Automated Document Intelligence: Extracting Structured JSON from Invoices & Identity Documents

import { z } from 'zod';

export const InvoiceSchema = z.object({
  invoiceNumber: z.string(),
  vendorName: z.string(),
  taxIdentificationNumber: z.string().optional(),
  invoiceDate: z.string().regex(/^\d{4}-\d{2}-\d{2}$/),
  lineItems: z.array(z.object({
    description: z.string(),
    quantity: z.number().positive(),
    unitPrice: z.number().nonnegative(),
    totalPrice: z.number().nonnegative()
  })),
  subtotal: z.number(),
  vatRate: z.number(),
  totalAmountDue: z.number()
});

export type ExtractedInvoice = z.infer<typeof InvoiceSchema>;

export async function parseInvoiceImage(imageBase64: string): Promise<ExtractedInvoice> {
  const response = await aiClient.chat.completions.create({
    model: "gpt-4o-mini",
    response_format: { type: "json_object" },
    messages: [
      {
        role: "system",
        content: "Extract invoice data matching the JSON schema precisely. Calculate mathematical sums."
      },
      {
        role: "user",
        content: [
          { type: "text", text: "Extract all structured line items and totals." },
          { type: "image_url", image_url: { url: `data:image/jpeg;base64,${imageBase64}` } }
        ]
      }
    ]
  });

  const parsedJson = JSON.parse(response.choices[0].message.content!);
  return InvoiceSchema.parse(parsedJson);
}