rudeshark.net/packages/client/src/scripts/popup-position.ts

import { Ref } from "vue";

export function calcPopupPosition(
	el: HTMLElement,
	props: {
		anchorElement: HTMLElement | null;
		innerMargin: number;
		direction: "top" | "bottom" | "left" | "right";
		align: "top" | "bottom" | "left" | "right" | "center";
		alignOffset?: number;
		x?: number;
		y?: number;
	},
): { top: number; left: number; transformOrigin: string } {
	const contentWidth = el.offsetWidth;
	const contentHeight = el.offsetHeight;

	let rect: DOMRect;

	if (props.anchorElement) {
		rect = props.anchorElement.getBoundingClientRect();
	}

	const calcPosWhenTop = () => {
		let left: number;
		let top: number;

		if (props.anchorElement) {
			left =
				rect.left + window.pageXOffset + props.anchorElement.offsetWidth / 2;
			top = rect.top + window.pageYOffset - contentHeight - props.innerMargin;
		} else {
			left = props.x;
			top = props.y - contentHeight - props.innerMargin;
		}

		left -= el.offsetWidth / 2;

		if (left + contentWidth - window.pageXOffset > window.innerWidth) {
			left = window.innerWidth - contentWidth + window.pageXOffset - 1;
		}

		return [left, top];
	};

	const calcPosWhenBottom = () => {
		let left: number;
		let top: number;

		if (props.anchorElement) {
			left =
				rect.left + window.pageXOffset + props.anchorElement.offsetWidth / 2;
			top =
				rect.top +
				window.pageYOffset +
				props.anchorElement.offsetHeight +
				props.innerMargin;
		} else {
			left = props.x;
			top = props.y + props.innerMargin;
		}

		left -= el.offsetWidth / 2;

		if (left + contentWidth - window.pageXOffset > window.innerWidth) {
			left = window.innerWidth - contentWidth + window.pageXOffset - 1;
		}

		return [left, top];
	};

	const calcPosWhenLeft = () => {
		let left: number;
		let top: number;

		if (props.anchorElement) {
			left = rect.left + window.pageXOffset - contentWidth - props.innerMargin;
			top =
				rect.top + window.pageYOffset + props.anchorElement.offsetHeight / 2;
		} else {
			left = props.x - contentWidth - props.innerMargin;
			top = props.y;
		}

		top -= el.offsetHeight / 2;

		if (top + contentHeight - window.pageYOffset > window.innerHeight) {
			top = window.innerHeight - contentHeight + window.pageYOffset - 1;
		}

		return [left, top];
	};

	const calcPosWhenRight = () => {
		let left: number;
		let top: number;

		if (props.anchorElement) {
			left =
				rect.left +
				props.anchorElement.offsetWidth +
				window.pageXOffset +
				props.innerMargin;

			if (props.align === "top") {
				top = rect.top + window.pageYOffset;
				if (props.alignOffset != null) top += props.alignOffset;
			} else if (props.align === "bottom") {
				// TODO
			} else {
				// center
				top =
					rect.top + window.pageYOffset + props.anchorElement.offsetHeight / 2;
				top -= el.offsetHeight / 2;
			}
		} else {
			left = props.x + props.innerMargin;
			top = props.y;
			top -= el.offsetHeight / 2;
		}

		if (top + contentHeight - window.pageYOffset > window.innerHeight) {
			top = window.innerHeight - contentHeight + window.pageYOffset - 1;
		}

		return [left, top];
	};

	const calc = (): {
		left: number;
		top: number;
		transformOrigin: string;
	} => {
		switch (props.direction) {
			case "top": {
				const [left, top] = calcPosWhenTop();

				// ツールチップを上に向かって表示するスペースがなければ下に向かって出す
				if (top - window.pageYOffset < 0) {
					const [left, top] = calcPosWhenBottom();
					return { left, top, transformOrigin: "center top" };
				}

				return { left, top, transformOrigin: "center bottom" };
			}

			case "bottom": {
				const [left, top] = calcPosWhenBottom();
				// TODO: ツールチップを下に向かって表示するスペースがなければ上に向かって出す
				return { left, top, transformOrigin: "center top" };
			}

			case "left": {
				const [left, top] = calcPosWhenLeft();

				// ツールチップを左に向かって表示するスペースがなければ右に向かって出す
				if (left - window.pageXOffset < 0) {
					const [left, top] = calcPosWhenRight();
					return { left, top, transformOrigin: "left center" };
				}

				return { left, top, transformOrigin: "right center" };
			}

			case "right": {
				const [left, top] = calcPosWhenRight();
				// TODO: ツールチップを右に向かって表示するスペースがなければ左に向かって出す
				return { left, top, transformOrigin: "left center" };
			}
		}
	};

	return calc();
}