"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.getFallbackMetricsFromFontFile = getFallbackMetricsFromFontFile;
// The font metadata of the fallback fonts, retrieved with fontkit on system font files
// The average width is calculated with the calcAverageWidth function below
const DEFAULT_SANS_SERIF_FONT = {
    name: 'Arial',
    azAvgWidth: 934.5116279069767,
    unitsPerEm: 2048,
};
const DEFAULT_SERIF_FONT = {
    name: 'Times New Roman',
    azAvgWidth: 854.3953488372093,
    unitsPerEm: 2048,
};
/**
 * Calculate the average character width of a font file.
 * Used to calculate the size-adjust property by comparing the fallback average with the loaded font average.
 */
function calcAverageWidth(font) {
    try {
        /**
         * Finding the right characters to use when calculating the average width is tricky.
         * We can't just use the average width of all characters, because we have to take letter frequency into account.
         * We also have to take word length into account, because the font's space width usually differ a lot from other characters.
         * The goal is to find a string that'll give you a good average width, given most texts in most languages.
         *
         * TODO: Currently only works for the latin alphabet. Support more languages by finding the right characters for additional languages.
         *
         * The used characters were decided through trial and error with letter frequency and word length tables as a guideline.
         * E.g. https://en.wikipedia.org/wiki/Letter_frequency
         */
        const avgCharacters = 'aaabcdeeeefghiijklmnnoopqrrssttuvwxyz      ';
        // Check if the font file has all the characters we need to calculate the average width
        const hasAllChars = font
            .glyphsForString(avgCharacters)
            .flatMap((glyph) => glyph.codePoints)
            .every((codePoint) => font.hasGlyphForCodePoint(codePoint));
        if (!hasAllChars)
            return undefined;
        const widths = font
            .glyphsForString(avgCharacters)
            .map((glyph) => glyph.advanceWidth);
        const totalWidth = widths.reduce((sum, width) => sum + width, 0);
        return totalWidth / widths.length;
    }
    catch {
        // Could not calculate average width from the font file, skip size-adjust
        return undefined;
    }
}
function formatOverrideValue(val) {
    return Math.abs(val * 100).toFixed(2) + '%';
}
/**
 * Given a font file and category, calculate the fallback font override values.
 * The returned values can be used to generate a CSS @font-face declaration.
 *
 * For example:
 * @font-face {
 *   font-family: local-font;
 *   src: local(Arial);
 *   size-adjust: 90%;
 * }
 *
 * Read more about this technique in these texts by the Google Aurora team:
 * https://developer.chrome.com/blog/font-fallbacks/
 * https://docs.google.com/document/d/e/2PACX-1vRsazeNirATC7lIj2aErSHpK26hZ6dA9GsQ069GEbq5fyzXEhXbvByoftSfhG82aJXmrQ_sJCPBqcx_/pub
 */
function getFallbackMetricsFromFontFile(font, category = 'serif') {
    const fallbackFont = category === 'serif' ? DEFAULT_SERIF_FONT : DEFAULT_SANS_SERIF_FONT;
    const azAvgWidth = calcAverageWidth(font);
    const { ascent, descent, lineGap, unitsPerEm } = font;
    const fallbackFontAvgWidth = fallbackFont.azAvgWidth / fallbackFont.unitsPerEm;
    let sizeAdjust = azAvgWidth
        ? azAvgWidth / unitsPerEm / fallbackFontAvgWidth
        : 1;
    return {
        ascentOverride: formatOverrideValue(ascent / (unitsPerEm * sizeAdjust)),
        descentOverride: formatOverrideValue(descent / (unitsPerEm * sizeAdjust)),
        lineGapOverride: formatOverrideValue(lineGap / (unitsPerEm * sizeAdjust)),
        fallbackFont: fallbackFont.name,
        sizeAdjust: formatOverrideValue(sizeAdjust),
    };
}
