Implement MatchData#offset

include/natalie/match_data_object.hpp

@@ -37,6 +37,7 @@ class MatchDataObject : public Object {
 
     Value array(int);
     Value group(Env *, size_t);
+    Value offset(Env *, Value);
 
     Value captures(Env *);
     Value to_a(Env *);
@@ -54,6 +55,6 @@ class MatchDataObject : public Object {
 
 private:
     OnigRegion *m_region { nullptr };
-    const StringObject *m_string { nullptr };
+    StringObject *m_string { nullptr };
 };
 }

include/natalie/string_object.hpp

@@ -193,6 +193,8 @@ class StringObject : public Object {
 
     Value convert_float();
 
+    static size_t byte_index_to_char_index(ArrayObject *chars, size_t byte_index);
+
     template <typename... Args>
     static StringObject *format(const char *fmt, Args... args) {
         String out;

lib/natalie/compiler/binding_gen.rb

@@ -685,6 +685,7 @@ def generate_name
 gen.binding('MatchData', 'captures', 'MatchDataObject', 'captures', argc: 0, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('MatchData', 'size', 'MatchDataObject', 'size', argc: 0, pass_env: false, pass_block: false, return_type: :size_t)
 gen.binding('MatchData', 'length', 'MatchDataObject', 'size', argc: 0, pass_env: false, pass_block: false, return_type: :size_t)
+gen.binding('MatchData', 'offset', 'MatchDataObject', 'offset', argc: 1, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('MatchData', 'to_a', 'MatchDataObject', 'to_a', argc: 0, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('MatchData', 'to_s', 'MatchDataObject', 'to_s', argc: 0, pass_env: true, pass_block: false, return_type: :Object)
 gen.binding('MatchData', '[]', 'MatchDataObject', 'ref', argc: 1, pass_env: true, pass_block: false, return_type: :Object)

spec/core/matchdata/offset_spec.rb

@@ -0,0 +1,30 @@
+# -*- encoding: utf-8 -*-
+
+require_relative '../../spec_helper'
+
+describe "MatchData#offset" do
+  it "returns a two element array with the begin and end of the nth match" do
+    match_data = /(.)(.)(\d+)(\d)/.match("THX1138.")
+    match_data.offset(0).should == [1, 7]
+    match_data.offset(4).should == [6, 7]
+  end
+
+  it "returns [nil, nil] when the nth match isn't found" do
+    match_data = /something is( not)? (right)/.match("something is right")
+    match_data.offset(1).should == [nil, nil]
+  end
+
+  it "returns the offset for multi byte strings" do
+    match_data = /(.)(.)(\d+)(\d)/.match("TñX1138.")
+    match_data.offset(0).should == [1, 7]
+    match_data.offset(4).should == [6, 7]
+  end
+
+  not_supported_on :opal do
+    it "returns the offset for multi byte strings with unicode regexp" do
+      match_data = /(.)(.)(\d+)(\d)/u.match("TñX1138.")
+      match_data.offset(0).should == [1, 7]
+      match_data.offset(4).should == [6, 7]
+    end
+  end
+end

src/match_data_object.cpp

@@ -29,6 +29,23 @@ Value MatchDataObject::group(Env *env, size_t index) {
     return new StringObject { str, length };
 }
 
+Value MatchDataObject::offset(Env *env, Value n) {
+    nat_int_t index = IntegerObject::convert_to_nat_int_t(env, n);
+    if (index >= (nat_int_t)size())
+        return NilObject::the();
+
+    auto begin = m_region->beg[index];
+    auto end = m_region->end[index];
+    if (begin == -1)
+        return new ArrayObject { NilObject::the(), NilObject::the() };
+
+    auto chars = m_string->chars(env);
+    return new ArrayObject {
+        Value::integer(StringObject::byte_index_to_char_index(chars, begin)),
+        Value::integer(StringObject::byte_index_to_char_index(chars, end))
+    };
+}
+
 Value MatchDataObject::captures(Env *env) {
     return this->array(1);
 }

src/string_object.cpp

@@ -604,6 +604,18 @@ Value StringObject::ref(Env *env, Value index_obj) {
     abort();
 }
 
+size_t StringObject::byte_index_to_char_index(ArrayObject *chars, size_t byte_index) {
+    size_t char_index = 0;
+    size_t current_byte_index = 0;
+    for (auto character : *chars) {
+        current_byte_index += character->as_string()->length();
+        if (current_byte_index > byte_index)
+            break;
+        ++char_index;
+    }
+    return char_index;
+}
+
 Value StringObject::sub(Env *env, Value find, Value replacement_value, Block *block) {
     if (!block && !replacement_value)
         env->raise("ArgumentError", "wrong number of arguments (given 1, expected 2)");