import { CIE } from './cie';
import { RGB } from './srgb';

/**
 * Wavelength defined by nanometers
 */
export class Wavelength {
    public value: number;

    public constructor(wavelength: number) {
        this.value = wavelength;
    }

    /**
     * Convert wavelength to RGB color model representation.
     * @returns RGB color model representation
     */
    public toRGB(): RGB {
        let x = this.xCIE();
        let y = this.yCIE();
        let z = this.zCIE();

        let r = this.gammaCorr(3.2404542 * x - 1.5371385 * y - 0.4985314 * z);
        let g = this.gammaCorr(-0.969266 * x + 1.8760108 * y + 0.041556 * z);
        let b = this.gammaCorr(0.0556434 * x - 0.2040259 * y + 1.0572252 * z);

        return new RGB(r, g, b);
    }

    /**
     * Convert wavelength to CIE color model representation.
     * @returns RGB color model representation
     */
    public toCIE(): CIE {
        return new CIE(this.xCIE(), this.yCIE(), this.zCIE());
    }

    private xCIE(): number {
        let t1 = (this.value - 442.0) * (this.value < 442.0 ? 0.0624 : 0.0374);
        let t2 = (this.value - 599.8) * (this.value < 599.8 ? 0.0264 : 0.0323);
        let t3 = (this.value - 501.1) * (this.value < 501.1 ? 0.049 : 0.0382);
        return (
            0.362 * Math.exp(-0.5 * t1 * t1) +
            1.056 * Math.exp(-0.5 * t2 * t2) -
            0.065 * Math.exp(-0.5 * t3 * t3)
        );
    }

    private yCIE(): number {
        let t1 = (this.value - 568.8) * (this.value < 568.8 ? 0.0213 : 0.0247);
        let t2 = (this.value - 530.9) * (this.value < 530.9 ? 0.0613 : 0.0322);
        return (
            0.821 * Math.exp(-0.5 * t1 * t1) + 0.286 * Math.exp(-0.5 * t2 * t2)
        );
    }

    private zCIE(): number {
        let t1 = (this.value - 437.0) * (this.value < 437.0 ? 0.0845 : 0.0278);
        let t2 = (this.value - 459.0) * (this.value < 459.0 ? 0.0385 : 0.0725);
        return (
            1.217 * Math.exp(-0.5 * t1 * t1) + 0.681 * Math.exp(-0.5 * t2 * t2)
        );
    }

    /**
     * Gamma correction for RGB, r, g, and b, values.
     * @param u value to be gamma corrected
     * @returns gamma corrected value u
     */
    private gammaCorr(u: number): number {
        if (Math.abs(u) < 0.0031308) return 12.92 * u;
        return 1.055 * Math.pow(u, 0.41666) - 0.055;
    }
}