"use client";

import { useCallback, useEffect, useMemo, useState, type ReactNode } from "react";
import { Alert, AlertDescription, AlertTitle } from "@/components/ui/alert";
import { Badge } from "@/components/ui/badge";
import { Button } from "@/components/ui/button";
import { Skeleton } from "@/components/ui/skeleton";
import { TransferApprovalCard } from "@/components/frontend/transfers/TransferApprovalCard";
import { TransferResolutionCard } from "@/components/frontend/transfers/TransferResolutionCard";
import { TransferRequestCard } from "@/components/frontend/transfers/TransferRequestCard";
import { LeadershipTransfersSection } from "@/components/frontend/transfers/LeadershipTransfersSection";
import {
  relationId,
  assignmentLeaderId,
  parseTransferPage,
  type TransferRequest,
  type TransferSide,
} from "@/components/frontend/transfers/transferTypes";
import {
  ClipboardCheckIcon,
  FileClockIcon,
  RefreshCwIcon,
  ShieldAlertIcon,
} from "lucide-react";
import type { LucideIcon } from "lucide-react";

interface TransfersViewProps {
  readonly currentUserId: number;
  readonly canResolve: boolean;
}

interface ApprovalEntry {
  readonly request: TransferRequest;
  readonly sides: readonly TransferSide[];
}

const TRANSFER_QUERY = new URLSearchParams({
  depth: "1",
  limit: "100",
  sort: "-createdAt",
});

function approvalSides(request: TransferRequest, currentUserId: number): readonly TransferSide[] {
  if (request.status !== "pending") return [];

  const sides: TransferSide[] = [];
  if (
    request.fromLeaderDecision === "pending" &&
    assignmentLeaderId(request.fromAssignment) === currentUserId
  ) {
    sides.push("from");
  }
  if (
    request.toLeaderDecision === "pending" &&
    assignmentLeaderId(request.toAssignment) === currentUserId
  ) {
    sides.push("to");
  }
  return sides;
}

function TransferSection({
  icon: Icon,
  title,
  count,
  children,
}: {
  readonly icon: LucideIcon;
  readonly title: string;
  readonly count: number;
  readonly children: ReactNode;
}) {
  return (
    <section aria-labelledby={`${title}-heading`} className="flex flex-col gap-3">
      <div className="flex items-center gap-2">
        <Icon className="size-4 text-muted-foreground" aria-hidden="true" />
        <h2 id={`${title}-heading`} className="text-sm font-semibold uppercase tracking-wider">
          {title}
        </h2>
        <Badge variant="outline" className="text-xs">
          {count}
        </Badge>
      </div>
      {children}
    </section>
  );
}

function EmptyTransferSection({ message }: { readonly message: string }) {
  return (
    <Alert>
      <AlertDescription>{message}</AlertDescription>
    </Alert>
  );
}

function LoadingTransferSections({ canResolve }: { readonly canResolve: boolean }) {
  return (
    <div className="flex flex-col gap-8" aria-busy="true" aria-label="Loading transfer requests">
      {["my-requests", "approvals", ...(canResolve ? ["appeals"] : [])].map((section) => (
        <div key={section} className="flex flex-col gap-3">
          <Skeleton className="h-5 w-48" />
          <Skeleton className="h-48 w-full" />
        </div>
      ))}
    </div>
  );
}

export function TransfersView({ currentUserId, canResolve }: TransfersViewProps) {
  const [requests, setRequests] = useState<readonly TransferRequest[] | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  const loadRequests = useCallback(async () => {
    setLoading(true);
    setError(null);
    try {
      const response = await fetch(`/api/assignment-transfers?${TRANSFER_QUERY.toString()}`, {
        cache: "no-store",
      });
      if (!response.ok) throw new Error("Could not load transfer requests.");

      const body: unknown = await response.json();
      const parsed = parseTransferPage(body);
      if (!parsed) throw new Error("The transfer request response was invalid.");
      setRequests(parsed);
    } catch (caughtError) {
      setError(
        caughtError instanceof Error ? caughtError.message : "Could not load transfer requests.",
      );
    } finally {
      setLoading(false);
    }
  }, []);

