The C# Receipt OCR API for Expense Tracking

// 💰 Get 20 free credits instantly to test your own receipts:
// 👉 https://structocr.com/register

using System;
using System.IO;
using System.Net.Http;
using System.Net.Http.Json;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Threading.Tasks;
using System.Collections.Generic;

public class ReceiptOcrExample
{
    private const string ApiKey = "YOUR_API_KEY_HERE";
    // Note the endpoint is specific to receipts
    private const string ApiEndpoint = "https://api.structocr.com/v1/receipt";

    private static readonly HttpClient client = new HttpClient();

    public static async Task Main(string[] args)
    {
        string imagePath = "coffee_receipt.jpg";

        if (!File.Exists(imagePath))
        {
            Console.WriteLine($"Error: File not found at {imagePath}");
            return;
        }

        try
        {
            // 1. Base64 Encode the Image
            byte[] imageBytes = await File.ReadAllBytesAsync(imagePath);
            string base64Image = Convert.ToBase64String(imageBytes);
            var payload = new { img = base64Image };

            // 2. Configure Headers
            client.DefaultRequestHeaders.Clear();
            client.DefaultRequestHeaders.Add("x-api-key", ApiKey);

            // 3. Execute POST Request
            Console.WriteLine($"Analyzing receipt via {ApiEndpoint}...");
            HttpResponseMessage response = await client.PostAsJsonAsync(ApiEndpoint, payload);
            string responseBody = await response.Content.ReadAsStringAsync();

            if (!response.IsSuccessStatusCode)
            {
                Console.WriteLine($"API Error ({response.StatusCode}): {responseBody}");
                return;
            }

            // 4. Parse the Structured Data
            var options = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };
            var result = JsonSerializer.Deserialize<ApiResponse>(responseBody, options);

            if (result?.Success == true && result.Data != null)
            {
                var data = result.Data;
                Console.WriteLine("\n✅ Receipt Parsed Successfully!");
                Console.WriteLine($"Merchant:  {data.Merchant?.Name}");
                Console.WriteLine($"Date:      {data.Date}");
                Console.WriteLine($"Subtotal:  {data.Financials?.Subtotal}");
                Console.WriteLine($"Tax:       {data.Financials?.TaxAmount}");
                Console.WriteLine($"Tip:       {data.Financials?.TipAmount}");
                Console.WriteLine($"Total:     {data.Financials?.TotalAmount} {data.Currency}");

                Console.WriteLine("\n--- Purchased Items ---");
                if (data.LineItems != null)
                {
                    foreach (var item in data.LineItems)
                    {
                        Console.WriteLine($"- {item.Description}: {item.Quantity}x @ {item.UnitPrice} = {item.Amount}");
                    }
                }
            }
            else
            {
                Console.WriteLine($"Extraction Failed: {result?.Error}");
            }
        }
        catch (Exception e)
        {
            Console.WriteLine($"Unexpected Error: {e.Message}");
        }
    }
}

// --- Data Models ---
public class ApiResponse
{
    public bool Success { get; set; }
    public ReceiptData Data { get; set; }
    public string Error { get; set; }
}

public class ReceiptData
{
    public string Date { get; set; }
    public string Time { get; set; }
    public string Currency { get; set; }
    public MerchantData Merchant { get; set; }
    public FinancialData Financials { get; set; }
    
    [JsonPropertyName("line_items")]
    public List<LineItem> LineItems { get; set; }
}

public class MerchantData
{
    public string Name { get; set; }
    public string Address { get; set; }
    public string Phone { get; set; }
}

public class FinancialData
{
    public decimal? Subtotal { get; set; }
    [JsonPropertyName("tax_amount")]
    public decimal? TaxAmount { get; set; }
    [JsonPropertyName("tip_amount")]
    public decimal? TipAmount { get; set; }
    [JsonPropertyName("total_amount")]
    public decimal? TotalAmount { get; set; }
}

public class LineItem
{
    public string Description { get; set; }
    public decimal? Quantity { get; set; }
    [JsonPropertyName("unit_price")]
    public decimal? UnitPrice { get; set; }
    public decimal? Amount { get; set; }
}