# Copyright (c) Qualcomm Innovation Center, Inc.
# All rights reserved
#
# This source code is licensed under the BSD-style license found in the
# LICENSE file in the root directory of this source tree.

import torch
from executorch.exir.pass_base import ExportPass, PassResult
from torch.fx.experimental.proxy_tensor import make_fx


class DecomposeEinsum(ExportPass):
    """
    Decompose einsum for quantization annotation to work properly.
    """

    def __init__(self) -> None:
        super().__init__()

    def call(self, graph_module: torch.fx.GraphModule) -> PassResult:
        graph = graph_module.graph
        for node in graph.nodes:
            if node.target == torch.ops.aten.einsum.default:
                decomposed_module = make_fx(
                    node.target,
                    tracing_mode="fake",
                )(node.args[0], [arg.meta["val"] for arg in node.args[1]])

                with graph.inserting_before(node):
                    # remap is used to map original node values to new node values,
                    # which ensures that reference to nodes are correclty updated in the new graph
                    remap = {}
                    # Different from other nodes, einsum args[0] is the einsum equation,
                    # while input nodes are stored in args[1]
                    for i, arg in enumerate(node.args[1]):
                        remap[f"arg1_{i+1}"] = arg

                    for decomposed_node in decomposed_module.graph.nodes:
                        # This is the arg[0] equation string, which is not required anymore after decomposition
                        if "arg0" in decomposed_node.name:
                            continue

                        # no need to copy existent 'output'
                        if decomposed_node.op == "output":
                            for user in node.users.copy():
                                # remap
                                user.replace_input_with(
                                    node,
                                    remap[decomposed_node.args[0][0]],
                                )
                        # no need to copy existent placeholders
                        elif decomposed_node.op == "placeholder":
                            # replace node map from string to graph node
                            remap[decomposed_node] = remap.pop(decomposed_node.name)
                        else:
                            remap[decomposed_node] = graph.node_copy(
                                decomposed_node,
                                arg_transform=lambda x, remap=remap: remap[x],
                            )

                    graph.erase_node(node)

        graph.eliminate_dead_code()
        graph_module.recompile()
        return PassResult(graph_module, True)