// node_api/jobs/depreciationCalculator.js
const { logger } = require('../utils/logger');

class DepreciationCalculator {
  constructor() {
    this.methods = {
      'straight_line': this.calculateStraightLine.bind(this),
      'declining_balance': this.calculateDecliningBalance.bind(this),
      'sum_of_years': this.calculateSumOfYears.bind(this),
      'units_of_production': this.calculateUnitsOfProduction.bind(this)
    };
  }

  /**
   * Calculate monthly depreciation for an asset
   * @param {Object} asset - Asset object with depreciation parameters
   * @param {Date} calculationDate - Date for which to calculate depreciation
   * @returns {Object} Depreciation calculation result
   */
  calculateMonthlyDepreciation(asset, calculationDate = new Date()) {
    try {
      const method = asset.depreciation_method || 'straight_line';
      const calculator = this.methods[method];

      if (!calculator) {
        throw new Error(`Unsupported depreciation method: ${method}`);
      }

      const result = calculator(asset, calculationDate);
      
      logger.depreciation(`Calculated ${method} depreciation for asset ${asset.id}`, {
        assetId: asset.id,
        method,
        monthlyDepreciation: result.monthlyDepreciation,
        calculationDate
      });

      return result;
    } catch (error) {
      logger.error(`Error calculating depreciation for asset ${asset.id}:`, error);
      throw error;
    }
  }

  /**
   * Straight-line depreciation calculation
   * Formula: (Cost - Salvage Value) / Useful Life
   */
  calculateStraightLine(asset, calculationDate) {
    const {
      acquisition_cost,
      salvage_value = 0,
      expected_useful_life_months,
      depreciation_percentage_rate
    } = asset;

    if (!acquisition_cost || !expected_useful_life_months) {
      throw new Error('Missing required parameters for straight-line depreciation');
    }

    const cost = parseFloat(acquisition_cost);
    const salvage = parseFloat(salvage_value);
    const usefulLifeMonths = parseInt(expected_useful_life_months);

    let monthlyDepreciation;

    // If depreciation rate is provided, use it
    if (depreciation_percentage_rate) {
      const rate = parseFloat(depreciation_percentage_rate);
      monthlyDepreciation = (cost * rate) / 100 / 12;
    } else {
      // Standard straight-line calculation
      monthlyDepreciation = (cost - salvage) / usefulLifeMonths;
    }

    return {
      method: 'straight_line',
      monthlyDepreciation,
      calculation: {
        acquisitionCost: cost,
        salvageValue: salvage,
        usefulLifeMonths,
        formula: depreciation_percentage_rate ? 
          `(${cost} * ${depreciation_percentage_rate}%) / 12` :
          `(${cost} - ${salvage}) / ${usefulLifeMonths}`
      }
    };
  }

  /**
   * Declining balance depreciation calculation
   * Formula: Book Value * (Depreciation Rate / 12)
   */
  calculateDecliningBalance(asset, calculationDate) {
    const {
      acquisition_cost,
      depreciation_percentage_rate,
      total_accumulated_depreciation = 0
    } = asset;

    if (!acquisition_cost || !depreciation_percentage_rate) {
      throw new Error('Missing required parameters for declining balance depreciation');
    }

    const cost = parseFloat(acquisition_cost);
    const rate = parseFloat(depreciation_percentage_rate) / 100;
    const accumulatedDepreciation = parseFloat(total_accumulated_depreciation);
    
    const currentBookValue = cost - accumulatedDepreciation;
    const monthlyDepreciation = currentBookValue * (rate / 12);

    // Ensure we don't depreciate below zero
    const adjustedDepreciation = Math.max(0, Math.min(monthlyDepreciation, currentBookValue));

    return {
      method: 'declining_balance',
      monthlyDepreciation: adjustedDepreciation,
      calculation: {
        acquisitionCost: cost,
        accumulatedDepreciation,
        currentBookValue,
        depreciationRate: rate,
        formula: `${currentBookValue} * (${rate} / 12)`
      }
    };
  }

  /**
   * Sum of years digits depreciation calculation
   * Formula: (Cost - Salvage) * (Remaining Life / Sum of Years) / 12
   */
  calculateSumOfYears(asset, calculationDate) {
    const {
      acquisition_cost,
      salvage_value = 0,
      expected_useful_life_months,
      acquisition_date
    } = asset;

    if (!acquisition_cost || !expected_useful_life_months || !acquisition_date) {
      throw new Error('Missing required parameters for sum of years depreciation');
    }

    const cost = parseFloat(acquisition_cost);
    const salvage = parseFloat(salvage_value);
    const usefulLifeMonths = parseInt(expected_useful_life_months);
    const usefulLifeYears = Math.ceil(usefulLifeMonths / 12);

