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App will now wait at least 1 week before requesting data from MongoDB…
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@DAG100
DAG100 committed Mar 10, 2024
1 parent 417841c commit 496b359
Showing 1 changed file with 136 additions and 109 deletions.
245 changes: 136 additions & 109 deletions components/data_worker.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -110,87 +110,128 @@ async function fetch_student_data() { //WILL throw errors when something goes wr
async function start_IDB() { //if this resolves, the global variable 'db' should contain a reference to the database - otherwise it should remain an empty string
return new Promise((resolve, reject) => {
db = "";
const openRequest = indexedDB.open("students", 1);
openRequest.addEventListener("error", (error) => {
// console.error("Failed to access local database.");
// console.log(error);
reject("Failed to access local database.");
}, {once: true});
openRequest.addEventListener("success", () => {
// console.log("Successfully opened IDB");
db = openRequest.result;
resolve("Success");
}, {once: true});
openRequest.addEventListener("upgradeneeded", (event) => {
//set up the DB, and if nothing goes wrong (i.e. no errors) then resolve successfully
// console.log("Setting up IDB");
db = event.target?.result;
const objStore = db.createObjectStore("students", {keyPath:"id", autoIncrement:true});
objStore.createIndex("students", "students", {unique: false}) //this will hold the array/json string of the response
// console.log("Finished setting up IDB");
//should trigger success event handler now, so we don't resolve the promise here
}, {once: true});
try {
const openRequest = indexedDB.open("students", 1);
openRequest.addEventListener("error", (error) => {
// console.error("Failed to access local database.");
// console.log(error);
reject("Failed to access local database.");
}, {once: true});
openRequest.addEventListener("success", () => {
// console.log("Successfully opened IDB");
db = openRequest.result;
resolve("Success");
}, {once: true});
openRequest.addEventListener("upgradeneeded", (event) => {
//set up the DB, and if nothing goes wrong (i.e. no errors) then resolve successfully
// console.log("Setting up IDB");
db = event.target?.result;
const objStore = db.createObjectStore("students", {keyPath:"id", autoIncrement:true});
objStore.createIndex("students", "students", {unique: false}) //this will hold the array/json string of the response
// console.log("Finished setting up IDB");
//should trigger success event handler now, so we don't resolve the promise here
}, {once: true});
} catch (error) {
reject(error);
}
})
}

async function get_time_IDB() {
//gets the last time data was added to the IDB (stored right after the actual array)
//same caveats as for update_ and check_IDB
//returns 0 on error so that any updates definitely go through
return new Promise(async (resolve, reject) => {
try {
await start_IDB();
let req = db
.transaction(["students"], "readonly")
.objectStore("students")
.get(2);
req.onerror = (e) => {
resolve(0);
}
req.onsuccess = (e) => {
if (!req.result) resolve(0);
resolve(req.result.time);
}
} catch (error) {
resolve(0);
}
});
}

//both of these assume that 'db' has the reference to the IndexedDB after 'start_IDB()' finishes - otherwise, will throw errors
async function update_IDB(students) {
await start_IDB();
//first: we get a cursor to see if there is already a record - if so, we delete it
//then, we store "students" into the DB
//this should all happen in one transaction so that if trxn fails, we don't end up with an empty DB or two items
let trxn = db.transaction(["students"], "readwrite");
// console.log("Opened transaction");
trxn.objectStore("students").openCursor().onsuccess = (event) => {
let cursor = event.target?.result;
if (cursor) {
// console.log("Deleting an entry");
trxn.objectStore("students").delete(cursor.value.id)
cursor.continue()
} else {
//no more entries left - so now we add the data from the global variable "students"
// console.log("All entries deleted");
// console.log("Adding students to DB");
// console.log(students);
trxn.objectStore("students").add({"students": students, "key":1});

return new Promise(async (resolve, reject) => {
try {
await start_IDB();
//first: delete all records (there will be 2: students and time)
//then, we store parameter students and Date.now() into the DB
//this should all happen in one transaction so that if trxn fails, we don't end up with an empty DB or two items
let trxn = db.transaction(["students"], "readwrite");
// console.log("Opened transaction");
trxn.objectStore("students").openCursor().onsuccess = (event) => {
let cursor = event.target?.result;
if (cursor) {
// console.log("Deleting an entry");
trxn.objectStore("students").delete(cursor.value.id)
cursor.continue() //move onto next item
} else {
//no more entries left, so store data now
// console.log("All entries deleted");
// console.log("Adding students to DB");
// console.log(students);
trxn.objectStore("students").add({"students": students, "key":1});
//add update time for future reference
trxn.objectStore("students").add({"time": Date.now(), "key": 2});
}
}
trxn.oncomplete = () => {
// console.log("Student data successfully saved locally.");
resolve("Success");
}
trxn.onerror = (error) => {
// console.error("Something went wrong when trying to update the local database.");
// console.error(error);
reject(error);
}
} catch (error) {
reject(error);
}
}
trxn.oncomplete = () => {
// console.log("Student data successfully saved locally.");
}
trxn.onerror = (error) => {
// console.error("Something went wrong when trying to update the local database.");
// console.error(error);
}
});
}

