package browse

import (
	"regexp"
	"strings"
)

// llmsLinkRe matches `- [title](url): description` (the optional quoted
// title and the optional description are both per spec).
var llmsLinkRe = regexp.MustCompile(`^\s*[-*]\s+\[([^\]]*)\]\(([^)\s]+)(?:\s+"[^"]*")?\)\s*(?::\s*(.*))?$`)

// parseLlmsTxt parses an llms.txt document per llmstxt.org:
//
//	# Title            (required, exactly once, first)
//	> Summary          (optional blockquote)
//	## Section         (optional, starts a curated list)
//	> Section note     (optional, directly after the heading)
//	- [Link](https://…): what it is
//
// Everything that is not one of those shapes is ignored — the parsed doc
// describes what an agent can rely on, not everything the file contains.
func parseLlmsTxt(content string) *LlmsDoc {
	doc := &LlmsDoc{Sections: []LlmsSection{}}
	var section *LlmsSection
	seenTitle := false

	for _, line := range strings.Split(content, "\n") {
		t := strings.TrimSpace(line)
		switch {
		case strings.HasPrefix(t, "# ") && !seenTitle:
			doc.Title = strings.TrimSpace(t[2:])
			seenTitle = true
		case strings.HasPrefix(t, "## "):
			doc.Sections = append(doc.Sections, LlmsSection{
				Heading: strings.TrimSpace(t[3:]),
				Links:   []LlmsLink{},
			})
			section = &doc.Sections[len(doc.Sections)-1]
		case strings.HasPrefix(t, ">"):
			note := strings.TrimSpace(strings.TrimLeft(t, "> "))
			if note == "" {
				continue
			}
			switch {
			case !seenTitle:
				continue // blockquote before the title is not the summary
			case section != nil && section.Description == "":
				section.Description = note
			case section == nil:
				if doc.Description != "" {
					doc.Description += " "
				}
				doc.Description += note
			}
		default:
			m := llmsLinkRe.FindStringSubmatch(line)
			if m == nil {
				continue
			}
			link := LlmsLink{Title: m[1], URL: m[2], Description: strings.TrimSpace(m[3])}
			if section == nil {
				doc.Sections = append(doc.Sections, LlmsSection{Links: []LlmsLink{}})
				section = &doc.Sections[len(doc.Sections)-1]
			}
			section.Links = append(section.Links, link)
			doc.LinkCount++
		}
	}
	return doc
}