/**
 * PURE config resolution — resolve MCP server configurations.
 *
 * Sources, in precedence order:
 * 1. cwd/.dispatch/mcp.json servers
 * 2. fallback cwd/opencode.json mcp key
 *
 * No I/O — callers pass the file contents as strings.
 */

import type { McpServerConfig, ResolvedMcpServer, ResolveResult } from "./types.js";

export interface ResolveServersDeps {
	readonly dispatchMcpJson: string | null;
	readonly opencodeJson: string | null;
}

export interface DispatchMcpConfig {
	readonly servers?: Readonly<Record<string, McpServerConfig>>;
}

export interface OpencodeJsonConfig {
	readonly mcp?: Readonly<Record<string, McpServerConfig>>;
}

export function resolveServers(deps: ResolveServersDeps): ResolveResult {
	const result = new Map<string, ResolvedMcpServer>();

	// Parse opencode.json once — used both as the fallback source and to detect
	// whether a present `.dispatch/mcp.json` silently shadows its `mcp` key.
	let opencodeConfig: OpencodeJsonConfig | null = null;
	if (deps.opencodeJson) {
		try {
			opencodeConfig = JSON.parse(deps.opencodeJson) as OpencodeJsonConfig;
		} catch {
			// ignore parse errors
		}
	}
	const opencodeHasMcp = !!opencodeConfig?.mcp && Object.keys(opencodeConfig.mcp).length > 0;

	// 1. cwd/.dispatch/mcp.json (highest precedence)
	let dispatchHadServers = false;
	if (deps.dispatchMcpJson) {
		try {
			const config = JSON.parse(deps.dispatchMcpJson) as DispatchMcpConfig;
			if (config.servers) {
				for (const [key, server] of Object.entries(config.servers)) {
					const resolved = resolveServer(key, server, ".dispatch/mcp.json");
					result.set(resolved.id, resolved);
				}
				dispatchHadServers = result.size > 0;
			}
		} catch {
			// ignore parse errors
		}
	}

	// 2. fallback cwd/opencode.json mcp key (only when dispatch yielded nothing)
	if (result.size === 0 && opencodeConfig?.mcp) {
		for (const [key, server] of Object.entries(opencodeConfig.mcp)) {
			const resolved = resolveServer(key, server, "opencode.json");
			result.set(resolved.id, resolved);
		}
	}

	// No built-in servers — MCP has no built-in registry.

	// `.dispatch/mcp.json` silently shadows `opencode.json`'s mcp key when both
	// declare servers — the opencode entry is skipped with no warning otherwise.
	const shadowed = dispatchHadServers && opencodeHasMcp;
	return { servers: [...result.values()], shadowed };
}

function resolveServer(
	key: string,
	config: McpServerConfig,
	configSource: ".dispatch/mcp.json" | "opencode.json",
): ResolvedMcpServer {
	const command = [config.command, ...(config.args ?? [])];
	const result: ResolvedMcpServer = {
		id: key,
		command,
		configSource,
	};
	if (config.env) {
		(result as { env?: Readonly<Record<string, string>> }).env = config.env;
	}
	return result;
}