// Package remote provides the SSH bootstrap and JSON-RPC client for
// split-brain remote execution. It connects to a remote host over SSH,
// ensures ollie-remote is deployed, and returns a Server that
// forwards execution calls over the RPC channel.
package toolsrv

import (
	"bufio"
	"bytes"
	"compress/gzip"
	"context"
	"crypto/sha256"
	_ "embed"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

)

//go:embed bootstrap.sh
var bootstrapTemplate string

// HostInfo holds environment details from the remote host.
type HostInfo struct {
	Platform  string `json:"platform"`
	Arch      string `json:"arch"`
	IsGitRepo bool   `json:"is_git_repo"`
}

// Server implements Server by forwarding calls to a remote
// ollie-remote process over SSH.
type RemoteServer struct {
	mu     sync.Mutex
	stdin  io.WriteCloser
	stdout io.ReadCloser
	cmd    *exec.Cmd
	enc    *json.Encoder
	dec    *json.Decoder
	nextID atomic.Int64
	Info   HostInfo
}

// Config holds the parameters for connecting to a remote host.
type RemoteConfig struct {
	// SSHTarget is the SSH destination (e.g., "user@host" or an SSH config alias).
	SSHTarget string
	// CWD is the working directory on the remote host.
	CWD string
	// ToolsPath overrides the remote tool scripts path.
	ToolsPath string
	// Yolo disables sandbox enforcement on the remote.
	Yolo bool
}

// Dial opens an SSH connection to the remote host, bootstraps ollie-remote
// (deploying the binary if needed), and returns a Server ready for tool calls.
func RemoteDial(ctx context.Context, cfg RemoteConfig) (*RemoteServer, error) {
	// Find the local ollie-remote binary to compute hash and transfer if needed.
	localBin, err := findLocalBinary()
	if err != nil {
		return nil, fmt.Errorf("find ollie-remote binary: %w", err)
	}
	binData, err := os.ReadFile(localBin)
	if err != nil {
		return nil, fmt.Errorf("read ollie-remote binary: %w", err)
	}
	hash := sha256.Sum256(binData)
	hashStr := hex.EncodeToString(hash[:])

	// Generate bootstrap script with hash and CWD baked in.
	bootstrap := bootstrapTemplate
	bootstrap = strings.ReplaceAll(bootstrap, "@@HASH@@", hashStr)
	cwdEscaped := shellEscape(cfg.CWD)
	extraArgs := ""
	if cfg.ToolsPath != "" {
		extraArgs += " --tools " + shellEscape(cfg.ToolsPath)
	}
	if cfg.Yolo {
		extraArgs += " --yolo"
	}
	bootstrap = strings.ReplaceAll(bootstrap, "@@CWD@@", cwdEscaped+extraArgs)

	// Parse optional port from SSHTarget (user@host:port or host:port)
	sshArgs := []string{}
	sshTarget := cfg.SSHTarget
	if host, port, ok := strings.Cut(sshTarget, ":"); ok && port != "" {
		sshTarget = host
		sshArgs = append(sshArgs, "-p", port)
	}
	// Run bash on the remote; we'll send the bootstrap script over stdin.
	sshArgs = append(sshArgs, sshTarget, "bash -s")

	cmd := exec.CommandContext(ctx, "ssh", sshArgs...)
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

	stdin, err := cmd.StdinPipe()
	if err != nil {
		return nil, fmt.Errorf("ssh stdin pipe: %w", err)
	}
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, fmt.Errorf("ssh stdout pipe: %w", err)
	}
	stderrPipe, err := cmd.StderrPipe()
	if err != nil {
		return nil, fmt.Errorf("ssh stderr pipe: %w", err)
	}

	if err := cmd.Start(); err != nil {
		return nil, fmt.Errorf("ssh start: %w", err)
	}

	// Send bootstrap script over stdin.
	if _, err := stdin.Write([]byte(bootstrap + "\n")); err != nil {
		cmd.Process.Kill()
		return nil, fmt.Errorf("send bootstrap: %w", err)
	}

