namespace Terminal.Gui;

/// <summary>
///     Navigates a collection of items using keystrokes. The keystrokes are used to build a search string. The
///     <see cref="SearchString"/> is used to find the next item in the collection that matches the search string when
///     <see cref="GetNextMatchingItem(int, char)"/> is called.
///     <para>
///         If the user types keystrokes that can't be found in the collection, the search string is cleared and the next
///         item is found that starts with the last keystroke.
///     </para>
///     <para>If the user pauses keystrokes for a short time (see <see cref="TypingDelay"/>), the search string is cleared.</para>
/// </summary>
public abstract class CollectionNavigatorBase
{
    private DateTime _lastKeystroke = DateTime.Now;
    private string _searchString = "";

    /// <summary>The comparer function to use when searching the collection.</summary>
    public StringComparer Comparer { get; set; } = StringComparer.InvariantCultureIgnoreCase;

    /// <summary>
    ///     Gets the current search string. This includes the set of keystrokes that have been pressed since the last
    ///     unsuccessful match or after <see cref="TypingDelay"/>) milliseconds. Useful for debugging.
    /// </summary>
    public string SearchString
    {
        get => _searchString;
        private set
        {
            _searchString = value;
            OnSearchStringChanged (new KeystrokeNavigatorEventArgs (value));
        }
    }

    /// <summary>
    ///     Gets or sets the number of milliseconds to delay before clearing the search string. The delay is reset on each
    ///     call to <see cref="GetNextMatchingItem(int, char)"/>. The default is 500ms.
    /// </summary>
    public int TypingDelay { get; set; } = 500;

    /// <summary>
    ///     Gets the index of the next item in the collection that matches the current <see cref="SearchString"/> plus the
    ///     provided character (typically from a key press).
    /// </summary>
    /// <param name="currentIndex">The index in the collection to start the search from.</param>
    /// <param name="keyStruck">The character of the key the user pressed.</param>
    /// <returns>
    ///     The index of the item that matches what the user has typed. Returns <see langword="-1"/> if no item in the
    ///     collection matched.
    /// </returns>
    public int GetNextMatchingItem (int currentIndex, char keyStruck)
    {
        if (!char.IsControl (keyStruck))
        {
            // maybe user pressed 'd' and now presses 'd' again.
            // a candidate search is things that begin with "dd"
            // but if we find none then we must fallback on cycling
            // d instead and discard the candidate state
            var candidateState = "";

            // is it a second or third (etc) keystroke within a short time
            if (SearchString.Length > 0 && DateTime.Now - _lastKeystroke < TimeSpan.FromMilliseconds (TypingDelay))
            {
                // "dd" is a candidate
                candidateState = SearchString + keyStruck;
            }
            else
            {
                // its a fresh keystroke after some time
                // or its first ever key press
                SearchString = new string (keyStruck, 1);
            }

            int idxCandidate = GetNextMatchingItem (
                                                    currentIndex,
                                                    candidateState,

                                                    // prefer not to move if there are multiple characters e.g. "ca" + 'r' should stay on "car" and not jump to "cart"
                                                    candidateState.Length > 1
                                                   );

            if (idxCandidate != -1)
            {
                // found "dd" so candidate search string is accepted
                _lastKeystroke = DateTime.Now;
                SearchString = candidateState;

                return idxCandidate;
            }

            //// nothing matches "dd" so discard it as a candidate
            //// and just cycle "d" instead
            _lastKeystroke = DateTime.Now;
            idxCandidate = GetNextMatchingItem (currentIndex, candidateState);

            // if a match wasn't found, the user typed a 'wrong' key in their search ("can" + 'z'
            // instead of "can" + 'd').
            if (SearchString.Length > 1 && idxCandidate == -1)
            {
                // ignore it since we're still within the typing delay
                // don't add it to SearchString either
                return currentIndex;
            }

