import os
import json
import subprocess
import sys
import pytest

from lib_py.layout import (
    compute_2xk_layout,
    LayoutDecision,
)


def test_empty_or_malformed_json_fallback():
    d = compute_2xk_layout({}, default_anchor_id="pane-123")
    assert d.target_pane_id == "pane-123"
    assert d.direction == "right"
    assert not d.is_overflow


def test_1_pane_split_down():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 120, "height": 80}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p1"
    assert d.direction == "down"
    assert not d.is_overflow


def test_1_pane_height_constrained_splits_right():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 160, "height": 30}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p1"
    assert d.direction == "right"
    assert not d.is_overflow


def test_1_pane_overflow():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 50, "height": 30}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p1"
    assert d.direction == "overflow"
    assert d.is_overflow


def test_2_panes_to_3_panes_new_column_right():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 160, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 160, "height": 40}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p1"
    assert d.direction == "right"
    assert not d.is_overflow


def test_3_panes_to_4_panes_fill_singleton():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 80, "y": 0, "width": 80, "height": 80}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p3"
    assert d.direction == "down"
    assert not d.is_overflow


def test_4_panes_to_5_panes_new_column():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 120, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 120, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 120, "y": 0, "width": 120, "height": 40}},
                {"pane_id": "p4", "rect": {"x": 120, "y": 40, "width": 120, "height": 40}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p3"
    assert d.direction == "right"
    assert not d.is_overflow


def test_4_panes_overflow_when_width_constrained():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 60, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 60, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 60, "y": 0, "width": 60, "height": 40}},
                {"pane_id": "p4", "rect": {"x": 60, "y": 40, "width": 60, "height": 40}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.direction == "overflow"
    assert d.is_overflow


def test_max_columns_limit():
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 100, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 100, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 100, "y": 0, "width": 100, "height": 40}},
                {"pane_id": "p4", "rect": {"x": 100, "y": 40, "width": 100, "height": 40}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=30, min_rows=20, max_columns=2)
    assert d.direction == "overflow"
    assert d.is_overflow


def test_headless_0x0_transitions():
    # N=1 -> down
    p1 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}}]}}
    assert compute_2xk_layout(p1).direction == "down"

    # N=2 -> right
    p2 = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p2", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}}
    ]}}
    assert compute_2xk_layout(p2).direction == "right"

    # N=3 -> down
    p3 = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p2", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p3", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}}
    ]}}
    assert compute_2xk_layout(p3).direction == "down"

    # N=4 -> right
    p4 = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p2", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p3", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}},
        {"pane_id": "p4", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}}
    ]}}
    assert compute_2xk_layout(p4).direction == "right"


def test_real_herdr_080_nested_layout_format():
    payload = {
        "result": {
            "layout": {
                "area": {"height": 78, "width": 120, "x": 26, "y": 1},
                "focused_pane_id": "wK:p1",
                "panes": [
                    {"pane_id": "wK:p1", "rect": {"height": 39, "width": 60, "x": 26, "y": 1, "focused": True}},
                    {"pane_id": "wK:p2", "rect": {"height": 39, "width": 60, "x": 26, "y": 40, "focused": False}},
                    {"pane_id": "wK:p3", "rect": {"height": 78, "width": 60, "x": 86, "y": 1, "focused": False}}
                ],
                "splits": [{"direction": "right", "id": "split_0_root", "ratio": 0.5}],
                "workspace_id": "wK",
                "tab_id": "wK:t1",
                "zoomed": False
            },
            "type": "pane_layout"
        }
    }
    d = compute_2xk_layout(payload, min_cols=30, min_rows=20)
    assert d.target_pane_id == "wK:p3"
    assert d.direction == "down"


def test_cli_invocation_pipe():
    payload = json.dumps({
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 120, "height": 80}}
            ]
        }
    })
    skills_dir = os.path.abspath(".agents/skills")
    env = {**os.environ, "PYTHONPATH": skills_dir}
    res = subprocess.run(
        [sys.executable, "-m", "lib_py.layout", "--min-cols", "60", "--min-rows", "20"],
        input=payload,
        capture_output=True,
        text=True,
        env=env
    )
    assert res.returncode == 0
    assert res.stdout.strip() == "down p1"

