"""Column statistics dialog — shows row count, nulls, distinct, min, max, avg."""
from PyQt6.QtWidgets import (
    QDialog, QVBoxLayout, QFormLayout, QLabel, QDialogButtonBox,
    QGroupBox, QProgressBar, QSizePolicy,
)
from PyQt6.QtCore import Qt, QThread, pyqtSignal
from PyQt6.QtGui import QFont


class _StatsWorker(QThread):
    result  = pyqtSignal(dict)
    error   = pyqtSignal(str)

    def __init__(self, driver, database: str, table: str, column: str):
        super().__init__()
        self._driver   = driver
        self._database = database
        self._table    = table
        self._column   = column

    def run(self):
        col  = self._column
        tbl  = self._table
        try:
            _, rows, _ = self._driver.execute_query(
                f'SELECT COUNT(*), COUNT("{col}"), COUNT(DISTINCT "{col}"), '
                f'MIN("{col}"), MAX("{col}") FROM "{tbl}"'
            )
            total, non_null, distinct, min_val, max_val = rows[0]
            null_count = (total or 0) - (non_null or 0)
        except Exception as e:
            self.error.emit(str(e))
            return

        avg_val = None
        try:
            _, avg_rows, _ = self._driver.execute_query(
                f'SELECT AVG("{col}") FROM "{tbl}"'
            )
            avg_val = avg_rows[0][0]
        except Exception:
            pass

        self.result.emit({
            "total":    total,
            "non_null": non_null,
            "nulls":    null_count,
            "distinct": distinct,
            "min":      min_val,
            "max":      max_val,
            "avg":      avg_val,
        })


class ColumnStatsDialog(QDialog):
    def __init__(self, driver, database: str, table: str, column: str, parent=None):
        super().__init__(parent)
        self.setWindowTitle(f"Column Statistics — {column}")
        self.setMinimumWidth(360)
        self._driver   = driver
        self._database = database
        self._table    = table
        self._column   = column
        self._build_ui()
        self._load()

    def _build_ui(self):
        root = QVBoxLayout(self)
        root.setSpacing(10)
        root.setContentsMargins(16, 16, 16, 16)

        subtitle = QLabel(f"<b>{self._table}</b>.<i>{self._column}</i>")
        subtitle.setTextFormat(Qt.TextFormat.RichText)
        root.addWidget(subtitle)

        # ── Stats group ───────────────────────────────────────────────────────
        box = QGroupBox("Statistics")
        self._form = QFormLayout(box)
        self._form.setSpacing(6)
        self._rows: dict[str, QLabel] = {}
        for key, label in [
            ("total",    "Total rows"),
            ("non_null", "Non-null"),
            ("nulls",    "Null count"),
            ("distinct", "Distinct values"),
            ("min",      "Min"),
            ("max",      "Max"),
            ("avg",      "Avg (numeric)"),
        ]:
            lbl = QLabel("…")
            lbl.setFont(QFont("Consolas", 10))
            self._form.addRow(label + ":", lbl)
            self._rows[key] = lbl
        root.addWidget(box)

        # ── Loading bar ───────────────────────────────────────────────────────
        self._progress = QProgressBar()
        self._progress.setMaximum(0)
        self._progress.setFixedHeight(6)
        self._progress.setTextVisible(False)
        root.addWidget(self._progress)

        bb = QDialogButtonBox(QDialogButtonBox.StandardButton.Close)
        bb.rejected.connect(self.reject)
        root.addWidget(bb)

    def _load(self):
        self._worker = _StatsWorker(
            self._driver, self._database, self._table, self._column
        )
        self._worker.result.connect(self._on_result)
        self._worker.error.connect(self._on_error)
        self._worker.finished.connect(self._progress.hide)
        self._worker.start()

    def _on_result(self, stats: dict):
        for key, lbl in self._rows.items():
            val = stats.get(key)
            if val is None:
                text = "N/A"
            elif isinstance(val, float):
                text = f"{val:,.4f}"
            else:
                try:
                    text = f"{int(val):,}"
                except (TypeError, ValueError):
                    text = str(val)
            lbl.setText(text)

    def _on_error(self, msg: str):
        for lbl in self._rows.values():
            lbl.setText("—")
        self._rows["total"].setText(f"Error: {msg[:60]}")
        self._rows["total"].setStyleSheet("color: #e78284;")