const rand: () => number = Math.random; // [todo]

function randBetween(x: number, y: number): number {
  const lo = min(x, y), hi = max(x, y);
  return lo + rand() * (hi - lo);
}

function oneOf<A>(...xs: A[]): A {
  return xs[Math.floor(rand() * xs.length)]!;
}

const max = Math.max;
const min = Math.min;


type LD = 'light' | 'dark';

namespace Oklch {
  export type Channel = 'l' | 'c' | 'h';
  export type Channels = Record<Channel, number>;
  export type ChannelMap = (x: number) => number;
  export type ChannelMaps = Record<Channel, ChannelMap>;
}

export class Oklch {
  static lightFor(baseL: number): number { return randBetween(baseL, MAXL); }

  static darkFor(baseL: number): number { return randBetween(MINL, baseL); }

  static isLight(l: number): boolean { return l >= MINL_LIGHT; }

  static brightFor(l: number, baseC: number): number {
    if (Oklch.isLight(l)) { return randBetween(baseC, MAXC_LIGHT); }
    else { return randBetween(baseC, MAXC_DARK); }
  }

  static dullFor(l: number, baseC: number): number {
    if (Oklch.isLight(l)) { return randBetween(baseC, MINC_LIGHT); }
    else { return randBetween(baseC, MINC_DARK); }
  }

  static analogous1(baseH: number): number {
    const size = randBetween(MINH_SEP, 2 * MINH_SEP);
    return rand() > 0.5 ? baseH + size : baseH - size;
  }

  static analogous(baseH: number, count: number): number[] {
    const minWidth = min(count * MINH_SEP, MAXH_WIDTH * 0.8);
    const width = randBetween(minWidth, MAXH_WIDTH);
    const sep = width / (count - 1);
    const start = baseH - (width / 2);
    const numbers = Array.from({length: count}, (_u, i) => start + i * sep);
    return rand() > 0.5 ? numbers : numbers.reverse();
  }

  static complementary1(baseH: number): number {
    return Oklch.analogous1((baseH + 180) % 360);
  }

  static complementary(baseH: number, count: number): number[] {
    const angle = randBetween(180 - MAXH_COMPL/2, 180 + MAXH_COMPL/2);
    return Oklch.analogous(baseH + angle, count);
  }

  static triad(baseH: number): [number, number] {
    const angle = randBetween(120 - MAXH_TRIAD/2, 120 + MAXH_TRIAD/2);
    return [baseH - angle, baseH + angle];
  }

  readonly l: number; readonly c: number; readonly h: number;

  static baseLuma(ld?: LD): number {
    if (ld == 'light') {
      return randBetween(MINL_LIGHT, MAXL);
    } else if (ld == 'dark') {
      return randBetween(MINL, MAXL_DARK);
    } else {
      return randBetween(MINL, MAXL);
    }
  }

  static baseChroma(l: number): number {
    if (l >= MINL_LIGHT) {
      return randBetween(MINC_LIGHT, MAXC_LIGHT);
    } else {
      return randBetween(MINC_DARK, MAXC_DARK);
    }
  }

  static baseHue(): number { return rand() * 360; }

  constructor();
  constructor(ld: LD);
  constructor(cs: Oklch.Channels);
  constructor(l: number, c: number, h: number);
  constructor(lcsld?: number | Oklch.Channels | LD,
              cc?: number, hh?: number) {
    if (typeof lcsld == 'string' || lcsld == undefined) {
      this.l = Oklch.baseLuma(lcsld as LD | undefined);
      this.c = Oklch.baseChroma(this.l);
      this.h = Oklch.baseHue();
    } else if (cc == undefined && hh == undefined) {
      const {l, c, h} = lcsld as Oklch.Channels;
      this.l = l; this.c = c; this.h = h;
    } else {
      this.l = lcsld as number; this.c = cc!; this.h = hh!;
    }
  }

  css(alpha: number = 1): string {
    return `oklch(${this.l} ${this.c} ${this.h} / ${alpha})`;
  }

