web-cad/frontend/src/canvas/SnapEngine.ts

import type { CADElement } from '../types/cad.types';
import type { SnapPoint } from './RenderEngine';

export type SnapMode =
  | 'endpoint' | 'midpoint' | 'center' | 'intersection'
  | 'nearest' | 'perpendicular' | 'tangent' | 'quadrant'
  | 'grid' | 'none';

export interface SnapConfig {
  enabled: boolean;
  modes: Set<SnapMode>;
  tolerance: number; // world units
  gridSpacing: number;
  polarEnabled: boolean;
  polarAngles: number[]; // angles in degrees for polar tracking
  polarTolerance: number; // angular tolerance in degrees
}

export interface SnapResult {
  point: SnapPoint | null;
  preview: SnapPoint[]; // nearby candidates for visual feedback
}

export class SnapEngine {
  private config: SnapConfig;
  private elements: CADElement[] = [];

  constructor(config?: Partial<SnapConfig>) {
    this.config = {
      enabled: true,
      modes: new Set<SnapMode>(['endpoint', 'midpoint', 'center', 'intersection', 'nearest']),
      tolerance: 10,
      gridSpacing: 20,
      polarEnabled: false,
      polarAngles: [0, 30, 45, 60, 90, 120, 135, 150, 180, 210, 225, 240, 270, 300, 315, 330],
      polarTolerance: 5,
      ...config,
    };
  }

  setElements(elements: CADElement[]): void {
    this.elements = elements;
  }

  setConfig(config: Partial<SnapConfig>): void {
    this.config = { ...this.config, ...config };
  }

  getConfig(): SnapConfig {
    return { ...this.config, modes: new Set(this.config.modes) };
  }

  toggleMode(mode: SnapMode): void {
    if (this.config.modes.has(mode)) {
      this.config.modes.delete(mode);
    } else {
      this.config.modes.add(mode);
    }
  }

  /**
   * Find the best snap point near the given world coordinates.
   * Returns null if no snap point is within tolerance.
   * If refPoint is provided and polar tracking is enabled, snaps to polar angles.
   */
  snap(worldX: number, worldY: number, refPoint?: { x: number; y: number }): SnapResult {
    if (!this.config.enabled || this.config.modes.size === 0) {
      return { point: null, preview: [] };
    }

    // Polar tracking: if we have a reference point, check polar angles first
    if (this.config.polarEnabled && refPoint) {
      const polarResult = this.polarSnap(worldX, worldY, refPoint);
      if (polarResult) {
        return { point: polarResult, preview: [polarResult] };
      }
    }

    const candidates: SnapPoint[] = [];
    const tol = this.config.tolerance;

    // Grid snap (lowest priority)
    if (this.config.modes.has('grid')) {
      const gs = this.config.gridSpacing;
      const gx = Math.round(worldX / gs) * gs;
      const gy = Math.round(worldY / gs) * gs;
      const dist = Math.sqrt((worldX - gx) ** 2 + (worldY - gy) ** 2);
      if (dist < tol) {
        candidates.push({ x: gx, y: gy, type: 'grid' });
      }
    }

    // Element-based snaps
    for (const el of this.elements) {
      if (this.config.modes.has('endpoint')) {
        this.collectEndpoints(el, worldX, worldY, tol, candidates);
      }
      if (this.config.modes.has('midpoint')) {
        this.collectMidpoints(el, worldX, worldY, tol, candidates);
      }
      if (this.config.modes.has('center')) {
        this.collectCenters(el, worldX, worldY, tol, candidates);
      }
      if (this.config.modes.has('nearest')) {
        this.collectNearest(el, worldX, worldY, tol, candidates);
      }
    }

