//! H3 spatial cell precomputation for property rows.

use anyhow::Context;
use rayon::prelude::*;

use crate::consts::H3_PRECOMPUTE_MAX;

/// Precompute H3 cell IDs for all rows at the maximum resolution only.
/// Parent cells for lower resolutions are derived on the fly via `CellIndex::parent()`.
pub fn precompute_h3(lat: &[f32], lon: &[f32]) -> anyhow::Result<Vec<u64>> {
    let res = H3_PRECOMPUTE_MAX;
    tracing::info!("Precomputing H3 cells at resolution {}", res);

    let h3_res =
        h3o::Resolution::try_from(res).with_context(|| format!("Invalid H3 resolution: {res}"))?;

    let cells: Vec<u64> = lat
        .par_iter()
        .zip(lon.par_iter())
        .enumerate()
        .map(|(i, (&latitude, &longitude))| {
            let coord = h3o::LatLng::new(latitude as f64, longitude as f64).unwrap_or_else(|err| {
                panic!(
                    "Invalid coordinates at row {}: lat={}, lon={}: {}",
                    i, latitude, longitude, err
                )
            });
            u64::from(coord.to_cell(h3_res))
        })
        .collect();

    tracing::info!("H3 precomputation complete ({} cells)", cells.len());
    Ok(cells)
}