// runs mods' server scripts: builds each one's ServerContext and keeps what they register.
// see "Server scripts" in MODS.md. parts not built yet throw when used, saying so
import { EverythingRegistry, ItemRegistry } from "$/common/everything_registry.ts";
import { ItemStack as EngineItemStack } from "$/common/inventory.ts";
import type {
	BlockComponent,
	BlockRef,
	Command,
	Container,
	EventSignal,
	ItemComponent,
	ItemStack,
	Player,
	ServerAfterEvents,
	ServerBeforeEvents,
	ServerContext,
} from "$/common/mod_api/server.ts";
import { ModLoadError } from "$/common/mod_loader.ts";
import { AIR_ID } from "$/common/protocol.ts";
import type { GameServer } from "./game_server.ts";
import type { ServerPlayer } from "./player.ts";

// a list of handlers that can't break each other: one throwing is logged under its mod and the rest still run
export class Signal<T> {
	#handlers: { mod: string; handler: (event: T) => void }[] = [];

	for_mod(mod: string): EventSignal<T> {
		return {
			subscribe: (handler) => {
				const entry = { mod, handler };
				this.#handlers.push(entry);
				return () => {
					this.#handlers = this.#handlers.filter((h) => h !== entry);
				};
			},
		};
	}

	emit(event: T) {
		for (const { mod, handler } of [...this.#handlers]) {
			run_guarded(mod, "an event handler", () => handler(event));
		}
	}

	get empty() {
		return this.#handlers.length === 0;
	}
}

export function run_guarded<T>(mod: string, what: string, fn: () => T): T | undefined {
	try {
		return fn();
	} catch (e) {
		console.error(`[${mod}] ${what} threw:`, e);
		return undefined;
	}
}

type Before = {
	[K in keyof ServerBeforeEvents]: ServerBeforeEvents[K] extends EventSignal<infer T> ? Signal<T> : never;
};
type After = { [K in keyof ServerAfterEvents]: ServerAfterEvents[K] extends EventSignal<infer T> ? Signal<T> : never };

interface Timer {
	mod: string;
	fn: () => void;
	at: number;
	every?: number;
}

export class ModRuntime {
	block_components = new Map<string, { mod: string; component: BlockComponent }>();
	item_components = new Map<string, { mod: string; component: ItemComponent }>();
	commands = new Map<string, { mod: string; name: string; command: Command }>();

	before: Before = {
		block_break: new Signal(),
		block_place: new Signal(),
		block_interact: new Signal(),
		chat_send: new Signal(),
	};
	after: After = {
		block_break: new Signal(),
		block_place: new Signal(),
		block_interact: new Signal(),
		chat_send: new Signal(),
		player_join: new Signal(),
		player_leave: new Signal(),
		server_start: new Signal(),
		tick: new Signal(),
	};

	// per mod key value storage, saved with the world
	storage: Record<string, Record<string, unknown>> = {};

	#timers = new Map<number, Timer>();
	#next_timer = 1;
	#setting_up = true;
	#players = new WeakMap<ServerPlayer, Player>();
	game!: GameServer;

	// imports each server script and calls its setup, in load order
	async load_scripts(game: GameServer, scripts: { mod: string; version: string; url: string }[]) {
		this.game = game;
		for (const { mod, version, url } of scripts) {
			const module = await import(url);
			if (typeof module.setup !== "function") {
				throw new ModLoadError(mod, "the server script doesn't export a setup function");
			}
			await module.setup(this.#context(mod, version));
		}
	}

	// after every setup ran: registration closes and every component blocks and items use must exist
	finish_setup() {
		this.#setting_up = false;

		for (const [id, block] of EverythingRegistry.entries<{ components?: Record<string, unknown> }>("blocks")) {
			for (const component of Object.keys(block.components ?? {})) {
				if (!this.block_components.has(component)) {
					throw new ModLoadError(
						id.split(":")[0],
						`block ${id} uses component ${component}, which nothing registered`,
					);
				}
			}
		}

		for (const [id, item] of EverythingRegistry.entries<ItemRegistry>("items")) {
			const components = Object.entries(item.components ?? {});
			if (components.length === 0) continue;
			for (const [component_id] of components) {
				if (!this.item_components.has(component_id)) {
					throw new ModLoadError(
						id.split(":")[0],
						`item ${id} uses component ${component_id}, which nothing registered`,
					);
				}
			}
			// items are created all over the engine, hook their creation once here
			const previous = item.on_create;
			item.on_create = (stack) => {
				previous?.(stack);
				for (const [component_id, params] of components) {
					const { mod, component } = this.item_components.get(component_id)!;
					if (component.on_create) {
						run_guarded(
							mod,
							`${component_id} on_create`,
							() => component.on_create!(item_api(stack), params),
						);
					}
				}
			};
		}
	}

