from __future__ import annotations

from dataclasses import dataclass
from datetime import datetime, timedelta
from pathlib import Path
import re

_VERSION_PATTERN = re.compile(r"^(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$")
_FEATURE_UPDATED_AT_PATTERN = re.compile(
    r"^[0-9]{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12][0-9]|3[01])T(?:[01][0-9]|2[0-3]):[0-5][0-9]\+08:00$"
)


@dataclass(frozen=True, order=True)
class SoftwareVersion:
    major: int
    minor: int
    patch: int

    @classmethod
    def parse(cls, value: str) -> "SoftwareVersion":
        if not isinstance(value, str):
            raise ValueError("software version must be a string")
        match = _VERSION_PATTERN.fullmatch(value.strip())
        if match is None:
            raise ValueError("software version must use strict MAJOR.MINOR.PATCH digits")
        return cls(*(int(part) for part in match.groups()))

    def __str__(self) -> str:
        return f"{self.major}.{self.minor}.{self.patch}"


def read_software_version(code_root: Path) -> SoftwareVersion:
    path = Path(code_root) / "VERSION"
    try:
        return SoftwareVersion.parse(path.read_text(encoding="utf-8"))
    except OSError as exc:
        raise RuntimeError(f"software VERSION file is unreadable: {path}") from exc


def read_feature_updated_at(code_root: Path) -> str:
    path = Path(code_root) / "FEATURE_UPDATED_AT"
    try:
        value = path.read_text(encoding="utf-8").strip()
    except OSError as exc:
        raise RuntimeError(f"feature update timestamp file is unreadable: {path}") from exc
    if _FEATURE_UPDATED_AT_PATTERN.fullmatch(value) is None:
        raise ValueError("feature update timestamp must use YYYY-MM-DDTHH:MM+08:00")
    try:
        parsed = datetime.fromisoformat(value)
    except ValueError as exc:
        raise ValueError("feature update timestamp is not a valid calendar time") from exc
    if parsed.utcoffset() != timedelta(hours=8):
        raise ValueError("feature update timestamp must use Beijing UTC+08:00")
    return value