using System.Collections.Generic;
using System.Linq;
using Godot;
using Godot.Collections;
using Mr.BrickAdventures.Progression;

namespace Mr.BrickAdventures.scripts.Resources;

/// <summary>
/// The authored list of Levels in campaign order, and the bridge from a <see cref="LevelId"/> back to
/// the Godot scene that implements it.
/// </summary>
/// <remarks>
/// Not a domain port. Nothing in the progression domain resolves a Level to a scene — the domain only
/// needs the ordering, which it takes as a <see cref="Campaign"/>. Scene lookup is wanted solely by
/// the composition root, which is engine-side anyway.
/// </remarks>
[GlobalClass]
public partial class LevelCatalogue : Resource
{
    /// <summary>
    /// Levels in campaign order. A Level absent from this list is not reachable, even if its
    /// <see cref="LevelResource"/> exists.
    /// </summary>
    [Export]
    public Array<LevelResource> Levels { get; set; } = [];

    /// <summary>
    /// The ordering the domain works from. Throws if the authored data is inconsistent — a blank or
    /// duplicated id cannot produce a <see cref="Campaign"/>, so a mistake fails at boot rather than
    /// corrupting a save later.
    /// </summary>
    public Campaign ToCampaign()
    {
        var ids = new List<LevelId>();

        for (var i = 0; i < Levels.Count; i++)
        {
            if (Levels[i] == null)
                throw new System.InvalidOperationException($"LevelCatalogue has an empty slot at index {i}.");

            ids.Add(LevelId.Of(Levels[i].Id));
        }

        return Campaign.Of(ids);
    }

    /// <summary>
    /// Checks every catalogued Level names a scene that actually exists, returning the problems found.
    /// </summary>
    /// <remarks>
    /// This is what keeps <see cref="LevelResource.ScenePath"/> honest. The path cannot be a typed
    /// <c>PackedScene</c> — several level scenes reference their own LevelResource, so a reference back
    /// to the scene is a cycle Godot reports as "Parse Error: Busy" and the level fails to load. A
    /// string plus this check gets the safety without the cycle.
    /// </remarks>
    public IReadOnlyList<string> Validate()
    {
        var problems = new List<string>();

        foreach (var level in Levels.Where(l => l != null))
        {
            if (string.IsNullOrWhiteSpace(level.ScenePath))
                problems.Add($"level '{level.Id}' has no scene path");
            else if (!ResourceLoader.Exists(level.ScenePath))
                problems.Add($"level '{level.Id}' points at '{level.ScenePath}', which does not exist");
        }

        return problems;
    }

    public LevelResource Find(LevelId id) =>
        Levels.FirstOrDefault(level => level != null && level.Id == id.Value);

    /// <summary>Loads a Level's scene on demand. Null when the Level is not catalogued.</summary>
    public PackedScene SceneFor(LevelId id)
    {
        var path = Find(id)?.ScenePath;
        return string.IsNullOrWhiteSpace(path) ? null : ResourceLoader.Load<PackedScene>(path);
    }

    public string DisplayNameKeyFor(LevelId id) => Find(id)?.LevelName ?? string.Empty;
}