From d1ee4fa329c73b909ce26e162355d87976528e43 Mon Sep 17 00:00:00 2001
From: Panos Mavrogiorgos <pmav99@gmail.com>
Date: Wed, 11 Sep 2024 12:59:42 +0300
Subject: [PATCH] feat: Add `parse_hgrid()`

---
 pyposeidon/utils/cfl.py | 75 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/pyposeidon/utils/cfl.py b/pyposeidon/utils/cfl.py
index 8ea82ea..e769844 100644
--- a/pyposeidon/utils/cfl.py
+++ b/pyposeidon/utils/cfl.py
@@ -1,7 +1,9 @@
 from __future__ import annotations
 
 import io
+import itertools
 import os
+import typing as T
 
 import numpy as np
 import numpy.typing as npt
@@ -49,6 +51,79 @@ def parse_hgrid_elements3(path: os.PathLike[str] | str) -> pd.DataFrame:
     return elements
 
 
+def parse_hgrid(path: os.PathLike[str] | str) -> dict[str, T.Any]:
+    """
+    Parse an hgrid.gr3 file.
+
+    Warning: The parser only works if the gr3 file uses `\t` as the delimiter!
+    """
+    with open(path, "rb") as fd:
+        _ = fd.readline()  # skip line
+        no_elements, no_points = map(int, fd.readline().strip().split())
+        nodes_buffer = io.BytesIO(b"\n".join(itertools.islice(fd, 0, no_points)))
+        # print(nodes_buffer.readline())
+        # print(nodes_buffer.readlines()[-1])
+        # nodes_buffer.seek(0)
+        # breakpoint()
+        # nodes = pd.read_csv(nodes_buffer, engine="pyarrow", sep=" ", header=None, names=["lon", "lat", "depth"], usecols=(1, 2, 3))
+        nodes = pd.read_csv(
+            nodes_buffer,
+            engine="pyarrow",
+            sep="\t",
+            header=None,
+            names=["lon", "lat", "depth"],
+            usecols=(1, 2, 3),
+        )
+        elements = pd.read_csv(
+            io.BytesIO(b"\n".join(itertools.islice(fd, 0, no_elements))),
+            engine="pyarrow",
+            sep="\t",
+            header=None,
+            names=["n1", "n2", "n3"],
+            usecols=(2, 3, 4),
+        )
+        elements -= 1  # We use 0-based index for the nodes
+        # open
+        boundaries = {
+            "open": [],
+            "land": [],
+            "island": [],
+        }
+        no_open_boundaries = int(fd.readline().split(b"=")[0].strip())
+        total_open_boundary_nodes = int(fd.readline().split(b"=")[0].strip())
+        for i in range(no_open_boundaries):
+            no_nodes_in_boundary = int(fd.readline().split(b"=")[0].strip())
+            boundary_nodes = np.fromiter(
+                fd,
+                count=no_nodes_in_boundary,
+                dtype=int,
+            )
+            boundaries["open"].append(boundary_nodes - 1)  # 0-based index
+        # closed boundaries
+        no_closed_boundaries = int(fd.readline().split(b"=")[0].strip())
+        total_closed_boundary_nodes = int(fd.readline().split(b"=")[0].strip())
+        for i in range(no_closed_boundaries):
+            no_nodes_in_boundary, boundary_type = map(
+                int, (fd.readline().split(b"=")[0].strip().split(b" "))
+            )
+            boundary_nodes = np.fromiter(
+                fd,
+                count=no_nodes_in_boundary,
+                dtype=int,
+            )
+            if boundary_type == 0:
+                boundaries["land"].append(boundary_nodes - 1)  # 0-based index
+            elif boundary_type == 1:
+                boundaries["island"].append(boundary_nodes - 1)  # 0-based index
+            else:
+                raise ValueError(f"Non-supported boundary type: {boundary_type}")
+    return {
+        "elements": elements,
+        "nodes": nodes,
+        "boundaries": boundaries,
+    }
+
+
 def get_skews_and_base_cfls(lons, lats, depths) -> tuple[npt.NDArray[np.float64], npt.NDArray[np.float64]]:
     # The shape of each one of the input arrays needs to be (3, <no_triangles>)
     # ell = pymap3d.Ellipsoid.from_name("wgs84")