/* !
 * Copyright 2020 Palantir Technologies, Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { AbstractPureComponent, DISPLAYNAME_PREFIX } from "../../common";

export type AsyncControllableInputProps = React.InputHTMLAttributes<HTMLInputElement> & {
    inputRef?: React.Ref<HTMLInputElement>;
};

type InputValue = AsyncControllableInputProps["value"];

export interface AsyncControllableInputState {
    /**
     * Whether we are in the middle of a composition event.
     *
     * @default false
     */
    isComposing: boolean;

    /**
     * The source of truth for the input value. This is not updated during IME composition.
     * It may be updated by a parent component.
     *
     * @default ""
     */
    value: InputValue;

    /**
     * The latest input value, which updates during IME composition. Defaults to props.value.
     */
    nextValue: InputValue;

    /**
     * Whether there is a pending update we are expecting from a parent component.
     *
     * @default false
     */
    hasPendingUpdate: boolean;
}

/**
 * A stateful wrapper around the low-level <input> component which works around a
 * [React bug](https://github.com/facebook/react/issues/3926). This bug is reproduced when an input
 * receives CompositionEvents (for example, through IME composition) and has its value prop updated
 * asychronously. This might happen if a component chooses to do async validation of a value
 * returned by the input's `onChange` callback.
 *
 * Note: this component does not apply any Blueprint-specific styling.
 */
export class AsyncControllableInput extends AbstractPureComponent<
    AsyncControllableInputProps,
    AsyncControllableInputState
> {
    public static displayName = `${DISPLAYNAME_PREFIX}.AsyncControllableInput`;

    /**
     * The amount of time (in milliseconds) which the input will wait after a compositionEnd event before
     * unlocking its state value for external updates via props. See `handleCompositionEnd` for more details.
     */
    public static COMPOSITION_END_DELAY = 10;

    public state: AsyncControllableInputState = {
        hasPendingUpdate: false,
        isComposing: false,
        nextValue: this.props.value,
        value: this.props.value,
    };

    private cancelPendingCompositionEnd: (() => void) | null = null;

    public static getDerivedStateFromProps(
        nextProps: AsyncControllableInputProps,
        nextState: AsyncControllableInputState,
    ): Partial<AsyncControllableInputState> | null {
        if (nextState.isComposing || nextProps.value === undefined) {
            // don't derive anything from props if:
            // - in uncontrolled mode, OR
            // - currently composing, since we'll do that after composition ends
            return null;
        }

        const userTriggeredUpdate = nextState.nextValue !== nextState.value;

        if (userTriggeredUpdate) {
            if (nextProps.value === nextState.nextValue) {
                // parent has processed and accepted our update
                if (nextState.hasPendingUpdate) {
                    return { hasPendingUpdate: false, value: nextProps.value };
                } else {
                    return { value: nextState.nextValue };
                }
            } else {
                if (nextProps.value === nextState.value) {
                    // we have sent the update to our parent, but it has not been processed yet. just wait.
                    // DO NOT set nextValue here, since that will temporarily render a potentially stale controlled value,
                    // causing the cursor to jump once the new value is accepted
                    return { hasPendingUpdate: true };
                }
                // accept controlled update overriding user action
                return { hasPendingUpdate: false, nextValue: nextProps.value, value: nextProps.value };
            }
        } else {
            // accept controlled update, could be confirming or denying user action
            return { hasPendingUpdate: false, nextValue: nextProps.value, value: nextProps.value };
        }
    }

    public render() {
        const { isComposing, hasPendingUpdate, value, nextValue } = this.state;
        const { inputRef, ...restProps } = this.props;
        return (
            <input
                {...restProps}
                ref={inputRef}
                // render the pending value even if it is not confirmed by a parent's async controlled update
                // so that the cursor does not jump to the end of input as reported in
                // https://github.com/palantir/blueprint/issues/4298
                value={isComposing || hasPendingUpdate ? nextValue : value}
                onCompositionStart={this.handleCompositionStart}
                onCompositionEnd={this.handleCompositionEnd}
                onChange={this.handleChange}
            />
        );
    }

    private handleCompositionStart = (e: React.CompositionEvent<HTMLInputElement>) => {
        this.cancelPendingCompositionEnd?.();
        this.setState({ isComposing: true });
        this.props.onCompositionStart?.(e);
    };

    private handleCompositionEnd = (e: React.CompositionEvent<HTMLInputElement>) => {
        // In some non-latin languages, a keystroke can end a composition event and immediately afterwards start another.
        // This can lead to unexpected characters showing up in the text input. In order to circumvent this problem, we
        // use a timeout which creates a delay which merges the two composition events, creating a more natural and predictable UX.
        // `this.state.nextValue` will become "locked" (it cannot be overwritten by the `value` prop) until a delay (10ms) has
        // passed without a new composition event starting.
        this.cancelPendingCompositionEnd = this.setTimeout(
            () => this.setState({ isComposing: false }),
            AsyncControllableInput.COMPOSITION_END_DELAY,
        );
        this.props.onCompositionEnd?.(e);
    };

    private handleChange = (e: React.ChangeEvent<HTMLInputElement>) => {
        const { value } = e.target;

        this.setState({ nextValue: value });
        this.props.onChange?.(e);
    };
}