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

import { PartListUnion } from '@google/genai';
import { Config, getErrorMessage } from '@gemini-code/server';
import {
  HistoryItem,
  IndividualToolCallDisplay,
  ToolCallStatus,
} from '../types.js';

const addHistoryItem = (
  setHistory: React.Dispatch<React.SetStateAction<HistoryItem[]>>,
  itemData: Omit<HistoryItem, 'id'>,
  id: number,
) => {
  setHistory((prevHistory) => [
    ...prevHistory,
    { ...itemData, id } as HistoryItem,
  ]);
};

interface HandleAtCommandParams {
  query: string;
  config: Config;
  setHistory: React.Dispatch<React.SetStateAction<HistoryItem[]>>;
  setDebugMessage: React.Dispatch<React.SetStateAction<string>>;
  getNextMessageId: (baseTimestamp: number) => number;
  userMessageTimestamp: number;
}

interface HandleAtCommandResult {
  processedQuery: PartListUnion | null;
  shouldProceed: boolean;
}

/**
 * Processes user input potentially containing an '@<path>' command.
 * It finds the first '@<path>', reads the specified path, updates the UI,
 * and prepares the query for the LLM, incorporating the file content
 * and surrounding text.
 *
 * @returns An object containing the potentially modified query (or null)
 *          and a flag indicating if the main hook should proceed.
 */
export async function handleAtCommand({
  query,
  config,
  setHistory,
  setDebugMessage,
  getNextMessageId,
  userMessageTimestamp,
}: HandleAtCommandParams): Promise<HandleAtCommandResult> {
  const trimmedQuery = query.trim();

  const atCommandRegex = /^(.*?)(@\S+)(.*)$/s;
  const match = trimmedQuery.match(atCommandRegex);

  if (!match) {
    // This should technically not happen if isPotentiallyAtCommand was true,
    // but handle defensively.
    const errorTimestamp = getNextMessageId(userMessageTimestamp);
    addHistoryItem(
      setHistory,
      { type: 'error', text: 'Error: Could not parse @ command.' },
      errorTimestamp,
    );
    return { processedQuery: null, shouldProceed: false };
  }

  const textBefore = match[1].trim();
  const atPath = match[2];
  const textAfter = match[3].trim();

  const pathPart = atPath.substring(1);

  addHistoryItem(
    setHistory,
    { type: 'user', text: query },
    userMessageTimestamp,
  );

  if (!pathPart) {
    const errorTimestamp = getNextMessageId(userMessageTimestamp);
    addHistoryItem(
      setHistory,
      { type: 'error', text: 'Error: No path specified after @.' },
      errorTimestamp,
    );
    return { processedQuery: null, shouldProceed: false };
  }

  const toolRegistry = config.getToolRegistry();
  const readManyFilesTool = toolRegistry.getTool('read_many_files');

  if (!readManyFilesTool) {
    const errorTimestamp = getNextMessageId(userMessageTimestamp);
    addHistoryItem(
      setHistory,
      { type: 'error', text: 'Error: read_many_files tool not found.' },
      errorTimestamp,
    );
    return { processedQuery: null, shouldProceed: false };
  }

  // --- Path Handling for @ command ---
  let pathSpec = pathPart;
  // Basic check: If no extension or ends with '/', assume directory and add globstar.
  if (!pathPart.includes('.') || pathPart.endsWith('/')) {
    pathSpec = pathPart.endsWith('/') ? `${pathPart}**` : `${pathPart}/**`;
  }
  const toolArgs = { paths: [pathSpec] };
  const contentLabel =
    pathSpec === pathPart ? pathPart : `directory ${pathPart}`;
  // --- End Path Handling ---

  let toolCallDisplay: IndividualToolCallDisplay;

  try {
    setDebugMessage(`Reading via @ command: ${pathSpec}`);
    const result = await readManyFilesTool.execute(toolArgs);
    const fileContent = result.llmContent || '';

    toolCallDisplay = {
      callId: `client-read-${userMessageTimestamp}`,
      name: readManyFilesTool.displayName,
      description: readManyFilesTool.getDescription(toolArgs),
      status: ToolCallStatus.Success,
      resultDisplay: result.returnDisplay,
      confirmationDetails: undefined,
    };

    // Construct the query for Gemini, combining parts
    const processedQueryParts = [];
    if (textBefore) {
      processedQueryParts.push({ text: textBefore });
    }
    processedQueryParts.push({
      text: `\n--- Content from: ${contentLabel} ---\n${fileContent}\n--- End Content ---`,
    });
    if (textAfter) {
      processedQueryParts.push({ text: textAfter });
    }

    const processedQuery: PartListUnion = processedQueryParts;

    const toolGroupId = getNextMessageId(userMessageTimestamp);
    addHistoryItem(
      setHistory,
      { type: 'tool_group', tools: [toolCallDisplay] } as Omit<
        HistoryItem,
        'id'
      >,
      toolGroupId,
    );

    return { processedQuery, shouldProceed: true };
  } catch (error) {
    // Construct error UI
    toolCallDisplay = {
      callId: `client-read-${userMessageTimestamp}`,
      name: readManyFilesTool.displayName,
      description: readManyFilesTool.getDescription(toolArgs),
      status: ToolCallStatus.Error,
      resultDisplay: `Error reading ${contentLabel}: ${getErrorMessage(error)}`,
      confirmationDetails: undefined,
    };

    const toolGroupId = getNextMessageId(userMessageTimestamp);
    addHistoryItem(
      setHistory,
      { type: 'tool_group', tools: [toolCallDisplay] } as Omit<
        HistoryItem,
        'id'
      >,
      toolGroupId,
    );

    return { processedQuery: null, shouldProceed: false };
  }
}