element-web/src/editor/position.ts

/*
Copyright 2024 New Vector Ltd.
Copyright 2019 The Matrix.org Foundation C.I.C.

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

import DocumentOffset from "./offset";
import EditorModel from "./model";
import { Part } from "./parts";

export interface IPosition {
    index: number;
    offset: number;
}

type Callback = (part: Part, startIdx: number, endIdx: number) => void;
export type Predicate = (index: number, offset: number, part: Part) => boolean;

export default class DocumentPosition implements IPosition {
    public constructor(
        public readonly index: number,
        public readonly offset: number,
    ) {}

    public compare(otherPos: DocumentPosition): number {
        if (this.index === otherPos.index) {
            return this.offset - otherPos.offset;
        } else {
            return this.index - otherPos.index;
        }
    }

    public iteratePartsBetween(other: DocumentPosition, model: EditorModel, callback: Callback): void {
        if (this.index === -1 || other.index === -1) {
            return;
        }
        const [startPos, endPos] = this.compare(other) < 0 ? [this, other] : [other, this];
        if (startPos.index === endPos.index) {
            callback(model.parts[this.index], startPos.offset, endPos.offset);
        } else {
            const firstPart = model.parts[startPos.index];
            callback(firstPart, startPos.offset, firstPart.text.length);
            for (let i = startPos.index + 1; i < endPos.index; ++i) {
                const part = model.parts[i];
                callback(part, 0, part.text.length);
            }
            const lastPart = model.parts[endPos.index];
            callback(lastPart, 0, endPos.offset);
        }
    }

    public forwardsWhile(model: EditorModel, predicate: Predicate): DocumentPosition {
        if (this.index === -1) {
            return this;
        }

        let { index, offset } = this;
        const { parts } = model;
        while (index < parts.length) {
            const part = parts[index];
            while (offset < part.text.length) {
                if (!predicate(index, offset, part)) {
                    return new DocumentPosition(index, offset);
                }
                offset += 1;
            }
            // end reached
            if (index === parts.length - 1) {
                return new DocumentPosition(index, offset);
            } else {
                index += 1;
                offset = 0;
            }
        }

        return this; // impossible but Typescript doesn't believe us
    }

    public backwardsWhile(model: EditorModel, predicate: Predicate): DocumentPosition {
        if (this.index === -1) {
            return this;
        }

        let { index, offset } = this;
        const parts = model.parts;
        while (index >= 0) {
            const part = parts[index];
            while (offset > 0) {
                if (!predicate(index, offset - 1, part)) {
                    return new DocumentPosition(index, offset);
                }
                offset -= 1;
            }
            // start reached
            if (index === 0) {
                return new DocumentPosition(index, offset);
            } else {
                index -= 1;
                offset = parts[index].text.length;
            }
        }

        return this; // impossible but Typescript doesn't believe us
    }

    public asOffset(model: EditorModel): DocumentOffset {
        if (this.index === -1) {
            return new DocumentOffset(0, true);
        }
        let offset = 0;
        for (let i = 0; i < this.index; ++i) {
            offset += model.parts[i].text.length;
        }
        offset += this.offset;
        const lastPart = model.parts[this.index];
        const atEnd = !lastPart || offset >= lastPart.text.length; // if no last part, we're at the end
        return new DocumentOffset(offset, atEnd);
    }

    public isAtEnd(model: EditorModel): boolean {
        if (model.parts.length === 0) {
            return true;
        }
        const lastPartIdx = model.parts.length - 1;
        const lastPart = model.parts[lastPartIdx];
        return this.index === lastPartIdx && this.offset === lastPart.text.length;
    }

    public isAtStart(): boolean {
        return this.index === 0 && this.offset === 0;
    }
}