"""Task 6: `tht sql preview --json` + `--offset` paging.

Pure-logic tests (no DB needed):
  1. inject_limit_offset — subquery wrapping, non-destructive.
  2. preview_cmd JSON-purity — monkeypatched do_run, verifies stdout is valid JSON.
"""
import json

import pytest

from tht.execute.limit import inject_limit_offset


def test_inject_limit_offset_wraps_query():
    sql = "SELECT a FROM t ORDER BY a"
    out = inject_limit_offset(sql, limit=10, offset=20)
    assert "LIMIT 10" in out and "OFFSET 20" in out
    # original query stays as a subquery (no clobber of an existing user LIMIT)
    assert "SELECT a FROM t ORDER BY a" in out


def test_inject_limit_offset_zero_offset_no_offset_clause():
    out = inject_limit_offset("SELECT 1", limit=5, offset=0)
    assert "LIMIT 5" in out
    assert "OFFSET" not in out


def test_inject_limit_offset_strips_trailing_semicolon():
    out = inject_limit_offset("SELECT 1;", limit=3, offset=0)
    assert "LIMIT 3" in out
    # semicolon should not appear in the inner subquery
    assert ";" not in out


def test_inject_limit_offset_default_offset_zero():
    out = inject_limit_offset("SELECT x FROM y", limit=7)
    assert "LIMIT 7" in out
    assert "OFFSET" not in out


def test_preview_json_pure_stdout(monkeypatch, tmp_path, capsys):
    from types import SimpleNamespace

    from tht.cli import sql_cmd

    fake = SimpleNamespace(columns=["a"], rows=[[1], [2]], execution_ms=3, truncated=False)
    monkeypatch.setattr(sql_cmd, "do_run", lambda *a, **k: fake)
    monkeypatch.setattr(sql_cmd, "validate_or_exit", lambda *a, **k: SimpleNamespace(ast=None))
    monkeypatch.setattr(sql_cmd, "require_action", lambda *a, **k: None)
    monkeypatch.setattr(
        sql_cmd,
        "_load_config_or_exit",
        lambda *a, **k: SimpleNamespace(execution=SimpleNamespace(max_preview_rows=100)),
    )
    f = tmp_path / "q.sql"
    f.write_text("SELECT 1")
    sql_cmd.preview_cmd(file=f, limit=None, offset=0, session=None, json_out=True, config=None)
    out = capsys.readouterr().out.strip()
    data = json.loads(out)  # must parse: stdout pristine
    assert data["columns"] == ["a"]
    assert data["rows"] == [[1], [2]]
    assert data["execution_ms"] == 3
    assert data["truncated"] is False
    assert "limit" in data
    assert data["offset"] == 0