backend/API/Controllers/FilamentsController.cs

@@ -295,6 +295,66 @@ public class FilamentsController : ControllerBase
         return Ok(MapToFilamentResponse(entity));
     }
 
+    /// <summary>
+    /// Deletes a filament spool by its unique identifier.
+    /// If the spool has associated print jobs, the deletion is rejected with a 409 Conflict
+    /// to preserve COGS and print history — the caller should archive the spool instead.
+    /// Associated filament usage records are removed before the spool is deleted.
+    /// AMS slots referencing this spool will have their SpoolId set to null by the database.
+    /// </summary>
+    /// <param name="id">The unique identifier of the filament spool to delete.</param>
+    /// <returns>No content on successful deletion.</returns>
+    /// <response code="204">The filament spool was successfully deleted.</response>
+    /// <response code="404">If the filament spool with the given ID is not found.</response>
+    /// <response code="409">If the spool has associated print jobs and cannot be deleted.</response>
+    [HttpDelete("{id:guid}")]
+    [ProducesResponseType(StatusCodes.Status204NoContent)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    [ProducesResponseType(StatusCodes.Status409Conflict)]
+    public async Task<IActionResult> DeleteFilament(Guid id)
+    {
+        _logger.LogInformation("Deleting filament {Id}", id);
+
+        var entity = await _dbContext.Spools.FindAsync(id);
+        if (entity is null)
+        {
+            _logger.LogWarning("Filament {Id} not found for deletion", id);
+            return NotFound(new { error = $"Filament with ID '{id}' not found." });
+        }
+
+        // Check for associated print jobs — these cannot be orphaned
+        var hasPrintJobs = await _dbContext.PrintJobs.AnyAsync(pj => pj.SpoolId == id);
+        if (hasPrintJobs)
+        {
+            _logger.LogWarning(
+                "Cannot delete filament {Id}: associated print jobs exist. Suggest archiving instead.", id);
+            return Conflict(new
+            {
+                error = $"Cannot delete filament '{id}' because it has associated print jobs. " +
+                        "Archive the filament instead to preserve print history and COGS data."
+            });
+        }
+
+        // Remove associated filament usage records (usage tracking data for this spool)
+        var usageRecords = await _dbContext.FilamentUsages
+            .Where(fu => fu.SpoolId == id)
+            .ToListAsync();
+
+        if (usageRecords.Count > 0)
+        {
+            _logger.LogInformation(
+                "Removing {Count} filament usage records for spool {Id}",
+                usageRecords.Count, id);
+            _dbContext.FilamentUsages.RemoveRange(usageRecords);
+        }
+
+        _dbContext.Spools.Remove(entity);
+        await _dbContext.SaveChangesAsync();
+
+        _logger.LogInformation("Filament {Id} deleted successfully", id);
+        return NoContent();
+    }
+
     // ── Mapping helper ─────────────────────────────────────────
 
     /// <summary>