#define ast_create_copy(parent_scope, T, ast) (T *)ast__create_copy(parent_scope, sizeof(T), ast)
Ast *ast__create_copy(Ast_Scope *parent_scope, size_t size, Ast *ast) {
    if (ast == 0) return 0;
    Ast *result = (Ast *)push_copy(pctx->perm, ast, size);
    result->parent_scope = parent_scope;
    result->di = ++pctx->unique_ids;
    return result;
}

// We are not copying module and file Ast's
// We are not copying resolved data
Ast *ast_copy(Ast *ast, Ast_Scope *parent_scope, Array<Ast_Decl *> *replace, Array<Ast_Call_Item *> *with) {
    if (!ast) return 0;
    switch (ast->kind) {
        case AST_SCOPE: {
            Ast_Scope *src = (Ast_Scope *)ast;
            Ast_Scope *dst = ast_create_copy(parent_scope, Ast_Scope, src);

            dst->decls = {};
            For(src->decls) {
                Ast_Decl *copy = (Ast_Decl *)ast_copy(it, src, replace, with);
                add(pctx->perm, &dst->decls, copy);
            }

            dst->stmts.init(pctx->perm, src->stmts.len);
            For(src->stmts) {
                Ast *copy = ast_copy(it, dst, replace, with);
                dst->stmts.add(copy);
            }
            return dst;
        } break;

        case AST_MODULE: invalid_codepath; break;
        case AST_FILE: invalid_codepath; break;

        case AST_IDENT: {
            Ast_Atom *src = (Ast_Atom *)ast;
            Ast_Atom *dst = ast_create_copy(parent_scope, Ast_Atom, ast);

            if ((dst->flags & AST_TYPESPEC)) {
                For(*replace) {
                    if (it->name == dst->intern_val) {
                        Breakpoint;
                    }
                }
            }

            return dst;
        } break;
        case AST_VALUE: {
            Ast_Atom *src = (Ast_Atom *)ast;
            Ast_Atom *dst = ast_create_copy(parent_scope, Ast_Atom, ast);
            return dst;
        } break;

        case AST_INDEX: {
            Ast_Index *src = (Ast_Index *)ast;
            Ast_Index *dst = ast_create_copy(parent_scope, Ast_Index, ast);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            dst->index = (Ast_Expr *)ast_copy(src->index, parent_scope, replace, with);
            return dst;
        } break;

        case AST_UNARY: {
            Ast_Unary *src = (Ast_Unary *)ast;
            Ast_Unary *dst = ast_create_copy(parent_scope, Ast_Unary, ast);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            return dst;
        } break;

        case AST_BINARY: {
            Ast_Binary *src = (Ast_Binary *)ast;
            Ast_Binary *dst = ast_create_copy(parent_scope, Ast_Binary, ast);
            dst->left = (Ast_Expr *)ast_copy(src->left, parent_scope, replace, with);
            dst->right = (Ast_Expr *)ast_copy(src->right, parent_scope, replace, with);
            return dst;
        } break;

        case AST_CALL_ITEM: {
            Ast_Call_Item *src = (Ast_Call_Item *)ast;
            Ast_Call_Item *dst = ast_create_copy(parent_scope, Ast_Call_Item, ast);
            dst->item = (Ast_Expr *)ast_copy(src->item, parent_scope, replace, with);
            if (src->call_flags & CALL_INDEX) {
                dst->index = (Ast_Expr *)ast_copy(src->index, parent_scope, replace, with);
            }
            else if (src->call_flags & CALL_NAME) {
                dst->name = (Ast_Atom *)ast_copy(src->name, parent_scope, replace, with);
            }
            return dst;
        } break;

        case AST_COMPOUND:
        case AST_CALL: {
            Ast_Call *src = (Ast_Call *)ast;
            Ast_Call *dst = ast_create_copy(parent_scope, Ast_Call, ast);
            dst->name = (Ast_Expr *)ast_copy(src->name, parent_scope, replace, with);

            dst->exprs.init(pctx->perm, src->exprs.len);
            For(dst->exprs) {
                auto copy = (Ast_Call_Item *)ast_copy(it, parent_scope, replace, with);
                dst->exprs.add(copy);
            }
            return dst;
        } break;

        case AST_TYPE_OF:
        case AST_LENGTH_OF:
        case AST_ALIGN_OF:
        case AST_SIZE_OF:
        case AST_RUNTIME_ASSERT:
        case AST_CONSTANT_ASSERT: {
            Ast_Builtin *src = (Ast_Builtin *)ast;
            Ast_Builtin *dst = ast_create_copy(parent_scope, Ast_Builtin, ast);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            return dst;
        } break;

