"""
Low-level state I/O — reads/writes the MEMB file format using llama-cpp-python's
exposed C functions directly.  No ABI conflict: we reuse the libllama.so that
llama-cpp-python already loaded instead of linking our own copy.
"""

from __future__ import annotations

import ctypes
import hashlib
import struct
import zlib
from pathlib import Path
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from llama_cpp import Llama

# ── File format ───────────────────────────────────────────────────
MAGIC          = b"MEMB"
VERSION        = 1
MODEL_ID_LEN   = 64

# little-endian: 4s magic | I version | 64s model_id | I n_ctx | I llama_ver | Q data_size
_HEADER_FMT  = "<4sI64sIIQ"
_HEADER_SIZE = struct.calcsize(_HEADER_FMT)  # == 88

# Optional Python trailer (appended after the V1 CRC32).  The C library reads
# only up to data_size+CRC and ignores anything past it, so adding a trailer
# keeps the file C-compatible.  The trailer carries llama-cpp-python's
# wrapper state (n_tokens) which is needed for `Llama.eval()` to append new
# tokens at the correct position instead of overwriting from offset 0.
_TRAILER_MAGIC  = b"MTRL"
_TRAILER_FMT    = "<4sII"   # magic | version | n_tokens
_TRAILER_SIZE   = struct.calcsize(_TRAILER_FMT)  # == 12
_TRAILER_VERSION = 1


# ── Helpers ───────────────────────────────────────────────────────

def compute_model_id(model_path: str) -> bytes:
    """SHA-256 of first 1 KiB of the GGUF file, hex-encoded and zero-padded to 64 bytes."""
    h = hashlib.sha256()
    try:
        with open(model_path, "rb") as f:
            h.update(f.read(1024))
    except OSError:
        h.update(model_path.encode("utf-8", errors="replace"))
    digest = h.hexdigest().encode("ascii")  # 64 chars exactly for SHA-256 hex
    return digest.ljust(MODEL_ID_LEN, b"\x00")[:MODEL_ID_LEN]


def _lib_and_ctx(llama_model: "Llama"):
    """Return (llama_cpp low-level module, raw llama_context_p pointer).

    Modern llama-cpp-python (≥0.3) wraps the raw `llama_context*` in a
    `_LlamaContext` helper object — the actual ctypes pointer lives one
    attribute deeper.  Older versions exposed the pointer directly.
    """
    try:
        from llama_cpp import llama_cpp as lib
    except ImportError as e:
        raise ImportError("llama-cpp-python is not installed: pip install llama-cpp-python") from e

    wrapper = getattr(llama_model, "_ctx", None) or getattr(llama_model, "ctx", None)
    if wrapper is None:
        raise RuntimeError(
            "Cannot find _ctx attribute on Llama instance — unsupported llama-cpp-python version"
        )

    # If wrapper is already a ctypes pointer (older llama-cpp-python), use directly
    if isinstance(wrapper, (int, ctypes.c_void_p)) or hasattr(wrapper, "_type_"):
        return lib, wrapper

    # Otherwise unwrap one level: `_LlamaContext.ctx` holds the raw pointer
    # (may be an int address, ctypes pointer, or c_void_p depending on version)
    for attr in ("ctx", "context", "_ctx"):
        raw = getattr(wrapper, attr, None)
        if raw is not None and (isinstance(raw, (int, ctypes.c_void_p)) or hasattr(raw, "_type_")):
            return lib, raw

    raise RuntimeError(
        f"Could not extract raw llama_context from {type(wrapper).__name__}; "
        "your llama-cpp-python version may have changed its internals."
    )


def _state_get_size(lib, ctx) -> int:
    try:
        return lib.llama_state_get_size(ctx)   # post-2024 API
    except AttributeError:
        return lib.llama_get_state_size(ctx)   # VERIFY: older API fallback


def _state_get_data(lib, ctx, buf: ctypes.Array, size: int) -> int:
    try:
        return lib.llama_state_get_data(ctx, buf, size)   # post-2024 API
    except AttributeError:
        return lib.llama_copy_state_data(ctx, buf)        # VERIFY: older API fallback


def _state_set_data(lib, ctx, buf: ctypes.Array, size: int) -> int:
    try:
        return lib.llama_state_set_data(ctx, buf, size)   # post-2024 API
    except AttributeError:
        return lib.llama_set_state_data(ctx, buf)         # VERIFY: older API fallback


def _n_ctx(lib, ctx) -> int:
    try:
        return lib.llama_n_ctx(ctx)
    except AttributeError:
        return 0


