SirRoboGarage/common_libs/guns/pattern_matcher.nim

## Pattern-matching gun: searches movement history for a matching sequence,
## then plays it forward to predict future position.
## Reference: https://robowiki.net/wiki/Pattern_Matching
## Coordinate system: 0° = East, CCW positive (Tank Royale standard).

import std/math
import gun_harness/gun_interface

const
  HistorySize* = 500
  PatternLen*  = 10  # ticks used as search key; ponytail: fixed, expose if tuning needed

type
  MoveTick = object
    velocity:     float  ## signed speed (px/tick)
    headingDelta: float  ## heading change in radians this tick

  PatternMatcherGun* = object
    buf:            array[HistorySize, MoveTick]
    head:           int   ## next write index (circular)
    count:          int   ## filled entries (capped at HistorySize)
    prevHeading:    float
    prevSpeed:      float
    prevTick:       int
    hasPrev:        bool
    # per-tick cache — avoid re-searching for multiple power bins
    cacheTick:      int
    cacheX:         float
    cacheY:         float
    cacheValid:     bool
    debugGraphics*: bool

# --- circular buffer helpers ---

proc write(g: var PatternMatcherGun, m: MoveTick) {.inline.} =
  g.buf[g.head] = m
  g.head = (g.head + 1) mod HistorySize
  if g.count < HistorySize: inc g.count

proc readAt(g: PatternMatcherGun, i: int): MoveTick {.inline.} =
  ## i = 0 is oldest, i = count-1 is newest
  g.buf[(g.head - g.count + i + HistorySize * 2) mod HistorySize]

# --- linear fallback (same style as linear.nim) ---

proc linearPredict(state: WorldState, bulletSpeed: float): (float, float) =
  let dist  = hypot(state.enemyX - state.selfX, state.enemyY - state.selfY)
  let t     = dist / bulletSpeed
  let hRad  = degToRad(state.enemyHeading)
  let ex    = clamp(state.enemyX + cos(hRad) * state.enemySpeed * t,
                    BotRadius, state.arenaWidth  - BotRadius)
  let ey    = clamp(state.enemyY + sin(hRad) * state.enemySpeed * t,
                    BotRadius, state.arenaHeight - BotRadius)
  (ex, ey)

# --- pattern search + play-forward ---

proc searchAndProject(g: PatternMatcherGun, state: WorldState,
                      bulletSpeed: float): (float, float) =
  ## Returns projected (x, y). Falls back to linear if history too short.
  if g.count < PatternLen * 2:
    return linearPredict(state, bulletSpeed)

  # key = last PatternLen entries
  let keyStart = g.count - PatternLen

  # scan backwards for best match (exclude the key itself)
  var bestScore = Inf
  var bestMatch = -1
  let scanEnd = g.count - PatternLen - 1  # last valid match start
  for i in countdown(scanEnd, 0):
    var score = 0.0
    for k in 0 ..< PatternLen:
      let a = g.readAt(keyStart + k)
      let b = g.readAt(i + k)
      let dv = a.velocity - b.velocity
      let dh = a.headingDelta - b.headingDelta
      score += dv * dv + dh * dh
    if score < bestScore:
      bestScore = score
      bestMatch = i

  if bestMatch < 0:
    return linearPredict(state, bulletSpeed)

  # play forward from bestMatch + PatternLen
  let playStart = bestMatch + PatternLen
  let playAvail = g.count - 1 - playStart  # ticks we can replay

  # iterative time estimate
  let dist0 = hypot(state.enemyX - state.selfX, state.enemyY - state.selfY)
  var t = dist0 / bulletSpeed
  var ex = state.enemyX
  var ey = state.enemyY

  for _ in 0..4:
    let steps = min(int(t + 0.5), playAvail)
    ex = state.enemyX
    ey = state.enemyY
    var heading = degToRad(state.enemyHeading)
    var speed   = state.enemySpeed
    for s in 0 ..< steps:
      let m = g.readAt(playStart + s)
      heading += m.headingDelta
      speed    = m.velocity
      ex += cos(heading) * speed
      ey += sin(heading) * speed
    # if we ran out of replay data, coast linearly from last simulated pos
    let remaining = t - steps.float
    if remaining > 0.0:
      ex += cos(heading) * speed * remaining
      ey += sin(heading) * speed * remaining
    let ndx = ex - state.selfX
    let ndy = ey - state.selfY
    t = sqrt(ndx * ndx + ndy * ndy) / bulletSpeed

  ex = clamp(ex, BotRadius, state.arenaWidth  - BotRadius)
  ey = clamp(ey, BotRadius, state.arenaHeight - BotRadius)
  (ex, ey)

# --- Gun interface ---

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

  # Update history once per tick
  if g.hasPrev and state.tick > g.prevTick:
    var dh = degToRad(state.enemyHeading) - degToRad(g.prevHeading)
    # wrap to [-π, π]
    while dh >  PI: dh -= 2.0 * PI
    while dh < -PI: dh += 2.0 * PI
    g.write(MoveTick(velocity: g.prevSpeed, headingDelta: dh))

  if not g.hasPrev or state.tick > g.prevTick:
    g.prevHeading = state.enemyHeading
    g.prevSpeed   = state.enemySpeed
    g.prevTick    = state.tick
    g.hasPrev     = true
    g.cacheValid  = false  # new tick invalidates cache

  # Return cached result for same-tick calls (multiple power bins)
  if g.cacheValid and state.tick == g.cacheTick:
    return GunPrediction(x: g.cacheX, y: g.cacheY)

  let (px, py) = g.searchAndProject(state, bulletSpeed)
  g.cacheX     = px
  g.cacheY     = py
  g.cacheTick  = state.tick
  g.cacheValid = true
  GunPrediction(x: px, y: py)

proc onResult*(g: var PatternMatcherGun, e: FeedbackEvent) =
  discard  # pattern matcher learns from movement observation, not feedback