class_name Upgrades
extends RefCounted
## Every upgrade in the game, in code, like the rest of `src/content/`.
##
## [constant ORDER] is a wire format: an upgrade's index is the byte that rides
## the upgrade-state message and the character save. Append, never reorder.

const SPLIT_SHOT := &"split_shot"
const GLASS_CANNON := &"glass_cannon"
const SPREAD := &"spread"
const SNIPER := &"sniper"
const DOUBLESHOT := &"doubleshot"
const POISON := &"poison"
const ERASER := &"eraser"

const ORDER: Array[StringName] = [
	SPLIT_SHOT,
	GLASS_CANNON,
	SPREAD,
	SNIPER,
	DOUBLESHOT,
	POISON,
	ERASER,
]

## Draw weights by rarity. Relative, not percentages -- what matters is that a
## legendary is a story and a common is Tuesday.
const WEIGHTS := {
	UpgradeDef.Rarity.COMMON: 100,
	UpgradeDef.Rarity.UNCOMMON: 45,
	UpgradeDef.Rarity.RARE: 18,
	UpgradeDef.Rarity.LEGENDARY: 4,
}


static func get_def(id: StringName) -> UpgradeDef:
	match id:
		SPLIT_SHOT: return split_shot()
		GLASS_CANNON: return glass_cannon()
		SPREAD: return spread()
		SNIPER: return sniper()
		DOUBLESHOT: return doubleshot()
		POISON: return poison()
		ERASER: return eraser()
	return null


## Wire value. 0 is reserved for "no upgrade", so an id's value is its position
## plus one -- same convention as [Items].
static func index_of(id: StringName) -> int:
	var at := ORDER.find(id)
	return at + 1 if at >= 0 else 0


static func by_index(index: int) -> StringName:
	if index <= 0 or index > ORDER.size():
		return &""
	return ORDER[index - 1]


## Pick [param count] distinct upgrades, weighted by rarity.
##
## Distinct within one offer only -- an upgrade you already hold can and should
## come up again, because taking Split Shot twice is how a shot splits twice.
static func roll_offer(rng: RandomNumberGenerator, count: int) -> Array[StringName]:
	var pool := ORDER.duplicate()
	var picked: Array[StringName] = []
	while picked.size() < count and not pool.is_empty():
		var total := 0
		for id in pool:
			total += _weight_of(id)
		var roll := rng.randi_range(1, maxi(total, 1))
		for i in pool.size():
			roll -= _weight_of(pool[i])
			if roll <= 0:
				picked.append(pool[i])
				pool.remove_at(i)
				break
	return picked


static func _weight_of(id: StringName) -> int:
	var def := get_def(id)
	return int(WEIGHTS.get(def.rarity, 1)) if def != null else 1


# --- The upgrades -----------------------------------------------------------

static func split_shot() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = SPLIT_SHOT
	u.display_name = "Split Shot"
	u.description = "Hitting an enemy spawns two more of the same shot, at 45° to either side, behind it. Take it again to split again."
	u.rarity = UpgradeDef.Rarity.COMMON
	u.split_charges = 1
	return u


static func glass_cannon() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = GLASS_CANNON
	u.display_name = "Glass Cannon"
	u.description = "Double damage, half health. The health is half of whatever your level gives you, so it stays a real price."
	u.rarity = UpgradeDef.Rarity.COMMON
	u.damage_add = 1.0
	u.max_hp_mult = 0.5
	return u


static func spread() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = SPREAD
	u.display_name = "Spread"
	u.description = "Two more shots in a cone either side of your aim. −10% damage."
	u.rarity = UpgradeDef.Rarity.COMMON
	u.side_shots = 2
	u.damage_add = -0.10
	return u


## The only multiplicative damage source, and the only thing that touches bullet
## speed. Both are capped downstream: PlayerStats clamps the speed under the
## tunnelling threshold, because a bullet that moves more than a tile per tick
## walks straight through walls.
static func sniper() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = SNIPER
	u.display_name = "Sniper"
	u.description = "Double damage, multiplied on top of everything else. Half the fire rate, double the bullet speed."
	u.rarity = UpgradeDef.Rarity.COMMON
	u.damage_mult = 2.0
	u.fire_rate_mult = 0.5
	u.bullet_speed_mult = 2.0
	return u


static func doubleshot() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = DOUBLESHOT
	u.display_name = "Doubleshot"
	u.description = "One more shot travelling parallel to the rest. −50% damage."
	u.rarity = UpgradeDef.Rarity.UNCOMMON
	u.parallel_shots = 1
	u.damage_add = -0.50
	return u


static func poison() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = POISON
	u.display_name = "Poison"
	u.description = "Every shot deals another 50% of its damage over the next 10 seconds. Stacks with itself — every hit adds another dose."
	u.rarity = UpgradeDef.Rarity.RARE
	u.poison_fraction = 0.5
	return u


static func eraser() -> UpgradeDef:
	var u := UpgradeDef.new()
	u.id = ERASER
	u.display_name = "Eraser"
	u.description = "Your shots have a 1% chance to delete an enemy projectile they pass through."
	u.rarity = UpgradeDef.Rarity.LEGENDARY
	u.erase_chance = 0.01
	return u