# Flowchart Parser

As mentioned in the previous section, we use [getDiagramFromText](https://github.com/mermaid-js/mermaid/blob/00d06c7282a701849793680c1e97da1cfdfcce62/packages/mermaid/src/Diagram.ts#L80) to parse the full defination and get the [Diagram](https://github.com/mermaid-js/mermaid/blob/00d06c7282a701849793680c1e97da1cfdfcce62/packages/mermaid/src/Diagram.ts#L15) json from it.

In this section we will be diving into how the [flowchart parser](https://github.com/excalidraw/mermaid-to-excalidraw/blob/master/src/parser/flowchart.ts#L256) works behind the scenes.

![image](https://github.com/excalidraw/excalidraw/assets/11256141/2a097bbb-64bf-49d6-bf7f-21172bdb538d)

We use `diagram.parser.yy` attribute to parse the data. If you want to know more about how the `diagram.parse.yy` attribute looks like, you can check it [here](https://github.com/mermaid-js/mermaid/blob/00d06c7282a701849793680c1e97da1cfdfcce62/packages/mermaid/src/diagrams/flowchart/flowDb.js#L768), however for scope of flowchart we are using **3** APIs from this parser to compute `vertices`, `edges` and `clusters` as we need these data to transform to [ExcalidrawElementSkeleton](https://github.com/excalidraw/excalidraw/blob/master/packages/excalidraw/data/transform.ts#L133C13-L133C38).

For computing `vertices` and `edge`s lets consider the below svg generated by mermaid

![image](https://github.com/excalidraw/excalidraw/assets/11256141/d7013305-0b90-4fa0-a66e-b4f4604ad0b2)

## Computing the vertices

We use `getVertices` API from `diagram.parse.yy` to get the vertices for a given flowchart.

Considering the same example this is the response from the API

```js
{
	"start": {
		"id": "start",
		"labelType": "text",
		"domId": "flowchart-start-1414",
		"styles": [],
		"classes": [],
		"text": "start",
		"props": {}
	},
	"stop": {
		"id": "stop",
		"labelType": "text",
		"domId": "flowchart-stop-1415",
		"styles": [],
		"classes": [],
		"text": "stop",
		"props": {}
	}
}
```

The dimensions and position is missing in this response and we need that to transform to [ExcalidrawElementSkeleton](https://github.com/excalidraw/excalidraw/blob/master/packages/excalidraw/data/transform.ts#L133C13-L133C38), for this we have our own parser [`parseVertex`](https://github.com/excalidraw/mermaid-to-excalidraw/blob/master/src/parseMermaid.ts#L178) which takes the above response and uses the `svg` together to compute position, dimensions and cleans up the response.

The final output from `parseVertex` looks like :point_down:

```js
{
	"start": {
		"id": "start",
		"labelType": "text",
		"text": "start",
		"x": 0,
		"y": 0,
		"width": 67.796875,
		"height": 44,
		"containerStyle": {},
		"labelStyle": {}
	},
	"stop": {
		"id": "stop",
		"labelType": "text",
		"text": "stop",
		"x": 117.796875,
		"y": 0,
		"width": 62.3828125,
		"height": 44,
		"containerStyle": {},
		"labelStyle": {}
	}
}
```

## Computing the edges

The lines and arrows are considered as `edges` in mermaid as shown in the above diagram. We use `getEdges` API from `diagram.parse.yy` to get the edges for a given flowchart. Considering the same example this is the response from the API

```js
[
  {
    start: "start",
    end: "stop",
    type: "arrow_point",
    text: "",
    labelType: "text",
    stroke: "normal",
    length: 1,
  },
];
```

Similarly here the dimensions and position is missing and we compute that from the svg. The [`parseEdge`](https://github.com/excalidraw/mermaid-to-excalidraw/blob/master/src/parseMermaid.ts#L245) takes the above response along with `svg` and computes the position, dimensions and cleans up the response.

The final output from `parseEdge` looks like :point_down:

```js
[
  {
    start: "start",
    end: "stop",
    type: "arrow_point",
    text: "",
    labelType: "text",
    stroke: "normal",
    startX: 67.797,
    startY: 22,
    endX: 117.797,
    endY: 22,
    reflectionPoints: [
      {
        x: 67.797,
        y: 22,
      },
      {
        x: 117.797,
        y: 22,
      },
    ],
  },
];
```

## Computing the Subgraphs

`Subgraphs` is collection of elements grouped together. The Subgraphs map to `grouping` elements in Excalidraw.

Lets consider the below example :point_down:

![image](https://github.com/excalidraw/excalidraw/assets/11256141/5243ce4c-beaa-43d2-812a-0577b0a574d7)

We use `getSubgraphs` API to get the subgraph data for a given flowchart. Considering the same example this is the response from the API

```js
[
  {
    id: "one",
    nodes: ["flowchart-a2-1399", "flowchart-a1-1400"],
    title: "one",
    classes: [],
    labelType: "text",
  },
];
```

For position and dimensions we use the svg to compute. The [`parseSubgraph`](https://github.com/excalidraw/mermaid-to-excalidraw/blob/master/src/parseMermaid.ts#L139) takes the above response along with `svg` and computes the position, dimensions and cleans up the response.

```js
[
  {
    id: "one",
    nodes: ["flowchart-a2-1399", "flowchart-a1-1400"],
    title: "one",
    labelType: "text",
    nodeIds: ["a2", "a1"],
    x: 75.4921875,
    y: 0,
    width: 121.25,
    height: 188,
    text: "one",
  },
];
```
