All files / src/domains/assets/services asset-depreciation.service.ts

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import { Injectable, BadRequestException } from '@nestjs/common';
import { InjectModel } from '@nestjs/mongoose';
import { Model, Types } from 'mongoose';
import { Asset, DepreciationSchedule, DepreciationRun } from '../schemas';
import { EventBusService } from '../../../platform/events/event-bus.service';
 
@Injectable()
export class AssetDepreciationService {
  constructor(
    @InjectModel(Asset.name)
    private readonly assetModel: Model<Asset>,
    @InjectModel(DepreciationSchedule.name)
    private readonly scheduleModel: Model<DepreciationSchedule>,
    @InjectModel(DepreciationRun.name)
    private readonly runModel: Model<DepreciationRun>,
    private readonly eventBus: EventBusService
  ) {}
 
  async calculateAssetPeriodDepreciation(
    tenantId: string,
    asset: Asset,
    fiscalYearId: string,
    periodNumber: number
  ): Promise<DepreciationSchedule | null> {
    if (asset.status !== 'capitalized' && asset.status !== 'assigned' && asset.status !== 'under_maintenance') {
      return null;
    }
 
    const nbv = asset.currentBookValueMinor;
    if (nbv <= asset.residualValueMinor) {
      return null; // Already reached residual floor - do not depreciate further
    }
 
    let depAmount = 0;
    if (asset.depreciationMethod === 'Straight Line') {
      // Monthly straight line: (capitalizationCost - residualValue) / usefulLife
      const depreciableAmount = asset.capitalizationCostMinor - asset.residualValueMinor;
      depAmount = Math.round(depreciableAmount / asset.usefulLifeMonths);
    } else if (asset.depreciationMethod === 'Written Down Value') {
      // WDV: book value * WDV rate (e.g. 15% per annum, monthly rate = 15/12 = 1.25%)
      const ratePerMonth = 0.15 / 12; 
      depAmount = Math.round(nbv * ratePerMonth);
    } else {
      return null; // No depreciation
    }
 
    // Floor constraint check: net book value cannot fall below residual value
    if (nbv - depAmount < asset.residualValueMinor) {
      depAmount = nbv - asset.residualValueMinor;
    }
 
    if (depAmount <= 0) return null;
 
    const schedule = new this.scheduleModel({
      tenantId,
      assetId: asset._id,
      fiscalYearId,
      periodNumber,
      depreciationAmountMinor: depAmount,
      bookValueBeforeMinor: nbv,
      bookValueAfterMinor: nbv - depAmount,
      status: 'pending'
    });
 
    return schedule.save();
  }
 
  async executeDepreciationRun(
    tenantId: string,
    fiscalYearId: string,
    periodNumber: number,
    userId: string
  ): Promise<DepreciationRun> {
    const count = await this.runModel.countDocuments({ tenantId }).exec();
    const runNumber = `DEP-RUN-${String(count + 1).padStart(6, '0')}`;
 
    // Find all active assets to depreciate
    const assets = await this.assetModel.find({
      tenantId,
      status: { $in: ['capitalized', 'assigned', 'under_maintenance'] }
    }).exec();
 
    let totalRunDepreciation = 0;
    const schedules: DepreciationSchedule[] = [];
 
    for (const asset of assets) {
      const schedule = await this.calculateAssetPeriodDepreciation(tenantId, asset, fiscalYearId, periodNumber);
      if (schedule) {
        totalRunDepreciation += schedule.depreciationAmountMinor;
        schedules.push(schedule);
      }
    }
 
    if (totalRunDepreciation === 0) {
      throw new BadRequestException('No assets are eligible for depreciation posting in this period.');
    }
 
    const run = new this.runModel({
      tenantId,
      runNumber,
      fiscalYearId,
      periodNumber,
      totalDepreciationMinor: totalRunDepreciation,
      status: 'posting_ready'
    });
    await run.save();
 
    // Link schedules to run in mock db logic or save
    for (const s of schedules) {
      s.status = 'pending';
      await s.save();
    }
 
    // Trigger Finance posting handshake
    await this.eventBus.publish('asset.depreciation-posting-ready.v1', {
      runId: run._id.toString(),
      runNumber: run.runNumber,
      tenantId,
      totalDepreciationMinor: totalRunDepreciation,
      fiscalYearId,
      periodNumber,
      userId
    }, tenantId);
 
    return run;
  }
 
  async handleFinanceDepreciationPosted(tenantId: string, runId: string): Promise<DepreciationRun> {
    const run = await this.runModel.findOne({ _id: runId, tenantId }).exec();
    if (!run) throw new Error('Depreciation run not found');
 
    run.status = 'posted';
    run.postedAt = new Date();
    await run.save();
 
    // Reconcile and update asset book values
    const schedules = await this.scheduleModel.find({
      tenantId,
      fiscalYearId: run.fiscalYearId,
      periodNumber: run.periodNumber,
      status: 'pending'
    }).exec();
 
    for (const s of schedules) {
      s.status = 'posted';
      await s.save();
 
      // Deduct from Asset book value
      await this.assetModel.updateOne(
        { _id: s.assetId },
        {
          $inc: {
            accumulatedDepreciationMinor: s.depreciationAmountMinor,
            currentBookValueMinor: -s.depreciationAmountMinor
          }
        }
      );
    }
 
    return run;
  }
}