            // if no changes to current state manifested
            if (idxCandidate == currentIndex || idxCandidate == -1)
            {
                // clear history and treat as a fresh letter
                ClearSearchString ();

                // match on the fresh letter alone
                SearchString = new string (keyStruck, 1);
                idxCandidate = GetNextMatchingItem (currentIndex, SearchString);

                return idxCandidate == -1 ? currentIndex : idxCandidate;
            }

            // Found another "d" or just leave index as it was
            return idxCandidate;
        }

        // clear state because keypress was a control char
        ClearSearchString ();

        // control char indicates no selection
        return -1;
    }

    /// <summary>
    ///     Returns true if <paramref name="a"/> is a searchable key (e.g. letters, numbers, etc) that are valid to pass
    ///     to this class for search filtering.
    /// </summary>
    /// <param name="a"></param>
    /// <returns></returns>
    public static bool IsCompatibleKey (Key a)
    {
        Rune rune = a.AsRune;

        return rune != default (Rune) && !Rune.IsControl (rune);
    }

    /// <summary>
    ///     Invoked when the <see cref="SearchString"/> changes. Useful for debugging. Invokes the
    ///     <see cref="SearchStringChanged"/> event.
    /// </summary>
    /// <param name="e"></param>
    public virtual void OnSearchStringChanged (KeystrokeNavigatorEventArgs e) { SearchStringChanged?.Invoke (this, e); }

    /// <summary>This event is invoked when <see cref="SearchString"/>  changes. Useful for debugging.</summary>
    public event EventHandler<KeystrokeNavigatorEventArgs> SearchStringChanged;

    /// <summary>Returns the collection being navigated element at <paramref name="idx"/>.</summary>
    /// <returns></returns>
    protected abstract object ElementAt (int idx);

    /// <summary>Return the number of elements in the collection</summary>
    protected abstract int GetCollectionLength ();

    /// <summary>Gets the index of the next item in the collection that matches <paramref name="search"/>.</summary>
    /// <param name="currentIndex">The index in the collection to start the search from.</param>
    /// <param name="search">The search string to use.</param>
    /// <param name="minimizeMovement">
    ///     Set to <see langword="true"/> to stop the search on the first match if there are
    ///     multiple matches for <paramref name="search"/>. e.g. "ca" + 'r' should stay on "car" and not jump to "cart". If
    ///     <see langword="false"/> (the default), the next matching item will be returned, even if it is above in the
    ///     collection.
    /// </param>
    /// <returns>The index of the next matching item or <see langword="-1"/> if no match was found.</returns>
    internal int GetNextMatchingItem (int currentIndex, string search, bool minimizeMovement = false)
    {
        if (string.IsNullOrEmpty (search))
        {
            return -1;
        }

        int collectionLength = GetCollectionLength ();

        if (currentIndex != -1 && currentIndex < collectionLength && IsMatch (search, ElementAt (currentIndex)))
        {
            // we are already at a match
            if (minimizeMovement)
            {
                // if we would rather not jump around (e.g. user is typing lots of text to get this match)
                return currentIndex;
            }

            for (var i = 1; i < collectionLength; i++)
            {
                //circular
                int idxCandidate = (i + currentIndex) % collectionLength;

                if (IsMatch (search, ElementAt (idxCandidate)))
                {
                    return idxCandidate;
                }
            }

            // nothing else starts with the search term
            return currentIndex;
        }

        // search terms no longer match the current selection or there is none
        for (var i = 0; i < collectionLength; i++)
        {
            if (IsMatch (search, ElementAt (i)))
            {
                return i;
            }
        }

        // Nothing matches
        return -1;
    }

    private void ClearSearchString ()
    {
        SearchString = "";
        _lastKeystroke = DateTime.Now;
    }

    private bool IsMatch (string search, object value) { return value?.ToString ().StartsWith (search, StringComparison.InvariantCultureIgnoreCase) ?? false; }
}
