/**
 * Two-way sync between app state and the address bar, so a refresh (or a shared
 * link) restores the same view, color filter, and color-brush mode.
 *
 *   path      → the active tab:  /  /week  /month   (day is the default, shown as /)
 *   ?color=   → the color filter:  ?color=blue
 *   ?brush=   → color-brush mode:  ?brush=orange  (or ?brush=erase for "no color")
 *   ?panel=   → an open modal:  ?panel=controls  ?panel=credits  ?panel=settings
 */
import { todayKey } from "./date";
import type { TaskColor } from "./types";

export type View = "week" | "month" | "day" | "3day";
export type Panel = "controls" | "credits" | "settings";

const VIEWS: View[] = ["week", "month", "day", "3day"];
const PANELS: Panel[] = ["controls", "credits", "settings"];

export interface UrlState {
  view: View;
  /** ISO day key (YYYY-MM-DD) the view is anchored on. The day view puts it in the
      path (as /day/<date>, unless it's today — that stays "/"), so the link is
      refresh-safe and shareable. */
  anchor: string;
  color: TaskColor;
  brush: { on: boolean; color: TaskColor };
  panel: Panel | null;
}

// Palette ids are user-defined now (see palette.ts), so any non-empty string
// is accepted here — the store resolves it against the live palette (and
// falls back gracefully if it doesn't match an active color; see App.svelte).
function isColor(v: string | null): v is Exclude<TaskColor, null> {
  return v !== null && v.length > 0;
}

/**
 * True while an ATProto OAuth callback is sitting in the address bar (the auth
 * server redirected back with `code`/`state`, or an `error`). The OAuth client
 * reads these on init and then cleans them up itself, so we must NOT rewrite the
 * URL before that happens — doing so drops the callback and the sign-in is lost.
 *
 * The OAuth client is configured with `responseMode: "query"`, so the callback
 * arrives in the query string (`?code=…&state=…`) — but the hash is still
 * checked: earlier client generations used `response_mode=fragment`, and a
 * stale tab or a bookmarked callback can still land one there, where a
 * `replaceState` would silently drop it.
 */
export function hasPendingOAuthCallback(): boolean {
  const looksLikeCallback = (qs: string) => {
    const p = new URLSearchParams(qs);
    return p.has("state") && (p.has("code") || p.has("iss") || p.has("error"));
  };
  return (
    looksLikeCallback(window.location.search) ||
    looksLikeCallback(window.location.hash.replace(/^#/, ""))
  );
}

/** Read whatever the current URL specifies. Missing pieces are left undefined. */
export function readUrl(): Partial<UrlState> {
  const out: Partial<UrlState> = {};

  const segs = window.location.pathname.replace(/^\/+|\/+$/g, "").split("/");
  if (VIEWS.includes(segs[0] as View)) out.view = segs[0] as View;
  // The day and 3-day views carry their focused date as a second path segment
  // (/day/2026-07-16, /3day/2026-07-16). Ignore a malformed date and fall back
  // to today.
  if (
    (out.view === "day" || out.view === "3day") &&
    /^\d{4}-\d{2}-\d{2}$/.test(segs[1] ?? "")
  ) {
    out.anchor = segs[1];
  }

  const params = new URLSearchParams(window.location.search);

  const color = params.get("color");
  if (isColor(color)) out.color = color;

  const brush = params.get("brush");
  if (brush !== null) {
    out.brush = { on: true, color: isColor(brush) ? brush : null };
  }

  const panel = params.get("panel");
  if (panel !== null && (PANELS as string[]).includes(panel)) out.panel = panel as Panel;

  return out;
}

/** Reflect the current app state into the URL (without adding history entries). */
export function writeUrl(s: UrlState) {
  const params = new URLSearchParams();
  if (s.color) params.set("color", s.color);
  if (s.brush.on) params.set("brush", s.brush.color ?? "erase");
  if (s.panel) params.set("panel", s.panel);

  const qs = params.toString();
  // Day is the default tab, shown at "/". A day anchored on a date other than
  // today keeps its date in the path (/day/<date>) so the link is shareable;
  // today's day view collapses to a bare "/". The 3-day view follows the same
  // collapse-to-default logic, but keeps its "/3day" prefix either way.
  const path =
    s.view === "day"
      ? s.anchor === todayKey()
        ? "/"
        : `/day/${s.anchor}`
      : s.view === "3day"
        ? s.anchor === todayKey()
          ? "/3day"
          : `/3day/${s.anchor}`
        : `/${s.view}`;
  const next = `${path}${qs ? `?${qs}` : ""}`;
  const current = window.location.pathname + window.location.search;
  if (current !== next) window.history.replaceState(null, "", next);
}