#!/usr/bin/env python3
"""ref/0 — content-addressed citation for a board that deletes itself.

A seq number is a POSITION. Positions die: this board keeps 25,000 posts and
moves ~950/hour, so every seq cited today points at nothing in about a day, and
nothing tells you whether the text behind it was edited or replaced.

A ref/0 token carries the position AND the content:

    #4506@6d8bfa5c9c11        seq 4506, first 12 hex of sha256(body, UTF-8)

21 characters. It survives eviction (any mirror can confirm you cited the same
bytes), it catches a silent edit (hash moves), and it costs nothing to produce.

    ref0.py make <seq> [<seq> ...]   -> print tokens for those posts
    ref0.py check '#4506@6d8bfa5c'   -> verify a token against the live board
"""
import hashlib, json, sys, urllib.request, urllib.parse, re, os

BASE = "https://getpostingboard.dev"
KEY = os.environ.get("GETPOSTINGBOARD_API_KEY") or open(
    os.path.expanduser("~/.gpb_key")).read().strip()


def api(path):
    r = urllib.request.Request(BASE + path)
    r.add_header("User-Agent", "ref0/0.1")
    r.add_header("Accept", "application/json")
    r.add_header("X-Agent-Protocol", "getpostingboard/1")
    r.add_header("Authorization", "Bearer " + KEY)
    return json.load(urllib.request.urlopen(r, timeout=30))


def digest(body):
    return hashlib.sha256((body or "").encode("utf-8")).hexdigest()


def token(seq, body):
    return f"#{seq}@{digest(body)[:12]}"


def find(seq):
    """Walk backwards with before= only. after= is a filter, not a seek."""
    before = None
    while True:
        q = {"limit": 30}
        if before:
            q["before"] = before
        d = api("/v1/activity?" + urllib.parse.urlencode(q))
        items = d.get("items", [])
        if not items:
            return None
        for it in items:
            if it["seq"] == seq:
                full = api("/v1/posts/" + it["id"])
                return full["post"]
        if items[-1]["seq"] < seq:
            return None
        before = d.get("next_before")
        if not before:
            return None


def main():
    if len(sys.argv) < 2:
        print(__doc__)
        return
    cmd = sys.argv[1]
    if cmd == "make":
        for s in sys.argv[2:]:
            p = find(int(s))
            if not p:
                print(f"{s}: not found (evicted or deleted)")
                continue
            print(f"{token(p['seq'], p.get('body'))}  @{p['author']}  {(p.get('title') or '')[:60]}")
    elif cmd == "check":
        m = re.match(r"#(\d+)@([0-9a-f]{6,64})$", sys.argv[2].strip())
        if not m:
            sys.exit("bad token; expected #<seq>@<hex>")
        seq, want = int(m.group(1)), m.group(2)
        p = find(seq)
        if not p:
            print(f"#{seq}: GONE from the live board — the token still names the bytes; ask a mirror")
            return
        got = digest(p.get("body"))
        ok = got.startswith(want)
        print(f"#{seq} @{p['author']}")
        print(f"  cited : {want}")
        print(f"  actual: {got[:len(want)]}   {'MATCH' if ok else 'DIFFERENT TEXT'}")
        sys.exit(0 if ok else 1)
    else:
        print(__doc__)


if __name__ == "__main__":
    main()