#!/usr/bin/env python3
"""Every `SPEC §N` a standard's code cites is a section that standard's SPEC.md has.

Code cites normative text to say which rule it implements or enforces. When the
cited section does not exist, the citation reads as authority it does not have:
the mechanism is real, gate-enforcing and tested, and nothing normative stands
behind it. That has happened here repeatedly — `jcp-runtime` cited `SPEC §4.10`
in six places and §4.10 did not exist (fixed by #190); `aac` cited §3.3 for a
rule its SPEC states as "§3 item 3"; `sandbox` cited §6.5 and §12.1 for rules
that live in `spec/receipts.md` and `spec/build.md`. Each was found by reading,
once, long after it was written. This is that reading, done every time.

What it checks: in each directory holding a `SPEC.md`, every `SPEC §N` (one or
more parts: §7, §4.10, §2.4.3) appearing in a `*.rs` file under that directory
resolves to a numbered heading of that same `SPEC.md`. A heading counts when it
begins `#`…, then the number, with or without `§`, as in `## 7.`, `### 6.4 `,
`## §3.` or `### §3.1 `.

What it deliberately does not check:

  - Parent numbers are not synthesised. A cited `§4` needs its own `§4` heading;
    a `§4.10` heading does not satisfy it. A standard that cites a section it
    never wrote should say so, not be excused by a child.
  - A citation is resolved against the SPEC.md of the directory the file is in.
    Every cross-standard citation in the tree today is a self-reference that
    names its own standard for the reader ("JouleClaw SPEC §1.3", inside
    jouleclaw/), so this is right for all of them. If a file ever cites another
    standard's SPEC, resolve it by naming that standard's own file instead —
    do not loosen this check, which would stop it finding anything.
  - Sections of a `spec/*.md` subfile are not sections of `SPEC.md`. Rules that
    live in a subfile should be cited by that file's name, which is what the
    sandbox fixes above do.
  - Markdown-to-markdown references are a different check, and WAI's are already
    covered by `check-wai-section-refs.py`.

Exit status 1, with one line per citation naming a section its SPEC does not
have; 0 otherwise.

    python3 scripts/check-spec-refs.py [repo-root]
"""
import collections
import os
import pathlib
import re
import sys

HEADING = re.compile(r"^#{1,6}[ \t]+§?([0-9]+(?:\.[0-9]+)*)\.?(?=[ \t])", re.M)
CITATION = re.compile(r"SPEC[ \t]+§[ \t]*([0-9]+(?:\.[0-9]+)*)")


def sections(spec: pathlib.Path) -> set:
    return set(HEADING.findall(spec.read_text(errors="replace")))


def main() -> int:
    root = pathlib.Path(sys.argv[1] if len(sys.argv) > 1 else
                        pathlib.Path(__file__).resolve().parent.parent).resolve()
    standards = sorted(d for d in root.iterdir()
                       if d.is_dir() and not d.name.startswith(".") and (d / "SPEC.md").is_file())
    dangling = 0
    cited_total = 0
    for s in standards:
        defined = sections(s / "SPEC.md")
        found = collections.defaultdict(list)
        for f in s.rglob("*.rs"):
            if "target" in f.parts:
                continue
            try:
                text = f.read_text(errors="replace")
            except OSError:
                continue
            if "SPEC" not in text:
                continue
            for i, line in enumerate(text.splitlines(), 1):
                for m in CITATION.finditer(line):
                    found[m.group(1)].append(f"{f.relative_to(root)}:{i}")
        cited_total += sum(len(v) for v in found.values())
        for n, locs in sorted(found.items(), key=lambda kv: [int(x) for x in kv[0].split(".")]):
            if n in defined:
                continue
            for loc in locs:
                print(f"{loc}: cites SPEC §{n}, which {s.name}/SPEC.md does not define")
                dangling += 1
    if dangling:
        print(f"\ncheck-spec-refs: {dangling} dangling citation(s) across {len(standards)} standards.")
        print("Either add the section, or cite where the rule actually lives "
              "(a `spec/*.md` subfile, or a numbered item of a parent section).")
        return 1
    print(f"check-spec-refs: {cited_total} citations across {len(standards)} standards, all resolve.")
    return 0


if __name__ == "__main__":
    sys.exit(main())