	// components on a block, with their params from its json
	components_of(block_id: string): { mod: string; id: string; component: BlockComponent; params: unknown }[] {
		const block = EverythingRegistry.get<{ components?: Record<string, unknown> }>("blocks", block_id);
		return Object.entries(block?.components ?? {}).map(([id, params]) => ({
			...this.block_components.get(id)!,
			id,
			params,
		}));
	}

	tick() {
		const now = this.game.current_tick;
		for (const [handle, timer] of [...this.#timers]) {
			if (timer.at > now) continue;
			if (timer.every) {
				timer.at = now + timer.every;
			} else {
				this.#timers.delete(handle);
			}
			run_guarded(timer.mod, "a timer", timer.fn);
		}
		if (!this.after.tick.empty) {
			this.after.tick.emit({ dt: 1 / 20 });
		}
	}

	player(player: ServerPlayer): Player {
		let api = this.#players.get(player);
		if (!api) {
			api = player_api(this.game, player);
			this.#players.set(player, api);
		}
		return api;
	}

	block_ref(x: number, y: number, z: number, id: string): BlockRef {
		const game = this.game;
		return {
			id,
			x,
			y,
			z,
			get data() {
				return game.world.get_tile(x, y, z)?.mod_data;
			},
			set data(value) {
				game.get_or_create_tile(x, y, z).mod_data = value;
				game.world.dirty = true;
			},
		};
	}

	#context(mod: string, version: string): ServerContext {
		const setup_only = (what: string) => {
			if (!this.#setting_up) {
				throw new Error(`[${mod}] ${what} can only be registered during setup`);
			}
		};
		const own = (id: string, what: string) => {
			if (!id.startsWith(`${mod}:`)) {
				throw new ModLoadError(mod, `${what} ${id} must be in the namespace "${mod}"`);
			}
		};
		const game = () => this.game;

		const ctx: ServerContext = {
			mod: { id: mod, version },
			components: {
				register_block: (id, component) => {
					setup_only("components");
					own(id, "component");
					if (this.block_components.has(id)) {
						throw new ModLoadError(mod, `component ${id} is registered twice`);
					}
					this.block_components.set(id, { mod, component: component as BlockComponent });
				},
				register_item: (id, component) => {
					setup_only("components");
					own(id, "component");
					if (this.item_components.has(id)) {
						throw new ModLoadError(mod, `component ${id} is registered twice`);
					}
					this.item_components.set(id, { mod, component: component as ItemComponent });
				},
			},
			commands: {
				register: (name, command) => {
					setup_only("commands");
					if (!/^[a-z0-9_]+$/.test(name)) {
						throw new ModLoadError(mod, `command name "${name}" must be a-z, 0-9 and _`);
					}
					if (name === "give") throw new ModLoadError(mod, `/give belongs to the base game`);
					const existing = this.commands.get(name);
					if (existing) {
						throw new ModLoadError(mod, `/${name} is also registered by ${existing.mod}`);
					}
					const entry = { mod, name, command };
					this.commands.set(name, entry);
					this.commands.set(`${mod}:${name}`, entry);
				},
			},
			events: {
				before: map_signals(this.before, mod),
				after: map_signals(this.after, mod),
			},
			system: {
				run_timeout: (fn, ticks) => this.#add_timer(mod, fn, ticks),
				run_interval: (fn, ticks) => this.#add_timer(mod, fn, ticks, Math.max(1, ticks)),
				clear_run: (handle) => void this.#timers.delete(handle),
				get current_tick() {
					return game().current_tick;
				},
			},
			world: {
				get_block: (x, y, z) => game().world.get_block_id(x, y, z),
				set_block: (x, y, z, id) => {
					if (id !== AIR_ID && !EverythingRegistry.get("blocks", id)) throw new Error(`unknown block ${id}`);
					game().set_block(x, y, z, id);
					return true;
				},
				get_state: not_yet(mod, "world.get_state", "block states aren't synced or saved yet"),
				set_state: not_yet(mod, "world.set_state", "block states aren't synced or saved yet"),
				get_block_data: (x, y, z) => game().world.get_tile(x, y, z)?.mod_data as never,
				is_loaded: () => true,
				get seed() {
					return game().world.seed;
				},
			},
			players: {
				all: () => game().players().map((p) => this.player(p)),
				get: (id) => {
					const p = game().players().find((p) => p.id === id);
					return p && this.player(p);
				},
				by_name: (name) => {
					const p = game().players().find((p) => p.name === name);
					return p && this.player(p);
				},
			},
			recipes: {
				furnace_result: (input) => {
					const recipe = game().recipes.furnace.get(input);
					return recipe && { output: { ...recipe.output }, cook_time: recipe.cook_time };
				},
				fuel_value: (item) => game().recipes.fuel.get(item) ?? 0,
				is_fuel: (item) => game().recipes.fuel.has(item),
				is_smeltable: (item) => game().recipes.furnace.has(item),
			},
			containers: not_yet_object(mod, "containers", "step 7 in MODS.md"),
			ui: not_yet_object(mod, "ui", "step 7 in MODS.md"),
			net: not_yet_object(mod, "net", "step 8 in MODS.md"),
			storage: {
				get: (key) => structuredClone(this.storage[mod]?.[key]) as never,
				set: (key, value) => {
					(this.storage[mod] ??= {})[key] = structuredClone(value);
					game().world.dirty = true;
				},
				delete: (key) => {
					delete this.storage[mod]?.[key];
					game().world.dirty = true;
				},
			},
			log: (...args) => console.log(`[${mod}]`, ...args),
		};
		return ctx;
	}