    res_json = subprocess.run(
        [sys.executable, "-m", "lib_py.layout", "--json"],
        input=payload,
        capture_output=True,
        text=True,
        env=env
    )
    assert res_json.returncode == 0
    data = json.loads(res_json.stdout)
    assert data["target_pane_id"] == "p1"
    assert data["direction"] == "down"
    assert not data["is_overflow"]


def test_lib_sh_no_local_in_shim_heredoc():
    """Verify F-1: No 'local' declarations inside the top-level shim heredoc dispatcher."""
    import os
    lib_path = os.path.abspath(".agents/skills/lib.sh")
    with open(lib_path, "r", encoding="utf-8") as f:
        content = f.read()

    start_idx = content.find("cat <<'EOF' > \"$tmp_file\"")
    end_idx = content.find("\nEOF\n", start_idx)
    assert start_idx != -1 and end_idx != -1

    heredoc = content[start_idx:end_idx]
    # Check specifically in the layout block
    layout_idx = heredoc.find('split_dir=""')
    assert layout_idx != -1
    layout_block = heredoc[layout_idx:layout_idx + 800]
    assert "local " not in layout_block, f"Forbidden 'local' found in top-level shim heredoc:\n{layout_block}"


def test_5_panes_to_6_panes_fill_singleton_in_3rd_column():
    """Verify 5 panes (2x2 full + 1 singleton in 3rd col) -> splits 3rd col singleton down to make 2x3 grid."""
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 80, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 80, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 80, "y": 0, "width": 80, "height": 40}},
                {"pane_id": "p4", "rect": {"x": 80, "y": 40, "width": 80, "height": 40}},
                {"pane_id": "p5", "rect": {"x": 160, "y": 0, "width": 80, "height": 80}}
            ]
        }
    }
    d = compute_2xk_layout(payload, min_cols=60, min_rows=20)
    assert d.target_pane_id == "p5"
    assert d.direction == "down"
    assert not d.is_overflow


def test_lib_sh_layout_split_in_set_e_subshell(tmp_path):
    """Verify F-1 & F-2: lib.sh layout split block executes cleanly in set -euo pipefail top-level script."""
    import os
    skills_dir = os.path.abspath(".agents/skills")
    script = f"""#!/usr/bin/env bash
set -euo pipefail
export PYTHONPATH="{skills_dir}"

_real_herdr() {{
  if [ "${{1:-}}" = "pane" ] && [ "${{2:-}}" = "layout" ]; then
    echo '{{"result": {{"panes": [{{"pane_id": "p1", "rect": {{"x": 0, "y": 0, "width": 120, "height": 80}}}}]}}}}'
    return 0
  fi
  return 1
}}

sample_pane="p1"
split_dir=""

# Exact snippet from lib.sh:429-435
if [ -n "$sample_pane" ]; then
  layout_raw=$(_real_herdr pane layout --pane "$sample_pane" 2>/dev/null || echo "")
  read -r split_dir split_target < <(printf '%s' "$layout_raw" | python3 -m lib_py.layout --min-cols "${{MAM_MIN_PANE_COLS:-15}}" --min-rows "${{MAM_MIN_PANE_ROWS:-0}}" --sample-pane "$sample_pane" 2>/dev/null || echo "right $sample_pane")
  split_dir="${{split_dir:-right}}"
  sample_pane="${{split_target:-$sample_pane}}"
fi

echo "SPLIT_DIR=$split_dir"
echo "SAMPLE_PANE=$sample_pane"
"""
    res = subprocess.run(["bash", "-c", script], capture_output=True, text=True)
    assert res.returncode == 0, f"Script failed with code {res.returncode}. Stderr: {res.stderr}"
    assert "SPLIT_DIR=down" in res.stdout
    assert "SAMPLE_PANE=p1" in res.stdout


def test_real_generated_shim_layout_split(tmp_path):
    """Verify generated shim executes layout.py without command not found or local aborts."""
    import os
    skills_dir = os.path.abspath(".agents/skills")
    ws_dir = str(tmp_path / "ws")
    os.makedirs(ws_dir, exist_ok=True)

    test_script = f"""#!/usr/bin/env bash
set -euo pipefail
export WORKSPACE_ROOT="{ws_dir}"
export SKILL_DIR="{skills_dir}"
source "{skills_dir}/lib.sh"

