## Gun harness — shared types and Gun concept.
## Coordinate system: 0° = East, CCW positive (Tank Royale standard).
## Bullet speed formula: 20 - 3 * power.

import std/math

const BotRadius* = 18.0  ## hit detection radius in px

type
  EnemyInfo* = object
    id*:                      int
    x*, y*:                   float
    heading*, speed*, energy*: float
    lastSeenTick*:            int  ## tracker tick this enemy was last scanned
                                   ## (the radar freshness signal; 0 if unknown)

  WorldState* = object
    ## All raw data given to every gun every tick.
    # Enemy (current TARGET)
    enemyX*, enemyY*:         float
    enemySpeed*, enemyHeading*: float
    # Self
    selfX*, selfY*:           float
    selfSpeed*, selfHeading*: float
    selfRadarHeading*:        float
    selfEnergy*:              float
    enemyEnergy*:             float
    # Arena
    arenaWidth*, arenaHeight*: float
    # Meta
    tick*:                    int
    # All alive enemies (for movement modules)
    enemies*:                 seq[EnemyInfo]

  GunPrediction* = object
    ## Absolute (x, y) where the gun predicts the enemy will be.
    x*, y*: float

  FeedbackEvent* = object
    ## Outcome of a resolved virtual bullet.
    prediction*:  GunPrediction
    actualX*, actualY*: float  ## actual enemy position at resolution time
    bulletPower*: float
    fireTick*:    int    ## tick the virtual bullet was spawned (predict time)
    powerBin*:    int    ## index into PowerBins the bullet belongs to
    missDistance*: float  ## px; < BotRadius = hit
    hit*:         bool

proc bulletSpeed*(power: float): float {.inline.} =
  20.0 - 3.0 * power

## Gun concept — any type T implementing these two procs is a valid gun.
template isGun*(T: typedesc): bool =
  compiles(
    block:
      var g: T
      let ws = WorldState()
      let p: GunPrediction = g.predict(ws, 0.0)
      let fe = FeedbackEvent()
      g.onResult(fe)
  )