const ACCEPT = "application/json, text/event-stream";

interface JsonRpcResponse {
  result?: unknown;
  error?: { code: number; message: string };
}

interface McpTool {
  name: string;
  description?: string;
  inputSchema?: unknown;
}

type McpContentBlock = { type: string; text: string } | { type: string; [key: string]: unknown };

interface McpToolResult {
  content?: McpContentBlock[];
}

function parseMcpResponse(text: string): JsonRpcResponse {
  const trimmed = text.trim();
  if (!trimmed) throw new Error("Empty MCP response");
  if (trimmed.startsWith("{")) {
    return JSON.parse(trimmed) as JsonRpcResponse;
  }
  if (trimmed.includes("event:") || trimmed.includes("data:")) {
    let payload = "";
    for (const line of trimmed.split(/\r?\n/)) {
      if (line.startsWith("data:")) payload += line.slice(5).trim();
    }
    if (payload.startsWith("{")) return JSON.parse(payload) as JsonRpcResponse;
  }
  throw new Error(`Unrecognized MCP response format: ${trimmed.slice(0, 200)}`);
}

export class McpClient {
  private url: string;
  private seq: number;

  constructor(url: string) {
    this.url = url;
    this.seq = 0;
  }

  async request(method: string, params: Record<string, unknown> = {}): Promise<JsonRpcResponse> {
    this.seq += 1;
    const res = await fetch(this.url, {
      method: "POST",
      headers: { "Content-Type": "application/json", Accept: ACCEPT },
      body: JSON.stringify({ jsonrpc: "2.0", id: this.seq, method, params }),
    });
    if (!res.ok) {
      throw new Error(`MCP HTTP ${res.status}: ${(await res.text()).slice(0, 300)}`);
    }
    const rpc = parseMcpResponse(await res.text());
    if (rpc.error) throw new Error(`MCP RPC error ${rpc.error.code}: ${rpc.error.message}`);
    return rpc;
  }

  async listTools(): Promise<McpTool[]> {
    const rpc = await this.request("tools/list");
    return (rpc.result as { tools?: McpTool[] })?.tools ?? [];
  }

  async callTool(name: string, args: Record<string, unknown> = {}): Promise<McpToolResult> {
    const rpc = await this.request("tools/call", { name, arguments: args });
    return rpc.result as McpToolResult;
  }
}

export function textContentFrom(result: McpToolResult | null | undefined): string {
  if (!result?.content) return "";
  return result.content
    .map((b) => (b.type === "text" ? b.text : JSON.stringify(b)))
    .join(" ");
}