Struct CalculationTrace 

pub struct CalculationTrace {
    pub explanation: String,
    pub input_quantity: Decimal,
    pub input_unit_price_eur: Decimal,
    pub gross_eur: Decimal,
    pub legal_refs: Vec<LegalReference>,
    pub tariff_source: Option<TariffSource>,
    pub regulatory_reduction_factor: Option<Decimal>,
    pub rounding_note: Option<&'static str>,
}

Full audit record for how one InvoicePosition was computed.

Answers the question: “Why is this amount on the invoice?”

Every CalculationTrace carries the input values, the applied legal rules, intermediate results, and the tariff source. This enables:

• Regulator audits (BNetzA §20 EnWG)
• Operator review
• LF dispute resolution
• AI-assisted invoice explainability (MCP tools)

Fields

explanation: String

Human-readable explanation of this position.

Example: "Arbeit 1500 kWh × 3.5 ct/kWh = 52.50 EUR"

input_quantity: Decimal

Input quantity used (before rounding).

input_unit_price_eur: Decimal

Input unit price in EUR (before rounding, already converted from ct).

gross_eur: Decimal

Intermediate result before rounding (qty × price).

legal_refs: Vec<LegalReference>

Applied legal references (at least one required).

tariff_source: Option<TariffSource>

Source of the tariff rate.

regulatory_reduction_factor: Option<Decimal>

Any §14a reductions applied, expressed as a fraction (0.0–1.0).

None when no regulatory reduction applies. Example: Some(Decimal::new(85, 2)) = 85% of full rate (15% reduction).

rounding_note: Option<&'static str>

Notes on rounding applied.

Example: "rounded to 5 dp per StromNEV §17".

Trait Implementations

impl Clone for CalculationTrace

fn clone(&self) -> CalculationTrace

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for CalculationTrace

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.