Image resource refactor

This commit pulls most of the image related logic into its own package, to make it easier to reason about and extend.

This is also a rewrite of the transformation logic used in Hugo Pipes, mostly to allow constructs like the one below:

    {{ ($myimg | fingerprint ).Width }}

Fixes #5903
Fixes #6234
Fixes #6266

resources/images/config_test.go

@@ -0,0 +1,125 @@
+// 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 images
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestDecodeConfig(t *testing.T) {
+	c := qt.New(t)
+	m := map[string]interface{}{
+		"quality":        42,
+		"resampleFilter": "NearestNeighbor",
+		"anchor":         "topLeft",
+	}
+
+	imaging, err := DecodeConfig(m)
+
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Quality, qt.Equals, 42)
+	c.Assert(imaging.ResampleFilter, qt.Equals, "nearestneighbor")
+	c.Assert(imaging.Anchor, qt.Equals, "topleft")
+
+	m = map[string]interface{}{}
+
+	imaging, err = DecodeConfig(m)
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Quality, qt.Equals, defaultJPEGQuality)
+	c.Assert(imaging.ResampleFilter, qt.Equals, "box")
+	c.Assert(imaging.Anchor, qt.Equals, "smart")
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"quality": 123,
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"resampleFilter": "asdf",
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	_, err = DecodeConfig(map[string]interface{}{
+		"anchor": "asdf",
+	})
+	c.Assert(err, qt.Not(qt.IsNil))
+
+	imaging, err = DecodeConfig(map[string]interface{}{
+		"anchor": "Smart",
+	})
+	c.Assert(err, qt.IsNil)
+	c.Assert(imaging.Anchor, qt.Equals, "smart")
+}
+
+func TestDecodeImageConfig(t *testing.T) {
+	for i, this := range []struct {
+		in     string
+		expect interface{}
+	}{
+		{"300x400", newImageConfig(300, 400, 0, 0, "", "")},
+		{"100x200 bottomRight", newImageConfig(100, 200, 0, 0, "", "BottomRight")},
+		{"10x20 topleft Lanczos", newImageConfig(10, 20, 0, 0, "Lanczos", "topleft")},
+		{"linear left 10x r180", newImageConfig(10, 0, 0, 180, "linear", "left")},
+		{"x20 riGht Cosine q95", newImageConfig(0, 20, 95, 0, "cosine", "right")},
+
+		{"", false},
+		{"foo", false},
+	} {
+
+		result, err := DecodeImageConfig("resize", this.in, Imaging{})
+		if b, ok := this.expect.(bool); ok && !b {
+			if err == nil {
+				t.Errorf("[%d] parseImageConfig didn't return an expected error", i)
+			}
+		} else {
+			if err != nil {
+				t.Fatalf("[%d] err: %s", i, err)
+			}
+			if fmt.Sprint(result) != fmt.Sprint(this.expect) {
+				t.Fatalf("[%d] got\n%v\n but expected\n%v", i, result, this.expect)
+			}
+		}
+	}
+}
+
+func newImageConfig(width, height, quality, rotate int, filter, anchor string) ImageConfig {
+	var c ImageConfig
+	c.Action = "resize"
+	c.Width = width
+	c.Height = height
+	c.Quality = quality
+	c.Rotate = rotate
+
+	if filter != "" {
+		filter = strings.ToLower(filter)
+		if v, ok := imageFilters[filter]; ok {
+			c.Filter = v
+			c.FilterStr = filter
+		}
+	}
+
+	if anchor != "" {
+		anchor = strings.ToLower(anchor)
+		if v, ok := anchorPositions[anchor]; ok {
+			c.Anchor = v
+			c.AnchorStr = anchor
+		}
+	}
+
+	return c
+}