package mcp

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"io"
)

// StdioTransport implements the MCP protocol over STDIO using line-delimited JSON-RPC.
type StdioTransport struct {
	server *Server
	reader io.Reader
	writer io.Writer
}

// NewStdioTransport creates a new STDIO transport.
func NewStdioTransport(server *Server, r io.Reader, w io.Writer) *StdioTransport {
	return &StdioTransport{
		server: server,
		reader: r,
		writer: w,
	}
}

// Run starts the STDIO transport, reading line-delimited JSON-RPC from the reader
// and writing responses to the writer.
func (t *StdioTransport) Run(ctx context.Context) error {
	scanner := bufio.NewScanner(t.reader)
	encoder := json.NewEncoder(t.writer)

	for scanner.Scan() {
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		line := scanner.Bytes()
		if len(line) == 0 {
			continue
		}

		resp, err := t.server.HandleMessage(ctx, line)
		if err != nil {
			t.server.logger.Printf("Error handling message: %v", err)
			continue
		}

		if resp != nil {
			if err := encoder.Encode(resp); err != nil {
				return fmt.Errorf("failed to write response: %w", err)
			}
		}
	}

	if err := scanner.Err(); err != nil {
		return fmt.Errorf("scanner error: %w", err)
	}

	return nil
}