## Guess-factor gun: statistical targeting via GF histogram.
## Bins: 31, ranging GF -1 (max CW escape) to +1 (max CCW escape).
## Learns from virtual bullet outcomes; queues one wave per (tick, power bin).
##
## Wave pairing is EXACT: a wave is stored in a ring slot keyed by
## (fireTick, powerBin) and `onResult` looks up the wave with the resolution
## event's `fireTick`, NOT the oldest queued wave. Under the shipped bmPath
## metric bullets leave the arena in non-FIFO order (the aim direction changes
## every tick), so FIFO pairing attached outcomes to the wrong wave. Measured
## over the committed DrussGT fixtures, FIFO mispaired 36.5% of resolutions
## (19.4% of which changed the recorded GF bin). See
## common_libs/tests/audit_wave_pairing.nim. The exact key is the same pattern
## guns/tsetlin.nim and guns/tm_selector.nim use.

import std/[math, strformat]
import gun_harness/gun_interface
import gun_harness/virtual_bullets as vb  # PowerBins: the four power bins the harness spawns
import guns/lead_forecast

const
  GFBins   = 31
  GFPrior  = 0.1
  DebugGF* = false
  WaveRingSlots = 1024
    ## (fireTick, powerBin) -> ring slot. Period = WaveRingSlots/bins = 256 ticks.
    ## A bmPath bullet leaves an 800x600 (Tank Royale max 1000x1000) arena within
    ## ~91 (128) ticks, so a live wave is never overwritten by a newer one.
    ## Identical sizing to tsetlin.nim's TM_TRACE_SLOTS.

type
  Wave = object
    fireX, fireY: float
    fireBearing:  float  # atan2(enemyY-selfY, enemyX-selfX) at fire tick (rad)
    fireTick:     int    # key part: tick the bullet was fired
    bin:          int    # key part: power bin the bullet belonged to
    alive:        bool
    # mea not stored — recomputed from FeedbackEvent.bulletPower at resolution time

  GFGun* = object
    bins:             array[GFBins, float]
    # Exact (fireTick, powerBin)-keyed ring. A resolved bullet is matched to the
    # wave it actually fired, no matter how many other shots resolved first.
    # Heap-backed (seq) so the gun value stays small on the stack — a 1024-slot
    # inline array overflowed the default 8 MB stack in test_power_selection.
    waves:            seq[Wave]
    waveStoredTick:   array[len(vb.PowerBins), int]   # last tick a wave was queued for this bin
    vt:               VelocityTracker  # enemy velocity history (base selection)
    cachedTick:       int   # last tick the velocity tracker was advanced
    wavePushes*:      int  # total waves enqueued (== one per (tick, bin))
    waveStarved*:     int  # onResult found no live wave for its (fireTick, bin)
    # ── pairing integrity ───────────────────────────────────────────────────
    waveResolved*:      int  # onResult calls that found their exact wave
    waveMispaired*:     int  # ring-slot collision (impossible by design): the
                             #     slot held a different fireTick
    debugGraphics*:   bool

proc initGFGun*(): GFGun =
  result.debugGraphics = false
  result.cachedTick = -1
  result.waves = newSeq[Wave](WaveRingSlots)
  for b in 0..<len(vb.PowerBins):
    result.waveStoredTick[b] = -1
  # Seed with a head-on prior: triangular bump at bin 15 (GF=0).
  # Prevents the cold-start tie-break to GF=-1 (bin 0) that poisons early fitness.
  let center = (GFBins - 1) div 2  # = 15
  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: GFGun): int =
  var best = 0
  for i in 1..<GFBins:
    if g.bins[i] > g.bins[best]:
      best = i
  best

proc binForSpeed(spd: float): int {.inline.} =
  ## Map a virtual-bullet speed back to its power-bin index. All four bin speeds
  ## are exactly representable floats; the epsilon is belt-and-braces only.
  for i in 0..<len(vb.PowerBins):
    if abs(spd - bulletSpeed(vb.PowerBins[i])) < 1e-6:
      return i
  -1

proc binForPower(power: float): int {.inline.} =
  ## Map a FeedbackEvent.bulletPower back to its power-bin index.
  for i in 0..<len(vb.PowerBins):
    if abs(power - vb.PowerBins[i]) < 1e-6:
      return i
  -1

proc waveSlot(fireTick, binIdx: int): int {.inline.} =
  ## Exact (fireTick, powerBin) key -> ring slot (same scheme as tsetlin.nim).
  ((fireTick * len(vb.PowerBins)) + binIdx) mod WaveRingSlots

