import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, BatchWriteCommand, PutCommand } from "@aws-sdk/lib-dynamodb";
import { parse } from "csv-parse/sync";

const s3 = new S3Client();
const ddb = DynamoDBDocumentClient.from(new DynamoDBClient());
const TABLE_NAME = process.env.TABLE_NAME;

export const handler = async (event) => {
  const record = event.Records[0];
  const bucket = record.s3.bucket.name;
  const key = decodeURIComponent(record.s3.object.key.replace(/\+/g, " "));

  // Download CSV from S3
  const { Body } = await s3.send(new GetObjectCommand({ Bucket: bucket, Key: key }));
  const csvText = await Body.transformToString("utf-8");

  // Parse CSV
  const rows = parse(csvText, {
    columns: true,
    skip_empty_lines: true,
    trim: true,
  });

  const normalizedRows = rows.map((row) => {
    const clean = {};
    for (const [k, v] of Object.entries(row)) {
      clean[String(k).trim()] = typeof v === "string" ? v.trim() : v;
    }
    return clean;
  });

  const parseAmount = (value) => {
    const num = parseFloat(String(value || "0").replace(/,/g, "").trim());
    return isNaN(num) ? 0 : num;
  };

  const payments = normalizedRows.map((row) => ({
    pk: `payment#${(row["Check Number"] || "").trim()}`,
    method: (row["Method"] || "").trim(),
    payee: (row["Payee"] || "").trim(),
    check_number: (row["Check Number"] || "").trim(),
    invoice_numbers: (row["Invoice Numbers"] || "").trim(),
    send_payment_on: (row["Send Payment On"] || "").trim(),
    amount_usd: parseAmount(row["Amount in USD"]),
    status: (row["Status"] || "").trim(),
    company_subsidiary: (row["Company/Subsidiary"] || "").trim(),
  }));

  // Write payments in batches of 25 (DynamoDB BatchWrite limit)
  const batches = [];
  for (let i = 0; i < payments.length; i += 25) {
    const batch = payments.slice(i, i + 25).map((item) => ({
      PutRequest: { Item: item },
    }));
    batches.push(batch);
  }

  for (const batch of batches) {
    await ddb.send(
      new BatchWriteCommand({
        RequestItems: { [TABLE_NAME]: batch },
      })
    );
  }

  // Update metadata record
  await ddb.send(
    new PutCommand({
      TableName: TABLE_NAME,
      Item: {
        pk: "metadata",
        file_name: key.split("/").pop(),
        last_updated: new Date().toISOString(),
        last_file_count: payments.length,
      },
    })
  );

  console.log(`Upserted ${payments.length} payments from ${key}`);
  return { statusCode: 200, body: `Upserted ${payments.length} payments` };
};