class_name Progression
extends RefCounted
## Levels, experience and what a level is worth.
##
## Pure functions over integers, so the curve can be tuned and tested without a
## server, a character, or a running game. The server is the only thing that
## ever calls the mutating side of this; a client is told its level and takes
## the server's word for it.

const MAX_LEVEL := 15
const START_LEVEL := 1
## Hit points added per level gained. Level 1 is SimConfig.PLAYER_MAX_HP, so a
## capped character has PLAYER_MAX_HP + 14 * this.
const HP_PER_LEVEL := 10

## Experience for the first level-up. The curve is tuned so one full clear of a
## depth-1 dungeon lands a little past this -- the first run should end with a
## level and some change, not exactly on the line.
const BASE_XP := 200
## How sharply the requirement grows. 1.0 would be linear; this makes level 15 a
## long-term goal without making level 2 feel far away.
const XP_CURVE := 1.35

## Experience awarded per kill, by what died.
const XP_DRIFTER := 10
const XP_TURRET := 12
const XP_STALKER := 8
const XP_BOSS := 200


## Experience needed to go from [param level] to the next one. Zero at the cap,
## which is what makes "already maxed" a total-ordering question rather than a
## special case at every call site.
static func xp_to_next(level: int) -> int:
	if level >= MAX_LEVEL:
		return 0
	return int(round(float(BASE_XP) * pow(float(level), XP_CURVE)))


## Total experience to reach [param level] from level 1.
static func total_xp_for_level(level: int) -> int:
	var total := 0
	for l in range(START_LEVEL, mini(level, MAX_LEVEL)):
		total += xp_to_next(l)
	return total


## The level a given lifetime experience total corresponds to.
static func level_for_xp(total_xp: int) -> int:
	var level := START_LEVEL
	var spent := 0
	while level < MAX_LEVEL:
		var need := xp_to_next(level)
		if total_xp - spent < need:
			break
		spent += need
		level += 1
	return level


## Progress through the current level, 0..1. Returns 1.0 at the cap so a
## progress bar reads as full rather than empty.
static func level_progress(total_xp: int) -> float:
	var level := level_for_xp(total_xp)
	if level >= MAX_LEVEL:
		return 1.0
	var into := total_xp - total_xp_for_level(level)
	var need := xp_to_next(level)
	return clampf(float(into) / float(maxi(need, 1)), 0.0, 1.0)


static func max_hp_for_level(level: int) -> int:
	var l := clampi(level, START_LEVEL, MAX_LEVEL)
	return SimConfig.PLAYER_MAX_HP + (l - START_LEVEL) * HP_PER_LEVEL


## Experience for killing an enemy, by content id. Unknown ids award nothing
## rather than a default, so a new enemy that nobody scored is obvious in play
## instead of quietly paying out.
static func xp_for_enemy(id: StringName) -> int:
	match id:
		Content.ENEMY_DRIFTER: return XP_DRIFTER
		Content.ENEMY_TURRET: return XP_TURRET
		Content.ENEMY_STALKER: return XP_STALKER
	return 0


static func xp_for_boss(_id: StringName) -> int:
	return XP_BOSS