Merge branch 'dev' into agent/dex/CUB-39-filament-usage-sync

backend/Infrastructure/Services/CostPerPrintService.cs

@@ -0,0 +1,158 @@
+using Extrudex.Domain.Interfaces;
+using Extrudex.Infrastructure.Data;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+
+namespace Extrudex.Infrastructure.Services;
+
+/// <summary>
+/// Calculates the cost of goods sold (COGS) per print job using the spool's
+/// purchase price and the print job's derived grams consumed.
+///
+/// Formula:
+///   cost_per_gram = purchase_price / weight_total_grams
+///   cost_per_print = grams_derived × cost_per_gram
+///
+/// Handles missing data gracefully — if the spool has no purchase price or
+/// weight recorded, the result includes warnings and null cost fields
+/// instead of throwing exceptions.
+/// </summary>
+public class CostPerPrintService : ICostPerPrintService
+{
+    private readonly ExtrudexDbContext _dbContext;
+    private readonly ILogger<CostPerPrintService> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CostPerPrintService"/> class.
+    /// </summary>
+    /// <param name="dbContext">The database context for data access.</param>
+    /// <param name="logger">The logger for diagnostic output.</param>
+    public CostPerPrintService(ExtrudexDbContext dbContext, ILogger<CostPerPrintService> logger)
+    {
+        _dbContext = dbContext;
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public async Task<CostPerPrintResult> CalculateAsync(Guid printJobId, CancellationToken cancellationToken = default)
+    {
+        _logger.LogDebug("Calculating cost per print for job {PrintJobId}", printJobId);
+
+        var job = await _dbContext.PrintJobs
+            .Include(j => j.Spool)
+            .ThenInclude(s => s!.MaterialBase)
+            .FirstOrDefaultAsync(j => j.Id == printJobId, cancellationToken);
+
+        if (job is null)
+        {
+            _logger.LogWarning("Print job {PrintJobId} not found for cost calculation", printJobId);
+            return new CostPerPrintResult
+            {
+                PrintJobId = printJobId,
+                Warnings = new List<string> { $"Print job with ID '{printJobId}' not found." }
+            };
+        }
+
+        return BuildResult(job);
+    }
+
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<CostPerPrintResult>> CalculateBySpoolAsync(
+        Guid spoolId, CancellationToken cancellationToken = default)
+    {
+        _logger.LogDebug("Calculating cost per print for all jobs on spool {SpoolId}", spoolId);
+
+        var jobs = await _dbContext.PrintJobs
+            .Include(j => j.Spool)
+            .ThenInclude(s => s!.MaterialBase)
+            .Where(j => j.SpoolId == spoolId)
+            .OrderByDescending(j => j.CreatedAt)
+            .ToListAsync(cancellationToken);
+
+        if (jobs.Count == 0)
+        {
+            _logger.LogDebug("No print jobs found for spool {SpoolId}", spoolId);
+            return Array.Empty<CostPerPrintResult>();
+        }
+
+        return jobs.Select(BuildResult).ToList();
+    }
+
+    /// <summary>
+    /// Builds a <see cref="CostPerPrintResult"/> from a print job entity.
+    /// Computes cost_per_gram and cost_per_print when all required data is available.
+    /// Populates warnings when data is missing or incomplete.
+    /// </summary>
+    /// <param name="job">The print job entity with Spool navigation loaded.</param>
+    /// <returns>A cost calculation result with breakdown and any warnings.</returns>
+    private CostPerPrintResult BuildResult(Domain.Entities.PrintJob job)
+    {
+        var warnings = new List<string>();
+        var spool = job.Spool;
+
+        // Map what we always have
+        var result = new CostPerPrintResult
+        {
+            PrintJobId = job.Id,
+            PrintName = job.PrintName,
+            SpoolId = job.SpoolId,
+            SpoolSerial = spool?.SpoolSerial ?? string.Empty,
+            MmExtruded = job.MmExtruded,
+            GramsDerived = job.GramsDerived,
+        };
+
+        // Guard: spool must be loaded
+        if (spool is null)
+        {
+            warnings.Add("Spool data is not available for this print job.");
+            result.Warnings = warnings;
+            return result;
+        }
+
+        // Capture purchase price
+        result.PurchasePrice = spool.PurchasePrice;
+        result.WeightTotalGrams = spool.WeightTotalGrams;
+
+        // Check for missing purchase price
+        if (!spool.PurchasePrice.HasValue)
+        {
+            warnings.Add(
+                "Spool purchase price is not recorded. Cost calculation requires a purchase price on the spool.");
+        }
+
+        // Check for zero or negative weight — prevents division by zero
+        if (spool.WeightTotalGrams <= 0)
+        {
+            warnings.Add(
+                "Spool total weight is zero or not recorded. Cost calculation requires a positive weight_total_grams on the spool.");
+        }
+
+        // Check for zero grams derived
+        if (job.GramsDerived <= 0)
+        {
+            warnings.Add(
+                "Derived grams consumed is zero. Ensure mm_extruded, filament diameter, and material density are recorded for this print job.");
+        }
+
+        // If all data is present and valid, compute the cost
+        if (spool.PurchasePrice.HasValue && spool.WeightTotalGrams > 0 && job.GramsDerived > 0)
+        {
+            var costPerGram = spool.PurchasePrice.Value / spool.WeightTotalGrams;
+            result.CostPerGram = Math.Round(costPerGram, 6);
+            result.CostPerPrint = Math.Round(job.GramsDerived * costPerGram, 4);
+
+            _logger.LogDebug(
+                "Cost calculated for job {PrintJobId}: {GramsDerived}g × {CostPerGram:C}/g = {CostPerPrint:C}",
+                job.Id, job.GramsDerived, result.CostPerGram, result.CostPerPrint);
+        }
+        else
+        {
+            _logger.LogDebug(
+                "Cost calculation incomplete for job {PrintJobId}: missing data (warnings: {WarningCount})",
+                job.Id, warnings.Count);
+        }
+
+        result.Warnings = warnings;
+        return result;
+    }
+}