"use client";

import { useCallback, useEffect, useMemo, useState } from "react";
import { toast } from "sonner";
import { UserMinusIcon } from "lucide-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 { Collapsible, CollapsibleContent, CollapsibleTrigger } from "@/components/ui/collapsible";
import { cancelDivisionRemoval } from "@/app/(frontend)/roster/actions";
import { LeadershipTransferCard } from "@/components/frontend/transfers/LeadershipTransferCard";
import { formatTransferDate } from "@/components/frontend/transfers/transferTypes";
import type { Assignment, LeadershipTransfer, User } from "@/payload-types";

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

const LEADERSHIP_QUERY = new URLSearchParams({
  depth: "1",
  limit: "50",
  sort: "-createdAt",
});

const STATUS_LABELS: Record<LeadershipTransfer["status"], string> = {
  pending: "Pending approval",
  approved: "Approved",
  denied: "Denied",
  cancelled: "Cancelled",
};

const STATUS_VARIANTS: Record<
  LeadershipTransfer["status"],
  "default" | "secondary" | "destructive" | "outline"
> = {
  pending: "secondary",
  approved: "default",
  denied: "destructive",
  cancelled: "outline",
};

function initiatorId(value: number | User | null | undefined): number | null {
  if (value == null) return null;
  return typeof value === "number" ? value : value.id;
}

function personRefLabel(value: number | User | null | undefined, fallback = "Unknown member"): string {
  if (value == null) return fallback;
  if (typeof value === "number") return `User #${value}`;
  return value.displayName || value.username || fallback;
}

function assignmentRef(value: number | Assignment | null | undefined): string {
  if (value == null) return "Unknown assignment";
  if (typeof value === "number") return `Assignment #${value}`;
  return value.callsign ? `[${value.callsign}] ${value.name}` : value.name;
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === "object" && value !== null;
}

/** Shallow-shape-check the REST page so a malformed response surfaces as an error. */
function parseDocs(data: unknown): LeadershipTransfer[] | null {
  if (!isRecord(data) || !Array.isArray(data.docs)) return null;
  return data.docs.filter((doc) => isRecord(doc) && typeof doc.id === "number") as LeadershipTransfer[];
}

/**
 * Leadership-initiated removal requests on the transfers page.
 *
 * Superusers get the pending queue (Approve/Deny with note) plus a collapsed
 * history. Regular members only ever see their own requests as status chips;
 * the whole section stays hidden when they have none (pending removals are
 * invisible to the unit by design).
 */
export function LeadershipTransfersSection({
  currentUserId,
  canResolve,
}: LeadershipTransfersSectionProps) {
  const [docs, setDocs] = useState<readonly LeadershipTransfer[] | null>(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);
  const [cancellingId, setCancellingId] = useState<number | null>(null);
  const [historyOpen, setHistoryOpen] = useState(false);

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

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

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

  const pending = useMemo(() => (docs ?? []).filter((doc) => doc.status === "pending"), [docs]);
  const mine = useMemo(
    () => (docs ?? []).filter((doc) => initiatorId(doc.initiator) === currentUserId),
    [currentUserId, docs],
  );
  const resolved = useMemo(() => (docs ?? []).filter((doc) => doc.status !== "pending"), [docs]);

  async function handleCancel(transferId: number) {
    setCancellingId(transferId);
    try {
      const result = await cancelDivisionRemoval(transferId);
      if (result.success) {
        toast.success("Removal request cancelled");
        void load();
      } else {
        toast.error(result.error ?? "Could not cancel the removal request.");
      }
    } finally {
      setCancellingId(null);
    }
  }