_init_herdr_isolation

shim_path="$WORKSPACE_ROOT/.mam/shim/herdr"
if [ ! -x "$shim_path" ]; then
  echo "ERROR: shim not generated or not executable" >&2
  exit 1
fi

# Verify no 'local ' inside the shim heredoc body
if grep -E '^[[:space:]]*local layout_' "$shim_path"; then
  echo "ERROR: 'local layout_' found in generated shim" >&2
  exit 1
fi
echo "SHIM_OK"
"""
    res = subprocess.run(["bash", "-c", test_script], capture_output=True, text=True)
    assert res.returncode == 0, f"Shim test failed: {res.stderr}"
    assert "SHIM_OK" in res.stdout


def _four_panes_two_columns():
    """GUI payload: 2 full columns x 2 rows (4 panes). Shared by the max-cols tests."""
    return {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 100, "height": 40}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 40, "width": 100, "height": 40}},
                {"pane_id": "p3", "rect": {"x": 100, "y": 0, "width": 100, "height": 40}},
                {"pane_id": "p4", "rect": {"x": 100, "y": 40, "width": 100, "height": 40}},
            ]
        }
    }


def test_cli_max_cols_flag_triggers_overflow():
    """CLI --max-cols reaches compute_2xk_layout (the lib.sh-facing path)."""
    payload = json.dumps(_four_panes_two_columns())
    skills_dir = os.path.abspath(".agents/skills")
    env = {**os.environ, "PYTHONPATH": skills_dir}
    res = subprocess.run(
        [sys.executable, "-m", "lib_py.layout",
         "--min-cols", "30", "--min-rows", "20", "--max-cols", "2", "--json"],
        input=payload, capture_output=True, text=True, env=env)
    assert res.returncode == 0, res.stderr
    d = json.loads(res.stdout)
    assert d["direction"] == "overflow" and d["is_overflow"]
    assert d["reason"] == "max_columns_reached"


def test_env_max_cols_applies_without_flag():
    """MAM_MAX_PANE_COLS is honoured with no --max-cols flag, which is exactly
    how lib.sh invokes the module (lib.sh passes no --max-cols)."""
    payload = json.dumps(_four_panes_two_columns())
    skills_dir = os.path.abspath(".agents/skills")
    env = {**os.environ, "PYTHONPATH": skills_dir, "MAM_MAX_PANE_COLS": "2"}
    res = subprocess.run(
        [sys.executable, "-m", "lib_py.layout",
         "--min-cols", "30", "--min-rows", "20", "--json"],
        input=payload, capture_output=True, text=True, env=env)
    assert res.returncode == 0, res.stderr
    assert json.loads(res.stdout)["reason"] == "max_columns_reached"


def test_headless_max_columns_growth_guard():
    """C-1: headless mode must honour max_columns too.

    A headless 2xK grid completes n // 2 columns, so at n=4 with max_columns=2
    a further `right` split would open a third column and must overflow instead.
    Note the cap blocks *opening* a new column; it does not force an existing
    over-cap layout to shrink -- the odd-n `down` branch (and the GUI's
    fill_singleton_column) deliberately ignore it.
    """
    def headless(n):
        return {"result": {"panes": [
            {"pane_id": f"p{i}", "rect": {"x": 0, "y": 0, "width": 0, "height": 0}}
            for i in range(1, n + 1)]}}

    d4 = compute_2xk_layout(headless(4), max_columns=2)
    assert d4.is_overflow and d4.direction == "overflow"
    assert d4.reason == "max_columns_reached"

    # Continues growing below the cap
    d2 = compute_2xk_layout(headless(2), max_columns=2)
    assert d2.direction == "right" and not d2.is_overflow

    # Filling an existing column is not blocked (mirrors GUI fill_singleton_column)
    d3 = compute_2xk_layout(headless(3), max_columns=2)
    assert d3.direction == "down" and not d3.is_overflow

    # n=5 is the first odd n that can discriminate: n//2 == 2 == max_columns, so an
    # over-correction that also checked the cap on the odd branch would return
    # overflow here. n=3 has n//2 == 1 and cannot reach the check at all.
    d5 = compute_2xk_layout(headless(5), max_columns=2)
    assert d5.direction == "down" and not d5.is_overflow
    assert d5.reason == "headless_odd_down"

