func newExamplesHandler()

in examples.go [55:122]
53 lines of code
11 McCabe index (conditional complexity)

func newExamplesHandler(gotip bool, modtime time.Time) (*examplesHandler, error) {
	const dir = "examples"
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, err
	}

	var examples []example
	for _, entry := range entries {
		name := entry.Name()

		// Read examples ending in .txt, skipping those ending in .gotip.txt if
		// gotip is not set.
		prefix := "" // if non-empty, this is a relevant example file
		if strings.HasSuffix(name, ".gotip.txt") {
			if gotip {
				prefix = strings.TrimSuffix(name, ".gotip.txt")
			}
		} else if strings.HasSuffix(name, ".txt") {
			prefix = strings.TrimSuffix(name, ".txt")
		}

		if prefix == "" {
			continue
		}

		data, err := os.ReadFile(filepath.Join(dir, name))
		if err != nil {
			return nil, err
		}
		content := string(data)

		// Extract the magic "// Title:" comment specifying the example's title.
		nl := strings.IndexByte(content, '\n')
		const titlePrefix = "// Title:"
		if nl == -1 || !strings.HasPrefix(content, titlePrefix) {
			return nil, fmt.Errorf("malformed example for %q: must start with a title line beginning %q", name, titlePrefix)
		}
		title := strings.TrimPrefix(content[:nl], titlePrefix)
		title = strings.TrimSpace(title)

		examples = append(examples, example{
			Title:   title,
			Path:    name,
			Content: content[nl+1:],
		})
	}

	// Sort by title, before prepending the hello example (we always want Hello
	// to be first).
	sort.Slice(examples, func(i, j int) bool {
		return examples[i].Title < examples[j].Title
	})

	// For Gotip, serve hello content that includes the Go version.
	hi := hello
	if gotip {
		hi = helloGotip
	}

	examples = append([]example{
		{"Hello, playground", "hello.txt", hi},
	}, examples...)
	return &examplesHandler{
		modtime:  modtime,
		examples: examples,
	}, nil
}