Move "core" folder out of "features" into "base"

src/base/components/inputs/ThreeStateCheckbox.tsx

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+import DisabledByDefaultRounded from '@mui/icons-material/DisabledByDefaultRounded';
+import Checkbox, { CheckboxProps } from '@mui/material/Checkbox';
+import React, { useCallback } from 'react';
+
+type CheckState = boolean | undefined | null;
+
+function nextState(state: CheckState): CheckState {
+    if (state === true) return false;
+    if (state === false) return undefined;
+    return true;
+}
+
+export interface ThreeStateCheckboxProps extends Omit<CheckboxProps, 'checked' | 'onChange'> {
+    checked?: boolean | undefined | null;
+    onChange?: (checked: boolean | undefined | null) => void;
+}
+
+/**
+ * When checked is true, checkbox contains checkmark
+ * When checked is false, checkbox contains cross
+ * When checked is null or undefined, checkbox is empty
+ */
+export const ThreeStateCheckbox: React.FC<ThreeStateCheckboxProps> = ({ checked, onChange, ...rest }) => {
+    const handleChange = useCallback(() => {
+        if (onChange) {
+            const newState = nextState(checked);
+            onChange(newState);
+        }
+    }, [onChange]);
+
+    return (
+        <Checkbox
+            indeterminateIcon={<DisabledByDefaultRounded />}
+            checked={checked === true}
+            indeterminate={checked === false}
+            onChange={handleChange}
+            {...rest}
+        />
+    );
+};