ba02f1bd

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Add the centjes-chart package

A 'centjes-chart' executable that renders an SVG chart of account balances
over time from a ledger.

The package is structured around a backend-agnostic, pure report so the data
pipeline is total and testable and rendering is isolated:

- Centjes.Chart.Report: the ChartReport/ChartSeries intermediate
  representation, a typed ChartError (unknown currency / no data / conversion
  failure) whose ToReport delegates to ConvertError, and a total
  produceChartReport. Accounts are selected by declared AccountType, balances
  are sampled onto a daily x-axis (sampleStepFunction) and re-valued at each
  day's rate. The days/series alignment is a checked Validity invariant.
- Centjes.Chart.Render: the only place precise money becomes Double. Renders a
  stacked area chart when all values are non-negative and overlaid lines
  otherwise, via Chart + Chart-diagrams (no cairo C dependency).
- Centjes.Chart.OptParse / Command.All: the 'all' command, with currency,
  account filter, output path and title as settings.
- centjes-chart-test: genValidSpec and an alignment-rejection test for the
  invariant, property tests for the sampling and stacking math, a golden for
  the report, and error goldens for every ChartError constructor.

Timeline