charton 0.5.0

A high-performance, layered charting system for Rust, featuring a flexible data core and multi-backend rendering.
Documentation 
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use crate::scale::ScaleTrait;
use std::sync::Arc;

/// Represents a complete mapping pipeline from a data field to a visual property.
/// This is the "Source of Truth" for how a specific aesthetic (like color)
/// behaves across all layers of a chart.
#[derive(Debug, Clone)]
pub struct AestheticMapping {
    /// The name of the data field being mapped (e.g., "mpg", "gear").
    /// This is crucial for merging different aesthetics into a single legend block.
    pub field: String,

    /// The mathematical implementation that normalizes data to [0, 1].
    pub scale_impl: Arc<dyn ScaleTrait>,
}

/// GlobalAesthetics maintains the unified visual language of the chart.
///
/// Following the Grammar of Graphics, it ensures that if multiple layers
/// map to the same aesthetic (e.g., Color), they share the same scale and
/// range, preventing visual inconsistency.
pub struct GlobalAesthetics {
    /// Mapping for the color channel.
    pub color: Option<AestheticMapping>,

    /// Mapping for the shape channel (typically discrete).
    pub shape: Option<AestheticMapping>,

    /// Mapping for the size channel (typically binned for legends).
    pub size: Option<AestheticMapping>,
}

impl GlobalAesthetics {
    /// Constructs a new `GlobalAesthetics` with fully resolved mappings.
    ///
    /// This is typically invoked after the "Scale Training" phase, where
    /// data domains from all layers have been aggregated.
    pub fn new(
        color: Option<AestheticMapping>,
        shape: Option<AestheticMapping>,
        size: Option<AestheticMapping>,
    ) -> Self {
        Self { color, shape, size }
    }

    /// Helper to identify if a specific field is used across multiple aesthetics.
    /// This is the foundation of ggplot2's automatic legend merging.
    pub fn get_mappings_for_field(&self, field_name: &str) -> Vec<(&str, &AestheticMapping)> {
        let mut found = Vec::new();
        if let Some(ref m) = self.color
            && m.field == field_name
        {
            found.push(("color", m));
        }
        if let Some(ref m) = self.shape
            && m.field == field_name
        {
            found.push(("shape", m));
        }
        if let Some(ref m) = self.size
            && m.field == field_name
        {
            found.push(("size", m));
        }
        found
    }
}