  with(lch: Partial<Record<Oklch.Channel, number | Oklch.ChannelMap>>): Oklch {
    function call(comp: undefined | number | Oklch.ChannelMap, x: number) {
      if (comp == undefined) { return x; }
      else if (typeof comp == 'function') { return comp(x); }
      else { return comp as number; }
    }
    return new Oklch({
      l: call(lch.l, this.l),
      c: call(lch.c, this.c),
      h: call(lch.h, this.h),
    });
  }
}


const MAXL = 0.9;
const MINL = 0.4;
const MINL_LIGHT = 0.7;
const MAXL_DARK = 0.65;

const MINC_LIGHT = 0.08;
const MAXC_LIGHT = 0.1;
const MINC_DARK = 0.12;
const MAXC_DARK = 0.175;

// max spread for a sequence of analogous colors. unless that would put them
// too close together
const MAXH_WIDTH = 80;

// minimum distance between adjacent analogous colors
const MINH_SEP = 5;

// size of the wedge a "complementary" color can be in
const MAXH_COMPL = 40;

// size of the wedge a "triadic" color can be in
const MAXH_TRIAD = 25;

export type SchemeType = 'triad' | 'fin-belly' | 'fin-body';

export type OuterLayer = 'outer' | 'spines' | 'vitiligo1';
export type SockLayer  = 'stripes' | 'cuffs';
export type FinLayer   = 'fins1' | 'fins2' | 'fins3' | 'vitiligo4';
export type BellyLayer = 'belly1' | 'vitiligo3' | 'belly2' | 'vitiligo2';
export type MiscLayer  = 'eyes' | 'masks' | 'claws' | 'lines';
export type Layer      =
  OuterLayer | SockLayer | FinLayer | BellyLayer | MiscLayer;

export type ColsOf<A extends string> = Record<A, Oklch>;
export type OuterCols = ColsOf<OuterLayer>;
export type SockCols  = ColsOf<SockLayer>;
export type FinCols   = ColsOf<FinLayer>;
export type BellyCols = ColsOf<BellyLayer>;
export type MiscCols  = ColsOf<MiscLayer>;
export type Colors    = ColsOf<Layer>;

export type Scheme = Colors & {type: SchemeType};

export const allLayers: Layer[] =
  ['outer', 'spines', 'stripes', 'cuffs', 'fins1', 'fins2', 'fins3',
   'belly1', 'belly2', 'masks', 'claws', 'vitiligo1', 'vitiligo2', 'vitiligo3',
   'vitiligo4', 'eyes', 'lines'];

export function makeColorInfo<A>(f: (l: Layer) => A): Record<Layer, A> {
  return Object.fromEntries(allLayers.map(l => [l, f(l)])) as Record<Layer, A>;
}


export function colors(): Scheme {
  const outer = new Oklch('dark');
  let outerCols: OuterCols =
    { outer, spines: mkSpines(outer), vitiligo1: mkVitiligo(outer) };

  const stripes = mkStripes();
  let sockCols: SockCols = { stripes, cuffs: mkCuffs(stripes) };

  let finCols: FinCols, bellyCols: BellyCols, type: SchemeType;
  const whichBody = rand();
  if (whichBody > 2/3) {
    type = 'triad';
    const [f, b] = Oklch.triad(outer.h);
    finCols = mkFins(f, outer); bellyCols = mkBelly(b);
  } else if (whichBody > 1/3) {
    type = 'fin-belly';
    const [f, b] = Oklch.complementary(outer.h, 2);
    finCols = mkFins(f!, outer); bellyCols = mkBelly(b!);
  } else {
    type = 'fin-body';
    finCols = mkFins(Oklch.analogous1(outer.h), outer);
    bellyCols = mkBelly(Oklch.complementary1(outer.h));
  }

  let miscCols = mkMisc(outerCols, finCols, bellyCols);

