#!/usr/bin/env python3
"""One exercise sheet per student, with their prefix filled in, in one PDF.

    python3 build-class.py 100            # students 1..100 -> class.pdf
    python3 build-class.py 100 -o out.pdf
    python3 build-class.py 5 12 -o few.pdf   # students 5..12

Student n gets 2a0d:d741:<n in hex>::/48; the lab /40 allows 1..255. Each
sheet is compiled separately and must come out to exactly two pages, so
the result prints double-sided with one student per leaf. Needs pdflatex
and pdfunite (poppler).
"""
import argparse
import os
import shutil
import subprocess
import sys
import tempfile

HERE = os.path.dirname(os.path.abspath(__file__))


def page_count(pdf):
    out = subprocess.run(["pdfinfo", pdf], capture_output=True, text=True, check=True).stdout
    return int(next(line.split()[-1] for line in out.splitlines() if line.startswith("Pages:")))


def main():
    ap = argparse.ArgumentParser(description=__doc__.split("\n")[0])
    ap.add_argument("first", type=int, help="first student number, or the count if it is the only number")
    ap.add_argument("last", type=int, nargs="?")
    ap.add_argument("-o", "--output", default=os.path.join(HERE, "class.pdf"))
    args = ap.parse_args()
    first, last = (1, args.first) if args.last is None else (args.first, args.last)
    if not 1 <= first <= last <= 255:
        sys.exit("student numbers must be within 1..255: the lab /40 has 255 usable /48s")

    with tempfile.TemporaryDirectory() as tmp:
        for name in os.listdir(HERE):
            if name.endswith((".tex", ".cls", ".sty", ".bst", ".bib")):
                shutil.copy(os.path.join(HERE, name), tmp)
        parts = []
        for n in range(first, last + 1):
            job = f"student-{n:03d}"
            tex = f"\\def\\studentnum{{{n}}}\\def\\studenthex{{{n:x}}}\\input{{handout.tex}}"
            for _ in range(2):  # twice, for the figure and table references
                r = subprocess.run(["pdflatex", "-interaction=nonstopmode", "-halt-on-error", "-jobname", job, tex],
                                   cwd=tmp, capture_output=True, text=True)
                if r.returncode != 0:
                    sys.exit(f"student {n}: pdflatex failed:\n{r.stdout[-2000:]}")
            pdf = os.path.join(tmp, job + ".pdf")
            pages = page_count(pdf)
            if pages != 2:
                sys.exit(f"student {n}: sheet is {pages} pages, not 2; double-sided printing would misalign")
            parts.append(pdf)
            print(f"\rstudent {n}: 2a0d:d741:{n:x}::/48", end="", flush=True)
        print()
        subprocess.run(["pdfunite", *parts, args.output], check=True)
    print(f"wrote {args.output}: students {first}..{last}, {page_count(args.output)} pages")


if __name__ == "__main__":
    main()