feat(01-04): implement typing exercise engine with TDD
- generateLetters: random 8-12 letters from level key set - handleKeyPress: correct/wrong input with adaptive tempo - Adaptive tempo: 3s start, -200ms after 2x correct, +500ms on error - Bounds: min 1500ms, max 4000ms - 18 passing tests covering all behavior Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude Opus 4.6
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import { describe, it, expect } from "vitest";
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import {
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generateLetters,
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createExerciseState,
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handleKeyPress,
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getCurrentLetter,
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isExerciseComplete,
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} from "./typing";
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import { getKeysUpToLevel } from "./levels";
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describe("generateLetters", () => {
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it("returns 8-12 letters for level 1", () => {
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for (let i = 0; i < 20; i++) {
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const letters = generateLetters(1);
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expect(letters.length).toBeGreaterThanOrEqual(8);
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expect(letters.length).toBeLessThanOrEqual(12);
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}
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});
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it("only uses keys from level 1 key set (f, j, space)", () => {
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const validKeys = ["f", "j", " "];
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for (let i = 0; i < 20; i++) {
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const letters = generateLetters(1);
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for (const letter of letters) {
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expect(validKeys).toContain(letter);
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}
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}
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});
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it("only uses keys from levels 1-3 key set for level 3", () => {
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const validKeys = getKeysUpToLevel(3);
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for (let i = 0; i < 20; i++) {
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const letters = generateLetters(3);
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for (const letter of letters) {
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expect(validKeys).toContain(letter);
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}
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}
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});
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});
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describe("createExerciseState", () => {
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it("sets initial interval to 3000ms", () => {
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const state = createExerciseState(1);
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expect(state.intervalMs).toBe(3000);
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});
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it("starts at letter index 0 with 0 correct, 0 errors, 0 streak", () => {
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const state = createExerciseState(1);
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expect(state.currentLetterIndex).toBe(0);
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expect(state.totalCorrect).toBe(0);
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expect(state.totalErrors).toBe(0);
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expect(state.correctStreak).toBe(0);
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});
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});
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describe("handleKeyPress", () => {
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it("increments currentLetterIndex and totalCorrect on correct key", () => {
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const state = createExerciseState(1);
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const expected = state.letters[0]!;
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const result = handleKeyPress(state, expected);
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expect(result.correct).toBe(true);
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expect(state.currentLetterIndex).toBe(1);
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expect(state.totalCorrect).toBe(1);
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});
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it("does NOT increment currentLetterIndex on wrong key, increments totalErrors", () => {
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const state = createExerciseState(1);
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// Pick a key that is definitely wrong
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const expected = state.letters[0]!;
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const wrongKey = expected === "f" ? "j" : "f";
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const result = handleKeyPress(state, wrongKey);
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expect(result.correct).toBe(false);
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expect(state.currentLetterIndex).toBe(0);
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expect(state.totalErrors).toBe(1);
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});
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it("increments correctStreak on correct key", () => {
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const state = createExerciseState(1);
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const expected = state.letters[0]!;
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handleKeyPress(state, expected);
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expect(state.correctStreak).toBe(1);
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});
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it("resets correctStreak to 0 on error", () => {
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const state = createExerciseState(1);
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// Get one correct to build streak
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handleKeyPress(state, state.letters[0]!);
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expect(state.correctStreak).toBe(1);
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// Now wrong key
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const expected = state.letters[1]!;
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const wrongKey = expected === "f" ? "j" : "f";
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handleKeyPress(state, wrongKey);
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expect(state.correctStreak).toBe(0);
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});
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it("decreases interval by 200ms after 2 correct in sequence", () => {
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const state = createExerciseState(1);
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expect(state.intervalMs).toBe(3000);
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handleKeyPress(state, state.letters[0]!);
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handleKeyPress(state, state.letters[1]!);
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expect(state.intervalMs).toBe(2800);
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});
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it("increases interval by 500ms after 1 error", () => {
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const state = createExerciseState(1);
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// Force an error
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const expected = state.letters[0]!;
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const wrongKey = expected === "f" ? "j" : "f";
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handleKeyPress(state, wrongKey);
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expect(state.intervalMs).toBe(3500);
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});
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it("interval never goes below 1500ms", () => {
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const state = createExerciseState(1);
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// Force interval down to minimum
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state.intervalMs = 1600;
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state.correctStreak = 1;
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handleKeyPress(state, state.letters[0]!);
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// After 2 correct streak, -200ms: 1600 -> 1500 (clamped)
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expect(state.intervalMs).toBe(1500);
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// Try again: force streak
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state.correctStreak = 1;
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handleKeyPress(state, state.letters[1]!);
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// Should stay at 1500
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expect(state.intervalMs).toBe(1500);
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});
