// server/sim/battle/displacement.js — Battle methods: displacement of enemies: 受力等级 (force − weight), push (radial /
// directional), pull, the raw mover displace and who can be moved at all.
// Installed on Battle.prototype by server/sim/Battle.js (a method container: never instantiated; `this` is the battle).

import { COLS, PUSH_TILES, PUSH_TILES_EFFECT, PULL_WEAK_SHARE, PULL_CRAWL, PULL_ORIGIN, PULL_STOP_RADIUS, PUSH_DIRECTIONAL_MIN_DIST } from '../constants.js';
import { fin } from './util.js';
import { hypot } from '../detmath.js';

/**
 * Official push distance (tiles) of a 受力等级 (constants.js PUSH_TILES: ≤ −3 → 0, ≥ 3 → the 3 value); `effect` = a 特效
 * push (PRTS 推与拉's 特效 column, PUSH_TILES_EFFECT: 见行者), else the 弹道 column.
 */
export function pushTiles(level, effect = false) {
  const l = Math.round(fin(level, -99));
  if (l <= -3) return 0;
  return (effect ? PUSH_TILES_EFFECT : PUSH_TILES)[Math.min(3, l)];
}

export class BattleDisplacement {
  /**
   * 受力等级 of enemy `e` under a push / pull of 力度 `force` (微小力 −1, 小力 0, 中力 1, 较大力 2, 大力 3, 大力+1 4, 特大力 5):
   * force − its current 重量等级 (massLevel incl. 失重) — PRTS 游戏数据基础 §重量公式, 推与拉 (user playtest #6 item 14).
   */
  forceLevel(e, force) {
    return Math.round(fin(force, 0)) - (e && e.s ? e.s.massLevel : 0);
  }

  /**
   * Push enemy `e` with 力度 `force` (PRTS 推与拉 §推力): the official distance of its 受力等级 (constants.js PUSH_TILES:
   * a 中力 push moves a weight-1 enemy 1.7 tiles, a weight-2 one 0.44, weight 3 0.12, weight ≥ 4 not at all). Radial
   * (the default: away from `from`, the pusher's centre — "沿着干员向自身中心点的射线方向"; the client's buff template
   * knockback[relative]: 琳琅诗怀雅 S3, 山 S3, 莫斯提马 S3) or directional (`dir` = the pusher's direction {x, y}; template
   * knockback[dir], Knockback {_useSourceDirection: true, _decreaseForceLevelWhenNotInDirection: 2}: 推击手, 野鬃 S2
   * "往攻击方向"); a directional push on a target more than 45° off `dir` or nearer than 0.25 tile becomes radial with
   * 受力等级 −2 ("特殊修正"). `fixed` waives both corrections (圣聆初雪 S1 "朝部署方向": KnockBackWithCharacterDirection,
   * PRTS 备注 "不会因角度过大或距离过近而变化方向与力度"); `fixedAngle` only the angle one (PRTS 见行者 S2 备注 "不会因为角度过大
   * 而改变推动的方向或削减力度" — the < 0.25 tile rule still applies). `inward` = a radial push towards `from` (薄绿 S2's "拖拽", PRTS 备注 "实际为
   * 反方向（指向薄绿方向）的推开"), never nearer than PULL_STOP_RADIUS to its centre [ASSUMED: "至面前"]. `effect` = a 特效
   * push (PRTS 推与拉: one frame less of travel than a 弹道 push — constants.js PUSH_TILES_EFFECT / PUSH_EFFECT_SKILLS).
   * Returns the tiles moved.
   */
  push(e, force, { from = null, dir = null, fixed = false, fixedAngle = false, inward = false, effect = false } = {}) {
    if (!this._displaceable(e)) return 0;
    let level = this.forceLevel(e, force);
    const fx0 = fin(from?.x, e.x), fy0 = fin(from?.y, e.y);
    const vx = e.x - fx0, vy = e.y - fy0, d = hypot(vx, vy);
    let ux = 0, uy = 0;
    const dirX = dir ? fin(dir.x, 0) : 0, dirY = dir ? fin(dir.y, 0) : 0;
    const dl = hypot(dirX, dirY);
    if (dl > 0) {
      ux = dirX / dl; uy = dirY / dl;
      if (from && !fixed && (d < PUSH_DIRECTIONAL_MIN_DIST || (!fixedAngle && vx * ux + vy * uy < d * Math.SQRT1_2))) {
        level -= 2;
        if (d > 1e-6) { ux = vx / d; uy = vy / d; }
      }
    } else if (d > 1e-6) { ux = vx / d; uy = vy / d; }
    else if (!inward && from && Array.isArray(from.fwd)) { ux = from.fwd[1]; uy = from.fwd[0]; }
    else return 0;
    let dist = pushTiles(level, effect);
    if (inward && !(dl > 0)) { ux = -ux; uy = -uy; dist = Math.min(dist, Math.max(0, d - PULL_STOP_RADIUS)); }
    return this.displace(e, { x: ux, y: uy }, dist);
  }

