refactor: split into packages and add tests

internal/nix/service.go

@@ -0,0 +1,110 @@
+package nix
+
+import (
+	"bytes"
+	"encoding/json"
+	"os"
+	"os/exec"
+	"strings"
+
+	apperrors "gitlab.com/technofab/nixtest/internal/errors"
+)
+
+// Service defines operations related to Nix
+type Service interface {
+	BuildDerivation(derivation string) (string, error)
+	BuildAndParseJSON(derivation string) (any, error)
+	BuildAndRunScript(derivation string, pureEnv bool) (exitCode int, stdout string, stderr string, err error)
+}
+
+type DefaultService struct {
+	commandExecutor func(command string, args ...string) *exec.Cmd
+}
+
+func NewDefaultService() *DefaultService {
+	return &DefaultService{commandExecutor: exec.Command}
+}
+
+// BuildDerivation builds a Nix derivation and returns the output path
+func (s *DefaultService) BuildDerivation(derivation string) (string, error) {
+	cmd := s.commandExecutor(
+		"nix",
+		"build",
+		derivation+"^*",
+		"--print-out-paths",
+		"--no-link",
+	)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	err := cmd.Run()
+	if err != nil {
+		return "", &apperrors.NixBuildError{Derivation: derivation, Stderr: stderr.String(), Err: err}
+	}
+
+	path := strings.TrimSpace(stdout.String())
+	if path == "" {
+		return "", &apperrors.NixNoOutputPathError{Derivation: derivation, Stderr: stderr.String()}
+	}
+	return path, nil
+}
+
+// BuildAndParseJSON builds a derivation and parses its output file as JSON
+func (s *DefaultService) BuildAndParseJSON(derivation string) (any, error) {
+	path, err := s.BuildDerivation(derivation)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, &apperrors.FileReadError{Path: path, Err: err}
+	}
+
+	var result any
+	err = json.Unmarshal(data, &result)
+	if err != nil {
+		return nil, &apperrors.JSONUnmarshalError{Source: path, Err: err}
+	}
+
+	return result, nil
+}
+
+// BuildAndRunScript builds a derivation and runs it as a script
+func (s *DefaultService) BuildAndRunScript(derivation string, pureEnv bool) (exitCode int, stdout string, stderr string, err error) {
+	exitCode = -1
+	path, err := s.BuildDerivation(derivation)
+	if err != nil {
+		return exitCode, "", "", err
+	}
+
+	var cmdArgs []string
+	if pureEnv {
+		cmdArgs = append([]string{"env", "-i"}, "bash", path)
+	} else {
+		cmdArgs = []string{"bash", path}
+	}
+
+	cmd := s.commandExecutor(cmdArgs[0], cmdArgs[1:]...)
+	var outBuf, errBuf bytes.Buffer
+	cmd.Stdout = &outBuf
+	cmd.Stderr = &errBuf
+
+	if err = cmd.Start(); err != nil {
+		return exitCode, "", "", &apperrors.ScriptExecutionError{Path: path, Err: err}
+	}
+
+	runErr := cmd.Wait()
+	stdout = outBuf.String()
+	stderr = errBuf.String()
+
+	if runErr != nil {
+		if exitErr, ok := runErr.(*exec.ExitError); ok {
+			return exitErr.ExitCode(), stdout, stderr, nil
+		}
+		return exitCode, stdout, stderr, &apperrors.ScriptExecutionError{Path: path, Err: runErr}
+	}
+
+	return 0, stdout, stderr, nil
+}