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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,155 @@ | ||
| import { DynamoDBClient } from "@aws-sdk/client-dynamodb" | ||
| import { DynamoDBDocumentClient, UpdateCommand, ScanCommand } from "@aws-sdk/lib-dynamodb" | ||
| import { Mutex, MutexInterface } from 'async-mutex' | ||
|
|
||
| type Coupon = { | ||
| id: string, | ||
| maxLimitAmount: number, | ||
| consumedAmount: number, | ||
| expiry: number, | ||
| } | ||
|
|
||
| type CouponConfig = { | ||
| IS_ENABLED: boolean, | ||
| MAX_LIMIT_CAP: number, | ||
| } | ||
|
|
||
| function validateCouponData(coupon: any, couponConfig: CouponConfig): Coupon | undefined { | ||
| if ( | ||
| coupon.id && | ||
| coupon.maxLimitAmount > 0 && | ||
| coupon.maxLimitAmount <= couponConfig.MAX_LIMIT_CAP && | ||
| coupon.consumedAmount <= coupon.maxLimitAmount && | ||
| coupon.expiry > 0 | ||
| ) { | ||
| return coupon | ||
| } | ||
|
|
||
| return undefined | ||
| } | ||
|
|
||
| export class CouponService { | ||
| private readonly mutex: MutexInterface | ||
| private readonly documentClient?: DynamoDBDocumentClient | ||
| private readonly couponConfig: CouponConfig | ||
| coupons: Map<string, Coupon> | ||
|
|
||
| constructor(couponConfig: CouponConfig) { | ||
| this.mutex = new Mutex() | ||
| this.coupons = new Map<string, Coupon>() | ||
| this.couponConfig = couponConfig | ||
|
|
||
| // Return early if coupon system is disabled | ||
| if (!couponConfig.IS_ENABLED) return | ||
|
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| const ddbClient = new DynamoDBClient({ region: 'us-east-1' }) | ||
| this.documentClient = DynamoDBDocumentClient.from(ddbClient) | ||
|
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||
| this.syncCoupons() | ||
|
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| // Syncs coupon between DynamoDB and memory at regular intervals | ||
| setInterval(() => { | ||
| this.syncCoupons() | ||
| }, 10_000) | ||
| } | ||
|
|
||
| /** | ||
| * Syncs coupons in memory with database | ||
| * 1. Fetches new coupons from database into memory | ||
| * 2. Remove coupons which were deleted in database from memory | ||
| * 3. Updates coupon usage limits in database | ||
| * 4. TODO(raj): Delete expired (or few days after expiry) coupons from database | ||
| */ | ||
| private async syncCoupons(): Promise<void> { | ||
| const params = new ScanCommand({ | ||
| TableName: 'coupons', | ||
| }) | ||
|
|
||
| const result = await this.documentClient?.send(params) | ||
|
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||
| // Required for quick lookup of coupons in DB fetched list | ||
| const dbItemSet = new Set<string>() | ||
|
|
||
| // Fetches new coupons from database into memory | ||
| result?.Items?.forEach((item: Record<string, any>) => { | ||
| const coupon: Coupon | undefined = validateCouponData(item, this.couponConfig) | ||
| if (coupon) { | ||
| dbItemSet.add(coupon.id) | ||
|
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||
| // Only load new coupons into memory | ||
| if (this.coupons.get(coupon.id) === undefined) { | ||
| this.coupons.set(coupon.id, coupon) | ||
| } | ||
| } else { | ||
| console.log("fetched invalid coupon data:", item) | ||
| } | ||
| }) | ||
|
|
||
| // Remove coupons which were deleted in database from memory | ||
| for (const [id, _item] of this.coupons.entries()) { | ||
| if (!dbItemSet.has(id)) { | ||
| this.coupons.delete(id) | ||
| } | ||
| } | ||
|
|
||
| // Updates coupon usage limits in database | ||
| await this.batchUpdateCoupons() | ||
| } | ||
|
|
||
| // Iterates over every coupon in memory and updates database with their `consumedAmount` | ||
| async batchUpdateCoupons(): Promise<void> { | ||
| this.coupons.forEach(async (couponItem, _id) => { | ||
| const updateRequest = { | ||
| TableName: 'coupons', | ||
| Key: { | ||
| id: couponItem.id, | ||
| }, | ||
| UpdateExpression: 'SET consumedAmount = :consumedAmount', | ||
| ExpressionAttributeValues: { | ||
| ':consumedAmount': couponItem.consumedAmount, | ||
| }, | ||
| } | ||
|
|
||
| const params = new UpdateCommand(updateRequest) | ||
| await this.documentClient?.send(params) | ||
| }) | ||
| } | ||
|
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||
| async consumeCouponAmount(id: string, amount: number): Promise<boolean> { | ||
| // Return `true` early, if coupon system is disabled (for debugging) | ||
| if (!this.couponConfig.IS_ENABLED) return true | ||
|
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||
| const release = await this.mutex.acquire() | ||
| try { | ||
| const coupon = this.coupons.get(id) | ||
| if ( | ||
| coupon && | ||
| coupon.expiry > (Date.now() / 1000) && | ||
| coupon.consumedAmount + amount < coupon.maxLimitAmount | ||
| ) { | ||
| coupon.consumedAmount += amount | ||
| return true | ||
| } | ||
| return false | ||
| } finally { | ||
| release() | ||
| } | ||
| } | ||
|
|
||
| async reclaimCouponAmount(id: string, amount: number): Promise<void> { | ||
| const release = await this.mutex.acquire() | ||
|
|
||
| try { | ||
| const coupon = this.coupons.get(id) | ||
| if ( | ||
| coupon && | ||
| coupon.expiry > (Date.now() / 1000) && | ||
| coupon.consumedAmount - amount > 0 | ||
| ) { | ||
| coupon.consumedAmount -= amount | ||
| } | ||
| } finally { | ||
| release() | ||
| } | ||
| } | ||
| } |
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