## Guard + measurement for the scale-aware power bar in `bestPower`.
##
## Before the fix `bestPower` required an ABSOLUTE virtual hit rate >= MinHitRate
## (0.40). On the shipped path-metric scale a gun's per-bin rates sit around
## 3-40%, so once every bin had data no bin cleared the bar and bestPower
## silently collapsed to bin 0 (power 1.0). The fix compares each bin's rate to
## PowerBarFrac * (the same gun's best bin rate) — dimensionless, so it
## discriminates at any scale.
##
## Run: nim c -r common_libs/tests/test_power_selection.nim

import std/[strformat, math, random, tables, os]
import gun_harness/gun_interface
import gun_harness/virtual_bullets
import gun_harness/offline_range
import range_guns

const fixturesDir = currentSourcePath().parentDir.parentDir.parentDir / "tools" / "fixtures"

var failures = 0
proc check(name: string, ok: bool) =
  if ok: echo "PASS: ", name
  else: echo "FAIL: ", name; inc failures

proc recordHit(fw: var FitnessWindow, hit: bool) =
  fw.hits[fw.head] = hit
  fw.head = (fw.head + 1) mod WindowSize
  inc fw.count

proc seedFromReport(t: var VirtualTracker, targetId, gunId: int, r: GunReport) =
  if targetId notin t.fitness:
    t.fitness[targetId] = newSeq[GunFitness](t.numGuns)
  var fw = addr t.fitness[targetId][gunId].bins
  for b in 0..<len(PowerBins):
    for _ in 0..<r.bins[b].hits: recordHit(fw[][b], true)
    for _ in 0..<(r.bins[b].shots - r.bins[b].hits): recordHit(fw[][b], false)

proc oldBestPower(fit: GunFitness): int =
  ## The pre-fix rule, reproduced for the A/B comparison only.
  var anyObs = false
  for b in 0..<len(PowerBins):
    if fit.bins[b].count > 0: anyObs = true
  if not anyObs: return 0
  for b in countdown(len(PowerBins) - 1, 0):
    if fit.bins[b].hitRate() >= MinHitRate or fit.bins[b].count == 0: return b
  0

proc main() =
  # A real closed-loop fixture where every gun's rates sit below the old 40%
  # absolute bar — the regime the bug lives in. Fall back to a synthetic fixture
  # if the committed capture is missing.
  let realPath = fixturesDir / "drussgt_vs_crazy.jsonl"
  let fx = if fileExists(realPath): loadFixture(realPath)
           else: synthesizeByName("energy-threshold-turner")
  echo "fixture: ", fx.meta.adversary, " (source=", fx.meta.source, ")"
  let reports = replayFixture(fx, buildAllGunDrivers(seed = 1), metric = bmPath)

  var t = initTracker(reports.len)
  let tid = fx.enemyId
  for gi, r in reports:
    seedFromReport(t, tid, gi, r)

  echo "per-gun per-bin virtual hit rate (measured) and selected bin (old | new):"
  var changed = 0
  var anyOldFellToZero = false
  for gi, r in reports:
    let fit = t.fitnessFor(tid)
    var rates = ""
    for b in 0..<len(PowerBins):
      rates.add fmt" p{PowerBins[b]:.1f}={fit[gi].bins[b].hitRate()*100:4.1f}%({r.bins[b].shots})"
    let ob = oldBestPower(fit[gi])
    let (nb, _) = t.bestPower(gi, tid)
    if ob != nb: inc changed
    # The bug: old rule returns bin 0 even though a higher bin is as good/better.
    if ob == 0 and nb > 0: anyOldFellToZero = true
    echo fmt"  {r.name:<11}{rates}  old=bin{ob} new=bin{nb}"

  echo ""
  echo fmt"selections changed by the fix: {changed}/{reports.len}"
  check "the scale-aware bar changes at least one gun's power selection",
        changed > 0
  check "at least one gun the old absolute 0.40 bar sent to power 1.0 now uses a heavier bullet",
        anyOldFellToZero

  # Relative bar still picks the best bin when it is the lowest power (no
  # pathological power-3 bias).
  block:
    var t2 = initTracker(1)
    # bin0 30%, bin1 25%, bin2 12%, bin3 5% -> bar=15%, only bins 0 and 1 clear
    # it; the HIGHEST acceptable is bin 1, not bin 0 and not bin 3.
    seedFromReport(t2, 7, 0, GunReport(name: "x", bins: [
      BinStat(shots: 100, hits: 30), BinStat(shots: 100, hits: 25),
      BinStat(shots: 100, hits: 12), BinStat(shots: 100, hits: 5)]))
    let (b, p) = t2.bestPower(0, 7)
    echo fmt"  synthetic [30,25,12,5]% -> bin {b} (power {p})"
    check "relative bar picks the highest bin clearing 50% of the best (bin 1)",
          b == 1

  if failures > 0:
    echo "\n", failures, " check(s) FAILED"
    quit(1)
  echo "\nAll power-selection checks passed."

when isMainModule:
  main()