Implement 'LeaveGroup' resolver

backend/src/db/graphql/groups.js

@@ -106,6 +106,17 @@ export const joinGroupMutation = gql`
   }
 `
 
+export const leaveGroupMutation = gql`
+  mutation ($groupId: ID!, $userId: ID!) {
+    LeaveGroup(groupId: $groupId, userId: $userId) {
+      id
+      name
+      slug
+      myRoleInGroup
+    }
+  }
+`
+
 export const changeGroupMemberRoleMutation = gql`
   mutation ($groupId: ID!, $userId: ID!, $roleInGroup: GroupMemberRole!) {
     ChangeGroupMemberRole(groupId: $groupId, userId: $userId, roleInGroup: $roleInGroup) {

backend/src/middleware/permissionsMiddleware.js

@@ -191,6 +191,36 @@ const isAllowedToJoinGroup = rule({
   }
 })
 
+const isAllowedToLeaveGroup = rule({
+  cache: 'no_cache',
+})(async (_parent, args, { user, driver }) => {
+  if (!(user && user.id)) return false
+  const { groupId, userId } = args
+  if (user.id !== userId) return false
+  const session = driver.session()
+  const readTxPromise = session.readTransaction(async (transaction) => {
+    const transactionResponse = await transaction.run(
+      `
+        MATCH (member:User {id: $userId})-[membership:MEMBER_OF]->(group:Group {id: $groupId})
+        RETURN group {.*}, member {.*, myRoleInGroup: membership.role}
+      `,
+      { groupId, userId },
+    )
+    return {
+      group: transactionResponse.records.map((record) => record.get('group'))[0],
+      member: transactionResponse.records.map((record) => record.get('member'))[0],
+    }
+  })
+  try {
+    const { group, member } = await readTxPromise
+    return !!group && !!member && !!member.myRoleInGroup && member.myRoleInGroup !== 'owner'
+  } catch (error) {
+    throw new Error(error)
+  } finally {
+    session.close()
+  }
+})
+
 const isAuthor = rule({
   cache: 'no_cache',
 })(async (_parent, args, { user, driver }) => {
@@ -284,6 +314,7 @@ export default shield(
       CreateGroup: isAuthenticated,
       UpdateGroup: isAllowedToChangeGroupSettings,
       JoinGroup: isAllowedToJoinGroup,
+      LeaveGroup: isAllowedToLeaveGroup,
       ChangeGroupMemberRole: isAllowedToChangeGroupMemberRole,
       CreatePost: isAuthenticated,
       UpdatePost: isAuthor,

backend/src/schema/resolvers/groups.js

@@ -251,6 +251,27 @@ export default {
         session.close()
       }
     },
+    LeaveGroup: async (_parent, params, context, _resolveInfo) => {
+      const { groupId, userId } = params
+      const session = context.driver.session()
+      const writeTxResultPromise = session.writeTransaction(async (transaction) => {
+        const leaveGroupCypher = `
+          MATCH (member:User {id: $userId})-[membership:MEMBER_OF]->(group:Group {id: $groupId})
+          DELETE membership
+          RETURN member {.*, myRoleInGroup: NULL}
+        `
+        const transactionResponse = await transaction.run(leaveGroupCypher, { groupId, userId })
+        const [member] = await transactionResponse.records.map((record) => record.get('member'))
+        return member
+      })
+      try {
+        return await writeTxResultPromise
+      } catch (error) {
+        throw new Error(error)
+      } finally {
+        session.close()
+      }
+    },
     ChangeGroupMemberRole: async (_parent, params, context, _resolveInfo) => {
       const { groupId, userId, roleInGroup } = params
       const session = context.driver.session()

backend/src/schema/types/type/Group.gql

@@ -117,6 +117,11 @@ type Mutation {
     userId: ID!
   ): User
 
+  LeaveGroup(
+    groupId: ID!
+    userId: ID!
+  ): User
+
   ChangeGroupMemberRole(
     groupId: ID!
     userId: ID!

webapp/graphql/groups.js

@@ -106,6 +106,17 @@ export const joinGroupMutation = gql`
   }
 `
 
+export const leaveGroupMutation = gql`
+  mutation ($groupId: ID!, $userId: ID!) {
+    LeaveGroup(groupId: $groupId, userId: $userId) {
+      id
+      name
+      slug
+      myRoleInGroup
+    }
+  }
+`
+
 export const changeGroupMemberRoleMutation = gql`
   mutation ($groupId: ID!, $userId: ID!, $roleInGroup: GroupMemberRole!) {
     ChangeGroupMemberRole(groupId: $groupId, userId: $userId, roleInGroup: $roleInGroup) {