Add invoice generation complex flow sample

[datalogics-erics]

Summary

Add a Complex Flow Example that generates a realistic invoice from structured application data through the public pdfRest API.

The sample reads fictional invoice metadata and styling from JSON, line items from CSV, and a local logo image. It creates a blank Letter PDF and composes the invoice with these endpoints:

• Create Blank PDF
• Add Shapes to PDF
• Add Text to PDF
• Add Tables to PDF
• Add Image to PDF

The table is built from every CSV row and uses automatic pagination, repeated headers, reserved page regions, totals, and optional tagging. The workflow also adds payment terms, notes, and page numbering after determining the generated page count. The logo is uploaded once and then referenced by its returned resource ID.

Included inputs

• metadata.json: Fictional seller, customer, invoice, tax, payment, and note data.
• style.json: Fonts, colors, table text size, and border settings.
• line-items.csv: Variable invoice line items used to build the table.
• northstar-logo.png: Fictional local logo image used in the invoice header.

Validation

Each language implementation was run against https://api.pdfrest.com with the same fictional JSON, CSV, and logo inputs:

• Python
• Java
• JavaScript
• PHP
• .NET
• cURL

Each workflow completed all nine API operations successfully with HTTP 200 responses, including the image upload operation. Every generated output was verified as a tagged, two-page Letter PDF. qpdf --check reported no syntax or stream encoding errors for any output. The PHP run also completed without the PHP 8.5 CSV deprecation warning.

[datalogics-cgreen]

Thanks for putting these together. I think the overall structure is solid, but I am requesting changes for a few sample-quality issues before this lands.

1. In the new .NET sample, the missing PDFREST_API_KEY branch prints an error and returns normally. That makes dotnet run -- create-invoice-from-structured-data exit 0 even though the sample did not run. The other .NET complex-flow samples call Environment.Exit(1); return; for the same precondition, so this one should match that behavior.

2. Please add a short inline comment near each invoice-data directory constant/path explaining that these samples are intentionally self-contained and read bundled JSON, CSV, and logo fixture files. That should make the new sample shape clear without needing to document it as an exception in every README.

3. Please add a few more inline comments describing the major API choreography, especially in the .NET and PHP samples. These are sample programs, and this workflow has enough steps that readers would benefit from signposts for: loading structured inputs, creating the blank PDF, adding header shapes/text, adding the auto-paginated table, uploading/reusing the logo resource ID, querying page count, adding final-page/footer content, and downloading the final PDF.

The runtime issue is small, but the readability points matter here because these files are teaching examples as much as runnable code.

[datalogics-erics]

Thanks for the review. Addressed all three points in commit 1701e79:

1. The .NET sample now calls Environment.Exit(1) when PDFREST_API_KEY is missing, matching the other .NET complex-flow samples. I verified the missing-key run exits with status 1.

2. Added a short comment beside the invoice-data path in each language implementation explaining that the JSON, CSV, and logo fixtures are intentionally bundled beside the sample.

3. Added workflow signposts to the .NET and PHP samples covering input loading, blank PDF creation, header content, table insertion, logo upload and reuse, page-count lookup, footer content, and final download.

Validation completed:

• Python compile check
• JavaScript syntax check
• PHP lint check
• cURL shell syntax check
• Java mvn verify with JDK 17
• .NET missing-key exit-code check

[datalogics-cgreen]

Rechecked the updates in 1701e79. The requested changes are addressed: the .NET missing-key path now exits non-zero, the fixture-path comments are present across the language samples, and the .NET/PHP samples now have useful workflow signposts for the major API steps.

Validation I reran locally:

• dotnet build passes, with existing nullability warnings elsewhere in the project.
• env -u PDFREST_API_KEY dotnet run --no-build -- create-invoice-from-structured-data now reports exit=1 after rebuilding.
• Python compile, JavaScript syntax check, cURL shell syntax check, and Java Spotless check pass.

I could not rerun PHP lint locally because this machine does not have php installed, but the updated PHP comments/readability changes look correct on review.

EDIT: I fixed my local issue with php and manually ran the sample code to confirm that the expected output was received.