using System.Text;

namespace Compiler;

public abstract class NubType
{
    public abstract override string ToString();
}

public sealed class NubTypeVoid : NubType
{
    public static readonly NubTypeVoid Instance = new();

    private NubTypeVoid()
    {
    }

    public override string ToString() => "void";
}

public sealed class NubTypeUInt : NubType
{
    private static readonly Dictionary<int, NubTypeUInt> Cache = new();

    public static NubTypeUInt Get(int width)
    {
        if (!Cache.TryGetValue(width, out var type))
            Cache[width] = type = new NubTypeUInt(width);

        return type;
    }

    public int Width { get; }

    private NubTypeUInt(int width)
    {
        Width = width;
    }

    public override string ToString() => $"u{Width}";
}

public sealed class NubTypeSInt : NubType
{
    private static readonly Dictionary<int, NubTypeSInt> Cache = new();

    public static NubTypeSInt Get(int width)
    {
        if (!Cache.TryGetValue(width, out var type))
            Cache[width] = type = new NubTypeSInt(width);

        return type;
    }

    public int Width { get; }

    private NubTypeSInt(int width)
    {
        Width = width;
    }

    public override string ToString() => $"i{Width}";
}

public sealed class NubTypeBool : NubType
{
    public static readonly NubTypeBool Instance = new();

    private NubTypeBool()
    {
    }

    public override string ToString() => "bool";
}

public sealed class NubTypeString : NubType
{
    public static readonly NubTypeString Instance = new();

    private NubTypeString()
    {
    }

    public override string ToString() => "string";
}

public sealed class NubTypeStruct : NubType
{
    public string Name { get; }
    public string Module { get; }
    public bool Packed { get; }

    private IReadOnlyList<Field>? _resolvedFields;

    public IReadOnlyList<Field> Fields => _resolvedFields ?? throw new InvalidOperationException();

    public NubTypeStruct(string module, string name, bool packed)
    {
        Module = module;
        Name = name;
        Packed = packed;
    }

    public void ResolveFields(IReadOnlyList<Field> fields)
    {
        if (_resolvedFields != null)
            throw new InvalidOperationException($"{Name} already resolved");

        _resolvedFields = fields;
    }

    public override string ToString() => _resolvedFields == null ? $"struct {Module}::{Name} <unresolved>" : $"struct {Module}::{Name} {{ {string.Join(' ', Fields.Select(f => $"{f.Name}: {f.Type}"))} }}";

    public sealed class Field(string name, NubType type)
    {
        public string Name { get; } = name;
        public NubType Type { get; } = type;
    }
}

public sealed class NubTypePointer : NubType
{
    private static readonly Dictionary<NubType, NubTypePointer> Cache = new();

    public static NubTypePointer Get(NubType to)
    {
        if (!Cache.TryGetValue(to, out var ptr))
            Cache[to] = ptr = new NubTypePointer(to);

        return ptr;
    }

    public NubType To { get; }

    private NubTypePointer(NubType to)
    {
        To = to;
    }

    public override string ToString() => $"^{To}";
}

public sealed class NubTypeFunc : NubType
{
    private static readonly Dictionary<Signature, NubTypeFunc> Cache = new();

    public static NubTypeFunc Get(List<NubType> parameters, NubType returnType)
    {
        var sig = new Signature(parameters, returnType);

        if (!Cache.TryGetValue(sig, out var func))
            Cache[sig] = func = new NubTypeFunc(parameters, returnType);

        return func;
    }

    public IReadOnlyList<NubType> Parameters { get; }
    public NubType ReturnType { get; }

    public string MangledName(string name, string module) => SymbolNameGen.Exported(name, module, this);

    private NubTypeFunc(List<NubType> parameters, NubType returnType)
    {
        Parameters = parameters;
        ReturnType = returnType;
    }

    public override string ToString() => $"func({string.Join(' ', Parameters)}): {ReturnType}";

    private readonly record struct Signature(IReadOnlyList<NubType> Parameters, NubType ReturnType);
}

static class TypeMangler
{
    public static string Encode(NubType type)
    {
        var sb = new StringBuilder();
        Encode(type, sb);
        return sb.ToString();
    }

    private static void Encode(NubType type, StringBuilder sb)
    {
        switch (type)
        {
            case NubTypeVoid:
                sb.Append('V');
                break;

            case NubTypeBool:
                sb.Append('B');
                break;

            case NubTypeUInt u:
                sb.Append("U(");
                sb.Append(u.Width);
                sb.Append(')');
                break;

            case NubTypeSInt s:
                sb.Append("U(");
                sb.Append(s.Width);
                sb.Append(')');
                break;

            case NubTypeString:
                sb.Append('S');
                break;

            case NubTypePointer p:
                sb.Append("P(");
                Encode(p.To, sb);
                sb.Append(')');
                break;

            case NubTypeStruct st:
                sb.Append($"T({st.Module}::{st.Name})").Append(st.Module).Append("::").Append(st.Name).Append(')');
                break;

            case NubTypeFunc fn:
                sb.Append("F(");
                for (int i = 0; i < fn.Parameters.Count; i++)
                {
                    Encode(fn.Parameters[i], sb);
                    sb.Append(',');
                }
                Encode(fn.ReturnType, sb);
                sb.Append(')');
                break;

            default:
                throw new NotSupportedException(type.GetType().Name);
        }
    }
}

static class Hashing
{
    public static ulong Fnv1a64(string text)
    {
        const ulong offset = 14695981039346656037UL;
        const ulong prime  = 1099511628211UL;

        ulong hash = offset;
        foreach (var c in Encoding.UTF8.GetBytes(text))
        {
            hash ^= c;
            hash *= prime;
        }

        return hash;
    }
}

static class SymbolNameGen
{
    public static string Exported(string module, string function, NubType type)
    {
        var canonical = TypeMangler.Encode(type);
        var hash = Hashing.Fnv1a64(canonical);

        return $"nub_{Sanitize(module)}_{Sanitize(function)}_{hash:x16}";
    }

    private static string Sanitize(string s)
    {
        var sb = new StringBuilder(s.Length);
        foreach (var c in s)
        {
            if (char.IsLetterOrDigit(c))
                sb.Append(c);
            else
                sb.Append('_');
        }
        return sb.ToString();
    }
}