Feature: Stock spending report

[tbrkkup]

Closes #995

Implements the report discussed in the issue.

Commits

Split by layer, so the build change, the query and the UI can be read apart from one another.

Commit	Layer
Add AndroidChart dependency	build
Query purchase transactions from the stock log	API
Add spending aggregation view model	logic
Add spending report screen	UI
Add spending report entry to the stock overview menu	entry point

Query and arithmetic

Built on the stock_log source proposed in the issue:

/objects/stock_log?query[]=transaction_type=purchase
                  &query[]=undone=0
                  &query[]=purchased_date>=<start>
                  &query[]=purchased_date<=<end>

Per row the spend is |amount| × price. Two details worth confirming against how the web report behaves:

• Rows with a null price contribute zero rather than being dropped, so a row's absence from the total never silently changes the row count.
• amount is taken as an absolute value, so a correction row recorded with a negative amount still registers as spend rather than subtracting
  from the period.

Loading

Products, product groups and stores are updated, then read back in one Single.zip() before the purchase log is fetched. The update matters because those three resolve the grouping labels: without it, whichever entity no other screen had synced yet would leave raw ids on screen. It is not forced, so it is a cheap no-op once the data is current.

Switching the grouping afterwards re-aggregates in memory with no second round trip; only a period change or pull-to-refresh hits the network.

Chart decisions

The top eight slices are shown individually and the remainder is collapsed into a single Others slice; past that the legend stops being readable at phone width. The list below is not truncated, so the full breakdown stays available.

Labels on narrow slices are drawn smaller so they still fit their segment. The library supports only one value text size per data set, so rather than reimplementing the slice geometry, the renderer draws the values in two passes — wide slices at the regular size, narrow ones reduced — with the formatter blanking out whichever group is not part of the current pass. That is the one piece of custom drawing code here and the part I would look at first in review.

Slice colours are a fixed twelve-colour palette rather than theme colours, because adjacent slices have to stay distinguishable from one another. The chart hole, legend text and surrounding chrome do follow the active theme in both light and dark.

For an empty period the chart is hidden and an inline label takes its place. Deliberately not InfoFullscreenHelper: that helper injects into a container sitting behind the scroll view, which on this screen draws the illustration underneath the filter chips.

Dependency

com.github.AppDevNext.AndroidChart:chartLib:5.2.4, which also required adding the JitPack repository to settings.gradle — Maven Central holds only snapshots of it. This is the only addition to the dependency set.

It is Apache 2.0 and needs minSdk 23, both matching this project, and the Kotlin standard library it brings was already on the runtime classpath, so it adds no new runtime.

Formatting

Amounts use the configured PREF.CURRENCY with the device locale's decimal separators. English and German strings are included.

Testing

Ran on device Pixel 9 Pro running LineageOS 24 against a production server across all three periods and all three groupings, with the resulting figures reconciled line by line against the same report in the web UI. Also covered: a period with no purchases, a dataset with more than eight groups to confirm the Others collapse, and purchases with a missing price and with a null shopping location.