/**
 * v1.15.0-mcp-multi: MCP config file schema + loader.
 *
 * Reads a JSON config file (default `/data/mcp.json`) that declares MCP
 * servers — their transport type, connection parameters, and enabled state.
 * Schema shape matches opencode's `mcpServers` key for copy-paste compat.
 */
import { readFileSync } from 'node:fs';
import { z } from 'zod';
import type { FastifyBaseLogger } from 'fastify';

// ---- Zod schema ----

const McpServerConfigSchema = z.discriminatedUnion('type', [
  z.object({
    type: z.literal('streamableHttp'),
    url: z.string().url(),
    headers: z.record(z.string()).optional(),
    enabled: z.boolean().default(true),
  }),
  z.object({
    type: z.literal('stdio'),
    command: z.string().min(1),
    args: z.array(z.string()).default([]),
    env: z.record(z.string()).optional(),
    enabled: z.boolean().default(true),
  }),
]);

const McpConfigSchema = z.object({
  mcpServers: z.record(z.string(), McpServerConfigSchema).default({}),
});

export type McpServerConfig = z.infer<typeof McpServerConfigSchema>;

export interface McpServerEntry {
  name: string;
  config: McpServerConfig;
}

// ---- Loader ----

/**
 * Read and validate the MCP config file. Returns enabled servers only.
 * File missing → log info, return []. Parse/validation error → log warn, return [].
 */
export function loadMcpConfig(configPath: string, log: FastifyBaseLogger): McpServerEntry[] {
  let raw: string;
  try {
    raw = readFileSync(configPath, 'utf8');
  } catch {
    log.info(`mcp: config not found at ${configPath}, skipping`);
    return [];
  }

  let json: unknown;
  try {
    json = JSON.parse(raw);
  } catch (err) {
    log.warn({ err }, `mcp: failed to parse ${configPath} as JSON`);
    return [];
  }

  const result = McpConfigSchema.safeParse(json);
  if (!result.success) {
    log.warn({ errors: result.error.flatten().fieldErrors }, `mcp: invalid config at ${configPath}`);
    return [];
  }

  const entries: McpServerEntry[] = [];
  for (const [name, config] of Object.entries(result.data.mcpServers)) {
    if (config.enabled) {
      entries.push({ name, config });
    }
  }

  return entries;
}