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it("interval never goes above 4000ms", () => {
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const state = createExerciseState(1);
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state.intervalMs = 3800;
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const expected = state.letters[0]!;
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const wrongKey = expected === "f" ? "j" : "f";
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handleKeyPress(state, wrongKey);
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// 3800 + 500 = 4300, clamped to 4000
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expect(state.intervalMs).toBe(4000);
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});
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it("exercise is complete when currentLetterIndex equals letters.length", () => {
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const state = createExerciseState(1);
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// Type all letters correctly
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let lastResult = { correct: false, exerciseComplete: false, newInterval: 0 };
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for (let i = 0; i < state.letters.length; i++) {
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lastResult = handleKeyPress(state, state.letters[i]!);
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}
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expect(lastResult.exerciseComplete).toBe(true);
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expect(isExerciseComplete(state)).toBe(true);
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});
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});
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describe("getCurrentLetter", () => {
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it("returns the current letter", () => {
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const state = createExerciseState(1);
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expect(getCurrentLetter(state)).toBe(state.letters[0]);
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});
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it("returns null when exercise is complete", () => {
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const state = createExerciseState(1);
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state.currentLetterIndex = state.letters.length;
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expect(getCurrentLetter(state)).toBeNull();
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});
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});
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describe("isExerciseComplete", () => {
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it("returns false when exercise is in progress", () => {
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const state = createExerciseState(1);
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expect(isExerciseComplete(state)).toBe(false);
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});
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it("returns true when all letters are typed", () => {
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const state = createExerciseState(1);
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state.currentLetterIndex = state.letters.length;
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expect(isExerciseComplete(state)).toBe(true);
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});
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});
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@@ -0,0 +1,88 @@
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import type { TypingExerciseState } from "../types";
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import { getKeysUpToLevel } from "./levels";
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const MIN_LETTERS = 8;
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const MAX_LETTERS = 12;
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const INITIAL_INTERVAL = 3000;
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const INTERVAL_DECREASE = 200;
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const INTERVAL_INCREASE = 500;
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const MIN_INTERVAL = 1500;
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const MAX_INTERVAL = 4000;
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const STREAK_THRESHOLD = 2;
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export interface KeyPressResult {
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correct: boolean;
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exerciseComplete: boolean;
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newInterval: number;
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}
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export function generateLetters(level: number): string[] {
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const keys = getKeysUpToLevel(level);
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const letterKeys = keys.filter((k) => k !== " ");
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const count =
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MIN_LETTERS + Math.floor(Math.random() * (MAX_LETTERS - MIN_LETTERS + 1));
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const letters: string[] = [];
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for (let i = 0; i < count; i++) {
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if (keys.includes(" ") && Math.random() < 0.2) {
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letters.push(" ");
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} else {
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letters.push(letterKeys[Math.floor(Math.random() * letterKeys.length)]!);
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}
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}
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return letters;
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}
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export function createExerciseState(level: number): TypingExerciseState {
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return {
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currentLetterIndex: 0,
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letters: generateLetters(level),
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intervalMs: INITIAL_INTERVAL,
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correctStreak: 0,
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totalCorrect: 0,
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totalErrors: 0,
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};
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}
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export function handleKeyPress(
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state: TypingExerciseState,
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pressedKey: string,
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): KeyPressResult {
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const expectedKey = state.letters[state.currentLetterIndex]!;
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const correct = pressedKey.toLowerCase() === expectedKey.toLowerCase();
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if (correct) {
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state.currentLetterIndex++;
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state.totalCorrect++;
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state.correctStreak++;
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if (state.correctStreak >= STREAK_THRESHOLD) {
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state.intervalMs = Math.max(
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MIN_INTERVAL,
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state.intervalMs - INTERVAL_DECREASE,
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);
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state.correctStreak = 0;
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}
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} else {
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state.totalErrors++;
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state.correctStreak = 0;
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state.intervalMs = Math.min(
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MAX_INTERVAL,
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state.intervalMs + INTERVAL_INCREASE,
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);
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}
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return {
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correct,
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exerciseComplete: state.currentLetterIndex >= state.letters.length,
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newInterval: state.intervalMs,
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};
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}
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export function getCurrentLetter(state: TypingExerciseState): string | null {
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if (state.currentLetterIndex >= state.letters.length) return null;
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return state.letters[state.currentLetterIndex]!;
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}
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export function isExerciseComplete(state: TypingExerciseState): boolean {
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return state.currentLetterIndex >= state.letters.length;
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}
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