Add user blocking (#29028)

Fixes #17453

This PR adds the abbility to block a user from a personal account or
organization to restrict how the blocked user can interact with the
blocker. The docs explain what's the consequence of blocking a user.

Screenshots:


![grafik](https://github.com/go-gitea/gitea/assets/1666336/4ed884f3-e06a-4862-afd3-3b8aa2488dc6)


![grafik](https://github.com/go-gitea/gitea/assets/1666336/ae6d4981-f252-4f50-a429-04f0f9f1cdf1)


![grafik](https://github.com/go-gitea/gitea/assets/1666336/ca153599-5b0f-4b4a-90fe-18bdfd6f0b6b)

---------

Co-authored-by: Lauris BH <lauris@nix.lv>

routers/api/v1/shared/block.go

@@ -0,0 +1,98 @@
+// Copyright 2024 The Gitea Authors.
+// SPDX-License-Identifier: MIT
+
+package shared
+
+import (
+	"errors"
+	"net/http"
+
+	user_model "code.gitea.io/gitea/models/user"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/routers/api/v1/utils"
+	"code.gitea.io/gitea/services/context"
+	"code.gitea.io/gitea/services/convert"
+	user_service "code.gitea.io/gitea/services/user"
+)
+
+func ListBlocks(ctx *context.APIContext, blocker *user_model.User) {
+	blocks, total, err := user_model.FindBlockings(ctx, &user_model.FindBlockingOptions{
+		ListOptions: utils.GetListOptions(ctx),
+		BlockerID:   blocker.ID,
+	})
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "FindBlockings", err)
+		return
+	}
+
+	if err := user_model.BlockingList(blocks).LoadAttributes(ctx); err != nil {
+		ctx.Error(http.StatusInternalServerError, "LoadAttributes", err)
+		return
+	}
+
+	users := make([]*api.User, 0, len(blocks))
+	for _, b := range blocks {
+		users = append(users, convert.ToUser(ctx, b.Blockee, blocker))
+	}
+
+	ctx.SetTotalCountHeader(total)
+	ctx.JSON(http.StatusOK, &users)
+}
+
+func CheckUserBlock(ctx *context.APIContext, blocker *user_model.User) {
+	blockee, err := user_model.GetUserByName(ctx, ctx.Params("username"))
+	if err != nil {
+		ctx.NotFound("GetUserByName", err)
+		return
+	}
+
+	status := http.StatusNotFound
+	blocking, err := user_model.GetBlocking(ctx, blocker.ID, blockee.ID)
+	if err != nil {
+		ctx.Error(http.StatusInternalServerError, "GetBlocking", err)
+		return
+	}
+	if blocking != nil {
+		status = http.StatusNoContent
+	}
+
+	ctx.Status(status)
+}
+
+func BlockUser(ctx *context.APIContext, blocker *user_model.User) {
+	blockee, err := user_model.GetUserByName(ctx, ctx.Params("username"))
+	if err != nil {
+		ctx.NotFound("GetUserByName", err)
+		return
+	}
+
+	if err := user_service.BlockUser(ctx, ctx.Doer, blocker, blockee, ctx.FormString("note")); err != nil {
+		if errors.Is(err, user_model.ErrCanNotBlock) || errors.Is(err, user_model.ErrBlockOrganization) {
+			ctx.Error(http.StatusBadRequest, "BlockUser", err)
+		} else {
+			ctx.Error(http.StatusInternalServerError, "BlockUser", err)
+		}
+		return
+	}
+
+	ctx.Status(http.StatusNoContent)
+}
+
+func UnblockUser(ctx *context.APIContext, doer, blocker *user_model.User) {
+	blockee, err := user_model.GetUserByName(ctx, ctx.Params("username"))
+	if err != nil {
+		ctx.NotFound("GetUserByName", err)
+		return
+	}
+
+	if err := user_service.UnblockUser(ctx, doer, blocker, blockee); err != nil {
+		if errors.Is(err, user_model.ErrCanNotUnblock) || errors.Is(err, user_model.ErrBlockOrganization) {
+			ctx.Error(http.StatusBadRequest, "UnblockUser", err)
+		} else {
+			ctx.Error(http.StatusInternalServerError, "UnblockUser", err)
+		}
+		return
+	}
+
+	ctx.Status(http.StatusNoContent)
+}