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import { describe, expect, it } from "vitest";
import { computeChangeRange, offsetToPosition } from "./diff.js";
describe("offsetToPosition", () => {
it("returns 0:0 for offset 0", () => {
expect(offsetToPosition("hello", 0)).toEqual({ line: 0, character: 0 });
});
it("counts characters on the first line", () => {
expect(offsetToPosition("hello", 3)).toEqual({ line: 0, character: 3 });
});
it("resets character count after newline", () => {
expect(offsetToPosition("ab\ncd", 4)).toEqual({ line: 1, character: 1 });
});
it("handles multiple lines", () => {
expect(offsetToPosition("a\nb\nc", 4)).toEqual({ line: 2, character: 0 });
});
it("clamps offset beyond text length", () => {
expect(offsetToPosition("ab", 100)).toEqual({ line: 0, character: 2 });
});
it("handles empty string", () => {
expect(offsetToPosition("", 0)).toEqual({ line: 0, character: 0 });
});
});
describe("computeChangeRange", () => {
it("detects a single-line insertion", () => {
const oldText = "hello world";
const newText = "hello cruel world";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 6 });
expect(change.range.end).toEqual({ line: 0, character: 6 });
expect(change.text).toBe("cruel ");
});
it("detects a single-line deletion", () => {
const oldText = "hello cruel world";
const newText = "hello world";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 6 });
expect(change.range.end).toEqual({ line: 0, character: 12 });
expect(change.text).toBe("");
});
it("detects a single-line replacement", () => {
const oldText = "hello world";
const newText = "hello earth";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 6 });
expect(change.range.end).toEqual({ line: 0, character: 11 });
expect(change.text).toBe("earth");
});
it("handles multi-line changes with correct line positions", () => {
const oldText = "line1\nline2\nline3";
const newText = "line1\nCHANGED\nline3";
const change = computeChangeRange(oldText, newText);
// Common prefix: "line1\n" → start at beginning of line 1
expect(change.range.start).toEqual({ line: 1, character: 0 });
// Common suffix: "\nline3" → end after "line2" on line 1
expect(change.range.end).toEqual({ line: 1, character: 5 });
expect(change.text).toBe("CHANGED");
});
it("handles insertion at end of file", () => {
const oldText = "abc";
const newText = "abcdef";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 3 });
expect(change.range.end).toEqual({ line: 0, character: 3 });
expect(change.text).toBe("def");
});
it("handles complete file replacement (no common prefix/suffix)", () => {
const oldText = "abc";
const newText = "xyz";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 0 });
expect(change.range.end).toEqual({ line: 0, character: 3 });
expect(change.text).toBe("xyz");
});
it("handles empty old text (new file)", () => {
const oldText = "";
const newText = "hello\nworld";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 0 });
expect(change.range.end).toEqual({ line: 0, character: 0 });
expect(change.text).toBe("hello\nworld");
});
it("handles identical text (no change)", () => {
const oldText = "same text";
const newText = "same text";
const change = computeChangeRange(oldText, newText);
expect(change.range.start).toEqual({ line: 0, character: 9 });
expect(change.range.end).toEqual({ line: 0, character: 9 });
expect(change.text).toBe("");
});
it("handles change spanning multiple lines", () => {
const oldText = "function foo() {\n return 1;\n}\n";
const newText = "function foo() {\n return 2;\n console.log('hi');\n}\n";
const change = computeChangeRange(oldText, newText);
// Common prefix: "function foo() {\n return " (26 chars)
// The change starts at "1" on line 1, character 9
expect(change.range.start).toEqual({ line: 1, character: 9 });
// Common suffix: ";\n}\n" (4 chars) → end at offset 27 (the ";")
// offset 27 = line 1, char 10 (after " return 1")
expect(change.range.end).toEqual({ line: 1, character: 10 });
expect(change.text).toBe("2;\n console.log('hi')");
});
});
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