from __future__ import annotations

import os
import random
import urllib.error
import urllib.request
from dataclasses import dataclass
from pathlib import Path


TINYSHAKESPEARE_URL = (
    "https://raw.githubusercontent.com/karpathy/char-rnn/master/data/"
    "tinyshakespeare/input.txt"
)


def _cache_dir() -> Path:
    base = os.environ.get("SGJM_CACHE_DIR")
    if base:
        path = Path(base)
    else:
        path = Path.home() / ".cache" / "sgjm"
    path.mkdir(parents=True, exist_ok=True)
    return path


def download_tinyshakespeare(force: bool = False) -> Path:
    target = _cache_dir() / "tinyshakespeare.txt"
    if target.exists() and not force:
        return target
    try:
        with urllib.request.urlopen(TINYSHAKESPEARE_URL, timeout=30) as resp:
            data = resp.read()
    except (urllib.error.URLError, TimeoutError) as e:
        raise RuntimeError(
            f"failed to download tinyshakespeare from {TINYSHAKESPEARE_URL}: {e}. "
            "Pre-download it manually and pass --data-path."
        ) from e
    target.write_bytes(data)
    return target


def synthetic_corpus(n_bytes: int = 1 << 20, seed: int = 0) -> bytes:
    # Deterministic byte stream with both periodic structure and a 2nd-order
    # Markov component. Gives the model something learnable but non-trivial
    # without pulling external data.
    rng = random.Random(seed)
    pattern = bytes(rng.randrange(256) for _ in range(96))
    period = len(pattern)
    out = bytearray(n_bytes)
    prev1 = 0
    prev2 = 0
    for i in range(n_bytes):
        mix = (pattern[i % period] ^ ((prev1 * 17 + prev2 * 31 + i * 7) & 0xFF))
        out[i] = mix & 0xFF
        prev2 = prev1
        prev1 = out[i]
    return bytes(out)


def _python_stdlib_root() -> Path:
    """Return the root directory of the active Python stdlib."""
    import sysconfig
    stdlib = sysconfig.get_path("stdlib")
    if stdlib and Path(stdlib).is_dir():
        return Path(stdlib)
    import sys
    return Path(sys.prefix) / "lib" / f"python{sys.version_info.major}.{sys.version_info.minor}"


_EXCLUDE_PARTS = {"test", "tests", "__pycache__", ".egg-info", "dist-info"}


def _collect_py_files(root: Path) -> list[Path]:
    """Return sorted .py files under root, excluding test and cache directories."""
    return sorted(
        p for p in root.rglob("*.py")
        if not any(part in _EXCLUDE_PARTS for part in p.parts)
    )


def _assemble_corpus(py_files: list[Path], n_bytes: int) -> bytes:
    sep = b"\n# ---\n"
    chunks: list[bytes] = []
    total = 0
    for p in py_files:
        try:
            chunk = p.read_bytes()
        except OSError:
            continue
        chunks.append(chunk)
        total += len(chunk) + len(sep)
        if total >= n_bytes:
            break
    return sep.join(chunks)[:n_bytes]


def _site_packages_root() -> Path | None:
    """Return the site-packages directory for the active Python installation."""
    import sysconfig
    sp = sysconfig.get_path("purelib")
    if sp and Path(sp).is_dir():
        return Path(sp)
    return None


def load_python_corpus(
    path: str | None = None,
    n_bytes: int = 1 << 20,
    extended: bool = False,
) -> bytes:
    """Collect .py files into a byte corpus.

    If `path` is given: collect from that directory.
    If `extended=True` (and no path): collect from Python stdlib + site-packages.
    Otherwise: collect from Python stdlib only.
    """
    if path:
        root = Path(path)
        if not root.is_dir():
            raise FileNotFoundError(f"Python corpus directory not found: {root}")
        py_files = _collect_py_files(root)
        if not py_files:
            raise ValueError(f"no .py files found under {root}")
        return _assemble_corpus(py_files, n_bytes)

    roots: list[Path] = [_python_stdlib_root()]
    if extended:
        sp = _site_packages_root()
        if sp:
            roots.append(sp)

    py_files: list[Path] = []
    for r in roots:
        if r.is_dir():
            py_files.extend(_collect_py_files(r))

    if not py_files:
        raise ValueError("no .py files found in Python stdlib or site-packages")

    # Deduplicate (stdlib and site-packages can overlap)
    seen: set[Path] = set()
    unique: list[Path] = []
    for p in py_files:
        if p not in seen:
            seen.add(p)
            unique.append(p)

    return _assemble_corpus(unique, n_bytes)


def load_corpus(
    path: str | None = None,
    n_bytes: int = 1 << 20,
    seed: int = 0,
    source: str = "auto",
) -> bytes:
    """Load a byte corpus from `path`, a known source, or synthetic fallback.

    source:
      "auto"            — use path if given, else synthetic
      "synthetic"       — always synthetic, ignore path
      "tinyshakespeare" — download (and cache) Karpathy's tinyshakespeare
      "file"            — require path; raise if missing
      "python"          — collect .py files from path (or Python stdlib)
    """
    if source == "synthetic":
        return synthetic_corpus(n_bytes, seed)
    if source == "tinyshakespeare":
        target = download_tinyshakespeare()
        return target.read_bytes()
    if source == "python":
        return load_python_corpus(path=path, n_bytes=n_bytes)
    if source == "python_extended":
        return load_python_corpus(path=path, n_bytes=n_bytes, extended=True)
    if source == "file":
        if not path or not os.path.exists(path):
            raise FileNotFoundError(f"data file not found: {path!r}")
        with open(path, "rb") as f:
            return f.read()
    # auto
    if path and os.path.exists(path):
        with open(path, "rb") as f:
            return f.read()
    return synthetic_corpus(n_bytes, seed)


@dataclass
class ByteDataset:
    data: bytes
    seq_len: int

    def __post_init__(self) -> None:
        if len(self.data) <= self.seq_len + 1:
            raise ValueError(
                f"corpus too small ({len(self.data)} bytes) for seq_len={self.seq_len}"
            )

    def __len__(self) -> int:
        return len(self.data) - self.seq_len - 1

    def sample(self, rng: random.Random) -> tuple[list[int], list[int]]:
        i = rng.randrange(len(self))
        chunk = self.data[i : i + self.seq_len + 1]
        return list(chunk[:-1]), list(chunk[1:])

    def batch(
        self,
        batch_size: int,
        rng: random.Random,
    ) -> tuple[list[list[int]], list[list[int]]]:
        xs: list[list[int]] = []
        ys: list[list[int]] = []
        for _ in range(batch_size):
            x, y = self.sample(rng)
            xs.append(x)
            ys.append(y)
        return xs, ys