import lzma
from pathlib import Path
import struct
import time
from typing import Literal

from src.snapshot import Snapshot


class RecordFile:
    VERSION = 1

    def __init__(self, path: str | Path, mode: Literal["w", "r"]) -> None:
        self.path: str | Path = path
        self.mode: Literal["w", "r"] = mode
        self.file: lzma.LZMAFile = lzma.LZMAFile(self.path, self.mode)

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        self.file.close()

    def write_header(self, n_snapshots: int):
        data: bytes = struct.pack(">IId", self.VERSION, n_snapshots, time.time())
        self.file.write(data)

    def write_snapshots(self, snapshots: list[Snapshot]):
        self.write_header(len(snapshots))
        for snapshot in snapshots:
            data: bytes = snapshot.pack()
            self.file.write(struct.pack(">I", len(data)) + data)

    def read_snapshots(self) -> list[Snapshot]:
        version: int = struct.unpack(">I", self.file.read(4))[0]
        if version != self.VERSION:
            raise ValueError(
                f"Cannot parse record file with format version {version} (current version: {self.VERSION})"
            )

        n_snapshots: int
        timestamp: float
        n_snapshots, timestamp = struct.unpack(">Id", self.file.read(12))
        snapshots: list[Snapshot] = []

        for _ in range(n_snapshots):
            size: int = struct.unpack(">I", self.file.read(4))[0]
            snapshots.append(Snapshot.unpack(self.file.read(size)))

        return snapshots