"""Answer provenance and reproducible annotation spacing (200 dpi pixels)."""
from hashlib import sha256
from pathlib import Path
import shutil

import pymupdf

from copienator import configuration
from copienator.json_io import atomic_write_json, read_json


def fingerprint(path):
    return sha256(Path(path).read_bytes()).hexdigest()


def metadata_path(pdf):
    return Path(pdf).with_suffix('.layout.json')


def answer_parts(pdf):
    """Ignore stale sidecars after a PDF is replaced or manually edited."""
    if pdf is None or not Path(pdf).is_file():
        return []
    try:
        data = read_json(metadata_path(pdf), default={})
        if data.get('sha256') == fingerprint(pdf):
            parts = data.get('parts', [])
            if isinstance(parts, list) and all(isinstance(part, dict) for part in parts):
                return parts
    except (OSError, ValueError, TypeError, AttributeError):
        pass
    return []


def save_parts(pdf, parts):
    atomic_write_json(metadata_path(pdf), {
        'version': 1, 'sha256': fingerprint(pdf), 'parts': parts,
    })


def page_parts(pdf):
    parts = answer_parts(pdf)
    if not Path(pdf).is_file():
        return []
    with pymupdf.open(pdf) as document:
        if len(parts) == len(document):
            return parts
        return [{'margin_status': 'unknown'} for _ in document]


def copy_answer_pdf(source, destination):
    parts = answer_parts(source)
    shutil.copy(source, destination)
    save_parts(destination, parts)


def move_answer_pdf(source, destination):
    parts = answer_parts(source)
    shutil.move(str(source), str(destination))
    save_parts(destination, parts)
    metadata_path(source).unlink(missing_ok=True)


def added_margin(margin_mm):
    """Interpolate the configured (millimetres, pixels) points, clamping at ends."""
    if margin_mm is None:
        return configuration.ANNOTATION_MARGIN_LEFT
    points = configuration.ANNOTATION_MARGIN_POINTS
    if (not points or any(x < 0 or type(y) is not int or y < 0 for x, y in points)
            or any(a[0] >= b[0] for a, b in zip(points, points[1:]))):
        raise ValueError('Annotation margin points must have increasing mm and non-negative integer pixels')
    if margin_mm <= points[0][0]:
        return points[0][1]
    for (x0, y0), (x1, y1) in zip(points, points[1:]):
        if margin_mm <= x1:
            return round(y0 + (y1 - y0) * (margin_mm - x0) / (x1 - x0))
    return points[-1][1]


def layout_for(pdf):
    margins = [added_margin(part.get('margin_mm')) for part in answer_parts(pdf)]
    return {'version': 2, 'margin_left': max(margins, default=added_margin(None)),
            'page_margins': margins, 'narrow_left_pad_limit': 0}


def legacy_layout():
    # Old annotation scans were produced with these literal constants.
    return {'version': 1, 'margin_left': 300, 'narrow_left_pad_limit': 300}