use axum::http::StatusCode;
use rustc_hash::FxHashMap;
use tracing::warn;

use crate::consts::{H3_PRECOMPUTE_MAX, H3_REQUEST_MAX, H3_REQUEST_MIN};

/// Validate that an H3 resolution is within the allowed range and convert to h3o::Resolution.
pub fn validate_h3_resolution(resolution: u8) -> Result<h3o::Resolution, (StatusCode, String)> {
    if !(H3_REQUEST_MIN..=H3_REQUEST_MAX).contains(&resolution) {
        warn!(
            resolution,
            "Resolution out of range [{}, {}]", H3_REQUEST_MIN, H3_REQUEST_MAX
        );
        return Err((
            StatusCode::BAD_REQUEST,
            format!(
                "resolution must be between {} and {}",
                H3_REQUEST_MIN, H3_REQUEST_MAX
            ),
        ));
    }
    h3o::Resolution::try_from(resolution).map_err(|error| {
        (
            StatusCode::INTERNAL_SERVER_ERROR,
            format!("Invalid H3 resolution {}: {}", resolution, error),
        )
    })
}

/// Resolve a row's H3 cell at the requested resolution, using precomputed max-resolution cells.
#[inline]
pub fn cell_for_row(
    row: usize,
    precomputed: &[u64],
    h3_res: h3o::Resolution,
    need_parent: bool,
) -> u64 {
    let max_cell = precomputed[row];
    if !need_parent || max_cell == 0 {
        return max_cell;
    }
    let cell = h3o::CellIndex::try_from(max_cell).expect("precomputed H3 cell must be valid");
    u64::from(
        cell.parent(h3_res)
            .expect("parent resolution must be valid for precomputed cell"),
    )
}

/// Like cell_for_row but caches parent lookups in the provided map.
#[inline]
pub fn cell_for_row_cached(
    row: usize,
    precomputed: &[u64],
    h3_res: h3o::Resolution,
    need_parent: bool,
    cache: &mut FxHashMap<u64, u64>,
) -> u64 {
    let max_cell = precomputed[row];
    if !need_parent || max_cell == 0 {
        return max_cell;
    }
    *cache.entry(max_cell).or_insert_with(|| {
        let cell = h3o::CellIndex::try_from(max_cell).expect("precomputed H3 cell must be valid");
        u64::from(
            cell.parent(h3_res)
                .expect("parent resolution must be valid"),
        )
    })
}

/// Whether the given resolution requires computing a parent from precomputed cells.
#[inline]
pub fn needs_parent(resolution: u8) -> bool {
    resolution < H3_PRECOMPUTE_MAX
}