# Config Validation Refactoring Plan

**Status: COMPLETED ✅**

## Overview

Refactor config validation logic to separate it from parsing logic in `config_loader.cpp`, creating a dedicated `config_validator` module.

## Phase 1: Create Config Validator Module - ✅ COMPLETE

**Goal**: Separate validation logic from parsing logic

**Tasks**:
1. Create `src/config_validator.h` with function declarations:
   - `bool validate_initial_positions(SimulationState* sim)` - move from simulation
   - `bool validate_mass_ratios(SimulationState* sim)` - new
   - `bool validate_soi_overlap(SimulationState* sim)` - new
   - `bool validate_nested_orbits(SimulationState* sim)` - new
   - `bool run_all_config_validations(SimulationState* sim)` - wrapper

2. Create `src/config_validator.cpp` with implementations:
   - Move `validate_initial_positions()` from `simulation.cpp`
   - Implement `validate_mass_ratios()` - check parent mass / child mass >= MIN_MASS_RATIO (1000)
   - Implement `validate_soi_overlap()` - for bodies sharing same parent, check if `distance < (soi_a + soi_b)`, ERROR if true
   - Implement `validate_nested_orbits()` - for chains like Sun→Earth→Moon, ensure child's orbital radius is < (fraction) of parent's SOI
   - Implement `run_all_config_validations()` - calls all validators and returns false if any fail

**Design Decisions**:
- SOI overlap: **ERROR** (reject configs with overlapping SOIs)
- Mass ratio threshold: **MACRO/DEFINE** for easy adjustment (default 1000)
- Nested orbit check: Use SOI (not Hill sphere), check `child_semi_major_axis < (0.5 * parent_soi_radius)`

---

## Phase 2: Update Existing Modules - ✅ COMPLETE

- **Updated**: `src/config_loader.h` - Added `#include "config_validator.h"`
- **Updated**: `src/config_loader.cpp`:
  - Replaced `validate_initial_positions()` call with `run_all_config_validations()`
  - Removed inline validation blocks (parent_index_ordering, orbital_elements)
- **Updated**: `src/simulation.h` - Removed declaration of `validate_initial_positions()`
- **Updated**: `src/simulation.cpp` - Removed implementation of `validate_initial_positions()`

---

## Phase 3: Update Tests - ✅ COMPLETE

- **Updated**: `tests/test_invalid_parent_assignment.cpp`:
  - Deleted Test 1: "Earth should not become child of spacecraft" (obsolete)
  - Deleted Test 3: "Detect placeholder config values" (obsolete)
  - Updated Test 4: "Mutual SOI" to expect `load_system_config()` failure

---

## Phase 4: Update Build System - ✅ COMPLETE

- **Updated**: `Makefile`:
  - Added `config_validator.o` to test-build dependencies

---

## File Changes Summary - ✅ COMPLETE

**New Files**:
- `src/config_validator.h`
- `src/config_validator.cpp`

**Modified Files**:
- `src/config_loader.h`
- `src/config_loader.cpp`
- `src/simulation.h`
- `src/simulation.cpp`
- `Makefile`
- `tests/test_invalid_parent_assignment.cpp`

**New Test Configs**:
- `tests/configs/small_comet_bad_mass_ratio.toml` (invalid config for Test 2)

**Existing Test Configs** (keep as-is):
- `tests/configs/mutual_soi_close.toml` (invalid config for Test 4)

---

## Implementation Order

1. Create config_validator module (Phase 1)
2. Update simulation and config_loader (Phase 2)
3. Update build system (Phase 4 - test compile)
4. Update tests and configs (Phase 3)
5. Run full test suite to verify changes

---

## Validation Logic Details

### `validate_mass_ratios(SimulationState* sim)`
- For all bodies with parent_index >= 0:
  - Calculate ratio = parent_mass / child_mass
  - If ratio < MIN_MASS_RATIO (1000), print error and return false
  - Skip check for spacecraft (they have their own validation)

### `validate_soi_overlap(SimulationState* sim)`
- For all pairs of bodies sharing the same parent:
  - Calculate distance between their orbital positions
  - Calculate sum of their SOI radii
  - If distance < (soi_a + soi_b), print error and return false

### `validate_nested_orbits(SimulationState* sim)`
- For all bodies with parent that is not root (parent_index != 0):
  - Calculate child's orbital radius (semi_major_axis)
  - Get parent's SOI radius
  - If child_semi_major_axis > (0.5 * parent_soi_radius), print error and return false
  - Ensures child is well within parent's gravitational dominance region

### `run_all_config_validations(SimulationState* sim)`
- Calls all validators in sequence:
  1. validate_parent_index_ordering()
  2. validate_orbital_elements()
  3. validate_mass_ratios()
  4. validate_soi_overlap()
  5. validate_nested_orbits()
  6. validate_initial_positions()
- Returns false if any validator fails
- Stops on first failure for efficiency

---

## Constants and Thresholds

```cpp
#define MIN_MASS_RATIO 1000.0
#define NESTED_ORBIT_FRACTION 0.5  // Child orbit must be < 50% of parent SOI
```