improvement in invalid cluster detection

src/histr.py

@@ -1,15 +1,18 @@
 import unicodedata
 
+
 "Class to split devnagri text in shabdansh"
+# for more details refer to https://www.unicode.org/versions/Unicode11.0.0/ch12.pdf
 
 
 class Shabdansh(str):
     VIRAMA = "\N{DEVANAGARI SIGN VIRAMA}"
-    HALLANK = "्"
+    HALANT = "्"
     LEFT_MATRA = ["ि"]
     RIGHT_MATRA = ["ॉ", "ो", "ौ", "ा", "ी", "ः"]
     TOP_MATRA = ["ँ", "ं", "ॅ", "े", "ै"]
     BOTTOM_MATRA = ["़", "ु", "ू", "ृ"]
+    MATRA = LEFT_MATRA + RIGHT_MATRA + TOP_MATRA + BOTTOM_MATRA
 
     def __init__(self, devnagari_text: str):
         self.str = devnagari_text
@@ -42,7 +45,29 @@ def splitclusters(devnagari_text: str):
 
     @staticmethod
     def is_valid_cluster(cluster: str) -> bool:
+        """Identify if a grapheme cluster is valid or not
+
+        Following are the rules:
+            1. Cluster cannot contain both left and right matra
+            2. Cluster cannot have multiple matra from in the same position, i.e. there
+               can't be more than >1 matra in top, bottom, left, right position
+            3. Cluster can contain top and bottom matra at the same time
+            4. There has to be consonant, i.e. unicode category Mn after a halant
+            5. Cluster cannot contain bottom matra and halant at the same time
+
+        Parameters
+        ----------
+        cluster : str
+            grapheme cluster for evaluation
+
+        Returns
+        -------
+        bool
+            whether the grapheme cluster is valid or not
+        """
+
         left_matra_count, right_matra_count, top_matra_count, bottom_matra_count = 0, 0, 0, 0
+        halant_count = 0
         for char in cluster:
             if char in Shabdansh.LEFT_MATRA:
                 left_matra_count += 1
@@ -52,8 +77,16 @@ def is_valid_cluster(cluster: str) -> bool:
                 top_matra_count += 1
             elif char in Shabdansh.BOTTOM_MATRA:
                 bottom_matra_count += 1
+            elif char == Shabdansh.HALANT:
+                halant_count += 1
+
+        # invalidated because of invalid combination
+        if halant_count and bottom_matra_count:
+            return False
         if left_matra_count and right_matra_count:
             return False
+
+        # invalidated because of more than one matra from the same category
         if left_matra_count > 1:
             return False
         if right_matra_count > 1:
@@ -62,9 +95,15 @@ def is_valid_cluster(cluster: str) -> bool:
             return False
         if bottom_matra_count > 1:
             return False
+        if halant_count > 1:
+            return False
 
         return True
 
+    @staticmethod
+    def contains_hanging_matras(cluster: str) -> bool:
+        return False
+
     def __getitem__(self, index):
         return self.str_ls[index]