package gallery

import (
	"sort"
	"strings"

	"amadan.net/rastrillo/fiesta"
)

// formerRTL is the directory a theme's right-to-left twin had before
// every page moved under a locale: <theme>/rtl/<page>, beside the
// English <theme>/<page>. Those addresses were published, so they are
// redirected rather than left to 404.
const formerRTL = "rtl"

// Redirects are the _redirects rules, for a tree rendered for mount,
// that send each address the gallery had before its pages moved under
// a locale to the page that is there now, with a 301:
//
//	<theme>/                         <theme>/en/
//	<theme>/index.html               <theme>/en/
//	<theme>/<page>.html              <theme>/en/<page>.html
//	<theme>/frames/<example>/<state> <theme>/en/frames/<example>/<state>
//	<theme>/rtl/...                  the same under <theme>/ar/
//
// An index goes to its directory, the address the edge serves it at,
// since the edge sends .../index.html on to ./ and that would be a
// second hop. The rules are written so that no source can match a
// file of the tree, and no destination can match a source, so none
// shadows a page and none leads to another: every file of today's tree
// sits under <theme>/<locale>/ or assets/, and no locale is "frames",
// "rtl", "index.html" or a page's name. So <theme>/rtl/:page can be one
// rule, but an English page is named rule by rule: <theme>/:page would
// also match <theme>/en, the English tree's own directory. The pages
// named are the ones tree holds at <theme>/en/ in every theme, so each
// destination is a page whatever the theme. The order is fixed, so the
// same tree gives the same rules.
func Redirects(mount string, tree map[string][]byte) []string {
	m := cleanMount(mount)
	en, ar := Locales[0], rtlLocale()
	var out []string
	rule := func(from, to string) { out = append(out, m+from+"  "+m+to+"  301") }

	themes := fiesta.ThemeNames()
	for _, theme := range themes {
		rule("/"+theme, "/"+theme+"/"+en+"/")
	}
	rule("/:theme/index.html", "/:theme/"+en+"/")
	rule("/:theme/frames/:example/:state", "/:theme/"+en+"/frames/:example/:state")
	for _, page := range everyThemesPages(tree, themes, en) {
		rule("/:theme/"+page, "/:theme/"+en+"/"+page)
	}

	twin := "/:theme/" + formerRTL
	rule(twin, "/:theme/"+ar+"/")
	rule(twin+"/index.html", "/:theme/"+ar+"/")
	rule(twin+"/frames/:example/:state", "/:theme/"+ar+"/frames/:example/:state")
	rule(twin+"/:page", "/:theme/"+ar+"/:page")
	return out
}

// rtlLocale is the locale that renders right to left, where the former
// twins now live.
func rtlLocale() string {
	for _, l := range Locales {
		if Dir(l) == "rtl" {
			return l
		}
	}
	panic("gallery: no locale renders right to left")
}

// everyThemesPages are the names of the HTML pages directly under
// <theme>/<locale>/ for every theme, the index aside, sorted.
func everyThemesPages(tree map[string][]byte, themes []string, locale string) []string {
	count := map[string]int{}
	for name := range tree {
		for _, theme := range themes {
			page, ok := strings.CutPrefix(name, theme+"/"+locale+"/")
			if ok && !strings.Contains(page, "/") && strings.HasSuffix(page, ".html") && page != "index.html" {
				count[page]++
			}
		}
	}
	var pages []string
	for page, n := range count {
		if n == len(themes) {
			pages = append(pages, page)
		}
	}
	sort.Strings(pages)
	return pages
}