client/src/lib/roadDesignCalculator.ts

// MargYantra – Road Design Tool
// IRC standards-based calculations for superelevation, camber, and transition curves

interface RoadDesignInput {
  road_type: 'highway' | 'arterial' | 'collector' | 'local' | 'expressway';
  design_speed: number; // km/h
  curve_radius: number; // meters
  cross_slope: number; // percentage
  terrain: 'plain' | 'rolling' | 'mountainous';
  pavement_type: 'flexible' | 'rigid' | 'composite';
}

interface RoadDesignOutput {
  superelevation: number; // percentage
  camber: number; // percentage
  transition_length: number; // meters
  sight_distance: number; // meters
  widening_required: number; // meters
  banking_angle: number; // degrees
  design_considerations: string[];
  irc_references: string[];
  safety_warnings: string[];
  confidence: number;
}

class RoadDesignCalculator {
  private readonly MAX_SUPERELEVATION = 7.0; // IRC standard maximum
  private readonly MIN_CURVE_RADIUS = 30; // minimum for any road
  private readonly MAX_DESIGN_SPEED = 120; // km/h for highways

  // IRC standard values for different road types
  private roadStandards = new Map([
    ['highway', { 
      max_speed: 100, 
      min_radius: 230, 
      camber_flexible: 2.5, 
      camber_rigid: 2.0,
      lane_width: 3.5 
    }],
    ['arterial', { 
      max_speed: 80, 
      min_radius: 120, 
      camber_flexible: 2.5, 
      camber_rigid: 2.0,
      lane_width: 3.5 
    }],
    ['collector', { 
      max_speed: 65, 
      min_radius: 80, 
      camber_flexible: 3.0, 
      camber_rigid: 2.5,
      lane_width: 3.25 
    }],
    ['local', { 
      max_speed: 50, 
      min_radius: 50, 
      camber_flexible: 3.0, 
      camber_rigid: 2.5,
      lane_width: 3.0 
    }],
    ['expressway', { 
      max_speed: 120, 
      min_radius: 360, 
      camber_flexible: 2.0, 
      camber_rigid: 1.7,
      lane_width: 3.75 
    }]
  ]);

  calculateRoadDesign(input: RoadDesignInput): RoadDesignOutput {
    try {
      // Validate inputs
      this.validateInputs(input);

      const roadStd = this.roadStandards.get(input.road_type);
      if (!roadStd) {
        throw new Error(`Unknown road type: ${input.road_type}`);
      }

      // Calculate superelevation
      const superelevation = this.calculateSuperelevation(input.design_speed, input.curve_radius);
      
      // Determine camber
      const camber = this.calculateCamber(input.pavement_type, input.road_type);
      
      // Calculate transition curve length
      const transitionLength = this.calculateTransitionLength(input.design_speed, input.curve_radius, superelevation);
      
      // Calculate sight distance
      const sightDistance = this.calculateSightDistance(input.design_speed, input.curve_radius);
      
      // Calculate mechanical widening
      const widening = this.calculateWidening(input.curve_radius, roadStd.lane_width);
      
      // Convert superelevation to banking angle
      const bankingAngle = Math.atan(superelevation / 100) * (180 / Math.PI);

      // Generate design considerations and warnings
      const designConsiderations = this.getDesignConsiderations(input, superelevation, transitionLength);
      const safetyWarnings = this.getSafetyWarnings(input, superelevation, sightDistance);
      const ircReferences = this.getIRCReferences(input.road_type);

      // Calculate confidence based on design adequacy
      const confidence = this.calculateConfidence(input, superelevation, sightDistance);

      return {
        superelevation: Math.round(superelevation * 100) / 100,
        camber: camber,
        transition_length: Math.round(transitionLength),
        sight_distance: Math.round(sightDistance),
        widening_required: Math.round(widening * 100) / 100,
        banking_angle: Math.round(bankingAngle * 100) / 100,
        design_considerations: designConsiderations,
        irc_references: ircReferences,
        safety_warnings: safetyWarnings,
        confidence: confidence
      };

