From cdb6f1c3fe5223d7bc8623b73fc58745505ce190 Mon Sep 17 00:00:00 2001
From: forceoranj <forceoranj@gmail.com>
Date: Tue, 16 Nov 2021 17:32:58 +0100
Subject: [PATCH] Adds gSheet read cache

---
 src/gsheets/DBManager.ts              | 64 +++++++++++++++++++++++++++
 src/gsheets/accessors.ts              | 12 ++---
 src/gsheets/sequentialDBOperations.ts | 30 -------------
 3 files changed, 70 insertions(+), 36 deletions(-)
 create mode 100644 src/gsheets/DBManager.ts
 delete mode 100644 src/gsheets/sequentialDBOperations.ts

diff --git a/src/gsheets/DBManager.ts b/src/gsheets/DBManager.ts
new file mode 100644
index 0000000..03e0728
--- /dev/null
+++ b/src/gsheets/DBManager.ts
@@ -0,0 +1,64 @@
+const CACHE_RENEW_DELAY = 10000
+
+export default function DBManager<OperationReturn>(): any {
+    type OperationType = "add" | "list" | "set"
+
+    interface Operation {
+        task: () => Promise<OperationReturn>
+        type: OperationType
+        resolve: (value: OperationReturn) => void
+        reject: (reason: unknown) => void
+    }
+
+    let cache: any
+    let cacheTime = 0
+
+    const operations: Operation[] = []
+
+    async function addDBOperation(type: OperationType, task: () => Promise<OperationReturn>) {
+        console.log(`New ${type} DB Operation in line.`)
+        return new Promise(
+            (resolve: (value: OperationReturn) => void, reject: (reason: unknown) => void) => {
+                operations.push({ task, type, resolve, reject })
+                if (operations.length === 1) {
+                    runOperation(operations[0])
+                }
+            }
+        )
+    }
+
+    function runNextDBOperation(): void {
+        operations.shift()
+        console.log("DB Operation completed.")
+        if (operations[0]) {
+            runOperation(operations[0])
+        }
+    }
+
+    function runOperation(operation: Operation): void {
+        const { task, type, resolve, reject } = operation
+        if (type === "list") {
+            const now = +new Date()
+            if (now < cacheTime + CACHE_RENEW_DELAY) {
+                console.log("Using cache")
+                resolve(cache)
+                runNextDBOperation()
+            } else {
+                console.log("Refreshing cache")
+                task()
+                    .then((val: OperationReturn) => {
+                        cache = val
+                        cacheTime = now
+                        resolve(val)
+                    })
+                    .catch(reject)
+                    .finally(runNextDBOperation)
+            }
+        } else {
+            cacheTime = 0
+            task().then(resolve).catch(reject).finally(runNextDBOperation)
+        }
+    }
+
+    return addDBOperation
+}
diff --git a/src/gsheets/accessors.ts b/src/gsheets/accessors.ts
index b2137b1..854f35b 100644
--- a/src/gsheets/accessors.ts
+++ b/src/gsheets/accessors.ts
@@ -3,9 +3,9 @@ import _ from "lodash"
 import { promises as fs } from "fs"
 import { GoogleSpreadsheet, GoogleSpreadsheetWorksheet } from "google-spreadsheet"
 
-import sequentialDBOperations from "./sequentialDBOperations"
+import DBManager from "./DBManager"
 
-const addDBOperation = sequentialDBOperations()
+const addDBOperation = DBManager()
 
 const SCOPES = ["https://www.googleapis.com/auth/spreadsheets"]
 const CRED_PATH = path.resolve(process.cwd(), "access/gsheets.json")
@@ -17,7 +17,7 @@ export async function listGet<Element extends ElementWithId>(
     specimen: Element
 ): Promise<Element[]> {
     type StringifiedElement = Record<keyof Element, string>
-    return addDBOperation(async () => {
+    return addDBOperation("list", async () => {
         const sheet = await getGSheet(sheetName)
 
         // Load sheet into an array of objects
@@ -57,7 +57,7 @@ export async function setList<Element extends ElementWithId>(
     sheetName: string,
     elements: Element[]
 ): Promise<true | undefined> {
-    return addDBOperation(async () => {
+    return addDBOperation("listSet", async () => {
         const sheet = await getGSheet(sheetName)
 
         // Load sheet into an array of objects
@@ -117,7 +117,7 @@ export async function set<Element extends ElementWithId>(
     if (!element) {
         return undefined
     }
-    return addDBOperation(async () => {
+    return addDBOperation("set", async () => {
         const sheet = await getGSheet(sheetName)
 
         // Load sheet into an array of objects
@@ -148,7 +148,7 @@ export async function add<ElementNoId extends object, Element extends ElementNoI
     if (!partialElement) {
         return undefined
     }
-    return addDBOperation(async () => {
+    return addDBOperation("add", async () => {
         const sheet = await getGSheet(sheetName)
 
         // Load sheet into an array of objects
diff --git a/src/gsheets/sequentialDBOperations.ts b/src/gsheets/sequentialDBOperations.ts
deleted file mode 100644
index 62c3105..0000000
--- a/src/gsheets/sequentialDBOperations.ts
+++ /dev/null
@@ -1,30 +0,0 @@
-export default function sequentialDBOperations<OperationReturn>(): any {
-    interface Operation {
-        task: () => Promise<OperationReturn>
-        resolve: (value: OperationReturn) => void
-        reject: (reason: unknown) => void
-    }
-
-    const operations: Operation[] = []
-
-    async function addDBOperation(task: () => Promise<OperationReturn>) {
-        return new Promise(
-            (resolve: (value: OperationReturn) => void, reject: (reason: unknown) => void) => {
-                operations.push({ task, resolve, reject })
-                if (operations.length === 1) {
-                    task().then(resolve).catch(reject).finally(runNextDBOperation)
-                }
-            }
-        )
-    }
-
-    function runNextDBOperation(): void {
-        operations.shift()
-        if (operations[0]) {
-            const { task, resolve, reject } = operations[0]
-            task().then(resolve).catch(reject).finally(runNextDBOperation)
-        }
-    }
-
-    return addDBOperation
-}