From a7abf75794eb29bb4ea031cc186b562c44b737cb Mon Sep 17 00:00:00 2001
From: Adrien Delorme <adrien.delorme@icloud.com>
Date: Thu, 16 Jul 2020 15:14:04 +0200
Subject: [PATCH] Add snippet-extract cmd that allows to extract parts of
 examples for docs

---
 cmd/snippet-extractor/main.go | 146 ++++++++++++++++++++++++++++++++++
 1 file changed, 146 insertions(+)
 create mode 100644 cmd/snippet-extractor/main.go

diff --git a/cmd/snippet-extractor/main.go b/cmd/snippet-extractor/main.go
new file mode 100644
index 000000000..331ea4404
--- /dev/null
+++ b/cmd/snippet-extractor/main.go
@@ -0,0 +1,146 @@
+// snippet-extract --begin=#_BEGIN_WRAP_TAG_ --end=#_END_WRAP_TAG_ -output_dir=./docs/ [./file|./directory/]...
+// Extracts markdown snippets from relative files into output_dir, keeping the
+// directory layout.
+// It is not mandatory to terminate a snippet, the extractor will simply add
+// line until EOF.
+// Lines matching begin or end tags will not be put in the resulting file.
+// When a directory is passed, all files from directory will be parsed.
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type options struct {
+	filenames  []string
+	begin, end string
+	outputDir  string
+	extension  string
+}
+
+func (o *options) AddFlagSets(fs *flag.FlagSet) {
+	fs.StringVar(&o.begin, "begin", "#_BEGIN_WRAP_TAG_", "flag to mark beginning of a snippet")
+	fs.StringVar(&o.end, "end", "#_END_WRAP_TAG_", "flag to mark ending of a snippet")
+	fs.StringVar(&o.outputDir, "output_dir", "./docs/", "flag to mark ending of a snippet")
+	fs.StringVar(&o.extension, "extension", ".mdx", "extension for generated files")
+}
+
+func main() {
+	fs := flag.NewFlagSet("snippet-extract", flag.ContinueOnError)
+	opts := options{}
+	opts.AddFlagSets(fs)
+	if err := fs.Parse(os.Args[1:]); err != nil {
+		fs.Usage()
+		os.Exit(1)
+	}
+	wd, _ := os.Getwd()
+	fmt.Printf("working from %s\n", wd)
+	opts.filenames = extactFilenames(fs.Args())
+	for _, filename := range opts.filenames {
+		ext := filepath.Ext(filename)
+		snippets := extractSnippets(opts.begin, opts.end, filename)
+		for _, snippet := range snippets {
+			outputFile := filepath.Join(opts.outputDir, filepath.Base(filename), snippet.Identifier+opts.extension)
+			folder := filepath.Dir(outputFile)
+			err := os.MkdirAll(folder, os.ModePerm)
+			if err != nil {
+				log.Printf("cannot mkdir %s: %s", folder, err)
+			}
+			f := bytes.NewBuffer(nil)
+			fmt.Fprintf(f, `<!-- Code generated by snippet-extractor %s; DO NOT EDIT MANUALLY -->`, strings.Join(os.Args[1:], " "))
+			fmt.Fprintf(f, "\n\n```%s\n%s```\n", ext, snippet.Text)
+			err = ioutil.WriteFile(outputFile, f.Bytes(), 0600)
+			if err != nil {
+				log.Printf("cannot write %s in %s: %s", filepath.Base(outputFile), folder, err)
+			}
+		}
+	}
+}
+
+type snippet struct {
+	Identifier string
+	Text       string
+	Closed     bool
+}
+
+func extractSnippets(beginPattern, endPattern, filename string) []snippet {
+	file, err := os.Open(filename)
+	if err != nil {
+		log.Printf("could not open file: %s", err)
+		os.Exit(1)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+
+	snippets := []snippet{}
+	for scanner.Scan() {
+		line := scanner.Text()
+		if identifier := matches(line, beginPattern); identifier != "" {
+			snippets = append(snippets, snippet{
+				Identifier: identifier,
+			})
+			continue
+		}
+		if identifier := matches(line, endPattern); identifier != "" {
+			for i := range snippets {
+				snippet := &snippets[i]
+				if snippet.Identifier == identifier {
+					snippet.Closed = true
+				}
+			}
+			continue
+		}
+		for i := range snippets {
+			snippet := &snippets[i]
+			if snippet.Closed {
+				continue
+			}
+			snippet.Text = snippet.Text + line + "\n"
+		}
+	}
+	return snippets
+}
+
+func matches(s, prefix string) string {
+	trimmed := strings.TrimSpace(s)
+	lenDiff := len(s) - len(trimmed)
+	if strings.HasPrefix(trimmed, prefix) {
+		return s[len(prefix)+lenDiff:]
+	}
+	return ""
+}
+
+// if an entry is a directory all files from directory will be listed.
+func extactFilenames(in []string) []string {
+	out := []string{}
+	for _, path := range in {
+		fi, err := os.Stat(path)
+		if err != nil {
+			log.Fatalf("%s: %s", path, err)
+		}
+		if !fi.IsDir() {
+			out = append(out, path)
+			continue
+		}
+		files, err := ioutil.ReadDir(path)
+		if err != nil {
+			log.Fatalf("could not read directory %s: %s", path, err)
+		}
+		for _, file := range files {
+			if file.IsDir() {
+				continue
+			}
+			out = append(out, file.Name())
+		}
+	}
+	return in
+}