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

  let mea = arcsin(clamp(8.0 / bulletSpeed, -1.0, 1.0))
  # Base forecast: the GF learns the residual against a self-consistent base
  # prediction, so the aim point sits at the radius the bullet actually travels
  # to (see lead_forecast.nim for why this is required, and why the range is
  # radial-fraction blended rather than a plain constant-velocity lead).
  if state.tick != g.cachedTick:
    g.cachedTick = state.tick
    g.vt.observe(state)
  let f = forecastRadialBlend(state, bulletSpeed, g.vt)

  # Queue at most one wave per (tick, power bin). The fire site's extra predict()
  # call for the selected bin lands on the same tick and reuses the queued wave.
  let binIdx = binForSpeed(bulletSpeed)
  if binIdx >= 0 and g.waveStoredTick[binIdx] != state.tick:
    let slot = waveSlot(state.tick, binIdx)
    g.waves[slot] = Wave(
      fireX:       state.selfX,
      fireY:       state.selfY,
      fireBearing: f.bearing,
      fireTick:    state.tick,
      bin:         binIdx,
      alive:       true,
    )
    g.waveStoredTick[binIdx] = state.tick
    inc g.wavePushes

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

  when DebugGF:
    echo fmt"[gf-dbg] predict: peakGF={peakGF:.2f} peakBin={peak} mea={radToDeg(mea):.1f}° aimAngle={radToDeg(gfAngle):.1f}° tick={state.tick}"

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

proc onResult*(g: var GFGun, e: FeedbackEvent) =
  ## Called when a virtual bullet resolves. Look up the wave with this event's
  ## exact (fireTick, powerBin), compute the actual GF, and smooth-add it. A
  ## missing key is counted, never silently mislabelled.
  let binIdx =
    if e.powerBin >= 0 and e.powerBin < len(vb.PowerBins): e.powerBin
    else: binForPower(e.bulletPower)
  if binIdx < 0: return

  let slot = waveSlot(e.fireTick, binIdx)
  var w = addr g.waves[slot]
  if not w.alive:
    inc g.waveStarved
    return
  if w.fireTick != e.fireTick:
    # Ring slot collision: impossible while the ring period exceeds max flight.
    inc g.waveMispaired
    inc g.waveStarved
    return
  inc g.waveResolved

  # Recompute mea from the actual bullet power (correct per-bin, not the cached first-bin mea)
  let speed = bulletSpeed(e.bulletPower)
  let mea   = arcsin(clamp(8.0 / speed, -1.0, 1.0))

  # Compute actual bearing from fire position to where the enemy actually was
  let actualDx = e.actualX - w.fireX
  let actualDy = e.actualY - w.fireY
  let actualBearing = arctan2(actualDy, actualDx)
  var bearingDelta = actualBearing - w.fireBearing
  # Normalize to [-PI, PI]
  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)

  when DebugGF:
    echo fmt"[gf-dbg] onResult: fireBearing={radToDeg(w.fireBearing):.1f}° actualBearing={radToDeg(actualBearing):.1f}° delta={radToDeg(bearingDelta):.1f}° MEA={radToDeg(mea):.1f}° GF={gf:.2f} peakBin={centerIdx}"

  # Triangular smoothing kernel over adjacent bins
  for i in 0..<GFBins:
    let dist = abs(i - centerIdx)
    g.bins[i] += 1.0 / float(1 + dist)

  w.alive = false