using NubLang.Diagnostics;
using NubLang.Syntax.Parsing.Node;

namespace NubLang.Syntax.Templating;

public class TemplateGenerator
{
    private readonly SyntaxTree _syntaxTree;
    private readonly TemplateTable _templateTable;

    public TemplateGenerator(SyntaxTree syntaxTree, TemplateTable templateTable)
    {
        _syntaxTree = syntaxTree;
        _templateTable = templateTable;
    }

    public IReadOnlyList<DefinitionSyntax> Generate()
    {
        var definitions = new List<DefinitionSyntax>();

        foreach (var type in _syntaxTree.ReferencedTemplatedCustomTypes)
        {
            definitions.Add(CreateDefinition(type));
        }

        return definitions;
    }

    private DefinitionSyntax CreateDefinition(TemplatedCustomTypeSyntax type)
    {
        var structTemplates = _templateTable.LookupStructTemplate(type.Namespace, type.Name).ToArray();
        if (structTemplates.Length > 0)
        {
            if (structTemplates.Length > 1)
            {
                throw new TemplateGeneratorException(Diagnostic.Error($"Struct template {type.Namespace}::{type.Name} has multiple definitions").Build());
            }

            var structTemplate = structTemplates[0];

            var transformations = new Dictionary<string, TypeSyntax>();

            for (var i = 0; i < structTemplate.TemplateParameters.Count; i++)
            {
                transformations[structTemplate.TemplateParameters[i]] = type.Arguments[i];
            }

            var transformer = new TypeTransformer(transformations);
            var transformed = transformer.TransformStruct(structTemplate.Struct);
            return transformed with { Name = type.MangledName() };
        }

        throw new TemplateGeneratorException(Diagnostic.Error($"Template {type.Namespace}::{type.Name} is not defined").Build());
    }
}

public class TemplateGeneratorException : Exception
{
    public Diagnostic Diagnostic { get; }

    public TemplateGeneratorException(Diagnostic diagnostic) : base(diagnostic.Message)
    {
        Diagnostic = diagnostic;
    }
}