initial commit

src/world/Encounter.lua

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+-- Wild encounters from generated encounter tables.
+-- Gen 1: on each step into a grass/water cell, a battle starts when
+-- rand(0..255) < map encounter rate; the slot is picked with the original
+-- probability buckets.
+
+local Encounter = {}
+
+-- cumulative slot thresholds out of 256 (engine/battle/wild_encounters.asm)
+local SLOT_BUCKETS = { 51, 102, 141, 166, 191, 216, 229, 242, 253, 256 }
+
+function Encounter.roll(encounterDef, rng)
+  rng = rng or love.math.random
+  if not encounterDef then return nil end
+  local grass = encounterDef.grass
+  if not grass or grass.rate == 0 then return nil end
+  if rng(0, 255) >= grass.rate then return nil end
+  local pick = rng(0, 255)
+  for i, threshold in ipairs(SLOT_BUCKETS) do
+    if pick < threshold then
+      local slot = grass.slots[i]
+      if slot then
+        return { species = slot.species, level = slot.level }
+      end
+      return nil
+    end
+  end
+  return nil
+end
+
+return Encounter