SirRoboGarage/common_libs/tests/test_vbullet_metric.nim

## Focused guard for the virtual-bullet METRIC switch
## (`GUN_VBULLET_METRIC`, see common_libs/gun_harness/virtual_bullets.nim).
##
## The switch selects how a virtual bullet is scored:
##   point (default) — single point at the fire-time aim distance;
##   path            — swept-segment collision along the whole flight.
##
## This test pins the geometry that actually distinguishes the two models, and
## proves the switch is a real runtime override (not a compile-time constant) by
## driving BOTH models from one process via the explicit `initTracker` /
## `replayFixture` metric parameter.
##
## Run: nim c -r common_libs/tests/test_vbullet_metric.nim

import std/[math, tables, strformat]
import gun_harness/gun_interface
import gun_harness/virtual_bullets
import gun_harness/offline_range
import guns/head_on
import guns/linear

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

# ── parsing / default ─────────────────────────────────────────────────────────

proc testParsing() =
  check "metric parse: empty -> shipped default",
        parseMetric("") == DefaultMetric
  check "metric parse: 'point' -> bmPoint",
        parseMetric("point") == bmPoint
  check "metric parse: 'path' -> bmPath",
        parseMetric("path") == bmPath
  check "metric parse: case/space insensitive",
        parseMetric("  PaTh ") == bmPath
  check "metric parse: unknown -> shipped default (safe fallback, warns)",
        parseMetric("definitely-not-a-metric") == DefaultMetric

# ── geometry that distinguishes the models ────────────────────────────────────

proc mkState(tick: int, ex, ey: float): WorldState =
  WorldState(selfX: 100.0, selfY: 100.0,
             enemyX: ex, enemyY: ey, enemySpeed: 0.0, enemyHeading: 0.0,
             arenaWidth: 1000.0, arenaHeight: 1000.0, tick: tick)

proc runOneBullet(metric: BulletMetric, states: seq[WorldState],
                  targetId = 7): tuple[hits, shots: int] =
  ## Spawn one bullet per power bin at tick 0, aimed at the enemy's tick-0
  ## position, then tick the tracker over the rest of the stream.
  var t = initTracker(1, metric)
  let s0 = states[0]
  let preds = [GunPrediction(x: s0.enemyX, y: s0.enemyY),
               GunPrediction(x: s0.enemyX, y: s0.enemyY),
               GunPrediction(x: s0.enemyX, y: s0.enemyY),
               GunPrediction(x: s0.enemyX, y: s0.enemyY)]
  t.spawnBullets(0, preds, s0, targetId)
  for i in 1..<states.len:
    let st = states[i]
    var enemies: Table[int, tuple[x, y: float, lastSeenTick: int, alive: bool]]
    enemies[targetId] = (x: st.enemyX, y: st.enemyY,
                         lastSeenTick: st.tick, alive: true)
    t.tickBullets(st, enemies,
      proc(gid: GunId, bin: int, e: FeedbackEvent) = discard)
  let fit = t.fitnessFor(targetId)
  for bin in 0..<len(PowerBins):
    let n = min(fit[0].bins[bin].count, WindowSize)
    result.shots += n
    for k in 0..<n:
      if fit[0].bins[bin].hits[k]: inc result.hits

proc testRecedingTarget() =
  ## Enemy recedes radially along the bullet's own ray, faster than the slowest
  ## bullet. The point model fires at the tick-0 aim distance (200 px) and the
  ## enemy has already moved past it -> miss. The path model keeps the bullet
  ## flying until the wall and it physically catches up -> hit.
  var states: seq[WorldState]
  for t in 0..<140:
    states.add mkState(t, 300.0 + 4.0*t.float, 100.0)
  let p = runOneBullet(bmPoint, states)
  let q = runOneBullet(bmPath, states)
  check "receding target: point model scores 0 hits (enemy left the aim point)",
        p.hits == 0
  check "receding target: path model catches the receding enemy", q.hits > 0
  check "receding target: both models emit the same number of samples",
        p.shots == q.shots and q.shots == len(PowerBins)
  echo fmt"   receding: point {p.hits}/{p.shots}, path {q.hits}/{q.shots}"

proc testPerpendicularTarget() =
  ## Enemy crosses the ray perpendicularly. The ray and the enemy's trajectory
  ## intersect at the enemy's tick-0 position, but the bullet is 200 px away at
  ## that instant. A physical swept-collision model must MISS; a naive
  ## path-intersection model would wrongly hit.
  var states: seq[WorldState]
  for t in 0..<140:
    states.add mkState(t, 300.0, 100.0 + 8.0*t.float)
  let q = runOneBullet(bmPath, states)
  check "perpendicular target: path model misses (timing matters, not just path)",
        q.hits == 0
  echo fmt"   perpendicular: path {q.hits}/{q.shots}"

# ── switch drives the offline replay ─────────────────────────────────────────

proc testReplayMetricOverride() =
  let fx = synthesizeConstantVelocity(ticks = 140)
  let p = replayFixture(fx, @[makeDriver("Linear", LinearGun())], metric = bmPoint)
  let q = replayFixture(fx, @[makeDriver("Linear", LinearGun())], metric = bmPath)
  check "replay: both metrics record samples on a fixture",
        p[0].shots > 0 and q[0].shots > 0
  check "replay: path model is deterministic run-to-run",
        block:
          let q2 = replayFixture(fx, @[makeDriver("Linear", LinearGun())], metric = bmPath)
          q2[0].hits == q[0].hits and q2[0].shots == q[0].shots
  echo fmt"   constant-velocity Linear: point {p[0].hits}/{p[0].shots}, path {q[0].hits}/{q[0].shots}"

# ── driver ────────────────────────────────────────────────────────────────────

testParsing()
testRecedingTarget()
testPerpendicularTarget()
testReplayMetricOverride()

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