    # When max_columns is not set, existing alternation is preserved (behavior neutrality)
    assert compute_2xk_layout(headless(4)).direction == "right"


_LAYOUT_ENV_VARS = ("MAM_MIN_COLS", "MAM_MIN_PANE_COLS", "MAM_MIN_ROWS",
                    "MAM_MIN_PANE_ROWS", "MAM_MAX_COLS", "MAM_MAX_PANE_COLS")


def _run_layout(payload, args=(), env_extra=None):
    env = {**os.environ, "PYTHONPATH": os.path.abspath(".agents/skills")}
    for k in _LAYOUT_ENV_VARS:
        env.pop(k, None)          # 호출자 셸의 오염 차단
    env.update(env_extra or {})
    res = subprocess.run([sys.executable, "-m", "lib_py.layout", "--json", *args],
                         input=json.dumps(payload), capture_output=True, text=True, env=env)
    assert res.returncode == 0, res.stderr
    return json.loads(res.stdout)


# height//2 = 15 < min_rows(20) 로 제약 분기 진입, width//2 = 25 가 min_cols 와 비교됨.
_ZERO_TRAP = {"result": {"panes": [
    {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 50, "height": 30}}]}}


def test_j1_env_zero_min_cols_matches_flag_zero():
    """J-1: MAM_MIN_PANE_COLS=0 must mean 0, not fall through to the 15 default."""
    flag = _run_layout(_ZERO_TRAP, ("--min-cols", "0", "--min-rows", "20"))
    assert flag["direction"] == "right" and flag["reason"] == "single_pane_height_constrained"
    for var in ("MAM_MIN_COLS", "MAM_MIN_PANE_COLS"):
        assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {var: "0"}) == flag, var


def test_j1_env_zero_min_rows_matches_flag_zero():
    flag = _run_layout(_ZERO_TRAP, ("--min-rows", "0"))
    assert flag["direction"] == "down" and flag["reason"] == "single_pane_split_down"
    for var in ("MAM_MIN_ROWS", "MAM_MIN_PANE_ROWS"):
        assert _run_layout(_ZERO_TRAP, (), {var: "0"}) == flag, var


def test_j1_nonzero_and_malformed_env_behaviour_unchanged():
    """Behaviour neutrality: non-zero env still applies, and a lone typo still
    lands on the documented default instead of crashing on a None comparison."""
    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "25", "MAM_MIN_PANE_ROWS": "20"}) == \
           _run_layout(_ZERO_TRAP, ("--min-cols", "25", "--min-rows", "20"))
    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_PANE_COLS": "abc"}) == _run_layout(_ZERO_TRAP)


def test_j1b_invalid_alias_does_not_shadow_the_documented_var():
    """C-2: MAM_MIN_COLS is a legacy alias checked first; MAM_MIN_PANE_COLS is the
    name .mam.env.example documents. An unparsable value in the alias must be
    skipped, not abort the search and discard the documented setting.

    Empty values already fell through (`if raw:`); this makes invalid values
    behave the same way. When every candidate is unusable, `default` still wins.
    """
    good = _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_PANE_COLS": "25"})
    assert good["direction"] == "right"
    # 별칭이 깨져 있어도 문서화된 변수가 적용된다
    assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_COLS": "foo",
                                        "MAM_MIN_PANE_COLS": "25"}) == good
    # 0 도 마찬가지 (J-1 과의 상호작용)
    assert _run_layout(_ZERO_TRAP, ("--min-rows", "20"), {"MAM_MIN_COLS": "foo",
                                        "MAM_MIN_PANE_COLS": "0"}) == \
           _run_layout(_ZERO_TRAP, ("--min-cols", "0", "--min-rows", "20"))
    # 모든 후보가 무효면 문서화된 기본값으로 흡수 (Rev.1 불변식 보존)
    assert _run_layout(_ZERO_TRAP, (), {"MAM_MIN_COLS": "foo",
                                        "MAM_MIN_PANE_COLS": "bar"}) == _run_layout(_ZERO_TRAP)


