/**
 * Locus / allele model for the German gerbil colour-genetics system.
 *
 * Identifiers are English/canonical; all user-facing texts live in de.ts.
 *
 * Each locus owns an ordered list of alleles, most-dominant first. The
 * dominance order drives phenotype resolution and lets us pick the
 * "expressed" allele of a genotype pair.
 *
 * Sources (German gerbil-breeder community):
 *  - rennmaus-info.jimdoweb.com/zucht/farb-genloci-bei-rennmäusen
 *  - de.wikibooks.org/wiki/Die_Rennmaus/_Farbvarianten_und_Farbgenetik
 */

/**
 * Canonical locus keys, in conventional display order. Sls (second spotting
 * locus) is appended LAST so legacy 8-locus genotype strings still parse — a
 * missing Sls token defaults to wild-type sl/sl.
 */
export const LOCUS_ORDER = ['A', 'C', 'D', 'E', 'G', 'P', 'Sp', 'Re', 'Sls'] as const
export type LocusKey = (typeof LOCUS_ORDER)[number]

export interface LocusDef {
  readonly key: LocusKey
  /** German locus name (for tooltips/UI; kept here as reference, mirror in de.ts). */
  readonly nameDe: string
  /** Allele symbols, most-dominant first. Symbols are the canonical serialised form. */
  readonly alleles: readonly string[]
}

/**
 * The eight loci. Multi-allele C series modelled explicitly:
 *   C  = full colour (dominant)
 *   cchm = marked colourpoint ("chinchilla-medium") — more residual pigment
 *   ch = himalayan colourpoint — least pigment
 * E series:
 *   E  = full extension
 *   ef = Schimmel/roan (progressive whitening)
 *   e  = Fox (suppresses eumelanin)
 * Sp/Re/Sls are dominant markers, lethal/semi-lethal when homozygous (see lethality.ts):
 *   Sp  = Schecke (checkered); checkered animals are always Spsp, SpSp dies in utero.
 *   Re  = Rex (curly coat); rex animals are Re-, ReRe is semi-lethal.
 *   Sls = second spotting locus (S(l), WP/Minimalschecke). S(l)s(l) het = the WP
 *         phenotype; S(l)S(l) homozygous = lethal (Rumpback/megacolon). Sp + Sls
 *         together => Superschecke (very high white, deafness-prone).
 */
export const LOCI: Readonly<Record<LocusKey, LocusDef>> = {
  A: { key: 'A', nameDe: 'Agouti', alleles: ['A', 'a'] },
  C: { key: 'C', nameDe: 'Farbe (Albino-Serie)', alleles: ['C', 'cchm', 'ch'] },
  D: { key: 'D', nameDe: 'Verdünnung (Dilute)', alleles: ['D', 'd'] },
  E: { key: 'E', nameDe: 'Extension (Fox/Schimmel)', alleles: ['E', 'ef', 'e'] },
  G: { key: 'G', nameDe: 'Grau (Underwhite)', alleles: ['G', 'g'] },
  P: { key: 'P', nameDe: 'Rotaugenaufhellung (Pink-Eye)', alleles: ['P', 'p'] },
  Sp: { key: 'Sp', nameDe: 'Schecke', alleles: ['Sp', 'sp'] },
  Re: { key: 'Re', nameDe: 'Rex', alleles: ['Re', 're'] },
  Sls: { key: 'Sls', nameDe: 'Zweite Scheckung (WP)', alleles: ['Sl', 'sl'] },
}

/** Set of all valid allele symbols, longest-first (for maximal-munch parsing). */
export const ALLELE_SYMBOLS: readonly string[] = Array.from(
  new Set(LOCUS_ORDER.flatMap((k) => LOCI[k].alleles)),
).sort((a, b) => b.length - a.length)

/** Map every allele symbol to the locus it belongs to. */
export const ALLELE_TO_LOCUS: Readonly<Record<string, LocusKey>> = Object.fromEntries(
  LOCUS_ORDER.flatMap((k) => LOCI[k].alleles.map((al) => [al, k] as const)),
)

/** Dominance rank within a locus (0 = most dominant). */
export function dominanceRank(locus: LocusKey, allele: string): number {
  const idx = LOCI[locus].alleles.indexOf(allele)
  if (idx < 0) throw new Error(`Unknown allele "${allele}" for locus ${locus}`)
  return idx
}

/** The dominant (expressed) allele of a pair at a locus. */
export function dominantAllele(locus: LocusKey, a: string, b: string): string {
  return dominanceRank(locus, a) <= dominanceRank(locus, b) ? a : b
}

/** Wild-type homozygous allele (the most dominant) for a locus. */
export function wildTypeAllele(locus: LocusKey): string {
  return LOCI[locus].alleles[0]
}