//! u16 quantization: decoding stored feature values and encoding filter bounds.

use crate::consts::{NAN_U16, QUANT_SCALE};

/// Lightweight reference to quantization parameters for decoding u16 feature data.
pub struct QuantRef<'a> {
    pub dequant_a: &'a [f32],
    pub quant_min: &'a [f32],
    pub quant_range: &'a [f32],
    pub num_numeric: usize,
}

impl QuantRef<'_> {
    /// Decode a raw u16 value back to f32.
    #[inline]
    pub fn decode(&self, feat_idx: usize, raw: u16) -> f32 {
        if raw == NAN_U16 {
            return f32::NAN;
        }
        if feat_idx >= self.num_numeric {
            raw as f32
        } else {
            raw as f32 * self.dequant_a[feat_idx] + self.quant_min[feat_idx]
        }
    }

    /// Encode a filter minimum bound to u16 (floors to include boundary values).
    #[inline]
    pub fn encode_min(&self, feat_idx: usize, value: f32) -> u16 {
        if !value.is_finite() || self.quant_range[feat_idx] == 0.0 {
            return 0;
        }
        let norm = (value - self.quant_min[feat_idx]) / self.quant_range[feat_idx];
        (norm * QUANT_SCALE).floor().clamp(0.0, QUANT_SCALE) as u16
    }

    /// Encode a filter maximum bound to u16 (ceils to include boundary values).
    #[inline]
    pub fn encode_max(&self, feat_idx: usize, value: f32) -> u16 {
        if !value.is_finite() || self.quant_range[feat_idx] == 0.0 {
            return QUANT_SCALE as u16;
        }
        let norm = (value - self.quant_min[feat_idx]) / self.quant_range[feat_idx];
        (norm * QUANT_SCALE).ceil().clamp(0.0, QUANT_SCALE) as u16
    }
}