	// Monitor stderr for bootstrap messages.
	type loaderMsg struct {
		NeedDownload bool `json:"need_download"`
	}

	stderrScanner := bufio.NewScanner(stderrPipe)
	loaderCh := make(chan loaderMsg, 1)
	readyCh := make(chan struct{}, 1)
	go func() {
		for stderrScanner.Scan() {
			line := strings.TrimSpace(stderrScanner.Text())
			if after, ok := strings.CutPrefix(line, "LoaderStart "); ok {
				var msg loaderMsg
				json.Unmarshal([]byte(after), &msg)
				loaderCh <- msg
				if !msg.NeedDownload {
					close(readyCh)
				}
			} else if line == "LoaderReady" {
				close(readyCh)
			}
		}
	}()

	// Wait for loader start message.
	select {
	case msg := <-loaderCh:
		if msg.NeedDownload {
			if err := transferBinary(stdin, binData); err != nil {
				cmd.Process.Kill()
				return nil, fmt.Errorf("transfer binary: %w", err)
			}
			// Wait for ready signal.
			select {
			case <-readyCh:
			case <-time.After(30 * time.Second):
				cmd.Process.Kill()
				return nil, fmt.Errorf("bootstrap timeout waiting for ready")
			}
		}
	case <-time.After(30 * time.Second):
		cmd.Process.Kill()
		return nil, fmt.Errorf("bootstrap timeout waiting for loader start")
	}

	// Bootstrap complete — stdin/stdout are now JSON-RPC.
	s := &RemoteServer{
		stdin:  stdin,
		stdout: stdout,
		cmd:    cmd,
		enc:    json.NewEncoder(stdin),
		dec:    json.NewDecoder(bufio.NewReader(stdout)),
	}

	// Verify connectivity with a ping.
	if err := s.ping(ctx); err != nil {
		s.Close()
		return nil, fmt.Errorf("remote ping failed: %w", err)
	}

	// Fetch remote host info for prompt resolution.
	// FIXME: This duplicates information that prime scripts also try to detect
	// locally (platform, is_git_repo). Eventually unify so prompt resolution
	// always uses these env vars rather than running local checks against a
	// non-existent remote CWD.
	if info, err := s.fetchHostInfo(ctx); err == nil {
		s.Info = info
	}

	return s, nil
}

// findLocalBinary locates the ollie-remote binary on the local system.
func findLocalBinary() (string, error) {
	// Check common locations in priority order.
	home, _ := os.UserHomeDir()
	candidates := []string{
		filepath.Join(home, "bin", "ollie-remote"),
		filepath.Join(home, ".local", "bin", "ollie-remote"),
	}
	for _, p := range candidates {
		if _, err := os.Stat(p); err == nil {
			return p, nil
		}
	}
	// Try PATH as last resort.
	if p, err := exec.LookPath("ollie-remote"); err == nil {
		return p, nil
	}
	return "", fmt.Errorf("ollie-remote not found (checked %s)", strings.Join(candidates, ", "))
}

// transferBinary sends the ollie-remote binary gzipped+base64 over stdin.
func transferBinary(stdin io.Writer, binData []byte) error {
	var compressed bytes.Buffer
	gzw := gzip.NewWriter(&compressed)
	if _, err := gzw.Write(binData); err != nil {
		return err
	}
	if err := gzw.Close(); err != nil {
		return err
	}
	encoded := base64.StdEncoding.EncodeToString(compressed.Bytes())
	if _, err := fmt.Fprintf(stdin, "Download %d\n", len(encoded)); err != nil {
		return err
	}
	if _, err := stdin.Write([]byte(encoded)); err != nil {
		return err
	}
	return nil
}

// Close shuts down the SSH connection.
func (s *RemoteServer) Close() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.stdin != nil {
		s.stdin.Close()
	}
	if s.cmd != nil && s.cmd.Process != nil {
		syscall.Kill(-s.cmd.Process.Pid, syscall.SIGTERM)
		s.cmd.Wait()
	}
	return nil
}