    // Intersection snap (between pairs)
    if (this.config.modes.has('intersection')) {
      this.collectIntersections(worldX, worldY, tol, candidates);
    }

    if (candidates.length === 0) {
      return { point: null, preview: [] };
    }

    // Sort by distance, pick closest
    candidates.sort((a, b) => {
      const da = (a.x - worldX) ** 2 + (a.y - worldY) ** 2;
      const db = (b.x - worldX) ** 2 + (b.y - worldY) ** 2;
      return da - db;
    });

    // Priority: endpoint > intersection > center > midpoint > nearest > grid
    const priority: Record<string, number> = {
      endpoint: 0, intersection: 1, center: 2, midpoint: 3, nearest: 4, grid: 5,
    };

    // Find best within tolerance — prefer higher priority if distances are close
    const best = candidates[0];
    const closeOnes = candidates.filter(c => {
      const d = Math.sqrt((c.x - worldX) ** 2 + (c.y - worldY) ** 2);
      return d < tol * 1.5;
    });
    closeOnes.sort((a, b) => {
      const pa = priority[a.type] ?? 99;
      const pb = priority[b.type] ?? 99;
      if (pa !== pb) return pa - pb;
      const da = (a.x - worldX) ** 2 + (a.y - worldY) ** 2;
      const db = (b.x - worldX) ** 2 + (b.y - worldY) ** 2;
      return da - db;
    });

    return {
      point: closeOnes[0] || best,
      preview: candidates.slice(0, 10),
    };
  }

  private collectEndpoints(el: CADElement, wx: number, wy: number, tol: number, out: SnapPoint[]): void {
    const p = el.properties;
    const check = (x: number, y: number) => {
      const d = Math.sqrt((wx - x) ** 2 + (wy - y) ** 2);
      if (d < tol) out.push({ x, y, type: 'endpoint' });
    };

    switch (el.type) {
      case 'line':
        check(p.x1 ?? el.x, p.y1 ?? el.y);
        check(p.x2 ?? el.x + el.width, p.y2 ?? el.y + el.height);
        break;
      case 'polyline':
      case 'polygon': {
        const pts = p.points || [];
        for (const pt of pts) check(pt.x, pt.y);
        break;
      }
      case 'rect':
        check(el.x - el.width / 2, el.y - el.height / 2);
        check(el.x + el.width / 2, el.y - el.height / 2);
        check(el.x - el.width / 2, el.y + el.height / 2);
        check(el.x + el.width / 2, el.y + el.height / 2);
        break;
      case 'arc': {
        const r = p.radius || el.width / 2;
        const sa = (p.startAngle || 0) * Math.PI / 180;
        const ea = (p.endAngle || 360) * Math.PI / 180;
        check(el.x + r * Math.cos(sa), el.y + r * Math.sin(sa));
        check(el.x + r * Math.cos(ea), el.y + r * Math.sin(ea));
        break;
      }
    }
  }

  private collectMidpoints(el: CADElement, wx: number, wy: number, tol: number, out: SnapPoint[]): void {
    const p = el.properties;
    const check = (x: number, y: number) => {
      const d = Math.sqrt((wx - x) ** 2 + (wy - y) ** 2);
      if (d < tol) out.push({ x, y, type: 'midpoint' });
    };

    switch (el.type) {
      case 'line': {
        const x1 = p.x1 ?? el.x, y1 = p.y1 ?? el.y;
        const x2 = p.x2 ?? el.x + el.width, y2 = p.y2 ?? el.y + el.height;
        check((x1 + x2) / 2, (y1 + y2) / 2);
        break;
      }
      case 'polyline':
      case 'polygon': {
        const pts = p.points || [];
        for (let i = 0; i < pts.length - 1; i++) {
          check((pts[i].x + pts[i + 1].x) / 2, (pts[i].y + pts[i + 1].y) / 2);
        }
        if (el.type === 'polygon' && pts.length > 2) {
          check((pts[pts.length - 1].x + pts[0].x) / 2, (pts[pts.length - 1].y + pts[0].y) / 2);
        }
        break;
      }
      case 'rect':
        check(el.x, el.y - el.height / 2);
        check(el.x, el.y + el.height / 2);
        check(el.x - el.width / 2, el.y);
        check(el.x + el.width / 2, el.y);
        break;
    }
  }

