Function lowerCalcExpression

src/utils/color.ts:456–488

(color: string)

// expressions from the given string. It can only lower expressions to a certain
// degree so we can keep this function easy and simple to understand.
export function lowerCalcExpression(color: string): string {
    // searchIndex will be used as searchIndex and as a "cursor" within
    // the calc(...) expression.
    let searchIndex = 0;

    // Replace the content between two indices.
    const replaceBetweenIndices = (start: number, end: number, replacement: string) => {
        color = color.substring(0, start) + replacement + color.substring(end);
    };

    // Run this code until it doesn't find any `calc(...)`.
    while ((searchIndex = color.indexOf('calc(')) !== -1) {
        // Get the parentheses ranges of `calc(...)`.
        const range = getParenthesesRange(color, searchIndex);
        if (!range) {
            break;
        }

        // Get the content between the parentheses.
        let slice = color.slice(range.start + 1, range.end - 1);
        // Does the content include a percentage?
        const includesPercentage = slice.includes('%');
        // Remove all percentages.
        slice = slice.split('%').join('');

        // Pass the content to the evalMath library and round its output.
        const output = Math.round(evalMath(slice));

        // Replace `calc(...)` with the result.
        replaceBetweenIndices(range.start - 4, range.end, output + (includesPercentage ? '%' : ''));
    }
    return color;
}

const knownColors: Map<string, number> = new Map(Object.entries({
    aliceblue: 0xf0f8ff,