import path from "path";
import fs from "node:fs/promises";
import { EventEmitter } from "events";

import { safeOutputFile } from "./file_ops";
import { SubscribableValue } from "./subscriptions";
import { logger } from "./logging";
import { ControllerConfig } from "./config";

type DatastoreKey = string | number;
type DatastoreValue = string | number | boolean | object;

// Abstract class which can provide saving and loading capabilities to a datastore
export abstract class DatastoreProvider<
	K extends DatastoreKey,
	V extends DatastoreValue,
> {
	abstract save(data: Map<K, V>): Promise<void>
	abstract load(): Promise<Map<K, V>>

	// Load data from the source and return it, this should be passed to the constructor of a datastore
	async bootstrap() {
		return [this, await this.load()] as const;
	}
}

// Store all data in memory, used as a default and should be avoided
export class MemoryDatastoreProvider<
	K extends DatastoreKey,
	V extends DatastoreValue,
> extends DatastoreProvider<K, V> {
	constructor(
		private value = new Map<K, V>()
	) {
		super();
	}

	async save(data: Map<K, V>) {
		this.value = new Map(data);
	}

	async load(): Promise<Map<K, V>> {
		return new Map(this.value);
	}
}

// Store all data within a json object file and validate the result against a schema
export class JsonDatastoreProvider<
	V extends DatastoreValue,
	J, // Intermediate type returned from migrations
> extends DatastoreProvider<string, V> {
	constructor(
		private filePath: string,
		private fromJson: (json: J) => V = v => v as any as V,
		private migrations: (rawJson: Record<string, unknown>) => Record<string, J> = v => v as Record<string, J>,
		private finalise: (obj: V, map: Map<string, V>) => V | undefined = v => v,
	) {
		super();
	}

	// Save the data to the json file
	async save(data: Map<string, V>) {
		logger.verbose(`Saving ${this.filePath}`);
		await safeOutputFile(this.filePath, JSON.stringify(Object.fromEntries(data), null, "\t"));
	}

	// Load the data from the json file
	async load(): Promise<Map<string, V>> {
		// Read the raw json from the file
		let rawJson;
		try {
			logger.verbose(`Loading ${this.filePath}`);
			rawJson = JSON.parse(await fs.readFile(this.filePath, { encoding: "utf8" }));
		} catch (err: any) {
			if (err.code !== "ENOENT") {
				throw err;
			}
			return new Map();
		}

		// Apply migrations
		const serialized = this.migrations(rawJson);

		// Convert to data class objects
		let serializedCount = 0;
		const result = new Map<string, V>();
		for (const [key, raw] of Object.entries(serialized)) {
			const final = this.finalise(this.fromJson(raw), result);
			if (final !== undefined) { result.set(key, final); }
			serializedCount += 1;
		}

		// Save a backup if the map does not contain all values (happens where there are duplicates)
		if (result.size < serializedCount) {
			const backupPath = `${this.filePath}.${Date.now()}.bak`;
			logger.warn(
				`Duplicates detected in ${this.filePath}, a backup was written to: ${backupPath}`
			);
			await safeOutputFile(backupPath, JSON.stringify(rawJson, null, "\t"));
		}

		return result;
	}
}

// Store all data within a json array file where each element has a unique id
export class JsonIdDatastoreProvider<
	V extends DatastoreValue & { id: DatastoreKey },
	J, // Intermediate type returned from migrations
> extends DatastoreProvider<V["id"], V> {
	constructor(
		private filePath: string,
		private fromJson: (json: J) => V = v => v as any as V,
		private migrations: (rawJson: Array<unknown>) => Array<J> = v => v as Array<J>,
		private finalise: (obj: V, map: Map<V["id"], V>) => V | undefined = v => v,
	) {
		super();
	}

	// Save the data to the json file
	async save(data: Map<V["id"], V>) {
		logger.verbose(`Saving ${this.filePath}`);
		await safeOutputFile(this.filePath, JSON.stringify([...data.values()], null, "\t"));
	}

	// Load the data from the json file
	async load(): Promise<Map<V["id"], V>> {
		// Read the raw json from the file
		let rawJson;
		try {
			logger.verbose(`Loading ${this.filePath}`);
			rawJson = JSON.parse(await fs.readFile(this.filePath, { encoding: "utf8" }));
		} catch (err: any) {
			if (err.code !== "ENOENT") {
				throw err;
			}
			return new Map();
		}

		// Apply migrations
		const serialized = this.migrations(rawJson);

		// Convert to data class objects
		let serializedCount = 0;
		const result = new Map<V["id"], V>();
		for (const raw of serialized) {
			const final = this.finalise(this.fromJson(raw), result);
			if (final !== undefined) { result.set(final.id, final); }
			serializedCount += 1;
		}

		// Save a backup if the map does not contain all values (happens where there are duplicates)
		if (result.size < serializedCount) {
			const backupPath = `${this.filePath}.${Date.now()}.bak`;
			logger.warn(
				`Duplicates detected in ${this.filePath}, a backup was written to: ${backupPath}`
			);
			await safeOutputFile(backupPath, JSON.stringify(rawJson, null, "\t"));
		}

		return result;
	}
}

// Implements a similar interface to a map
export abstract class Datastore<
	K extends DatastoreKey,
	V extends DatastoreValue,
	U = V,
> extends EventEmitter<{
		"update": [ updates: U[] ],
	}> {
	private dirty = false;

	constructor(
		private provider: DatastoreProvider<K, V> = new MemoryDatastoreProvider(),
		protected data = new Map<K, V>(),
	) {
		super();
	}

