exercism-ts/resistor-color-trio/resistor-color-trio.ts

export function decodedResistorValue(colors: string[]): string {
    if (colors.length < 3) {
        throw new Error("Unexpected number of colors");
    }
    // Ignore extra colors.
    const first = colors.slice(0, 2);
    let value = colorCode(first[0]) * 10 + colorCode(first[1]);
    let scale = colorCode(colors[2]);
    if (value % 10 === 0) {
        value /= 10;
        scale++;
    }
    let prefix: string = '';
    switch (scale) {
        case 9:
            prefix = 'giga';
            break;
        case 8:
            prefix = 'mega';
            value *= 100;
            break;
        case 7:
            prefix = 'mega';
            value *= 10;
            break;
        case 6:
            prefix = 'mega';
            break;
        case 5:
            prefix = 'kilo';
            value *= 100;
            break;
        case 4:
            prefix = 'kilo';
            value *= 10;
            break;
        case 3:
            prefix = 'kilo';
            break;
        case 2:
            value *= 100;
            break;
        case 1:
            value *= 10;
            break;
    }
    return `${value} ${prefix}ohms`;
}

export const colorCode = (name: string): number => {
    const num = COLORS.indexOf(name.toLowerCase())
    if (num == -1) {
        throw new Error(`Invalid color name "${name}"`);
    }
    return num;
}

export const COLORS: string[] = [
    'black',
    'brown',
    'red',
    'orange',
    'yellow',
    'green',
    'blue',
    'violet',
    'grey',
    'white',
];