import type { NetworkModel } from './inpModel';
import type { BasemapType, Scenario, SimulationResult, UserGisLayer } from './types';
import type { CRS } from './crs';
import type { DisplayUnitMode } from './unitSystem';
import type { MapStyleSettings } from './StyleSettingsPanel';

// Legacy "GISPipe" prefix kept on purpose (here and in the gispipe_* localStorage
// keys): renaming storage keys would drop every user's saved session/settings.
const DATABASE_NAME = 'gispipe-session';
const DATABASE_VERSION = 1;
const STORE_NAME = 'autosave';
const LATEST_KEY = 'latest';
const TAB_KEY_STORAGE_NAME = 'gispipe_tab_session_key';
// Autosave keeps one record per browser tab (see getTabSessionKey), so the
// store is trimmed to the most recently-saved tabs to avoid growing forever
// as tabs are opened and closed over time.
const MAX_RETAINED_SNAPSHOTS = 10;

export interface SessionSnapshot {
  version: 2;
  savedAt: string;
  fileName: string | null;
  networkModel: NetworkModel;
  crs: CRS;
  basemap: BasemapType;
  displayUnitMode: DisplayUnitMode;
  styleSettings: MapStyleSettings;
  isModified: boolean;
  // Full project state -- without these, restoring a session silently lost
  // every alternative scenario, its results, and any GIS reference layers.
  rawInp: string | null;
  scenarios: Scenario[];
  activeScenarioId: string;
  wasmResult: SimulationResult | null;
  serverResult: SimulationResult | null;
  resultInpSnapshot: string | null;
  userLayers: UserGisLayer[];
}

/** Pre-P0-8 snapshot shape, kept only so an old autosave record from a
 * previous session doesn't hard-fail to load; it restores with no
 * scenarios/results/layers rather than being discarded outright. */
interface LegacySessionSnapshotV1 {
  version: 1;
  savedAt: string;
  fileName: string | null;
  networkModel: NetworkModel;
  crs: CRS;
  basemap: BasemapType;
  displayUnitMode: DisplayUnitMode;
  styleSettings: MapStyleSettings;
  isModified: boolean;
}

type StoredSnapshot = (SessionSnapshot | LegacySessionSnapshotV1) & { id: string };

/**
 * A stable id for this browser TAB (sessionStorage, unlike localStorage/
 * IndexedDB, is private per tab and survives reloads of that same tab but
 * not a fresh tab/window). Using it as the IndexedDB record key means
 * multiple tabs autosaving concurrently each get their own record instead of
 * clobbering a single shared 'latest' record.
 */
function getTabSessionKey(): string {
  try {
    let key = sessionStorage.getItem(TAB_KEY_STORAGE_NAME);
    if (!key) {
      key = `tab_${Date.now()}_${Math.random().toString(36).slice(2, 10)}`;
      sessionStorage.setItem(TAB_KEY_STORAGE_NAME, key);
    }
    return key;
  } catch {
    // sessionStorage unavailable (e.g. private-mode restrictions): fall back
    // to the old shared key rather than failing autosave entirely.
    return LATEST_KEY;
  }
}

function openSessionDatabase(): Promise<IDBDatabase> {
  const { promise, resolve, reject } = Promise.withResolvers<IDBDatabase>();
  const request = indexedDB.open(DATABASE_NAME, DATABASE_VERSION);
  request.onerror = () => reject(request.error ?? new Error('IndexedDB 열기 실패'));
  request.onupgradeneeded = () => {
    const database = request.result;
    if (!database.objectStoreNames.contains(STORE_NAME)) {
      database.createObjectStore(STORE_NAME, { keyPath: 'id' });
    }
  };
  request.onsuccess = () => resolve(request.result);
  return promise;
}

function requestToPromise<T>(request: IDBRequest<T>): Promise<T> {
  const { promise, resolve, reject } = Promise.withResolvers<T>();
  request.onsuccess = () => resolve(request.result);
  request.onerror = () => reject(request.error ?? new Error('IndexedDB 요청 실패'));
  return promise;
}

export async function saveSessionSnapshot(snapshot: SessionSnapshot): Promise<void> {
  const database = await openSessionDatabase();
  try {
    const key = getTabSessionKey();
    const { promise, resolve, reject } = Promise.withResolvers<void>();
    const transaction = database.transaction(STORE_NAME, 'readwrite');
    transaction.oncomplete = () => resolve();
    transaction.onerror = () => reject(transaction.error ?? new Error('자동 저장 실패'));
    transaction.onabort = () => reject(transaction.error ?? new Error('자동 저장 중단'));
    const store = transaction.objectStore(STORE_NAME);
    const stored: StoredSnapshot = { ...snapshot, id: key };
    store.put(stored);

    // Trim to the most recently-saved MAX_RETAINED_SNAPSHOTS records so
    // autosaving from many tabs over time doesn't grow the store forever.
    const allRequest = store.getAll();
    allRequest.onsuccess = () => {
      const all = (allRequest.result as StoredSnapshot[]) || [];
      if (all.length > MAX_RETAINED_SNAPSHOTS) {
        const sorted = [...all].sort((a, b) => (a.savedAt < b.savedAt ? 1 : -1));
        for (const stale of sorted.slice(MAX_RETAINED_SNAPSHOTS)) {
          store.delete(stale.id);
        }
      }
    };
    await promise;
  } finally {
    database.close();
  }
}

/** Exported for unit testing the v1 -> v2 migration without a real IndexedDB. */
export function normalizeStoredSnapshot(stored: StoredSnapshot): SessionSnapshot | null {
  if (!stored || !stored.networkModel) return null;
  if (stored.version === 2) {
    const { id: _id, ...snapshot } = stored;
    return snapshot;
  }
  if (stored.version === 1) {
    const { id: _id, ...legacy } = stored;
    return {
      ...legacy,
      version: 2,
      rawInp: null,
      scenarios: [],
      activeScenarioId: 'base',
      wasmResult: null,
      serverResult: null,
      resultInpSnapshot: null,
      userLayers: [],
    };
  }
  return null;
}

export async function loadSessionSnapshot(): Promise<SessionSnapshot | null> {
  const database = await openSessionDatabase();
  try {
    const key = getTabSessionKey();
    const transaction = database.transaction(STORE_NAME, 'readonly');
    const stored = (await requestToPromise(
      transaction.objectStore(STORE_NAME).get(key)
    )) as StoredSnapshot | undefined;
    if (!stored) return null;
    return normalizeStoredSnapshot(stored);
  } finally {
    database.close();
  }
}

export async function clearSessionSnapshot(): Promise<void> {
  const database = await openSessionDatabase();
  try {
    const key = getTabSessionKey();
    const { promise, resolve, reject } = Promise.withResolvers<void>();
    const transaction = database.transaction(STORE_NAME, 'readwrite');
    transaction.oncomplete = () => resolve();
    transaction.onerror = () => reject(transaction.error ?? new Error('자동 저장본 삭제 실패'));
    transaction.objectStore(STORE_NAME).delete(key);
    await promise;
  } finally {
    database.close();
  }
}