// lambdas/po-sync/index.js
// DynamoDB Streams handler — syncs new/updated POs from the external
// purchase-orders table into ledgerflow-pos in near-real-time.

const {
  GetCommand, PutCommand, UpdateCommand, ScanCommand,
} = require("@aws-sdk/lib-dynamodb");
const { getDocClient, TABLES, genId } = require("@ledgerflow/shared");

const TABLE = TABLES.POS;

exports.handler = async (event) => {
  const db = getDocClient();
  let synced = 0;
  let skipped = 0;

  for (const record of event.Records) {
    try {
      // Only process inserts and modifications
      if (record.eventName !== "INSERT" && record.eventName !== "MODIFY") continue;

      const raw = unmarshallImage(record.dynamodb.NewImage);
      const poNumber = (raw.po_number || raw.poNumber || "").toString().trim();
      const vendor   = (raw.supplier?.name || raw.vendor_name || raw.vendor || "").toString().trim();
      const amount   = parseFloat(raw.total_amount || raw.amount || 0);

      if (!poNumber || !vendor) { skipped++; continue; }

      // Check if this PO already exists in our table
      const existing = await db.send(new ScanCommand({
        TableName: TABLE,
        FilterExpression: "poNumber = :p",
        ExpressionAttributeValues: { ":p": poNumber },
        ProjectionExpression: "id, poNumber",
        Limit: 1,
      }));

      const now = new Date().toISOString();
      const firstLine = Array.isArray(raw.line_items) ? raw.line_items[0] : null;

      if (existing.Count > 0 && record.eventName === "MODIFY") {
        // Update existing PO with latest external data
        const existingId = existing.Items[0].id;
        await db.send(new UpdateCommand({
          TableName: TABLE,
          Key: { id: existingId },
          UpdateExpression: "SET vendor = :v, amount = :a, #s = :s, issueDate = :isd, dueDate = :dd, notes = :n, updatedAt = :u",
          ExpressionAttributeNames: { "#s": "status" },
          ExpressionAttributeValues: {
            ":v": vendor,
            ":a": amount,
            ":s": (raw.po_status || raw.status || "open").toLowerCase(),
            ":isd": raw.order_date || raw.issue_date || raw.issueDate || now.split("T")[0],
            ":dd": firstLine?.need_by || raw.due_date || raw.dueDate || null,
            ":n": firstLine?.description || raw.notes || raw.description || "",
            ":u": now,
          },
        }));
        synced++;
      } else if (existing.Count === 0) {
        // Insert new PO
        await db.send(new PutCommand({
          TableName: TABLE,
          Item: {
            id:        genId("PO"),
            poNumber,
            vendor,
            amount,
            billed:    0,
            status:    (raw.po_status || raw.status || "open").toLowerCase(),
            issueDate: raw.order_date || raw.issue_date || raw.issueDate || now.split("T")[0],
            dueDate:   firstLine?.need_by || raw.due_date || raw.dueDate || null,
            notes:     firstLine?.description || raw.notes || raw.description || "",
            source:    "auto-sync",
            createdBy: "stream",
            createdAt: now,
            updatedAt: now,
          },
        }));
        synced++;
      } else {
        skipped++;
      }
    } catch (err) {
      console.error("[po-sync] Error processing record:", err.message, JSON.stringify(record));
    }
  }

  console.log(`[po-sync] Processed ${event.Records.length} records: ${synced} synced, ${skipped} skipped`);
  return { synced, skipped };
};

// Convert DynamoDB stream image (marshalled) to plain object.
// Stream records use raw DynamoDB attribute format, not DocumentClient format.
function unmarshallImage(image) {
  if (!image) return {};
  const { unmarshall } = require("@aws-sdk/util-dynamodb");
  return unmarshall(image);
}