Cat food calculator

app.py

# Editor: https://shinylive.io/py/editor/#gist=697a9f02c3c000de6ae4b10ac1e725eb
# App: https://shinylive.io/py/app/#gist=697a9f02c3c000de6ae4b10ac1e725eb

from pathlib import Path
from shiny import ui, render, App, Inputs, Outputs, Session


calories_target = 200

app_ui = ui.page_fluid(
    ui.panel_title("Cat food calculator"),
    ui.tags.p(f"Specify daily intake for 1 cat (target intake is {calories_target} kcal)."),
    ui.row(
        ui.column(6, ui.panel_well(
            ui.tags.h4("Wet food"),
            ui.input_numeric("calories_per_can", "Calories per can [kcal]:", 177),
            ui.input_numeric("n_cans", "Number of cans:", 0.5)
        )),
        ui.column(6, ui.panel_well(
            ui.tags.h4("Dry food"),
            ui.input_numeric("calories_per_gram", "Calories per gram [kcal]:", 3.99),
            ui.tags.b("Calculated meal size:", style="color:green"),
            ui.output_text("result")
        ))
    )   
)

def check_positive_number(x, msg):
    if x is None or x <= 0:
        raise ValueError(msg)

def server(input: Inputs, output: Outputs, session: Session):
    @output
    @render.text
    def result():
        check_positive_number(input.calories_per_can(), "Invalid calories per can")
        check_positive_number(input.n_cans(), "Invalid number of cans")
        check_positive_number(input.calories_per_gram(), "Invalid calories per gram")
        
        calories_wet = input.n_cans() * input.calories_per_can()
        calories_dry = calories_target - calories_wet
        grams_dry = calories_dry / input.calories_per_gram()
        return f"{grams_dry:.0f} g"


app = App(app_ui, server)