Add 'environment' package

This commit adds a new environment package that manages all calls to the
underlying operating system.

pkg/environment/globals.go

@@ -0,0 +1,69 @@
+package environment
+
+import (
+	"bytes"
+	"io"
+	"io/fs"
+	"os"
+
+	"github.com/tkw1536/goprogram/stream"
+)
+
+// ExecCommandError is returned by Exec when a command could not be executed.
+// This typically hints that the executable cannot be found, but may have other causes.
+const ExecCommandError = 127
+
+// DefaultFilePerm is the default mode to use for files
+const DefaultFilePerm fs.FileMode = 0666
+
+// DefaultDirPerm is the default mode to use for directories
+const DefaultDirPerm fs.FileMode = os.ModeDir & fs.ModePerm
+
+// IsExist checks if the provided error represents a 'does not exist' errror
+func IsExist(err error) bool {
+	return os.IsExist(err)
+}
+
+// IsNotExist checks if the provided error represents a 'does exist' error
+func IsNotExist(err error) bool {
+	return os.IsNotExist(err)
+}
+
+// WriteFile is like [os.WriteFile].
+func WriteFile(env Environment, path string, data []byte, mode fs.FileMode) error {
+	handle, err := env.Create(path, mode)
+	if err != nil {
+		return err
+	}
+	defer handle.Close()
+
+	if _, err := handle.Write(data); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// ReadFile is like [os.ReadFile]
+func ReadFile(env Environment, path string) ([]byte, error) {
+	// open the file!
+	file, err := env.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	// copy everything into a buffer!
+	var buffer bytes.Buffer
+	if _, err := io.Copy(&buffer, file); err != nil {
+		return nil, err
+	}
+
+	// return the buffer contents!
+	return buffer.Bytes(), nil
+}
+
+// MustExec is like Exec, except that it returns true if the command exited successfully, and else false.
+func MustExec(env Environment, io stream.IOStream, workdir string, exe string, argv ...string) bool {
+	return env.Exec(io, workdir, exe, argv...) == 0
+}