Problem 2.42 - Bearing Stress

[Problem adapted from © Kurt Gramoll CC BY NC-SA 4.0]

#| standalone: true
#| viewerHeight: 600
#| components: [viewer]

from shiny import App, render, ui, reactive
import random
import asyncio
import io
import math
import string
from datetime import datetime
from pathlib import Path

def generate_random_letters(length):
    # Generate a random string of letters of specified length
    return "".join(random.choice(string.ascii_lowercase) for _ in range(length))

problem_ID = "172"
a = reactive.Value("__")
b = reactive.Value("__")
F = reactive.Value("__")

attempts = ["Timestamp,Attempt,Answer,Feedback\n"]

app_ui = ui.page_fluid(
    ui.markdown(
        "**Please enter your ID number from your instructor and click to generate your problem**"
    ),
    ui.input_text("ID", "", placeholder="Enter ID Number Here"),
    ui.input_action_button(
        "generate_problem", "Generate Problem", class_="btn-primary"
    ),
    ui.markdown("**Problem Statement**"),
    ui.output_ui("ui_problem_statement"),
    ui.input_text(
        "answer", "Your Answer in units of MPa", placeholder="Please enter your answer"
    ),
    ui.input_action_button("submit", "Submit Answer", class_="btn-primary"),
    ui.download_button("download", "Download File to Submit", class_="btn-success"),
)

def server(input, output, session):
    # Initialize a counter for attempts
    attempt_counter = reactive.Value(0)

    @output
    @render.ui
    def ui_problem_statement():
        return [
            ui.markdown(
                f"A hanger is mounted to a wall with a rectangular bar as shown. Let dimension a = {a()} mm and b = {b()} mm. Determine the largest stress in either the hanger or the bar holding it to the wall. Assume load F = {F()} kN. Consider the normal stress in both components, the shear stress in both components, and the bearing stress between the components."
            )
        ]

    @reactive.Effect
    @reactive.event(input.generate_problem)
    def randomize_vars():
        random.seed(input.ID())
        a.set(random.randrange(100,300,2)/10)
        b.set(round(a()*1.2,1))
        F.set(random.randrange(10,70,1))

    @reactive.Effect
    @reactive.event(input.submit)
    def _():
        attempt_counter.set(
            attempt_counter() + 1
        )  # Increment the attempt counter on each submission.
        sigmaN = F()/2/(b()*a())*10**3
        sigmaBH = F()/(a()*a())*10**3
        tauH = F()/2/(a()*a())*10**3
        tauR = F()/(a()*b())*10**3
        instr = max(sigmaN, sigmaBH, tauH, tauR)
        
        if math.isclose(float(input.answer()), instr, rel_tol=0.01):
            check = "*Correct*"
            correct_indicator = "JL"
        else:
            check = "*Not Correct.*"
            correct_indicator = "JG"

        # Generate random parts for the encoded attempt.
        random_start = generate_random_letters(4)
        random_middle = generate_random_letters(4)
        random_end = generate_random_letters(4)
        encoded_attempt = f"{random_start}{problem_ID}-{random_middle}{attempt_counter()}{correct_indicator}-{random_end}{input.ID()}"

        # Store the most recent encoded attempt in a reactive value so it persists across submissions
        session.encoded_attempt = reactive.Value(encoded_attempt)

        # Append the attempt data to the attempts list without the encoded attempt
        attempts.append(
            f"{datetime.now()}, {attempt_counter()}, {input.answer()}, {check}\n"
        )

        # Show feedback to the user.
        feedback = ui.markdown(
            f"Your answer of {input.answer()} is {check}."
        )
        m = ui.modal(feedback, title="Feedback", easy_close=True)
        ui.modal_show(m)

    @session.download(filename=lambda: f"Problem_Log-{problem_ID}-{input.ID()}.csv")
    async def download():
        # Start the CSV with the encoded attempt (without label)
        final_encoded = (
            session.encoded_attempt()
            if session.encoded_attempt is not None
            else "No attempts"
        )
        yield f"{final_encoded}\n\n"

        # Write the header for the remaining CSV data once
        yield "Timestamp,Attempt,Answer,Feedback\n"

        # Write the attempts data, ensure that the header from the attempts list is not written again
        for attempt in attempts[1:]:  # Skip the first element which is the header
            await asyncio.sleep(
                0.25
            )  # This delay may not be necessary; adjust as needed
            yield attempt

# App installation
app = App(app_ui, server)