Refactor and extend argument spec helper, use for ACME modules (#749)

* Refactor argument spec helper.

* Remove superfluous comments.

plugins/module_utils/argspec.py

@@ -0,0 +1,75 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright (c) 2020, Felix Fontein <felix@fontein.de>
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+
+from ansible.module_utils.basic import AnsibleModule
+
+
+def _ensure_list(value):
+    if value is None:
+        return []
+    return list(value)
+
+
+class ArgumentSpec:
+    def __init__(self, argument_spec=None, mutually_exclusive=None, required_together=None, required_one_of=None, required_if=None, required_by=None):
+        self.argument_spec = argument_spec or {}
+        self.mutually_exclusive = _ensure_list(mutually_exclusive)
+        self.required_together = _ensure_list(required_together)
+        self.required_one_of = _ensure_list(required_one_of)
+        self.required_if = _ensure_list(required_if)
+        self.required_by = required_by or {}
+
+    def update_argspec(self, **kwargs):
+        self.argument_spec.update(kwargs)
+        return self
+
+    def update(self, mutually_exclusive=None, required_together=None, required_one_of=None, required_if=None, required_by=None):
+        if mutually_exclusive:
+            self.mutually_exclusive.extend(mutually_exclusive)
+        if required_together:
+            self.required_together.extend(required_together)
+        if required_one_of:
+            self.required_one_of.extend(required_one_of)
+        if required_if:
+            self.required_if.extend(required_if)
+        if required_by:
+            for k, v in required_by.items():
+                if k in self.required_by:
+                    v = list(self.required_by[k]) + list(v)
+                self.required_by[k] = v
+        return self
+
+    def merge(self, other):
+        self.update_argspec(other.argument_spec)
+        self.update(
+            mutually_exclusive=other.mutually_exclusive,
+            required_together=other.required_together,
+            required_one_of=other.required_one_of,
+            required_if=other.required_if,
+            required_by=other.required_by,
+        )
+        return self
+
+    def create_ansible_module_helper(self, clazz, args, **kwargs):
+        return clazz(
+            *args,
+            argument_spec=self.argument_spec,
+            mutually_exclusive=self.mutually_exclusive,
+            required_together=self.required_together,
+            required_one_of=self.required_one_of,
+            required_if=self.required_if,
+            required_by=self.required_by,
+            **kwargs)
+
+    def create_ansible_module(self, **kwargs):
+        return self.create_ansible_module_helper(AnsibleModule, (), **kwargs)
+
+
+__all__ = ('ArgumentSpec', )