"""Burst sizing and row-splitting, exercised without any instrument."""
import pytest

from core.scope_burst import (
    frame_means_block, normalize_row, rows_per_burst, split_row_counts,
)

SPF = 8


# ── rows_per_burst ───────────────────────────────────────────────────────────

def test_rows_per_burst_rounds_down():
    # 9.7 rows' worth of capacity is 9 rows: a partial row is unusable.
    assert rows_per_burst(97, 10, SPF, rows_remaining=100) == 9
    assert rows_per_burst(100, 10, SPF, rows_remaining=100) == 10


def test_rows_per_burst_clamped_by_rows_remaining():
    assert rows_per_burst(1000, 10, SPF, rows_remaining=3) == 3


def test_rows_per_burst_clamped_by_memory_budget():
    # Budget holds 4 rows of 10 frames × 8 samples; the scope would hold 100.
    assert rows_per_burst(1000, 10, SPF, rows_remaining=100,
                          memory_budget=4 * 10 * SPF) == 4


def test_rows_per_burst_headroom_reserves_slack_per_row():
    assert rows_per_burst(100, 10, SPF, rows_remaining=100, headroom=0) == 10
    assert rows_per_burst(100, 10, SPF, rows_remaining=100, headroom=2) == 8


def test_rows_per_burst_never_returns_zero():
    """A row too big for any budget still goes, or the scan cannot progress."""
    assert rows_per_burst(5, 10, SPF, rows_remaining=100) == 1
    assert rows_per_burst(1000, 10, SPF, rows_remaining=100,
                          memory_budget=1) == 1


def test_rows_per_burst_rejects_degenerate_geometry():
    with pytest.raises(ValueError):
        rows_per_burst(100, 0, SPF, rows_remaining=1)


# ── split_row_counts ─────────────────────────────────────────────────────────

def test_split_row_counts_differences_the_cumulative_counter():
    assert split_row_counts([4, 8, 12]) == [4, 4, 4]
    assert split_row_counts([4, 7, 12]) == [4, 3, 5]
    assert split_row_counts([]) == []


def test_split_row_counts_rejects_a_counter_that_went_backwards():
    # Only happens if the acquisition restarted mid-burst, which would
    # misattribute every later row.
    with pytest.raises(RuntimeError, match="backwards"):
        split_row_counts([8, 4])


# ── normalize_row ────────────────────────────────────────────────────────────

def test_normalize_row_passes_an_exact_row_through():
    buf = bytes(range(4 * SPF))
    assert bytes(normalize_row(buf, 0, 4, 4, SPF)) == buf


def test_normalize_row_pads_a_short_row():
    buf = bytes(range(3 * SPF))
    out = bytes(normalize_row(buf, 0, 3, 4, SPF))
    assert len(out) == 4 * SPF
    assert out[:3 * SPF] == buf
    assert out[3 * SPF:] == bytes(SPF)


def test_normalize_row_truncates_a_long_row():
    buf = bytes(range(6 * SPF))
    out = bytes(normalize_row(buf, 0, 6, 4, SPF))
    assert out == buf[:4 * SPF]


def test_normalize_row_reads_at_an_offset():
    buf = bytes(range(8 * SPF))
    out = bytes(normalize_row(buf, 2 * SPF, 4, 4, SPF))
    assert out == buf[2 * SPF:6 * SPF]


def test_normalize_row_pads_a_buffer_that_ends_early():
    """Defensive: a truncated transfer must not shorten the row on disk."""
    out = bytes(normalize_row(bytes(2 * SPF), 0, 4, 4, SPF))
    assert len(out) == 4 * SPF


# ── frame_means_block ────────────────────────────────────────────────────────

def test_frame_means_block_is_per_frame():
    buf = bytes([1] * SPF + [3] * SPF)
    assert frame_means_block(buf, 0, 2, SPF) == [1.0, 3.0]


def test_frame_means_block_reads_signed_samples_at_an_offset():
    buf = bytes([0] * SPF) + bytes([0xFF] * SPF)     # 0xFF == -1 as int8
    assert frame_means_block(buf, SPF, 1, SPF) == [-1.0]