import { useCallback, useEffect, useRef, useState } from 'react';
import { CircleAlert, CircleCheck, Loader2, RefreshCw, Wand2 } from 'lucide-react';
import { useClient } from 'hooks/useClient';
import { Button } from '@/components/ui/button';
import { readableError } from './errors';
import { Block } from './Block';

/**
 * Building `derived/` from `originals/`.
 *
 * ── Why this is visible at all ──
 *
 * The work happens without anybody watching: a file arrives and something converts it minutes later.
 * That is the right behaviour and the wrong experience — a person who has just uploaded forty
 * photographs has no way to tell "being converted" from "nothing happened". So the state of the run is
 * on the screen, whether the run was started here or by an upload.
 *
 * ── It polls, and only while something is running ──
 *
 * A full pass takes minutes, so the request that starts it returns immediately and this asks how it is
 * going. The poll stops the moment the answer says it is not running — an idle panel makes no requests,
 * which is what keeps a screen somebody left open from being a request every second all afternoon.
 *
 * ── The counts distinguish built from skipped, deliberately ──
 *
 * Re-running is normal and cheap: everything already correct is skipped, because each derived folder
 * carries the size and mtime it was built from. A run reporting "412 skipped" is the system saying it
 * had nothing to do, which is a different and more reassuring answer than "412 done".
 *
 * ── Failures stay ──
 *
 * A file that could not be converted is listed with the reason and does not clear itself. One bad file
 * out of four hundred is exactly the thing a progress bar hides, and it is the only part of this
 * anybody has to act on.
 */

type SyncError = { file: string; message: string };

type SyncState = {
  running: boolean;
  total: number | null;
  done: number;
  built: number;
  skipped: number;
  errors: SyncError[];
  current: string[];
  startedAt: string | null;
  finishedAt: string | null;
  fatal: string | null;
};

/** How often to ask, while something is happening. Fast enough to look live, slow enough to be free. */
const POLL_MS = 1000;

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

  const [state, setState] = useState<SyncState | null>(null);
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState<string | null>(null);

  const load = useCallback(async () => {
    try {
      setState(await clientRef.current.get<SyncState>('/fofos-admin/_config/media/sync'));
    } catch {
      // Owner-only, and Root Location above has already said so once if that is the reason.
      setState(null);
    }
  }, []);

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

  /*
    The poll, keyed on whether a run is in progress.

    The interval is torn down and not replaced when `running` goes false, so the last tick that
    observes the finish is also the one that stops the asking. No separate "should I still be polling"
    flag to get out of step with the answer.
  */
  useEffect(() => {
    if (!state?.running) return;
    const timer = setInterval(() => void load(), POLL_MS);
    return () => clearInterval(timer);
  }, [state?.running, load]);

  const start = async () => {
    setBusy(true);
    setError(null);
    try {
      const result = await clientRef.current.post<{ started: boolean; state: SyncState }>(
        '/fofos-admin/_config/media/sync',
        {},
      );
      setState(result.state);
    } catch (caught) {
      setError(readableError(caught));
    } finally {
      setBusy(false);
    }
  };

  const running = state?.running ?? false;
  const total = state?.total ?? null;
  const done = state?.done ?? 0;
  // Null total means the walk has not finished, so there is nothing honest to divide by yet.
  const percent = total && total > 0 ? Math.round((done / total) * 100) : null;

  return (
    <Block
      icon={Wand2}
      title="Derived media"
      hint="Web-ready copies of everything in originals — resized, converted, and safe to rebuild."
      status={
        running ? (
          <span className="flex items-center gap-1.5 text-xs text-muted-foreground">
            <Loader2 className="size-3.5 animate-spin" />
            {percent === null ? 'Looking' : `${percent}%`}
          </span>
        ) : state?.finishedAt ? (
          <span className="flex items-center gap-1.5 text-xs text-muted-foreground">
            <CircleCheck className="size-3.5" />
            Finished
          </span>
        ) : undefined
      }
    >
      {running && (
        <div className="space-y-2">
          <div className="h-1.5 w-full overflow-hidden rounded-full bg-muted">
            <div
              className="h-full rounded-full bg-primary transition-[width] duration-500"
              // Indeterminate until the walk has counted: a bar that starts full and shrinks is worse
              // than one that has not started.
              style={{ width: `${percent ?? 0}%` }}
            />
          </div>
          <p className="truncate text-xs text-muted-foreground">
            {total === null ? 'Reading originals…' : `${done} of ${total}`}
            {state?.current.length ? ` · ${state.current.join(', ')}` : ''}
          </p>
        </div>
      )}

      {!running && state && (state.built > 0 || state.skipped > 0 || state.errors.length > 0) && (
        <p className="text-xs text-muted-foreground">
          {state.built} built · {state.skipped} already current
          {state.errors.length > 0 ? ` · ${state.errors.length} failed` : ''}
        </p>
      )}

      {state?.fatal && (
        <p className="flex items-start gap-1.5 text-xs text-destructive">
          <CircleAlert className="mt-px size-3.5 shrink-0" />
          {state.fatal}
        </p>
      )}

      {state && state.errors.length > 0 && (
        <ul className="max-h-40 space-y-1 overflow-auto rounded border border-border/60 p-2">
          {state.errors.map((failure) => (
            <li key={failure.file} className="text-xs">
              <span className="font-medium">{failure.file}</span>
              <span className="text-muted-foreground"> — {failure.message}</span>
            </li>
          ))}
        </ul>
      )}

      {error && <p className="text-xs text-destructive">{error}</p>}

      {/* Bottom row, like every other block here: the actions are not part of what you are reading. */}
      <div className="flex justify-end gap-2">
        <Button variant="outline" size="sm" onClick={() => void start()} disabled={busy || running}>
          {running ? <Loader2 className="size-4 animate-spin" /> : <RefreshCw className="size-4" />}
          {running ? 'Syncing' : state?.finishedAt ? 'Sync again' : 'Sync now'}
        </Button>
      </div>
    </Block>
  );
};