"""
services/study_parser.py
--------------------------
MRIStudy: ZIP extraction + BraTS sequence discovery + validation.

Responsible only for turning "a ZIP file landed on disk" into
"four validated NIfTI paths" (t1, t1ce, t2, flair). Knows nothing
about models, meshes, or payloads — pipeline.py wires those together.
"""

from __future__ import annotations

import os
import re
import zipfile
from dataclasses import dataclass
from typing import Optional


class StudyValidationError(Exception):
    """Raised when a study ZIP is missing a required sequence or is malformed."""


# Sequence -> regex patterns to match against (case-insensitive) filenames.
# Ordered so more-specific patterns (t1ce) are checked before substrings
# that could also match t1.
_SEQUENCE_PATTERNS: dict[str, list[str]] = {
    "t1ce":  [r"t1ce", r"t1c\b", r"t1-ce", r"t1_ce"],
    "flair": [r"flair"],
    "t2":    [r"(?<!t1)t2(?!ce)"],
    "t1":    [r"(?<!t1ce)(?<!t1c)t1(?!ce)"],
}

_NIFTI_SUFFIXES = (".nii.gz", ".nii")


@dataclass
class MRIStudy:
    """
    Extracts a BraTS-style ZIP into a session directory and resolves
    the four required sequence files.

    Usage:
        study = MRIStudy.from_zip(zip_path, session_dir)
        study.validate()
        study.t1_path / study.t1ce_path / study.t2_path / study.flair_path
    """

    session_dir: str
    t1_path: Optional[str] = None
    t1ce_path: Optional[str] = None
    t2_path: Optional[str] = None
    flair_path: Optional[str] = None
    study_id: Optional[str] = None

    # ------------------------------------------------------------------
    # Construction
    # ------------------------------------------------------------------

    @classmethod
    def from_zip(cls, zip_path: str, session_dir: str) -> "MRIStudy":
        """Extract `zip_path` into `session_dir` and discover sequences."""
        os.makedirs(session_dir, exist_ok=True)

        try:
            with zipfile.ZipFile(zip_path, "r") as zf:
                zf.extractall(session_dir)
        except zipfile.BadZipFile as e:
            raise StudyValidationError(f"'{zip_path}' is not a valid ZIP file: {e}")

        study = cls(session_dir=session_dir)
        study._discover_sequences()
        study.study_id = study._infer_study_id()
        return study

    @classmethod
    def from_directory(cls, session_dir: str) -> "MRIStudy":
        """Discover sequences in an already-extracted directory (no ZIP step)."""
        study = cls(session_dir=session_dir)
        study._discover_sequences()
        study.study_id = study._infer_study_id()
        return study

    # ------------------------------------------------------------------
    # Discovery
    # ------------------------------------------------------------------

    def _all_nifti_files(self) -> list[str]:
        found = []
        for root, _dirs, files in os.walk(self.session_dir):
            for fname in files:
                if fname.lower().endswith(_NIFTI_SUFFIXES):
                    found.append(os.path.join(root, fname))
        return found

    def _discover_sequences(self) -> None:
        candidates = self._all_nifti_files()

        for seq_name, patterns in _SEQUENCE_PATTERNS.items():
            match = self._match_sequence(candidates, patterns)
            setattr(self, f"{seq_name}_path", match)

    @staticmethod
    def _match_sequence(candidates: list[str], patterns: list[str]) -> Optional[str]:
        for path in candidates:
            fname = os.path.basename(path).lower()
            for pat in patterns:
                if re.search(pat, fname):
                    return path
        return None

    def _infer_study_id(self) -> str:
        """Best-effort patient/study identifier from any discovered filename."""
        for path in (self.t1_path, self.t1ce_path, self.t2_path, self.flair_path):
            if path:
                base = os.path.basename(path)
                for suffix in _NIFTI_SUFFIXES:
                    if base.lower().endswith(suffix):
                        base = base[: -len(suffix)]
                        break
                # Strip a trailing sequence tag like "-t1", "_flair", etc.
                base = re.sub(
                    r"[-_]?(t1ce|t1c|t1|t2|flair)$", "", base, flags=re.IGNORECASE
                )
                return base
        return "unknown_study"

    # ------------------------------------------------------------------
    # Validation
    # ------------------------------------------------------------------

    def validate(self) -> None:
        """Raise StudyValidationError if any required sequence is missing."""
        missing = [
            name
            for name, path in (
                ("T1", self.t1_path),
                ("T1ce", self.t1ce_path),
                ("T2", self.t2_path),
                ("FLAIR", self.flair_path),
            )
            if path is None
        ]
        if missing:
            raise StudyValidationError(
                f"Study at '{self.session_dir}' is missing required sequence(s): "
                f"{', '.join(missing)}."
            )

    def as_paths(self) -> dict:
        return {
            "t1_path": self.t1_path,
            "t1ce_path": self.t1ce_path,
            "t2_path": self.t2_path,
            "flair_path": self.flair_path,
        }