from __future__ import annotations

import hashlib
import io
import pathlib
import re

import PIL.Image
import PIL.ImageChops

import generator.engraving.types
import generator.theme

ENGINE_NAME = 'Vamp Python'
PAGE_WIDTH = 976
PAGE_HEIGHT = 484

def check_content(data: bytes, name: str) -> None:
  with PIL.Image.open(io.BytesIO(data)) as image:
    if image.format != 'PNG' or image.size != (PAGE_WIDTH, PAGE_HEIGHT):
      raise generator.engraving.types.EngravingError(f'{name}: expected a {PAGE_WIDTH}x{PAGE_HEIGHT} PNG page')
    image.load()
    background = PIL.Image.new('RGB', image.size, generator.theme.rgb('background'))
    composited = background.convert('RGBA')
    composited.alpha_composite(image.convert('RGBA'))
    ink = PIL.ImageChops.difference(composited.convert('RGB'), background).convert('L').point(lambda x: 255 if x > 32 else 0)
    bounds = ink.getbbox()
    if not bounds:
      raise generator.engraving.types.EngravingError(f'{name}: engraver produced a blank page')
    if bounds[0] < 4 or bounds[1] < 4 or bounds[2] > PAGE_WIDTH - 4 or bounds[3] > PAGE_HEIGHT - 4:
      raise generator.engraving.types.EngravingError(f'{name}: notation reaches the page edge; refusing potentially clipped output')

def check_page(path: pathlib.Path, validated_pages: set[str] | None = None, *, expected_sha256: str | None = None) -> str:
  # Trust content, never a filename or a caller-supplied checksum alone.
  if path.is_symlink() or not path.is_file():
    raise generator.engraving.types.EngravingError(f'{path.name}: expected a regular PNG file')
  data = path.read_bytes()
  digest = hashlib.sha256(data).hexdigest()
  if expected_sha256 is not None and (not isinstance(expected_sha256, str) or not re.fullmatch('[0-9a-f]{64}', expected_sha256) or digest != expected_sha256):
    raise generator.engraving.types.EngravingError(f'{path.name}: score page checksum mismatch')
  if validated_pages is None or digest not in validated_pages:
    check_content(data, path.name)
    if validated_pages is not None:
      validated_pages.add(digest)
  return digest