Add flash messages.

components/createFlashMessageComponent/index.tsx

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+import * as React from "react";
+import { StyleSheet, Text, TextStyle, ViewStyle } from "react-native";
+import { useRefresh } from "../../hooks/useRefresh";
+import type { FlashMessageState } from "../../types/FlashMessageState";
+import type { FlashMessageStyle } from "../../types/FlashMessageStyle";
+import { Hitbox } from "../Hitbox";
+
+/**
+ * Creates a new React component representing a flash message.
+ * @template T              The names of the types available.
+ * @param flashMessageStyle The style of the flash message to create.
+ * @returns                 The created React component.
+ */
+export function createFlashMessageComponent<T extends string>(
+  flashMessageStyle: FlashMessageStyle<T>
+): React.FunctionComponent<{
+  /**
+   * When null, the flash message is closed.  When non-null, the details of the
+   * flash message which may be displayed (the user can dismiss the current
+   * message).
+   */
+  readonly state: null | FlashMessageState<T>;
+}> {
+  const hitboxStylesInput: { [TKey in T]?: ViewStyle } = {};
+  const textStylesInput: { [TKey in T]?: TextStyle } = {};
+
+  for (const typeKey in flashMessageStyle.types) {
+    const typeValue = flashMessageStyle.types[typeKey];
+
+    const hitboxStyle: ViewStyle = {
+      backgroundColor: typeValue.backgroundColor,
+    };
+
+    if (typeValue.border !== null) {
+      hitboxStyle.borderWidth = typeValue.border.width;
+      hitboxStyle.borderColor = typeValue.border.color;
+    }
+
+    if (flashMessageStyle.horizontalPadding !== 0) {
+      hitboxStyle.paddingHorizontal = flashMessageStyle.horizontalPadding;
+    }
+
+    if (flashMessageStyle.verticalPadding !== 0) {
+      hitboxStyle.paddingVertical = flashMessageStyle.verticalPadding;
+    }
+
+    if (flashMessageStyle.radius !== 0) {
+      hitboxStyle.borderRadius = flashMessageStyle.radius;
+    }
+
+    hitboxStylesInput[typeKey] = hitboxStyle;
+
+    const textStyle: TextStyle = {
+      fontFamily: flashMessageStyle.fontFamily,
+      fontSize: flashMessageStyle.fontSize,
+      lineHeight: flashMessageStyle.fontSize * 1.4,
+      color: typeValue.color,
+    };
+
+    textStylesInput[typeKey] = textStyle;
+  }
+
+  const hitboxStyles = StyleSheet.create(
+    hitboxStylesInput as { readonly [TKey in T]: ViewStyle }
+  );
+
+  const textStyles = StyleSheet.create(
+    textStylesInput as { readonly [TKey in T]: TextStyle }
+  );
+
+  return ({ state }) => {
+    const refresh = useRefresh();
+    const internalState = React.useRef({
+      open: state !== null,
+      type: state === null ? null : state.type,
+      message: state === null ? null : state.message,
+    });
+
+    if (state === null) {
+      internalState.current.open = false;
+      internalState.current.type = null;
+      internalState.current.message = null;
+    } else if (
+      state.type !== internalState.current.type ||
+      state.message !== internalState.current.message
+    ) {
+      internalState.current.open = true;
+      internalState.current.type = state.type;
+      internalState.current.message = state.message;
+    }
+
+    if (state !== null && internalState.current.open) {
+      return (
+        <Hitbox
+          disabled={false}
+          onPress={() => {
+            console.log("let us go!");
+            internalState.current.open = false;
+            refresh();
+          }}
+          style={hitboxStyles[state.type]}
+        >
+          <Text style={textStyles[state.type]}>{state.message}</Text>
+        </Hitbox>
+      );
+    } else {
+      return null;
+    }
+  };
+}

components/createFlashMessageComponent/readme.md

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+# `react-native-app-helpers/createFlashMessageComponent`
+
+Creates a new React component representing a flash message.
+
+## Usage
+
+```tsx
+import { createFlashMessageComponent, FlashMessageState } from "react-native-app-helpers";
+import { Button } from "react-native";
+
+const ExampleFlashMessage = createFlashMessageComponent(
+{
+    fontFamily: `Example Font Family`,
+    fontSize: 25,
+    radius: 12,
+    horizontalPadding: 41,
+    verticalPadding: 57,
+    types: {
+      exampleTypeA: {
+        backgroundColor: `red`,
+        color: `green`,
+        border: null,
+      },
+      exampleTypeB: {
+        backgroundColor: `blue`,
+        color: `yellow`,
+        border: {
+          width: 15,
+          color: `orange`,
+        },
+      },
+      exampleTypeC: {
+        backgroundColor: `purple`,
+        color: `cyan`,
+        border: null,
+      },
+      exampleTypeD: {
+        backgroundColor: `magenta`,
+        color: `black`,
+        border: {
+          width: 24,
+          color: `white`,
+        },
+      },
+    },
+  }
+);
+
+const ExampleScreen = () => {
+  const [state, setState] = React.useState<null | FlashMessageState<`exampleTypeA` | `exampleTypeB` | `exampleTypeC` | `exampleTypeD`>>(null);
+
+  return (
+    <React.Fragment>
+      <ExampleFlashMessage state={state} />
+      <Button
+        onPress={() => {
+          setState({
+            type: `exampleTypeB`,
+            message: `This is example message B.`,
+          })
+        }}
+        title="Show Message B"
+      />
+      <Button
+        onPress={() => {
+          setState({
+            type: `exampleTypeC`,
+            message: `This is example message C.`,
+          })
+        }}
+        title="Show Message C"
+      />
+    </React.Fragment>
+  );
+};
+```