// MCP server registration. gemini's `gemini mcp add -s user` writes
// into the user's settings.json; we use a per-agent stable name so
// multiple Plexum agents using gemini don't collide. Registration is
// idempotent and performed lazily before the first turn that needs it.

package runner

import (
	"context"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"sync"
)

var registered sync.Map // agentID → bool (registration done this process)

// EnsureGeminiMCPRegistered makes sure gemini's user settings has an
// MCP server entry for this agent named plexum-host-<sanitized>.
// Socket path is the stable StableSocketPath(agentID); same path the
// per-turn bridge listens on.
func EnsureGeminiMCPRegistered(ctx context.Context, geminiBinary, pluginBinary, agentID string) (string, error) {
	name := geminiServerName(agentID)
	if _, ok := registered.Load(name); ok {
		return name, nil
	}
	// Remove first so we don't double-register; ignore error.
	_ = exec.CommandContext(ctx, geminiBinary, "mcp", "remove", "-s", "user", name).Run()

	args := []string{
		"mcp", "add",
		"-s", "user", "--trust",
		"-e", "PLEXUM_MCP_SOCKET=" + StableSocketPath(agentID),
		"-e", "PLEXUM_MCP_AGENT_ID=" + agentID,
		name, pluginBinary, "mcp-host",
	}
	cmd := exec.CommandContext(ctx, geminiBinary, args...)
	if out, err := cmd.CombinedOutput(); err != nil {
		return "", fmt.Errorf("gemini mcp add: %w: %s", err, strings.TrimSpace(string(out)))
	}
	registered.Store(name, true)
	return name, nil
}

// StableSocketPath returns the per-agent unix socket path the bridge
// listens on AND gemini's mcp-host subprocess dials into.
func StableSocketPath(agentID string) string {
	return filepath.Join(os.TempDir(), "plexum-gemini-mcp-"+sanitize(agentID)+".sock")
}

func geminiServerName(agentID string) string {
	return "plexum-host-" + sanitize(agentID)
}

func sanitize(s string) string {
	out := make([]byte, 0, len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case c >= 'a' && c <= 'z', c >= 'A' && c <= 'Z',
			c >= '0' && c <= '9', c == '-', c == '_':
			out = append(out, c)
		default:
			out = append(out, '_')
		}
	}
	return string(out)
}