Data Fetching

Learn how the GitHub Contributions Chart fetches contribution data from the GitHub API

Overview

The application fetches GitHub contribution data using a third-party API service that aggregates GitHub activity data. The data is retrieved in JSON format and parsed to extract contribution information.

API Endpoint

The app uses the following API endpoint:

https://github-contributions.vercel.app/api/v1/{username}

This endpoint returns a JSON response containing:

• years: Array of years with available contribution data
• contributions: Array of daily contribution records with date and intensity

DownloadWeb Function

The DownloadWeb function is a simple HTTP client wrapper that retrieves content from a URL:

function DownloadWeb(aURL: string): string;
var httpClient: TNetHTTPClient;
begin
  httpClient := TNetHTTPClient.Create(nil);
  try
    Result := httpClient.Get(aURL).ContentAsString;
  finally
    httpClient.Free;
  end;
end;

The function uses Delphi’s TNetHTTPClient component to perform the HTTP GET request and returns the response as a string.

GetGitHubContributions Function

This function combines URL formatting, HTTP request, and JSON parsing:

function GetGitHubContributions(username: string): TJSONObject;
var
  response: string;
begin
  response := DownloadWeb(Format('https://github-contributions.vercel.app/api/v1/%s', [username]));
  Result := TJSONObject.ParseJSONValue(TEncoding.ASCII.GetBytes(response), 0) as TJSONObject;
end;

How it works:

1. Format URL: Inserts the username into the API endpoint URL
2. Download: Calls DownloadWeb to retrieve the JSON response
3. Parse: Converts the JSON string to a TJSONObject for easy access

JSON Data Structure

The API returns JSON in the following format:

{
  "years": ["2024", "2023", "2022"],
  "contributions": [
    {
      "date": "2024-01-01",
      "intensity": 2
    },
    {
      "date": "2024-01-02",
      "intensity": 4
    }
  ]
}

Data Fields

• date: ISO 8601 date format (YYYY-MM-DD)
• intensity: Integer from 0-4 representing contribution level
  • 0: No contributions
  • 1: Low activity
  • 2: Medium activity
  • 3: High activity
  • 4: Very high activity

Parsing the Response

The application parses the JSON response using Delphi’s JSON iterator:

procedure TForm1.BGetContributionsClick(Sender: TObject);
var
  iterator:     TJSONIterator;
  years:        TJSONArray;
begin
  Screen.Cursor := crHourGlass;
  CBYears.Enabled := False;
  CBYears.Clear;

  gitHubContributions := GetGitHubContributions(EUsername.Text);

  if not gitHubContributions.TryGetValue<TJSONArray>('years', years) then
    Exit;

  iterator := TJSONIterator.Create(TJsonObjectReader.Create(years));
  while iterator.Next do
  begin
    iterator.Recurse;
    iterator.Next;
    CBYears.Items.Add(iterator.AsString);
    iterator.Return;
  end;

  if CBYears.Items.Count>0 then
  begin
    CBYears.Enabled := True;
    CBYears.ItemIndex := 0;
    CBYearsChange(Self);

    CBFirstDayOfWeek.Enabled := True;
  end;

  Screen.Cursor := crDefault;
end;

Parsing Steps

1. Fetch Data

   Call GetGitHubContributions with the username from the input field

2. Extract Years

   Use TryGetValue to safely extract the years array from the JSON

3. Iterate Years

   Use TJSONIterator to loop through available years and populate the dropdown

4. Enable UI

   Enable year selection and trigger chart rendering

The application doesn’t implement error handling for network failures or invalid usernames. In production, you should add try-catch blocks and user-friendly error messages.

Global State

The fetched data is stored in a global variable for access throughout the application:

var
  gitHubContributions: TJSONObject;

This allows the chart rendering functions to access contribution data without re-fetching from the API.