/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import { SlashCommand, CommandContext } from './types.js';
import {
  Config,
  BackgroundAgentMessage,
  partListUnionToString,
} from '@google/gemini-cli-core';

const MAX_STATUS_MESSAGE_LENGTH = 100;

function toMessageString(message?: BackgroundAgentMessage): string {
  return partListUnionToString(message?.parts ?? []).trim();
}

function toOneliner(input: string, maxlength: number) {
  let output = input.replace(/\r?\n|\r/g, ' ');
  if (output.length > maxlength) {
    output = output.substring(0, maxlength) + '...';
  }
  return output;
}

function getActiveAgent(context: CommandContext) {
  const agent =
    context.services.config?.getBackgroundAgentManager()?.activeAgent;
  if (!agent) {
    throw Error('There is no active background agent.');
  }
  return agent;
}

function addClientHistory(context: CommandContext, text: string) {
  context.services.config!.getGeminiClient().addHistory({
    role: 'user',
    parts: [{ text }],
  });

  context.services.config!.getGeminiClient().addHistory({
    role: 'model',
    parts: [{ text: 'Got it.' }],
  });
}

const startSubcommand: SlashCommand = {
  name: 'start',
  description:
    'Start a new task with the provided prompt. Usage: /bg start <prompt>',
  action: async (context, args) => {
    if (!args || args.trim() === '') {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `start` command requires a prompt.',
      };
    }

    const agent = getActiveAgent(context);
    const task = await agent.startTask(args);

    addClientHistory(
      context,
      `I started a background task with id '${task.id}' and prompt:\n${args}`,
    );

    return {
      type: 'message',
      messageType: 'info',
      content: `Started background task with id '${task.id}' and prompt:\n${args}`,
    };
  },
};

const stopSubcommand: SlashCommand = {
  name: 'stop',
  description: 'Stops a running task. Usage: /bg stop <task_id>',
  action: async (context, args) => {
    if (!args || args.trim() === '') {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `stop` command requires a task id.',
      };
    }
    const agent = getActiveAgent(context);
    await agent.cancelTask(args);
    addClientHistory(context, `I canceled the background task with id ${args}`);
    return {
      type: 'message',
      messageType: 'info',
      content: `Stopped background task with id ${args}.`,
    };
  },
};

const listSubcommand: SlashCommand = {
  name: 'list',
  description: 'List all tasks',
  action: async (context, args) => {
    if (args && args.trim() !== '') {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `list` command takes no arguments.',
      };
    }

    const agent = getActiveAgent(context);
    const tasks = await agent.listTasks();
    let content: string;
    if (tasks.length === 0) {
      content = 'No background tasks found.';
    } else {
      const taskList = tasks
        .map((task) => {
          const shortStatus = toOneliner(
            toMessageString(task.status.message),
            MAX_STATUS_MESSAGE_LENGTH,
          );
          return `  - ${task.id}: (${task.status.state}) ${shortStatus}`;
        })
        .join('\n');
      content = `Background tasks:\n${taskList}`;
    }
    return {
      type: 'message',
      messageType: 'info',
      content,
    };
  },
};

const getSubcommand: SlashCommand = {
  name: 'get',
  description: 'View a task. Usage: /bg get <task_id>',
  action: async (context, args) => {
    if (!args || args.trim() === '') {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `get` command requires a task id.',
      };
    }
    const agent = getActiveAgent(context);
    const task = await agent.getTask(args);
    const content = `Task Details for ${task.id}:
Status: (${task.status.state}) ${toMessageString(task.status.message)}}`;

    return {
      type: 'message',
      messageType: 'info',
      content,
    };
  },
};

const logsSubcommand: SlashCommand = {
  name: 'logs',
  description: "View a task's recent logs. Usage: /bg log <task_id>",
  action: async (context, args) => {
    if (!args || args.trim() === '') {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `log` command requires a task id.',
      };
    }
    const agent = getActiveAgent(context);
    const task = await agent.getTask(args, 5);
    const contents = [
      `Task logs for ${task.id}. status: (${task.status.state})`,
    ];
    (task.history ?? []).forEach((message) => {
      contents.push(toMessageString(message));
    });
    return {
      type: 'message',
      messageType: 'info',
      content: contents.join('\n\n'),
    };
  },
};

const messageSubcommand: SlashCommand = {
  name: 'message',
  description:
    'Send a message to a task. Usage: /bg message <task_id> <message>',
  action: async (context, args) => {
    if (!args || args.trim() === '' || !args.trim().includes(' ')) {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `message` command requires a task id and a message.',
      };
    }

    const firstSpaceIndex = args.indexOf(' ');
    const id = args.substring(0, firstSpaceIndex);
    const message = args.substring(firstSpaceIndex + 1);

    const agent = getActiveAgent(context);
    await agent.messageTask(id, message);
    addClientHistory(
      context,
      `I sent a message to the background task with id '${id}':\n${message}`,
    );

    return {
      type: 'message',
      messageType: 'info',
      content: `Sent a message to the background task with id '${id}':\n${message}`,
    };
  },
};

const deleteSubcommand: SlashCommand = {
  name: 'delete',
  description: 'Deletes a task. Usage: /bg delete <task_id>',
  action: async (context, args) => {
    if (!args) {
      return {
        type: 'message',
        messageType: 'error',
        content: 'The `delete` command requires a task id.',
      };
    }
    const agent = getActiveAgent(context);
    await agent.deleteTask(args);
    addClientHistory(context, `I deleted the background task with id ${args}`);
    return {
      type: 'message',
      messageType: 'info',
      content: `Task ${args} deleted.`,
    };
  },
};

export const backgroundCommand = (
  config: Config | null,
): SlashCommand | null => {
  if (!config?.getBackgroundAgentManager()?.activeAgent) {
    return null;
  }
  return {
    name: 'background',
    altName: 'bg',
    description: "Commands for managing the background agent's tasks",
    subCommands: [
      startSubcommand,
      stopSubcommand,
      listSubcommand,
      getSubcommand,
      logsSubcommand,
      messageSubcommand,
      deleteSubcommand,
    ],
  };
};