G2 support

src/core/gen2/NpcTrade.lua

@@ -0,0 +1,165 @@
+-- The in-game trades (engine/events/npc_trade.asm, data/events/npc_trades.asm).
+--
+-- Six of them, one per NPC_TRADE_* constant, reached by the `trade` script
+-- command.  Each row names the mon the NPC wants, the mon it hands over, and
+-- everything that mon arrives wearing: its nickname, its DVs, its held item,
+-- its original trainer's name and ID, and which gender of the requested mon it
+-- will accept.
+--
+-- love-free: the conversation is src/ui/gen2/TradeMenu.lua, this is the rules.
+--
+-- Facts worth keeping:
+--
+--   * NPCTRADE_GIVEMON is what YOU hand over and NPCTRADE_GETMON what you get,
+--     which is the opposite way round from the macro's own argument comment
+--     ("requested mon, offered mon").  GetTradeAttr reads them by name, so the
+--     comment is the only thing that is backwards.
+--   * The row's DVs are TWO RAW BYTES, not a number: attack/defense in the
+--     high and low nibbles of the first, speed/special of the second.  The
+--     mon's gender and shininess fall straight out of them, which is why every
+--     one of these trades hands over the same mon to every player.
+--   * The OT ID is stored little-endian in the table and byte-swapped into the
+--     party struct (Trade_CopyTwoBytesReverseEndian), so the number the table
+--     holds IS the ID the player sees.
+--   * `trade` writes no wScriptVar.  Every outcome -- the refusal, the wrong
+--     mon, the completed trade -- prints its line and returns, and the script
+--     after it carries on either way.
+--   * The trade is one-shot, tracked in wTradeFlags by the trade's own id.  A
+--     second visit prints TRADE_DIALOG_AFTER and nothing else, which is the
+--     check that happens BEFORE the intro line.
+--   * ComputeNPCTrademonStats runs at the END, on the mon that just landed in
+--     the last party slot: the received mon keeps the LEVEL of the one handed
+--     over and recomputes its stats from the new species' bases.
+
+local Mail = require("src.core.gen2.Mail")
+local Mon = require("src.battle.gen2.Mon")
+
+local NpcTrade = {}
+
+-- constants/npc_trade_constants.asm
+NpcTrade.NUM_NPC_TRADES = 6
+NpcTrade.TRADE_GENDER_EITHER = "TRADE_GENDER_EITHER"
+NpcTrade.TRADE_GENDER_MALE = "TRADE_GENDER_MALE"
+NpcTrade.TRADE_GENDER_FEMALE = "TRADE_GENDER_FEMALE"
+
+-- The outcomes, which are also the TRADE_DIALOG_* rows PrintTradeText picks.
+NpcTrade.DIALOG_INTRO = "TRADE_DIALOG_INTRO"
+NpcTrade.DIALOG_CANCEL = "TRADE_DIALOG_CANCEL"
+NpcTrade.DIALOG_WRONG = "TRADE_DIALOG_WRONG"
+NpcTrade.DIALOG_COMPLETE = "TRADE_DIALOG_COMPLETE"
+NpcTrade.DIALOG_AFTER = "TRADE_DIALOG_AFTER"
+
+-- data/generated/events.lua `trades`, 1-based over the 0-based NPC_TRADE_*.
+function NpcTrade.row(eventTables, id)
+  local rows = type(eventTables) == "table" and eventTables.trades
+  if type(rows) ~= "table" then return nil end
+  return rows[(tonumber(id) or 0) + 1]
+end
+
+-- wTradeFlags, a bit per trade id.  Save-side it is a plain set.
+function NpcTrade.done(save, id)
+  local flags = save and save.tradeFlags
+  return (flags and flags[tonumber(id) or -1]) == true
+end
+
+function NpcTrade.markDone(save, id)
+  if not save then return end
+  save.tradeFlags = save.tradeFlags or {}
+  save.tradeFlags[tonumber(id) or 0] = true
+end
+
+-- The row's two DV bytes as the port's named-DV table.  `dn attack, defense`
+-- then `dn speed, special` -- the same packing wild mons use.
