Port the fishing rods and wild Magikarp

The Old, Good and Super Rods run FishFunction facing water: the map's fish
group and Fish pick no fish, no bite, or a Pokémon from FishGroups and the
time of day's TimeFishGroups. The player casts and jiggles with the
fishing frames drawn from LoadFishingGFX's tiles, shows "!" on a bite, and
the hooked Pokémon attacks as BATTLETYPE_FISH. Facing pieces now use
signed offsets, which the rod above and left of the player needs.

Wild Magikarp no longer stop a battle: LoadEnemyMon redraws their DVs
through CalcMagikarpLength and its filters, as the original does. The
length routine matches the original in the reference emulator.

Part of #27

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/field-items.test.ts

@@ -13,13 +13,16 @@ import {
 import { StartMenuRun } from "../src/game/scripts/start-menu";
 import { defaultTextContext } from "../src/game/scripts/text";
 import { OVERWORLD } from "../src/game/rom/profile";
-import { close, useItem } from "./menu-driver";
+import { fish } from "../src/game/scripts/fish";
+import { Battle, magikarpLength } from "../src/game/battle/battle";
+import { close, open, pick, pickItem, useItem } from "./menu-driver";
 import { settle } from "./world-driver";
 
 const romPath =
   process.env.CRYSTAL_ROM_PATH ??
   "Pokemon - Crystal Version (UE) (V1.1) [C][!].gbc";
 const PLAYERS_ROOM = "24:7",
+  NEW_BARK_TOWN = "24:4",
   ROUTE_30 = "26:1",
   RADIO_TOWER_3F = "3:19",
   GOLDENROD_UNDERGROUND = "3:53",
@@ -38,7 +41,16 @@ const POTION = 0x12,
   ITEMFINDER = 0x37,
   CARD_KEY = 0x7f,
   BASEMENT_KEY = 0x85,
-  SQUIRTBOTTLE = 0xaf;
+  SQUIRTBOTTLE = 0xaf,
+  OLD_ROD = 0x3a,
+  GOOD_ROD = 0x3b,
+  SUPER_ROD = 0x3d;
+const MAGIKARP = 129,
+  KRABBY = 98,
+  CORSOLA = 222,
+  STARYU = 120;
+const FISHGROUP_SHORE = 1;
+const FACING_FISH_RIGHT = 0x13;
 const SPRITEMOVEDATA_SUDOWOODO = 0x17;
 const OAK_WARNING = "OAK: CHRIS! This isn't the time to use that!";
 
