Refactoring core structure of datamodel to accomodate v2 model.

There is a lot of overlap on these models, to create a much more sensible design, a new 'base' package has been added which contains shared models that both versions make use of.

datamodel/low/base/external_doc_test.go

@@ -0,0 +1,55 @@
+// Copyright 2022 Princess B33f Heavy Industries / Dave Shanley
+// SPDX-License-Identifier: MIT
+
+package base
+
+import (
+	"github.com/pb33f/libopenapi/datamodel/low"
+	"github.com/pb33f/libopenapi/index"
+	"github.com/stretchr/testify/assert"
+	"gopkg.in/yaml.v3"
+	"testing"
+)
+
+func TestExternalDoc_FindExtension(t *testing.T) {
+
+	yml := `x-fish: cake`
+
+	var idxNode yaml.Node
+	_ = yaml.Unmarshal([]byte(yml), &idxNode)
+	idx := index.NewSpecIndex(&idxNode)
+
+	var n ExternalDoc
+	err := low.BuildModel(&idxNode, &n)
+	assert.NoError(t, err)
+
+	err = n.Build(idxNode.Content[0], idx)
+	assert.NoError(t, err)
+	assert.Equal(t, "cake", n.FindExtension("x-fish").Value)
+
+}
+
+func TestExternalDoc_Build(t *testing.T) {
+
+	yml := `url: https://pb33f.io
+description: the ranch
+x-b33f: princess`
+
+	var idxNode yaml.Node
+	mErr := yaml.Unmarshal([]byte(yml), &idxNode)
+	assert.NoError(t, mErr)
+	idx := index.NewSpecIndex(&idxNode)
+
+	var n ExternalDoc
+	err := low.BuildModel(&idxNode, &n)
+	assert.NoError(t, err)
+
+	err = n.Build(idxNode.Content[0], idx)
+	assert.NoError(t, err)
+	assert.Equal(t, "https://pb33f.io", n.URL.Value)
+	assert.Equal(t, "the ranch", n.Description.Value)
+	ext := n.FindExtension("x-b33f")
+	assert.NotNil(t, ext)
+	assert.Equal(t, "princess", ext.Value)
+
+}