# WASM Value Interface Implementation Summary

This document summarizes the WASM interface implementation for the `Value` enum in arora-schema.

## Implementation Overview

The WASM interface provides JavaScript/TypeScript bindings for Arora's type system, allowing seamless interoperation between Rust and JavaScript environments.

## Key Components

### 1. ValueType Enum (`#[repr(u8)]`)

- Directly exposed enum with 33 variants (Unit through Uuid)
- Each variant has an explicit numeric value for stable ABI
- Mirrors the Rust `Value` enum structure

### 2. Value Wrapper Class

Exposes the following methods:

- `new(type: ValueType, value: any)` - Constructor with explicit type
- `get type(): ValueType` - Property getter for the value's type
- `set(value: any)` - Updates value with type checking
- `get()` - Returns the value as a JavaScript value
- `getAs(registry: any)` - Future-ready method for type registry support
- `static from(value: any)` - Factory method with automatic type detection

## Type Conversion Strategy

### Primitive Types

- Direct mapping between Rust and JavaScript primitives
- Range validation for integer types (u8, i16, etc.)
- Numbers default to `f64` when auto-detecting

### Arrays

- Homogeneous arrays: Type-specific (e.g., `ArrayF64`, `ArrayString`)
- Heterogeneous arrays: `ArrayValue` for mixed types
- Auto-detection checks if all elements share the same type

### Objects

- Plain JavaScript objects → `KeyValue`
- Objects with `id` + `fields` → `Structure`
- Objects with `id` + `variant_id` + `value` → `Enumeration`

### Complex Types

- `Structure`: Exposed as `{ id: string, fields: { [key: string]: any } }`
- `Enumeration`: Exposed as `{ id: string, variant_id: string, value: any }`
- `KeyValue`: HashMap-like structure with UUID-based field IDs
- Recursive conversion: Nested `Value` types are properly wrapped/unwrapped

## Design Decisions

1. **Error Handling**: Uses `String` errors (wasm-bindgen auto-wraps as `JsValue`)
2. **Type Enum**: `#[repr(u8)]` like `DeviceStatus` for stable representation
3. **Separate Type Enums**: `ValueType` (WASM) is separate from `Type` (Rust) because:
   - `ValueType` requires `#[repr(u8)]` for stable WASM FFI
   - `Type` requires `#[serde(rename)]` for JSON serialization
   - These attributes don't compose well together
   - `From` implementations provide seamless conversion between them
4. **Complex Types**: Returns raw `JsValue` objects preserving structure IDs
5. **Auto-Detection**: Recursively processes arrays and objects
6. **Type Registry**: Placeholder parameter (`JsValue`) for future implementation
7. **Number Defaults**: JavaScript numbers → `f64` by default

## Files Modified

- `src/wasm_value.rs` - New module with WASM bindings
- `src/lib.rs` - Conditionally exports `wasm_value` module
- `src/value.rs` - Removed unused wasm-bindgen import
- `Cargo.toml` - Added WASM dependencies and configuration
- `package.json` - NPM scripts for building and testing
- `tests/integration/wasm-api.test.js` - Integration test suite
- `readme.md` - Documentation for WASM interface

## Test Coverage

Integration tests verify:

1. ✅ ValueType enum exposure (all 33 variants)
2. ✅ Primitive value creation (Boolean, F64, String)
3. ✅ Integer range validation (u8 max, overflow rejection)
4. ✅ Unit and Option types
5. ✅ Array types (Boolean, F64, String)
6. ✅ Auto-detection from JavaScript values
7. ✅ Auto-detected arrays (homogeneous)
8. ✅ set() method with type checking
9. ✅ KeyValue from plain objects
10. ✅ Mixed-type arrays (ArrayValue)
11. ✅ Empty arrays
12. ✅ getAs() method placeholder

All 30+ test assertions pass successfully.

## Usage Example

```typescript
import { Value, ValueType } from './pkg/arora_types.js';

// Explicit typing
const num = new Value(ValueType.F64, 3.14);
console.log(num.type);  // 11 (ValueType.F64)
console.log(num.get()); // 3.14

// Auto-detection
const obj = Value.from({ x: 10, y: 20, label: "point" });
console.log(obj.type);  // 31 (ValueType.KeyValue)
const retrieved = obj.get();
console.log(retrieved.x);  // 10
console.log(retrieved.label);  // "point"

// Type-checked mutation
num.set(2.71);  // ✅ Works
num.set("pi");  // ❌ Throws error
```

## Build Commands

```bash
# Build WASM module
npm run build:wasm

# Run integration tests
npm test

# Build + test
npm run build:wasm && npm test
```

## Future Enhancements

1. Type registry implementation for `getAs()` method
2. Additional type introspection methods
3. Serialization/deserialization helpers
4. Performance optimizations for large arrays
5. Support for streaming/chunked data

## Notes

- The implementation follows the same pattern as `studio-bridge/device_status.rs`
- Type registry is a placeholder for future UUID-based type resolution
- All conversions are recursive and handle nested structures
- Range validation prevents JavaScript number precision issues with integers
