#!/usr/bin/env python3
"""
validate-skill-bundle.py — the pre-delivery gate, as assertions.

Checks a staged skill directory (and optionally its packed .skill bundle)
against the criteria the INSTALLER enforces, not against what seems
sensible. Every check compares a measurement to a bound in the same step:
an unasserted metric manufactures confidence that no defect exists.

Usage
-----
  python3 validate-skill-bundle.py <staged-skill-dir> [--bundle file.skill] [--pack out.skill]

  --pack   writes a well-formed bundle (POSIX separators on any platform)
           after the directory checks pass, then validates it.

Exit status 0 = every check passed; 1 = at least one failed (all failures
are listed, not just the first).

Limits are stated as numbers and labelled with where they come from, so
the check is implementable without guessing and can be updated when the
consumer changes them.
"""

import pathlib
import re
import struct
import sys
import zipfile

MAX_DESCRIPTION_CHARS = 1024   # installer's documented cap on the folded description
NAME_RE = re.compile(r"^[a-z0-9]+(-[a-z0-9]+)*$")   # kebab-case
PATH_RE = re.compile(r"`((?:references|scripts|assets)/[^`\s*?]+\.[A-Za-z0-9]+)`")
BUILD_JUNK = {"__pycache__", ".DS_Store"}
# Edit residue: strings that only ever enter a file through a failed
# replacement, an unresolved template slot or an unfinished merge. The gate
# checks bundle FORM; this is the one CONTENT assertion, because a literal
# backreference passed apply, gate and install once.
SLOT_WHY = "unresolved template slot"
RESIDUE_RES = [
    (re.compile(r"(?m)^\\[0-9]\s*$"), "literal regex backreference on its own line"),
    (re.compile(r"(?<![\w`])\\[1-9](?![\w])"), "literal regex backreference in prose"),
    (re.compile(r"(?m)^(<<<<<<<|=======|>>>>>>>)( |$)"), "merge conflict marker"),
    (re.compile(r"\{\{[A-Za-z_][A-Za-z0-9_ .-]*\}\}"), SLOT_WHY),
    (re.compile(r"\b(TODO|FIXME|XXX)\b: ?(fill|replace|write)", re.I), "placeholder note left in"),
]
# A file that IS a template carries its slots as the deliverable, not as
# residue: exempt it from the SLOT rule only — every other residue rule and
# every other gate check still runs on it, so the exemption never becomes the
# hand-zip that also skips the checks nobody questioned.
TEMPLATE_MARKER = "<!-- template: slots intentional -->"


def slots_are_intentional(path, body):
    return "template" in str(path).lower() or body.lstrip().startswith(TEMPLATE_MARKER)
SECOND_FRONTMATTER_RE = re.compile(r"^---\n.*?\n---\n\s*(---\n|name:|description:)", re.S)


def frontmatter(text):
    m = re.match(r"^---\n(.*?)\n---\n", text, re.S)
    return m.group(1) if m else None


def folded_description(fm):
    m = re.search(r"(?ms)^description:\s*>-?\s*\n(.*?)(?=^\S|\Z)", fm)
    if m:
        return " ".join(m.group(1).split())
    m = re.search(r"(?m)^description:\s*(.+)$", fm)
    return m.group(1).strip().strip('"\'') if m else ""


