Refactor and other improvements

server-rs/src/parsing/h3.rs

@@ -0,0 +1,52 @@
+use axum::http::StatusCode;
+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;
+    }
+    h3o::CellIndex::try_from(max_cell)
+        .ok()
+        .and_then(|ci| ci.parent(h3_res))
+        .map(u64::from)
+        .unwrap_or(0)
+}
+
+/// Whether the given resolution requires computing a parent from precomputed cells.
+#[inline]
+pub fn needs_parent(resolution: u8) -> bool {
+    resolution < H3_PRECOMPUTE_MAX
+}