# presentation/components/diagram.component.ts

> 73 lines of code and 16 definitions.

Tree: Site tree
Language: typescript
Layer: product
Canonical: https://banes-lab.com/anatomy/tree#file-presentation-components-diagram-component-ts
Source text: https://banes-lab.com/assets/sources/source.7f43ad98934bb14f5d4874c807c983ce8c0736651323a2213d71037ef28dc8af.generated.txt

## Definitions

- `clear` (lexical_declaration, line 39, exported)
- `attachDiagramWalk` (lexical_declaration, line 30, exported)
- `prefersStill` (lexical_declaration, line 13)
- `track` (lexical_declaration, line 66, exported)
- `stepsIn` (lexical_declaration, line 17)
- `tick` (lexical_declaration, line 45, exported)
- `nodes` (lexical_declaration, line 18)
- `edges` (lexical_declaration, line 19)
- `byId` (lexical_declaration, line 20)
- `element` (lexical_declaration, line 25)
- `steps` (lexical_declaration, line 31, exported)
- `head` (lexical_declaration, line 36, exported)
- `visible` (lexical_declaration, line 37, exported)
- `timer` (lexical_declaration, line 38, exported)
- `step` (lexical_declaration, line 50, exported)
- `observer` (lexical_declaration, line 60, exported)

## Uses

- [core/analyzers/diagram.analyzer.ts](https://banes-lab.com/source/tree/core/analyzers/diagram.analyzer.ts.md)

## Used by

- [presentation/renderers/diagram.renderer.ts](https://banes-lab.com/source/tree/presentation/renderers/diagram.renderer.ts.md)

## Source

```typescript
import {
    DIAGRAM_EDGE_SELECTOR,
    DIAGRAM_NODE_SELECTOR,
    DIAGRAM_WALKED_CLASS,
    DIAGRAM_WALKING_CLASS,
    DIAGRAM_WALK_PAUSE_MS,
    DIAGRAM_WALK_STEP_MS,
    REDUCED_MOTION_QUERY,
} from "#configuration/constants/diagram.constants";
import type { Disposer } from "#types/base.types";
import { walkOrder } from "#core/analyzers/diagram.analyzer";

const prefersStill = function prefersStill(): boolean {
    return typeof globalThis.matchMedia === "function" && globalThis.matchMedia(REDUCED_MOTION_QUERY).matches;
};

const stepsIn = function stepsIn(canvas: Element): readonly Element[] {
    const nodes = [...canvas.querySelectorAll(DIAGRAM_NODE_SELECTOR)];
    const edges = [...canvas.querySelectorAll(DIAGRAM_EDGE_SELECTOR)];
    const byId = new Map([...nodes, ...edges].map((element) => [element.id, element]));
    return walkOrder(
        nodes.map((node) => node.id),
        edges.map((edge) => edge.id),
    ).flatMap((step) => {
        const element = byId.get(step.id);
        return element === undefined ? [] : [element];
    });
};

export const attachDiagramWalk = function attachDiagramWalk(canvas: Element): Disposer {
    const steps = stepsIn(canvas);
    if (steps.length === 0 || prefersStill()) {
        return () => {};
    }
    canvas.classList.add(DIAGRAM_WALKING_CLASS);
    let head = 0;
    let visible = false;
    let timer: ReturnType<typeof setTimeout> | null = null;
    const clear = function clear(): void {
        for (const step of steps) {
            step.classList.remove(DIAGRAM_WALKED_CLASS);
        }
        head = 0;
    };
    const tick = function tick(): void {
        timer = null;
        if (!visible) {
            return;
        }
        const step = steps[head];
        if (step === undefined) {
            clear();
            timer = setTimeout(tick, DIAGRAM_WALK_STEP_MS);
            return;
        }
        step.classList.add(DIAGRAM_WALKED_CLASS);
        head += 1;
        timer = setTimeout(tick, head >= steps.length ? DIAGRAM_WALK_PAUSE_MS : DIAGRAM_WALK_STEP_MS);
    };
    const observer = new IntersectionObserver((entries) => {
        visible = entries.some((entry) => entry.isIntersecting);
        if (visible && timer === null) {
            tick();
        }
    });
    const track = observer.observe.bind(observer);
    track(canvas);
    return () => {
        observer.disconnect();
        if (timer !== null) {
            clearTimeout(timer);
        }
        clear();
        canvas.classList.remove(DIAGRAM_WALKING_CLASS);
    };
};
```