portal/gesture.js

// The `type: gesture` requirement widget: draw one stroke on a canvas,
// and the stroke becomes the field's value. Mirrors the two house
// patterns at once:
//
// - prosekit-editor.js's hidden-input bridge: the widget writes JSON
//   into a paired hidden <input> and fires a real bubbling `input`
//   event, so the Rust side reuses the exact same RwSignal/on:input
//   wiring every other field kind uses - no bespoke value channel.
// - yes.js's lifecycle: mountGesture returns a handle whose stop()
//   tears everything down (socket, listeners, rAF), because SPA
//   navigation never unloads the document.
//
// When a relay URL is given, the widget also speaks the redoal-relay
// protocol (ADR-0013 in the redoal repo): announce the stroke, receive
// an ack carrying the stroke's gesture key (the decoded path it also
// carries is ignored: decode_key's sketch is too rough to show), and
// receive echoes of similar strokes other visitors drew, shown as
// thumbnails.
// Everything network is best-effort: no relay, refused connection, or
// a dropped socket all degrade to a plain offline drawing input.
//
// Canvas colors can't come from CSS custom properties (same
// constraint yes.js documents), so the widget carries its own copy of
// the palette for both themes - any palette change must land here AND
// in style/main.css.

const THEMES = {
    dark: {
        stroke: '#8ec2c0',
        echo: '#8ec2c0',
    },
    light: {
        stroke: '#47807e',
        echo: '#47807e',
    },
};

const MIN_POINT_DISTANCE = 3; // css px between recorded points
const MAX_ECHOES = 8;
const RECONNECT_BASE_MS = 1000;
const RECONNECT_MAX_MS = 30000;

class GestureWidget {
    constructor(container, hidden, relayUrl) {
        this.container = container;
        this.hidden = hidden || null;
        this.relayUrl = relayUrl || '';
        this.points = [];
        this.drawing = false;
        this.stopped = false;
        this.ws = null;
        this.reconnectDelay = RECONNECT_BASE_MS;
        this.reconnectTimer = null;
        this.pendingAnnounce = null;

        this.canvas = document.createElement('canvas');
        this.canvas.className = 'gesture-canvas';
        container.appendChild(this.canvas);
        this.echoes = document.createElement('div');
        this.echoes.className = 'gesture-echoes';
        container.appendChild(this.echoes);
        if (this.relayUrl) {
            this.status = document.createElement('span');
            this.status.className = 'gesture-status offline';
            this.status.setAttribute('aria-label', 'relay connection');
            container.appendChild(this.status);
        }

        this._themeQuery = window.matchMedia('(prefers-color-scheme: light)');
        this._onTheme = () => this.render();
        this._themeQuery.addEventListener('change', this._onTheme);

        this._onResize = () => { this.sizeCanvas(); this.render(); };
        window.addEventListener('resize', this._onResize);
        this.sizeCanvas();

        this._onDown = (e) => this.beginStroke(e);
        this._onMove = (e) => this.extendStroke(e);
        this._onUp = (e) => this.endStroke(e);
        this.canvas.addEventListener('pointerdown', this._onDown);
        this.canvas.addEventListener('pointermove', this._onMove);
        this.canvas.addEventListener('pointerup', this._onUp);
        this.canvas.addEventListener('pointercancel', this._onUp);

        if (this.relayUrl) this.connect();
    }

    theme() {
        return this._themeQuery.matches ? THEMES.light : THEMES.dark;
    }

    sizeCanvas() {
        const rect = this.canvas.getBoundingClientRect();
        const dpr = window.devicePixelRatio || 1;
        this.canvas.width = Math.max(1, Math.round(rect.width * dpr));
        this.canvas.height = Math.max(1, Math.round(rect.height * dpr));
        this.ctx = this.canvas.getContext('2d');
        this.ctx.scale(dpr, dpr);
        this.cssWidth = rect.width;
        this.cssHeight = rect.height;
    }

    pos(e) {
        const rect = this.canvas.getBoundingClientRect();
        return { x: e.clientX - rect.left, y: e.clientY - rect.top };
    }

    beginStroke(e) {
        e.preventDefault();
        this.canvas.setPointerCapture(e.pointerId);
        // One stroke only - a new pointerdown replaces the old drawing
        // (and any ambient trails from the previous round).
        this.drawing = true;
        this.points = [this.pos(e)];
        this.render();
    }

    extendStroke(e) {
        if (!this.drawing) return;
        const p = this.pos(e);
        const last = this.points[this.points.length - 1];
        const dx = p.x - last.x, dy = p.y - last.y;
        if (Math.sqrt(dx * dx + dy * dy) < MIN_POINT_DISTANCE) return;
        this.points.push(p);
        this.render();
    }

    endStroke() {
        if (!this.drawing) return;
        this.drawing = false;
        if (this.points.length < 2) return;
        const normalized = this.normalized();
        this.setValue({ points: normalized, key: null });
        this.announce(normalized);
    }

    // Canvas-frame normalization into the -1..1 square (the relay
    // re-normalizes around the stroke itself before keying - this
    // just bounds the payload and keeps the stored value
    // resolution-independent).
    normalized() {
        const half = Math.max(this.cssWidth, this.cssHeight) / 2;
        const cx = this.cssWidth / 2, cy = this.cssHeight / 2;
        return this.points.map((p) => [
            Math.round(((p.x - cx) / half) * 10000) / 10000,
            Math.round(((p.y - cy) / half) * 10000) / 10000,
        ]);
    }

    setValue(value) {
        if (!this.hidden) return;
        this.hidden.value = JSON.stringify(value);
        this.hidden.dispatchEvent(new Event('input', { bubbles: true }));
    }

