Implement the gemtext to HTML converter, along with a standalone executable

hugofs/files/classifier.go

@@ -43,6 +43,7 @@ var (
 		"mmark",
 		"org",
 		"pandoc", "pdc",
+		"gmi",
 	}
 
 	contentFileExtensionsSet map[string]bool

markup/gemtext/convert.go

@@ -0,0 +1,224 @@
+// 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 gemtext converts Gemtext (text/gemini) to HTML.
+package gemtext
+
+import (
+	"fmt"
+	"html"
+	"strings"
+
+	"github.com/gohugoio/hugo/identity"
+	"github.com/gohugoio/hugo/markup/converter"
+)
+
+/// Provider is the package entry point.
+var Provider converter.ProviderProvider = provider{}
+
+type provider struct {
+}
+
+func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error) {
+	return converter.NewProvider("gemtext", func(ctx converter.DocumentContext) (converter.Converter, error) {
+		return &gemtextConverter{
+			ctx: ctx,
+			cfg: cfg,
+		}, nil
+	}), nil
+}
+
+type gemtextConverter struct {
+	ctx converter.DocumentContext
+	cfg converter.ProviderConfig
+}
+
+func (c *gemtextConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
+	return &gemtextResult{
+		output: Convert(string(ctx.Src)),
+	}, nil
+}
+
+func Convert(src string) string {
+	var output strings.Builder
+
+	const (
+		stateDefault = iota
+		stateParagraph
+		stateQuote
+		stateList
+		stateLinks
+		statePreformatted
+	)
+	state := stateDefault
+
+	switchState := func(newState int) {
+		switch state {
+		case stateParagraph:
+			output.WriteString("</p>\n")
+		case stateQuote:
+			output.WriteString("</p>\n</blockquote>\n")
+		case statePreformatted:
+			output.WriteString("</pre>\n</figure>\n")
+		case stateList:
+			fallthrough
+		case stateLinks:
+			output.WriteString("</ul>\n")
+		}
+
+		state = newState
+	}
+
+	// iterate line by line
+	for _, line := range strings.Split(src, "\n") {
+		if state == statePreformatted {
+			if strings.HasPrefix(line, "```") {
+				switchState(stateDefault)
+			} else {
+				output.WriteString(html.EscapeString(line))
+				output.WriteString("\n")
+			}
+			continue
+		}
+
+		// check line type
+		if strings.HasPrefix(line, "###") {
+			switchState(stateDefault)
+
+			stripped := strings.TrimPrefix(line, "###")
+
+			output.WriteString("<h3>")
+			output.WriteString(html.EscapeString(stripped))
+			output.WriteString("</h3>\n")
+		} else if strings.HasPrefix(line, "##") {
+			switchState(stateDefault)
+
+			stripped := strings.TrimPrefix(line, "##")
+
+			output.WriteString("<h2>")
+			output.WriteString(html.EscapeString(stripped))
+			output.WriteString("</h2>\n")
+		} else if strings.HasPrefix(line, "#") {
+			switchState(stateDefault)
+
+			stripped := strings.TrimPrefix(line, "#")
+
+			output.WriteString("<h1>")
+			output.WriteString(html.EscapeString(stripped))
+			output.WriteString("</h1>\n")
+		} else if strings.HasPrefix(line, "=>") {
+			// link line
+			if state != stateLinks {
+				switchState(stateLinks)
+				output.WriteString(`<ul class="links">`)
+				output.WriteString("\n")
+			}
+			// extract url and link name
+			url := ""
+			linkName := ""
+
+			withoutPrefix := strings.TrimSpace(strings.TrimPrefix(line, "=>"))
+			split := strings.SplitN(withoutPrefix, " ", 2)
+
+			if len(split) >= 1 {
+				url = split[0]
+			}
+			if len(split) >= 2 {
+				linkName = strings.TrimSpace(split[1])
+			}
+
+			output.WriteString("<li>")
