"""Read raw pixel annotations; no coordinate quantization or target formatting."""
import base64
import io
import json
from pathlib import Path
from PIL import Image


class RawTSVDataset:
    def __init__(self, root, positive_only=False):
        self.root = Path(root)
        self.manifest = json.loads((self.root/'manifest.json').read_text())
        name = 'train.positive.annotations.tsv.lineidx' if positive_only else 'train.annotations.tsv.lineidx'
        self.offsets = [int(x) for x in (self.root/name).read_text().splitlines()]

    def __len__(self):
        return len(self.offsets)

    def __getitem__(self, index):
        # Open per request: safe under fork/spawn and concurrent readers.
        with (self.root/'train.annotations.tsv').open('rb') as f:
            f.seek(self.offsets[index])
            offset, payload = f.readline().split(b'\t', 1)
        annotation = json.loads(payload)
        with (self.root/'train.images.tsv').open('rb') as f:
            f.seek(int(offset))
            key, encoded = f.readline().rstrip(b'\n').split(b'\t', 1)
        if int(key) != int(offset):
            raise ValueError('Image offset mismatch')
        data = base64.b64decode(encoded, validate=True)
        return {'image_bytes': data, 'annotation': annotation}

    @staticmethod
    def decode(sample):
        # Do not EXIF-transpose: all coordinates describe the stored raster.
        with Image.open(io.BytesIO(sample['image_bytes'])) as source:
            image = source.convert('RGB')
        image.info.pop('exif', None)
        ann = sample['annotation']
        if image.size != (ann['width'], ann['height']):
            raise ValueError('Image size mismatch')
        return {'image': image, 'annotation': ann}