({ type: "section", fields: topFields });
    blocks.push({ type: "divider" });

    const detailFields = [];
    if (employee.netPay != null) {
      detailFields.push({
        type: "mrkdwn",
        text: `*Employee Net Pay*\n${formatCurrency(employee.netPay)}`,
      });
    }
    if (employee.taxes != null) {
      detailFields.push({
        type: "mrkdwn",
        text: `*Taxes*\n${formatCurrency(employee.taxes)}`,
      });
    }
    if (detailFields.length) blocks.push({ type: "section", fields: detailFields });

    const extraFields = [];
    if (employee.reimbursements != null) {
      extraFields.push({
        type: "mrkdwn",
        text: `*Reimbursements*\n${formatCurrency(employee.reimbursements)}`,
      });
    }
    extraFields.push({
      type: "mrkdwn",
      text: `*Bank Account*\n...${employee.bankSuffix}`,
    });
    blocks.push({ type: "section", fields: extraFields });
  }

  if (contractors.length > 0) {
    blocks.push({ type: "divider" });
    blocks.push({
      type: "section",
      text: {
        type: "mrkdwn",
        text: `*Contractor Payments*`,
      },
    });
    for (const c of contractors) {
      blocks.push({
        type: "section",
        fields: [
          { type: "mrkdwn", text: `*Contractor*\n${c.contractorName}` },
          { type: "mrkdwn", text: `*Amount*\n${formatCurrency(c.totalDebit)}` },
        ],
      });
    }
  }

  const grandTotal =
    (employee ? employee.totalDebit : 0) +
    contractors.reduce((sum, c) => sum + c.totalDebit, 0);

  blocks.push({ type: "divider" });
  blocks.push({
    type: "section",
    text: {
      type: "mrkdwn",
      text: `:moneybag: *Total Bank Debit: ${formatCurrency(grandTotal)}*`,
    },
  });
  blocks.push({
    type: "context",
    elements: [
      { type: "mrkdwn", text: "Source: Gusto payroll confirmation emails" },
    ],
  });

  return { blocks, grandTotal };
}

async function postSlack(token, blocks, text) {
  const res = await fetch("https://slack.com/api/chat.postMessage", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${token}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify({ channel: CHANNEL_ID, blocks, text }),
  });
  const data = await res.json();
  if (!data.ok) {
    console.error("Slack post failed:", data.error);
    throw new Error(`Slack API error: ${data.error}`);
  }
  return data.ts;
}

const ttl90Days = () => Math.floor(Date.now() / 1000) + 90 * 24 * 60 * 60;

async function handleS3Event(record) {
  const bucket = record.s3.bucket.name;
  const key = decodeURIComponent(record.s3.object.key.replace(/\+/g, " "));

  const { Body } = await s3.send(
    new GetObjectCommand({ Bucket: bucket, Key: key })
  );
  const rawEmail = await Body.transformToByteArray();
  const parsed = await simpleParser(Buffer.from(rawEmail));

  const type = classifyEmail(parsed.from, parsed.subject, parsed.text);
  if (!type) {
    console.log("Unrecognized email, skipping:", parsed.subject);
    return;
  }

  if (type === "employee") {
    const data = parseEmployeePayroll(parsed.subject, parsed.text);
    if (!data) {
      console.error("Failed to parse employee payroll:", parsed.subject);
      return;
    }

    const pk = `PAYROLL_EMAIL#employee#${data.dateKey}`;
    const existing = await ddb.send(
      new GetCommand({ TableName: TABLE_NAME, Key: { pk } })
    );
    if (existing.Item) {
      console.log(`Already recorded: employee ${data.dateKey}`);
      return;
    }

    await ddb.send(
      new PutCommand({
        TableName: TABLE_NAME,
        Item: {
          pk,
          type: "employee",
          status: "pending",
          checkDate: data.checkDate,
          dateKey: data.dateKey,
          totalDebit: data.totalDebit,
          bankSuffix: data.bankSuffix,
          payPeriod: data.payPeriod,
          netPay: data.netPay,
          taxes: data.taxes,
          reimbursements: data.reimbursements,
          processedAt: new Date().toISOString(),
          ttl: ttl90Days(),
        },
      })
    );

