ScadaBridge/src/ScadaLink.TemplateEngine/Services/TemplateDeletionService.cs

using ScadaLink.Commons.Entities.Templates;
using ScadaLink.Commons.Interfaces.Repositories;
using ScadaLink.Commons.Types;

namespace ScadaLink.TemplateEngine.Services;

/// <summary>
/// Enforces template deletion constraints (WP-25).
/// Template deletion is blocked when:
/// - Instances reference the template
/// - Child templates reference it (as parent)
/// - Other templates compose it
/// Returns clear error messages listing the referencing entities.
/// </summary>
public class TemplateDeletionService
{
    private readonly ITemplateEngineRepository _repository;

    public TemplateDeletionService(ITemplateEngineRepository repository)
    {
        _repository = repository ?? throw new ArgumentNullException(nameof(repository));
    }

    /// <summary>
    /// Checks whether a template can be safely deleted and returns any blocking reasons.
    /// </summary>
    public async Task<Result<bool>> CanDeleteTemplateAsync(int templateId, CancellationToken cancellationToken = default)
    {
        var template = await _repository.GetTemplateByIdAsync(templateId, cancellationToken);
        if (template == null)
            return Result<bool>.Failure($"Template with ID {templateId} not found.");

        var errors = new List<string>();

        // Check 1: Instances reference this template
        var instances = await _repository.GetInstancesByTemplateIdAsync(templateId, cancellationToken);
        if (instances.Count > 0)
        {
            var names = string.Join(", ", instances.Select(i => i.UniqueName).Take(10));
            errors.Add($"Cannot delete template '{template.Name}': {instances.Count} instance(s) reference it ({names}{(instances.Count > 10 ? "..." : "")}).");
        }

        // Check 2: Child templates reference it as parent
        var allTemplates = await _repository.GetAllTemplatesAsync(cancellationToken);
        var childTemplates = allTemplates.Where(t => t.ParentTemplateId == templateId).ToList();
        if (childTemplates.Count > 0)
        {
            var names = string.Join(", ", childTemplates.Select(t => t.Name).Take(10));
            errors.Add($"Cannot delete template '{template.Name}': {childTemplates.Count} child template(s) inherit from it ({names}{(childTemplates.Count > 10 ? "..." : "")}).");
        }

        // Check 3: Other templates compose it
        var composingTemplates = new List<(string TemplateName, string InstanceName)>();
        foreach (var t in allTemplates)
        {
            var compositions = await _repository.GetCompositionsByTemplateIdAsync(t.Id, cancellationToken);
            foreach (var comp in compositions)
            {
                if (comp.ComposedTemplateId == templateId)
                    composingTemplates.Add((t.Name, comp.InstanceName));
            }
        }

        if (composingTemplates.Count > 0)
        {
            var details = string.Join(", ",
                composingTemplates.Take(10).Select(c => $"'{c.TemplateName}' (as '{c.InstanceName}')"));
            errors.Add($"Cannot delete template '{template.Name}': {composingTemplates.Count} template(s) compose it ({details}{(composingTemplates.Count > 10 ? "..." : "")}).");
        }

        if (errors.Count > 0)
            return Result<bool>.Failure(string.Join(" ", errors));

        return Result<bool>.Success(true);
    }

    /// <summary>
    /// Deletes a template after checking all constraints.
    /// </summary>
    public async Task<Result<bool>> DeleteTemplateAsync(int templateId, CancellationToken cancellationToken = default)
    {
        var canDelete = await CanDeleteTemplateAsync(templateId, cancellationToken);
        if (canDelete.IsFailure)
            return canDelete;

        await _repository.DeleteTemplateAsync(templateId, cancellationToken);
        await _repository.SaveChangesAsync(cancellationToken);
        return Result<bool>.Success(true);
    }
}