    } catch (error) {
      throw new Error(`Road design calculation failed: ${error instanceof Error ? error.message : 'Unknown error'}`);
    }
  }

  private validateInputs(input: RoadDesignInput): void {
    if (!input.road_type || !this.roadStandards.has(input.road_type)) {
      throw new Error('Invalid road type. Must be one of: highway, arterial, collector, local, expressway');
    }

    if (!input.design_speed || input.design_speed <= 0 || input.design_speed > this.MAX_DESIGN_SPEED) {
      throw new Error(`Design speed must be between 1 and ${this.MAX_DESIGN_SPEED} km/h`);
    }

    if (!input.curve_radius || input.curve_radius < this.MIN_CURVE_RADIUS) {
      throw new Error(`Curve radius must be at least ${this.MIN_CURVE_RADIUS} meters`);
    }

    if (input.cross_slope !== undefined && (input.cross_slope < -10 || input.cross_slope > 10)) {
      throw new Error('Cross slope must be between -10% and +10%');
    }

    if (!input.terrain || !['plain', 'rolling', 'mountainous'].includes(input.terrain)) {
      throw new Error('Invalid terrain type. Must be one of: plain, rolling, mountainous');
    }

    if (!input.pavement_type || !['flexible', 'rigid', 'composite'].includes(input.pavement_type)) {
      throw new Error('Invalid pavement type. Must be one of: flexible, rigid, composite');
    }
  }

  private calculateSuperelevation(speed: number, radius: number): number {
    // IRC 73-1980 formula for superelevation
    // e = V²/(127R) - f, where f = lateral friction coefficient
    
    const lateralFriction = this.getLateralFrictionCoefficient(speed);
    const superelevation = (speed * speed) / (127 * radius) - lateralFriction;
    
    // Apply IRC limits
    if (superelevation < 0) return 0;
    if (superelevation > this.MAX_SUPERELEVATION) return this.MAX_SUPERELEVATION;
    
    return superelevation;
  }

  private getLateralFrictionCoefficient(speed: number): number {
    // IRC 73-1980 values for lateral friction
    if (speed <= 50) return 0.15;
    if (speed <= 65) return 0.14;
    if (speed <= 80) return 0.13;
    if (speed <= 100) return 0.12;
    return 0.10;
  }

  private calculateCamber(pavementType: string, roadType: string): number {
    const roadStd = this.roadStandards.get(roadType);
    if (!roadStd) return 2.5;

    switch (pavementType) {
      case 'flexible':
        return roadStd.camber_flexible;
      case 'rigid':
        return roadStd.camber_rigid;
      case 'composite':
        return (roadStd.camber_flexible + roadStd.camber_rigid) / 2;
      default:
        return 2.5;
    }
  }

  private calculateTransitionLength(speed: number, radius: number, superelevation: number): number {
    // IRC 73-1980 formula for transition curve length
    // L = 0.0215 * V³ / R (minimum formula)
    // Also consider superelevation development length
    
    const minLength = (0.0215 * speed * speed * speed) / radius;
    const superelevationLength = speed * superelevation / 0.5; // 0.5% per meter development rate
    
    return Math.max(minLength, superelevationLength, 30); // minimum 30m
  }

  private calculateSightDistance(speed: number, radius: number): number {
    // IRC SP 73-2018 stopping sight distance
    const reactionTime = 2.5; // seconds
    const brakingEfficiency = 0.35; // for wet roads
    const grade = 0; // assuming level road
    
    const reactionDistance = (speed * 1000 / 3600) * reactionTime;
    const brakingDistance = (speed * speed) / (254 * (brakingEfficiency + grade / 100));
    
    const stoppingSightDistance = reactionDistance + brakingDistance;
    
    // Check if horizontal curve affects sight distance
    const availableSightDistance = this.calculateHorizontalSightDistance(radius);
    
    return Math.min(stoppingSightDistance, availableSightDistance);
  }

  private calculateHorizontalSightDistance(radius: number): number {
    // For horizontal curves, sight distance is limited by curve geometry
    const middleOrdinate = 1.5; // typical clearance from centerline
    return 2 * Math.sqrt(2 * radius * middleOrdinate - middleOrdinate * middleOrdinate);
  }

  private calculateWidening(radius: number, laneWidth: number): number {
    // IRC SP 73-2018 mechanical widening formula
    const vehicleLength = 6; // meters (design vehicle)
    const wheelBase = 3.5; // meters
    
    const widening = (vehicleLength * vehicleLength) / (2 * radius) + (wheelBase * wheelBase) / (2 * radius);
    
    return Math.max(0, widening);
  }

  private getDesignConsiderations(input: RoadDesignInput, superelevation: number, transitionLength: number): string[] {
    const considerations: string[] = [];
    
    if (superelevation > 5.0) {
      considerations.push('High superelevation - ensure proper drainage design');
    }
    
    if (transitionLength > 200) {
      considerations.push('Long transition curve - check for adequate sight distance');
    }
    
    if (input.terrain === 'mountainous') {
      considerations.push('Mountainous terrain - consider additional safety measures and escape ramps');
    }
    
    if (input.design_speed > 80) {
      considerations.push('High speed design - implement enhanced safety features');
    }
    
    considerations.push('Ensure proper signage and pavement markings as per IRC 35');
    considerations.push('Consider weather conditions and seasonal variations');
    
