Inital commit

common/trie.h

@@ -0,0 +1,73 @@
+#pragma once
+
+#include <cstdint>
+#include <map>
+#include <set>
+#include <string>
+#include <string_view>
+#include <vector>
+
+// Trie for matching multiple literals.
+// This is used in common_peg_until_parser and to build a GBNF exclusion grammar
+struct common_trie {
+    struct node {
+        std::map<uint32_t, size_t> children;  // Use uint32_t to store Unicode codepoints
+        int32_t pattern = -1;                 // index of the pattern ending at this node, -1 if none
+    };
+
+    std::vector<node> nodes;
+
+    common_trie() {
+        create_node(); // root node
+    }
+
+    common_trie(const std::vector<std::string> & words) : common_trie() {
+        for (const auto & w : words) {
+            insert(w);
+        }
+    }
+
+    enum match_result { NO_MATCH, PARTIAL_MATCH, COMPLETE_MATCH };
+
+    // Check if a delimiter starts at the given position
+    match_result check_at(std::string_view sv, size_t start_pos) const;
+
+    // Insert a word as a sequence of Unicode codepoints, returns its pattern index
+    int32_t insert(const std::string & word);
+
+    // Insert a raw symbol sequence, returns its pattern index (insertion order,
+    // duplicates keep the first index)
+    int32_t insert(const std::vector<uint32_t> & symbols);
+
+  private:
+    int32_t n_patterns = 0;
+
+    size_t create_node() {
+        size_t index = nodes.size();
+        nodes.emplace_back();
+        return index;
+    }
+};
+
+// Aho-Corasick automaton
+struct common_aho_corasick {
+    common_trie          t;
+    std::vector<size_t>  fail;     // failure links
+    std::vector<size_t>  order;    // states in BFS order
+    std::vector<int32_t> match;    // longest pattern ending at each state (directly or via a suffix link), -1 if none
+    std::set<uint32_t>   alphabet; // every character with a transition
+
+    common_aho_corasick(common_trie trie);
+
+    common_aho_corasick(const std::vector<std::string> & strings)
+        : common_aho_corasick(common_trie(strings)) {}
+
+    size_t num_states()          const { return t.nodes.size(); }
+    bool   is_terminal(size_t s) const { return match[s] >= 0; }
+
+    // index of the longest pattern ending at this state, -1 if none
+    int32_t match_pattern(size_t s) const { return match[s]; }
+
+    // follow failure links until a transition on `ch` exists.
+    size_t next(size_t state, uint32_t ch) const;
+};