  useEffect(() => {
    void loadRequests();
  }, [loadRequests]);

  const myRequests = useMemo(
    () =>
      (requests ?? []).filter((request) => relationId(request.requester) === currentUserId),
    [currentUserId, requests],
  );
  const approvals = useMemo<readonly ApprovalEntry[]>(
    () =>
      (requests ?? [])
        .map((request) => ({ request, sides: approvalSides(request, currentUserId) }))
        .filter((entry) => entry.sides.length > 0),
    [currentUserId, requests],
  );
  const appeals = useMemo(
    () => (canResolve ? (requests ?? []).filter((request) => request.status === "awaiting_superuser") : []),
    [canResolve, requests],
  );

  if (!requests && loading) return <LoadingTransferSections canResolve={canResolve} />;

  if (!requests && error) {
    return (
      <div className="flex flex-col gap-8">
        <Alert variant="destructive">
          <AlertTitle>Transfer requests unavailable</AlertTitle>
          <AlertDescription className="flex flex-wrap items-center gap-3">
            <span>{error}</span>
            <Button size="sm" variant="outline" onClick={() => void loadRequests()}>
              <RefreshCwIcon data-icon="inline-start" />
              Try again
            </Button>
          </AlertDescription>
        </Alert>
        <LeadershipTransfersSection currentUserId={currentUserId} canResolve={canResolve} />
      </div>
    );
  }

  return (
    <div className="flex flex-col gap-8">
      {error && (
        <Alert variant="destructive">
          <AlertTitle>Could not refresh transfer requests</AlertTitle>
          <AlertDescription className="flex flex-wrap items-center gap-3">
            <span>{error}</span>
            <Button size="sm" variant="outline" onClick={() => void loadRequests()}>
              <RefreshCwIcon data-icon="inline-start" />
              Try again
            </Button>
          </AlertDescription>
        </Alert>
      )}

      <div className="flex items-center justify-end" aria-live="polite">
        {loading && <span className="text-xs text-muted-foreground">Refreshing requests...</span>}
      </div>

      <TransferSection icon={FileClockIcon} title="My Requests" count={myRequests.length}>
        {myRequests.length === 0 ? (
          <EmptyTransferSection message="You have not requested an assignment transfer." />
        ) : (
          <div className="grid grid-cols-1 gap-4 xl:grid-cols-2">
            {myRequests.map((request) => (
              <TransferRequestCard
                key={request.id}
                transfer={request}
                currentUserId={currentUserId}
                onUpdated={loadRequests}
              />
            ))}
          </div>
        )}
      </TransferSection>

      <TransferSection
        icon={ClipboardCheckIcon}
        title="Awaiting Your Approval"
        count={approvals.length}
      >
        {approvals.length === 0 ? (
          <EmptyTransferSection message="No pending requests need your approval." />
        ) : (
          <div className="grid grid-cols-1 gap-4 xl:grid-cols-2">
            {approvals.map((entry) => (
              entry.sides.map((side) => (
                <TransferApprovalCard
                  key={`${entry.request.id}-${side}`}
                  transfer={entry.request}
                  side={side}
                  onUpdated={loadRequests}
                />
              ))
            ))}
          </div>
        )}
      </TransferSection>

      {canResolve && (
        <TransferSection icon={ShieldAlertIcon} title="Appeals" count={appeals.length}>
          {appeals.length === 0 ? (
            <EmptyTransferSection message="No escalated transfer requests need a final call." />
          ) : (
            <div className="grid grid-cols-1 gap-4 xl:grid-cols-2">
              {appeals.map((request) => (
                <TransferResolutionCard
                  key={request.id}
                  transfer={request}
                  onUpdated={loadRequests}
                />
              ))}
            </div>
          )}
        </TransferSection>
      )}

      <LeadershipTransfersSection currentUserId={currentUserId} canResolve={canResolve} />
    </div>
  );
}