  // Regular members: hide the section entirely while loading, on fetch errors,
  // and whenever they have no requests of their own.
  if (!canResolve) {
    if (docs === null || mine.length === 0) return null;
    return (
      <section aria-labelledby="leadership-transfers-heading" className="flex flex-col gap-3">
        <div className="flex items-center gap-2">
          <UserMinusIcon className="size-4 text-muted-foreground" aria-hidden="true" />
          <h2
            id="leadership-transfers-heading"
            className="text-sm font-semibold uppercase tracking-wider"
          >
            Leadership transfers
          </h2>
          <Badge variant="outline" className="text-xs">
            {mine.length}
          </Badge>
        </div>
        <div className="flex flex-col gap-2">
          {mine.map((doc) => (
            <div
              key={doc.id}
              className="flex flex-wrap items-center gap-2 rounded-md border bg-muted/20 px-3 py-2 text-sm"
            >
              <Badge variant={STATUS_VARIANTS[doc.status]}>{STATUS_LABELS[doc.status]}</Badge>
              <span>
                Removal of <span className="font-medium">{personRefLabel(doc.subject)}</span> from{" "}
                {assignmentRef(doc.fromAssignment)} to {assignmentRef(doc.toAssignment)}
              </span>
              <span className="text-xs text-muted-foreground">
                requested {formatTransferDate(doc.createdAt)}
              </span>
              {doc.status === "pending" && (
                <Button
                  size="sm"
                  variant="outline"
                  className="ml-auto"
                  onClick={() => void handleCancel(doc.id)}
                  disabled={cancellingId === doc.id}
                >
                  Cancel request
                </Button>
              )}
            </div>
          ))}
        </div>
      </section>
    );
  }

  if (docs === null && loading) {
    return (
      <div className="flex flex-col gap-3" aria-busy="true" aria-label="Loading leadership transfers">
        <Skeleton className="h-5 w-48" />
        <Skeleton className="h-40 w-full" />
      </div>
    );
  }

  if (docs === null && error) {
    return (
      <Alert variant="destructive">
        <AlertTitle>Leadership transfers unavailable</AlertTitle>
        <AlertDescription className="flex flex-wrap items-center gap-3">
          <span>{error}</span>
          <Button size="sm" variant="outline" onClick={() => void load()}>
            Try again
          </Button>
        </AlertDescription>
      </Alert>
    );
  }

  return (
    <section aria-labelledby="leadership-transfers-heading" className="flex flex-col gap-3">
      <div className="flex items-center gap-2">
        <UserMinusIcon className="size-4 text-muted-foreground" aria-hidden="true" />
        <h2
          id="leadership-transfers-heading"
          className="text-sm font-semibold uppercase tracking-wider"
        >
          Leadership transfers
        </h2>
        <Badge variant="outline" className="text-xs">
          {pending.length}
        </Badge>
      </div>

      {error && (
        <Alert variant="destructive">
          <AlertTitle>Could not refresh leadership transfers</AlertTitle>
          <AlertDescription className="flex flex-wrap items-center gap-3">
            <span>{error}</span>
            <Button size="sm" variant="outline" onClick={() => void load()}>
              Try again
            </Button>
          </AlertDescription>
        </Alert>
      )}

      {pending.length === 0 ? (
        <Alert>
          <AlertDescription>No pending removal requests need a final call.</AlertDescription>
        </Alert>
      ) : (
        <div className="grid grid-cols-1 gap-4 xl:grid-cols-2">
          {pending.map((doc) => (
            <LeadershipTransferCard key={doc.id} transfer={doc} onUpdated={load} />
          ))}
        </div>
      )}

      {resolved.length > 0 && (
        <Collapsible
          open={historyOpen}
          onOpenChange={setHistoryOpen}
          className="flex flex-col gap-2"
        >
          <CollapsibleTrigger asChild>
            <Button variant="ghost" size="sm" className="w-fit">
              History ({resolved.length})
            </Button>
          </CollapsibleTrigger>
          <CollapsibleContent className="flex flex-col gap-1.5">
            {resolved.map((doc) => (
              <div
                key={doc.id}
                className="flex flex-wrap items-center gap-2 border-b border-border/60 pb-1.5 text-sm"
              >
                <span className="font-medium">{personRefLabel(doc.initiator)}</span>
                <span className="text-muted-foreground">removed</span>
                <span>{personRefLabel(doc.subject)}</span>
                <span className="text-muted-foreground">
                  from {assignmentRef(doc.fromAssignment)} to {assignmentRef(doc.toAssignment)}
                </span>
                <Badge variant={STATUS_VARIANTS[doc.status]}>{STATUS_LABELS[doc.status]}</Badge>
                {doc.resolvedAt && (
                  <span className="ml-auto text-xs text-muted-foreground">
                    {formatTransferDate(doc.resolvedAt)}
                  </span>
                )}
              </div>
            ))}
          </CollapsibleContent>
        </Collapsible>
      )}
    </section>
  );
}