// Package runner starts the claude subprocess with a pre-built environment,
// transparently forwards stdio and signals, and returns claude's exit code as
// cc-switch's own.
//
// The contract (spec: provider-launch):
//   - stdin/stdout/stderr are inherited verbatim.
//   - SIGINT/SIGTERM/SIGHUP are forwarded to the child; cc-switch waits for
//     the child to finish and then returns.
//   - Exit code passthrough: normal exit -> child's code; signal termination
//     -> 128 + signum (POSIX convention).
//   - We never mutate os.Environ; the supplied childEnv is the whole
//     environment the child sees.
package runner

import (
	"errors"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"

	"github.com/kotoyuuko/cc-switch-cli/internal/config"
)

// ResolveClaudePath returns the absolute path of the claude executable to
// launch. Precedence: cfg.ClaudePath (if non-empty) > exec.LookPath("claude").
// If neither succeeds, an error is returned that suggests the `config set
// claude-path` escape hatch.
func ResolveClaudePath(cfg config.Config) (string, error) {
	if cfg.ClaudePath != "" {
		expanded, err := config.ExpandUser(cfg.ClaudePath)
		if err != nil {
			return "", fmt.Errorf("expand claude_path %q: %w", cfg.ClaudePath, err)
		}
		abs, err := filepath.Abs(expanded)
		if err != nil {
			return "", fmt.Errorf("resolve claude_path %q: %w", cfg.ClaudePath, err)
		}
		info, err := os.Stat(abs)
		if err != nil {
			return "", fmt.Errorf("claude_path %q: %w", abs, err)
		}
		if !info.Mode().IsRegular() {
			return "", fmt.Errorf("claude_path %q is not a regular file", abs)
		}
		if info.Mode().Perm()&0o111 == 0 {
			return "", fmt.Errorf("claude_path %q is not executable", abs)
		}
		return abs, nil
	}
	p, err := exec.LookPath("claude")
	if err != nil {
		return "", fmt.Errorf(
			"claude not found in PATH and no claude_path configured; try `cc-switch config set claude-path <path>`",
		)
	}
	return p, nil
}

// ExitError is returned by Run when the child was killed by a signal. Its
// ExitCode already follows the 128+signum convention.
type ExitError struct {
	Signal   os.Signal // nil if exited normally
	ExitCode int
}

func (e *ExitError) Error() string {
	if e.Signal != nil {
		return fmt.Sprintf("claude terminated by signal %v (exit code %d)", e.Signal, e.ExitCode)
	}
	return fmt.Sprintf("claude exited with code %d", e.ExitCode)
}

// asExitError converts a cmd.Wait error into an ExitCode value consistent with
// the spec: normal exit -> err.ExitCode(); signal kill -> 128+signum.
func asExitError(err error) (int, error) {
	if err == nil {
		return 0, nil
	}
	var exitErr *exec.ExitError
	if !errors.As(err, &exitErr) {
		// Something went wrong that isn't the child reporting an exit (e.g.
		// we couldn't wait on it at all). Surface the raw error and a
		// generic 1 so callers can still print something useful.
		return 1, err
	}
	if code := exitErr.ExitCode(); code >= 0 {
		return code, nil
	}
	// code == -1 means the child was killed by a signal. Look up which.
	if sig, ok := extractSignal(exitErr); ok {
		return 128 + int(sig), nil
	}
	return 1, err
}

// Run starts claudePath with the given env and args and returns its exit code.
// It installs the signal-forwarding handler as configured per platform
// (see runner_unix.go / runner_other.go).
func Run(claudePath string, childEnv []string, args []string) (int, error) {
	cmd := exec.Command(claudePath, args...)
	cmd.Env = childEnv
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	if err := cmd.Start(); err != nil {
		return 1, fmt.Errorf("start claude: %w", err)
	}

	stopForward := startSignalForwarding(cmd.Process)
	defer stopForward()

	return asExitError(cmd.Wait())
}