namespace meowlang.typechecker;

public class Scope
{
    private readonly Dictionary<string, TypeId> _variableScope = new();
    private readonly Dictionary<(string, int), Guid> _typeScope = new();

    private readonly TypeRegistry _typeRegistry;
    
    private readonly Scope? _parent;


    public Scope? DebugGetParent => _parent;
    public Dictionary<string, TypeId> DebugGetVariableScope => _variableScope;
    public Dictionary<(string, int), Guid> DebugGetTypeScope => _typeScope;


    public Scope(TypeRegistry typeRegistry, Scope? parent = null)
    {
        _typeRegistry = typeRegistry;
        _parent = parent;
    }

    public void AddVariable(string name, TypeId type)
    {
        if (_variableScope.ContainsKey(name))
        {
            throw new DuplicateVariableNameException(name);
        }

        _variableScope[name] = type;
    }

    public bool HasVariable(string name)
    {
        if (_variableScope.ContainsKey(name)) return true;
        return _parent?.HasVariable(name) ?? false;
    }

    public TypeId GetVariableType(string name)
    {
        return _variableScope.TryGetValue(name, out var value) ? value : throw new UnknownVariableNameException(name);
    }

    public Guid AddAnonymousType(TypeDescription type)
    {
        var guid = Guid.NewGuid();
        _typeRegistry.Add(guid, type);
        return guid;
    }

    public Guid AddNamedType(string name, int arity, TypeDescription type)
    {
        Guid guid;
        if (_typeScope.TryGetValue((name, arity), out guid))
        {
            if (_typeRegistry.Has(guid))
            {
                throw new DuplicateTypeNameException(name, arity);
            }
        }
        else
        {
            if (HasType(name, arity))
            {
                throw new DuplicateTypeNameException(name, arity);
            }
            guid = Guid.NewGuid();
            _typeScope[(name, arity)] = guid;
        }
        _typeRegistry.Add(guid, type);
        return guid;
    }

    public bool HasType(string name, int arity)
    {
        if (_typeScope.ContainsKey((name, arity))) return true;
        return _parent?.HasType(name, arity) ?? false;
    }

    public TypeDescription GetType(Guid guid)
    {
        return _typeRegistry.Get(guid);
    }

    private Guid? GetTypeGuidWithoutCreate(string name, int arity)
    {
        if (_typeScope.ContainsKey((name, arity))) return _typeScope[(name, arity)];
        return _parent?.GetTypeGuidWithoutCreate(name, arity);
    }
    
    public Guid GetTypeGuid(string name, int arity)
    {
        var key = GetTypeGuidWithoutCreate(name, arity);
        if (key == null)
        {
            key = Guid.NewGuid();
            _typeScope[(name, arity)] = key.Value;
        }

        return key.Value;
    }
}

public class UnknownTypeException : Exception
{
    private readonly string _name;
    private readonly int _arity;

    public UnknownTypeException(string name, int arity): base($"unknown type `{name}` with arity {arity}")
    {
        _name = name;
        _arity = arity;
    }
}

public class UnknownVariableNameException : Exception
{
    public string Name { get; }

    public UnknownVariableNameException(string name) : base($"unknown variable `{name}`")
    {
        Name = name;
    }
}