GroupsService: Create new GroupsService

This service is necessary as we plan to have functions to create and manipulate groups in the future.
The GroupInfoDto was moved from the file note-permissions.dto.ts to mimic the UserInfoDto.

Signed-off-by: Philip Molares <philip.molares@udo.edu>

src/groups/groups.service.ts

@@ -0,0 +1,57 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { Injectable } from '@nestjs/common';
+import { ConsoleLoggerService } from '../logger/console-logger.service';
+import { InjectRepository } from '@nestjs/typeorm';
+import { Repository } from 'typeorm';
+import { Group } from './group.entity';
+import { NotInDBError } from '../errors/errors';
+import { GroupInfoDto } from './group-info.dto';
+
+@Injectable()
+export class GroupsService {
+  constructor(
+    private readonly logger: ConsoleLoggerService,
+    @InjectRepository(Group) private groupRepository: Repository<Group>,
+  ) {
+    this.logger.setContext(GroupsService.name);
+  }
+
+  /**
+   * @async
+   * Get a group by their name.
+   * @param {string} name - the groups name
+   * @return {Group} the group
+   * @throws {NotInDBError} there is no group with this name
+   */
+  async getGroupByName(name: string): Promise<Group> {
+    const group = await this.groupRepository.findOne({
+      where: { name: name },
+    });
+    if (group === undefined) {
+      throw new NotInDBError(`Group with name '${name}' not found`);
+    }
+    return group;
+  }
+
+  /**
+   * Build GroupInfoDto from a group.
+   * @param {Group} group - the group to use
+   * @return {GroupInfoDto} the built GroupInfoDto
+   */
+  toGroupDto(group: Group | null | undefined): GroupInfoDto | null {
+    if (!group) {
+      this.logger.warn(`Recieved ${group} argument!`, 'toGroupDto');
+      return null;
+    }
+    return {
+      name: group.name,
+      displayName: group.displayName,
+      special: group.special,
+    };
+  }
+}