"""
Tests for the SLA engine (app/utils/sla.py).

sla_status/deadline/hours_remaining read only .status, .severity, .reported_at,
so a lightweight stand-in object is enough — no DB or app context needed. Time
is controlled by positioning reported_at relative to now_eastern().
"""
from datetime import timedelta
from types import SimpleNamespace

import pytest

from app.utils.sla import (
    sla_status, sla_deadline, sla_hours_remaining, SLA_HOURS, AT_RISK_THRESHOLD,
)
from app.utils.time_utils import now_eastern


def issue(severity='high', status='open', hours_ago=0):
    return SimpleNamespace(
        severity=severity,
        status=status,
        reported_at=now_eastern() - timedelta(hours=hours_ago),
    )


def test_resolved_issue_has_no_sla():
    assert sla_status(issue(status='resolved', hours_ago=999)) is None


def test_unknown_severity_returns_none():
    assert sla_status(issue(severity='nonsense', hours_ago=1)) is None


def test_fresh_issue_is_ok():
    # high = 24h window, at-risk at 18h; 1h in is comfortably OK
    assert sla_status(issue(severity='high', hours_ago=1)) == 'ok'


def test_issue_past_at_risk_threshold():
    # high at-risk at 18h; 20h in is at_risk but not yet breached (24h)
    assert sla_status(issue(severity='high', hours_ago=20)) == 'at_risk'


def test_issue_past_deadline_is_breached():
    assert sla_status(issue(severity='high', hours_ago=25)) == 'breached'


@pytest.mark.parametrize('severity', list(SLA_HOURS.keys()))
def test_at_risk_boundary_for_each_severity(severity):
    window = SLA_HOURS[severity]
    # Just past the at-risk fraction, still before the deadline.
    at_risk_hours = window * AT_RISK_THRESHOLD
    assert sla_status(issue(severity=severity, hours_ago=at_risk_hours + 0.1)) == 'at_risk'
    # Just before the at-risk fraction is still OK.
    assert sla_status(issue(severity=severity, hours_ago=at_risk_hours - 0.5)) == 'ok'


def test_deadline_is_reported_at_plus_window():
    iss = issue(severity='medium', hours_ago=0)
    expected = iss.reported_at + timedelta(hours=SLA_HOURS['medium'])
    assert sla_deadline(iss) == expected


def test_hours_remaining_positive_when_within_window():
    remaining = sla_hours_remaining(issue(severity='critical', hours_ago=1))
    # critical window is 4h; ~3h should remain
    assert 2.5 < remaining < 3.5


def test_hours_remaining_negative_when_overdue():
    remaining = sla_hours_remaining(issue(severity='critical', hours_ago=6))
    assert remaining < 0


def test_hours_remaining_none_for_resolved():
    assert sla_hours_remaining(issue(status='resolved', hours_ago=1)) is None