import type { Low } from 'lowdb';
import { JSONFilePreset } from 'lowdb/node';
import {
  AutomationSettings,
  CustomFields,
  DatabaseModel,
  ProjectData,
  ProjectRundowns,
  Rundown,
  Settings,
  URLPreset,
  ViewSettings,
} from 'ontime-types';

import { isTest } from '../../setup/environment.js';
import { shouldCrashDev } from '../../utils/development.js';
import { isPath } from '../../utils/fileManagement.js';
import { safeMerge } from './DataProvider.utils.js';

type ReadonlyPromise<T> = Promise<Readonly<T>>;

let db = {} as Low<DatabaseModel>;

/**
 * Initialises the JSON adapter to persist data to a file
 */
export async function initPersistence(filePath: string, fallbackData: DatabaseModel) {
  // eslint-disable-next-line no-unused-labels -- dev code path
  DEV: shouldCrashDev(!isPath(filePath), 'initPersistence should be called with a path');
  const newDb = await JSONFilePreset<DatabaseModel>(filePath, fallbackData);

  // Read the database to initialize it
  newDb.data = fallbackData;
  await newDb.write();
  await newDb.read();

  db = newDb;
}

export function getDataProvider() {
  if (db === null) throw new Error('Database not initialized');

  return {
    getData,
    setProjectData,
    getProjectData,
    setCustomFields,
    getCustomFields,
    setRundown,
    mergeRundown,
    getSettings,
    setSettings,
    getUrlPresets,
    setUrlPresets,
    getViewSettings,
    setViewSettings,
    getAutomation,
    setAutomation,
    getRundown,
    getProjectRundowns,
    mergeIntoData,
    deleteRundown,
  };
}

function getData(): Readonly<DatabaseModel> {
  return db.data;
}

async function setProjectData(newData: Partial<ProjectData>): ReadonlyPromise<ProjectData> {
  db.data.project = { ...structuredClone(db.data.project), ...structuredClone(newData) }; // Performing deep copy as we're updating / merging data
  await persist();
  return db.data.project;
}

function getProjectData(): Readonly<ProjectData> {
  return db.data.project;
}

async function setCustomFields(newData: CustomFields): ReadonlyPromise<CustomFields> {
  db.data.customFields = { ...newData };
  await persist();
  return db.data.customFields;
}

async function mergeRundown(
  newCustomFields: CustomFields,
  newRundowns: ProjectRundowns,
): ReadonlyPromise<{ rundowns: ProjectRundowns; customFields: CustomFields }> {
  db.data.customFields = { ...db.data.customFields, ...newCustomFields };

  Object.entries(newRundowns).forEach(([id, rundown]) => {
    // Note that entries with the same key will be overridden
    db.data.rundowns[id] = rundown;
  });
  await persist();
  return { rundowns: db.data.rundowns, customFields: db.data.customFields };
}

function getCustomFields(): Readonly<CustomFields> {
  return db.data.customFields;
}

async function setRundown(rundownKey: string, newData: Rundown): ReadonlyPromise<ProjectRundowns> {
  db.data.rundowns[rundownKey] = structuredClone(newData);
  await persist();
  return db.data.rundowns;
}

function getSettings(): Readonly<Settings> {
  return db.data.settings;
}

async function setSettings(newData: Settings): ReadonlyPromise<Settings> {
  db.data.settings = { ...newData };
  await persist();
  return db.data.settings;
}

function getUrlPresets(): Readonly<URLPreset[]> {
  return db.data.urlPresets;
}

async function setUrlPresets(newData: URLPreset[]): ReadonlyPromise<URLPreset[]> {
  db.data.urlPresets = newData;
  await persist();
  return db.data.urlPresets;
}

function getViewSettings(): Readonly<ViewSettings> {
  return db.data.viewSettings;
}

async function setViewSettings(newData: ViewSettings): ReadonlyPromise<ViewSettings> {
  db.data.viewSettings = { ...newData };
  await persist();
  return db.data.viewSettings;
}

function getAutomation(): Readonly<AutomationSettings> {
  return db.data.automation;
}

async function setAutomation(newData: AutomationSettings): ReadonlyPromise<AutomationSettings> {
  db.data.automation = { ...newData };
  await persist();
  return db.data.automation;
}

function getRundown(rundownKey: string): Readonly<Rundown> {
  if (!(rundownKey in db.data.rundowns)) throw new Error(`Rundown with id: ${rundownKey} not found`);
  const rundown = db.data.rundowns[rundownKey];
  if (!rundown) throw new Error(`Rundown with id: ${rundownKey} not found`);
  return rundown;
}

async function deleteRundown(rundownKey: string): Promise<ProjectRundowns> {
  if (!(rundownKey in db.data.rundowns)) throw new Error(`Rundown with id: ${rundownKey} not found`);
  delete db.data.rundowns[rundownKey];
  await persist();
  return db.data.rundowns;
}

function getProjectRundowns(): Readonly<ProjectRundowns> {
  return db.data.rundowns;
}

async function mergeIntoData(newData: Partial<DatabaseModel>): ReadonlyPromise<DatabaseModel> {
  const mergedData = safeMerge(db.data, newData);
  db.data.project = mergedData.project;
  db.data.settings = mergedData.settings;
  db.data.viewSettings = mergedData.viewSettings;
  db.data.automation = mergedData.automation;
  db.data.urlPresets = mergedData.urlPresets;
  db.data.customFields = mergedData.customFields;
  db.data.rundowns = mergedData.rundowns;

  await persist();
  return db.data;
}

// Module-level state for debounced writes
let pendingWrite: NodeJS.Timeout | null = null;
let activeWrite: Promise<void> | null = null;
const writeDelayMs = 3000; // 3 seconds

/**
 * Handles persisting data to file with trailing-edge debounce
 * Multiple rapid calls will be coalesced into a single write
 */
async function persist() {
  if (isTest) return;

  // Cancel any pending write and reschedule
  if (pendingWrite) {
    clearTimeout(pendingWrite);
  }

  // Schedule new write after quiet period
  pendingWrite = setTimeout(async () => {
    pendingWrite = null;

    // Wait for any in-progress write to finish first
    if (activeWrite) {
      await activeWrite;
    }

    try {
      activeWrite = db.write();
      await activeWrite;
    } catch (error) {
      console.error('Failed to persist database:', error);
    } finally {
      activeWrite = null;
    }
  }, writeDelayMs);
}

/**
 * Force immediate write of any pending changes
 */
export async function flushPendingWrites() {
  if (isTest) return;

  if (pendingWrite) {
    clearTimeout(pendingWrite);
    pendingWrite = null;
  }

  // Wait for any in-progress write to finish
  if (activeWrite) {
    await activeWrite;
  }

  await db.write();
}