import { useState } from "react";
import { useClient } from "urql";
import { graphql, type ResultOf, type VariablesOf } from "@/graphql";
import { useToast } from "@/hooks/use-toast";
import { fetchAllPages } from "@/lib/fetch-all-pages";
import { toDateInputValue } from "@/lib/format-date";
import { csvTimestamp, downloadCsv, toCsv, type CsvColumn } from "@/lib/to-csv";

/**
 * CSV export for the Purchase Orders dashboard (issue #605).
 *
 * The dashboard query is cursor-paginated (25/page); `fetchAllPages` walks every
 * page (1000/page, the Tailor cap) so the export covers the full filtered/sorted
 * result set. If PO volume grows past what this can fetch in a reasonable time,
 * this is the seam to swap for a backend bulk-export resolver.
 */
const PurchaseOrdersCsvQuery = graphql(`
  query PurchaseOrdersCsv(
    $first: Int
    $after: String
    $order: [PurchaseOrderOrderInput]
    $query: PurchaseOrderQueryInput
  ) {
    purchaseOrders(first: $first, after: $after, order: $order, query: $query) {
      pageInfo {
        hasNextPage
        endCursor
      }
      edges {
        node {
          docNumber
          supplierSnapshotName
          orderDate
          orderStatus
          receiptStatus
          billingStatus
          externalSupplierOrderReference
          createdAt
          receivingSite {
            name
          }
          lines(first: 1000) {
            edges {
              node {
                quantity
                unitPrice
              }
            }
          }
        }
      }
    }
  }
`);

type CsvVariables = VariablesOf<typeof PurchaseOrdersCsvQuery>;
type CsvResult = ResultOf<typeof PurchaseOrdersCsvQuery>;
type PurchaseOrderCsvRow = NonNullable<
  NonNullable<CsvResult["purchaseOrders"]>["edges"]
>[number]["node"];

const lineTotal = (row: PurchaseOrderCsvRow): number =>
  row.lines.edges.reduce(
    (sum, edge) => sum + Number(edge.node.quantity ?? 0) * Number(edge.node.unitPrice ?? 0),
    0,
  );

// Columns follow the order issue #605 specifies, with header labels matching the
// PO UI (detail page / create form). Total Amount + Created Date are the "other
// fields visible in the dashboard" the issue also asks for.
const columns: CsvColumn<PurchaseOrderCsvRow>[] = [
  { header: "Document Number", value: (r) => r.docNumber },
  { header: "Supplier Name", value: (r) => r.supplierSnapshotName },
  { header: "Receiving Site", value: (r) => r.receivingSite?.name },
  { header: "Order Date", value: (r) => toDateInputValue(r.orderDate) },
  { header: "Status", value: (r) => r.orderStatus },
  { header: "Receipt Status", value: (r) => r.receiptStatus },
  { header: "Billing Status", value: (r) => r.billingStatus },
  { header: "External Reference", value: (r) => r.externalSupplierOrderReference },
  { header: "Total Amount", value: (r) => lineTotal(r).toFixed(2) },
  { header: "Created Date", value: (r) => toDateInputValue(r.createdAt) },
];

export function useExportPoCsv() {
  const client = useClient();
  const toast = useToast();
  const [isExporting, setIsExporting] = useState(false);

  /**
   * Export all rows matching the current dashboard filter/sort to a CSV.
   * Pass the same `order` and `query` the dashboard query uses so the export
   * respects the active filter + sort state.
   */
  async function exportCsv(order: CsvVariables["order"], query: CsvVariables["query"]) {
    if (isExporting) return;
    setIsExporting(true);

    try {
      const rows = await fetchAllPages(
        client,
        PurchaseOrdersCsvQuery,
        { order, query },
        (data) => data.purchaseOrders,
      );

      if (rows.length === 0) {
        toast.error("No purchase orders to export");
        return;
      }

      downloadCsv(toCsv(rows, columns), `purchase-orders-${csvTimestamp()}.csv`);
      toast.success(`${rows.length.toLocaleString()} rows exported`);
    } catch (err) {
      console.error("CSV export failed:", err);
      toast.error("Failed to export CSV");
    } finally {
      setIsExporting(false);
    }
  }

  return { exportCsv, isExporting };
}