internal/shell/shell.go

// Package shell provides cross-platform shell execution capabilities.
//
// This package provides Shell instances for executing commands with their own
// working directory and environment. Each shell execution is independent.
//
// WINDOWS COMPATIBILITY:
// This implementation provides POSIX shell emulation (mvdan.cc/sh/v3) even on
// Windows. Commands should use forward slashes (/) as path separators to work
// correctly on all platforms.
package shell

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"slices"
	"strings"
	"sync"

	"github.com/charmbracelet/x/exp/slice"
	"mvdan.cc/sh/v3/interp"
	"mvdan.cc/sh/v3/syntax"
)

// ShellType represents the type of shell to use
type ShellType int

const (
	ShellTypePOSIX ShellType = iota
	ShellTypeCmd
	ShellTypePowerShell
)

// CrushEnvMarkers returns a fresh slice of the environment variables that
// Crush unconditionally sets on every shell it spawns — both the interactive
// bash tool's [Shell] and the hook runner's [Run] calls. Tools that want to
// detect "am I being invoked by an AI agent?" can check any of these.
// Keeping them in one place guarantees the two shell surfaces cannot drift.
// A fresh slice is returned on every call so callers may append freely.
func CrushEnvMarkers() []string {
	return []string{
		"CRUSH=1",
		"AGENT=crush",
		"AI_AGENT=crush",
	}
}

// Logger interface for optional logging
type Logger interface {
	InfoPersist(msg string, keysAndValues ...any)
}

// noopLogger is a logger that does nothing
type noopLogger struct{}

func (noopLogger) InfoPersist(msg string, keysAndValues ...any) {}

// BlockFunc is a function that determines if a command should be blocked
type BlockFunc func(args []string) bool

// Shell provides cross-platform shell execution with optional state persistence
type Shell struct {
	env        []string
	cwd        string
	mu         sync.Mutex
	logger     Logger
	blockFuncs []BlockFunc
}

// Options for creating a new shell
type Options struct {
	WorkingDir string
	Env        []string
	Logger     Logger
	BlockFuncs []BlockFunc
}

// NewShell creates a new shell instance with the given options
func NewShell(opts *Options) *Shell {
	if opts == nil {
		opts = &Options{}
	}

	cwd := opts.WorkingDir
	if cwd == "" {
		cwd, _ = os.Getwd()
	}

	env := opts.Env
	if env == nil {
		env = os.Environ()
	}

	// Strip herdr pane-ownership vars so subprocesses (including test
	// binaries and nested crush instances) can't attach to or release
	// the parent pane's agent authority.
	env = withoutHerdrEnv(env)

	// Allow tools to detect execution by Crush.
	env = append(env, CrushEnvMarkers()...)

	logger := opts.Logger
	if logger == nil {
		logger = noopLogger{}
	}

	return &Shell{
		cwd:        cwd,
		env:        env,
		logger:     logger,
		blockFuncs: opts.BlockFuncs,
	}
}

// Exec executes a command in the shell
func (s *Shell) Exec(ctx context.Context, command string) (string, string, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.exec(ctx, command)
}

// ExecStream executes a command in the shell with streaming output to provided writers
func (s *Shell) ExecStream(ctx context.Context, command string, stdout, stderr io.Writer) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.execStream(ctx, command, stdout, stderr)
}

// GetWorkingDir returns the current working directory
func (s *Shell) GetWorkingDir() string {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.cwd
}

// SetWorkingDir sets the working directory
func (s *Shell) SetWorkingDir(dir string) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Verify the directory exists
	if _, err := os.Stat(dir); err != nil {
		return fmt.Errorf("directory does not exist: %w", err)
	}

	s.cwd = dir
	return nil
}

// GetEnv returns a copy of the environment variables
func (s *Shell) GetEnv() []string {
	s.mu.Lock()
	defer s.mu.Unlock()

	env := make([]string, len(s.env))
	copy(env, s.env)
	return env
}

// SetEnv sets an environment variable
func (s *Shell) SetEnv(key, value string) {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Update or add the environment variable
	keyPrefix := key + "="
	for i, env := range s.env {
		if strings.HasPrefix(env, keyPrefix) {
			s.env[i] = keyPrefix + value
			return
		}
	}
	s.env = append(s.env, keyPrefix+value)
}

