using System;
using System.Collections.Generic;
using System.Linq;
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 && phrases[index].StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
                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 wordCount = Math.Min(count, GetCountByPrefix(phrases, prefix));
            var topByPrefix = new string[wordCount];
            var leftBorder = LeftBorderTask.GetLeftBorderIndex(phrases, prefix, -1, phrases.Count);
            for (var i = 0; i < wordCount; i++)
            {
                topByPrefix[i] = phrases[leftBorder + 1 + i];
            }
            return topByPrefix;
        }

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

    [TestFixture]
    public class AutocompleteTests
    {
        [Test]
        public void TopByPrefix_IsEmpty_WhenNoPhrases()
        {
            // ...
            //CollectionAssert.IsEmpty(actualTopWords);
        }

        // ...

        [Test]
        public void CountByPrefix_IsTotalCount_WhenEmptyPrefix()
        {
            // ...
            //Assert.AreEqual(expectedCount, actualCount);
        }

        // ...
    }
}