using System;
using System.Collections.Generic;
using System.Linq;

namespace Penumbra.Mods;

public partial class ModFolder
{
    public ModFolder? Parent;

    public string FullName
    {
        get
        {
            var parentPath = Parent?.FullName ?? string.Empty;
            return parentPath.Any() ? $"{parentPath}/{Name}" : Name;
        }
    }

    private string _name = string.Empty;

    public string Name
    {
        get => _name;
        set => _name = value.Replace( '/', '\\' );
    }

    public List< ModFolder > SubFolders { get; } = new();
    public List< Mod > Mods { get; } = new();

    public ModFolder( ModFolder parent, string name )
    {
        Parent = parent;
        Name   = name;
    }

    public override string ToString()
        => FullName;

    public int TotalDescendantMods()
        => Mods.Count + SubFolders.Sum( f => f.TotalDescendantMods() );

    public int TotalDescendantFolders()
        => SubFolders.Sum( f => f.TotalDescendantFolders() );

    // Return all descendant mods in the specified order.
    public IEnumerable< Mod > AllMods( bool foldersFirst )
    {
        if( foldersFirst )
        {
            return SubFolders.SelectMany( f => f.AllMods( foldersFirst ) ).Concat( Mods );
        }

        return GetSortedEnumerator().SelectMany( f =>
        {
            if( f is ModFolder folder )
            {
                return folder.AllMods( false );
            }

            return new[] { ( Mod )f };
        } );
    }

    // Return all descendant subfolders.
    public IEnumerable< ModFolder > AllFolders()
        => SubFolders.SelectMany( f => f.AllFolders() ).Prepend( this );

    // Iterate through all descendants in the specified order, returning subfolders as well as mods.
    public IEnumerable< object > GetItems( bool foldersFirst )
        => foldersFirst ? SubFolders.Cast< object >().Concat( Mods ) : GetSortedEnumerator();

    // Find a subfolder by name. Returns true and sets folder to it if it exists.
    public bool FindSubFolder( string name, out ModFolder folder )
    {
        var subFolder = new ModFolder( this, name );
        var idx       = SubFolders.BinarySearch( subFolder, FolderComparer );
        folder = idx >= 0 ? SubFolders[ idx ] : this;
        return idx >= 0;
    }

    // Checks if an equivalent subfolder as folder already exists and returns its index.
    // If it does not exist, inserts folder as a subfolder and returns the new index.
    // Also sets this as folders parent.
    public int FindOrAddSubFolder( ModFolder folder )
    {
        var idx = SubFolders.BinarySearch( folder, FolderComparer );
        if( idx >= 0 )
        {
            return idx;
        }

        idx = ~idx;
        SubFolders.Insert( idx, folder );
        folder.Parent = this;
        return idx;
    }

    // Checks if a subfolder with the given name already exists and returns it and its index.
    // If it does not exists, creates and inserts it and returns the new subfolder and its index.
    public (ModFolder, int) FindOrCreateSubFolder( string name )
    {
        var subFolder = new ModFolder( this, name );
        var idx       = FindOrAddSubFolder( subFolder );
        return ( SubFolders[ idx ], idx );
    }

    // Remove folder as a subfolder if it exists.
    // If this folder is empty afterwards, remove it from its parent.
    public void RemoveSubFolder( ModFolder folder )
    {
        RemoveFolderIgnoreEmpty( folder );
        CheckEmpty();
    }

    // Add the given mod as a child, if it is not already a child.
    // Returns the index of the found or inserted mod.
    public int AddMod( Mod mod )
    {
        var idx = Mods.BinarySearch( mod, ModComparer );
        if( idx >= 0 )
        {
            return idx;
        }

        idx = ~idx;
        Mods.Insert( idx, mod );

        return idx;
    }

    // Remove mod as a child if it exists.
    // If this folder is empty afterwards, remove it from its parent.
    public void RemoveMod( Mod mod )
    {
        RemoveModIgnoreEmpty( mod );
        CheckEmpty();
    }
}

// Internals
public partial class ModFolder
{
    // Create a Root folder without parent.
    internal static ModFolder CreateRoot()
        => new(null!, string.Empty);

    internal class ModFolderComparer : IComparer< ModFolder >
    {
        public StringComparison CompareType = StringComparison.InvariantCultureIgnoreCase;

        // Compare only the direct folder names since this is only used inside an enumeration of subfolders of one folder.
        public int Compare( ModFolder? x, ModFolder? y )
            => ReferenceEquals( x, y )
                ? 0
                : string.Compare( x?.Name ?? string.Empty, y?.Name ?? string.Empty, CompareType );
    }

    internal class ModDataComparer : IComparer< Mod >
    {
        public StringComparison CompareType = StringComparison.InvariantCultureIgnoreCase;

        // Compare only the direct SortOrderNames since this is only used inside an enumeration of direct mod children of one folder.
        // Since mod SortOrderNames do not have to be unique inside a folder, also compare their BasePaths (and thus their identity) if necessary.
        public int Compare( Mod? x, Mod? y )
        {
            if( ReferenceEquals( x, y ) )
            {
                return 0;
            }

            var cmp = string.Compare( x?.Order.SortOrderName, y?.Order.SortOrderName, CompareType );
            if( cmp != 0 )
            {
                return cmp;
            }

            return string.Compare( x?.BasePath.Name, y?.BasePath.Name, StringComparison.InvariantCulture );
        }
    }

    internal static readonly ModFolderComparer FolderComparer = new();
    internal static readonly ModDataComparer   ModComparer    = new();

    // Get an enumerator for actually sorted objects instead of folder-first objects.
    private IEnumerable< object > GetSortedEnumerator()
    {
        var modIdx = 0;
        foreach( var folder in SubFolders )
        {
            var folderString = folder.Name;
            for( ; modIdx < Mods.Count; ++modIdx )
            {
                var mod       = Mods[ modIdx ];
                var modString = mod.Order.SortOrderName;
                if( string.Compare( folderString, modString, StringComparison.InvariantCultureIgnoreCase ) > 0 )
                {
                    yield return mod;
                }
                else
                {
                    break;
                }
            }

            yield return folder;
        }

        for( ; modIdx < Mods.Count; ++modIdx )
        {
            yield return Mods[ modIdx ];
        }
    }

    private void CheckEmpty()
    {
        if( Mods.Count == 0 && SubFolders.Count == 0 )
        {
            Parent?.RemoveSubFolder( this );
        }
    }

    // Remove a subfolder but do not remove this folder from its parent if it is empty afterwards.
    internal void RemoveFolderIgnoreEmpty( ModFolder folder )
    {
        var idx = SubFolders.BinarySearch( folder, FolderComparer );
        if( idx < 0 )
        {
            return;
        }

        SubFolders[ idx ].Parent = null;
        SubFolders.RemoveAt( idx );
    }

    // Remove a mod, but do not remove this folder from its parent if it is empty afterwards.
    internal void RemoveModIgnoreEmpty( Mod mod )
    {
        var idx = Mods.BinarySearch( mod, ModComparer );
        if( idx >= 0 )
        {
            Mods.RemoveAt( idx );
        }
    }
}