    return considerations;
  }

  private getSafetyWarnings(input: RoadDesignInput, superelevation: number, sightDistance: number): string[] {
    const warnings: string[] = [];
    const roadStd = this.roadStandards.get(input.road_type);
    
    if (input.curve_radius < (roadStd?.min_radius || 100)) {
      warnings.push(`Curve radius below recommended minimum for ${input.road_type} roads`);
    }
    
    if (superelevation === this.MAX_SUPERELEVATION) {
      warnings.push('Maximum superelevation reached - consider increasing curve radius');
    }
    
    if (sightDistance < this.getMinimumSightDistance(input.design_speed)) {
      warnings.push('Inadequate sight distance - reduce design speed or increase radius');
    }
    
    if (input.design_speed > (roadStd?.max_speed || 50)) {
      warnings.push('Design speed exceeds recommended maximum for this road type');
    }
    
    return warnings;
  }

  private getMinimumSightDistance(speed: number): number {
    // IRC minimum sight distance requirements
    return speed * 2; // simplified minimum requirement
  }

  private getIRCReferences(roadType: string): string[] {
    const references = [
      'IRC 73-1980: Geometric Design Standards for Rural Highways',
      'IRC SP 73-2018: Manual of Specifications & Standards for Four Laning of Highways',
      'IRC 35-2015: Code of Practice for Road Markings',
      'IRC 103-2012: Guidelines for Pedestrian Facilities'
    ];
    
    if (roadType === 'expressway') {
      references.push('IRC 5-2015: Standard Specifications and Code of Practice for Road Bridges');
    }
    
    return references;
  }

  private calculateConfidence(input: RoadDesignInput, superelevation: number, sightDistance: number): number {
    let confidence = 90;
    
    const roadStd = this.roadStandards.get(input.road_type);
    
    // Reduce confidence for edge cases
    if (input.curve_radius < (roadStd?.min_radius || 100) * 1.2) {
      confidence -= 15;
    }
    
    if (superelevation > 6.0) {
      confidence -= 10;
    }
    
    if (sightDistance < this.getMinimumSightDistance(input.design_speed) * 1.1) {
      confidence -= 20;
    }
    
    return Math.max(50, confidence);
  }

  // Helper method to get design speed recommendations
  getDesignSpeedRecommendations(): Record<string, { recommended: number; maximum: number }> {
    return {
      'expressway': { recommended: 100, maximum: 120 },
      'highway': { recommended: 80, maximum: 100 },
      'arterial': { recommended: 65, maximum: 80 },
      'collector': { recommended: 50, maximum: 65 },
      'local': { recommended: 40, maximum: 50 }
    };
  }

  // Method to check design adequacy
  checkDesignAdequacy(input: RoadDesignInput): { adequate: boolean; issues: string[] } {
    const issues: string[] = [];
    const roadStd = this.roadStandards.get(input.road_type);
    
    if (!roadStd) {
      return { adequate: false, issues: ['Invalid road type'] };
    }
    
    if (input.design_speed > roadStd.max_speed) {
      issues.push(`Design speed exceeds maximum for ${input.road_type} (${roadStd.max_speed} km/h)`);
    }
    
    if (input.curve_radius < roadStd.min_radius) {
      issues.push(`Curve radius below minimum for ${input.road_type} (${roadStd.min_radius}m)`);
    }
    
    return {
      adequate: issues.length === 0,
      issues
    };
  }

  // Generate detailed design report
  generateDesignReport(input: RoadDesignInput, output: RoadDesignOutput): string {
    return `
ROAD GEOMETRIC DESIGN REPORT
===========================

INPUT PARAMETERS:
- Road Type: ${input.road_type}
- Design Speed: ${input.design_speed} km/h
- Curve Radius: ${input.curve_radius} m
- Cross Slope: ${input.cross_slope}%
- Terrain: ${input.terrain}
- Pavement Type: ${input.pavement_type}

DESIGN RESULTS:
- Superelevation: ${output.superelevation}%
- Camber: ${output.camber}%
- Transition Length: ${output.transition_length} m
- Sight Distance: ${output.sight_distance} m
- Widening Required: ${output.widening_required} m
- Banking Angle: ${output.banking_angle}°

DESIGN CONSIDERATIONS:
${output.design_considerations.map(c => `- ${c}`).join('\n')}

SAFETY WARNINGS:
${output.safety_warnings.map(w => `- ${w}`).join('\n')}

IRC REFERENCES:
${output.irc_references.map(ref => `- ${ref}`).join('\n')}

Design Confidence: ${output.confidence}%

Generated by Prithvi Guardian AI - MargYantra Module
Date: ${new Date().toLocaleDateString('en-IN')}
`;
  }
}

export const roadDesignCalculator = new RoadDesignCalculator();
export { RoadDesignInput, RoadDesignOutput };