From 021f7106ccfffa762885c7fb814fb8796be484b9 Mon Sep 17 00:00:00 2001
From: Louis <louis@alexander-kerst.de>
Date: Sat, 17 Oct 2026 15:51:27 +0200
Subject: [PATCH] replica(rechner): architecture and schema

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 replica/rechner/architecture.md | 43 +++++++++++++++++++++++++++++++++
 replica/rechner/schema.sql      |  9 +++++++
 2 files changed, 52 insertions(+)
 create mode 100644 replica/rechner/architecture.md
 create mode 100644 replica/rechner/schema.sql

diff --git a/replica/rechner/architecture.md b/replica/rechner/architecture.md
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+++ b/replica/rechner/architecture.md
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+# Architecture: Rechner (Android, ohne Google)
+
+Same conventions as `wetter/` and `uhr/`: one native app, no server, **no network permission**.
+
+## Stack
+
+| Schicht | Wahl | warum |
+| --- | --- | --- |
+| UI | Kotlin + Compose, Material 3 Expressive, dynamic colour | same look and pipeline as the other apps |
+| Rechenkern | own recursive-descent parser → AST → evaluator on `BigDecimal` (MathContext 50 digits), integers stay exact `BigInteger` | no floating-point surprises (0.1+0.2 = 0.3), 100! exact; pure Kotlin, unit-tested on the JVM |
+| Funktionen | sin/cos/tan/ln/log/eˣ/√/^ via `Math` on doubles only where unavoidable, results rounded to 15 significant digits, exact values snapped (sin 30° = 0.5, cos π = −1) | readable answers without fake precision |
+| Persistenz | Room (history) + DataStore (memory, angle unit, current expression) | – |
+| Build/Verteilung | minSdk 29, `scripts/release.sh rechner` (Obtainium) | – |
+
+## Schema
+
+`schema.sql`: 1 table `history`. Single user, app-private storage.
+
+## Interne API
+
+| Aufruf | macht | Flow |
+| --- | --- | --- |
+| `Engine.evaluate(expr, angle)` | parse + evaluate, tolerant of unfinished input (auto-closes parentheses, ignores a trailing operator) | F01, F02 |
+| `Editor.input(key)` | cursor-aware editing: digits, operators (replace a trailing operator), smart parentheses, %, functions insert `sin(`, backspace removes whole tokens | F01, F02 |
+| `Calc.equals()` | evaluate, store history row, result becomes the expression | F01 |
+| `History.observe()/clear()` | grouped by local day | F03 |
+| `Memory.store(value)/recall()` | DataStore | F05 |
+| `Clipboard.copy/paste` | system clipboard; paste is sanitised to calculator tokens | F04 |
+
+## Was beißt
+
+- **Precision:** division keeps 50 digits internally; display rounds to fit and strips trailing zeros; repeating decimals shown truncated with an ellipsis rather than rounded up wrongly.
+- **Percent:** `50+10%` = 55 (percent of the left operand for + and −), `50×10%` = 5; standalone `10%` = 0.1.
+- **Locale:** German uses comma decimal and dot grouping; the parser accepts the locale separator only.
+- **Big results:** 100! has 158 digits; display shows them scientifically (1,5E157) and the full value on scroll.
+- **Domain errors:** √(−1), ln 0, tan 90°, 0÷0, factorial of non-integers → error text, never a crash.
+
+## Build-Reihenfolge
+
+1. Vertical slice (S01): engine + keypad + live result + equals; engine unit tests.
+2. Must: scientific row and panel (S02), Deg/Rad, Inv, errors, auto-shrinking display, history (S03), copy/paste (S04), expressive keys, dynamic colour.
+3. Should: memory, implicit multiplication, pull-down history, haptics, big numbers, locale separators, clear history.
+4. Could: landscape layout with all functions.
diff --git a/replica/rechner/schema.sql b/replica/rechner/schema.sql
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+-- Local SQLite (Room). No network, no accounts.
+CREATE TABLE history (
+  id          INTEGER PRIMARY KEY AUTOINCREMENT,
+  expression  TEXT    NOT NULL CHECK (length(expression) > 0),
+  result      TEXT    NOT NULL,
+  created_at  INTEGER NOT NULL            -- epoch ms UTC; grouped by local day in the UI
+);
+CREATE INDEX history_created ON history(created_at);
+-- Memory value, angle unit, theme and the current (unfinished) expression live in DataStore.