package harness

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"sync"
)

var (
	binOnce sync.Once
	binPath string
	binErr  error
)

// Binary 返回已编译好的 nixmsg 可执行文件路径（整个进程只编译一次）。
func Binary() (string, error) {
	binOnce.Do(func() {
		root, err := moduleRoot()
		if err != nil {
			binErr = err
			return
		}
		dir, err := os.MkdirTemp("", "nixmsg-harness-bin-*")
		if err != nil {
			binErr = err
			return
		}
		name := "nixmsg"
		if runtime.GOOS == "windows" {
			name += ".exe"
		}
		out := filepath.Join(dir, name)
		cmd := exec.Command("go", "build", "-o", out, "./cmd/nixmsg")
		cmd.Dir = root
		cmd.Env = append(os.Environ(), "CGO_ENABLED=0")
		if outBytes, runErr := cmd.CombinedOutput(); runErr != nil {
			binErr = fmt.Errorf("build nixmsg: %w\n%s", runErr, outBytes)
			return
		}
		binPath = out
	})
	return binPath, binErr
}

func moduleRoot() (string, error) {
	dir, err := os.Getwd()
	if err != nil {
		return "", err
	}
	for {
		if _, statErr := os.Stat(filepath.Join(dir, "go.mod")); statErr == nil {
			return dir, nil
		}
		parent := filepath.Dir(dir)
		if parent == dir {
			return "", fmt.Errorf("go.mod not found from %s", dir)
		}
		dir = parent
	}
}