1 files changed, 94 insertions, 0 deletions
diff --git a/src/prompt_toolkit/contrib/regular_languages/completion.py b/src/prompt_toolkit/contrib/regular_languages/completion.py
new file mode 100644
index 0000000..2e353e8
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+++ b/src/prompt_toolkit/contrib/regular_languages/completion.py
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+"""
+Completer for a regular grammar.
+"""
+from __future__ import annotations
+
+from typing import Iterable
+
+from prompt_toolkit.completion import CompleteEvent, Completer, Completion
+from prompt_toolkit.document import Document
+
+from .compiler import Match, _CompiledGrammar
+
+__all__ = [
+    "GrammarCompleter",
+]
+
+
+class GrammarCompleter(Completer):
+    """
+    Completer which can be used for autocompletion according to variables in
+    the grammar. Each variable can have a different autocompleter.
+
+    :param compiled_grammar: `GrammarCompleter` instance.
+    :param completers: `dict` mapping variable names of the grammar to the
+                       `Completer` instances to be used for each variable.
+    """
+
+    def __init__(
+        self, compiled_grammar: _CompiledGrammar, completers: dict[str, Completer]
+    ) -> None:
+        self.compiled_grammar = compiled_grammar
+        self.completers = completers
+
+    def get_completions(
+        self, document: Document, complete_event: CompleteEvent
+    ) -> Iterable[Completion]:
+        m = self.compiled_grammar.match_prefix(document.text_before_cursor)
+
+        if m:
+            completions = self._remove_duplicates(
+                self._get_completions_for_match(m, complete_event)
+            )
+
+            yield from completions
+
+    def _get_completions_for_match(
+        self, match: Match, complete_event: CompleteEvent
+    ) -> Iterable[Completion]:
+        """
+        Yield all the possible completions for this input string.
+        (The completer assumes that the cursor position was at the end of the
+        input string.)
+        """
+        for match_variable in match.end_nodes():
+            varname = match_variable.varname
+            start = match_variable.start
+
+            completer = self.completers.get(varname)
+
+            if completer:
+                text = match_variable.value
+
+                # Unwrap text.
+                unwrapped_text = self.compiled_grammar.unescape(varname, text)
+
+                # Create a document, for the completions API (text/cursor_position)
+                document = Document(unwrapped_text, len(unwrapped_text))
+
+                # Call completer
+                for completion in completer.get_completions(document, complete_event):
+                    new_text = (
+                        unwrapped_text[: len(text) + completion.start_position]
+                        + completion.text
+                    )
+
+                    # Wrap again.
+                    yield Completion(
+                        text=self.compiled_grammar.escape(varname, new_text),
+                        start_position=start - len(match.string),
+                        display=completion.display,
+                        display_meta=completion.display_meta,
+                    )
+
+    def _remove_duplicates(self, items: Iterable[Completion]) -> list[Completion]:
+        """
+        Remove duplicates, while keeping the order.
+        (Sometimes we have duplicates, because the there several matches of the
+        same grammar, each yielding similar completions.)
+        """
+        result: list[Completion] = []
+        for i in items:
+            if i not in result:
+                result.append(i)
+        return result