package issue

import (
	"regexp"
	"strings"
)

// A reference is a slug, or `#N` on an issue that came from a tracker.
var depRefRe = regexp.MustCompile(`#(\d+)|\b([a-z0-9]+(?:-[a-z0-9]+)+)\b`)

// DepRef is one dependency reference written in the body prose, carried out
// with the section it was found in.
//
// The section travels with the reference so a caller can name the one the
// reader actually has in front of them: a container's children come from
// `## Issues`, and pointing at `## Depends on` would name a section that is not
// in the file.
type DepRef struct {
	Section string
	Ref     string
}

// BodyDepRefs returns every reference under one of DepSections, deduplicated
// on first sight, in order of first appearance.
//
// Never from prose elsewhere, or a graph walk would drag in half the backlog.
func BodyDepRefs(body string) []DepRef {
	var out []DepRef
	seen := map[string]bool{}
	section := ""

	for _, line := range splitLines(body) {
		if strings.HasPrefix(line, "## ") {
			head := strings.TrimSpace(line)
			section = ""
			for _, s := range DepSections {
				if head == s {
					section = head
					break
				}
			}
			continue
		}
		if section == "" {
			continue
		}
		for _, tok := range depRefRe.FindAllStringSubmatch(line, -1) {
			ref := tok[2]
			if tok[1] != "" {
				ref = "#" + tok[1]
			}
			if !seen[ref] {
				seen[ref] = true
				out = append(out, DepRef{Section: section, Ref: ref})
			}
		}
	}
	return out
}