def check_dir(skill_dir, fails):
    # Resolve before comparing names: Path('.').name is '' for a relative
    # argument naming the current directory, which false-fails a correct
    # bundle and blames the frontmatter for an argument problem.
    skill_dir = pathlib.Path(skill_dir).resolve()
    skill_md = skill_dir / "SKILL.md"
    if not skill_md.is_file():
        fails.append("SKILL.md missing"); return
    text = skill_md.read_text(encoding="utf-8")
    fm = frontmatter(text)
    if fm is None:
        fails.append("frontmatter: no leading --- block"); return
    try:
        import yaml  # optional; fall back to regex checks if absent
        data = yaml.safe_load(fm)
        if not isinstance(data, dict):
            fails.append("frontmatter: does not parse to a mapping")
            data = {}
    except ImportError:
        data = {"name": (re.search(r"(?m)^name:\s*(.+)$", fm) or [None, ""])[1].strip(),
                "description": folded_description(fm)}
    except Exception as e:  # yaml error
        fails.append(f"frontmatter: YAML parse error: {e}"); data = {}
    name = str(data.get("name") or "").strip()
    if not name:
        fails.append("frontmatter: `name` missing")
    elif not NAME_RE.match(name):
        fails.append(f"frontmatter: `name` not kebab-case: {name!r}")
    elif name != skill_dir.name:
        fails.append(f"frontmatter: `name` {name!r} != directory {skill_dir.name!r}")
    desc = folded_description(fm)
    if not desc:
        fails.append("frontmatter: `description` missing")
    elif len(desc) > MAX_DESCRIPTION_CHARS:
        fails.append(f"description {len(desc)} chars > cap {MAX_DESCRIPTION_CHARS}")
    elif len(desc) > 900:
        print(f"warn: description {len(desc)} chars (cap {MAX_DESCRIPTION_CHARS}) — near the boundary")
    # Every cited bundled path exists (backticked, real extension — globs in
    # prose are skipped). Ownership is inferred from the shape of the span, so
    # the convention has to make the two cases distinguishable: PATH_RE requires
    # the reserved prefix IMMEDIATELY after the backtick, which means a path
    # qualified with its owning skill's name — `<skill-name>/references/x.md` —
    # does not match and is exempt by construction. That qualified form is how a
    # skill cites a file belonging to a different skill; re-wording a legitimate
    # cross-reference so the backtick no longer starts with the prefix is not.
    # The failure message names the convention, because a false FAIL here is
    # otherwise indistinguishable from a genuinely missing file.
    for rel in sorted(set(PATH_RE.findall(text))):
        if not (skill_dir / rel).is_file():
            fails.append(
                f"cited path missing from staged set: {rel} "
                f"— if this file belongs to another skill, cite it as "
                f"`<skill-name>/{rel}`, which this check exempts")
    # exactly one frontmatter block: a second `---` block (or stray
    # name:/description: lines) directly after the first is a duplicated
    # header that every field check passes by construction
    if SECOND_FRONTMATTER_RE.match(text):
        fails.append("frontmatter: a second frontmatter block follows the first")
    for p in skill_dir.rglob("*"):
        if p.name in BUILD_JUNK or p.suffix == ".pyc" or p.name.startswith(".~lock"):
            fails.append(f"build artefact in staged tree: {p.relative_to(skill_dir)}")
        # content residue in every text file of the bundle, not only SKILL.md
        if p.is_file() and p.suffix.lower() in (".md", ".txt", ".yml", ".yaml", ".json"):
            body = p.read_text(encoding="utf-8", errors="replace")
            # code is where backreferences legitimately live: blank out
            # fenced blocks and inline spans, keeping line numbers intact
            prose = re.sub(r"(?ms)^```.*?^```[ \t]*$", lambda m: re.sub(r"[^\n]", " ", m.group(0)), body)
            prose = re.sub(r"`[^`\n]*`", lambda m: " " * len(m.group(0)), prose)
            rel = p.relative_to(skill_dir)
            exempt_slots = slots_are_intentional(rel, body)
            for rx, why in RESIDUE_RES:
                if why == SLOT_WHY and exempt_slots:
                    continue
                m = rx.search(prose)
                if m:
                    line = body.count("\n", 0, m.start()) + 1
                    fails.append(f"edit residue in {p.relative_to(skill_dir)}:{line}: {why} ({m.group(0).strip()!r})")


def pack(src, out):
    """Always writes POSIX separators, on any platform."""
    src = pathlib.Path(src)
    with zipfile.ZipFile(out, "w", zipfile.ZIP_DEFLATED) as z:
        for f in sorted(p for p in src.rglob("*") if p.is_file()):
            arc = f"{src.name}/{f.relative_to(src).as_posix()}"
            assert "\\" not in arc, arc
            z.write(f, arcname=arc)


def check_bundle(path, fails):
    """Central directory as raw bytes: a convenience reader (zipfile.namelist)
    rewrites 0x5C to '/' and would report a malformed archive as clean."""
    data, i, n_members = pathlib.Path(path).read_bytes(), 0, 0
    while True:
        i = data.find(b"PK\x01\x02", i)
        if i < 0:
            break
        n, m, k = (struct.unpack_from("<H", data, i + o)[0] for o in (28, 30, 32))
        name = data[i + 46:i + 46 + n]
        n_members += 1
        if b"\x5c" in name:
            fails.append(f"bundle: backslash in member path {name!r} (installer rejects it)")
        i += 46 + n + m + k
    if n_members == 0:
        fails.append("bundle: no members found")


def main(argv):
    if len(argv) < 2:
        print(__doc__); return 2
    skill_dir = argv[1]
    bundle = pack_to = None
    if "--bundle" in argv:
        bundle = argv[argv.index("--bundle") + 1]
    if "--pack" in argv:
        pack_to = argv[argv.index("--pack") + 1]
    fails = []
    check_dir(skill_dir, fails)
    if pack_to and not fails:
        pack(skill_dir, pack_to); bundle = pack_to
        print(f"packed {pack_to}")
    if bundle:
        check_bundle(bundle, fails)
    if fails:
        print("FAIL:")
        for f in fails:
            print("  -", f)
        return 1
    print("OK: all gate checks passed")
    return 0


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