package com.gathin.photodream;

/**
 * Time-of-day sky palette: night blues, a warm horizon at dawn and sunset, a glow where the sun sits. Pure maths,
 * the caller passes minutes since midnight; every colour stays dark enough for white text on top.
 * From Photo Prints by @shivamsingh262 (#936).
 */
final class Sky {

    private static final class Stop {
        final int minute;
        final int top;
        final int mid;
        final int bottom;
        /** Alpha of the sun/moon glow near the horizon, 0 to 255. */
        final int sun;
        /** Horizontal position of the glow, 0 = left edge, 1 = right edge. */
        final float sunX;

        Stop(int minute, int top, int mid, int bottom, int sun, float sunX) {
            this.minute = minute;
            this.top = top;
            this.mid = mid;
            this.bottom = bottom;
            this.sun = sun;
            this.sunX = sunX;
        }
    }

    /** The palette at one instant: the three gradient colours plus the glow. */
    static final class Palette {
        final int top;
        final int mid;
        final int bottom;
        final int sun;
        final float sunX;

        Palette(int top, int mid, int bottom, int sun, float sunX) {
            this.top = top;
            this.mid = mid;
            this.bottom = bottom;
            this.sun = sun;
            this.sunX = sunX;
        }
    }

    private static final int NIGHT_TOP = 0xFF04060E;
    private static final int NIGHT_MID = 0xFF070C1A;
    private static final int NIGHT_BOTTOM = 0xFF0B1326;

    private static final Stop[] STOPS = {
            new Stop(0, NIGHT_TOP, NIGHT_MID, NIGHT_BOTTOM, 0, 0.30f),
            new Stop(320, NIGHT_TOP, NIGHT_MID, NIGHT_BOTTOM, 0, 0.30f),
            new Stop(390, 0xFF160F2E, 0xFF3B2352, 0xFF8A4A6B, 100, 0.24f),
            new Stop(450, 0xFF12203F, 0xFF5C3A63, 0xFFD3674F, 160, 0.30f),
            new Stop(570, 0xFF0E1A33, 0xFF1F3557, 0xFF43648B, 90, 0.38f),
            new Stop(780, 0xFF0B1524, 0xFF17304F, 0xFF31587F, 60, 0.50f),
            new Stop(1020, 0xFF0D1526, 0xFF20395C, 0xFF4C5470, 90, 0.62f),
            new Stop(1140, 0xFF1B1030, 0xFF6C2E52, 0xFFE2704A, 190, 0.76f),
            new Stop(1185, 0xFF140C27, 0xFF4A2049, 0xFFA54A5C, 130, 0.82f),
            new Stop(1260, 0xFF0A0A1C, 0xFF191230, 0xFF3A1F49, 60, 0.86f),
            new Stop(1350, NIGHT_TOP, NIGHT_MID, NIGHT_BOTTOM, 0, 0.30f),
            new Stop(1440, NIGHT_TOP, NIGHT_MID, NIGHT_BOTTOM, 0, 0.30f),
    };

    private Sky() {}

    /** The palette at {@code minuteOfDay}, clamped to a day. */
    static Palette at(int minuteOfDay) {
        int m = Math.max(0, Math.min(1440, minuteOfDay));
        Stop a = STOPS[0];
        Stop b = STOPS[STOPS.length - 1];
        for (int i = 0; i < STOPS.length - 1; i++) {
            if (m >= STOPS[i].minute && m <= STOPS[i + 1].minute) {
                a = STOPS[i];
                b = STOPS[i + 1];
                break;
            }
        }
        float t = b.minute == a.minute ? 0f : (m - a.minute) / (float) (b.minute - a.minute);
        return new Palette(
                lerpColor(a.top, b.top, t),
                lerpColor(a.mid, b.mid, t),
                lerpColor(a.bottom, b.bottom, t),
                Math.round(a.sun + (b.sun - a.sun) * t),
                a.sunX + (b.sunX - a.sunX) * t);
    }

    /** Blends two opaque ARGB colours channel by channel; {@code t} is 0 to 1. */
    static int lerpColor(int from, int to, float t) {
        float f = Math.max(0f, Math.min(1f, t));
        int a = Math.round(((from >>> 24) & 0xFF) + (((to >>> 24) & 0xFF) - ((from >>> 24) & 0xFF)) * f);
        int r = Math.round(((from >> 16) & 0xFF) + (((to >> 16) & 0xFF) - ((from >> 16) & 0xFF)) * f);
        int g = Math.round(((from >> 8) & 0xFF) + (((to >> 8) & 0xFF) - ((from >> 8) & 0xFF)) * f);
        int b = Math.round((from & 0xFF) + ((to & 0xFF) - (from & 0xFF)) * f);
        return (a << 24) | (r << 16) | (g << 8) | b;
    }
}