    // ── Relay ──────────────────────────────────────────────────────

    connect() {
        if (this.stopped) return;
        let ws;
        try {
            ws = new WebSocket(this.relayUrl);
        } catch {
            this.scheduleReconnect();
            return;
        }
        this.ws = ws;
        ws.addEventListener('open', () => {
            if (this.stopped) return;
            this.reconnectDelay = RECONNECT_BASE_MS;
            this.status?.classList.replace('offline', 'live');
            if (this.pendingAnnounce) {
                ws.send(JSON.stringify({ type: 'announce', points: this.pendingAnnounce }));
                this.pendingAnnounce = null;
            }
        });
        ws.addEventListener('message', (e) => this.onMessage(e));
        ws.addEventListener('close', () => {
            this.status?.classList.replace('live', 'offline');
            this.ws = null;
            this.scheduleReconnect();
        });
        // 'error' is always followed by 'close'; nothing to do here.
    }

    scheduleReconnect() {
        if (this.stopped || this.reconnectTimer) return;
        this.reconnectTimer = setTimeout(() => {
            this.reconnectTimer = null;
            this.connect();
        }, this.reconnectDelay);
        this.reconnectDelay = Math.min(this.reconnectDelay * 2, RECONNECT_MAX_MS);
    }

    announce(points) {
        if (!this.relayUrl) return;
        if (this.ws && this.ws.readyState === WebSocket.OPEN) {
            this.ws.send(JSON.stringify({ type: 'announce', points }));
        } else {
            this.pendingAnnounce = points;
        }
    }

    onMessage(e) {
        let msg;
        try {
            msg = JSON.parse(e.data);
        } catch {
            return;
        }
        if (msg.type === 'ack') {
            if (this.points.length >= 2) {
                this.setValue({ points: this.normalized(), key: msg.key });
            }
        } else if (msg.type === 'echo') {
            this.addEchoThumbnail(msg);
        }
        // 'error' frames are intentionally silent: the widget is a
        // form field first, and a rate-limited announce shouldn't
        // alarm anyone mid-form.
    }

    addEchoThumbnail(msg) {
        const thumb = document.createElement('canvas');
        thumb.className = 'gesture-echo';
        // Closer strokes render stronger; 500 is comfortably past the
        // relay's default threshold, so everything stays visible.
        const strength = Math.max(0.35, Math.min(1, 1 - msg.distance / 500));
        thumb.style.setProperty('--echo-strength', String(strength));
        this.echoes.prepend(thumb);
        while (this.echoes.children.length > MAX_ECHOES) {
            this.echoes.lastChild.remove();
        }
        const dpr = window.devicePixelRatio || 1;
        const rect = thumb.getBoundingClientRect();
        thumb.width = Math.max(1, Math.round(rect.width * dpr));
        thumb.height = Math.max(1, Math.round(rect.height * dpr));
        const ctx = thumb.getContext('2d');
        ctx.scale(dpr, dpr);
        this.drawPath(ctx, msg.path, rect.width, rect.height, this.theme().echo, 1.5, 0.15);
        // A timeout, not requestAnimationFrame: the class must land on
        // a later tick for the opacity transition to run, and rAF
        // doesn't tick at all in headless engines.
        setTimeout(() => thumb.classList.add('shown'), 30);
    }

    // ── Rendering ──────────────────────────────────────────────────

    // Draw a normalized (-1..1) path fitted into w×h with padding.
    drawPath(ctx, path, w, h, color, width, pad) {
        if (!path || path.length < 2) return;
        const scale = (Math.min(w, h) / 2) * (1 - pad);
        const cx = w / 2, cy = h / 2;
        ctx.strokeStyle = color;
        ctx.lineWidth = width;
        ctx.lineCap = 'round';
        ctx.lineJoin = 'round';
        ctx.beginPath();
        path.forEach(([x, y], i) => {
            const px = cx + x * scale, py = cy + y * scale;
            if (i === 0) ctx.moveTo(px, py);
            else ctx.lineTo(px, py);
        });
        ctx.stroke();
    }

    render() {
        if (!this.ctx) return;
        const t = this.theme();
        this.ctx.clearRect(0, 0, this.cssWidth, this.cssHeight);
        if (this.points.length >= 1) {
            this.ctx.strokeStyle = t.stroke;
            this.ctx.lineWidth = 2;
            this.ctx.lineCap = 'round';
            this.ctx.lineJoin = 'round';
            this.ctx.beginPath();
            this.points.forEach((p, i) => {
                if (i === 0) this.ctx.moveTo(p.x, p.y);
                else this.ctx.lineTo(p.x, p.y);
            });
            this.ctx.stroke();
        }
    }

    stop() {
        this.stopped = true;
        if (this.reconnectTimer) clearTimeout(this.reconnectTimer);
        if (this.ws) {
            // The close event still fires, but scheduleReconnect
            // no-ops once stopped is set.
            try { this.ws.close(); } catch { /* already dead */ }
            this.ws = null;
        }
        window.removeEventListener('resize', this._onResize);
        this._themeQuery.removeEventListener('change', this._onTheme);
        this.canvas.removeEventListener('pointerdown', this._onDown);
        this.canvas.removeEventListener('pointermove', this._onMove);
        this.canvas.removeEventListener('pointerup', this._onUp);
        this.canvas.removeEventListener('pointercancel', this._onUp);
    }
}

export function mountGesture(container, hidden, relayUrl) {
    return new GestureWidget(container, hidden, relayUrl);
}