feat: add Challenges.seedFor and Challenges.forDay

src/challenges.lua

@@ -0,0 +1,69 @@
+-- Named challenge presets: a fixed class, a fixed mutator set and a
+-- deterministic seed, bound together so "today's challenge" means the same
+-- run for everyone who plays it - the daily-seed ritual familiar
+-- roguelikes build around, reproduced here without this module ever
+-- touching the wall clock itself (see Challenges.seedFor's own
+-- caller-supplied day index), so a test can pin any "day" it likes and get
+-- the exact same answer back every time.
+
+local Ascension = require("ascension")
+
+local Challenges = {}
+
+Challenges.CATALOG = {
+  { key = "iron_gauntlet", name = "Iron Gauntlet", class = "fighter", mutators = { "bloodbound" } },
+  { key = "arcane_sprint", name = "Arcane Sprint", class = "mage", mutators = { "famine" } },
+  { key = "shadow_creed", name = "Shadow Creed", class = "rogue", mutators = {} },
+  { key = "wild_hunt", name = "Wild Hunt", class = "ranger", mutators = { "nightblind" } },
+}
+
+Challenges.byKey = {}
+for _, def in ipairs(Challenges.CATALOG) do
+  Challenges.byKey[def.key] = def
+end
+
+-- A Knuth multiplicative hash of `dayIndex`, folded into the same 16-bit
+-- range warren.lua's own default seed (os.time() & 0xFFFF) already uses, so
+-- a challenge seed is never distinguishable from an ordinary one downstream.
+function Challenges.seedFor(dayIndex)
+  return (dayIndex * 2654435761) % 65536
+end
+
+-- The preset and seed "day `dayIndex`" always resolves to - a pure function
+-- of dayIndex alone, so the same day always hands out the same challenge to
+-- everyone who asks it, and a test can walk arbitrary days without waiting
+-- on a clock.
+function Challenges.forDay(dayIndex)
+  local preset = Challenges.CATALOG[(dayIndex % #Challenges.CATALOG) + 1]
+  return preset, Challenges.seedFor(dayIndex)
+end
+
+-- True iff `game` was actually played under `preset`'s own terms: started
+-- as its class, with every mutator it demands active (see
+-- Ascension.isActive) - extra mutators beyond the preset's own are fine,
+-- only a missing requirement fails it. Returns (false, reason) naming
+-- exactly what fell short, so a caller never has to re-derive why.
+function Challenges.satisfiedBy(preset, game)
+  if game.player.class ~= preset.class then
+    return false, "started as " .. tostring(game.player.class) .. " instead of " .. preset.class
+  end
+  for _, key in ipairs(preset.mutators) do
+    if not Ascension.isActive(game.ascension, key) then
+      return false, "missing mutator " .. key
+    end
+  end
+  return true, nil
+end
+
+-- One human-readable line describing `preset`: its display name, the class
+-- it demands, and every mutator it demands active - exactly the terms
+-- Challenges.satisfiedBy itself checks, spelled out for a player deciding
+-- whether to attempt it.
+function Challenges.describe(preset)
+  if #preset.mutators == 0 then
+    return string.format("%s (%s)", preset.name, preset.class)
+  end
+  return string.format("%s (%s + %s)", preset.name, preset.class, table.concat(preset.mutators, ", "))
+end
+
+return Challenges