## Anti-surfer gun: inverse of GF histogram — aim at the VALLEY bin.
## Wave surfers dodge to where they predict bullets won't be (the GF peak).
## They congregate at the valley → aim there to punish their dodge.
## Bins: 31, same as GFGun. Learns from virtual bullet outcomes.

import std/[math, strformat]
import gun_harness/gun_interface

const
  ASBins   = 31
  ASPrior  = 0.1
  DebugAS* = false

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

  AntiSurferGun* = object
    bins:             array[ASBins, float]
    waves:            seq[ASWave]
    cachedTick:       int
    cachedWaveStored: bool

proc initAntiSurferGun*(): AntiSurferGun =
  result.cachedTick = -1
  # Same triangular head-on prior as GFGun — cold-start aims head-on.
  let center = (ASBins - 1) div 2  # = 15
  for i in 0..<ASBins:
    let d = abs(i - center)
    result.bins[i] = ASPrior + 0.5 / float(1 + d)

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

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

proc valleyBin(g: AntiSurferGun): int =
  ## Find the bin with MINIMUM value — where the surfer thinks is safe.
  var best = 0
  for i in 1..<ASBins:
    if g.bins[i] < g.bins[best]:
      best = i
  best

proc predict*(g: var AntiSurferGun, 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:
    g.cachedTick = state.tick
    g.cachedWaveStored = false

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

  let valley   = g.valleyBin()
  let valleyGF = indexToAS(valley)
  let gfAngle  = bearing + valleyGF * mea
  let px = state.selfX + cos(gfAngle) * dist
  let py = state.selfY + sin(gfAngle) * dist

  when DebugAS:
    echo fmt"[as-dbg] predict: valleyGF={valleyGF:.2f} valleyBin={valley} mea={radToDeg(mea):.1f}° aimAngle={radToDeg(gfAngle):.1f}°"

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

proc onResult*(g: var AntiSurferGun, e: FeedbackEvent) =
  ## Same learning as GFGun — track where the enemy actually goes.
  ## ponytail: O(n) scan over waves; stays tiny (< a dozen at a time)
  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 = asToIndex(gf)

  when DebugAS:
    echo fmt"[as-dbg] onResult: delta={radToDeg(bearingDelta):.1f}° MEA={radToDeg(mea):.1f}° GF={gf:.2f} bin={centerIdx}"

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