1 files changed, 170 insertions, 0 deletions
diff --git a/packages/instant/src/components/scaling_input.tsx b/packages/instant/src/components/scaling_input.tsx
new file mode 100644
index 000000000..34cb0b5fd
--- /dev/null
+++ b/packages/instant/src/components/scaling_input.tsx
@@ -0,0 +1,170 @@
+import * as _ from 'lodash';
+import * as React from 'react';
+
+import { ColorOption } from '../style/theme';
+import { util } from '../util/util';
+
+import { Input } from './ui';
+
+export enum ScalingInputPhase {
+    FixedFontSize,
+    ScalingFontSize,
+}
+
+export interface ScalingSettings {
+    percentageToReduceFontSizePerCharacter: number;
+    constantPxToIncreaseWidthPerCharacter: number;
+}
+
+export interface ScalingInputProps {
+    textLengthThreshold: number;
+    maxFontSizePx: number;
+    value: string;
+    emptyInputWidthCh: number;
+    onChange: (event: React.ChangeEvent<HTMLInputElement>) => void;
+    onFontSizeChange: (fontSizePx: number) => void;
+    fontColor?: ColorOption;
+    placeholder?: string;
+    maxLength?: number;
+    scalingSettings: ScalingSettings;
+}
+
+export interface ScalingInputState {
+    inputWidthPxAtPhaseChange?: number;
+}
+
+export interface ScalingInputSnapshot {
+    inputWidthPx: number;
+}
+
+// These are magic numbers that were determined experimentally.
+const defaultScalingSettings: ScalingSettings = {
+    percentageToReduceFontSizePerCharacter: 0.125,
+    constantPxToIncreaseWidthPerCharacter: 4,
+};
+
+export class ScalingInput extends React.Component<ScalingInputProps, ScalingInputState> {
+    public static defaultProps = {
+        onChange: util.boundNoop,
+        onFontSizeChange: util.boundNoop,
+        maxLength: 7,
+        scalingSettings: defaultScalingSettings,
+    };
+    public state: ScalingInputState = {
+        inputWidthPxAtPhaseChange: undefined,
+    };
+    private readonly _inputRef = React.createRef<HTMLInputElement>();
+    public static getPhase(textLengthThreshold: number, value: string): ScalingInputPhase {
+        if (value.length <= textLengthThreshold) {
+            return ScalingInputPhase.FixedFontSize;
+        }
+        return ScalingInputPhase.ScalingFontSize;
+    }
+    public static getPhaseFromProps(props: ScalingInputProps): ScalingInputPhase {
+        const { value, textLengthThreshold } = props;
+        return ScalingInput.getPhase(textLengthThreshold, value);
+    }
+    public static calculateFontSize(
+        textLengthThreshold: number,
+        maxFontSizePx: number,
+        phase: ScalingInputPhase,
+        value: string,
+        percentageToReduceFontSizePerCharacter: number,
+    ): number {
+        if (phase !== ScalingInputPhase.ScalingFontSize) {
+            return maxFontSizePx;
+        }
+        const charactersOverMax = value.length - textLengthThreshold;
+        const scalingFactor = (1 - percentageToReduceFontSizePerCharacter) ** charactersOverMax;
+        const fontSize = scalingFactor * maxFontSizePx;
+        return fontSize;
+    }
+    public static calculateFontSizeFromProps(props: ScalingInputProps, phase: ScalingInputPhase): number {
+        const { textLengthThreshold, value, maxFontSizePx, scalingSettings } = props;
+        return ScalingInput.calculateFontSize(
+            textLengthThreshold,
+            maxFontSizePx,
+            phase,
+            value,
+            scalingSettings.percentageToReduceFontSizePerCharacter,
+        );
+    }
+    public getSnapshotBeforeUpdate(): ScalingInputSnapshot {
+        return {
+            inputWidthPx: this._getInputWidthInPx(),
+        };
+    }
+    public componentDidUpdate(
+        prevProps: ScalingInputProps,
+        prevState: ScalingInputState,
+        snapshot: ScalingInputSnapshot,
+    ): void {
+        const prevPhase = ScalingInput.getPhaseFromProps(prevProps);
+        const curPhase = ScalingInput.getPhaseFromProps(this.props);
+        // if we went from fixed to scaling, save the width from the transition
+        if (prevPhase !== ScalingInputPhase.ScalingFontSize && curPhase === ScalingInputPhase.ScalingFontSize) {
+            this.setState({
+                inputWidthPxAtPhaseChange: snapshot.inputWidthPx,
+            });
+        }
+        // if we went from scaling to fixed, revert back to scaling using `ch`
+        if (prevPhase === ScalingInputPhase.ScalingFontSize && curPhase !== ScalingInputPhase.ScalingFontSize) {
+            this.setState({
+                inputWidthPxAtPhaseChange: undefined,
+            });
+        }
+        const prevFontSize = ScalingInput.calculateFontSizeFromProps(prevProps, prevPhase);
+        const curFontSize = ScalingInput.calculateFontSizeFromProps(this.props, curPhase);
+        // If font size has changed, notify.
+        if (prevFontSize !== curFontSize) {
+            this.props.onFontSizeChange(curFontSize);
+        }
+    }
+    public render(): React.ReactNode {
+        const { fontColor, onChange, placeholder, value, maxLength } = this.props;
+        const phase = ScalingInput.getPhaseFromProps(this.props);
+        return (
+            <Input
+                ref={this._inputRef as any}
+                fontColor={fontColor}
+                onChange={onChange}
+                value={value}
+                placeholder={placeholder}
+                fontSize={`${this._calculateFontSize(phase)}px`}
+                width={this._calculateWidth(phase)}
+                maxLength={maxLength}
+            />
+        );
+    }
+    private readonly _calculateWidth = (phase: ScalingInputPhase): string => {
+        const { value, textLengthThreshold, scalingSettings } = this.props;
+        if (_.isEmpty(value)) {
+            return `${this.props.emptyInputWidthCh}ch`;
+        }
+        switch (phase) {
+            case ScalingInputPhase.FixedFontSize:
+                return `${value.length}ch`;
+            case ScalingInputPhase.ScalingFontSize:
+                const { inputWidthPxAtPhaseChange } = this.state;
+                if (!_.isUndefined(inputWidthPxAtPhaseChange)) {
+                    const charactersOverMax = value.length - textLengthThreshold;
+                    const scalingAmount = scalingSettings.constantPxToIncreaseWidthPerCharacter * charactersOverMax;
+                    const width = inputWidthPxAtPhaseChange + scalingAmount;
+                    return `${width}px`;
+                }
+                return `${textLengthThreshold}ch`;
+            default:
+                return '1ch';
+        }
+    };
+    private readonly _calculateFontSize = (phase: ScalingInputPhase): number => {
+        return ScalingInput.calculateFontSizeFromProps(this.props, phase);
+    };
+    private readonly _getInputWidthInPx = (): number => {
+        const ref = this._inputRef.current;
+        if (!ref) {
+            return 0;
+        }
+        return ref.getBoundingClientRect().width;
+    };
+}