# Matching Engine Implementation

This document describes the implemented matching engine based on the concept documents.

## Overview

The matching engine implements a multi-stage pipeline for discovering and evaluating resource exchange opportunities between organizations. The implementation follows the algorithms and formulas specified in the concept documents.

## Architecture

### Multi-Stage Matching Pipeline

1. **Pre-filtering Stage**
   - Resource type compatibility checks
   - Geographic constraints (distance filtering using Haversine formula)
   - Basic quality requirements validation

2. **Compatibility Assessment**
   - Quality compatibility scoring (temperature, pressure, purity)
   - Temporal overlap analysis
   - Quantity matching
   - Trust factors based on data precision and source

3. **Economic Viability Analysis**
   - Net Present Value (NPV) calculations
   - Internal Rate of Return (IRR) using Newton-Raphson method
   - Payback period analysis
   - Annual savings estimation

4. **Multi-Criteria Decision Support**
   - Weighted scoring based on concept spec formula:

     ```
     score = 0.25*quality + 0.20*temporal + 0.15*quantity + 0.15*trust
             - 0.10*transport_penalty - 0.10*regulatory_risk
     ```

## Key Components

### 1. MatchingService (`internal/service/matching_service.go`)

Core matching engine with methods:

- `FindMatches()` - Discovers potential matches based on criteria
- `CreateMatch()` - Creates a match with full economic analysis
- `calculateCompatibilityScore()` - Assesses technical compatibility
- `calculateEconomicScore()` - Evaluates economic viability
- `calculateTemporalScore()` - Analyzes temporal compatibility
- `calculateQualityScore()` - Assesses data quality
- `calculateOverallScore()` - Computes weighted final score

**Scoring Tolerances (from concept spec):**

- Temperature: ±10°C tolerance
- Pressure: ±20% tolerance
- Purity: ±5% tolerance

### 2. EconomicCalculator (`internal/service/economic_calculator.go`)

Comprehensive economic analysis tool:

- `CalculateEconomicImpact()` - Full NPV, IRR, payback analysis
- `calculateNPV()` - Net Present Value calculation
- `calculateIRR()` - Internal Rate of Return using iterative method
- `calculatePaybackPeriod()` - Simple payback period
- `calculateCO2Avoided()` - Environmental impact (t CO₂/year)
- `estimateCapex()` - Infrastructure investment estimation
- `PerformSensitivityAnalysis()` - Sensitivity analysis on key parameters

**Economic Formulas:**

```
NPV = -CAPEX + Σ(cash_flow / (1 + r)^t) for t=1 to n
IRR = discount rate where NPV = 0 (Newton-Raphson)
Payback = CAPEX / annual_cash_flow
CO₂_avoided = heat_MWh × 0.3 × 0.9 × 0.7 (for heat/energy)
```

### 3. CacheService (`internal/service/match_cache_service.go`)

Tiered caching for performance:

- **Fast Matching** (<100ms): Redis/memory cache for pre-computed matches
- **Standard Matching** (<5s): Real-time computation with caching
- In-memory implementation for development
- Redis implementation placeholder for production

**Cache TTL:** 15 minutes (concept spec recommendation)

### 4. EnhancedMatchingHandler (`internal/handler/enhanced_matching_handler.go`)

REST API implementation matching concept schemas:

- `POST /api/matching/query` - Find matches (implements `match_query_request.json`)
- `POST /api/matching/create-from-query` - Create match from query result
- `GET /api/matching/:matchId` - Get match details
- `PUT /api/matching/:matchId/status` - Update match status
- `GET /api/matching/top` - Get top matches

## API Examples

### Find Matches

```bash
POST /api/matching/query
Content-Type: application/json

{
  "resource": {
    "type": "heat",
    "direction": "output",
    "site_id": "site-123"
  },
  "constraints": {
    "max_distance_km": 25,
    "min_economic_value": 1000
  },
  "pagination": {
    "limit": 20,
    "offset": 0
  }
}
```

**Response:**

```json
{
  "matches": [
    {
      "id": "match-uuid",
      "compatibility_score": 0.85,
      "economic_value": 15000,
      "distance_km": 3.2,
      "source_resource": { ... },
      "target_resource": { ... }
    }
  ],
  "metadata": {
    "total_count": 15,
    "query_time_ms": 45,
    "cache_hit": false,
    "precision_levels": {
      "measured": 10,
      "estimated": 5,
      "rough": 0
    }
  }
}
```

