genrules

genrules - EN 16931 Business Rule Generator

Auto-generates Go code for EN 16931 electronic invoicing business rules from official schematron specifications.

Overview

genrules parses EN 16931 schematron XML files and generates type-safe Go constants for business rule validation. It extracts rule codes, BT-/BG- field references, and descriptions from the official CEN/TC 434 specifications.

Installation

go install github.com/speedata/einvoice/cmd/genrules@latest

Or build from source:

go build -o genrules cmd/genrules/main.go

Usage

Basic Usage

Generate rules from a URL:

genrules \
  --source https://raw.githubusercontent.com/ConnectingEurope/eInvoicing-EN16931/master/cii/schematron/abstract/EN16931-CII-model.sch \
  --version v1.3.14.1 \
  --package rules \
  --output rules/en16931.go

Generate rules from a local file:

genrules \
  --source path/to/EN16931-CII-model.sch \
  --version v1.3.14.1 \
  --package rules \
  --output rules/en16931.go

Using go generate

The recommended workflow uses go generate for reproducible builds:

# Generate from rules/ directory
cd rules && go generate

# Or generate all packages
go generate ./...

Flags

• --source (required): Path or URL to schematron XML file
• --version (required): Source file version (e.g., "v1.3.14.1")
• --package (default: "rules"): Target Go package name
• --output (default: "rules/en16931.go"): Output file path

Output Format

Generates Go code with:

• Package declaration and Rule struct definition
• Generation metadata (source, version, timestamp)
• 203 business rule constants from EN 16931 specification
• Sorted by rule code (BR-1, BR-2, ..., BR-CO-10, ..., BR-S-1, ...)

Example output:

// Code generated by genrules from EN16931-CII-model.sch; DO NOT EDIT.
// Source: https://github.com/ConnectingEurope/eInvoicing-EN16931
// Version: v1.3.14.1
// Generated: 2025-10-07T12:31:26Z

package rules

type Rule struct {
    Code        string
    Fields      []string
    Description string
}

var (
    BR1 = Rule{
        Code:        "BR-01",
        Fields:      []string{"BT-24"},
        Description: `An Invoice shall have a Specification identifier (BT-24).`,
    }
    // ... 202 more rules
)

Rule Naming Conventions

The generator converts schematron rule codes to Go identifiers:

• BR-01 → BR1 (remove leading zeros)
• BR-S-08 → BRS8 (remove dashes and leading zeros)
• BR-CO-14 → BRCO14 (remove all dashes)
• BR-AE-1 → BRAE1 (standard format)

Architecture

Parsing

1. Fetch schematron XML from URL or file
2. Parse <pattern>, <rule>, and <assert> elements
3. Extract rule code from assert @id attribute
4. Extract description from assert test text
5. Extract BT-/BG- field references using regex \(B[TG]-\d+\)

Code Generation

1. Clean descriptions (remove [BR-XX]- prefix, normalize whitespace)
2. Deduplicate and sort field references
3. Convert rule codes to Go identifiers
4. Sort rules alphabetically by code
5. Generate Go code using text/template
6. Format output with gofmt

Custom Rules

The generated rules/en16931.go file includes a custom rules section that must be manually preserved:

• Check: Line total calculation validation
• BR34-40: Non-negative amount validations (not in official spec)
• BRIG1-10: IGIC aliases (BR-AF-* in spec)
• BRIP1-10: IPSI aliases (BR-AG-* in spec)

⚠️ Important: When regenerating rules, manually add back the custom rules section marked by the comment banner.

Testing

The generator includes built-in validation:

1. Verifies 200+ rules are extracted
2. Checks rule code format
3. Validates field references (BT-/BG- format)
4. Ensures descriptions are non-empty
5. Reports generation statistics

Sources

• EN 16931 Specification: ConnectingEurope/eInvoicing-EN16931
• Schematron File: cii/schematron/abstract/EN16931-CII-model.sch
• Current Version: v1.3.14.1

Maintenance

To update rules to a new EN 16931 version:

1. Check for new releases at ConnectingEurope/eInvoicing-EN16931
2. Update --version flag in rules/en16931.go go:generate directive
3. Run cd rules && go generate
4. Manually re-add custom rules section
5. Run tests: go test ./...
6. Commit changes with version number in message

License

Generated rules are derived from the EN 16931 specification, which is maintained by CEN/TC 434.