"use client";

import { createContext, useCallback, useContext, useEffect, useRef, useState } from "react";
import { clsx } from "clsx";
import type { ActionResult } from "@/app/actions/library";

/**
 * Kurze Rückmeldungen am unteren Rand — mit optionalem „Rückgängig".
 *
 * Warum überhaupt: Beim Abhaken einer Episode passiert die eigentliche Wirkung
 * weit weg vom Klick (Fortschrittsbalken, Status, „nächste Episode"). Eine
 * kurze Bestätigung sagt, was gerade geschehen ist — und lässt es zurücknehmen,
 * ohne die Stelle wiederfinden zu müssen.
 */

type Toast = {
  id: number;
  message: string;
  tone: "info" | "error" | "erfolg";
  undo?: () => Promise<void> | void;
};

type ToastContext = {
  show(message: string, options?: { tone?: Toast["tone"]; undo?: Toast["undo"] }): void;
  /** Bequemer Weg für Aktionsergebnisse samt Rückgängig-Möglichkeit. */
  report(result: ActionResult, undo?: (watchIds: string[]) => Promise<unknown>): void;
};

const Context = createContext<ToastContext | null>(null);

const VISIBLE_MS = 6000;

export function ToastProvider({ children }: { children: React.ReactNode }) {
  const [toasts, setToasts] = useState<Toast[]>([]);
  const nextId = useRef(1);

  const dismiss = useCallback((id: number) => {
    setToasts((current) => current.filter((toast) => toast.id !== id));
  }, []);

  const show = useCallback<ToastContext["show"]>((message, options) => {
    const id = nextId.current++;
    setToasts((current) => [
      ...current.slice(-2),
      { id, message, tone: options?.tone ?? "info", undo: options?.undo },
    ]);
  }, []);

  const report = useCallback<ToastContext["report"]>(
    (result, undo) => {
      if (!result.ok) {
        show(result.message ?? "Das hat nicht geklappt.", { tone: "error" });
        return;
      }
      if (!result.message) return;

      const ids = result.watchIds ?? [];
      show(result.message, {
        undo: undo && ids.length > 0 ? () => void undo(ids) : undefined,
      });

      // Errungenschaften bekommen eine eigene Einblendung — sie sollen nicht
      // in der Meldung über das Abhaken untergehen.
      for (const name of result.achievements ?? []) {
        show(`Errungenschaft: ${name}`, { tone: "erfolg" });
      }
    },
    [show],
  );

  return (
    <Context.Provider value={{ show, report }}>
      {children}
      <div
        aria-live="polite"
        aria-atomic="false"
        className="pointer-events-none fixed inset-x-0 bottom-4 z-50 flex flex-col items-center gap-2 px-4"
      >
        {toasts.map((toast) => (
          <ToastItem key={toast.id} toast={toast} onDismiss={() => dismiss(toast.id)} />
        ))}
      </div>
    </Context.Provider>
  );
}

function ToastItem({ toast, onDismiss }: { toast: Toast; onDismiss: () => void }) {
  useEffect(() => {
    const timer = setTimeout(onDismiss, VISIBLE_MS);
    return () => clearTimeout(timer);
  }, [onDismiss]);

  return (
    <div
      role={toast.tone === "error" ? "alert" : "status"}
      className={clsx(
        "pointer-events-auto flex max-w-md items-center gap-3 rounded-xl border px-4 py-2.5 text-sm shadow-[var(--fl-shadow)] backdrop-blur-xl",
        "motion-safe:animate-[fl-toast-in_240ms_var(--ease-glow)]",
      )}
      style={{
        backgroundColor: "var(--fl-surface-solid)",
        borderColor:
          toast.tone === "error"
            ? "color-mix(in oklab, var(--fl-danger) 50%, transparent)"
            : toast.tone === "erfolg"
              ? "color-mix(in oklab, var(--fl-success) 50%, transparent)"
              : "var(--fl-border)",
        color:
          toast.tone === "error"
            ? "var(--fl-danger)"
            : toast.tone === "erfolg"
              ? "var(--fl-success)"
              : "var(--fl-text)",
      }}
    >
      <span className="flex-1">{toast.message}</span>
      {toast.undo && (
        <button
          type="button"
          onClick={() => {
            void toast.undo?.();
            onDismiss();
          }}
          className="shrink-0 rounded-lg px-2 py-1 text-sm font-semibold text-[var(--fl-accent)] underline-offset-2 hover:underline"
        >
          Rückgängig
        </button>
      )}
      <button
        type="button"
        onClick={onDismiss}
        aria-label="Meldung schließen"
        className="shrink-0 text-[var(--fl-faint)] hover:text-[var(--fl-text)]"
      >
        <svg viewBox="0 0 24 24" className="h-4 w-4" fill="none" stroke="currentColor" strokeWidth="2" aria-hidden>
          <path d="m6 6 12 12M18 6 6 18" strokeLinecap="round" />
        </svg>
      </button>
    </div>
  );
}

export function useToasts(): ToastContext {
  const context = useContext(Context);
  if (!context) {
    throw new Error("useToasts braucht einen ToastProvider im Elternbaum.");
  }
  return context;
}