# ── Public API ────────────────────────────────────────────────────

def get_state_size(llama_model: "Llama") -> int:
    """Return the byte size of the current SSM hidden state."""
    lib, ctx = _lib_and_ctx(llama_model)
    return _state_get_size(lib, ctx)


def save_state(llama_model: "Llama", model_path: str, file_path: str) -> None:
    """Serialise the current SSM state to *file_path* in MEMB format."""
    lib, ctx = _lib_and_ctx(llama_model)

    size = _state_get_size(lib, ctx)
    if size == 0:
        raise RuntimeError("llama context returned state size 0 — is it initialised?")

    buf     = (ctypes.c_uint8 * size)()
    written = _state_get_data(lib, ctx, buf, size)
    if written == 0:
        raise RuntimeError("llama_state_get_data returned 0 bytes")

    data = bytes(buf[:written])
    crc  = zlib.crc32(data) & 0xFFFFFFFF

    model_id = compute_model_id(model_path)
    n_ctx    = _n_ctx(lib, ctx)

    header = struct.pack(
        _HEADER_FMT,
        MAGIC,
        VERSION,
        model_id,
        n_ctx,
        0,            # llama_ver — reserved
        len(data),
    )

    # Python-only trailer with Llama wrapper position so eval() resumes
    # at the right offset instead of overwriting from 0 after load_state.
    n_tokens = getattr(llama_model, "n_tokens", 0)
    trailer = struct.pack(_TRAILER_FMT, _TRAILER_MAGIC, _TRAILER_VERSION, n_tokens)

    out = Path(file_path)
    out.parent.mkdir(parents=True, exist_ok=True)
    out.write_bytes(header + data + struct.pack("<I", crc) + trailer)


def load_state(llama_model: "Llama", model_path: str, file_path: str) -> None:
    """Restore SSM state from *file_path* into *llama_model*."""
    lib, ctx = _lib_and_ctx(llama_model)
    expected_model_id = compute_model_id(model_path)

    raw = Path(file_path).read_bytes()
    if len(raw) < _HEADER_SIZE + 4:
        raise ValueError(f"State file too small: {file_path}")

    magic, version, file_model_id, n_ctx, llama_ver, data_size = struct.unpack_from(
        _HEADER_FMT, raw, 0
    )

    if magic != MAGIC:
        raise ValueError(f"Bad magic: expected {MAGIC!r}, got {magic!r}")
    if version != VERSION:
        raise ValueError(f"Unsupported state version {version} (expected {VERSION})")
    if file_model_id != expected_model_id:
        raise ValueError(
            "Model identity mismatch — state file was created with a different GGUF.\n"
            f"  file model_id : {file_model_id.rstrip(b'\\x00').decode()}\n"
            f"  current model : {expected_model_id.rstrip(b'\\x00').decode()}"
        )

    offset = _HEADER_SIZE
    if len(raw) < offset + data_size + 4:
        raise ValueError("Truncated state file")

    data       = raw[offset : offset + data_size]
    stored_crc = struct.unpack_from("<I", raw, offset + data_size)[0]
    computed   = zlib.crc32(data) & 0xFFFFFFFF

    if computed != stored_crc:
        raise ValueError(
            f"CRC-32 mismatch (stored={stored_crc:#010x}, computed={computed:#010x}) — "
            "file may be corrupted"
        )

    buf     = (ctypes.c_uint8 * len(data)).from_buffer_copy(data)
    restored = _state_set_data(lib, ctx, buf, len(data))
    if restored == 0:
        raise RuntimeError("llama_state_set_data returned 0 — state restore failed")

    # Optional trailer: restore llama-cpp-python wrapper position
    trailer_off = offset + data_size + 4
    if len(raw) >= trailer_off + _TRAILER_SIZE:
        magic, version, n_tokens = struct.unpack_from(_TRAILER_FMT, raw, trailer_off)
        if magic == _TRAILER_MAGIC and version == _TRAILER_VERSION:
            # Restore Llama wrapper state so eval() appends at the right
            # offset instead of overwriting the loaded KV-cache from 0.
            try:
                llama_model.n_tokens = n_tokens
            except AttributeError:
                pass  # wrapper version doesn't expose .n_tokens — eval may misbehave