thi-ng/umbrella

export interface Unit {
    /**
     * SI base dimension vector ({@link Dimensions})
     */
    dim: Dimensions;
    /**
     * Scaling factor relative to the coherent unit
     */
    scale: number;
    /**
     * Zero offset value
     */
    offset: number;
    /**
     * True, if this unit is coherent.
     *
     * @remarks
     * Reference:
     * - https://en.wikipedia.org/wiki/Coherence_(units_of_measurement)
     */
    coherent: boolean;
}

export interface NamedUnit extends Unit {
    /**
     * Symbol under which this unit can be looked up with via {@link asUnit} and
     * others.
     */
    sym: string;
    /**
     * This unit's human readable description/name.
     */
    name: string;
}

export type MaybeUnit = Unit | string;

/**
 * Vector of the 7 basic SI unit dimensions.
 *
 * @remarks
 * In order:
 *
 * - 0 = mass
 * - 1 = length
 * - 2 = time
 * - 3 = current
 * - 4 = temperature
 * - 5 = amount of substance
 * - 6 = luminous intensity
 *
 * Note: For dimensionless units, all dimensions are zero.
 *
 * Reference:
 * - https://en.wikipedia.org/wiki/SI_base_unit
 */
export type Dimensions = [
    number,
    number,
    number,
    number,
    number,
    number,
    number
];

/**
 * A known metric prefix.
 */
export type Prefix = keyof typeof PREFIXES;

/**
 * @remarks
 * Reference:
 * - https://en.wikipedia.org/wiki/Metric_prefix
 */
export const PREFIXES = {
    Q: 1e30,
    R: 1e27,
    Y: 1e24,
    Z: 1e21,
    E: 1e18,
    P: 1e15,
    T: 1e12,
    G: 1e9,
    M: 1e6,
    k: 1e3,
    h: 1e2,
    d: 1e-1,
    c: 1e-2,
    m: 1e-3,
    µ: 1e-6,
    n: 1e-9,
    p: 1e-12,
    f: 1e-15,
    a: 1e-18,
    z: 1e-21,
    y: 1e-24,
    r: 1e-27,
    q: 1e-30,
};

/**
 * Dimensionless unit preset.
 */
export const NONE: Unit = {
    dim: [0, 0, 0, 0, 0, 0, 0],
    scale: 1,
    offset: 0,
    coherent: false,
};