// TEMPLATE: PromptRepository.cs
// PURPOSE: Loads agent system prompts from the agent_prompts table, with in-memory caching.
// READS STANDARD: ai-agents-prompt-sources
// PLACEHOLDERS:
//   {{PROJECT_NAMESPACE}}  — root namespace of the project
// LAST-VERIFIED: 2026-05-19

using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Caching.Memory;

namespace {{PROJECT_NAMESPACE}}.AI;

// ---------------------------------------------------------------------------
// Entity — map this to the agent_prompts table (EF Core convention mapping).
// Alternatively, configure via Fluent API in your DbContext.OnModelCreating.
// ---------------------------------------------------------------------------

/// <summary>
/// EF Core entity for the agent_prompts table.
/// Content is immutable once written — use INSERT + flip is_active for versioning.
/// </summary>
public sealed class AgentPrompt
{
    public Guid Id { get; init; } = Guid.CreateVersion7();
    public required string AgentKey { get; init; }
    public int Version { get; init; }
    public required string Content { get; init; }
    public bool IsActive { get; set; }
    public DateTimeOffset CreatedAt { get; init; } = DateTimeOffset.UtcNow;
}

// ---------------------------------------------------------------------------
// Interface
// ---------------------------------------------------------------------------

/// <summary>
/// Provides the active system-prompt content for a named agent.
/// </summary>
public interface IPromptRepository
{
    /// <summary>
    /// Returns the content of the currently active prompt for <paramref name="agentKey"/>.
    /// </summary>
    /// <exception cref="InvalidOperationException">
    /// Thrown when no row with <c>is_active = true</c> exists for <paramref name="agentKey"/>.
    /// </exception>
    Task<string> GetActivePromptAsync(string agentKey, CancellationToken ct = default);
}

// ---------------------------------------------------------------------------
// Implementation
// ---------------------------------------------------------------------------

// NOTE: Register in Program.cs (or a bootstrap extension):
//   builder.Services.AddMemoryCache();
//   builder.Services.AddScoped<IPromptRepository, PromptRepository>();
//
// The DbContext must expose:  public DbSet<AgentPrompt> AgentPrompts { get; set; }
// Replace YourDbContext below with the actual DbContext type of the project.

/// <summary>
/// Reads the active agent prompt from the database with an in-memory cache
/// (default TTL: 5 minutes sliding). Cache invalidation is time-based;
/// for immediate invalidation after a prompt update call
/// <c>IMemoryCache.Remove($"agent_prompt:{agentKey}")</c>.
/// </summary>
public sealed class PromptRepository(YourDbContext db, IMemoryCache cache) : IPromptRepository
{
    private static readonly TimeSpan CacheTtl = TimeSpan.FromMinutes(5);

    public async Task<string> GetActivePromptAsync(string agentKey, CancellationToken ct = default)
    {
        var cacheKey = $"agent_prompt:{agentKey}";

        if (cache.TryGetValue(cacheKey, out string? cached) && cached is not null)
            return cached;

        var content = await db.AgentPrompts
            .Where(p => p.AgentKey == agentKey && p.IsActive)
            .Select(p => p.Content)
            .FirstOrDefaultAsync(ct);

        if (content is null)
            throw new InvalidOperationException(
                $"No active prompt found for agent '{agentKey}'. " +
                "Insert a row in agent_prompts with is_active = true for this agent_key.");

        cache.Set(cacheKey, content, new MemoryCacheEntryOptions
        {
            SlidingExpiration = CacheTtl
        });

        return content;
    }
}