        case AST_SWITCH: {
            Ast_Switch *src = (Ast_Switch *)ast;
            Ast_Switch *dst = ast_create_copy(parent_scope, Ast_Switch, ast);
            dst->value = (Ast_Expr *)ast_copy(src->value, parent_scope, replace, with);
            dst->default_scope = (Ast_Scope *)ast_copy(src->default_scope, parent_scope, replace, with);

            dst->cases.init(pctx->perm, src->cases.len);
            For(src->cases) {
                auto copy = (Ast_Switch_Case *)ast_copy(it, parent_scope, replace, with);
                assert(copy->kind == AST_SWITCH_CASE);
                dst->cases.add(copy);
            }
            return dst;
        } break;

        case AST_SWITCH_CASE: {
            Ast_Switch_Case *src = (Ast_Switch_Case *)ast;
            Ast_Switch_Case *dst = ast_create_copy(parent_scope, Ast_Switch_Case, ast);

            dst->scope = (Ast_Scope *)ast_copy(src->scope, parent_scope, replace, with);
            dst->labels.init(pctx->perm, src->labels.len);
            For(src->labels) {
                auto copy = (Ast_Expr *)ast_copy(it, parent_scope, replace, with);
                dst->labels.add(copy);
            }
            return dst;
        } break;

        case AST_VAR_UNPACK: {
            Ast_Var_Unpack *src = (Ast_Var_Unpack *)ast;
            Ast_Var_Unpack *dst = ast_create_copy(parent_scope, Ast_Var_Unpack, ast);

            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            dst->vars.init(pctx->perm, src->vars.len);
            For(src->vars) {
                auto copy = (Ast_Decl *)ast_copy(it, parent_scope, replace, with);
                dst->vars.add(copy);
            }
            return dst;
        } break;

        case AST_PASS:
        case AST_BREAK: {
            Ast *src = (Ast *)ast;
            Ast *dst = ast_create_copy(parent_scope, Ast, ast);
            return dst;
        } break;

        case AST_NAMESPACE:
        case AST_STRUCT:
        case AST_UNION:
        case AST_ENUM:
        case AST_LAMBDA:
        case AST_TYPE: // @cleanup: what is this used for?
        case AST_CONST:
        case AST_VAR: {
            Ast_Decl *src = (Ast_Decl *)ast;
            Ast_Decl *dst = ast_create_copy(parent_scope, Ast_Decl, ast);
            // dst->overload_op_info = ast_create_copy(parent_scope, Ast_Operator_Info, src->overload_op_info);
            // omitting polymorphs
            // omitting polymorph parameters
            dst->scope = (Ast_Scope *)ast_copy(src->scope, parent_scope, replace, with);
            dst->typespec = (Ast_Expr *)ast_copy(src->typespec, parent_scope, replace, with);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            return dst;
        } break;

        case AST_ARRAY: {
            Ast_Array *src = (Ast_Array *)ast;
            Ast_Array *dst = ast_create_copy(parent_scope, Ast_Array, ast);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            return dst;
        } break;

        case AST_FOR: {
            Ast_For *src = (Ast_For *)ast;
            Ast_For *dst = ast_create_copy(parent_scope, Ast_For, ast);
            dst->scope = (Ast_Scope *)ast_copy(src->scope, parent_scope, replace, with);
            dst->init = (Ast_Expr *)ast_copy(src->init, parent_scope, replace, with);
            dst->cond = (Ast_Expr *)ast_copy(src->cond, parent_scope, replace, with);
            dst->iter = (Ast_Expr *)ast_copy(src->iter, parent_scope, replace, with);
            return dst;
        } break;

        case AST_IF: {
            Ast_If *src = (Ast_If *)ast;
            Ast_If *dst = ast_create_copy(parent_scope, Ast_If, ast);
            dst->ifs.init(pctx->perm, src->ifs.len);
            For(src->ifs) {
                auto copy = (Ast_If_Node *)ast_copy(it, parent_scope, replace, with);
                assert(copy->kind == AST_IF_NODE);
                dst->ifs.add(copy);
            }
            return dst;
        } break;

        case AST_IF_NODE: {
            Ast_If_Node *src = (Ast_If_Node *)ast;
            Ast_If_Node *dst = ast_create_copy(parent_scope, Ast_If_Node, ast);
            dst->expr = (Ast_Expr *)ast_copy(src->expr, parent_scope, replace, with);
            dst->init = (Ast_Binary *)ast_copy(src->init, parent_scope, replace, with);
            dst->scope = (Ast_Scope *)ast_copy(src->scope, parent_scope, replace, with);
            return dst;
        } break;

        case AST_RETURN: {
            Ast_Return *src = (Ast_Return *)ast;
            Ast_Return *dst = ast_create_copy(parent_scope, Ast_Return, ast);

