Support getting line for diagnostic

src/Diagnostics/DiagnosticsHolder.hpp

@@ -3,6 +3,7 @@
 #define PORYGONLANG_DIAGNOSTICSHOLDER_HPP
 
 #include <vector>
+#include <string>
 #include "DiagnosticSeverity.hpp"
 #include "DiagnosticCode.hpp"
 #include "Diagnostic.hpp"
@@ -13,9 +14,21 @@ namespace Porygon::Diagnostics {
     class DiagnosticsHolder {
         bool _hasErrors;
         vector<Diagnostic> _diagnostics;
+        vector<size_t> _lineStarts;
+        vector<size_t> _lineLength;
     public:
-        DiagnosticsHolder() {
+        explicit DiagnosticsHolder(const u16string& str) {
             _hasErrors = false;
+            _lineStarts = vector<size_t>{0};
+            size_t lineLength = 0;
+            for (size_t i = 0; i < str.size(); i++){
+                lineLength++;
+                if (str[i] == '\n'){
+                    _lineStarts.push_back(i + 1);
+                    _lineLength.push_back(lineLength);
+                    lineLength = 0;
+                }
+            }
         }
 
         ~DiagnosticsHolder() {
@@ -37,6 +50,29 @@ namespace Porygon::Diagnostics {
         int DiagnosticsCount();
 
         Diagnostic *GetDiagnosticAt(int position);
+
+        size_t GetLineFromPosition(size_t i){
+            size_t topLimit = _lineStarts.size() - 1;
+            size_t bottomLimit = 0;
+            while (true){
+                if (bottomLimit == topLimit){
+                    return bottomLimit;
+                }
+                size_t half = (topLimit - bottomLimit) / 2;
+                size_t pos = _lineStarts[half];
+                size_t length = _lineLength[half];
+                if (pos < i && pos + length > i){
+                    return half;
+                }
+                if (pos > i){
+                    bottomLimit = half;
+                } else if (pos < i){
+                    topLimit = half;
+                } else{
+                    return half;
+                }
+            }
+        }
     };
 }