def test_default_min_cols_is_15_and_min_rows_is_0():
    """Verify compute_2xk_layout default min_cols is 15 and min_rows is 0.
    With 1 pane of 54x23:
    - min_rows=0 -> splits down without height overflow
    With 2 panes of 30x23 (width//2 = 15):
    - min_cols=15 -> 15 >= 15 -> split right (new column).
    - min_cols=40 -> 15 < 40 -> overflow.
    Default invocation (no min_cols/min_rows passed) must split right for 30 cols.
    """
    # 1. 1 pane of 54x23 splits down (no height constraint)
    p1_54x23 = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 23}}]}}
    d1 = compute_2xk_layout(p1_54x23)
    assert d1.direction == "down"
    assert not d1.is_overflow

    # 2. 2 panes with width 30 (30 // 2 = 15 == min_cols 15) -> splits right cleanly
    payload = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 30, "height": 20}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 30, "height": 20}},
            ]
        }
    }
    decision = compute_2xk_layout(payload)
    assert decision.direction == "right"
    assert not decision.is_overflow
    assert decision.reason == "new_column_right"


def test_30_col_2_column_splitting_boundary():
    """Verify width >= 30 cols allows 2-column splitting with default min_cols=15,
    while width < 30 (e.g. 29) triggers column_width_overflow.
    """
    # 30 cols: 30 // 2 = 15 == min_cols(15) -> splits right
    payload_30 = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 30, "height": 20}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 30, "height": 20}},
            ]
        }
    }
    d30 = compute_2xk_layout(payload_30)
    assert d30.direction == "right"
    assert not d30.is_overflow

    # 29 cols: 29 // 2 = 14 < min_cols(15) -> overflow
    payload_29 = {
        "result": {
            "panes": [
                {"pane_id": "p1", "rect": {"x": 0, "y": 0, "width": 29, "height": 20}},
                {"pane_id": "p2", "rect": {"x": 0, "y": 20, "width": 29, "height": 20}},
            ]
        }
    }
    d29 = compute_2xk_layout(payload_29)
    assert d29.direction == "overflow"
    assert d29.is_overflow
    assert d29.reason == "column_width_overflow"


def test_54x23_compact_viewport_single_workspace_multi_pane_tiling():
    """Verify complete 1 -> 2 -> 3 -> 4 pane tiling in standard 80x24 (54x23 content area) workspace.
    - 1 pane (54x23): splits down to p1(54x11), p2(54x11)
    - 2 panes: splits right (54//2 = 27 >= 15) to start col 2 -> p3(27x23)
    - 3 panes: fills singleton col 2 down -> p4(27x11)
    - 4 panes (2x2 grid): 5th agent overflows because 27 // 2 = 13 < 15
    """
    # 1 -> 2 (splits down)
    p1_layout = {"result": {"panes": [{"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 23}}]}}
    d1 = compute_2xk_layout(p1_layout)
    assert d1.direction == "down"
    assert d1.target_pane_id == "p1"
    assert not d1.is_overflow

    # 2 -> 3 (splits right)
    p2_layout = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 54, "height": 11}},
        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 54, "height": 11}},
    ]}}
    d2 = compute_2xk_layout(p2_layout)
    assert d2.direction == "right"
    assert d2.target_pane_id == "p1"
    assert not d2.is_overflow

    # 3 -> 4 (fills singleton col 2 down)
    p3_layout = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 23}},
    ]}}
    d3 = compute_2xk_layout(p3_layout)
    assert d3.direction == "down"
    assert d3.target_pane_id == "p3"
    assert not d3.is_overflow

    # 4 -> 5 (overflow to new workspace because 27 // 2 = 13 < 15)
    p4_layout = {"result": {"panes": [
        {"pane_id": "p1", "rect": {"x": 26, "y": 1, "width": 27, "height": 11}},
        {"pane_id": "p2", "rect": {"x": 26, "y": 12, "width": 27, "height": 11}},
        {"pane_id": "p3", "rect": {"x": 53, "y": 1, "width": 27, "height": 11}},
        {"pane_id": "p4", "rect": {"x": 53, "y": 12, "width": 27, "height": 11}},
    ]}}
    d4 = compute_2xk_layout(p4_layout)
    assert d4.direction == "overflow"
    assert d4.is_overflow
    assert d4.reason == "column_width_overflow"