Improve theme display (#30671)

Document: https://gitea.com/gitea/docs/pulls/180

![image](https://github.com/go-gitea/gitea/assets/2114189/68e38573-b911-45d9-b7aa-40d96d836ecb)

services/webtheme/webtheme.go

@@ -4,6 +4,7 @@
 package webtheme
 
 import (
+	"regexp"
 	"sort"
 	"strings"
 	"sync"
@@ -12,63 +13,154 @@ import (
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/public"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/util"
 )
 
 var (
-	availableThemes    []string
-	availableThemesSet container.Set[string]
-	themeOnce          sync.Once
+	availableThemes             []*ThemeMetaInfo
+	availableThemeInternalNames container.Set[string]
+	themeOnce                   sync.Once
 )
 
+const (
+	fileNamePrefix = "theme-"
+	fileNameSuffix = ".css"
+)
+
+type ThemeMetaInfo struct {
+	FileName     string
+	InternalName string
+	DisplayName  string
+}
+
+func parseThemeMetaInfoToMap(cssContent string) map[string]string {
+	/*
+		The theme meta info is stored in the CSS file's variables of `gitea-theme-meta-info` element,
+		which is a privately defined and is only used by backend to extract the meta info.
+		Not using ":root" because it is difficult to parse various ":root" blocks when importing other files,
+		it is difficult to control the overriding, and it's difficult to avoid user's customized overridden styles.
+	*/
+	metaInfoContent := cssContent
+	if pos := strings.LastIndex(metaInfoContent, "gitea-theme-meta-info"); pos >= 0 {
+		metaInfoContent = metaInfoContent[pos:]
+	}
+
+	reMetaInfoItem := `
+(
+\s*(--[-\w]+)
+\s*:
+\s*(
+("(\\"|[^"])*")
+|('(\\'|[^'])*')
+|([^'";]+)
+)
+\s*;
+\s*
+)
+`
+	reMetaInfoItem = strings.ReplaceAll(reMetaInfoItem, "\n", "")
+	reMetaInfoBlock := `\bgitea-theme-meta-info\s*\{(` + reMetaInfoItem + `+)\}`
+	re := regexp.MustCompile(reMetaInfoBlock)
+	matchedMetaInfoBlock := re.FindAllStringSubmatch(metaInfoContent, -1)
+	if len(matchedMetaInfoBlock) == 0 {
+		return nil
+	}
+	re = regexp.MustCompile(strings.ReplaceAll(reMetaInfoItem, "\n", ""))
+	matchedItems := re.FindAllStringSubmatch(matchedMetaInfoBlock[0][1], -1)
+	m := map[string]string{}
+	for _, item := range matchedItems {
+		v := item[3]
+		if strings.HasPrefix(v, `"`) {
+			v = strings.TrimSuffix(strings.TrimPrefix(v, `"`), `"`)
+			v = strings.ReplaceAll(v, `\"`, `"`)
+		} else if strings.HasPrefix(v, `'`) {
+			v = strings.TrimSuffix(strings.TrimPrefix(v, `'`), `'`)
+			v = strings.ReplaceAll(v, `\'`, `'`)
+		}
+		m[item[2]] = v
+	}
+	return m
+}
+
+func defaultThemeMetaInfoByFileName(fileName string) *ThemeMetaInfo {
+	themeInfo := &ThemeMetaInfo{
+		FileName:     fileName,
+		InternalName: strings.TrimSuffix(strings.TrimPrefix(fileName, fileNamePrefix), fileNameSuffix),
+	}
+	themeInfo.DisplayName = themeInfo.InternalName
+	return themeInfo
+}
+
+func defaultThemeMetaInfoByInternalName(fileName string) *ThemeMetaInfo {
+	return defaultThemeMetaInfoByFileName(fileNamePrefix + fileName + fileNameSuffix)
+}
+
+func parseThemeMetaInfo(fileName, cssContent string) *ThemeMetaInfo {
+	themeInfo := defaultThemeMetaInfoByFileName(fileName)
+	m := parseThemeMetaInfoToMap(cssContent)
+	if m == nil {
+		return themeInfo
+	}
+	themeInfo.DisplayName = m["--theme-display-name"]
+	return themeInfo
+}
+
 func initThemes() {
 	availableThemes = nil
 	defer func() {
-		availableThemesSet = container.SetOf(availableThemes...)
-		if !availableThemesSet.Contains(setting.UI.DefaultTheme) {
+		availableThemeInternalNames = container.Set[string]{}
+		for _, theme := range availableThemes {
+			availableThemeInternalNames.Add(theme.InternalName)
+		}
+		if !availableThemeInternalNames.Contains(setting.UI.DefaultTheme) {
 			setting.LogStartupProblem(1, log.ERROR, "Default theme %q is not available, please correct the '[ui].DEFAULT_THEME' setting in the config file", setting.UI.DefaultTheme)
 		}
 	}()
 	cssFiles, err := public.AssetFS().ListFiles("/assets/css")
 	if err != nil {
 		log.Error("Failed to list themes: %v", err)
-		availableThemes = []string{setting.UI.DefaultTheme}
+		availableThemes = []*ThemeMetaInfo{defaultThemeMetaInfoByInternalName(setting.UI.DefaultTheme)}
 		return
 	}
-	var foundThemes []string
-	for _, name := range cssFiles {
-		name, ok := strings.CutPrefix(name, "theme-")
-		if !ok {
-			continue
+	var foundThemes []*ThemeMetaInfo
+	for _, fileName := range cssFiles {
+		if strings.HasPrefix(fileName, fileNamePrefix) && strings.HasSuffix(fileName, fileNameSuffix) {
+			content, err := public.AssetFS().ReadFile("/assets/css/" + fileName)
+			if err != nil {
+				log.Error("Failed to read theme file %q: %v", fileName, err)
+				continue
+			}
+			foundThemes = append(foundThemes, parseThemeMetaInfo(fileName, util.UnsafeBytesToString(content)))
 		}
-		name, ok = strings.CutSuffix(name, ".css")
-		if !ok {
-			continue
-		}
-		foundThemes = append(foundThemes, name)
 	}
 	if len(setting.UI.Themes) > 0 {
 		allowedThemes := container.SetOf(setting.UI.Themes...)
 		for _, theme := range foundThemes {
-			if allowedThemes.Contains(theme) {
+			if allowedThemes.Contains(theme.InternalName) {
 				availableThemes = append(availableThemes, theme)
 			}
 		}
 	} else {
 		availableThemes = foundThemes
 	}
-	sort.Strings(availableThemes)
+	sort.Slice(availableThemes, func(i, j int) bool {
+		if availableThemes[i].InternalName == setting.UI.DefaultTheme {
+			return true
+		}
+		return availableThemes[i].DisplayName < availableThemes[j].DisplayName
+	})
 	if len(availableThemes) == 0 {
 		setting.LogStartupProblem(1, log.ERROR, "No theme candidate in asset files, but Gitea requires there should be at least one usable theme")
-		availableThemes = []string{setting.UI.DefaultTheme}
+		availableThemes = []*ThemeMetaInfo{defaultThemeMetaInfoByInternalName(setting.UI.DefaultTheme)}
 	}
 }
 
-func GetAvailableThemes() []string {
+func GetAvailableThemes() []*ThemeMetaInfo {
 	themeOnce.Do(initThemes)
 	return availableThemes
 }
 
-func IsThemeAvailable(name string) bool {
+func IsThemeAvailable(internalName string) bool {
 	themeOnce.Do(initThemes)
-	return availableThemesSet.Contains(name)
+	return availableThemeInternalNames.Contains(internalName)
 }