docs(07): create phase plan for weight unit selection

2026-03-16 12:10:22 +01:00
parent 0b30d5a260
commit f1f63eced9
3 changed files with 489 additions and 4 deletions
--- a/.planning/phases/07-weight-unit-selection/07-01-PLAN.md
+++ b/.planning/phases/07-weight-unit-selection/07-01-PLAN.md
@@ -0,0 +1,238 @@
+---
+phase: 07-weight-unit-selection
+plan: 01
+type: tdd
+wave: 1
+depends_on: []
+files_modified:
+  - src/client/lib/formatters.ts
+  - src/client/hooks/useWeightUnit.ts
+  - tests/lib/formatters.test.ts
+autonomous: true
+requirements:
+  - UNIT-02
+  - UNIT-03
+
+must_haves:
+  truths:
+    - "formatWeight converts grams to g, oz, lb, kg with correct precision"
+    - "formatWeight defaults to grams when no unit is specified (backward compatible)"
+    - "formatWeight handles null/undefined input for all units"
+    - "useWeightUnit hook returns a valid WeightUnit from settings, defaulting to 'g'"
+  artifacts:
+    - path: "src/client/lib/formatters.ts"
+      provides: "WeightUnit type export and parameterized formatWeight function"
+      exports: ["WeightUnit", "formatWeight", "formatPrice"]
+      contains: "WeightUnit"
+    - path: "src/client/hooks/useWeightUnit.ts"
+      provides: "Convenience hook wrapping useSetting for weight unit"
+      exports: ["useWeightUnit"]
+    - path: "tests/lib/formatters.test.ts"
+      provides: "Unit tests for formatWeight with all 4 units and edge cases"
+      min_lines: 30
+  key_links:
+    - from: "src/client/hooks/useWeightUnit.ts"
+      to: "src/client/hooks/useSettings.ts"
+      via: "useSetting('weightUnit')"
+      pattern: "useSetting.*weightUnit"
+    - from: "src/client/hooks/useWeightUnit.ts"
+      to: "src/client/lib/formatters.ts"
+      via: "imports WeightUnit type"
+      pattern: "import.*WeightUnit.*formatters"
+---
+
+<objective>
+Create the weight unit conversion core: a parameterized `formatWeight` function with a `WeightUnit` type and a `useWeightUnit` convenience hook, all backed by tests.
+
+Purpose: Establish the conversion contracts (type, function, hook) that Plan 02 will wire into every component. TDD approach ensures the conversion math is correct before any UI work.
+Output: Working `formatWeight(grams, unit)` with tests green, `useWeightUnit()` hook ready for consumption.
+</objective>
+
+<execution_context>
+@/home/jlmak/.claude/get-shit-done/workflows/execute-plan.md
+@/home/jlmak/.claude/get-shit-done/templates/summary.md
+</execution_context>
+
+<context>
+@.planning/PROJECT.md
+@.planning/ROADMAP.md
+@.planning/STATE.md
+@.planning/phases/07-weight-unit-selection/07-RESEARCH.md
+
+@src/client/lib/formatters.ts
+@src/client/hooks/useSettings.ts
+</context>
+
+<interfaces>
+<!-- Key types and contracts the executor needs. Extracted from codebase. -->
+
+From src/client/lib/formatters.ts (current):
+```typescript
+export function formatWeight(grams: number | null | undefined): string {
+  if (grams == null) return "--";
+  return `${Math.round(grams)}g`;
+}
+
+export function formatPrice(cents: number | null | undefined): string {
+  if (cents == null) return "--";
+  return `$${(cents / 100).toFixed(2)}`;
+}
+```
+
+From src/client/hooks/useSettings.ts:
+```typescript
+export function useSetting(key: string) {
+  return useQuery({
+    queryKey: ["settings", key],
+    queryFn: async () => {
+      try {
+        const result = await apiGet<Setting>(`/api/settings/${key}`);
+        return result.value;
+      } catch (err: any) {
+        if (err?.status === 404) return null;
+        throw err;
+      }
+    },
+  });
+}
+
+export function useUpdateSetting() {
+  const queryClient = useQueryClient();
+  return useMutation({
+    mutationFn: ({ key, value }: { key: string; value: string }) =>
+      apiPut<Setting>(`/api/settings/${key}`, { value }),
+    onSuccess: (_data, variables) => {
+      queryClient.invalidateQueries({ queryKey: ["settings", variables.key] });
+    },
+  });
+}
+```
+</interfaces>
+
+<feature>
+  <name>formatWeight unit conversion</name>
+  <files>src/client/lib/formatters.ts, tests/lib/formatters.test.ts</files>
+  <behavior>
+    Conversion constants: 1 oz = 28.3495g, 1 lb = 453.592g, 1 kg = 1000g
+
+    - formatWeight(100, "g") -> "100g"
+    - formatWeight(100, "oz") -> "3.5 oz"
+    - formatWeight(1000, "lb") -> "2.20 lb"
+    - formatWeight(1500, "kg") -> "1.50 kg"
+    - formatWeight(null, "oz") -> "--"
+    - formatWeight(undefined, "kg") -> "--"
+    - formatWeight(100) -> "100g" (default unit, backward compatible)
+    - formatWeight(0, "oz") -> "0.0 oz"
+    - formatWeight(5, "lb") -> "0.01 lb" (small weight precision)
+    - formatWeight(50000, "kg") -> "50.00 kg" (large weight)
+  </behavior>
+  <implementation>
+    1. Add `WeightUnit` type export: `"g" | "oz" | "lb" | "kg"`