// SetBlockFuncs sets the command block functions for the shell
func (s *Shell) SetBlockFuncs(blockFuncs []BlockFunc) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.blockFuncs = blockFuncs
}

// CommandsBlocker creates a BlockFunc that blocks exact command matches
func CommandsBlocker(cmds []string) BlockFunc {
	bannedSet := make(map[string]struct{})
	for _, cmd := range cmds {
		bannedSet[cmd] = struct{}{}
	}

	return func(args []string) bool {
		if len(args) == 0 {
			return false
		}
		_, ok := bannedSet[args[0]]
		return ok
	}
}

// ArgumentsBlocker creates a BlockFunc that blocks specific subcommand
func ArgumentsBlocker(cmd string, args []string, flags []string) BlockFunc {
	return func(parts []string) bool {
		if len(parts) == 0 || parts[0] != cmd {
			return false
		}

		argParts, flagParts := splitArgsFlags(parts[1:])
		if len(argParts) < len(args) || len(flagParts) < len(flags) {
			return false
		}

		argsMatch := slices.Equal(argParts[:len(args)], args)
		flagsMatch := slice.IsSubset(flags, flagParts)

		return argsMatch && flagsMatch
	}
}

func splitArgsFlags(parts []string) (args []string, flags []string) {
	args = make([]string, 0, len(parts))
	flags = make([]string, 0, len(parts))
	for _, part := range parts {
		if strings.HasPrefix(part, "-") {
			// Extract flag name before '=' if present
			flag := part
			if before, _, ok := strings.Cut(part, "="); ok {
				flag = before
			}
			flags = append(flags, flag)
		} else {
			args = append(args, part)
		}
	}
	return args, flags
}

// newInterp creates a new interpreter with the current shell state. A nil
// stdin is equivalent to an empty input stream.
func (s *Shell) newInterp(stdin io.Reader, stdout, stderr io.Writer) (*interp.Runner, error) {
	return newRunner(s.cwd, s.env, stdin, stdout, stderr, s.blockFuncs)
}

// updateShellFromRunner updates the shell from the interpreter after execution.
func (s *Shell) updateShellFromRunner(runner *interp.Runner) {
	s.cwd = runner.Dir
	s.env = s.env[:0]
	for name, vr := range runner.Vars {
		if vr.Exported {
			s.env = append(s.env, name+"="+vr.Str)
		}
	}
}

// execCommon is the shared implementation for executing commands
func (s *Shell) execCommon(ctx context.Context, command string, stdout, stderr io.Writer) (err error) {
	var runner *interp.Runner
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("command execution panic: %v", r)
		}
		if runner != nil {
			s.updateShellFromRunner(runner)
		}
		s.logger.InfoPersist("command finished", "command", command, "err", err)
	}()

	line, err := syntax.NewParser().Parse(strings.NewReader(command), "")
	if err != nil {
		return fmt.Errorf("could not parse command: %w", err)
	}

	runner, err = s.newInterp(nil, stdout, stderr)
	if err != nil {
		return fmt.Errorf("could not run command: %w", err)
	}

	err = runner.Run(ctx, line)
	return err
}

// exec executes commands using a cross-platform shell interpreter.
func (s *Shell) exec(ctx context.Context, command string) (string, string, error) {
	var stdout, stderr bytes.Buffer
	err := s.execCommon(ctx, command, &stdout, &stderr)
	return stdout.String(), stderr.String(), err
}

// execStream executes commands using POSIX shell emulation with streaming output
func (s *Shell) execStream(ctx context.Context, command string, stdout, stderr io.Writer) error {
	return s.execCommon(ctx, command, stdout, stderr)
}

// IsInterrupt checks if an error is due to interruption
func IsInterrupt(err error) bool {
	return errors.Is(err, context.Canceled) ||
		errors.Is(err, context.DeadlineExceeded)
}

// ExitCode extracts the exit code from an error
func ExitCode(err error) int {
	if err == nil {
		return 0
	}
	if exitErr, ok := errors.AsType[interp.ExitStatus](err); ok {
		return int(exitErr)
	}
	return 1
}