"""Tests for deterministic VIN year resolution.

Covers: all three 30-year cycles (1980-2009, 2010-2039, 2040-2050),
position 7 disambiguation, edge cases, and invalid inputs.
"""

import pytest
from unittest.mock import patch
from datetime import datetime

from app.engines.gemini_engine import resolve_vin_year


class TestSecondCycle:
    """Position 7 alphabetic -> 2010-2039 cycle (NHTSA MY2010+ requirement)."""

    def test_p_with_alpha_pos7_returns_2023(self):
        """P=2023 when position 7 is alphabetic (the bug that triggered this fix)."""
        # VIN: 1G1YE2D32P5602473 -- pos7='D' (alphabetic), pos10='P'
        assert resolve_vin_year("1G1YE2D32P5602473") == 2023

    def test_a_with_alpha_pos7_returns_2010(self):
        """A=2010 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D12A5602473") == 2010

    def test_l_with_alpha_pos7_returns_2020(self):
        """L=2020 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D12L5602473") == 2020

    def test_9_with_alpha_pos7_returns_2039(self):
        """9=2039 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D1295602473") == 2039

    def test_digit_1_with_alpha_pos7_returns_2031(self):
        """1=2031 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D1215602473") == 2031

    def test_s_with_alpha_pos7_returns_2025(self):
        """S=2025 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D12S5602473") == 2025

    def test_t_with_alpha_pos7_returns_2026(self):
        """T=2026 when position 7 is alphabetic."""
        assert resolve_vin_year("1G1YE2D12T5602473") == 2026


class TestFirstCycle:
    """Position 7 numeric -> 1980-2009 cycle."""

    def test_m_with_numeric_pos7_returns_1991(self):
        """M=1991 when position 7 is numeric."""
        assert resolve_vin_year("1G1YE2132M5602473") == 1991

    def test_n_with_numeric_pos7_returns_1992(self):
        """N=1992 when position 7 is numeric."""
        assert resolve_vin_year("1G1YE2132N5602473") == 1992

    def test_p_with_numeric_pos7_returns_1993(self):
        """P=1993 when position 7 is numeric."""
        assert resolve_vin_year("1G1YE2132P5602473") == 1993

    def test_y_with_numeric_pos7_returns_2000(self):
        """Y=2000 when position 7 is numeric."""
        assert resolve_vin_year("1G1YE2132Y5602473") == 2000


class TestThirdCycle:
    """Position 7 numeric + third cycle year (2040-2050) is plausible."""

    @patch("app.engines.gemini_engine.datetime")
    def test_a_with_numeric_pos7_returns_2040_when_plausible(self, mock_dt):
        """A=2040 when position 7 is numeric and year 2040 is plausible."""
        mock_dt.now.return_value = datetime(2039, 1, 1)
        # 2039 + 2 = 2041 >= 2040, so third cycle is plausible
        assert resolve_vin_year("1G1YE2132A5602473") == 2040

    @patch("app.engines.gemini_engine.datetime")
    def test_l_with_numeric_pos7_returns_2050_when_plausible(self, mock_dt):
        """L=2050 when position 7 is numeric and year 2050 is plausible."""
        mock_dt.now.return_value = datetime(2049, 6, 1)
        assert resolve_vin_year("1G1YE2132L5602473") == 2050

    @patch("app.engines.gemini_engine.datetime")
    def test_a_with_numeric_pos7_returns_1980_when_2040_not_plausible(self, mock_dt):
        """A=1980 when third cycle year (2040) exceeds max plausible."""
        mock_dt.now.return_value = datetime(2026, 2, 20)
        # 2026 + 2 = 2028 < 2040, so third cycle not plausible -> first cycle
        assert resolve_vin_year("1G1YE2132A5602473") == 1980

    @patch("app.engines.gemini_engine.datetime")
    def test_k_with_numeric_pos7_returns_2049_when_plausible(self, mock_dt):
        """K=2049 when position 7 is numeric and year is plausible."""
        mock_dt.now.return_value = datetime(2048, 1, 1)
        assert resolve_vin_year("1G1YE2132K5602473") == 2049


class TestEdgeCases:
    """Invalid inputs and boundary conditions."""

    def test_short_vin_returns_none(self):
        """VIN shorter than 17 chars returns None."""
        assert resolve_vin_year("1G1YE2D32") is None

    def test_empty_vin_returns_none(self):
        """Empty string returns None."""
        assert resolve_vin_year("") is None

    def test_invalid_year_code_returns_none(self):
        """Position 10 with invalid code (e.g., 'Z') returns None."""
        # Z is not a valid year code
        assert resolve_vin_year("1G1YE2D32Z5602473") is None

    def test_lowercase_vin_handled(self):
        """Lowercase VIN characters are handled correctly."""
        assert resolve_vin_year("1g1ye2d32p5602473") == 2023

    def test_i_o_q_not_valid_year_codes(self):
        """Letters I, O, Q are not valid VIN year codes."""
        # These are excluded from VINs entirely but test graceful handling
        assert resolve_vin_year("1G1YE2D32I5602473") is None
        assert resolve_vin_year("1G1YE2D32O5602473") is None
        assert resolve_vin_year("1G1YE2D32Q5602473") is None