using System;
using System.Collections.Generic;
using NUnit.Framework;

namespace Autocomplete
{
    internal class AutocompleteTask
    {
        public static string FindFirstByPrefix(IReadOnlyList<string> phrases, string prefix)
        {
            var index = LeftBorderTask.GetLeftBorderIndex(phrases, prefix, -1, phrases.Count) + 1;
            if (index < phrases.Count)
                return phrases[index];

            return null;
        }

        public static string[] GetTopByPrefix(IReadOnlyList<string> phrases, string prefix, int count)
        {
            if (FindFirstByPrefix(phrases, prefix) == null)
            {
                return new string[0];
            }
            var topByPrefix = new List<string>();
            var leftBorder = LeftBorderTask.GetLeftBorderIndex(phrases, prefix, -1, phrases.Count);
            var wordCount = 0;
            while (wordCount < count
                   && leftBorder + wordCount + 1 < phrases.Count
                   && phrases[leftBorder + wordCount + 1].StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
            {
                topByPrefix.Add(phrases[leftBorder + wordCount + 1]);
                wordCount++;
            }
            return topByPrefix.ToArray();
        }

        public static int GetCountByPrefix(IReadOnlyList<string> phrases, string prefix)
        {
            var rightBorder = RightBorderTask.GetRightBorderIndex(phrases, prefix, -1, phrases.Count);
            var leftBorder = LeftBorderTask.GetLeftBorderIndex(phrases, prefix, -1, phrases.Count);
            return rightBorder - leftBorder - 1;
        }
    }

    [TestFixture]
    public class AutocompleteTests
    {
        [Test]
        public void TopByPrefix_IsEmpty_WhenNoPhrases()
        {
            var receivedTopWords = AutocompleteTask.GetTopByPrefix(new string[] { }, "a", 10);
            CollectionAssert.IsEmpty(receivedTopWords);
        }

        [Test]
        public void TopByPrefix_IsNoEmpty_WhenExistPhrases()
        {
            var receivedTopWords = AutocompleteTask.GetTopByPrefix(new string[] { "a", "ab", "abc", "abcd" }, "c", 10);
            CollectionAssert.IsEmpty(receivedTopWords);
        }

        [Test]
        public void CountByPrefix_IsTotalCount_WhenEmptyPrefix()
        {
            var receivedlCount = AutocompleteTask.GetCountByPrefix(new string[] { "a", "ab", "abc", "abcd" }, "");
            Assert.AreEqual(4, receivedlCount);
        }

        [Test]
        public void CountByPrefix_IsTotalCount_WhenNoEmptyPrefix()
        {
            var receivedlCount = AutocompleteTask.GetCountByPrefix(new string[] { "a", "bb", "bbc", "abcd" }, "b");
            Assert.AreEqual(2, receivedlCount);
        }

        [Test]
        public void TopByPrefix_OneRecommendedWord()
        {
            var receivedlCount = AutocompleteTask.GetTopByPrefix(new string[] { "abc", "abcd", "adb" }, "adb", 10);
            CollectionAssert.AreEqual(new string[] { "adb" }, receivedlCount);
        }

        [Test]
        public void TopByPrefix_IsEmpty()
        {
            var receivedTopWords = AutocompleteTask.GetTopByPrefix(new string[] { "abc", "abcd", "adb" }, "d", 10);
            CollectionAssert.IsEmpty(receivedTopWords);
        }
    }
}