## Recency-weighted GF gun: exponential decay on histogram bins.
## decay=0.998/tick gives ~350-tick half-life — adapts to mid-battle strategy shifts.
## Everything else identical to guess_factor.nim.

import std/math
import gun_harness/gun_interface

const
  GFBins     = 31
  GFPrior    = 0.1
  DecayRate  = 0.998  # ponytail: single global decay, tune if adaptation too slow/fast

type
  DWave = object
    fireX, fireY: float
    fireBearing:  float

  DecayGFGun* = object
    bins:             array[GFBins, float]
    waves:            seq[DWave]
    cachedTick:       int
    cachedWaveStored: bool

proc initDecayGFGun*(): DecayGFGun =
  result.cachedTick = -1
  let center = (GFBins - 1) div 2
  for i in 0..<GFBins:
    let d = abs(i - center)
    result.bins[i] = GFPrior + 0.5 / float(1 + d)

proc gfToIndex(gf: float): int {.inline.} =
  clamp(int(round((gf + 1.0) * 0.5 * float(GFBins - 1))), 0, GFBins - 1)

proc indexToGF(idx: int): float {.inline.} =
  float(idx) / float(GFBins - 1) * 2.0 - 1.0

proc peakBin(g: DecayGFGun): int =
  var best = 0
  for i in 1..<GFBins:
    if g.bins[i] > g.bins[best]:
      best = i
  best

proc predict*(g: var DecayGFGun, state: WorldState, bulletSpeed: float): GunPrediction =
  if bulletSpeed <= 0.0:
    return GunPrediction(x: state.enemyX, y: state.enemyY)

  let dx = state.enemyX - state.selfX
  let dy = state.enemyY - state.selfY
  let dist    = sqrt(dx*dx + dy*dy)
  let bearing = arctan2(dy, dx)
  let mea     = arcsin(clamp(8.0 / bulletSpeed, -1.0, 1.0))

  if state.tick != g.cachedTick:
    # Decay all bins once per tick
    for i in 0..<GFBins:
      g.bins[i] *= DecayRate
    g.cachedTick       = state.tick
    g.cachedWaveStored = false

  if not g.cachedWaveStored:
    g.waves.add DWave(fireX: state.selfX, fireY: state.selfY, fireBearing: bearing)
    g.cachedWaveStored = true

  let peak    = g.peakBin()
  let peakGF  = indexToGF(peak)
  let gfAngle = bearing + peakGF * mea
  let px = state.selfX + cos(gfAngle) * dist
  let py = state.selfY + sin(gfAngle) * dist

  GunPrediction(
    x: clamp(px, BotRadius, state.arenaWidth  - BotRadius),
    y: clamp(py, BotRadius, state.arenaHeight - BotRadius),
  )

proc onResult*(g: var DecayGFGun, e: FeedbackEvent) =
  if g.waves.len == 0: return

  let w = g.waves[0]
  g.waves.delete(0)

  let speed  = bulletSpeed(e.bulletPower)
  let mea    = arcsin(clamp(8.0 / speed, -1.0, 1.0))
  let actualDx      = e.actualX - w.fireX
  let actualDy      = e.actualY - w.fireY
  let actualBearing = arctan2(actualDy, actualDx)
  var bearingDelta  = actualBearing - w.fireBearing
  while bearingDelta >  PI: bearingDelta -= 2.0*PI
  while bearingDelta < -PI: bearingDelta += 2.0*PI

  let gf        = if mea > 1e-10: clamp(bearingDelta / mea, -1.0, 1.0) else: 0.0
  let centerIdx = gfToIndex(gf)

  for i in 0..<GFBins:
    let d = abs(i - centerIdx)
    g.bins[i] += 1.0 / float(1 + d)