feat(main): implement paragraph choosing

knowledge_verificator/main.py

@@ -7,6 +7,7 @@
 from knowledge_verificator.materials import MaterialDatabase
 from knowledge_verificator.nli import NaturalLanguageInference, Relation
 from knowledge_verificator.qg import QuestionGeneration
+from knowledge_verificator.utils.string import clip_text
 
 
 if __name__ == '__main__':
@@ -61,8 +62,28 @@
                     continue
 
                 material = material_db.materials[chosen_index]
-                # TODO: A user should be able to choose a paragraph.
-                paragraph = material.paragraphs[0]
+
+                MAX_LENGTH_OF_CLIPPED_PARAGRAPH = 15
+                console.print('Available paragraphs: ')
+                for i, paragraph in enumerate(material.paragraphs):
+                    console.print(
+                        f'{i+1} {clip_text(paragraph, MAX_LENGTH_OF_CLIPPED_PARAGRAPH)}'
+                    )
+
+                console.print('Which paragraph you want to learn? ')
+                paragraph_choice = input()
+
+                if not paragraph_choice.isnumeric():
+                    console.print(INCORRECT_CHOICE_WARNING)
+                    continue
+
+                chosen_index = int(paragraph_choice) - 1
+                if chosen_index < 0 or chosen_index >= len(material.paragraphs):
+                    console.print(INCORRECT_CHOICE_WARNING)
+                    continue
+
+                # TODO: Refactor this fragment to apply DRY principle.
+                paragraph = material.paragraphs[chosen_index]
 
                 console.print('Learn this paragraph: ')
                 console.print(paragraph)

knowledge_verificator/utils/string.py

@@ -0,0 +1,26 @@
+"""Module with string-related utility function."""
+
+
+def clip_text(text: str, max_length: int) -> str:
+    """
+    Clip `text` if its length exceeds `max_length`.
+
+    If the text was clipped, it has three dots `...` at the end. Otherwise,
+    the text is returned unchanged.
+
+    Args:
+        text (str): Text to clip.
+        max_length (int): Maximum allowed length. It will not be exceeded.
+
+    Returns:
+        str: Clipped text.
+    """
+    if max_length <= 4:
+        raise ValueError(
+            'Minimal reasonable value of `max_length` is 4 (one character '
+            f'and three dots). Supplied value of {max_length}.'
+        )
+    text_length = len(text)
+    if text_length > max_length:
+        return text[: max_length - 3] + '...'
+    return text