"""
ix_bridge.py — Load ix_moe_bridge C++ extension at runtime.

Calls ixformer::infer::topk_softmax() via C++ torch extension,
bypassing the missing Python binding in ixformer.functions.

Build: JIT-compiled on first import via torch.utils.cpp_extension.load()
       (same mechanism as flash_qla_sm70 GDN kernel — proven to work on BI-V100)
"""

import os
import logging
import torch

logger = logging.getLogger("ex_engine.ix_bridge")

_ix_bridge = None
_ix_bridge_available = False

def _load_bridge():
    """JIT-compile and load ix_moe_bridge.so"""
    global _ix_bridge, _ix_bridge_available
    if _ix_bridge is not None:
        return _ix_bridge_available
    
    csrc_dir = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "csrc")
    cpp_file = os.path.join(csrc_dir, "ix_moe_bridge.cpp")
    
    if not os.path.exists(cpp_file):
        # Try deployed path (inside vllm model dir)
        alt_dir = os.path.dirname(os.path.abspath(__file__))
        cpp_file = os.path.join(alt_dir, "ix_moe_bridge.cpp")
    
    if not os.path.exists(cpp_file):
        logger.warning("ix_moe_bridge.cpp not found at %s", cpp_file)
        _ix_bridge_available = False
        return False
    
    try:
        from torch.utils.cpp_extension import load
        logger.info("JIT-compiling ix_moe_bridge.cpp ...")
        _ix_bridge = load(
            name="ix_moe_bridge",
            sources=[cpp_file],
            extra_cflags=["-O2"],
            verbose=False,
        )
        _ix_bridge_available = True
        logger.info("ix_moe_bridge loaded successfully: %s", dir(_ix_bridge))
        return True
    except Exception as e:
        logger.warning("ix_moe_bridge JIT compile failed: %s", e)
        _ix_bridge_available = False
        return False

def topk_softmax(gating_output: torch.Tensor, topk: int, renormalize: bool = True):
    """
    Fused topk+softmax via ixformer C++ API.
    
    FAIL FAST: if bridge not available, raises RuntimeError immediately.
    No silent fallback — 0 score with no error log is worse than a crash.
    """
    if not _ix_bridge_available:
        if not _load_bridge():
            raise RuntimeError(
                "ix_moe_bridge: FATAL — ixformer C++ topk_softmax not available. "
                "JIT compile failed. Run probe_ixformer_symbols.py on real machine "
                "to diagnose. Cannot fall back silently — would produce 0 score."
            )
    
    return _ix_bridge.topk_softmax(gating_output, topk, renormalize)