// --- Server interface ---

func (s *RemoteServer) ListTools() ([]ToolInfo, error) {
	id := s.nextID.Add(1)
	req := rpcRequest{
		JSONRPC: "2.0",
		ID:      id,
		Method:  "list_tools",
	}

	s.mu.Lock()
	if err := s.enc.Encode(req); err != nil {
		s.mu.Unlock()
		return nil, fmt.Errorf("remote list_tools write: %w", err)
	}
	var resp rpcResponse
	if err := s.dec.Decode(&resp); err != nil {
		s.mu.Unlock()
		return nil, fmt.Errorf("remote list_tools read: %w", err)
	}
	s.mu.Unlock()

	if resp.Error != nil {
		return nil, fmt.Errorf("remote list_tools: %s", resp.Error.Message)
	}

	var infos []ToolInfo
	if err := json.Unmarshal(resp.Result, &infos); err != nil {
		return nil, fmt.Errorf("remote list_tools unmarshal: %w", err)
	}
	return infos, nil
}

func (s *RemoteServer) CallTool(ctx context.Context, tool string, args json.RawMessage) (json.RawMessage, error) {
	// Forward the call with the tool name as the RPC method.
	id := s.nextID.Add(1)

	req := rpcRequest{
		JSONRPC: "2.0",
		ID:      id,
		Method:  tool,
		Params:  args,
	}

	s.mu.Lock()
	if err := s.enc.Encode(req); err != nil {
		s.mu.Unlock()
		return nil, fmt.Errorf("remote rpc write: %w", err)
	}

	// Read responses, handling interleaved streaming notifications.
	for {
		var resp rpcResponse
		if err := s.dec.Decode(&resp); err != nil {
			s.mu.Unlock()
			return nil, fmt.Errorf("remote rpc read: %w", err)
		}

		// Notification: id == 0 and method is "output".
		// (JSON-RPC notifications have no id; our struct decodes missing id as 0.)
		if resp.ID == 0 && resp.Result != nil {
			// Streaming output notification — emit to context callback.
			var notif outputNotification
			if json.Unmarshal(resp.Result, &notif) == nil && notif.Data != "" {
				StreamOutput(ctx, notif.Data)
			}
			continue
		}

		// Actual response for our request.
		s.mu.Unlock()
		if resp.Error != nil {
			return nil, fmt.Errorf("remote error: %s", resp.Error.Message)
		}
		return resp.Result, nil
	}
}

type outputNotification struct {
	Data string `json:"data"`
}

// fetchHostInfo retrieves environment details from the remote host.
func (s *RemoteServer) fetchHostInfo(ctx context.Context) (HostInfo, error) {
	id := s.nextID.Add(1)
	req := rpcRequest{
		JSONRPC: "2.0",
		ID:      id,
		Method:  "host_info",
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	if err := s.enc.Encode(req); err != nil {
		return HostInfo{}, err
	}
	var resp rpcResponse
	if err := s.dec.Decode(&resp); err != nil {
		return HostInfo{}, err
	}
	if resp.Error != nil {
		return HostInfo{}, fmt.Errorf("%s", resp.Error.Message)
	}
	var info HostInfo
	if err := json.Unmarshal(resp.Result, &info); err != nil {
		return HostInfo{}, err
	}
	return info, nil
}

// ping verifies the remote server is responsive.
func (s *RemoteServer) ping(ctx context.Context) error {
	id := s.nextID.Add(1)
	req := rpcRequest{
		JSONRPC: "2.0",
		ID:      id,
		Method:  "ping",
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	if err := s.enc.Encode(req); err != nil {
		return err
	}
	var resp rpcResponse
	if err := s.dec.Decode(&resp); err != nil {
		return err
	}
	if resp.Error != nil {
		return fmt.Errorf("%s", resp.Error.Message)
	}
	return nil
}

// --- JSON-RPC types ---

type rpcRequest struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type rpcResponse struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Result  json.RawMessage `json:"result,omitempty"`
	Error   *rpcError       `json:"error,omitempty"`
}

type rpcError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

// --- helpers ---

func shellEscape(s string) string {
	if s == "" {
		return "''"
	}
	if !strings.ContainsAny(s, " \t\n\r'\"\\$`!#&|;(){}") {
		return s
	}
	return "'" + strings.ReplaceAll(s, "'", "'\\''") + "'"
}