    // Calculate months elapsed since acquisition
    const startDate = new Date(acquisition_date);
    const monthsElapsed = this.getMonthsDifference(startDate, calculationDate);
    const remainingMonths = Math.max(0, usefulLifeMonths - monthsElapsed);
    const remainingYears = Math.ceil(remainingMonths / 12);

    // Sum of years digits
    const sumOfYears = (usefulLifeYears * (usefulLifeYears + 1)) / 2;
    
    // Annual depreciation for current year
    const annualDepreciation = (cost - salvage) * (remainingYears / sumOfYears);
    const monthlyDepreciation = annualDepreciation / 12;

    return {
      method: 'sum_of_years',
      monthlyDepreciation,
      calculation: {
        acquisitionCost: cost,
        salvageValue: salvage,
        usefulLifeYears,
        remainingYears,
        sumOfYears,
        annualDepreciation,
        formula: `(${cost} - ${salvage}) * (${remainingYears} / ${sumOfYears}) / 12`
      }
    };
  }

  /**
   * Units of production depreciation calculation
   * Formula: (Cost - Salvage) * (Units Used / Total Expected Units)
   */
  calculateUnitsOfProduction(asset, calculationDate) {
    const {
      acquisition_cost,
      salvage_value = 0,
      expected_total_units,
      current_month_units = 0
    } = asset;

    if (!acquisition_cost || !expected_total_units) {
      throw new Error('Missing required parameters for units of production depreciation');
    }

    const cost = parseFloat(acquisition_cost);
    const salvage = parseFloat(salvage_value);
    const totalUnits = parseFloat(expected_total_units);
    const monthlyUnits = parseFloat(current_month_units);

    const depreciationPerUnit = (cost - salvage) / totalUnits;
    const monthlyDepreciation = depreciationPerUnit * monthlyUnits;

    return {
      method: 'units_of_production',
      monthlyDepreciation,
      calculation: {
        acquisitionCost: cost,
        salvageValue: salvage,
        totalExpectedUnits: totalUnits,
        currentMonthUnits: monthlyUnits,
        depreciationPerUnit,
        formula: `(${cost} - ${salvage}) / ${totalUnits} * ${monthlyUnits}`
      }
    };
  }

  /**
   * Validate asset for depreciation calculation
   */
  validateAsset(asset) {
    const errors = [];

    if (!asset.acquisition_cost || asset.acquisition_cost <= 0) {
      errors.push('Acquisition cost must be greater than 0');
    }

    if (!asset.acquisition_date) {
      errors.push('Acquisition date is required');
    }

    if (!asset.depreciation_method) {
      errors.push('Depreciation method is required');
    }

    const method = asset.depreciation_method;
    
    if (method === 'straight_line' && !asset.expected_useful_life_months) {
      errors.push('Expected useful life is required for straight-line depreciation');
    }

    if (method === 'declining_balance' && !asset.depreciation_percentage_rate) {
      errors.push('Depreciation rate is required for declining balance method');
    }

    if (method === 'sum_of_years' && !asset.expected_useful_life_months) {
      errors.push('Expected useful life is required for sum of years method');
    }

    if (method === 'units_of_production' && !asset.expected_total_units) {
      errors.push('Expected total units is required for units of production method');
    }

    return errors;
  }

  /**
   * Check if asset should be depreciated
   */
  shouldDepreciate(asset, calculationDate = new Date()) {
    // Don't depreciate if asset is fully depreciated
    const acquisitionCost = parseFloat(asset.acquisition_cost) || 0;
    const accumulatedDepreciation = parseFloat(asset.total_accumulated_depreciation) || 0;
    const salvageValue = parseFloat(asset.salvage_value) || 0;

    if (accumulatedDepreciation >= (acquisitionCost - salvageValue)) {
      return false;
    }

    // Don't depreciate if asset is not active
    if (asset.status !== 'active') {
      return false;
    }

    // Don't depreciate if acquisition date is in the future
    const acquisitionDate = new Date(asset.acquisition_date);
    if (acquisitionDate > calculationDate) {
      return false;
    }

    // Don't depreciate if asset is beyond useful life
    if (asset.expected_useful_life_months) {
      const monthsElapsed = this.getMonthsDifference(acquisitionDate, calculationDate);
      if (monthsElapsed >= asset.expected_useful_life_months) {
        return false;
      }
    }

    return true;
  }

  /**
   * Helper method to calculate months difference between two dates
   */
  getMonthsDifference(startDate, endDate) {
    const start = new Date(startDate);
    const end = new Date(endDate);
    
    const yearsDiff = end.getFullYear() - start.getFullYear();
    const monthsDiff = end.getMonth() - start.getMonth();
    
    return yearsDiff * 12 + monthsDiff;
  }
}

module.exports = { DepreciationCalculator };