import asyncio
from datetime import datetime, timezone
import json
import math
import struct

import pytest

from app.services.hydraulic_playback import build_geometry, read_frames, result_factors


def fixture_geometry(longitude=121.5):
    return build_geometry([
        {"id": "J1", "longitude": longitude, "latitude": 30.8},
        {"id": "J2", "longitude": longitude + .001, "latitude": 30.8},
    ], [{"id": "P1", "start_node_id": "J1", "diameter": 600,
         "geometry": {"type": "LineString", "coordinates": [[longitude + .001, 30.8], [longitude, 30.8]]}}],
        {"flow": "LPS", "pressure": "METERS"})


def unpack(content):
    length = struct.unpack_from("<I", content)[0]
    header = json.loads(content[4:4 + length])
    count = (len(content) - 4 - length) // 4
    return header, struct.unpack_from(f"<{count}f", content, 4 + length)


def test_geometry_version_tracks_absolute_location_and_orients_geometry_with_start_node():
    geometry = fixture_geometry()
    header, values = unpack(geometry.content)
    assert header["nodeIds"] == ["J1", "J2"]
    assert header["pipeIds"] == ["P1"]
    assert header["segmentCount"] == 1
    assert values[4:6] == values[:2]  # reversed GIS geometry is oriented J1 -> J2
    assert values[6:8] == values[2:4]
    assert fixture_geometry().version == geometry.version
    assert fixture_geometry(121.6).version != geometry.version


def test_unit_factors_preserve_signed_flow_and_reject_unknown_units():
    assert result_factors({"flow": "LPS", "pressure": "METERS"}) == (3.6, 1, 1)
    flow, pressure, velocity = result_factors({"flow": "GPM", "pressure": "PSI"})
    assert flow == pytest.approx(.003785411784 * 60)
    assert pressure == pytest.approx(.7032496149)
    assert velocity == .3048
    with pytest.raises(ValueError):
        result_factors({"flow": "unknown", "pressure": "METERS"})


class Cursor:
    def __init__(self, time):
        self.time = time
        self.rows = []
    async def __aenter__(self):
        return self
    async def __aexit__(self, *_):
        pass
    async def execute(self, query, params):
        assert len(params[0]) == 2
        if "node_results" in query:
            self.rows = [{"time": self.time, "node_id": "J1", "pressure": 25},
                         {"time": self.time, "node_id": "J2", "pressure": None}]
        else:
            self.rows = [{"time": self.time, "link_id": "P1", "flow": -10, "velocity": .7}]
    def __aiter__(self):
        self.iterator = iter(self.rows)
        return self
    async def __anext__(self):
        try:
            return next(self.iterator)
        except StopIteration:
            raise StopAsyncIteration


class Connection:
    def __init__(self, time):
        self.time = time
    def cursor(self):
        return Cursor(self.time)


def test_frames_pack_exact_sample_times_signed_values_and_missing_values_without_extrapolation():
    time = datetime(2026, 7, 15, 16, tzinfo=timezone.utc)
    content = asyncio.run(read_frames(Connection(time), fixture_geometry(), time, 2, 900))
    header, values = unpack(content)
    assert header["times"] == [1784131200000, 1784132100000]
    assert header["available"] == [True, False]
    assert header["validCounts"]["pressure"] == [1, 0]
    assert values[0] == 25
    assert math.isnan(values[1])
    assert values[2] == -36
    assert values[3] == pytest.approx(.7)
    assert all(math.isnan(value) for value in values[4:])