"""Apollo GraphOS API client with retry + exponential backoff."""

import json
import sys
import time
import urllib.request

from src.config import GRAPHOS_API, USAGE_QUERY


def fetch_usage_for_type(
    api_key: str,
    graph_id: str,
    since_str: str,
    parent_type: str,
    retries: int = 3,
) -> dict[str, dict[str, int]] | None:
    """Fetch field usage for all fields of a parentType.

    Returns:
        {fieldName: {"executions": int, "operations": int}} or None on failure.
    """
    query = USAGE_QUERY % (graph_id, since_str, parent_type)
    payload = json.dumps({'query': query}).encode()

    req = urllib.request.Request(
        GRAPHOS_API,
        data=payload,
        headers={
            'Content-Type': 'application/json',
            'x-api-key': api_key,
        },
    )

    last_err = None
    data = None
    for attempt in range(retries):
        try:
            with urllib.request.urlopen(req, timeout=30) as resp:
                data = json.loads(resp.read())
            break
        except (urllib.error.URLError, urllib.error.HTTPError, TimeoutError) as e:
            last_err = e
            if attempt < retries - 1:
                wait = 2**attempt
                print(f'RETRY ({attempt + 1}/{retries}, waiting {wait}s: {e})')
                sys.stdout.flush()
                time.sleep(wait)
                sys.stdout.write(f'  [retry] {parent_type} ... ')
                sys.stdout.flush()
            else:
                print(f'FAILED after {retries} attempts: {last_err}')
                return None

    if data is None:
        return None

    if 'errors' in data:
        msgs = [e.get('message', str(e)) for e in data['errors']]
        print(f'  GraphQL errors for {parent_type}: {"; ".join(msgs)}', file=sys.stderr)
        return None

    records = data['data']['service']['statsWindow']['fieldUsage']
    usage: dict[str, dict[str, int]] = {}
    for rec in records:
        fname = rec['groupBy']['fieldName']
        execs = rec['metrics']['estimatedExecutionCount']
        ops = rec['metrics']['referencingOperationCount']
        if fname in usage:
            usage[fname]['executions'] += execs
            usage[fname]['operations'] += ops
        else:
            usage[fname] = {'executions': execs, 'operations': ops}
    return usage