import type { RomReader } from "../rom/reader";
import { OVERWORLD } from "../rom/profile";

/** The fishing rods' encounters (engine/events/fish.asm and
 * data/wild/fish.asm). */
export interface FishMon {
  species: number;
  level: number;
}

/** FISHGROUP_DATA_LENGTH: the bite chance, then a table per rod. */
const FISHGROUP_DATA_LENGTH = 7;
/** NITE_F: TimeFishGroups' second species from the night on. */
const NITE_F = 2;

/** Fish: rod 0 (Old), 1 (Good) or 2 (Super) in FishGroups entry `group`
 * (FISHGROUP_*, never FISHGROUP_NONE). A bite when Random falls below the
 * group's chance, then the first entry whose chance a second Random does
 * not exceed; species 0 picks the time of day's TimeFishGroups entry.
 * Undefined when nothing bites. GetFishGroupIndex's swarm groups need
 * DAILYFLAGS1_FISH_SWARM_F and wFishingSwarmFlag, which only trainer calls
 * set; they are not ported, so the map's own group is used. */
export function fish(
  r: RomReader,
  group: number,
  rod: number,
  timeOfDay: number,
  random: () => number,
): FishMon | undefined {
  const entry = OVERWORLD.FishGroups + (group - 1) * FISHGROUP_DATA_LENGTH;
  if (random() >= r.byte(entry)) return undefined;
  let p = r.near(entry + 1 + rod * 2, r.bank(entry));
  const roll = random();
  while (roll > r.byte(p)) p += 3;
  let species = r.byte(p + 1),
    level = r.byte(p + 2);
  if (!species) {
    // .TimeEncounter: the level byte indexes TimeFishGroups.
    const time =
      OVERWORLD.TimeFishGroups + level * 4 + (timeOfDay >= NITE_F ? 2 : 0);
    species = r.byte(time);
    level = r.byte(time + 1);
  }
  return { species, level };
}