scanproc/pdfutil.py

#!/usr/bin/env python3

"""
    Copyright © 2022 Mia Herkt
    Licensed under the EUPL, Version 1.2 or - as soon as approved
    by the European Commission - subsequent versions of the EUPL
    (the "License");
    You may not use this work except in compliance with the License.
    You may obtain a copy of the license at:

        https://joinup.ec.europa.eu/software/page/eupl

    Unless required by applicable law or agreed to in writing,
    software distributed under the License is distributed on an
    "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
    either express or implied.
    See the License for the specific language governing permissions
    and limitations under the License.
"""

import struct
import fitz
import cv2 as cv

class Dict:
    def __init__(self, values={}):
        self.d = {}
        self.d.update(values)

    def __bytes__(self):
        s = [b"<< "]

        for (x, y) in self.d.items():
            s.append(b"/" + x + b" " + y + b"\n")

        s.append(b">>\n")
        return b"".join(s)

class Obj:
    def __init__(self, d={}, stream=None):
        if stream is not None:
            d[b"Length"] = str(len(stream)).encode()

        self.d = Dict(d)
        self.stream = stream
        self.idx = 0

    def __bytes__(self):
        s = [bytes(self.d)]

        if self.stream is not None:
            s.append(b"stream\n")
            s.append(self.stream)
            s.append(b"\nendstream\n")
        s.append(b"endobj\n")

        return b"".join(s)

class Doc:
    def __init__(self):
        self.objs = []
        self.pages = []

    def add_object(self, o):
        o.idx = len(self.objs) + 1
        self.objs.append(o)
        return o

    def add_page(self, o):
        self.pages.append(o)
        return self.add_object(o)

    def __bytes__(self):
        a = []
        j = [0]
        offsets = []

        def add(x):
            a.append(x)
            j[0] += len(x) + 1

        add(b'%PDF-1.4')
        for o in self.objs:
            offsets.append(j[0])
            add(f"{o.idx} 0 obj".encode())
            add(bytes(o))

        xrefstart = j[0]
        a.append(b'xref')
        a.append(f'0 {len(offsets) + 1}'.encode())
        a.append(b'0000000000 65535 f ')

        for o in offsets:
            a.append(f"{o:010d} 00000 n ".encode())

        a.append(b'')
        a.append(b'trailer')
        a.append(f'<< /Size {len(offsets) + 1}\n/Root 1 0 R >>'.encode())
        a.append(b'startxref')
        a.append(str(xrefstart).encode())
        a.append(b'%EOF')

        return b'\n'.join(a)

def ref(x):
    return f"{x} 0 R".encode()

def mkpdf(symtab, pageblobs, colorimgs, texts, dpi):
    doc = Doc()
    doc.add_object(Obj({
        b'Type' : b'/Catalog',
        b'Outlines' : ref(2),
        b'Pages' : ref(3)
        }))
    doc.add_object(Obj({
        b'Type' : b'/Outlines',
        b'Count': b'0'
        }))
    pages = Obj({b'Type' : b'/Pages'})
    doc.add_object(pages)
    with open(symtab, "rb") as stab:
        symd = doc.add_object(Obj({}, stab.read()))
    page_objs = []

    for f in pageblobs:
        with open(f, "rb") as pf:
            blob = pf.read()
        (w, h, xres, yres) = struct.unpack(">IIII", blob[11:27])

        if xres == 0:
            xres = dpi
        if yres == 0:
            yres = dpi

        xobj = Obj({
            b'Type': b'/XObject',
            b'Subtype': b'/Image',
            b'Width': str(w).encode(),
            b'Height': str(h).encode(),
            b'ColorSpace': b'/DeviceGray',
            b'BitsPerComponent': b'1',
            b'Filter': b'/JBIG2Decode',
            b'DecodeParms': f' << /JBIG2Globals {symd.idx} 0 R >>'.encode()
            }, blob)
        xobj = doc.add_object(xobj)

        fw = float(w * 72) / xres
        fh = float(h * 72) / yres

        contents = Obj({}, f'q {fw:.1f} 0 0 {fh:.1f} 0 0 cm /Im1 Do Q'.encode())
        contents = doc.add_object(contents)

        resources = Obj({
            b'ProcSet': b'[/PDF /ImageB]',
            b'XObject': f'<< /Im1 {xobj.idx} 0 R >>'.encode()
            })
        resources = doc.add_object(resources)

        page = Obj({
            b'Type': b'/Page',
            b'Parent': b'3 0 R',
            b'MediaBox': f'[ 0 0 {fw:.1f} {fh:.1f} ]'.encode(),
            b'Contents': ref(contents.idx),
            b'Resources': ref(resources.idx)
            })
        doc.add_object(page)

        page_objs.append(page)

        pages.d.d[b'Count'] = str(len(page_objs)).encode()
        pages.d.d[b'Kids'] = b'[' + b' '.join([ref(x.idx) for x in page_objs]) + b']'

    pdf = fitz.open(stream=bytes(doc))
    for p, imgs in enumerate(colorimgs):
        for rect, img, mask in imgs:
            with open(mask, "rb") as mf:
                m = mf.read()
            pdf[p].insert_image(fitz.Rect(*[(c*72.0)/dpi for c in rect]), filename=img, mask=m)

    for p, txt in enumerate(texts):
        for box in txt:
            if len(box[1]):
                bbox = box[0]
                r = fitz.Rect(
                    min((bbox[0][0]*72.0)/dpi, (bbox[3][0]*72.0)/dpi),
                    min((bbox[0][1]*72.0)/dpi, (bbox[1][1]*72.0)/dpi),
                    max((bbox[1][0]*72.0)/dpi, (bbox[2][0]*72.0)/dpi),
                    max((bbox[2][1]*72.0)/dpi, (bbox[3][1]*72.0)/dpi)
                )
                fs = round(r.height)
                w = fitz.get_text_length(box[1], fontsize=fs)
                pivot = fitz.Point(r.x0, r.y0)
                matrix = fitz.Matrix(r.width/w, 1.0)
                pdf[p].insert_text(fitz.Point(r.x0, r.y0+r.height*0.8),
                                   box[1], fontsize=fs,
                                   morph=(pivot, matrix),
                                   render_mode=3)
    return pdf.tobytes(garbage=4, clean=True, deflate=True)