resources: Move resource interfaces into its own package

resources/resource_transformers/postcss/postcss.go

@@ -0,0 +1,185 @@
+// Copyright 2018 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 postcss
+
+import (
+	"io"
+	"path/filepath"
+
+	"github.com/gohugoio/hugo/hugofs"
+	"github.com/pkg/errors"
+
+	"os"
+	"os/exec"
+
+	"github.com/mitchellh/mapstructure"
+
+	"github.com/gohugoio/hugo/common/herrors"
+	"github.com/gohugoio/hugo/resources"
+	"github.com/gohugoio/hugo/resources/resource"
+)
+
+// Some of the options from https://github.com/postcss/postcss-cli
+type Options struct {
+
+	// Set a custom path to look for a config file.
+	Config string
+
+	NoMap bool `mapstructure:"no-map"` // Disable the default inline sourcemaps
+
+	// Options for when not using a config file
+	Use         string // List of postcss plugins to use
+	Parser      string //  Custom postcss parser
+	Stringifier string // Custom postcss stringifier
+	Syntax      string // Custom postcss syntax
+}
+
+func DecodeOptions(m map[string]interface{}) (opts Options, err error) {
+	if m == nil {
+		return
+	}
+	err = mapstructure.WeakDecode(m, &opts)
+	return
+}
+
+func (opts Options) toArgs() []string {
+	var args []string
+	if opts.NoMap {
+		args = append(args, "--no-map")
+	}
+	if opts.Use != "" {
+		args = append(args, "--use", opts.Use)
+	}
+	if opts.Parser != "" {
+		args = append(args, "--parser", opts.Parser)
+	}
+	if opts.Stringifier != "" {
+		args = append(args, "--stringifier", opts.Stringifier)
+	}
+	if opts.Syntax != "" {
+		args = append(args, "--syntax", opts.Syntax)
+	}
+	return args
+}
+
+// Client is the client used to do PostCSS transformations.
+type Client struct {
+	rs *resources.Spec
+}
+
+// New creates a new Client with the given specification.
+func New(rs *resources.Spec) *Client {
+	return &Client{rs: rs}
+}
+
+type postcssTransformation struct {
+	options Options
+	rs      *resources.Spec
+}
+
+func (t *postcssTransformation) Key() resources.ResourceTransformationKey {
+	return resources.NewResourceTransformationKey("postcss", t.options)
+}
+
+// Transform shells out to postcss-cli to do the heavy lifting.
+// For this to work, you need some additional tools. To install them globally:
+// npm install -g postcss-cli
+// npm install -g autoprefixer
+func (t *postcssTransformation) Transform(ctx *resources.ResourceTransformationCtx) error {
+
+	const localPostCSSPath = "node_modules/postcss-cli/bin/"
+	const binaryName = "postcss"
+
+	// Try first in the project's node_modules.
+	csiBinPath := filepath.Join(t.rs.WorkingDir, localPostCSSPath, binaryName)
+
+	binary := csiBinPath
+
+	if _, err := exec.LookPath(binary); err != nil {
+		// Try PATH
+		binary = binaryName
+		if _, err := exec.LookPath(binary); err != nil {
+			// This may be on a CI server etc. Will fall back to pre-built assets.
+			return herrors.ErrFeatureNotAvailable
+		}
+	}
+
+	var configFile string
+	logger := t.rs.Logger
+
+	if t.options.Config != "" {
+		configFile = t.options.Config
+	} else {
+		configFile = "postcss.config.js"
+	}
+
+	configFile = filepath.Clean(configFile)
+
+	// We need an abolute filename to the config file.
+	if !filepath.IsAbs(configFile) {
+		// We resolve this against the virtual Work filesystem, to allow
+		// this config file to live in one of the themes if needed.
+		fi, err := t.rs.BaseFs.Work.Fs.Stat(configFile)
+		if err != nil {
+			if t.options.Config != "" {
+				// Only fail if the user specificed config file is not found.
+				return errors.Wrapf(err, "postcss config %q not found:", configFile)
+			}
+			configFile = ""
+		} else {
+			configFile = fi.(hugofs.RealFilenameInfo).RealFilename()
+		}
+	}
+
+	var cmdArgs []string
+
+	if configFile != "" {
+		logger.INFO.Println("postcss: use config file", configFile)
+		cmdArgs = []string{"--config", configFile}
+	}
+
+	if optArgs := t.options.toArgs(); len(optArgs) > 0 {
+		cmdArgs = append(cmdArgs, optArgs...)
+	}
+
+	cmd := exec.Command(binary, cmdArgs...)
+
+	cmd.Stdout = ctx.To
+	cmd.Stderr = os.Stderr
+
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+
+	go func() {
+		defer stdin.Close()
+		io.Copy(stdin, ctx.From)
+	}()
+
+	err = cmd.Run()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Process transforms the given Resource with the PostCSS processor.
+func (c *Client) Process(res resource.Resource, options Options) (resource.Resource, error) {
+	return c.rs.Transform(
+		res,
+		&postcssTransformation{rs: c.rs, options: options},
+	)
+}