# Config Validation Refactoring Plan

## 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

**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

**Tasks**:
1. Update `src/config_loader.h`:
   - Add `#include "config_validator.h"`

2. Update `src/config_loader.cpp`:
   - Replace call to `validate_initial_positions(sim)` (line 281) with `run_all_config_validations(sim)`
   - Move inline validation blocks into separate functions in `config_validator.cpp`:
     - `validate_parent_index_ordering()`
     - `validate_orbital_elements()`
   - Keep parsing functions (`parse_toml_body`, `parse_toml_spacecraft`, etc.) focused on TOML parsing only

3. Update `src/simulation.h`:
   - Remove declaration of `validate_initial_positions()`

4. Update `src/simulation.cpp`:
   - Remove implementation of `validate_initial_positions()` (lines 181-219)

---

## Phase 3: Update Tests

**Tasks**:
1. Update `tests/test_invalid_parent_assignment.cpp`:
   - **Test 1** ("Earth should not become child of spacecraft"): **DELETE**
     - Spacecraft are now in separate array
     - Cannot become parent to bodies

   - **Test 2** ("Massive bodies never become children of small bodies"): **UPDATE**
     - Create new test config with small comet orbiting Earth/Mars
     - Test should now call `load_system_config()` which will run `validate_mass_ratios()`
     - Config should fail if mass ratio < 1000

   - **Test 3** ("Detect placeholder config values"): **DELETE**
     - This checked distance validation which is now in `validate_initial_positions()`
     - Validation happens at load time, not needed as separate test

   - **Test 4** ("Mutual SOI"): **UPDATE** to expect load failure
     - Keep `mutual_soi_close.toml` as-is (invalid config)
     - Test should expect `load_system_config()` to fail
     - Verify error message about SOI overlap

2. Update `tests/configs/`:
   - Create new config for Test 2 (small comet around Earth/Mars with mass ratio < 1000)
   - Keep `mutual_soi_close.toml` as-is (invalid for Test 4)

---

## Phase 4: Update Build System

**Tasks**:
1. Update `Makefile`:
   - Add `config_validator.o` to build target
   - Update dependencies for `orbit_sim` and `orbit_test`

---

## File Changes Summary

**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
```