            dst->expr.init(pctx->perm, src->expr.len);
            For(src->expr) {
                auto copy = (Ast_Expr *)ast_copy(it, parent_scope, replace, with);
                dst->expr.add(copy);
            }
            return dst;
        } break;

        case AST_LAMBDA_EXPR: {
            Ast_Lambda *src = (Ast_Lambda *)ast;
            Ast_Lambda *dst = ast_create_copy(parent_scope, Ast_Lambda, ast);

            dst->args.init(pctx->perm, src->args.len);
            For(src->args) {
                auto copy = (Ast_Decl *)ast_copy(it, parent_scope, replace, with);
                dst->args.add(copy);
            }

            dst->ret.init(pctx->perm, src->ret.len);
            For(src->ret) {
                auto copy = (Ast_Expr *)ast_copy(it, parent_scope, replace, with);
                dst->ret.add(copy);
            }
            dst->scope = (Ast_Scope *)ast_copy(src->scope, parent_scope, replace, with);
            return dst;
        } break;

        default: assert(!"Invalid default case");
    }
    invalid_return;
}

Ast_Decl *get_or_instantiate_polymorph_type(Token *pos, Ast_Decl *poly, Array<Ast_Call_Item *> params, Ast_Scope *field_access_scope) {
    if (params.len != poly->polymorph_parameters.len) compiler_error(pos, "Invalid count of polymorphic arguments");

    int i = 0;
    uint64_t hash = 91;
    For(params) {
        bool indexed = (it->flags & CALL_INDEX);
        bool named = (it->flags & CALL_NAME);
        if (indexed == false && named == false) compiler_error(it->pos, "Polymorphic type cannot have named/indexed arguments");

        Ast_Decl *poly_decl = poly->polymorph_parameters[i++];
        resolve_decl(poly_decl);
        if (poly_decl->type != pctx->type_type) compiler_error(poly_decl->pos, "Invalid type of polymorphic struct argument");

        Operand op = resolve_expr(it->item, AST_CANT_BE_NULL, 0, field_access_scope);
        if (!op.is_const) compiler_error(it->pos, "Argument is required to be compile time known");
        if (op.type != pctx->type_type) compiler_error(it->pos, "Struct argument required to be a type");

        hash = hash_mix(hash, hash_ptr(op.type_val));
    }

    Ast_Decl *result = 0;
    For(poly->polymorphs) {
        if (it->polymorph_hash == hash) {
            result = it;
            break;
        }
    }

    if (!result) {
        result = (Ast_Decl *)ast_copy(poly, poly->parent_scope, &poly->polymorph_parameters, &params);
        poly->polymorphs.add(result);
    }

    return result;
}

//
// ITERATOR
//

const unsigned AST_NODE_END = 128;

struct Ast_Iter {
    Array<Ast *> stack;
    Ast *ast;
    Ast_Kind kind;
    bool skip_children;
    uint32_t visit_id;
    uint32_t di;
};

uint32_t Ast_Iter_VisitIDGen;
Ast_Iter iterate_depth_first(Allocator *a, Ast *ast) {
    assert(ast);
    Ast_Iter result = {};
    result.stack = {a};
    result.ast = ast;
    result.kind = ast->kind;
    result.visit_id = ++Ast_Iter_VisitIDGen;
    return result;
}

void next(Ast_Iter *iter) {
    Ast *ast = iter->ast;
    ast->visit_id = iter->visit_id;

    if (iter->skip_children) {
        iter->skip_children = false;
        goto end_of_switch;
    }

    switch (iter->kind) {
        case AST_SCOPE: {
            Ast_Scope *node = (Ast_Scope *)ast;
            iter->stack.add(node);
            For(node->stmts) iter->stack.add(it);
            For(node->decls) iter->stack.add(it);
        } break;

        case AST_MODULE: break; // This happens when we import stuff
        case AST_FILE: invalid_codepath; break;

        case AST_IDENT:
        case AST_VALUE: {
            Ast_Atom *node = (Ast_Atom *)ast;
        } break;

        case AST_INDEX: {
            Ast_Index *node = (Ast_Index *)ast;
            iter->stack.add(node);
            iter->stack.add(node->index);
            iter->stack.add(node->expr);
            assert(node->index);
            assert(node->expr);
        } break;

        case AST_UNARY: {
            Ast_Unary *node = (Ast_Unary *)ast;
            iter->stack.add(node);
            iter->stack.add(node->expr);
            assert(node->expr);
        } break;

        case AST_BINARY: {
            Ast_Binary *node = (Ast_Binary *)ast;
            iter->stack.add(node);
            iter->stack.add(node->right);
            iter->stack.add(node->left);
            assert(node->right);
            assert(node->left);
        } break;

