Move BufferLines.ts into Buffer.ts

Part of #791

src/Buffer.ts

@@ -6,6 +6,9 @@ import { ITerminal, IBuffer } from './Interfaces';
 import { CircularList } from './utils/CircularList';
 import { LineData, CharData } from './Types';
 
+const CHAR_DATA_CHAR_INDEX = 1;
+const CHAR_DATA_WIDTH_INDEX = 2;
+
 /**
  * This class represents a terminal buffer (an internal state of the terminal), where the
  * following information is stored (in high-level):
@@ -146,4 +149,52 @@ export class Buffer implements IBuffer {
     this.scrollTop = 0;
     this.scrollBottom = newRows - 1;
   }
+
+  /**
+   * Translates a buffer line to a string, with optional start and end columns.
+   * Wide characters will count as two columns in the resulting string. This
+   * function is useful for getting the actual text underneath the raw selection
+   * position.
+   * @param line The line being translated.
+   * @param trimRight Whether to trim whitespace to the right.
+   * @param startCol The column to start at.
+   * @param endCol The column to end at.
+   */
+  public translateBufferLineToString(lineIndex: number, trimRight: boolean, startCol: number = 0, endCol: number = null): string {
+    // Get full line
+    let lineString = '';
+    let widthAdjustedStartCol = startCol;
+    let widthAdjustedEndCol = endCol;
+    const line = this.lines.get(lineIndex);
+    for (let i = 0; i < line.length; i++) {
+      const char = line[i];
+      lineString += char[CHAR_DATA_CHAR_INDEX];
+      // Adjust start and end cols for wide characters if they affect their
+      // column indexes
+      if (char[CHAR_DATA_WIDTH_INDEX] === 0) {
+        if (startCol >= i) {
+          widthAdjustedStartCol--;
+        }
+        if (endCol >= i) {
+          widthAdjustedEndCol--;
+        }
+      }
+    }
+
+    // Calculate the final end col by trimming whitespace on the right of the
+    // line if needed.
+    let finalEndCol = widthAdjustedEndCol || line.length;
+    if (trimRight) {
+      const rightWhitespaceIndex = lineString.search(/\s+$/);
+      if (rightWhitespaceIndex !== -1) {
+        finalEndCol = Math.min(finalEndCol, rightWhitespaceIndex);
+      }
+      // Return the empty string if only trimmed whitespace is selected
+      if (finalEndCol <= widthAdjustedStartCol) {
+        return '';
+      }
+    }
+
+    return lineString.substring(widthAdjustedStartCol, finalEndCol);
+  }
 }