Make Page an interface

The main motivation of this commit is to add a `page.Page` interface to replace the very file-oriented `hugolib.Page` struct.
This is all a preparation step for issue  #5074, "pages from other data sources".

But this also fixes a set of annoying limitations, especially related to custom output formats, and shortcodes.

Most notable changes:

* The inner content of shortcodes using the `{{%` as the outer-most delimiter will now be sent to the content renderer, e.g. Blackfriday.
  This means that any markdown will partake in the global ToC and footnote context etc.
* The Custom Output formats are now "fully virtualized". This removes many of the current limitations.
* The taxonomy list type now has a reference to the `Page` object.
  This improves the taxonomy template `.Title` situation and make common template constructs much simpler.

See #5074
Fixes #5763
Fixes #5758
Fixes #5090
Fixes #5204
Fixes #4695
Fixes #5607
Fixes #5707
Fixes #5719
Fixes #3113
Fixes #5706
Fixes #5767
Fixes #5723
Fixes #5769
Fixes #5770
Fixes #5771
Fixes #5759
Fixes #5776
Fixes #5777
Fixes #5778

1 files changed, 83 insertions, 0 deletions

diff --git a/hugolib/page__paginator.go b/hugolib/page__paginator.go
new file mode 100644
index 000000000..93701e799
--- /dev/null
+++ b/hugolib/page__paginator.go
@@ -0,0 +1,83 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hugolib
+
+import (
+	"sync"
+
+	"github.com/gohugoio/hugo/resources/page"
+)
+
+type pagePaginator struct {
+	paginatorInit sync.Once
+	current       *page.Pager
+
+	source *pageState
+}
+
+func (p *pagePaginator) Paginate(seq interface{}, options ...interface{}) (*page.Pager, error) {
+	var initErr error
+	p.paginatorInit.Do(func() {
+		pagerSize, err := page.ResolvePagerSize(p.source.s.Cfg, options...)
+		if err != nil {
+			initErr = err
+			return
+		}
+
+		pd := p.source.targetPathDescriptor
+		pd.Type = p.source.outputFormat()
+		paginator, err := page.Paginate(pd, seq, pagerSize)
+		if err != nil {
+			initErr = err
+			return
+		}
+
+		p.current = paginator.Pagers()[0]
+
+	})
+
+	if initErr != nil {
+		return nil, initErr
+	}
+
+	return p.current, nil
+}
+
+func (p *pagePaginator) Paginator(options ...interface{}) (*page.Pager, error) {
+	var initErr error
+	p.paginatorInit.Do(func() {
+		pagerSize, err := page.ResolvePagerSize(p.source.s.Cfg, options...)
+		if err != nil {
+			initErr = err
+			return
+		}
+
+		pd := p.source.targetPathDescriptor
+		pd.Type = p.source.outputFormat()
+		paginator, err := page.Paginate(pd, p.source.Pages(), pagerSize)
+		if err != nil {
+			initErr = err
+			return
+		}
+
+		p.current = paginator.Pagers()[0]
+
+	})
+
+	if initErr != nil {
+		return nil, initErr
+	}
+
+	return p.current, nil
+}