feat: selectedTextFromLines() function

src/selection.tsx

@@ -5,12 +5,7 @@
 import React from "./deps/react.ts";
 import { defaultPosition } from "./line.tsx";
 import { Rect } from "./rect.ts";
-import { Position } from "./types.ts";
-
-export type Selection = {
-  start: Position;
-  end: Position;
-};
+import { Selection } from "./types.ts";
 
 export const defaultSelection: Selection = {
   start: defaultPosition,

src/types.ts

@@ -13,3 +13,8 @@ export type CursorView = {
   top: number;
   height: number;
 };
+
+export type Selection = {
+  start: Position;
+  end: Position;
+};

src/util.test.ts

@@ -1,5 +1,7 @@
+import { assertEquals, assertStrictEquals } from "./deps/std/asserts.ts";
 import { clamp, countIndent } from "./util.ts";
-import { assertStrictEquals } from "./deps/std/asserts.ts";
+import { Selection } from "./types.ts";
+import { selectedTextFromLines } from "./util.ts";
 
 Deno.test("clamp()", () => {
   assertStrictEquals(clamp(34, 56, 43.0), 43.0);
@@ -13,3 +15,28 @@ Deno.test("countIndent()", () => {
   assertStrictEquals(countIndent("　 hoge"), 2);
   assertStrictEquals(countIndent(" \tfuga"), 2);
 });
+
+function mkSelection(...args: number[]): Selection {
+  return {
+    start: {
+      line: args[0],
+      column: args[1],
+    },
+    end: {
+      line: args[2],
+      column: args[3],
+    },
+  };
+}
+
+Deno.test("selectedTextFromLines()", () => {
+  const lines = ["one", "two", "three"].map((s) => ({ text: s }));
+  const tests: [number[], string[]][] = [
+    [[2, 1, 2, 4], ["t", "hre", "e"]],
+    [[0, 2, 2, 2], ["on", "e\ntwo\nth", "ree"]],
+  ];
+  for (const [sel, expected] of tests) {
+    const actual = selectedTextFromLines(lines, mkSelection(...sel));
+    assertEquals(actual, expected);
+  }
+});

src/util.ts

@@ -1,7 +1,35 @@
+import { Selection } from "./types.ts";
+
 export function clamp(min: number, num: number, max: number) {
   return Math.max(min, Math.min(num, max));
 }
 
 export function countIndent(text: string) {
   return text.length - text.trimStart().length;
 }
+
+export type SelectedText = [start: string, selected: string, end: string];
+
+export function selectedTextFromLines(
+  lines: { text: string }[],
+  selection: Selection,
+): SelectedText {
+  const text = lines.slice(
+    selection.start.line,
+    selection.end.line + 1,
+  )
+    .map((l) => l.text);
+
+  const start = text[0].slice(0, selection.start.column);
+  const end = text[text.length - 1].slice(selection.end.column);
+
+  text[text.length - 1] = text[text.length - 1].slice(
+    0,
+    selection.end.column,
+  );
+  text[0] = text[0].slice(selection.start.column, text[0].length);
+
+  const selected = text.join("\n");
+
+  return [start, selected, end];
+}