from __future__ import annotations

import hashlib
import importlib.util
import json
from pathlib import Path
from typing import Any, Iterable, Sequence


CACHE_VERSION = 1


def _json_hash(value: Any) -> str:
    encoded = json.dumps(value, ensure_ascii=False, sort_keys=True).encode("utf-8")
    return hashlib.sha256(encoded).hexdigest()


def _hash_text(value: Any) -> str:
    return hashlib.sha256(str(value or "").encode("utf-8")).hexdigest()


def parquet_reader_available() -> bool:
    return any(
        importlib.util.find_spec(package) is not None
        for package in ("pyarrow", "polars", "pandas")
    )


def dataset_source_files(dataset_name: str, data_dir: str | Path) -> list[Path]:
    root = Path(data_dir)

    if dataset_name == "multimodal":
        return sorted((root / "MultimodalReasoning").glob("*.jsonl"))

    if dataset_name == "reasoning_dpo":
        return sorted((root / "ReasoningDPO").glob("*.jsonl"))

    if dataset_name == "limo":
        return [root / "limo.jsonl"]

    if dataset_name == "complex_bespoke":
        return [root / "ComplexReasoningBespoke.parquet"]

    if dataset_name == "all":
        files: list[Path] = []
        files.extend(dataset_source_files("multimodal", root))
        files.extend(dataset_source_files("reasoning_dpo", root))
        files.extend(dataset_source_files("limo", root))
        files.extend(dataset_source_files("complex_bespoke", root))
        return files

    return []


def file_metadata(path: Path) -> dict[str, Any]:
    if not path.exists():
        return {
            "path": str(path),
            "exists": False,
        }

    stat = path.stat()

    return {
        "path": str(path),
        "exists": True,
        "size": stat.st_size,
        "mtime_ns": stat.st_mtime_ns,
    }


def data_digest(records: Sequence[dict[str, str]]) -> dict[str, Any]:
    digest = hashlib.sha256()

    for record in records:
        digest.update(str(record.get("user", "")).encode("utf-8"))
        digest.update(b"\0")
        digest.update(str(record.get("assistant", "")).encode("utf-8"))
        digest.update(b"\0\0")

    return {
        "rows": len(records),
        "sha256": digest.hexdigest(),
    }


def tokenizer_metadata(tokenizer: Any) -> dict[str, Any]:
    return {
        "name_or_path": str(getattr(tokenizer, "name_or_path", "")),
        "class": tokenizer.__class__.__name__,
        "eos_token": str(getattr(tokenizer, "eos_token", "")),
        "pad_token": str(getattr(tokenizer, "pad_token", "")),
        "padding_side": str(getattr(tokenizer, "padding_side", "")),
        "chat_template_sha256": _hash_text(getattr(tokenizer, "chat_template", "")),
        "vocab_size": len(tokenizer) if hasattr(tokenizer, "__len__") else None,
    }


def build_cache_metadata(
    *,
    config: dict[str, Any],
    tokenizer: Any,
    provided_records: Sequence[dict[str, str]] | None = None,
) -> dict[str, Any]:
    relevant_config = {
        key: config.get(key)
        for key in (
            "model_name",
            "data_dir",
            "dataset_name",
            "parquet_limit",
            "system_prompt",
            "dataset_format",
            "append_eos_to_completion",
            "max_samples",
            "eval_split_size",
            "max_eval_samples",
            "shuffle_data",
            "seed",
            "max_length",
            "completion_only_loss",
            "assistant_only_loss",
        )
    }

    metadata: dict[str, Any] = {
        "cache_version": CACHE_VERSION,
        "config": relevant_config,
        "tokenizer": tokenizer_metadata(tokenizer),
        "parquet_reader_available": parquet_reader_available(),
    }

    if provided_records is not None:
        metadata["provided_data"] = data_digest(provided_records)
    else:
        metadata["source_files"] = [
            file_metadata(path)
            for path in dataset_source_files(
                str(config.get("dataset_name", "all")),
                str(config.get("data_dir", "data")),
            )
        ]

    metadata["cache_key"] = _json_hash(metadata)[:24]

    return metadata


def cache_path(cache_root: str | Path, metadata: dict[str, Any]) -> Path:
    dataset_name = str(metadata["config"].get("dataset_name") or "dataset")
    safe_name = "".join(
        char if char.isalnum() or char in ("-", "_") else "_"
        for char in dataset_name
    )

    return Path(cache_root) / f"{safe_name}_{metadata['cache_key']}"


def metadata_path(path: str | Path) -> Path:
    return Path(path) / "metadata.json"


def read_metadata(path: str | Path) -> dict[str, Any] | None:
    meta_path = metadata_path(path)

    if not meta_path.exists():
        return None

    with meta_path.open("r", encoding="utf-8") as f:
        return json.load(f)


def write_metadata(path: str | Path, metadata: dict[str, Any]) -> None:
    meta_path = metadata_path(path)
    meta_path.parent.mkdir(parents=True, exist_ok=True)

    with meta_path.open("w", encoding="utf-8") as f:
        json.dump(metadata, f, ensure_ascii=False, indent=2, sort_keys=True)


def metadata_matches(path: str | Path, metadata: dict[str, Any]) -> bool:
    cached = read_metadata(path)

    return cached == metadata