"""Safe conversion between MCP Base64 inputs and Pillow images."""

from __future__ import annotations

import base64
import binascii
import io
import json
from typing import Any

from PIL import Image, PngImagePlugin, UnidentifiedImageError

from .errors import InvalidImageError

MAX_ENCODED_LENGTH = 36_000_000
MAX_PIXELS = 40_000_000
SUPPORTED_FORMATS = frozenset({"PNG", "JPEG"})


def decode_image(value: str, *, mask: bool = False) -> Image.Image:
    """Decode a bounded PNG/JPEG Base64 value or data URI and fully validate it."""
    if not isinstance(value, str) or len(value) > MAX_ENCODED_LENGTH:
        raise InvalidImageError("image Base64 input is missing or too large")
    payload = value.strip()
    if payload.startswith("data:"):
        try:
            header, payload = payload.split(",", 1)
        except ValueError as exc:
            raise InvalidImageError("malformed image data URI") from exc
        if header.lower() not in {
            "data:image/png;base64",
            "data:image/jpeg;base64",
            "data:image/jpg;base64",
        }:
            raise InvalidImageError("data URI must contain a Base64 PNG or JPEG")
    try:
        raw = base64.b64decode(payload, validate=True)
    except (binascii.Error, ValueError) as exc:
        raise InvalidImageError("image is not valid Base64") from exc
    try:
        with Image.open(io.BytesIO(raw)) as opened:
            if opened.format not in SUPPORTED_FORMATS:
                raise InvalidImageError("only PNG and JPEG images are supported")
            if opened.width * opened.height > MAX_PIXELS:
                raise InvalidImageError("image pixel count exceeds the safety limit")
            opened.load()
            return opened.convert("L" if mask else "RGB")
    except InvalidImageError:
        raise
    except (OSError, UnidentifiedImageError, Image.DecompressionBombError) as exc:
        raise InvalidImageError("input is not a valid PNG or JPEG image") from exc


def encode_png(image: Image.Image, metadata: dict[str, Any]) -> bytes:
    """Serialize one RGB image as PNG with stable textual generation metadata."""
    info = PngImagePlugin.PngInfo()
    for key, value in metadata.items():
        text = json.dumps(value) if isinstance(value, (dict, list)) else str(value)
        info.add_text(str(key), text)
    output = io.BytesIO()
    image.convert("RGB").save(output, format="PNG", pnginfo=info)
    return output.getvalue()