Notes/src/routes/api/fonts.ts

import type { Request, Response } from "express";
import optionService from "../../services/options.js";
import type { OptionMap } from "../../services/options_interface.js";

const SYSTEM_SANS_SERIF = [
    "system-ui",
    "-apple-system",
    "BlinkMacSystemFont",
    "Segoe UI",
    "Cantarell",
    "Ubuntu",
    "Noto Sans",
    "Helvetica",
    "Arial",
    "sans-serif",
    "Apple Color Emoji",
    "Segoe UI Emoji"
].join(",");

const SYSTEM_MONOSPACE = ["ui-monospace", "SFMono-Regular", "SF Mono", "Consolas", "Source Code Pro", "Ubuntu Mono", "Menlo", "Liberation Mono", "monospace"].join(",");

function getFontCss(req: Request, res: Response) {
    res.setHeader("Content-Type", "text/css");

    if (!optionService.getOptionBool("overrideThemeFonts")) {
        res.send("");

        return;
    }

    const optionsMap = optionService.getOptionMap();

    // using body to be more specific than themes' :root
    let style = "body {";
    style += getFontFamily(optionsMap);
    style += getFontSize(optionsMap);
    style += "}";

    res.send(style);
}

function getFontFamily({ mainFontFamily, treeFontFamily, detailFontFamily, monospaceFontFamily }: OptionMap) {
    let style = "";

    // System override
    if (mainFontFamily === "system") {
        mainFontFamily = SYSTEM_SANS_SERIF;
    }

    if (treeFontFamily === "system") {
        treeFontFamily = SYSTEM_SANS_SERIF;
    }

    if (detailFontFamily === "system") {
        detailFontFamily = SYSTEM_SANS_SERIF;
    }

    if (monospaceFontFamily === "system") {
        monospaceFontFamily = SYSTEM_MONOSPACE;
    }

    // Apply the font override if not using theme fonts.
    if (mainFontFamily !== "theme") {
        style += `--main-font-family: ${mainFontFamily};`;
    }

    if (treeFontFamily !== "theme") {
        style += `--tree-font-family: ${treeFontFamily};`;
    }

    if (detailFontFamily !== "theme") {
        style += `--detail-font-family: ${detailFontFamily};`;
    }

    if (monospaceFontFamily !== "theme") {
        style += `--monospace-font-family: ${monospaceFontFamily};`;
    }

    return style;
}

function getFontSize(optionsMap: OptionMap) {
    let style = "";
    style += `--main-font-size: ${optionsMap.mainFontSize}%;`;
    style += `--tree-font-size: ${optionsMap.treeFontSize}%;`;
    style += `--detail-font-size: ${optionsMap.detailFontSize}%;`;
    style += `--monospace-font-size: ${optionsMap.monospaceFontSize}%;`;

    return style;
}

export default {
    getFontCss
};