  /**
   * Pull enemy `e` with 力度 `force` towards the point `to` (PRTS 推与拉 §拉力 / §捕网): 受力等级 ≥ 0 — all the way, until it
   * is within `stop` tiles of `center` (急停; `center` defaults to `to`, `stop` to PULL_STOP_RADIUS) or reaches `to`;
   * −1 — PULL_WEAK_SHARE of its starting distance to `to`; −2 — PULL_CRAWL tiles; ≤ −3 — nothing. `pullToFront` aims at
   * the official 拉力起点 in front of an operator. Returns the tiles moved.
   */
  pull(e, force, { to, center = null, stop = PULL_STOP_RADIUS } = {}) {
    if (!this._displaceable(e) || !to) return 0;
    // an enemy the puller itself blocks already stands in front of it (at contact) [ASSUMED: no pull, no unblocking]
    if (center && center.side === 'ally' && e.blockedBy === center) return 0;
    const tx = fin(to.x, e.x), ty = fin(to.y, e.y);
    const dx = tx - e.x, dy = ty - e.y, d0 = hypot(dx, dy);
    if (!(d0 > 1e-6)) return 0;
    const ux = dx / d0, uy = dy / d0;
    // travel until inside the stop circle around `center` (smaller root of |e + t·u − c| = stop), else up to `to`
    let full = d0;
    const cx = fin(center?.x, tx), cy = fin(center?.y, ty), r = Math.max(0, fin(stop, 0));
    const wx = e.x - cx, wy = e.y - cy, wu = wx * ux + wy * uy, w2 = wx * wx + wy * wy;
    if (w2 <= r * r) full = 0;
    else {
      const disc = wu * wu - w2 + r * r;
      if (disc >= 0) { const t = -wu - Math.sqrt(disc); if (t >= 0) full = Math.min(full, t); }
    }
    const level = this.forceLevel(e, force);
    const dist = level >= 0 ? full : level === -1 ? Math.min(full, PULL_WEAK_SHARE * d0) : level === -2 ? Math.min(full, PULL_CRAWL) : 0;
    return dist > 1e-6 ? this.displace(e, { x: ux, y: uy }, dist) : 0;
  }

  /** Official distance (tiles) a push of 力度 `force` would move `e` on open ground (0 when it cannot be displaced). */
  pushDistance(e, force, { effect = false } = {}) {
    return this._displaceable(e) ? pushTiles(this.forceLevel(e, force), effect) : 0;
  }

  /** Pull `e` "至面前" of ally `unit` (拉力起点 PULL_ORIGIN tiles ahead along its direction, 急停 around its centre). */
  pullToFront(e, unit, force) {
    if (!unit) return 0;
    const f = Array.isArray(unit.fwd) ? unit.fwd : [0, 1];
    return this.pull(e, force, { to: { x: unit.x + f[1] * PULL_ORIGIN, y: unit.y + f[0] * PULL_ORIGIN }, center: unit, stop: PULL_STOP_RADIUS });
  }

  /**
   * Can `e` be displaced at all: a living enemy, not a leader part of the boss pool, not 失衡免疫 (flag `noDisplace`:
   * 近地悬浮, 浮空, the 胄 parts …) and not a 静态刚体 (data `staticBody`). PRTS 特殊机制 静态刚体: such a unit "可以进入
   * 失衡状态 … 但物理层面上无法产生任何速度或移动" — every air unit of the mode except “炎佑”, plus the boss 昆图斯 (build-data
   * STATIC_BODIES; player report after 0.1.0, "飞机可以被薄绿的技能拉走"). A skill that reaches it still hits it (its targeting
   * is the skill's own: 锏 S3, 薄绿, the 钩索师 …); only the movement is 0, so distance-based effects (drag damage, 见行者 S2's
   * wall stun) come to nothing. [ASSUMED] the 0.1 s 失衡硬直 a 静态刚体 still gets is not modelled (no displacement models it).
   */
  _displaceable(e) {
    return !!(e && e.alive && e.side === 'enemy' && !e.isBoss && !e.s.flags.noDisplace && !(e.def && e.def.staticBody));
  }

  /**
   * Move an enemy `distance` tiles along `dir` = {x, y} (normalised internally) over passable tiles — the raw mover of
   * push() / pull(), which apply the official 力度 − 重量 rules (content uses those; the old `force` option is gone).
   * 失衡免疫 (flag `noDisplace`: 近地悬浮, 浮空 — PRTS 异常效果 "不会被位移影响"), 静态刚体 (data `staticBody`) and leaders
   * ⇒ no movement (_displaceable). The tiles it may cross follow its movement (`motion`): a hovering enemy walks the
   * ground, so it stays on ground-passable tiles.
   */
  displace(e, dir, distance) {
    if (!this._displaceable(e) || !dir) return 0;
    const dxv = fin(dir.x, 0), dyv = fin(dir.y, 0);
    const len = hypot(dxv, dyv);
    if (!(len > 0)) return 0;
    const eff = Math.min(fin(distance, 0), 2 * COLS);
    if (!(eff > 0)) return 0;
    const ux = dxv / len, uy = dyv / len;
    let moved = 0;
    const stepLen = 0.1;
    while (moved + 1e-9 < eff) {
      const s = Math.min(stepLen, eff - moved); // (the last step is a partial one: 0.12 tiles moves 0.12, not 0.2)
      const nx = e.x + ux * s, ny = e.y + uy * s;
      const r = Math.round(ny), c = Math.round(nx);
      const ok = e.motion === 'FLY' ? this.grid.inRect(r, c) : this.grid.groundPassable(r, c);
      if (!ok) break;
      e.x = nx; e.y = ny; moved += s;
    }
    if (moved > 0) {
      this._unblock(e);
      // 失衡 ends the attack clip it stood for (PRTS 状态机: the states are exclusive — UNBALANCE, then DEFAULT → MOVE)
      e.atkStandUntil = -Infinity;
      if (e.route) e.route.pts = null;
      this.fx('displace', { x: e.x, y: e.y, id: e.id });
    }
    return moved;
  }
}