"""Provisioning — turn a freshly-logged-in Google user into a billed account.

One entry point: provision(user_id, email, username).
  1. derive a unique deposit address from the wallet xpub
  2. mint a personal API key (dr_u_<hex>)
  3. create the per-user gist (5 files, seeded with the free grant)
  4. register the user in the master registry
  5. return the full record (caller caches the key->user map)

Idempotent: if the user is already registered, returns the existing record.
"""
from __future__ import annotations

import hashlib
from typing import Optional

from .. import wallet
from . import registry, user_store

FREE_CREDITS = 500  # one-time grant on signup (decision 4B)


def _build_key(deposit_address: str) -> tuple[str, str, str]:
    """Build a user's API key FROM their deposit address.

    The key is deterministic: it's `sk-` + the checksummed ETH deposit address.
    Because it's derived from the (always-visible) deposit address, it can be
    recovered at any time — there's no "lost key" problem. Returns
    (full_key, display_prefix, sha256_hex_hash).
    """
    full = f"sk-{deposit_address}"  # e.g. sk-0xAbC1… (the user's credential)
    a = deposit_address.lower()  # lowercase for a tidy display
    prefix = f"sk-{a[:6]}…{a[-4:]}"  # short display: sk-0xabc1…wxyz
    digest = hashlib.sha256(full.encode()).hexdigest()  # stored for record-keeping
    return full, prefix, digest


async def provision(user_id: str, email: str, username: str) -> Optional[dict]:
    """Provision a new user OR return their existing record. Returns None if disabled."""
    # idempotency: already registered?
    existing = registry.find_user(user_id)
    if existing:
        return existing
    # need the wallet + registry both configured
    if not wallet.is_configured():
        return None
    _, reg = await registry.get_or_create()
    index = reg["wallet"]["next_index"]  # this user's permanent derivation slot
    deposit = wallet.derive_deposit_address(index)
    full_key, prefix, digest = _build_key(deposit)  # key derived from the address
    identity = {
        "user_id": user_id,
        "email": email,
        "username": username,
        "deposit_address": deposit,
        "derivation_index": index,
        "api_keys": [
            {"key_id": "k1", "prefix": prefix, "hash": digest, "created": registry._now(), "active": True}
        ],
    }
    gist_id = await user_store.provision_gist(identity, free_credits=FREE_CREDITS)
    record = {
        "user_id": user_id,
        "email": email,
        "username": username,
        "gist_id": gist_id,
        "deposit_address": deposit,
        "derivation_index": index,
        "status": "active",
        "created_at": registry._now(),
        "api_key_prefix": prefix,  # convenience for display (full key returned once to the caller)
        "api_key_hash": digest,  # for key->user resolution at the gate
        "_plaintext_key": full_key,  # ONLY returned once, then stripped by the caller
    }
    await registry.register_user(record)
    return record