Added classes to support formatting

src/myfasthtml/core/formatting/dataclasses.py

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+from dataclasses import dataclass, field
+from typing import Any
+
+
+# === Condition ===
+
+@dataclass
+class Condition:
+    """
+    Represents a condition for conditional formatting.
+
+    Attributes:
+        operator: Comparison operator ("==", "!=", "<", "<=", ">", ">=",
+                  "contains", "startswith", "endswith", "in", "between",
+                  "isempty", "isnotempty")
+        value: Value to compare against (literal, list, or {"col": "..."} for reference)
+        negate: If True, inverts the condition result
+        case_sensitive: If True, string comparisons are case-sensitive (default False)
+        col: Column ID for row-level conditions (evaluate this column instead of current cell)
+        row: Row index for column-level conditions (evaluate this row instead of current cell)
+    """
+    operator: str
+    value: Any = None
+    negate: bool = False
+    case_sensitive: bool = False
+    col: str = None
+    row: int = None
+
+
+# === Style ===
+
+@dataclass
+class Style:
+    """
+    Represents style properties for cell formatting.
+
+    Attributes:
+        preset: Name of a style preset ("primary", "success", "error", etc.)
+        background_color: Background color (hex, CSS name, or CSS variable)
+        color: Text color
+        font_weight: "normal" or "bold"
+        font_style: "normal" or "italic"
+        font_size: Font size ("12px", "0.9em")
+        text_decoration: "none", "underline", or "line-through"
+    """
+    preset: str = None
+    background_color: str = None
+    color: str = None
+    font_weight: str = None
+    font_style: str = None
+    font_size: str = None
+    text_decoration: str = None
+
+
+# === Formatters ===
+
+@dataclass
+class Formatter:
+    """Base class for all formatters."""
+    preset: str = None
+
+
+@dataclass
+class NumberFormatter(Formatter):
+    """
+    Formatter for numbers, currencies, and percentages.
+
+    Attributes:
+        prefix: Text before value (e.g., "$")
+        suffix: Text after value (e.g., " EUR")
+        thousands_sep: Thousands separator (e.g., ",", " ")
+        decimal_sep: Decimal separator (e.g., ".", ",")
+        precision: Number of decimal places
+        multiplier: Multiply value before display (e.g., 100 for percentage)
+    """
+    prefix: str = ""
+    suffix: str = ""
+    thousands_sep: str = ""
+    decimal_sep: str = "."
+    precision: int = 0
+    multiplier: float = 1.0
+
+
+@dataclass
+class DateFormatter(Formatter):
+    """
+    Formatter for dates and datetimes.
+
+    Attributes:
+        format: strftime format pattern (default: "%Y-%m-%d")
+    """
+    format: str = "%Y-%m-%d"
+
+
+@dataclass
+class BooleanFormatter(Formatter):
+    """
+    Formatter for boolean values.
+
+    Attributes:
+        true_value: Display string for True
+        false_value: Display string for False
+        null_value: Display string for None/null
+    """
+    true_value: str = "true"
+    false_value: str = "false"
+    null_value: str = ""
+
+
+@dataclass
+class TextFormatter(Formatter):
+    """
+    Formatter for text transformations.
+
+    Attributes:
+        transform: Text transformation ("uppercase", "lowercase", "capitalize")
+        max_length: Maximum length before truncation
+        ellipsis: Suffix when truncated (default: "...")
+    """
+    transform: str = None
+    max_length: int = None
+    ellipsis: str = "..."
+
+
+@dataclass
+class EnumFormatter(Formatter):
+    """
+    Formatter for mapping values to display labels.
+
+    Attributes:
+        source: Data source dict with "type" and "value" keys
+                - {"type": "mapping", "value": {"key": "label", ...}}
+                - {"type": "datagrid", "value": "grid_id", "value_column": "id", "display_column": "name"}
+        default: Label for unknown values
+        allow_empty: Show empty option in Select dropdowns
+        empty_label: Label for empty option
+        order_by: Sort order ("source", "display", "value")
+    """
+    source: dict = field(default_factory=dict)
+    default: str = ""
+    allow_empty: bool = True
+    empty_label: str = "-- Select --"
+    order_by: str = "source"
+
+
+# === Format Rule ===
+
+@dataclass
+class FormatRule:
+    """
+    A formatting rule combining condition, style, and formatter.
+
+    Rules:
+        - style and formatter can appear alone (unconditional formatting)
+        - condition cannot appear alone - must be paired with style and/or formatter
+        - If condition is present, style/formatter is applied only if condition is met
+
+    Attributes:
+        condition: Optional condition for conditional formatting
+        style: Optional style to apply
+        formatter: Optional formatter to apply
+    """
+    condition: Condition = None
+    style: Style = None
+    formatter: Formatter = None