+    2. Add conversion constants as module-level consts (not exported)
+    3. Modify `formatWeight` signature to `(grams: number | null | undefined, unit: WeightUnit = "g"): string`
+    4. Keep the null guard as-is at the top
+    5. Add switch statement for unit-specific formatting:
+       - g: `Math.round(grams)` + "g" (0 decimals, current behavior)
+       - oz: `.toFixed(1)` + " oz" (1 decimal)
+       - lb: `.toFixed(2)` + " lb" (2 decimals)
+       - kg: `.toFixed(2)` + " kg" (2 decimals)
+    6. Do NOT modify `formatPrice` — leave it untouched
+  </implementation>
+</feature>
+
+<tasks>
+
+<task type="auto" tdd="true">
+  <name>Task 1: TDD formatWeight with unit parameter</name>
+  <files>src/client/lib/formatters.ts, tests/lib/formatters.test.ts</files>
+  <behavior>
+    - formatWeight(100, "g") returns "100g"
+    - formatWeight(100, "oz") returns "3.5 oz"
+    - formatWeight(1000, "lb") returns "2.20 lb"
+    - formatWeight(1500, "kg") returns "1.50 kg"
+    - formatWeight(null) returns "--" for all units
+    - formatWeight(undefined, "kg") returns "--"
+    - formatWeight(100) returns "100g" (backward compatible, no second arg)
+    - formatWeight(0, "oz") returns "0.0 oz"
+  </behavior>
+  <action>
+    RED: Create `tests/lib/formatters.test.ts`. Import `formatWeight` from `@/client/lib/formatters`. Write tests for:
+    - All 4 units with a known gram value (e.g., 1000g = "1000g", "35.3 oz", "2.20 lb", "1.00 kg")
+    - Null and undefined input returning "--" for each unit
+    - Default parameter (no second arg) producing current "g" behavior
+    - Zero grams producing "0g", "0.0 oz", "0.00 lb", "0.00 kg"
+    - Precision edge cases (small values like 5g in lb = "0.01 lb")
+
+    Run tests — they should fail because formatWeight does not accept a unit parameter yet.
+
+    GREEN: Modify `src/client/lib/formatters.ts`:
+    - Export `type WeightUnit = "g" | "oz" | "lb" | "kg"`
+    - Add constants: `GRAMS_PER_OZ = 28.3495`, `GRAMS_PER_LB = 453.592`, `GRAMS_PER_KG = 1000`
+    - Change signature to `formatWeight(grams: number | null | undefined, unit: WeightUnit = "g")`
+    - Add switch statement after the null guard for unit-specific conversion and formatting
+    - Leave `formatPrice` completely untouched
+
+    Run tests — all should pass.
+
+    REFACTOR: None expected — the code is already minimal.
+  </action>
+  <verify>
+    <automated>bun test tests/lib/formatters.test.ts</automated>
+  </verify>
+  <done>formatWeight handles all 4 units with correct precision, null handling, and backward-compatible default. WeightUnit type is exported. All tests pass.</done>
+</task>
+
+<task type="auto">
+  <name>Task 2: Create useWeightUnit convenience hook</name>
+  <files>src/client/hooks/useWeightUnit.ts</files>
+  <action>
+    Create `src/client/hooks/useWeightUnit.ts`:
+
+    ```typescript
+    import { useSetting } from "./useSettings";
+    import type { WeightUnit } from "../lib/formatters";
+
+    const VALID_UNITS: WeightUnit[] = ["g", "oz", "lb", "kg"];
+
+    export function useWeightUnit(): WeightUnit {
+      const { data } = useSetting("weightUnit");
+      if (data && VALID_UNITS.includes(data as WeightUnit)) {
+        return data as WeightUnit;
+      }
+      return "g";
+    }
+    ```
+
+    This hook:
+    - Wraps `useSetting("weightUnit")` for a typed return value
+    - Validates the stored value is a known unit (protects against bad data)
+    - Defaults to "g" when no setting exists (backward compatible — UNIT-03 persistence works via existing settings API)
+    - Returns `WeightUnit` type so components can pass directly to `formatWeight`
+  </action>
+  <verify>
+    <automated>bun run lint</automated>
+  </verify>
+  <done>useWeightUnit hook exists, imports from useSettings and formatters, returns typed WeightUnit with "g" default. Lint passes.</done>
+</task>
+
+</tasks>
+
+<verification>
+- `bun test tests/lib/formatters.test.ts` passes with all unit conversion tests green
+- `bun run lint` passes with no errors
+- `src/client/lib/formatters.ts` exports `WeightUnit` type and updated `formatWeight` function
+- `src/client/hooks/useWeightUnit.ts` exists and exports `useWeightUnit`
+- Existing tests still pass: `bun test` (full suite)
+</verification>
+
+<success_criteria>
+- formatWeight("g") produces identical output to the old function (backward compatible)
+- formatWeight with oz/lb/kg produces correct conversions with appropriate decimal precision
+- WeightUnit type is exported for use by Plan 02 components
+- useWeightUnit hook is ready for components to consume
+- All existing tests remain green (no regressions)
+</success_criteria>
+
+<output>
+After completion, create `.planning/phases/07-weight-unit-selection/07-01-SUMMARY.md`
+</output>