### Create Match

```bash
POST /api/matching/create-from-query
Content-Type: application/json

{
  "source_flow_id": "flow-output-123",
  "target_flow_id": "flow-input-456"
}
```

**Response includes:**

- Full economic analysis (NPV, IRR, payback period)
- Risk assessment (technical, regulatory, market)
- Transportation estimate (cost, method, feasibility)
- CO₂ avoided calculation

## Transport Cost Calculation

Based on distance and resource type (concept spec values):

| Resource Type | Cost per km per unit |
|---------------|---------------------|
| Heat/Steam    | €0.0005/km/MWh     |
| Water         | €0.001/km/m³       |
| CO₂/Biowaste  | €0.002-0.003/km    |
| Materials     | €0.002/km          |
| Service       | €0 (no transport)  |

## CAPEX Estimation

Infrastructure costs by resource type:

| Resource Type | CAPEX per km |
|---------------|--------------|
| Heat piping   | €50,000/km   |
| Water piping  | €30,000/km   |
| Steam piping  | €60,000/km   |
| Trucking      | €5,000-10,000 (minimal) |

Plus connection costs (heat exchangers, meters): ~€20,000

## CO₂ Avoided Calculation

Based on concept spec environmental model:

**Heat/Energy:**

```
CO₂_avoided = heat_MWh × 0.3 (grid factor) × 0.9 (efficiency) × 0.7 (utilization)
            = heat_MWh × 0.189 tonnes CO₂/MWh
```

**Water:**

```
CO₂_avoided = water_m³ × 0.001 MWh/m³ × 0.3 (grid factor)
            = water_m³ × 0.0003 tonnes CO₂/m³
```

**Biowaste:**

```
CO₂_avoided = waste_tonnes × 0.5 (avoided emissions factor)
```

## Scoring Weights

Based on concept spec formula:

| Component  | Weight | Description |
|------------|--------|-------------|
| Quality    | 25%    | Technical compatibility |
| Temporal   | 20%    | Availability overlap |
| Quantity   | 15%    | Volume matching |
| Trust      | 15%    | Data quality/precision |
| Transport  | -10%   | Distance penalty |
| Regulatory | -10%   | Compliance complexity |
| Economic   | 5%     | Additional economic factor |

## Performance Targets

Based on concept spec:

- **Fast Matching:** <100ms (cached results)
- **Standard Matching:** <5s (real-time computation)
- **Deep Optimization:** <5min (background jobs, not yet implemented)

## Data Quality Factors

**Precision Level Scores:**

- Measured: 1.0
- Estimated: 0.75
- Rough: 0.5

**Source Type Scores:**

- Device: 1.0 (IoT sensors)
- Calculated: 0.7 (derived data)
- Declared: 0.6 (self-reported)

## Risk Assessment

**Technical Risk:**

- Low: combined quality + compatibility > 0.8
- Medium: 0.5 - 0.8
- High: < 0.5

**Market Risk:**

- Based on economic viability score
- Lower economic score = higher market risk

**Regulatory Risk:**

- CO₂/Biowaste: 0.6-0.7 (high complexity)
- Heat/Water: 0.2-0.3 (low complexity)

## Next Steps

### Implemented ✅

- [x] Multi-stage matching pipeline
- [x] Economic calculator (NPV, IRR, payback)
- [x] Transport cost calculation
- [x] Compatibility scoring with tolerances
- [x] Cache service (in-memory)
- [x] Enhanced API matching concept schemas
- [x] Risk assessment
- [x] CO₂ avoided calculation

### TODO

- [ ] Redis cache implementation
- [ ] PostGIS spatial prefiltering
- [ ] Deep optimization (multi-party matches)
- [ ] Background job processing
- [ ] WebSocket real-time updates
- [ ] Graph federation for multi-region queries
- [ ] Machine learning recommenders
- [ ] Sensitivity analysis UI

## Testing

Build and run:

```bash
cd bugulma/backend
go build ./cmd/server
./server
```

Test endpoints:

```bash
# Health check
curl http://localhost:8080/health

# Find matches
curl -X POST http://localhost:8080/api/matching/query \
  -H "Content-Type: application/json" \
  -d '{
    "resource": {"type": "heat", "direction": "output"},
    "constraints": {"max_distance_km": 25}
  }'
```

## References

- Concept: `concept/10_matching_engine_core_algorithm.md`
- Concept: `concept/MATHEMATICAL_MODEL.md`
- Concept: `concept/11_technical_architecture_implementation.md`
- Schemas: `concept/schemas/match*.json`