        case AST_CALL_ITEM: {
            Ast_Call_Item *node = (Ast_Call_Item *)ast;
            iter->stack.add(node);
            iter->stack.add(node->item);
            assert(node->item);
            if (node->call_flags & CALL_INDEX) {
                iter->stack.add(node->index);
                assert(node->index);
            }
            else if (node->call_flags & CALL_NAME) {
                iter->stack.add(node->name);
                assert(node->name);
            }
        } break;

        case AST_COMPOUND:
        case AST_CALL: {
            Ast_Call *node = (Ast_Call *)ast;
            iter->stack.add(node);
            For(node->exprs) iter->stack.add(it);
            if (node->name) iter->stack.add(node->name);
        } break;

        case AST_TYPE_OF:
        case AST_LENGTH_OF:
        case AST_ALIGN_OF:
        case AST_SIZE_OF:
        case AST_RUNTIME_ASSERT:
        case AST_CONSTANT_ASSERT: {
            Ast_Builtin *node = (Ast_Builtin *)ast;
            iter->stack.add(node);
            iter->stack.add(node->expr);
            assert(node->expr);
        } break;

        case AST_SWITCH: {
            Ast_Switch *node = (Ast_Switch *)ast;
            iter->stack.add(node);
            if (node->default_scope) iter->stack.add(node->default_scope);
            For(node->cases) iter->stack.add(it);
            iter->stack.add(node->value);
            assert(node->value);
        } break;

        case AST_SWITCH_CASE: {
            Ast_Switch_Case *node = (Ast_Switch_Case *)ast;
            iter->stack.add(node);
            iter->stack.add(node->scope);
            assert(node->scope);
            For(node->labels) iter->stack.add(it);
        } break;

        case AST_VAR_UNPACK: {
            Ast_Var_Unpack *node = (Ast_Var_Unpack *)ast;
            iter->stack.add(node);
            iter->stack.add(node->expr);
            assert(node->expr);
            For(node->vars) iter->stack.add(it);
        } break;

        case AST_PASS:
        case AST_BREAK: {
            Ast *node = (Ast *)ast;
        } break;

        case AST_NAMESPACE:
        case AST_STRUCT:
        case AST_UNION:
        case AST_ENUM:
        case AST_LAMBDA:
        case AST_TYPE: // @cleanup: what is this used for?
        case AST_CONST:
        case AST_VAR: {
            Ast_Decl *node = (Ast_Decl *)ast;

            iter->stack.add(node);
            if (node->scope) iter->stack.add(node->scope);
            if (node->expr) iter->stack.add(node->expr);
            if (node->typespec) iter->stack.add(node->typespec);

            // omitting polymorphs
            // omitting polymorph parameters
        } break;

        case AST_ARRAY: {
            Ast_Array *node = (Ast_Array *)ast;
            iter->stack.add(node);
            if (node->expr) iter->stack.add(node->expr);
        } break;

        case AST_FOR: {
            Ast_For *node = (Ast_For *)ast;
            iter->stack.add(node);
            iter->stack.add(node->scope);
            assert(node->scope);
            if (node->iter) iter->stack.add(node->iter);
            if (node->cond) iter->stack.add(node->cond);
            if (node->init) iter->stack.add(node->init);
        } break;

        case AST_IF: {
            Ast_If *node = (Ast_If *)ast;
            iter->stack.add(node);
            For(node->ifs) iter->stack.add(it);
        } break;

        case AST_IF_NODE: {
            Ast_If_Node *node = (Ast_If_Node *)ast;
            iter->stack.add(node);
            iter->stack.add(node->scope);
            assert(node->scope);
            if (node->expr) iter->stack.add(node->expr);
            if (node->init) iter->stack.add(node->init);
        } break;

        case AST_RETURN: {
            Ast_Return *node = (Ast_Return *)ast;
            iter->stack.add(node);
            For(node->expr) iter->stack.add(it);
        } break;

        case AST_LAMBDA_EXPR: {
            Ast_Lambda *node = (Ast_Lambda *)ast;
            iter->stack.add(node);
            if (node->scope) iter->stack.add(node->scope);
            For(node->ret) iter->stack.add(it);
            For(node->args) iter->stack.add(it);
        } break;

        default: assert(!"Invalid default case");
    }
end_of_switch:

    if (iter->stack.len <= 0) {
        iter->ast = 0;
        iter->kind = AST_NONE;
        iter->stack.dealloc();
        return;
    }

    iter->ast = iter->stack.pop();
    assert(iter->ast != 0);
    iter->di += 1;
    iter->kind = iter->ast->kind;
    if (iter->ast->visit_id == iter->visit_id) {
        iter->kind = (Ast_Kind)((unsigned)iter->kind + AST_NODE_END);
    }
}