51 lines
2.0 KiB
Markdown
51 lines
2.0 KiB
Markdown
---
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epic: 2
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story: 2.1
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title: "Unit Registry & Base Conversion"
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status: draft
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---
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## Epic 2 — Unit Conversion System
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**Goal:** Support 200+ units across all major categories with SI prefix support.
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### Story 2.1: Unit Registry & Base Conversion
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As a CalcPad user,
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I want a comprehensive unit registry covering all major measurement categories with correct base-unit conversions,
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So that I can convert between any supported units accurately.
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**Acceptance Criteria:**
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**Given** the unit registry is initialized
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**When** the list of supported categories is queried
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**Then** it includes length, mass, volume, area, speed, temperature, data, angle, time, pressure, energy, power, and force
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**And** at least 200 units are registered across all categories
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**Given** a linear unit conversion such as `5 miles in km`
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**When** the engine evaluates it
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**Then** it converts via the base unit (meters) using the stored conversion ratio
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**And** the result is `8.04672 km`
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**Given** a non-linear unit conversion such as `100 °F in °C`
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**When** the engine evaluates it
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**Then** it applies the formula `(F - 32) * 5/9` rather than a simple ratio
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**And** the result is `37.777... °C`
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**Given** a conversion between units in the same category such as `1 gallon in liters`
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**When** the engine evaluates it
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**Then** it converts via the base unit for volume
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**And** the result is `3.78541 liters` (US gallon)
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**Given** a conversion between incompatible categories such as `5 kg in meters`
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**When** the engine evaluates it
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**Then** it returns a `CalcResult::Error` indicating that mass and length are incompatible
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**Given** the registry data
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**When** the engine is compiled
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**Then** the registry is static (built at compile time, not loaded at runtime)
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**And** lookup of any unit by name or abbreviation is O(1) or near-O(1)
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**Given** a unit that has multiple common names (e.g., `meter`, `metre`, `m`)
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**When** any of these names is used in an expression
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**Then** they all resolve to the same unit definition
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