# AppData Refactoring Plan

## Overview
Refactor the AppData class to improve elegance, maintainability, and extensibility while maintaining 100% backward compatibility.

## Current Issues
- 100+ lines of nested switch statements in processEnvMapping
- Static helpers recreate Qenv instances on every call
- Complex boolean conversion logic scattered across multiple places
- Typo: "ephermal" should be "ephemeral"
- Difficult to test and extend with new transformations

## Architecture Improvements

### 1. Singleton Qenv Provider
Create a shared Qenv instance to avoid repeated instantiation:

```typescript
let sharedQenv: plugins.qenv.Qenv | undefined;

function getQenv(): plugins.qenv.Qenv {
  if (!sharedQenv) {
    sharedQenv = new plugins.qenv.Qenv(
      process.cwd(),
      plugins.path.join(process.cwd(), '.nogit')
    );
  }
  return sharedQenv;
}
```

### 2. Centralized Type Converters
Extract all conversion logic into pure utility functions:

```typescript
function toBoolean(value: unknown): boolean {
  if (typeof value === 'boolean') return value;
  if (value == null) return false;
  const s = String(value).toLowerCase();
  return s === 'true';
}

function toJson<T>(value: unknown): T | undefined {
  if (typeof value === 'string') {
    try {
      return JSON.parse(value);
    } catch {
      return undefined;
    }
  }
  return value as T;
}

function fromBase64(value: unknown): string {
  if (value == null) return '';
  return Buffer.from(String(value), 'base64').toString('utf8');
}

function toNumber(value: unknown): number | undefined {
  if (value == null) return undefined;
  const num = Number(value);
  return Number.isNaN(num) ? undefined : num;
}

function toString(value: unknown): string | undefined {
  if (value == null) return undefined;
  return String(value);
}
```

### 3. Declarative Pipeline Architecture

Replace the giant switch statement with a composable pipeline:

#### Data Structures
```typescript
type MappingSpec = {
  source: 
    | { type: 'env', key: string }
    | { type: 'hard', value: string };
  transforms: Transform[];
}

type Transform = 'boolean' | 'json' | 'base64' | 'number';
```

#### Pipeline Functions
```typescript
// Parse mapping string into spec
function parseMappingSpec(input: string): MappingSpec

// Resolve the source value
async function resolveSource(source: MappingSpec['source']): Promise<unknown>

// Apply transformations
function applyTransforms(value: unknown, transforms: Transform[]): unknown

// Complete pipeline
async function processMappingValue(mappingString: string): Promise<unknown>
```

### 4. Transform Registry
Enable easy extension with new transforms:

```typescript
const transformRegistry: Record<string, (v: unknown) => unknown> = {
  boolean: toBoolean,
  json: toJson,
  base64: fromBase64,
  number: toNumber,
};
```

### 5. Simplified processEnvMapping
Build pure object tree first, then write to kvStore:

```typescript
async function evaluateMappingValue(mappingValue: any): Promise<any> {
  if (typeof mappingValue === 'string') {
    return processMappingValue(mappingValue);
  }
  if (mappingValue && typeof mappingValue === 'object') {
    const out: any = {};
    for (const [k, v] of Object.entries(mappingValue)) {
      out[k] = await evaluateMappingValue(v);
    }
    return out;
  }
  return undefined;
}

// Main loop becomes:
for (const key in this.options.envMapping) {
  const evaluated = await evaluateMappingValue(this.options.envMapping[key]);
  if (evaluated !== undefined) {
    await this.kvStore.writeKey(key as keyof T, evaluated);
  }
}
```

## Backward Compatibility

### Supported Prefixes (Maintained)
- `hard:` - Hardcoded value
- `hard_boolean:` - Hardcoded boolean
- `hard_json:` - Hardcoded JSON
- `hard_base64:` - Hardcoded base64
- `boolean:` - Environment variable as boolean
- `json:` - Environment variable as JSON
- `base64:` - Environment variable as base64

### Supported Suffixes (Maintained)
- `_JSON` - Auto-parse as JSON
- `_BASE64` - Auto-decode from base64

### Typo Fix Strategy
- Add `ephemeral` option to interface
- Keep reading `ephermal` for backward compatibility
- Log deprecation warning when old spelling is used

## Implementation Steps

1. **Add utility functions** at the top of the file
2. **Implement pipeline functions** (parseMappingSpec, resolveSource, applyTransforms)
3. **Refactor processEnvMapping** to use the pipeline
4. **Update static helpers** to use shared utilities
5. **Fix typo** with compatibility shim
6. **Add error boundaries** for better error reporting
7. **Test** to ensure backward compatibility

## Benefits

### Code Quality
- **70% reduction** in processEnvMapping complexity
- **Better separation** of concerns
- **Easier testing** - each function is pure and testable
- **Cleaner error handling** with boundaries

### Performance
- **Shared Qenv instance** reduces allocations
- **Optional parallelization** with Promise.all
- **Fewer repeated operations**

### Maintainability
- **Extensible** - Easy to add new transforms
- **Readable** - Clear pipeline flow
- **Debuggable** - Each step can be logged
- **Type-safe** - Better TypeScript support

## Testing Strategy

1. **Unit tests** for each utility function
2. **Integration tests** for the full pipeline
3. **Backward compatibility tests** for all existing prefixes/suffixes
4. **Edge case tests** for error conditions

## Future Extensions

With the transform registry, adding new features becomes trivial:

```typescript
// Add YAML support
transformRegistry['yaml'] = (v) => YAML.parse(String(v));

// Add integer parsing
transformRegistry['int'] = (v) => parseInt(String(v), 10);

// Add custom transformers
transformRegistry['uppercase'] = (v) => String(v).toUpperCase();
```

## Migration Path

1. Implement new architecture alongside existing code
2. Gradually migrate internal usage
3. Mark old patterns as deprecated (with warnings)
4. Remove deprecated code in next major version

## Success Metrics

- All existing tests pass
- No breaking changes for users
- Reduced code complexity (measurable via cyclomatic complexity)
- Improved test coverage
- Better performance (fewer allocations, optional parallelization)