codegraph/src/installer/targets/gemini.ts

/**
 * Gemini CLI target (also covers the rebranded "Antigravity CLI" —
 * Google is in the middle of unifying its CLI tools under
 * Antigravity, and the new CLI continues to read `~/.gemini/settings.json`
 * + project-local `.gemini/settings.json`). Writes:
 *
 *   - MCP server entry to `~/.gemini/settings.json` (global) or
 *     `./.gemini/settings.json` (local) under the standard
 *     `mcpServers.codegraph` key. Same shape as Claude / Cursor.
 *   - Instructions to `~/.gemini/GEMINI.md` (global) or `./GEMINI.md`
 *     (local — Gemini reads the project root file directly, not
 *     under `.gemini/`).
 *
 * No permissions concept — Gemini CLI gates tool invocations through
 * the `trust` field per server, not an external allowlist. We leave
 * `trust` unset so the user controls confirmation prompts.
 *
 * The Antigravity IDE shares `~/.gemini/GEMINI.md` for instructions
 * but uses a separate MCP config file (`~/.gemini/antigravity/mcp_config.json`)
 * — see `./antigravity.ts`. Both targets writing to GEMINI.md is
 * safe: the marker-based section replacement makes the second write
 * a byte-identical no-op.
 */

import * as fs from 'fs';
import * as path from 'path';
import * as os from 'os';
import {
  AgentTarget,
  DetectionResult,
  InstallOptions,
  Location,
  WriteResult,
} from './types';
import {
  getMcpServerConfig,
  jsonDeepEqual,
  readJsonFile,
  removeMarkedSection,
  replaceOrAppendMarkedSection,
  writeJsonFile,
} from './shared';
import {
  CODEGRAPH_SECTION_END,
  CODEGRAPH_SECTION_START,
  INSTRUCTIONS_TEMPLATE,
} from '../instructions-template';

function configDir(loc: Location): string {
  return loc === 'global'
    ? path.join(os.homedir(), '.gemini')
    : path.join(process.cwd(), '.gemini');
}
function settingsJsonPath(loc: Location): string {
  return path.join(configDir(loc), 'settings.json');
}
function instructionsPath(loc: Location): string {
  // Global GEMINI.md lives under ~/.gemini/; project-local GEMINI.md
  // lives at the project root (NOT under .gemini/), matching how
  // Gemini CLI's hierarchical context loader searches.
  return loc === 'global'
    ? path.join(configDir('global'), 'GEMINI.md')
    : path.join(process.cwd(), 'GEMINI.md');
}

class GeminiTarget implements AgentTarget {
  readonly id = 'gemini' as const;
  readonly displayName = 'Gemini CLI';
  readonly docsUrl = 'https://geminicli.com/docs/tools/mcp-server/';

  supportsLocation(_loc: Location): boolean {
    return true;
  }

  detect(loc: Location): DetectionResult {
    const file = settingsJsonPath(loc);
    const config = readJsonFile(file);
    const alreadyConfigured = !!config.mcpServers?.codegraph;
    const installed = loc === 'global'
      ? fs.existsSync(configDir('global')) || fs.existsSync(file)
      : fs.existsSync(file) || fs.existsSync(configDir('local'));
    return { installed, alreadyConfigured, configPath: file };
  }

  install(loc: Location, _opts: InstallOptions): WriteResult {
    const files: WriteResult['files'] = [];
    files.push(writeMcpEntry(loc));
    files.push(writeInstructionsEntry(loc));
    return { files };
  }

  uninstall(loc: Location): WriteResult {
    const files: WriteResult['files'] = [];

    const file = settingsJsonPath(loc);
    const config = readJsonFile(file);
    if (config.mcpServers?.codegraph) {
      delete config.mcpServers.codegraph;
      if (Object.keys(config.mcpServers).length === 0) {
        delete config.mcpServers;
      }
      // If the file is now an empty `{}` we still leave it — other
      // (top-level) Gemini settings the user might add later can
      // share the file; deleting it would be surprising.
      writeJsonFile(file, config);
      files.push({ path: file, action: 'removed' });
    } else {
      files.push({ path: file, action: 'not-found' });
    }

    const instr = instructionsPath(loc);
    const action = removeMarkedSection(instr, CODEGRAPH_SECTION_START, CODEGRAPH_SECTION_END);
    files.push({ path: instr, action });

    return { files };
  }

  printConfig(loc: Location): string {
    const target = settingsJsonPath(loc);
    const snippet = JSON.stringify({ mcpServers: { codegraph: getMcpServerConfig() } }, null, 2);
    return `# Add to ${target}\n\n${snippet}\n`;
  }

  describePaths(loc: Location): string[] {
    return [settingsJsonPath(loc), instructionsPath(loc)];
  }
}

function writeMcpEntry(loc: Location): WriteResult['files'][number] {
  const file = settingsJsonPath(loc);
  const dir = path.dirname(file);
  if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });

  const existing = readJsonFile(file);
  const before = existing.mcpServers?.codegraph;
  const after = getMcpServerConfig();

  if (jsonDeepEqual(before, after)) {
    return { path: file, action: 'unchanged' };
  }
  const action: 'created' | 'updated' =
    before ? 'updated' : (fs.existsSync(file) ? 'updated' : 'created');
  if (!existing.mcpServers) existing.mcpServers = {};
  existing.mcpServers.codegraph = after;
  writeJsonFile(file, existing);
  return { path: file, action };
}

function writeInstructionsEntry(loc: Location): WriteResult['files'][number] {
  const file = instructionsPath(loc);
  const dir = path.dirname(file);
  if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });

  const action = replaceOrAppendMarkedSection(
    file,
    INSTRUCTIONS_TEMPLATE,
    CODEGRAPH_SECTION_START,
    CODEGRAPH_SECTION_END,
  );
  const mapped: 'created' | 'updated' | 'unchanged' =
    action === 'created' ? 'created'
      : action === 'unchanged' ? 'unchanged'
        : 'updated';
  return { path: file, action: mapped };
}

export const geminiTarget: AgentTarget = new GeminiTarget();