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

These are pure-logic tests — they build a lightweight fake issue object with the
three attributes `sla_status`/`sla_deadline`/`sla_hours_remaining` read
(`severity`, `status`, `reported_at`) and assert the boundary behaviour of the
SLA state machine. No database, no app context required.
"""

from datetime import timedelta

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


class FakeIssue:
    """Minimal stand-in for the Issue ORM object used by the SLA helpers."""
    def __init__(self, severity, status='open', hours_ago=0.0):
        self.severity = severity
        self.status = status
        self.reported_at = now_eastern() - timedelta(hours=hours_ago)


# ── sla_deadline ─────────────────────────────────────────────────────────────

def test_deadline_matches_window():
    issue = FakeIssue('high', hours_ago=0)
    expected = issue.reported_at + timedelta(hours=SLA_HOURS['high'])
    assert sla_deadline(issue) == expected


def test_deadline_none_for_unknown_severity():
    assert sla_deadline(FakeIssue('bogus')) is None


# ── sla_status boundaries ────────────────────────────────────────────────────

def test_status_ok_when_fresh():
    # critical window is 4h; reported 1h ago → well inside → ok
    assert sla_status(FakeIssue('critical', hours_ago=1)) == 'ok'


def test_status_at_risk_past_threshold():
    # critical window 4h, at-risk at 3h (0.75 * 4). Reported 3.5h ago → at_risk.
    assert AT_RISK_THRESHOLD == 0.75
    assert sla_status(FakeIssue('critical', hours_ago=3.5)) == 'at_risk'


def test_status_breached_past_window():
    # critical window 4h; reported 5h ago → breached
    assert sla_status(FakeIssue('critical', hours_ago=5)) == 'breached'


def test_status_none_when_resolved():
    # A resolved issue has no SLA regardless of how old it is.
    assert sla_status(FakeIssue('critical', status='resolved', hours_ago=99)) is None


def test_status_none_for_unknown_severity():
    assert sla_status(FakeIssue('bogus', hours_ago=1)) is None


def test_low_severity_window_is_120h_not_168h():
    """Regression guard: CLAUDE.md once documented low=168h; code says 120h."""
    assert SLA_HOURS['low'] == 120


# ── sla_hours_remaining ──────────────────────────────────────────────────────

def test_hours_remaining_positive_when_fresh():
    issue = FakeIssue('medium', hours_ago=0)  # window 72h
    remaining = sla_hours_remaining(issue)
    assert 71.0 <= remaining <= 72.0


def test_hours_remaining_negative_when_breached():
    issue = FakeIssue('critical', hours_ago=6)  # window 4h → ~-2h
    assert sla_hours_remaining(issue) < 0


def test_hours_remaining_none_when_resolved():
    assert sla_hours_remaining(FakeIssue('high', status='resolved')) is None