    await sqs.send(
      new SendMessageCommand({
        QueueUrl: QUEUE_URL,
        MessageBody: JSON.stringify({ dateKey: data.dateKey }),
      })
    );
    console.log(`Queued employee payroll for ${data.dateKey}`);
  }

  if (type === "contractor") {
    const data = parseContractorPayment(parsed.subject, parsed.text);
    if (!data) {
      console.error("Failed to parse contractor payment:", parsed.subject);
      return;
    }

    const pk = `PAYROLL_EMAIL#contractor#${data.dateKey}#${data.bankSuffix}`;
    const existing = await ddb.send(
      new GetCommand({ TableName: TABLE_NAME, Key: { pk } })
    );
    if (existing.Item) {
      console.log(
        `Already recorded: contractor ${data.contractorName} ${data.dateKey}`
      );
      return;
    }

    await ddb.send(
      new PutCommand({
        TableName: TABLE_NAME,
        Item: {
          pk,
          type: "contractor",
          status: "pending",
          checkDate: data.checkDate,
          dateKey: data.dateKey,
          totalDebit: data.totalDebit,
          bankSuffix: data.bankSuffix,
          contractorName: data.contractorName,
          processedAt: new Date().toISOString(),
          ttl: ttl90Days(),
        },
      })
    );

    await sqs.send(
      new SendMessageCommand({
        QueueUrl: QUEUE_URL,
        MessageBody: JSON.stringify({ dateKey: data.dateKey }),
      })
    );
    console.log(
      `Queued contractor: ${data.contractorName} for ${data.dateKey}`
    );
  }
}

async function handleSqsEvent(sqsRecord) {
  const { dateKey } = JSON.parse(sqsRecord.body);

  const batchPk = `PAYROLL_BATCH#${dateKey}`;
  const batchCheck = await ddb.send(
    new GetCommand({ TableName: TABLE_NAME, Key: { pk: batchPk } })
  );
  if (batchCheck.Item) {
    console.log(`Batch already posted for ${dateKey}`);
    return;
  }

  const { Items } = await ddb.send(
    new ScanCommand({
      TableName: TABLE_NAME,
      FilterExpression: "begins_with(pk, :prefix) AND #s = :pending",
      ExpressionAttributeNames: { "#s": "status" },
      ExpressionAttributeValues: {
        ":prefix": `PAYROLL_EMAIL#`,
        ":pending": "pending",
      },
    })
  );

  const pending = (Items || []).filter((i) => i.dateKey === dateKey);
  if (pending.length === 0) {
    console.log(`No pending items for ${dateKey}`);
    return;
  }

  const employee = pending.find((i) => i.type === "employee") || null;
  const contractors = pending.filter((i) => i.type === "contractor");
  const dateDisplay = pending[0].checkDate;

  const token = await getSlackToken();
  const { blocks, grandTotal } = buildCombinedBlocks(dateDisplay, employee, contractors);
  const slackTs = await postSlack(
    token,
    blocks,
    `Payroll processed for ${dateDisplay}: ${formatCurrency(grandTotal)}`
  );

  await ddb.send(
    new PutCommand({
      TableName: TABLE_NAME,
      Item: {
        pk: batchPk,
        dateKey,
        checkDate: dateDisplay,
        employeeCount: employee ? 1 : 0,
        contractorCount: contractors.length,
        totalDebit: grandTotal,
        slackTs,
        processedAt: new Date().toISOString(),
        ttl: ttl90Days(),
      },
    })
  );

  const updateBatch = pending.map((item) => ({
    PutRequest: {
      Item: { ...item, status: "notified" },
    },
  }));
  for (let i = 0; i < updateBatch.length; i += 25) {
    await ddb.send(
      new BatchWriteCommand({
        RequestItems: { [TABLE_NAME]: updateBatch.slice(i, i + 25) },
      })
    );
  }

  console.log(
    `Posted batch: ${employee ? 1 : 0} employee + ${contractors.length} contractor(s) for ${dateKey}`
  );
}

export const handler = async (event) => {
  if (event.Records?.[0]?.eventSource === "aws:s3") {
    for (const record of event.Records) {
      await handleS3Event(record);
    }
  } else if (event.Records?.[0]?.eventSource === "aws:sqs") {
    for (const record of event.Records) {
      await handleSqsEvent(record);
    }
  } else {
    console.log("Unknown event source:", JSON.stringify(event).slice(0, 200));
  }

  return { statusCode: 200 };
};