package web

import (
	"crypto/sha256"
	"embed"
	"encoding/hex"
	"fmt"
	"io/fs"
	"path"
	"strings"
)

//go:embed static
var staticFS embed.FS

var assetTypes = map[string]string{
	".css": "text/css; charset=utf-8",
	".js":  "text/javascript; charset=utf-8",
	".svg": "image/svg+xml",
}

type asset struct {
	contentType string
	etag        string
	body        []byte
}

type assetNames struct {
	CSS  string
	JS   string
	Icon string
}

func (n assetNames) under(prefix string) assetNames {
	move := func(p string) string {
		if p == "" {
			return ""
		}
		return prefix + strings.TrimPrefix(p, "/static/")
	}
	return assetNames{CSS: move(n.CSS), JS: move(n.JS), Icon: move(n.Icon)}
}

type assetTable struct {
	byPath map[string]asset
	names  assetNames
}

func loadAssets(fsys fs.FS) (assetTable, error) {
	files, err := fs.Glob(fsys, "static/*")
	if err != nil {
		return assetTable{}, err
	}
	t := assetTable{byPath: map[string]asset{}}
	for _, f := range files {
		body, err := fs.ReadFile(fsys, f)
		if err != nil {
			return assetTable{}, err
		}
		ext := path.Ext(f)
		ct, ok := assetTypes[ext]
		if !ok {
			return assetTable{}, fmt.Errorf("static asset %s has no known content type", f)
		}
		sum := sha256.Sum256(body)
		hash := hex.EncodeToString(sum[:])[:12]
		stem := strings.TrimSuffix(path.Base(f), ext)
		p := "/static/" + stem + "." + hash + ext
		t.byPath[p] = asset{contentType: ct, etag: `"` + hash + `"`, body: body}
		switch path.Base(f) {
		case "tug.css":
			t.names.CSS = p
		case "enhance.js":
			t.names.JS = p
		case "favicon.svg":
			t.names.Icon = p
		}
	}
	if t.names.CSS == "" || t.names.Icon == "" {
		return assetTable{}, fmt.Errorf("the stylesheet and the favicon are required static assets")
	}
	return t, nil
}