package step

import "strings"

const frontMatterRule = "---"

// Meta represents optional metadata that can occur at the very start of
// a document.
type Meta = map[string] string

// SplitMeta parses the metadata (if it exists), returning a map representing it
// along with the rest of the input as a string. If there is no metadata, an
// empty map will be returned.
func SplitMeta (input string) (Meta, string, error) {
	// i hate crlf!!!!! uwehhh!!! TODO remove
	input = strings.ReplaceAll(input, "\r\n", "\n")
	// TODO call internal function that takes in an io.Reader and scans it
	// by line instead of operating directly on the string. have that call
	// yet another function which will solve #11
	
	// stop if there is no front matter
	if !strings.HasPrefix(input, frontMatterRule + "\n") {
		return Meta { }, input, nil
	}

	// get the start and the end of the front matter
	input = strings.TrimPrefix(input, frontMatterRule)
	index := strings.Index(input, "\n" + frontMatterRule + "\n")
	if index < 0 {
		return nil, "", ErrMetaNeverClosed
	}
	frontMatterRaw := input[:index]
	body           := input[index + len(frontMatterRule) + 2:]

	// parse meta
	meta, err := ParseMeta(frontMatterRaw)
	if err != nil { return Meta { }, "", err }
	
	return meta, body, nil
}

// ParseMeta parses isolated metadata (without the horizontal starting and
// ending rules).
func ParseMeta (input string) (Meta, error) {
	meta := make(Meta)
	for _, line := range strings.Split(input, "\n") {
		line = strings.TrimSpace(line)
		if line == "" { continue }
		key, value, ok := strings.Cut(line, ":")
		if !ok {
			return nil, ErrMetaMalformed
		}
		key   = strings.ToLower(strings.TrimSpace(key))
		value = strings.TrimSpace(value)
		if key == "" {
			return nil, ErrMetaMalformed
		}
		if _, exists := meta[key]; exists {
			return nil, ErrMetaDuplicateKey
		}
		meta[key] = value
	}
	return meta, nil
}