"""Decode only bounded, embedded raster assets. Never follow document filenames."""
import base64
import io
import struct
import warnings
import zlib
import olefile
from PIL import Image
from .record_decoder import binary_records, ParseError

MAX_ASSET = 16 * 1024 * 1024
MAX_PIXELS = 16_000_000
Image.MAX_IMAGE_PIXELS = MAX_PIXELS

def asset_name(name): return name.replace('\\', '/').rsplit('/', 1)[-1].casefold()

def read_images(data):
    if not data.startswith(olefile.MAGIC): return {}, []
    assets, errors = {}, []
    try:
        with olefile.OleFileIO(io.BytesIO(data)) as ole:
            if not ole.exists('Storage'): return assets, errors
            raw = ole.openstream('Storage').read()
        total = 0
        for record in binary_records(raw, 'Storage'):
            if not record.binary: continue
            payload = base64.b64decode(record.properties['BINARY_BASE64'])
            if len(payload) < 6 or payload[0] != 0xd0:
                errors.append('Unsupported embedded storage framing'); continue
            n = payload[1]
            if len(payload) < n+6: raise ParseError('Truncated embedded storage asset')
            name = asset_name(payload[2:2+n].decode('cp1252', errors='replace'))
            count = struct.unpack_from('<I', payload, 2+n)[0]
            if count != len(payload)-6-n: raise ParseError('Invalid embedded compressed size')
            decoder = zlib.decompressobj()
            raster = decoder.decompress(payload[6+n:], MAX_ASSET+1)
            if len(raster) > MAX_ASSET or not decoder.eof or decoder.unused_data:
                raise ParseError('Embedded raster exceeds decoding limit or has invalid compression')
            total += len(raster)
            if total > 32*1024*1024: raise ParseError('Total embedded raster size limit exceeded')
            with warnings.catch_warnings():
                warnings.simplefilter('error', Image.DecompressionBombWarning)
                with Image.open(io.BytesIO(raster)) as source:
                    if source.width*source.height > MAX_PIXELS: raise ParseError('Embedded raster pixel limit exceeded')
                    if source.format not in {'PNG','BMP','JPEG','TIFF','GIF'}:
                        errors.append('Unsupported embedded raster format'); continue
                    if getattr(source, 'n_frames', 1) != 1:
                        errors.append('Multi-frame raster skipped'); continue
                    image = source.convert('RGBA')
                    output = io.BytesIO(); image.save(output, format='PNG')
                    png = output.getvalue()
                    if len(png) > MAX_ASSET: raise ParseError('Converted raster exceeds asset limit')
                    if name in assets:
                        errors.append('Ambiguous embedded filename skipped'); assets[name] = None
                    else: assets[name] = 'data:image/png;base64,' + base64.b64encode(png).decode('ascii')
    except Exception as exc:
        errors.append('Embedded storage not completely decoded: ' + str(exc)[:160])
    return assets, errors