logic-gates/js/bus.js

// Bus system — shift+drag to cut wires and create paired bus terminals + cable
import { state } from './state.js';
import { getOutputPorts, getInputPorts, evaluateAll } from './gates.js';

/**
 * Sample a cubic bezier curve into discrete line segments.
 */
function sampleBezier(p0x, p0y, p1x, p1y, p2x, p2y, p3x, p3y, steps = 24) {
    const points = [];
    for (let i = 0; i <= steps; i++) {
        const t = i / steps;
        const mt = 1 - t;
        const mt2 = mt * mt, mt3 = mt2 * mt;
        const t2 = t * t, t3 = t2 * t;
        points.push({
            x: mt3 * p0x + 3 * mt2 * t * p1x + 3 * mt * t2 * p2x + t3 * p3x,
            y: mt3 * p0y + 3 * mt2 * t * p1y + 3 * mt * t2 * p2y + t3 * p3y
        });
    }
    return points;
}

/**
 * Test intersection between two line segments.
 */
function segmentIntersect(ax1, ay1, ax2, ay2, bx1, by1, bx2, by2) {
    const dx1 = ax2 - ax1, dy1 = ay2 - ay1;
    const dx2 = bx2 - bx1, dy2 = by2 - by1;
    const d = dx1 * dy2 - dy1 * dx2;
    if (Math.abs(d) < 1e-10) return null;

    const t = ((bx1 - ax1) * dy2 - (by1 - ay1) * dx2) / d;
    const u = ((bx1 - ax1) * dy1 - (by1 - ay1) * dx1) / d;

    if (t >= 0 && t <= 1 && u >= 0 && u <= 1) {
        return { x: ax1 + t * dx1, y: ay1 + t * dy1, t };
    }
    return null;
}

/**
 * Get bezier control points for a connection (matching renderer.js drawConnection).
 */
function getConnectionBezier(conn) {
    const fromGate = state.gates.find(g => g.id === conn.from);
    const toGate = state.gates.find(g => g.id === conn.to);
    if (!fromGate || !toGate) return null;

    const fromPort = getOutputPorts(fromGate)[conn.fromPort];
    const toPort = getInputPorts(toGate)[conn.toPort];
    if (!fromPort || !toPort) return null;

    const midX = (fromPort.x + toPort.x) / 2;
    return {
        p0x: fromPort.x, p0y: fromPort.y,
        p1x: midX, p1y: fromPort.y,
        p2x: midX, p2y: toPort.y,
        p3x: toPort.x, p3y: toPort.y
    };
}

/**
 * Find all connections that intersect a cut line.
 * Returns array of { conn, hitPoint } sorted by position along the cut line.
 */
export function findIntersectingConnections(startX, startY, endX, endY) {
    const results = [];

    for (const conn of state.connections) {
        const bez = getConnectionBezier(conn);
        if (!bez) continue;

        const points = sampleBezier(
            bez.p0x, bez.p0y, bez.p1x, bez.p1y,
            bez.p2x, bez.p2y, bez.p3x, bez.p3y
        );

        for (let i = 0; i < points.length - 1; i++) {
            const hit = segmentIntersect(
                startX, startY, endX, endY,
                points[i].x, points[i].y, points[i + 1].x, points[i + 1].y
            );
            if (hit) {
                results.push({ conn, hitPoint: hit });
                break;
            }
        }
    }

    results.sort((a, b) => a.hitPoint.t - b.hitPoint.t);
    return results;
}

/**
 * Create two paired BUS terminals from a cut line and rewire connections through them.
 *
 * Layout:
 *   Wire1 ──┐             ┌── Wire1
 *   Wire2 ──┤  ═══════  ├── Wire2
 *   Wire3 ──┘             └── Wire3
 *        Terminal IN    Terminal OUT
 *
 * The thick cable between them is rendered by the renderer using busPairId.
 */
export function createBusFromCut() {
    const cut = state.busCutting;
    if (!cut) return;

    const hits = findIntersectingConnections(cut.startX, cut.startY, cut.endX, cut.endY);
    if (hits.length === 0) {
        console.log('[bus] no connections intersected');
        return;
    }

    const n = hits.length;
    console.log(`[bus] cut intersected ${n} connection(s)`);

    // Calculate position from hit points
    const avgX = hits.reduce((s, h) => s + h.hitPoint.x, 0) / n;
    const avgY = hits.reduce((s, h) => s + h.hitPoint.y, 0) / n;
    const busH = Math.max(40, (n + 1) * 22);
    const gap = 120; // horizontal distance between the two terminals

    // Reserve IDs
    const busInId = state.nextId++;
    const busOutId = state.nextId++;

    // Create BUS_IN terminal (left — collects wires into bus, only input pins)
    const busIn = {
        id: busInId,
        type: `BUS_IN:${n}`,
        x: avgX - gap / 2 - 15,
        y: avgY - busH / 2,
        value: 0,
        busValues: new Array(n).fill(0),
        busPairId: busOutId
    };

    // Create BUS_OUT terminal (right — distributes bus back to wires, only output pins)
    const busOut = {
        id: busOutId,
        type: `BUS_OUT:${n}`,
        x: avgX + gap / 2 - 15,
        y: avgY - busH / 2,
        value: 0,
        outputValues: new Array(n).fill(0),
        busPairId: busInId
    };

    state.gates.push(busIn, busOut);

    // Rewire: source → BUS_IN input, BUS_OUT output → destination
    // No internal connections — BUS_OUT reads from BUS_IN directly via busPairId
    hits.forEach((hit, i) => {
        const orig = hit.conn;

        // Remove original connection
        state.connections = state.connections.filter(c => c !== orig);

        // Source → BUS_IN input[i]
        state.connections.push({
            from: orig.from,
            fromPort: orig.fromPort,
            to: busIn.id,
            toPort: i
        });

        // BUS_OUT output[i] → original destination
        state.connections.push({
            from: busOut.id,
            fromPort: i,
            to: orig.to,
            toPort: orig.toPort
        });
    });

    console.log(`[bus] created BUS_IN#${busIn.id} ↔ BUS_OUT#${busOut.id} with ${n} channels`);
    evaluateAll();
}

/**
 * Get all bus pairs for rendering the bus cables.
 * Returns array of { inGate, outGate } for each pair.
 */
export function getBusPairs() {
    const pairs = [];
    const seen = new Set();
    for (const gate of state.gates) {
        if (!gate.type.startsWith('BUS_IN:') || !gate.busPairId || seen.has(gate.id)) continue;
        const outGate = state.gates.find(g => g.id === gate.busPairId);
        if (!outGate || !outGate.type.startsWith('BUS_OUT:')) continue;
        seen.add(gate.id);
        seen.add(outGate.id);
        pairs.push({ inGate: gate, outGate });
    }
    return pairs;
}