  private collectCenters(el: CADElement, wx: number, wy: number, tol: number, out: SnapPoint[]): void {
    const check = (x: number, y: number) => {
      const d = Math.sqrt((wx - x) ** 2 + (wy - y) ** 2);
      if (d < tol) out.push({ x, y, type: 'center' });
    };

    switch (el.type) {
      case 'circle':
      case 'arc':
        check(el.x, el.y);
        break;
      case 'rect':
        check(el.x, el.y);
        break;
    }
  }

  private collectNearest(el: CADElement, wx: number, wy: number, tol: number, out: SnapPoint[]): void {
    const p = el.properties;
    const check = (x: number, y: number) => {
      const d = Math.sqrt((wx - x) ** 2 + (wy - y) ** 2);
      if (d < tol) out.push({ x, y, type: 'nearest' });
    };

    switch (el.type) {
      case 'line': {
        const x1 = p.x1 ?? el.x, y1 = p.y1 ?? el.y;
        const x2 = p.x2 ?? el.x + el.width, y2 = p.y2 ?? el.y + el.height;
        const np = this.nearestOnSegment(wx, wy, x1, y1, x2, y2);
        check(np.x, np.y);
        break;
      }
      case 'circle': {
        const r = p.radius || el.width / 2;
        const d = Math.sqrt((wx - el.x) ** 2 + (wy - el.y) ** 2);
        if (d > 0) {
          check(el.x + r * (wx - el.x) / d, el.y + r * (wy - el.y) / d);
        }
        break;
      }
      case 'polyline':
      case 'polygon': {
        const pts = p.points || [];
        for (let i = 0; i < pts.length - 1; i++) {
          const np = this.nearestOnSegment(wx, wy, pts[i].x, pts[i].y, pts[i + 1].x, pts[i + 1].y);
          check(np.x, np.y);
        }
        if (el.type === 'polygon' && pts.length > 2) {
          const np = this.nearestOnSegment(wx, wy, pts[pts.length - 1].x, pts[pts.length - 1].y, pts[0].x, pts[0].y);
          check(np.x, np.y);
        }
        break;
      }
    }
  }

  private collectIntersections(wx: number, wy: number, tol: number, out: SnapPoint[]): void {
    // Check pairs of elements near the cursor
    const nearby = this.elements.filter(el => {
      const halfW = el.width / 2 + tol;
      const halfH = el.height / 2 + tol;
      return Math.abs(wx - el.x) < halfW && Math.abs(wy - el.y) < halfH;
    });

    for (let i = 0; i < nearby.length; i++) {
      for (let j = i + 1; j < nearby.length; j++) {
        const pts = this.findIntersection(nearby[i], nearby[j]);
        for (const pt of pts) {
          const d = Math.sqrt((wx - pt.x) ** 2 + (wy - pt.y) ** 2);
          if (d < tol) out.push({ x: pt.x, y: pt.y, type: 'intersection' });
        }
      }
    }
  }

  private findIntersection(a: CADElement, b: CADElement): Array<{ x: number; y: number }> {
    // Get line segments from both elements
    const segsA = this.getElementSegments(a);
    const segsB = this.getElementSegments(b);
    const results: Array<{ x: number; y: number }> = [];

    for (const sa of segsA) {
      for (const sb of segsB) {
        const pt = this.segmentIntersection(sa.x1, sa.y1, sa.x2, sa.y2, sb.x1, sb.y1, sb.x2, sb.y2);
        if (pt) results.push(pt);
      }
    }
    return results;
  }

