Added added maxPeriodical checks

refs https://github.com/TryGhost/Team/issues/588

- This bit is putting together all the pieces for periodical limit checks. More tests are to come

ghost/limit-service/lib/limit.js

@@ -1,6 +1,6 @@
 // run in context allows us to change the templateSettings without causing havoc
 const _ = require('lodash').runInContext();
-const {SUPPORTED_INTERVALS} = require('./date-utils');
+const {lastPeriodStart, SUPPORTED_INTERVALS} = require('./date-utils');
 
 _.templateSettings.interpolate = /{{([\s\S]+?)}}/g;
 
@@ -155,6 +155,63 @@ class MaxPeriodicLimit extends Limit {
         this.startDate = config.startDate;
         this.fallbackMessage = `This action would exceed the ${_.lowerCase(this.name)} limit on your current plan.`;
     }
+
+    generateError(count) {
+        let errorObj = super.generateError();
+
+        errorObj.message = this.fallbackMessage;
+
+        if (this.error) {
+            try {
+                errorObj.message = _.template(this.error)(
+                    {
+                        max: Intl.NumberFormat().format(this.maxPeriodic),
+                        count: Intl.NumberFormat().format(count)
+                    });
+            } catch (e) {
+                errorObj.message = this.fallbackMessage;
+            }
+        }
+
+        errorObj.errorDetails.limit = this.maxPeriodic;
+        errorObj.errorDetails.total = count;
+
+        return new this.errors.HostLimitError(errorObj);
+    }
+
+    async currentCountQuery() {
+        const lastPeriodStartDate = lastPeriodStart(this.startDate, this.interval);
+
+        return await this.currentCountQueryFn(this.db, lastPeriodStartDate);
+    }
+
+    /**
+     * Throws a HostLimitError if the configured or passed max limit is ecceded by currentCountQuery
+     *
+     * @param {Object} options
+     * @param {Number} [options.max] - overrides configured default maxPeriodic value to perform checks against
+     */
+    async errorIfWouldGoOverLimit({max} = {}) {
+        let currentCount = await this.currentCountQuery(this.db);
+
+        if ((currentCount + 1) > (max || this.maxPeriodic)) {
+            throw this.generateError(currentCount);
+        }
+    }
+
+    /**
+     * Throws a HostLimitError if the configured or passed max limit is ecceded by currentCountQuery
+     *
+     * @param {Object} options
+     * @param {Number} [options.max] - overrides configured default maxPeriodic value to perform checks against
+     */
+    async errorIfIsOverLimit({max} = {}) {
+        let currentCount = await this.currentCountQuery(this.db);
+
+        if (currentCount > (max || this.maxPeriodic)) {
+            throw this.generateError(currentCount);
+        }
+    }
 }
 
 class FlagLimit extends Limit {

ghost/limit-service/test/limit.test.js

@@ -294,6 +294,42 @@ describe('Limit Service', function () {
                 }
             });
         });
+
+        describe('Is over limit', function () {
+            it('throws if is over the limit', async function () {
+                const currentCountyQueryMock = sinon.mock().returns(11);
+
+                const config = {
+                    maxPeriodic: 3,
+                    error: 'You have exceeded the number of emails you can send within your billing period.',
+                    interval: 'month',
+                    startDate: '2021-01-01T00:00:00Z',
+                    currentCountQuery: currentCountyQueryMock
+                };
+
+                try {
+                    const limit = new MaxPeriodicLimit({name: 'mailguard', config, errors});
+                    await limit.errorIfIsOverLimit();
+                } catch (error) {
+                    error.errorType.should.equal('HostLimitError');
+                    error.errorDetails.name.should.equal('mailguard');
+                    error.errorDetails.limit.should.equal(3);
+                    error.errorDetails.total.should.equal(11);
+
+                    currentCountyQueryMock.callCount.should.equal(1);
+                    should(currentCountyQueryMock.args).not.be.undefined();
+                    should(currentCountyQueryMock.args[0][0]).be.undefined(); //knex db connection
+
+                    const nowDate = new Date();
+                    const startOfTheMonthDate = new Date(Date.UTC(
+                        nowDate.getUTCFullYear(),
+                        nowDate.getUTCMonth()
+                    )).toISOString();
+
+                    currentCountyQueryMock.args[0][1].should.equal(startOfTheMonthDate);
+                }
+            });
+        });
     });
 
     describe('Allowlist limit', function () {