import { useCallback, useEffect, useRef, useState } from "react";
import { useSearchParams } from "react-router";
import { FilePlus2, PenTool, RefreshCw, Trash2 } from "lucide-react";
import { useClient } from "hooks/useClient";
import { NEW_DOC } from "./doc-param";

/**
 * The list of designs — the one concept upstream does not have.
 *
 * Standalone M3E Canvas holds exactly one document, in one browser, in `localStorage`. Everything here
 * exists because Officer gives it several, belonging to a person rather than to a browser.
 *
 * Selection is `?doc=<id>` in the URL rather than a channel, so a design is addressable and survives a
 * reload — `docs/navigation-audit.md`. The canvas panel reads the same parameter rather than being
 * handed the id.
 */

type Row = { id: number; title: string; updatedAt: string };

export const DesignsPanel = () => {
  const client = useClient();
  const clientRef = useRef(client);
  clientRef.current = client;

  const [rows, setRows] = useState<Row[] | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [params, setParams] = useSearchParams();
  const selected = params.get("doc");

  const load = useCallback(async () => {
    try {
      setRows(await clientRef.current.get<Row[]>("/m3e-canvas/documents"));
      setError(null);
    } catch {
      setError("Could not load designs.");
      setRows(null);
    }
  }, []);

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

  /*
    The canvas creates the row on its first save, so New only has to ask for a blank one — a design
    with nothing drawn in it should not exist, and creating one here would leave empties behind every
    time somebody clicked New and changed their mind.

    `?doc=new`, and NOT clearing the parameter, which is what this did. No parameter means "open what
    I was last working on", which the canvas answers with `/documents/latest` — so New handed back the
    design already on screen and pointed the next save at it. The sentinel says the thing the absence
    could not: an empty one, on purpose.
  */
  const startNew = () => setParams((p) => { p.set("doc", NEW_DOC); return p; }, { replace: true });

  const remove = async (id: number, title: string) => {
    if (!confirm(`Delete "${title}"? This cannot be undone.`)) return;
    try {
      await clientRef.current.delete(`/m3e-canvas/documents/${id}`);
      if (selected === String(id)) startNew();
      await load();
    } catch {
      setError("Could not delete that design.");
    }
  };

  return (
    <div className="flex size-full flex-col">
      <header className="flex items-center justify-between border-b px-2 py-1.5">
        <button
          type="button"
          onClick={startNew}
          className="flex items-center gap-1.5 rounded-md px-2 py-1 text-sm hover:bg-muted"
        >
          <FilePlus2 className="size-4" /> New
        </button>
        <button type="button" onClick={() => void load()} className="p-1 text-muted-foreground hover:text-foreground">
          <RefreshCw className="size-3.5" />
        </button>
      </header>

      {error ? <p className="px-3 py-2 text-xs text-destructive">{error}</p> : null}

      {rows === null ? (
        <Centred>Loading…</Centred>
      ) : rows.length === 0 ? (
        <Centred>No designs yet. Draw something and it saves itself.</Centred>
      ) : (
        <ul className="flex-1 overflow-auto">
          {rows.map((row) => (
            <li key={row.id} className="group flex items-center">
              <button
                type="button"
                onClick={() => setParams((p) => { p.set("doc", String(row.id)); return p; }, { replace: true })}
                className={`flex min-w-0 flex-1 items-center gap-2 px-3 py-2 text-left hover:bg-muted/50 ${
                  selected === String(row.id) ? "bg-muted" : ""
                }`}
              >
                <PenTool className="size-3.5 shrink-0 text-muted-foreground" />
                <span className="min-w-0 flex-1">
                  <span className="block truncate text-sm">{row.title}</span>
                  <span className="block truncate text-xs text-muted-foreground">
                    {new Date(row.updatedAt).toLocaleDateString()}
                  </span>
                </span>
              </button>
              <button
                type="button"
                onClick={() => void remove(row.id, row.title)}
                aria-label={`Delete ${row.title}`}
                className="px-2 text-muted-foreground opacity-0 transition-opacity hover:text-destructive group-hover:opacity-100"
              >
                <Trash2 className="size-3.5" />
              </button>
            </li>
          ))}
        </ul>
      )}
    </div>
  );
};

const Centred = ({ children }: { children: React.ReactNode }) => (
  <div className="flex flex-1 items-center justify-center p-4 text-center text-xs text-muted-foreground">
    {children}
  </div>
);