import { randomUUID } from "node:crypto";
import { readdir, readFile, rename, unlink, writeFile } from "node:fs/promises";
import path from "node:path";

export const CALENDAR_TONES = ["cyan", "amber", "violet", "emerald", "rose"] as const;
export type CalendarTone = (typeof CALENDAR_TONES)[number];
export const MAX_CALENDARS = 10;
const HISTORY_LIMIT = 20;

export type CalendarSetting = {
  id: string;
  /** Display name override; empty means "use the feed's own name". */
  name: string;
  url: string;
  tone: CalendarTone;
  enabled: boolean;
};

export type Settings = {
  schema: 1;
  updatedAt: string;
  calendars: CalendarSetting[];
};

export type AuthState = {
  passwordHash: string;
  sessionSecret: string;
};

const dataDir = () => process.env.ORGANIZER_DATA_DIR || "/data";
const settingsPath = () => path.join(dataDir(), "settings.json");
const authPath = () => path.join(dataDir(), "auth.json");
const historyDir = () => path.join(dataDir(), "history");

export function validCalendarUrl(value: unknown) {
  let url: URL;
  try {
    url = new URL(String(value).trim());
  } catch {
    return null;
  }
  if (url.protocol !== "https:" || url.hostname !== "calendar.google.com" || !url.pathname.endsWith("/basic.ics")) return null;
  if (!/^\/calendar\/ical\/[A-Za-z0-9._~%+@-]+\/(private-[A-Za-z0-9._~%+@-]+|public)\/basic\.ics$/.test(url.pathname)) return null;
  return url.toString();
}

/** "…/ical/fam…%40group…/private-••••3854/basic.ics" — enough to tell feeds apart, not enough to use one. */
export function maskCalendarUrl(url: string) {
  const match = /\/calendar\/ical\/([^/]+)\/(private-[^/]+|public)\/basic\.ics$/.exec(new URL(url).pathname);
  if (!match) return "calendar.google.com/…";
  const owner = decodeURIComponent(match[1]);
  const shortOwner = owner.length > 18 ? `${owner.slice(0, 8)}…${owner.slice(owner.indexOf("@"))}` : owner;
  const key = match[2] === "public" ? "public" : `private-••••${match[2].slice(-4)}`;
  return `${shortOwner} · ${key}`;
}

function normalizeSettings(raw: unknown): Settings {
  const value = (raw ?? {}) as Partial<Settings>;
  const calendars = Array.isArray(value.calendars) ? value.calendars : [];
  return {
    schema: 1,
    updatedAt: typeof value.updatedAt === "string" ? value.updatedAt : new Date(0).toISOString(),
    calendars: calendars
      .map((entry) => {
        const url = validCalendarUrl(entry?.url);
        if (!url) return null;
        return {
          id: typeof entry.id === "string" && entry.id ? entry.id : randomUUID(),
          name: typeof entry.name === "string" ? entry.name.trim().slice(0, 50) : "",
          url,
          tone: CALENDAR_TONES.includes(entry.tone as CalendarTone) ? (entry.tone as CalendarTone) : "cyan",
          enabled: entry.enabled !== false,
        } satisfies CalendarSetting;
      })
      .filter((entry): entry is CalendarSetting => entry !== null)
      .slice(0, MAX_CALENDARS),
  };
}

async function readJson(file: string) {
  return JSON.parse(await readFile(file, "utf8")) as unknown;
}

async function writeJsonAtomic(file: string, value: unknown) {
  const temporary = `${file}.${process.pid}.${Date.now()}.tmp`;
  await writeFile(temporary, `${JSON.stringify(value, null, 2)}\n`, { mode: 0o600 });
  await rename(temporary, file);
}

// All writes go through one queue so concurrent saves cannot interleave.
let writeQueue: Promise<unknown> = Promise.resolve();
function serialized<T>(task: () => Promise<T>) {
  const run = writeQueue.then(task, task);
  writeQueue = run.catch(() => undefined);
  return run;
}

export async function readSettings(): Promise<Settings> {
  try {
    return normalizeSettings(await readJson(settingsPath()));
  } catch {
    return normalizeSettings({});
  }
}

export type HistoryEntry = { id: string; savedAt: string; calendarCount: number; note: string };

async function pruneHistory() {
  const files = (await readdir(historyDir())).filter((name) => name.endsWith(".json")).sort();
  for (const name of files.slice(0, Math.max(0, files.length - HISTORY_LIMIT))) {
    await unlink(path.join(historyDir(), name)).catch(() => undefined);
  }
}

/** Saves new settings, first snapshotting the current ones into history. */
export function saveSettings(calendars: CalendarSetting[], note: string) {
  return serialized(async () => {
    const current = await readSettings();
    const stamp = new Date().toISOString();
    const snapshotId = `${stamp.replace(/[:.]/g, "-")}`;
    await writeJsonAtomic(path.join(historyDir(), `${snapshotId}.json`), { ...current, note });
    await pruneHistory();
    const next = normalizeSettings({ schema: 1, updatedAt: stamp, calendars });
    await writeJsonAtomic(settingsPath(), next);
    return next;
  });
}

export async function listHistory(): Promise<HistoryEntry[]> {
  const files = (await readdir(historyDir()).catch(() => [] as string[])).filter((name) => name.endsWith(".json")).sort().reverse();
  const entries: HistoryEntry[] = [];
  for (const name of files) {
    try {
      const raw = (await readJson(path.join(historyDir(), name))) as Settings & { note?: string };
      entries.push({
        id: name.slice(0, -5),
        savedAt: raw.updatedAt,
        calendarCount: Array.isArray(raw.calendars) ? raw.calendars.length : 0,
        note: typeof raw.note === "string" ? raw.note : "",
      });
    } catch {
      // Skip an unreadable snapshot.
    }
  }
  return entries;
}

export async function readHistorySnapshot(id: string) {
  if (!/^[0-9TZ-]+$/.test(id)) return null;
  try {
    return normalizeSettings(await readJson(path.join(historyDir(), `${id}.json`)));
  } catch {
    return null;
  }
}

export async function readAuth(): Promise<AuthState> {
  const raw = (await readJson(authPath())) as Partial<AuthState>;
  if (typeof raw.sessionSecret !== "string" || raw.sessionSecret.length < 32) throw new Error("auth.json is missing a session secret");
  return { passwordHash: typeof raw.passwordHash === "string" ? raw.passwordHash : "", sessionSecret: raw.sessionSecret };
}

export function writeAuth(next: AuthState) {
  return serialized(() => writeJsonAtomic(authPath(), next));
}