FX Implementation Summary

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Masked-Kunsiquat edited this page Dec 25, 2025 · 4 revisions

FX Implementation Summary

This page summarizes the FX (multi-currency) system for CrewSplit.

Goals

Offline-first conversions using cached rates
Deterministic math for reproducible settlements
Clear audit trail of which rates were used

Schema Overview

fx_rates

Stores cached exchange rates from multiple sources.

Key fields: base_currency, quote_currency, rate, source, fetched_at, priority
Manual rates win via higher priority
Soft deletes preserve auditability

fx_rate_snapshots (optional)

Links trips to specific rates used at the time of settlement or export.

Rate Selection Rules

Same currency: return 1.0 and skip DB lookup.
Direct rate lookup (base -> quote) with priority + recency ordering.
Inverse lookup (quote -> base) and use 1/rate.
If missing, prompt for manual rate entry.

Data Flow (High Level)

Fetch rates when online and stale
Store rates in SQLite
Convert amounts on read using cached rates
Persist original + converted amounts for auditability

UI Integration Notes

Show a staleness warning when rates are old
Provide manual entry for missing pairs
Display both original and converted amounts

References