MCP server

package com.example.tnsai.docs;

import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import com.tnsai.annotations.Tool;
import com.tnsai.annotations.ToolParam;
import com.tnsai.mcp.model.McpToolDefinition;
import com.tnsai.mcp.model.Resource;
import com.tnsai.mcp.model.ResourceContent;
import com.tnsai.mcp.model.Root;
import com.tnsai.mcp.model.SamplingRequest;
import com.tnsai.mcp.model.SamplingResponse;
import com.tnsai.mcp.server.HttpMcpServer;
import com.tnsai.mcp.server.McpServer;
import com.tnsai.mcp.server.ResourceProvider;
import com.tnsai.mcp.server.TnsAIToolProvider;
import com.tnsai.mcp.server.ToolProvider;
import java.io.IOException;
import java.time.Duration;
import java.util.List;
import java.util.Map;
import java.util.function.Function;

/** Compilation contract for mcp/server.md. */
public final class McpServerExample {

    private McpServerExample() {
    }

    public static final class WeatherTools {

        @Tool(name = "get_forecast", description = "Get the forecast for a city")
        public String forecast(@ToolParam(description = "City name") String city) {
            return "Sunny in " + city;
        }
    }

    static void serveOverStdio() {
        McpServer server = McpServer.builder()
            .serverName("weather")
            .serverVersion("1.0.0")
            .addToolProvider(TnsAIToolProvider.fromPojos(new WeatherTools()))
            .build();
        server.start();                                   // blocks until stdin closes or stop()
    }

    static HttpMcpServer serveOverHttp() throws IOException {
        HttpMcpServer server = HttpMcpServer.builder()
            .port(8080)                                   // 0 picks a free port; read it with getPort()
            .path("/mcp")
            .serverName("weather")
            .sessionTtl(Duration.ofMinutes(10))
            .addToolProvider(TnsAIToolProvider.fromPojos(new WeatherTools()))
            .build();
        server.start();
        return server;
    }

    public static final class EchoToolProvider implements ToolProvider {

        @Override
        public List<McpToolDefinition> listTools() {
            return List.of(McpToolDefinition.builder()
                .name("echo")
                .description("Return the text unchanged")
                .inputSchema(Map.of(
                    "type", "object",
                    "properties", Map.of("text", Map.of("type", "string")),
                    "required", List.of("text")))
                .build());
        }

        @Override
        public ToolResult executeTool(String name, JsonNode arguments) {
            if (!arguments.hasNonNull("text")) {
                return ToolResult.error("text is required");     // the client gets isError: true
            }
            return ToolResult.text(arguments.get("text").asText());
        }
    }

    public static final class NotesResourceProvider implements ResourceProvider {

        @Override
        public List<Resource> listResources() {
            return List.of(new Resource("notes://today", "Today's notes", "Plain-text notes", "text/plain"));
        }

        @Override
        public List<ResourceContent> readResource(String uri) throws ResourceNotFoundException {
            if (!"notes://today".equals(uri)) {
                throw new ResourceNotFoundException(uri);
            }
            return List.of(ResourceContent.text(uri, "Ship the docs.", "text/plain"));
        }
    }

    static McpServer withSamplingAndRoots(Function<String, String> llm) {
        return McpServer.builder()
            .serverName("assistant")
            .addToolProvider(new EchoToolProvider())
            .addResourceProvider(new NotesResourceProvider())
            .samplingHandler((SamplingRequest request) -> {
                String prompt = request.getMessages().get(request.getMessages().size() - 1)
                    .getContent().path("text").asText();
                SamplingResponse response = new SamplingResponse();
                response.setRole("assistant");
                response.setModel("my-model");
                response.setContent(JsonNodeFactory.instance.objectNode()
                    .put("type", "text")
                    .put("text", llm.apply(prompt)));
                response.setStopReason("endTurn");
                return response;
            })
            .clientRoots(List.of(Root.of("file:///srv/data", "Data")))
            .build();
    }
}