/**
 * @license
 *
 * Copyright 2024 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * Plugin authoring utilities — factory functions (`model`, `embedder`,
 * `retriever`, etc.), plugin lifecycle types, and the v1/v2 plugin
 * interfaces for building Genkit plugins.
 *
 * ```ts
 * import { model, embedder, genkitPlugin } from 'genkit/plugin';
 * ```
 *
 * @module plugin
 */

import type { GenerateMiddleware } from '@genkit-ai/ai';
import { type GenkitPluginV2 } from '@genkit-ai/ai';
import { type ModelAction } from '@genkit-ai/ai/model';
import {
  GenkitError,
  type ActionMetadata,
  type ResolvableAction,
} from '@genkit-ai/core';
import type { Genkit } from './genkit.js';
import type { ActionType } from './registry.js';

export { embedder, embedderActionMetadata } from '@genkit-ai/ai/embedder';
export { evaluator } from '@genkit-ai/ai/evaluator';
export {
  backgroundModel,
  model,
  modelActionMetadata,
} from '@genkit-ai/ai/model';
export { reranker } from '@genkit-ai/ai/reranker';
export { indexer, retriever } from '@genkit-ai/ai/retriever';
export { type GenerateMiddleware, type GenkitPluginV2, type ResolvableAction };

/** A v1 plugin provider returned by a {@link GenkitPlugin} factory function. */
export interface PluginProvider {
  name: string;
  initializer: () => void | Promise<void>;
  resolver?: (action: ActionType, target: string) => Promise<void>;
  listActions?: () => Promise<ActionMetadata[]>;
}

/** A v1 Genkit plugin factory function. Returns a {@link PluginProvider} when called with a Genkit instance. */
export type GenkitPlugin = (genkit: Genkit) => PluginProvider;

/** Initialization function called during plugin setup. */
export type PluginInit = (genkit: Genkit) => void | Promise<void>;

/** Optional resolver function for lazily-resolved plugin actions. */
export type PluginActionResolver = (
  genkit: Genkit,
  action: ActionType,
  target: string
) => Promise<void>;

/**
 * Defines a Genkit plugin.
 */
export function genkitPlugin<T extends PluginInit>(
  pluginName: string,
  initFn: T,
  resolveFn?: PluginActionResolver,
  listActionsFn?: () => Promise<ActionMetadata[]>
): GenkitPlugin {
  return (genkit: Genkit) => ({
    name: pluginName,
    initializer: async () => {
      await initFn(genkit);
    },
    resolver: async (action: ActionType, target: string): Promise<void> => {
      if (resolveFn) {
        return await resolveFn(genkit, action, target);
      }
    },
    listActions: async (): Promise<ActionMetadata[]> => {
      if (listActionsFn) {
        return await listActionsFn();
      }
      return [];
    },
  });
}

/**
 * Concrete implementation of a v2 plugin that wraps a {@link GenkitPluginV2} definition
 * and provides default implementations for all optional hooks.
 */
export class GenkitPluginV2Instance implements Required<GenkitPluginV2> {
  readonly version = 'v2';
  readonly name: string;

  private plugin: Omit<GenkitPluginV2, 'version' | 'model'>;

  constructor(plugin: Omit<GenkitPluginV2, 'version' | 'model'>) {
    this.name = plugin.name;
    this.plugin = plugin;
  }

  init(): ResolvableAction[] | Promise<ResolvableAction[]> {
    if (!this.plugin.init) {
      return [];
    }
    return this.plugin.init();
  }

  list(): ActionMetadata[] | Promise<ActionMetadata[]> {
    if (!this.plugin.list) {
      return [];
    }
    return this.plugin.list();
  }

  middleware(): GenerateMiddleware<any, any>[] {
    if (!this.plugin.middleware) {
      return [];
    }
    return this.plugin.middleware();
  }

  resolve(
    actionType: ActionType,
    name: string
  ): ResolvableAction | undefined | Promise<ResolvableAction | undefined> {
    if (!this.plugin.resolve) {
      return undefined;
    }
    return this.plugin.resolve(actionType, name);
  }

  async model(name: string): Promise<ModelAction> {
    const model = await this.resolve('model', name);
    if (!model) {
      throw new GenkitError({
        message: `Failed to resolve model ${name} for plugin ${this.name}`,
        status: 'NOT_FOUND',
      });
    }
    return model as ModelAction;
  }
}

/**
 * Creates a new v2 plugin instance from the provided options.
 */
export function genkitPluginV2(
  options: Omit<GenkitPluginV2, 'version' | 'model'>
): GenkitPluginV2Instance {
  return new GenkitPluginV2Instance(options);
}

/** Checks whether the given plugin conforms to the v2 plugin interface. */
export function isPluginV2(plugin: unknown): plugin is GenkitPluginV2 {
  return (plugin as GenkitPluginV2).version === 'v2';
}