+function NpcTrade.dvs(row)
+  local raw = (row and row.dvs) or {}
+  local dvs = {
+    attack = math.floor((raw[1] or 0) / 16),
+    defense = (raw[1] or 0) % 16,
+    speed = math.floor((raw[2] or 0) / 16),
+    special = (raw[2] or 0) % 16,
+  }
+  dvs.hp = Mon.hpDV(dvs)
+  return dvs
+end
+
+-- NPCTRADE_ITEM is an item id BYTE (data/events/npc_trades.asm's `db \5, \6,
+-- \7` tail), and DoNPCTrade copies that byte straight into wPartyMon1Item of
+-- the last party slot, so the received mon wears it like any other held item.
+-- Everywhere else in this port a held item is a KEY of data/generated/items.lua
+-- -- wild base data, trainer party mons and `givepokemail` are named at
+-- extraction, and `givepoke` names its own byte at runtime through World's
+-- itemByIndex -- so the byte is named here too and nothing downstream has to
+-- know the row is raw.  A row item of 0 is NO_ITEM.  A cache that already
+-- carries the name passes straight through.
+function NpcTrade.item(data, row)
+  local raw = row and row.item
+  if raw == nil or raw == 0 then return nil end
+  if type(raw) == "string" then return raw end
+  local items = data and data.items
+  if type(items) == "table" then
+    for id, def in pairs(items) do
+      if type(def) == "table" and def.index == raw then return id end
+    end
+  end
+  local order = data and data.constants and data.constants.itemOrder
+  return (order and order[raw]) or nil
+end
+
+-- CheckTradeGender.  EITHER takes anything; the other two run GetGender on the
+-- mon the player picked and refuse on a mismatch.  A genderless species
+-- ("unknown") satisfies neither, which is the `jr nz` / `jr z` pair falling to
+-- .not_matching.
+function NpcTrade.genderOk(row, mon)
+  local want = row and row.gender
+  if not want or want == NpcTrade.TRADE_GENDER_EITHER then return true end
+  local gender = mon and mon.gender
+  if want == NpcTrade.TRADE_GENDER_MALE then return gender == "male" end
+  return gender == "female"
+end
+
+-- The three refusals NPCTrade checks in order, before any swap happens.
+-- Answers the TRADE_DIALOG_* the conversation should print, or nil for "go
+-- ahead".
+function NpcTrade.check(row, mon)
+  if not row then return NpcTrade.DIALOG_CANCEL end
+  if not mon then return NpcTrade.DIALOG_CANCEL end
+  if mon.species ~= row.give then return NpcTrade.DIALOG_WRONG end
+  if not NpcTrade.genderOk(row, mon) then return NpcTrade.DIALOG_WRONG end
+  return nil
+end
+
+-- DoNPCTrade: the mon at `index` leaves the party and the row's mon takes the
+-- last slot, at the SAME level, with the row's DVs, nickname, held item, OT
+-- name and OT ID.  Answers the two mons, given away first.
+--
+-- RemoveMonFromPartyOrBox runs before TryAddMonToParty, so the incoming mon
+-- lands in the slot vacated by the outgoing one only when that was the last
+-- slot -- otherwise the party closes up and the new mon goes on the end.  That
+-- reordering is visible in the party list, so it is reproduced rather than
+-- tidied into an in-place swap.
+function NpcTrade.perform(data, save, row, index)
+  local party = save and save.party
+  local given = party and party[index]
+  if not (data and given and row) then return nil end
+  local received = Mon.new(data, row.get, given.level, {
+    dvs = NpcTrade.dvs(row),
+    nickname = row.nickname,
+    item = NpcTrade.item(data, row),
+  })
+  if not received then return nil end
+  -- `ot` is what Breeding reads and `otName` what the summary screen prints;
+  -- both are set rather than picking one, because the two halves of the port
+  -- already disagree and a traded mon has to answer both.
+  received.ot, received.otName = row.otName, row.otName
+  received.otId = row.otId
+  table.remove(party, index)
+  -- RemoveMonFromPartyOrBox's "Mail time!" tail.  NPCTrade itself has no mail
+  -- check -- unlike the Day-Care and the PC, it will trade a mon holding a
+  -- letter away -- so the shift here is what stops the mon that closes up into
+  -- that slot inheriting it (src/core/gen2/Mail.lua).
+  Mail.removeSlot(save, index)
+  party[#party + 1] = received
+  return given, received
+end
+
+return NpcTrade