patchwork

package doc

import (
	"strings"

	"gopkg.in/yaml.v3"
)

// splitFrontmatter separates a leading YAML block delimited by "---" lines,
// the convention gray-matter, Hugo, Eleventy and Astro share. A file whose
// first line is "---" but never closes it has no frontmatter.
func splitFrontmatter(text string) (yamlSrc, body string, ok bool) {
	first, rest, found := strings.Cut(text, "\n")
	if !found || strings.TrimRight(first, " \t") != "---" {
		return "", text, false
	}
	offset := 0
	for {
		line, after, more := strings.Cut(rest[offset:], "\n")
		if t := strings.TrimRight(line, " \t"); t == "---" || t == "..." {
			return rest[:offset], after, true
		}
		if !more {
			return "", text, false
		}
		offset += len(line) + 1
	}
}

func parseFrontmatter(src string) (map[string]any, error) {
	fm := map[string]any{}
	if strings.TrimSpace(src) == "" {
		return fm, nil
	}
	if err := yaml.Unmarshal([]byte(src), &fm); err != nil {
		return map[string]any{}, err
	}
	if fm == nil {
		fm = map[string]any{}
	}
	return fm, nil
}

// stringField reads a scalar frontmatter value as trimmed text. YAML turns
// `revision: 2` into an int and `maturity: yes` into a bool; the author still
// meant the words.
func stringField(fm map[string]any, key string) string {
	v, ok := fm[key]
	if !ok || v == nil {
		return ""
	}
	switch t := v.(type) {
	case string:
		return strings.TrimSpace(t)
	case []any, map[string]any:
		return ""
	}
	b, err := yaml.Marshal(v)
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(b))
}