@@ -410,4 +422,190 @@ describe.skipIf(!existsSync(romPath))("field items", () => {
       "CHRIS used the\nSQUIRTBOTTLE.",
     ]);
   });
+
+  it("fishes from FishGroups by rod and time of day", () => {
+    const r = new CrystalAssets(new Uint8Array(readFileSync(romPath))).reader;
+    const cast = (rod: number, time: number, ...draws: number[]) =>
+      fish(r, FISHGROUP_SHORE, rod, time, () => {
+        const draw = draws.shift();
+        if (draw === undefined) throw new Error("No draw left.");
+        return draw;
+      });
+    // A bite below 50 percent + 1 ($80), then the first entry the roll
+    // does not exceed: 70 percent + 1, 85 percent + 1, 100 percent.
+    expect(cast(0, 1, 127, 0)).toEqual({ species: MAGIKARP, level: 10 });
+    expect(cast(0, 1, 128)).toBeUndefined();
+    expect(cast(0, 1, 0, 179)).toEqual({ species: MAGIKARP, level: 10 });
+    expect(cast(0, 1, 0, 255)).toEqual({ species: KRABBY, level: 10 });
+    // The Good Rod's last entry is TimeFishGroups 0: Corsola by day,
+    // Staryu from the night on.
+    expect(cast(1, 0, 0, 255)).toEqual({ species: CORSOLA, level: 20 });
+    expect(cast(1, 1, 0, 255)).toEqual({ species: CORSOLA, level: 20 });
+    expect(cast(1, 2, 0, 255)).toEqual({ species: STARYU, level: 20 });
+    expect(cast(2, 1, 0, 0)).toEqual({ species: KRABBY, level: 40 });
+  });
+
+  it("draws a wild Magikarp's DVs again below four feet, except at the Lake of Rage", () => {
+    const assets = new CrystalAssets(new Uint8Array(readFileSync(romPath)));
+    const id = 0x1234;
+    const feet = (dvs: number) => magikarpLength(assets.reader, dvs, id).feet;
+    // Nonzero, unlike the draws that follow.
+    const short = [...Array(0x10000).keys()].find(
+        (dvs) => dvs > 0x100 && feet(dvs) < 4,
+      )!,
+      long = [...Array(0x10000).keys()].find(
+        (dvs) => dvs > 0x100 && feet(dvs) >= 4,
+      )!;
+    /** The wild Magikarp's DVs for these Random draws (then zeros). */
+    const dvs = (mapId: string, ...draws: number[]) => {
+      const game = new Battle({
+        data: assets.pokemon,
+        party: [
+          generatePartyMon(assets.pokemon, {
+            species: 155,
+            level: 5,
+            item: 0,
+            otId: id,
+            ot: "CHRIS",
+            dvs: 0x823b,
+            caughtData: 0,
+          }),
+        ],
+        playerId: id,
+        playerName: "CHRIS",
+        timeOfDay: 1,
+        pokedex: { seen: new Set(), caught: new Set() },
+        random: () => draws.shift() ?? 0,
+        wild: { species: MAGIKARP, level: 10 },
+        fish: true,
+        mapId,
+        text: () => defaultTextContext("CHRIS"),
+      });
+      const first = game.run().next().value;
+      expect(first && "text" in first && first.text).toBe(
+        "The hooked\nMAGIKARP\nattacked!",
+      );
+      return game.enemy.mon.dvs;
+    };
+    const hi = (value: number) => value >> 8,
+      lo = (value: number) => value & 0xff;
+    // No item (0), the DVs, then 39 percent + 1 (100) skips the floor.
+    expect(dvs(NEW_BARK_TOWN, 0, hi(short), lo(short), 99)).toBe(short);
+    expect(
+      dvs(NEW_BARK_TOWN, 0, hi(short), lo(short), 100, hi(long), lo(long), 100),
+    ).toBe(long);
+    // The Lake of Rage (9:6) skips it without a draw, and so does any map
+    // in group 9 or numbered 6.
+    for (const map of ["9:6", "9:1", "24:6"])
+      expect(dvs(map, 0, hi(short), lo(short), 255)).toBe(short);
+  });
+
+  describe("fishing in New Bark Town", () => {
+    /** Facing the sea, with a rod and a constant random byte. */
+    function shore(random: number, rod = OLD_ROD) {
+      const assets = new CrystalAssets(new Uint8Array(readFileSync(romPath)));
+      const world = new GameWorld(
+        assets,
+        () => new Date("2026-09-22T12:00:00"),
+        () => random,
+      );
+      world.state.party = [
+        generatePartyMon(assets.pokemon, {
+          species: 155,
+          level: 5,
+          item: 0,
+          otId: world.playerId,
+          ot: "CHRIS",
+          dvs: 0x823b,
+          caughtData: 0,
+        }),
+      ];
+      world.state.bag.keyItems = [rod];
+      world.state.scenes[NEW_BARK_TOWN] = 1;
+      world.restore({
+        ...world.save(),
+        map: NEW_BARK_TOWN,
+        x: 17,
+        y: 7,
+        direction: "right",
+        objects: [],
+      });
+      return world;
+    }
+    /** USE from the pack, then tick until a page or a battle appears,
+     * recording the player's facings and emotes meanwhile. */
+    function cast(world: GameWorld, rod = OLD_ROD) {
+      open(world);
+      pick(world, "PACK");
+      pickItem(world, rod);
+      const items =
+        world.dialogue?.choice?.kind === "menu"
+          ? world.dialogue.choice.items
+          : [];
+      world.choose(items.indexOf("USE"));
+      const facings = new Set<number | undefined>(),
+        emotes = new Set<number>();
+      let ticks = 0;
+      for (; ticks < 400 && !world.dialogue && !world.battle; ticks++) {
+        world.tick();
+        facings.add(world.poses().find((pose) => pose.id === 0)?.facing);
+        if (world.emote) emotes.add(world.emote.emote);
+      }
+      return { facings, emotes, ticks };
+    }
+
+    it("hooks a Pokémon that attacks", () => {
+      const world = shore(0);
+      const { facings, emotes } = cast(world);
+      // Cast, four bites with the "!" bubble (EMOTE_SHOCK), then the rod
+      // is pulled in.
+      expect(facings).toContain(FACING_FISH_RIGHT);
+      expect([...emotes]).toEqual([0]);
+      expect(world.dialogue?.pages).toEqual(["Oh!\nA bite!"]);
+      // .Movement_RestoreRod hid the bubble before the text.
+      expect(world.emote).toBeUndefined();
+      expect(world.poses().find((pose) => pose.id === 0)?.facing).toBe(
+        FACING_FISH_RIGHT,
+      );
+      world.advanceDialogue();
+      // PutTheRodAway, then the battle: BATTLETYPE_FISH.
+      for (let tick = 0; tick < 100 && !world.battle?.message; tick++)
+        world.tick();
+      expect(
+        world.poses().find((pose) => pose.id === 0)?.facing,
+      ).toBeUndefined();
+      expect(world.battle?.message?.text).toBe(
+        "The hooked\nMAGIKARP\nattacked!",
+      );
+      expect(world.diagnostic).toBe("");
+    });
+
+    it("gets no bite, or nothing at all where the map has no fish", () => {
+      for (const group of [undefined, 0]) {
+        const world = shore(200, SUPER_ROD);
+        if (group !== undefined) world.map.fishGroup = group;
+        const { facings, emotes } = cast(world, SUPER_ROD);
+        expect(facings).toContain(FACING_FISH_RIGHT);
+        expect(emotes.size).toBe(0);
+        expect(world.dialogue?.pages).toEqual(["Not even a nibble!"]);
+        expect(close(world)).toEqual(["Not even a nibble!"]);
+        expect(
+          world.poses().find((pose) => pose.id === 0)?.facing,
+        ).toBeUndefined();
+        expect(world.battle).toBeUndefined();
+        expect(world.state.bag.keyItems).toEqual([SUPER_ROD]);
+      }
+    });
+
+    it("needs water ahead and no surfing, or Oak objects", () => {
+      const turned = shore(0, GOOD_ROD);
+      turned.restore({ ...turned.save(), direction: "left" });
+      expect(useItem(turned, GOOD_ROD)).toEqual([OAK_WARNING]);
+      close(turned);
+      const surfing = shore(0, GOOD_ROD);
+      surfing.restore({ ...surfing.save(), x: 18, playerState: 4 });
+      expect(useItem(surfing, GOOD_ROD)).toEqual([OAK_WARNING]);
+      close(surfing);
+    });
+  });
 });