	// Get the file path based on the controller config
	static getFilePath(config: ControllerConfig, file: string) {
		return path.resolve(config.get("controller.database_directory"), file);
	}

	// Save the datastore to the provider
	async save() {
		if (this.dirty) {
			await this.provider.save(this.data);
			this.dirty = false;
		}
	}

	// Load the datastore from the provider
	async load() {
		this.data = await this.provider.load();
		this.dirty = false;
	}

	// Set the dirty flag and call update handlers
	protected touch(updates: U[]) {
		if (updates.length) {
			this.dirty = true;
			this.emit("update", updates);
		}
	}

	// Returns true if the datastore has the value, false otherwise
	has(key: K) {
		return this.data.has(key);
	}

	// Get a value from from the datastore
	get(key: K) {
		return this.data.get(key) as Readonly<V> ?? undefined;
	}

	// Get a mutable reference to a value in the datastore, call set after use
	getMutable(key: K) {
		return this.data.get(key);
	}

	// Allow getting the size of the datastore
	get size() {
		return this.data.size;
	}

	// Allow iterating through the datastore like a Map.
	[Symbol.iterator](): IterableIterator<[K, Readonly<V>]> {
		return this.data.entries();
	}

	// Returns all values in the datastore
	values() {
		return this.data.values() as IterableIterator<Readonly<V>>;
	}

	// Returns all values in the datastore as mutable references, call setMany after use
	valuesMutable() {
		return this.data.values();
	}

	keys() {
		return this.data.keys();
	}
}

// General key value mapping which can be saved and loaded with the file system
export class KeyValueDatastore<
	K extends DatastoreKey,
	V extends DatastoreValue,
> extends Datastore<K, V, [key: K, value: V, isDeleted?: boolean]> {
	// Set the value in the datastore, be careful of race conditions if you await any functions before calling set
	set(key: K, value: V) {
		this.data.set(key, value);
		this.touch([[key, value]]);
	}

	// Set many values at once from an array of key value pairs
	setMany(pairs: [K, V][]) {
		for (const [k, v] of pairs) {
			this.data.set(k, v);
		}
		this.touch(pairs);
	}

	// Delete a value in the datastore
	delete(key: K) {
		const value = this.data.get(key);
		if (value !== undefined) {
			this.data.delete(key);
			this.touch([[key, value, true]]);
		}
	}

	// Delete many values at once from an array of keys
	deleteMany(keys: K[]) {
		const updates = [] as [K, V, true][];
		for (const key of keys) {
			const value = this.data.get(key);
			updates.push([key, value!, true]);
			this.data.delete(key);
		}
		this.touch(updates);
	}
}

// A special implementation of the datastore to work directly with subscribable values
export class SubscribableDatastore<
	V extends SubscribableValue,
> extends Datastore<V["id"], V> {
	/** Last time an update occurred */
	lastUpdatedAtMs: number = 0;

	private static maxUpdatedAtMs(values: Iterable<SubscribableValue>) {
		let max = 0;
		for (const value of values) {
			// Prevent one NaN, undefined, +Inf or similar from breaking the datastore.
			if (Number.isFinite(value.updatedAtMs)) {
				max = Math.max(max, value.updatedAtMs);
			}
		}
		return max;
	}

	private incrementLastUpdatedMs() {
		this.lastUpdatedAtMs = Math.max(Date.now(), this.lastUpdatedAtMs + 1);
	}

	constructor(
		provider: DatastoreProvider<V["id"], V> = new MemoryDatastoreProvider(),
		data = new Map<V["id"], V>(),
	) {
		super(provider, data);
		this.lastUpdatedAtMs = SubscribableDatastore.maxUpdatedAtMs(this.data.values());
	}

	async load() {
		await super.load();
		this.lastUpdatedAtMs = SubscribableDatastore.maxUpdatedAtMs(this.data.values());
	}

	// Set the value in the datastore, be careful of race conditions if you await any functions before calling set
	set(value: V) {
		this.incrementLastUpdatedMs();
		this.data.set(value.id, value);
		value.updatedAtMs = this.lastUpdatedAtMs;
		this.touch([value]);
	}

	// Set many values at once from an array of key value pairs
	setMany(values: V[]) {
		this.incrementLastUpdatedMs();
		for (const value of values) {
			value.updatedAtMs = this.lastUpdatedAtMs;
			this.data.set(value.id, value);
		}
		this.touch(values);
	}

	// Delete a value in the datastore
	delete(value: V) {
		this.incrementLastUpdatedMs();
		this.data.delete(value.id);
		value.updatedAtMs = this.lastUpdatedAtMs;
		value.isDeleted = true;
		this.touch([value]);
	}

	// Delete many values at once from an array of values
	deleteMany(values: V[]) {
		this.incrementLastUpdatedMs();
		for (const value of values) {
			value.isDeleted = true;
			value.updatedAtMs = this.lastUpdatedAtMs;
			this.data.delete(value.id);
		}
		this.touch(values);
	}
}