  private getElementSegments(el: CADElement): Array<{ x1: number; y1: number; x2: number; y2: number }> {
    const p = el.properties;
    switch (el.type) {
      case 'line':
        return [{
          x1: p.x1 ?? el.x, y1: p.y1 ?? el.y,
          x2: p.x2 ?? el.x + el.width, y2: p.y2 ?? el.y + el.height,
        }];
      case 'rect': {
        const hw = el.width / 2, hh = el.height / 2;
        return [
          { x1: el.x - hw, y1: el.y - hh, x2: el.x + hw, y2: el.y - hh },
          { x1: el.x + hw, y1: el.y - hh, x2: el.x + hw, y2: el.y + hh },
          { x1: el.x + hw, y1: el.y + hh, x2: el.x - hw, y2: el.y + hh },
          { x1: el.x - hw, y1: el.y + hh, x2: el.x - hw, y2: el.y - hh },
        ];
      }
      case 'polyline':
      case 'polygon': {
        const pts = p.points || [];
        const segs: Array<{ x1: number; y1: number; x2: number; y2: number }> = [];
        for (let i = 0; i < pts.length - 1; i++) {
          segs.push({ x1: pts[i].x, y1: pts[i].y, x2: pts[i + 1].x, y2: pts[i + 1].y });
        }
        if (el.type === 'polygon' && pts.length > 2) {
          segs.push({ x1: pts[pts.length - 1].x, y1: pts[pts.length - 1].y, x2: pts[0].x, y2: pts[0].y });
        }
        return segs;
      }
      default:
        return [];
    }
  }

  private segmentIntersection(
    x1: number, y1: number, x2: number, y2: number,
    x3: number, y3: number, x4: number, y4: number,
  ): { x: number; y: number } | null {
    const denom = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
    if (Math.abs(denom) < 1e-10) return null;
    const t = ((x1 - x3) * (y3 - y4) - (y1 - y3) * (x3 - x4)) / denom;
    const u = -((x1 - x2) * (y1 - y3) - (y1 - y2) * (x1 - x3)) / denom;
    if (t >= 0 && t <= 1 && u >= 0 && u <= 1) {
      return { x: x1 + t * (x2 - x1), y: y1 + t * (y2 - y1) };
    }
    return null;
  }

  private nearestOnSegment(px: number, py: number, x1: number, y1: number, x2: number, y2: number): { x: number; y: number } {
    const dx = x2 - x1;
    const dy = y2 - y1;
    const lenSq = dx * dx + dy * dy;
    if (lenSq === 0) return { x: x1, y: y1 };
    let t = ((px - x1) * dx + (py - y1) * dy) / lenSq;
    t = Math.max(0, Math.min(1, t));
    return { x: x1 + t * dx, y: y1 + t * dy };
  }

  /**
   * Polar tracking: snap cursor to the nearest polar angle from a reference point.
   * Returns a SnapPoint if the cursor is close to a polar angle, or null.
   */
  private polarSnap(worldX: number, worldY: number, refPoint: { x: number; y: number }): SnapPoint | null {
    const dx = worldX - refPoint.x;
    const dy = worldY - refPoint.y;
    const dist = Math.sqrt(dx * dx + dy * dy);
    if (dist < 1) return null; // too close to reference point

    const cursorAngle = (Math.atan2(dy, dx) * 180) / Math.PI;
    const normalizedCursor = ((cursorAngle % 360) + 360) % 360;

    // Find closest polar angle
    let bestAngle: number | null = null;
    let bestDiff = Infinity;
    for (const angle of this.config.polarAngles) {
      let diff = Math.abs(normalizedCursor - angle);
      if (diff > 180) diff = 360 - diff;
      if (diff < bestDiff) {
        bestDiff = diff;
        bestAngle = angle;
      }
    }

    if (bestAngle === null || bestDiff > this.config.polarTolerance) return null;

    // Project cursor position onto the polar angle line at the same distance
    const rad = (bestAngle * Math.PI) / 180;
    const snapX = refPoint.x + dist * Math.cos(rad);
    const snapY = refPoint.y + dist * Math.sin(rad);

    return { x: snapX, y: snapY, type: 'nearest' };
  }
}