element-web/src/components/structures/FileDropTarget.tsx

/*
Copyright 2024 New Vector Ltd.
Copyright 2022 The Matrix.org Foundation C.I.C.

SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE files in the repository root for full details.
*/

import React, { useEffect, useState } from "react";

import { _t } from "../../languageHandler";
import UploadBigSvg from "../../../res/img/upload-big.svg";

interface IProps {
    parent: HTMLElement | null;
    onFileDrop(dataTransfer: DataTransfer): void;
}

interface IState {
    dragging: boolean;
    counter: number;
}

const FileDropTarget: React.FC<IProps> = ({ parent, onFileDrop }) => {
    const [state, setState] = useState<IState>({
        dragging: false,
        counter: 0,
    });

    useEffect(() => {
        if (!parent || parent.ondrop) return;

        const onDragEnter = (ev: DragEvent): void => {
            ev.stopPropagation();
            ev.preventDefault();
            if (!ev.dataTransfer) return;

            setState((state) => ({
                // We always increment the counter no matter the types, because dragging is
                // still happening. If we didn't, the drag counter would get out of sync.
                counter: state.counter + 1,
                // See:
                // https://docs.w3cub.com/dom/datatransfer/types
                // https://developer.mozilla.org/en-US/docs/Web/API/HTML_Drag_and_Drop_API/Recommended_drag_types#file
                dragging:
                    ev.dataTransfer!.types.includes("Files") ||
                    ev.dataTransfer!.types.includes("application/x-moz-file")
                        ? true
                        : state.dragging,
            }));
        };

        const onDragLeave = (ev: DragEvent): void => {
            ev.stopPropagation();
            ev.preventDefault();

            setState((state) => ({
                counter: state.counter - 1,
                dragging: state.counter <= 1 ? false : state.dragging,
            }));
        };

        const onDragOver = (ev: DragEvent): void => {
            ev.stopPropagation();
            ev.preventDefault();
            if (!ev.dataTransfer) return;

            ev.dataTransfer.dropEffect = "none";

            // See:
            // https://docs.w3cub.com/dom/datatransfer/types
            // https://developer.mozilla.org/en-US/docs/Web/API/HTML_Drag_and_Drop_API/Recommended_drag_types#file
            if (ev.dataTransfer.types.includes("Files") || ev.dataTransfer.types.includes("application/x-moz-file")) {
                ev.dataTransfer.dropEffect = "copy";
            }
        };

        const onDrop = (ev: DragEvent): void => {
            ev.stopPropagation();
            ev.preventDefault();
            if (!ev.dataTransfer) return;
            onFileDrop(ev.dataTransfer);

            setState((state) => ({
                dragging: false,
                counter: state.counter - 1,
            }));
        };

        parent?.addEventListener("drop", onDrop);
        parent?.addEventListener("dragover", onDragOver);
        parent?.addEventListener("dragenter", onDragEnter);
        parent?.addEventListener("dragleave", onDragLeave);

        return () => {
            // disconnect the D&D event listeners from the room view. This
            // is really just for hygiene - we're going to be
            // deleted anyway, so it doesn't matter if the event listeners
            // don't get cleaned up.
            parent?.removeEventListener("drop", onDrop);
            parent?.removeEventListener("dragover", onDragOver);
            parent?.removeEventListener("dragenter", onDragEnter);
            parent?.removeEventListener("dragleave", onDragLeave);
        };
    }, [parent, onFileDrop]);

    if (state.dragging) {
        return (
            <div className="mx_FileDropTarget">
                <img src={UploadBigSvg} className="mx_FileDropTarget_image" alt="" />
                {_t("room|drop_file_prompt")}
            </div>
        );
    }

    return null;
};

export default FileDropTarget;