	#add_timer(mod: string, fn: () => void, ticks: number, every?: number) {
		const handle = this.#next_timer++;
		this.#timers.set(handle, { mod, fn, at: this.game.current_tick + Math.max(0, ticks), every });
		return handle;
	}
}

// each event's signal, as seen by one mod so errors say which mod threw
function map_signals<T extends { [name: string]: { for_mod(mod: string): unknown } }>(
	signals: T,
	mod: string,
): { [K in keyof T]: ReturnType<T[K]["for_mod"]> } {
	return Object.fromEntries(Object.entries(signals).map(([name, signal]) => [name, signal.for_mod(mod)])) as {
		[K in keyof T]: ReturnType<T[K]["for_mod"]>;
	};
}

function not_yet(mod: string, name: string, why: string) {
	return () => {
		throw new Error(`[${mod}] ctx.${name} isn't implemented yet: ${why}`);
	};
}

// every method on it throws, saying what isn't built yet
function not_yet_object<T>(mod: string, name: string, where: string): T {
	return new Proxy({}, {
		get: (_, prop) => not_yet(mod, `${name}.${String(prop)}`, where),
	}) as T;
}

// the engine's item stacks as mods see them: { id, count, data }
export function item_api(stack: EngineItemStack): ItemStack {
	return {
		get id() {
			return stack.type_id;
		},
		get count() {
			return stack.amount;
		},
		set count(value) {
			stack.amount = value;
		},
		get data() {
			return stack.data;
		},
		set data(value) {
			stack.data = value;
		},
	};
}

function new_stack(item: ItemStack): EngineItemStack {
	if (!EverythingRegistry.get("items", item.id)) throw new Error(`unknown item ${item.id}`);
	const stack = new EngineItemStack(item.id, item.count);
	if (item.data !== undefined) stack.data = structuredClone(item.data);
	return stack;
}

function player_api(game: GameServer, player: ServerPlayer): Player {
	const inventory: Container = {
		id: `player:${player.id}`,
		size: player.inventory.size,
		get: (slot) => {
			const stack = player.inventory.get_item(slot);
			return stack && item_api(stack);
		},
		set: (slot, item) => player.inventory.set_item(slot, item ? new_stack(item) : undefined),
		add: (item) => {
			const stack = new_stack(item);
			const left = player.inventory.add_item(stack);
			return left > 0 ? { id: item.id, count: left, data: stack.data } : undefined;
		},
		on_change: not_yet("player", "inventory.on_change", "containers are step 7 in MODS.md"),
	};

	return {
		get id() {
			return player.id;
		},
		get name() {
			return player.name;
		},
		get position() {
			return { x: player.x, y: player.y, z: player.z };
		},
		inventory,
		get selected_slot() {
			return player.selected_slot;
		},
		get held_item() {
			const stack = player.held_item;
			return stack && item_api(stack);
		},
		give_item(id, count = 1, data) {
			if (!EverythingRegistry.get("items", id)) throw new Error(`unknown item ${id}`);
			game.give(player, id, count, data);
		},
		send_message(text) {
			game.send_chat(player, String(text));
		},
		teleport(x, y, z) {
			game.teleport(player, x, y, z);
		},
	};
}