import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
import { z } from 'zod';
import { readdir, stat } from 'node:fs/promises';
import { join, relative } from 'node:path';
async function findSsiFiles(dir: string, files: string[] = []): Promise<string[]> {
let entries;
try {
entries = await readdir(dir);
} catch {
return files;
}
for (const entry of entries) {
const fullPath = join(dir, entry);
let s;
try {
s = await stat(fullPath);
} catch {
continue;
}
if (s.isDirectory()) {
await findSsiFiles(fullPath, files);
} else if (entry.endsWith('.ssi')) {
files.push(fullPath);
}
}
return files;
}
function resolveLibDir(): string {
const gerbilHome = process.env.GERBIL_HOME ?? '/opt/gerbil';
return join(gerbilHome, 'lib');
}
export function registerListModulesTool(server: McpServer): void {
server.registerTool(
'gerbil_list_std_modules',
{
title: 'List Gerbil Modules',
description:
'List available Gerbil standard library modules by scanning the installation. ' +
'Optionally filter by prefix (e.g. "std/text", "std/net", "gerbil"). ' +
'Returns module paths like :std/text/json, :std/iter, etc.',
annotations: {
readOnlyHint: true,
idempotentHint: true,
},
inputSchema: {
prefix: z
.string()
.optional()
.describe('Filter modules by prefix (e.g. "std/text", "std/net")'),
},
},
async ({ prefix }) => {
const libDir = resolveLibDir();
const ssiFiles = await findSsiFiles(libDir);
let modules = ssiFiles
.map((f) => {
const rel = relative(libDir, f);
// Remove .ssi extension, convert to module path
const modPath = rel.replace(/\.ssi$/, '');
return `:${modPath}`;
})
.filter((m) => {
// Skip internal modules (starting with underscore)
const parts = m.split('/');
return !parts.some((p) => p.startsWith('_'));
})
.sort();
if (prefix) {
const normalizedPrefix = prefix.startsWith(':') ? prefix : `:${prefix}`;
modules = modules.filter((m) => m.startsWith(normalizedPrefix));
}
if (modules.length === 0) {
const msg = prefix
? `No modules found matching prefix "${prefix}".`
: 'No modules found. Is GERBIL_HOME set correctly?';
return {
content: [{ type: 'text' as const, text: msg }],
};
}
// Group by top-level category
const groups = new Map<string, string[]>();
for (const mod of modules) {
// :std/text/json -> std
const parts = mod.slice(1).split('/');
const category = parts[0];
if (!groups.has(category)) groups.set(category, []);
groups.get(category)!.push(mod);
}
const lines: string[] = [];
if (prefix) {
lines.push(`Modules matching "${prefix}" (${modules.length} total):`);
} else {
lines.push(`Available modules (${modules.length} total):`);
}
lines.push('');
for (const [category, mods] of groups) {
lines.push(`[${category}] (${mods.length} modules)`);
for (const m of mods) {
lines.push(` ${m}`);
}
lines.push('');
}
return {
content: [{ type: 'text' as const, text: lines.join('\n') }],
};
},
);
}
