Add language statistics API endpoint (#11737)

* Add language statistics API

* Add tests

routers/api/v1/repo/language.go

@@ -0,0 +1,84 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package repo
+
+import (
+	"bytes"
+	"net/http"
+	"strconv"
+
+	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/log"
+)
+
+type languageResponse []*models.LanguageStat
+
+func (l languageResponse) MarshalJSON() ([]byte, error) {
+	var buf bytes.Buffer
+	if _, err := buf.WriteString("{"); err != nil {
+		return nil, err
+	}
+	for i, lang := range l {
+		if i > 0 {
+			if _, err := buf.WriteString(","); err != nil {
+				return nil, err
+			}
+		}
+		if _, err := buf.WriteString(strconv.Quote(lang.Language)); err != nil {
+			return nil, err
+		}
+		if _, err := buf.WriteString(":"); err != nil {
+			return nil, err
+		}
+		if _, err := buf.WriteString(strconv.FormatInt(lang.Size, 10)); err != nil {
+			return nil, err
+		}
+	}
+	if _, err := buf.WriteString("}"); err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+// GetLanguages returns languages and number of bytes of code written
+func GetLanguages(ctx *context.APIContext) {
+	// swagger:operation GET /repos/{owner}/{repo}/languages repository repoGetLanguages
+	// ---
+	// summary: Get languages and number of bytes of code written
+	// produces:
+	//   - application/json
+	// parameters:
+	// - name: owner
+	//   in: path
+	//   description: owner of the repo
+	//   type: string
+	//   required: true
+	// - name: repo
+	//   in: path
+	//   description: name of the repo
+	//   type: string
+	//   required: true
+	// responses:
+	//   "404":
+	//     "$ref": "#/responses/notFound"
+	//   "200":
+	//     "$ref": "#/responses/LanguageStatistics"
+
+	langs, err := ctx.Repo.Repository.GetLanguageStats()
+	if err != nil {
+		log.Error("GetLanguageStats failed: %v", err)
+		ctx.InternalServerError(err)
+		return
+	}
+
+	resp := make(languageResponse, len(langs))
+	for i, v := range langs {
+		resp[i] = v
+	}
+
+	ctx.JSON(http.StatusOK, resp)
+}