+			// output as an <a> tag
+			output.WriteString(fmt.Sprintf(`<a href="%s">`, html.EscapeString(url)))
+			if len(linkName) > 0 {
+				output.WriteString(html.EscapeString(linkName))
+			} else {
+				output.WriteString(html.EscapeString(url))
+			}
+			output.WriteString("</a>\n")
+		} else if strings.HasPrefix(line, "* ") {
+			// list item line
+			if state != stateList {
+				switchState(stateList)
+				output.WriteString(`<ul class="items">`)
+				output.WriteString("\n")
+			}
+
+			withoutPrefix := strings.TrimPrefix(line, "* ")
+			output.WriteString("<li>")
+			output.WriteString(html.EscapeString(withoutPrefix))
+			output.WriteString("\n")
+		} else if strings.HasPrefix(line, "```") {
+			// preformatted toggle
+			switchState(statePreformatted)
+
+			output.WriteString("<figure>\n")
+			alt := strings.TrimSpace(strings.TrimPrefix(line, "```"))
+			if len(alt) > 0 {
+				output.WriteString("<figcaption>")
+				output.WriteString(html.EscapeString(alt))
+				output.WriteString("</figcaption>\n")
+			}
+
+			output.WriteString("<pre>\n")
+		} else if strings.HasPrefix(line, ">") {
+			// quoted line
+			withoutPrefix := strings.TrimSpace(strings.TrimPrefix(line, ">"))
+
+			if len(withoutPrefix) == 0 {
+				output.WriteString("</p>\n<p>\n")
+			} else if state == stateQuote {
+				output.WriteString("<br>\n")
+			} else {
+				switchState(stateQuote)
+				output.WriteString("<blockquote>\n")
+				output.WriteString("<p>\n")
+			}
+
+			output.WriteString(html.EscapeString(withoutPrefix))
+			output.WriteString("\n")
+		} else if len(strings.TrimSpace(line)) == 0 {
+			// empty line, go back to default state
+			switchState(stateDefault)
+		} else {
+			// fallback to text line
+
+			if state == stateParagraph {
+				output.WriteString("<br>\n")
+			} else {
+				switchState(stateParagraph)
+				output.WriteString("<p>\n")
+			}
+
+			output.WriteString(html.EscapeString(line))
+			output.WriteString("\n")
+		}
+	}
+
+	// ensure no tags are left open
+	switchState(stateDefault)
+
+	return output.String()
+}
+
+func (c *gemtextConverter) Supports(feature identity.Identity) bool {
+	return false
+}
+
+type gemtextResult struct {
+	output string
+}
+
+func (r gemtextResult) Bytes() []byte {
+	return []byte(r.output)
+}

markup/gemtext/standalone/main.go

@@ -0,0 +1,33 @@
+// 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.
+
+// This program reads gemtext from standard input and outputs its conversion
+// to HTML.
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+
+	"github.com/gohugoio/hugo/markup/gemtext"
+)
+
+func main() {
+	input, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		panic(err)
+	}
+	output := gemtext.Convert(string(input))
+	fmt.Print(output)
+}

markup/markup.go

@@ -30,6 +30,7 @@ import (
 	"github.com/gohugoio/hugo/markup/mmark"
 	"github.com/gohugoio/hugo/markup/pandoc"
 	"github.com/gohugoio/hugo/markup/rst"
+	"github.com/gohugoio/hugo/markup/gemtext"
 )
 
 func NewConverterProvider(cfg converter.ProviderConfig) (ConverterProvider, error) {
@@ -88,6 +89,9 @@ func NewConverterProvider(cfg converter.ProviderConfig) (ConverterProvider, erro
 	if err := add(org.Provider); err != nil {
 		return nil, err
 	}
+	if err := add(gemtext.Provider, "gmi"); err != nil {
+		return nil, err
+	}
 
 	return &converterRegistry{
 		config:     cfg,