Platform-ts/src/di/DependencyManager.ts

import type {IDependencyProvider} from './IDependencyProvider';
import type IDisposable from '../lang/IDisposable';
import Disposable from '../lang/Disposable';
import {Type} from './Type';
import type {IDependencyManager} from './IDependencyManager';

type Constructor<T = unknown> = new (...args: unknown[]) => T;
type ModuleLoader = (modulePath: string) => Promise<Constructor | {default: Constructor}>;

export class DependencyManager implements IDependencyManager {
  private readonly _moduleLoader: ModuleLoader;
  private readonly _types: Type[];
  private readonly _eagerTypes: Type[];
  private readonly _providers: IDependencyProvider[];
  private readonly _injections: Map<string, Type[]>;
  private readonly _pending: Type[];

  constructor(moduleLoader: ModuleLoader) {
    if (typeof moduleLoader !== 'function') {
      throw new Error('Module loader must be a function');
    }

    this._moduleLoader = moduleLoader;
    this._types = [];
    this._eagerTypes = [];
    this._providers = [];
    this._injections = new Map();
    this._pending = [];
  }

  public defineDependencies(type: Type, dependencies: Type[]): IDisposable {
    if (!(type instanceof Type)) {
      throw new Error('Type must be a Type');
    }

    if (!Array.isArray(dependencies)) {
      throw new Error('Dependencies must be an array');
    }

    for (const dependency of dependencies) {
      if (!(dependency instanceof Type)) {
        throw new Error('Dependency must be a Type');
      }
    }

    const key = type.toURN();

    if (this._injections.has(key)) {
      throw new Error(`Dependencies already defined for type [${type.toString()}]`);
    }

    this._injections.set(key, dependencies);
    this._types.push(type);

    console.debug(`Dependencies for [${type}] defined as [${dependencies}]`);

    return new Disposable(() => this._injections.delete(key));
  }

  public getDependencies(type: Type): Type[] | undefined {
    if (!(type instanceof Type)) {
      throw new Error('Type must be an instance of Type');
    }

    return this._injections.get(type.toURN());
  }

  public addProvider(provider: IDependencyProvider): IDisposable {
    if (!this.isProvider(provider)) {
      throw new Error('Provider must implement IDependencyProvider');
    }

    this._providers.push(provider);

    return new Disposable(() => {
      const index = this._providers.indexOf(provider);
      if (index !== -1) {
        this._providers.splice(index, 1);
      }
    });
  }

  public async resolveProvider(type: Type): Promise<IDependencyProvider> {
    if (!(type instanceof Type)) {
      throw new Error('Type must be an instance of Type');
    }

    const candidates = this._providers.filter(provider => provider.canProvide(type));

    if (candidates.length === 0) {
      throw new Error(`No provider for [${type.toString()}]`);
    }

    if (candidates.length > 1) {
      const candidateNames = candidates.map(c => c.toString()).join(', ');
      throw new Error(`Multiple providers for ${type}: ${candidateNames}`);
    }

    return candidates[0] as IDependencyProvider;
  }

  public async instantiateType(type: Type): Promise<unknown> {
    if (!(type instanceof Type)) {
      throw new Error('Type must be an instance of Type');
    }

    const key = type.toURN();

    // Check for circular dependencies
    if (this._pending.includes(type)) {
      const pendingChain = this._pending.map(t => t.toString()).join(' -> ');
      throw new Error(`Failed to resolve ${type} due to circular dependency: ${pendingChain}`);
    }

    this._pending.push(type);

    try {
      // Get dependencies for this type
      const dependencies = this._injections.get(key) || [];

      // Resolve all dependencies
      const resolvedDependencies = await Promise.all(
        dependencies.map(async dependency => {
          const provider = await this.resolveProvider(dependency);
          let instance = await provider.provide(dependency);

          // Handle nested providers
          if (this.isProvider(instance)) {
            instance = await (instance as IDependencyProvider).provide(dependency);
          }

          return instance;
        })
      );

      // Load the module
      const module = await this._moduleLoader(type.getType());
      const Constructor = 'default' in module ? module.default : module;

      if (!Constructor) {
        throw new Error(`Could not load type "${type.getType()}"`);
      }

      // Instantiate with resolved dependencies
      const instance = this.injectDependencies(Constructor, resolvedDependencies);

      // Handle if the instance is itself a provider
      if (this.isProvider(instance)) {
        return await (instance as IDependencyProvider).provide(type);
      }

      return instance;
    } finally {
      // Remove from pending stack
      const index = this._pending.indexOf(type);
      if (index !== -1) {
        this._pending.splice(index, 1);
      }
    }
  }

  public addEagerType(type: Type): void {
    if (!(type instanceof Type)) {
      throw new Error('Type must be an instance of Type');
    }

    this._eagerTypes.push(type);
  }

  public async getEagerTypes(): Promise<Type[]> {
    return Promise.resolve([...this._eagerTypes]);
  }

  public async getTypes(): Promise<Type[]> {
    return Promise.resolve([...this._types]);
  }

  private isProvider(obj: unknown): obj is IDependencyProvider {
    return (
      obj !== null &&
      typeof obj === 'object' &&
      'canProvide' in obj &&
      'provide' in obj &&
      typeof (obj as IDependencyProvider).canProvide === 'function' &&
      typeof (obj as IDependencyProvider).provide === 'function'
    );
  }

  private injectDependencies(Constructor: Constructor, dependencies: unknown[]): unknown {
    if (dependencies.length === 0) {
      return new Constructor();
    }

    return new Constructor(...dependencies);
  }
}