async function check_IDB() {
return new Promise(async (resolve, reject) => {
await start_IDB();
//just get a cursor and see if the record is there - if yes, put it into the global variable "students" - if not, throw an error
let trxn = db.transaction(["students"],"readwrite")
trxn.objectStore("students").openCursor().onsuccess = (event) => {
let cursor = event.target?.result;
if (cursor) {//if there is an entry
if (!Array.isArray(cursor.value.students)) {reject("IDB entry is improper")}
// console.log("Found the students data locally");
resolve(cursor.value.students);
// console.log("Dumping value of students to console");
// console.log(cursor.value.students);
} else {
reject("IDB is empty.");
try {
await start_IDB();
//just get by key
let req = db
.transaction(["students"],"readonly")
.objectStore("students")
.get(1);
req.onerror = (e) => {
reject(e);
}
}
trxn.onerror = (error) => {
// console.error("Error occurred when trying to access IDB.");
req.onsuccess = () => {
if (!req.result) {
reject("No IDB entry");
return;
}
if (!Array.isArray(req.result.students)) {
reject("IDB entry is improper");
return;
}

resolve(req.result.students);
}
} catch(error) {
reject(error);
}
//no need for an oncomplete handler
})
}


function prepare_worker() {//student data should be in a global variable called "students", and there should be a global variable "options" to take the list of options for everything
//after filling the "options" variable, send "Worker ready" message and set up onmessage handler
// console.log("prepare_worker() logging students:");
Expand Down Expand Up @@ -243,63 +284,49 @@ function prepare_worker() {//student data should be in a global variable called
postMessage(["Options", options]); //when worker processes everything it should send out options headers again
}

//actually do everything
// (async function () {
// try {
// // console.log("Trying to fetch data...");
// students = await fetch_student_data();
// // console.log("Fetched data, updating IDB...");
// update_IDB();
// } catch (error) {
// // console.log("Failed to fetch data");
// // console.error(error)
// try {
// // console.log("Checking if student data is locally available...")
// students = await check_IDB(); //if there is an error here, everything should fail because nothing can be done
// } catch (error) {
// // console.error("Something went wrong when checking for data locally.");
// postMessage("Error"); //so that app knows something has gone wrong and can show an error message
// throw error; //fail evarythang
// }
//
// }
// prepare_worker();
// })(); //execute immediately

//execute when starting
(async function () {
let error_count = 0;
let noLocalData = false;
let cantGetData = false;
let time = 0;
try {
console.log("Grabbing data locally...");
students = await check_IDB();
time = await get_time_IDB();
console.log("Most recent data retrieval occurred on:");
console.log(time);
console.log("Preparing worker using local data...");
prepare_worker();
} catch (error) {
console.error("Failed to find data locally");
console.error(error);
error_count += 1;
noLocalData = true;
}
try {
console.log("Fetching data from API...");
new_students = await fetch_student_data();
if (new_students == undefined) {
throw new Error("Failed to fetch student data from DB")
if (noLocalData || Date.now() - time > 1000*60*60*24*7) {
//update data every week
try {
console.log("Fetching data from API...");
new_students = await fetch_student_data();
if (new_students == undefined) {
throw new Error("Failed to fetch student data from DB")
}
console.log("Updating local DB with API data...");
update_IDB(new_students);
} catch (error) {
console.error("Failed to fetch data from API and update local DB");
console.error(error);
cantGetData = true;
}
if (new_students != undefined) {
console.log("New data was fetched, so re-preparing worker...");
students = new_students;
prepare_worker();
} else {
console.log("Failed to fetch new data, so worker was not re-prepared.");
}
console.log("Updating local DB with API data...");
update_IDB(new_students);
} catch (error) {
console.error("Failed to fetch data from API and update local DB");
console.error(error);
error_count += 1;
}
if (new_students != undefined) {
console.log("New data was fetched, so re-preparing worker...");
students = new_students;
prepare_worker();
} else {
console.log("Failed to fetch new data, so worker was not re-prepared.");
}

if (error_count === 2) {
if (noLocalData && cantGetData) {
postMessage("Error");
console.error("Could not find data locally or fetch it. This web app will not work.");
}
Expand Down

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