"""Tests for chart binding validation rules."""

import pytest
from dataclasses import dataclass, field


# ---------------------------------------------------------------------------
# Stub domain objects -- replace with real imports later
# ---------------------------------------------------------------------------
@dataclass
class Binding:
    channel: str  # e.g. "x", "y", "color", "size"
    field_id: str


@dataclass
class ChartSpec:
    chart_type: str
    bindings: list[Binding] = field(default_factory=list)

    def validate(self) -> list[str]:
        """Return a list of validation error messages (empty == valid)."""
        errors: list[str] = []
        required = REQUIRED_BINDINGS.get(self.chart_type, [])
        bound_channels = {b.channel for b in self.bindings}
        for channel in required:
            if channel not in bound_channels:
                errors.append(
                    f"Chart type '{self.chart_type}' requires binding for '{channel}'."
                )
        return errors


REQUIRED_BINDINGS: dict[str, list[str]] = {
    "bar": ["x", "y"],
    "line": ["x", "y"],
    "pie": ["theta"],
    "scatter": ["x", "y"],
}


# ---------------------------------------------------------------------------
# Tests
# ---------------------------------------------------------------------------
class TestBindingValidation:
    """Ensure chart specs enforce required bindings per chart type."""

    def test_bar_chart_requires_x_and_y(self):
        spec = ChartSpec(chart_type="bar", bindings=[])
        errors = spec.validate()
        assert any("'x'" in e for e in errors)
        assert any("'y'" in e for e in errors)

    def test_bar_chart_valid_with_x_and_y(self):
        spec = ChartSpec(
            chart_type="bar",
            bindings=[
                Binding(channel="x", field_id="category"),
                Binding(channel="y", field_id="amount"),
            ],
        )
        assert spec.validate() == []

    def test_pie_chart_requires_theta(self):
        spec = ChartSpec(chart_type="pie", bindings=[])
        errors = spec.validate()
        assert any("'theta'" in e for e in errors)

    def test_pie_chart_valid_with_theta(self):
        spec = ChartSpec(
            chart_type="pie",
            bindings=[Binding(channel="theta", field_id="sales")],
        )
        assert spec.validate() == []

    def test_line_chart_missing_y(self):
        spec = ChartSpec(
            chart_type="line",
            bindings=[Binding(channel="x", field_id="date")],
        )
        errors = spec.validate()
        assert any("'y'" in e for e in errors)
        assert not any("'x'" in e for e in errors)

    def test_scatter_chart_requires_x_and_y(self):
        spec = ChartSpec(chart_type="scatter", bindings=[])
        errors = spec.validate()
        assert len(errors) == 2