package core

import "strings"

// NavItem is one entry in the repo-scoped navigation -- the top tab bar
// and the page-nav chips both render the same slice, built from the route
// table so a new tab is a one-line addition to site/routes.go, not a
// second place to remember.
type NavItem struct {
	Label  string
	Href   string
	Active bool
}

// BuildNav derives the repo-scoped nav from every route whose NavLabel is
// set, in route-table order. current is the name of the route being
// served, used to mark the matching tab active.
func BuildNav(routes []Route, current, slug, ref string) []NavItem {
	if slug == "" {
		return nil
	}
	var items []NavItem
	for _, rt := range routes {
		if rt.Scope != ScopeRepo || rt.NavLabel == "" {
			continue
		}
		items = append(items, NavItem{
			Label: rt.NavLabel,
			Href:  navHref(rt, slug, ref),
			// The "repo" route (bare /{repo}/) renders tree.html at its
			// root, same as "tree" does at path "" -- so the files tab
			// lights up on both, even though "repo" carries no NavLabel
			// of its own and never appears in this loop as a tab.
			Active: rt.Name == current || (rt.Name == "tree" && current == "repo"),
		})
	}
	return items
}

// navHref builds the href for a nav tab from its route pattern: the fixed
// segment right after {repo}, plus the ref if the route is ref-addressed
// ({rest...} or {rev}). Routes addressed only by {$} (graph, refs) link to
// their bare index instead.
func navHref(rt Route, slug, ref string) string {
	seg := navSegment(rt.Pattern)
	href := "/" + slug + "/"
	if seg != "" {
		href += seg + "/"
	}
	if strings.Contains(rt.Pattern, "{rest...}") || strings.Contains(rt.Pattern, "{rev}") {
		href += ref
	}
	return href
}

// navSegment extracts the literal path element between {repo} and the
// next wildcard, e.g. "GET /{repo}/tree/{rest...}" -> "tree". Returns ""
// for patterns with no such segment (e.g. "GET /{repo}/{$}").
func navSegment(pattern string) string {
	p := pattern
	if i := strings.IndexByte(p, ' '); i >= 0 {
		p = p[i+1:]
	}
	p = strings.TrimPrefix(p, "/{repo}/")
	seg, _, _ := strings.Cut(p, "/")
	if strings.HasPrefix(seg, "{") {
		return ""
	}
	return seg
}