  return merge(outerCols, sockCols, finCols, bellyCols, miscCols, type);
}


function mkSpines(outer: Oklch): Oklch {
  return outer.with({
    l: x => x * 0.8,
    c: x => x * 1.1,
    h: x => randBetween(x + 12, x - 12),
  })
}

function mkVitiligo(outer: Oklch): Oklch {
  return outer.with({
    l: x => randBetween(max(x, 0.94), 0.985), // exception to MAXL
    c: x => randBetween(min(x, 0.1), MINC_LIGHT),
  });
}

function mkStripes(): Oklch {
  return new Oklch({
    l: randBetween(0.8, MAXL),
    c: randBetween(MINC_LIGHT, MAXC_LIGHT),
    h: rand() * 360
  });
}

function mkCuffs(sock: Oklch): Oklch {
  return sock.with({
    l: x => randBetween(x * 0.85, x * 0.65),
    c: x => randBetween(x, MAXC_LIGHT),
    h: x => randBetween(x + 8, x - 8),
  });
}

function mkFins(h: number, outer: Oklch): FinCols {
  const [fin1Hue, fin2Hue, fin3Hue] = Oklch.analogous(h, 3);
  const [ll, cc] = oneOf(
    [Oklch.lightFor, Oklch.dullFor], [Oklch.darkFor, Oklch.brightFor]);

  const fins1 = new Oklch(ll(outer.l), cc(outer.l, outer.c), fin1Hue!);
  const fins2 = new Oklch(ll(fins1.l), cc(fins1.l, fins1.c), fin2Hue!);
  const fins3 = new Oklch(ll(fins2.l), cc(fins2.l, fins2.c), fin3Hue!);
  const vitiligo4 = mkVitiligo(fins1);
  return { fins1, fins2, fins3, vitiligo4 };
}

function mkBelly(h: number): BellyCols {
  const [belly1Hue, belly2Hue] = Oklch.analogous(h, 2);
  const belly1 = new Oklch({
    l: randBetween(0.7, MAXL),
    c: Oklch.baseChroma(1),
    h: belly1Hue!
  });
  const belly2 = belly1.with({
    l: x => min(MAXL, x * 1.1),
    c: x => x * 0.9,
    h: belly2Hue!,
  });
  const vitiligo3 = mkVitiligo(belly1);
  const vitiligo2 = mkVitiligo(belly2);
  return { belly1, belly2, vitiligo2, vitiligo3 };
}

function mkMisc(o: OuterCols, f: FinCols, b: BellyCols): MiscCols {
  const masks = new Oklch({
    l: randBetween(0.8, MAXL),
    c: randBetween(0.01, 0.06),
    h: Oklch.analogous1(oneOf(o.outer, b.belly1, f.fins1).h)
  });
  return {
    masks,
    eyes: new Oklch({
      l: Oklch.baseLuma('light'),
      c: randBetween(0.28, MAXC_LIGHT),
      h: oneOf(Oklch.analogous1, Oklch.complementary1)(o.outer.h)
    }),
    claws: masks.with({
      l: x => min(MAXL, x + randBetween(0, 0.1)),
      c: randBetween(0.01, 0.06),
      h: Oklch.analogous1,
    }),
    lines: new Oklch({
      l: randBetween(0.01, 0.06),
      c: Oklch.baseChroma(0),
      h: Oklch.analogous1(o.outer.h)
    }),
  };
}

function merge({ outer, spines, vitiligo1 }: OuterCols,
               { stripes, cuffs }: SockCols,
               { fins1, fins2, fins3, vitiligo4 }: FinCols,
               { belly1, vitiligo3, belly2, vitiligo2 }: BellyCols,
               { eyes, masks, claws, lines }: MiscCols,
               type: SchemeType): Scheme {
  return {
    outer, spines, vitiligo1, stripes, cuffs, fins1, fins2, fins3, vitiligo4,
    belly1, vitiligo3, belly2, vitiligo2, eyes, masks, claws, lines, type
  };
}