Add Gemini Style Guide

.gemini/styleguide.md

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+# Now In Android Style Guide
+
+# Introduction
+This style guide outlines the coding conventions for the Now In Android application. 
+Generally speaking, this application follows the official Kotlin coding styleguide and best practises used when writing modern Android mobile applications.
+
+# Key Principles
+* **Security:** Code should always follow security best practises and avoid introducing vulnerbilities.
+* **Readability:** Code should be easy to understand for all team members.
+* **Maintainability:** Code should be easy to modify and extend.
+* **Consistency:** Adhering to a consistent style across all projects improves
+  collaboration and reduces errors.
+* **Performance:** While readability is paramount, code should be efficient especially when working with custom UI or business logic.
+
+# Tooling
+* **Code formatter:**  [Spotless] - Enforces consistent formatting automatically.
+* **Linter:**  [ktlint] - Identifies potential issues and style violations.
+
+# Example
+```kotlin
+package com.google.samples.apps.nowinandroid
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.google.samples.apps.nowinandroid.MainActivityUiState.Loading
+import com.google.samples.apps.nowinandroid.MainActivityUiState.Success
+import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
+import com.google.samples.apps.nowinandroid.core.model.data.DarkThemeConfig
+import com.google.samples.apps.nowinandroid.core.model.data.ThemeBrand
+import com.google.samples.apps.nowinandroid.core.model.data.UserData
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.StateFlow
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.flow.stateIn
+import javax.inject.Inject
+
+@HiltViewModel
+class MainActivityViewModel @Inject constructor(
+    userDataRepository: UserDataRepository,
+) : ViewModel() {
+    val uiState: StateFlow<MainActivityUiState> = userDataRepository.userData.map {
+        Success(it)
+    }.stateIn(
+        scope = viewModelScope,
+        initialValue = Loading,
+        started = SharingStarted.WhileSubscribed(5_000),
+    )
+}
+
+sealed interface MainActivityUiState {
+    data object Loading : MainActivityUiState
+
+    data class Success(val userData: UserData) : MainActivityUiState {
+        override val shouldDisableDynamicTheming = !userData.useDynamicColor
+
+        override val shouldUseAndroidTheme: Boolean = when (userData.themeBrand) {
+            ThemeBrand.DEFAULT -> false
+            ThemeBrand.ANDROID -> true
+        }
+
+        override fun shouldUseDarkTheme(isSystemDarkTheme: Boolean) =
+            when (userData.darkThemeConfig) {
+                DarkThemeConfig.FOLLOW_SYSTEM -> isSystemDarkTheme
+                DarkThemeConfig.LIGHT -> false
+                DarkThemeConfig.DARK -> true
+            }
+    }
+
+    /**
+     * Returns `true` if the state wasn't loaded yet and it should keep showing the splash screen.
+     */
+    fun shouldKeepSplashScreen() = this is Loading
+
+    /**
+     * Returns `true` if the dynamic color is disabled.
+     */
+    val shouldDisableDynamicTheming: Boolean get() = true
+
+    /**
+     * Returns `true` if the Android theme should be used.
+     */
+    val shouldUseAndroidTheme: Boolean get() = false
+
+    /**
+     * Returns `true` if dark theme should be used.
+     */
+    fun shouldUseDarkTheme(isSystemDarkTheme: Boolean) = isSystemDarkTheme
+}
+```