package theme

import (
	"embed"
	"net/http"
	"strings"
)

// Onest is Calma's typeface: the Latin subset of the variable font
// (weights 300-800), SIL Open Font License 1.1. Provenance and the
// licence are in credits/notices/onest-*; list them on the app's credits
// page with credits.Onest().

//go:embed fonts/onest-latin.woff2
var fontFS embed.FS

// FontPrefix is the URL path FontHandler serves under. Its version moves
// whenever either file's bytes do (a new subset, a newer Onest, a changed
// unicode-range): browsers hold both for a year under this path.
const FontPrefix = "/static/estilo/fonts/v1/"

// fontCSS declares Onest for the Latin range; a character outside it
// falls through to the system face in --rst-font, glyph by glyph.
const fontCSS = `/* Onest, Calma's typeface (estilo theme/fonts.go). */
@font-face {
  font-family: "Onest";
  font-style: normal;
  font-weight: 300 800;
  font-display: swap;
  src: url("` + FontPrefix + `onest-latin.woff2") format("woff2");
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+0304, U+0308, U+0329, U+2000-206F, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
}
`

// FontCSS is the @font-face stylesheet, served by FontHandler as
// FontPrefix + "fonts.css". Link it before theme.css. Without it the
// theme still works, in the system face.
func FontCSS() []byte { return []byte(fontCSS) }

// FontHandler serves GET and HEAD for FontPrefix + "fonts.css" and
// FontPrefix + "onest-latin.woff2". Mount it at FontPrefix; anything else
// under it is 404. Public, sessionless, and the bytes never change under
// a name, so both are cached for a year.
func FontHandler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		name := strings.TrimPrefix(r.URL.Path, FontPrefix)
		var body []byte
		var kind string
		switch {
		case !strings.HasPrefix(r.URL.Path, FontPrefix):
		case name == "fonts.css":
			body, kind = FontCSS(), "text/css; charset=utf-8"
		case name == "onest-latin.woff2":
			body, _ = fontFS.ReadFile("fonts/onest-latin.woff2")
			kind = "font/woff2"
		}
		if body == nil {
			http.NotFound(w, r)
			return
		}
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			w.Header().Set("Allow", "GET, HEAD")
			http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
			return
		}
		w.Header().Set("Content-Type", kind)
		w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
		w.Header().Set("X-Content-Type-Options", "nosniff")
		if r.Method == http.MethodHead {
			return
		}
		_, _ = w.Write(body)
	})
}