wasifibnharun/bmi-calculator-app

Purpose and Runtime

A standalone Flutter Android BMI calculator. It accepts height in centimeters and weight in kilograms, computes BMI locally, classifies the result, and presents it with animated UI. There is no backend, persistence layer, authentication, or external API; the only named package integration is gauge_indicator.

Primary Dart runtime entry point: lib/main.dart. Android embeds the Flutter runtime through android/app/src/main/kotlin/com/bmi/calculator/bmi_calculator/MainActivity.kt.

Application Bootstrap and Navigation

lib/main.dart initializes the Material 3 application, global theme/color usage, and initial route/widget. The app begins at the animated splash screen, which transitions with replacement navigation to the calculator, preventing return to splash via back navigation.

Core paths:

• lib/main.dart

• lib/screens/splash_screen.dart

• lib/core/colors/app_colors.dart

Splash Stage

SplashScreen is a stateful, animation-driven entry stage. It owns an AnimationController via SingleTickerProviderStateMixin and combines fade/scale animation before invoking Navigator.pushReplacement to enter the calculator flow.

Boundary: splash owns only timed visual entry and navigation; BMI input/result state begins after the destination calculator screen is created.

Core path:

• lib/screens/splash_screen.dart

Calculator State and Domain Flow

BmiCalculatorScreen is the central state owner. It coordinates input values, form validation, calculated BMI, derived category, and reset behavior using StatefulWidget/setState.

Primary control flow:

1. User enters height and weight.

2. Form validation rejects empty or invalid values inline.

3. Screen converts cm to meters and computes weightKg / heightMeters².

4. BMI thresholds derive Underweight, Normal, Overweight, or Obese plus a category color.

5. Updated state renders the result card and reference legend.

6. Reset clears form fields and result state.

Core path:

• lib/screens/bmi_calculator_screen.dart

Input Boundary

The input component encapsulates height/weight field presentation and validation feedback, while the calculator screen retains submission, calculation, and result-state authority. This separates raw text/form concerns from BMI business decisions.

Core paths:

• lib/widgets/input_card.dart

• lib/screens/bmi_calculator_screen.dart

Result Visualization

ResultCard converts calculated state into the user-facing BMI score, category badge, and radial gauge. The gauge is animated and implemented through the external gauge_indicator Flutter package. It should receive already-calculated BMI/category data rather than recalculate domain logic.

Core paths:

• lib/widgets/result_card.dart

• lib/screens/bmi_calculator_screen.dart

• pubspec.yaml

Shared Visual Semantics

The centralized palette supplies application and BMI-category colors, ensuring calculator classification, result badge/gauge, and legend can use consistent visual semantics. The reference table is a static explanation of the same category thresholds/colors, always visible in the calculator UI.

Core paths:

• lib/core/colors/app_colors.dart

• lib/widgets/bmi_reference_table.dart

• lib/widgets/result_card.dart

Platform and Build Boundary

Flutter/Dart contains application behavior and UI. The Android Gradle project packages it as an Android app, with manifest and native launcher integration; it does not contain BMI logic.

Core paths:

• android/app/src/main/AndroidManifest.xml

• android/app/src/main/kotlin/com/bmi/calculator/bmi_calculator/MainActivity.kt

• android/app/build.gradle.kts