Steam inventory price API with source-level values

# Save as audit_snapshot.py; read one saved response, never make an HTTP request.
import json, math, sys, time
from collections import Counter
from decimal import Decimal

def need(condition, message):
    if not condition:
        raise SystemExit("Audit unavailable: " + message)

def finite(value):
    try:
        return type(value) in (int, float) and math.isfinite(value)
    except OverflowError:
        return False

need(len(sys.argv) == 4, "use audit_snapshot.py inventory.json STEAM_ID cs2")
filename, expected_id, game = sys.argv[1:]
need(len(expected_id) == 17 and expected_id.isascii() and expected_id.isdigit(), "expected SteamID64")
with open(filename, "rb") as saved:
    raw = saved.read(16 * 1024 * 1024 + 1)
need(len(raw) <= 16 * 1024 * 1024, "saved response exceeds this example's 16 MiB limit")
try:
    data = json.loads(raw)
except (ValueError, UnicodeError):
    raise SystemExit("Audit unavailable: invalid saved JSON") from None
need(isinstance(data, dict), "expected a native inventory object")
need(data.get("steamid") == expected_id and data.get("game") == game, "player or game mismatch")
need(data.get("status") in ("ok", "empty") and data.get("currency") == "USD", "unavailable status or currency")
rows, meta = data.get("items"), data.get("meta")
need(isinstance(rows, list) and isinstance(meta, dict), "missing items or metadata")
need(meta.get("price_source") == "skinport" and meta.get("strict", True) is True, "source or strict mismatch")
age, ttl, now = meta.get("cache_age"), meta.get("cache_ttl"), time.time()
need(finite(age) and finite(ttl) and 0 <= age <= 300 and age < ttl, "inventory age at response exceeds policy")
page = data.get("pagination")
need(page is None or isinstance(page, dict) and page.get("has_more") is False
     and page.get("offset") == 0 and page.get("next_cursor") is None, "partial page")
quantity = eligible = compared = 0
floor = median = Decimal("0")
excluded = Counter()
for row in rows:
    need(isinstance(row, dict) and row.get("game") == game, "item game or shape mismatch")
    count, tradable, marketable = row.get("count"), row.get("tradable"), row.get("marketable")
    need(type(count) is int and count > 0, "invalid owned count")
    need(all(type(flag) in (bool, int) and flag in (0, 1) for flag in (tradable, marketable)), "invalid eligibility flags")
    quantity += count
    if not (tradable and marketable):
        continue
    eligible += count
    sources = row.get("source_statistics", {})
    need(isinstance(sources, dict), "invalid source statistics")
    metric = sources.get("skinport", {})
    need(isinstance(metric, dict), "invalid Skinport statistics")
    low, mid, stamp = metric.get("min"), metric.get("median"), metric.get("updated_at")
    reason = ("missing_pair" if low is None or mid is None else
              "invalid_or_zero_pair" if not all(finite(v) and 0 < v < 100000 for v in (low, mid)) else
              "unsupported_basis_or_currency" if metric.get("basis") != "active_listing_statistics" or metric.get("currency") != "USD" else
              "stale_or_unknown_price_age" if not finite(stamp) or not 0 < stamp <= now or now - stamp > 21600 else None)
    if reason:
        excluded[reason] += count
        continue
    compared += count
    floor += Decimal(str(low)) * count
    median += Decimal(str(mid)) * count
need(type(data.get("items_total")) is int and data["items_total"] == quantity, "truncated or inconsistent item counts")
need(data["status"] != "empty" or quantity == 0, "empty status has items")
print(json.dumps({
    "scope": "same_response_common_priced_subset", "status": data["status"],
    "comparison": "available_subset" if compared else "no_comparable_prices",
    "inventory_quantity": quantity, "eligible_quantity": eligible, "compared_quantity": compared,
    "excluded_ineligible_quantity": quantity - eligible, "excluded_eligible_quantity": dict(excluded),
    "unpriced_for_comparison_quantity": excluded["missing_pair"] + excluded["invalid_or_zero_pair"],
    "common_floor_subtotal_usd": format(floor, ".2f") if compared else None,
    "common_listing_median_subtotal_usd": format(median, ".2f") if compared else None,
    "inventory_age_at_response_seconds": age, "price_age_limit_seconds": 21600,
}, sort_keys=True))