using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Dinah.Core;

namespace FileManager
{
    /// <summary>Get valid filename. Advanced features incl. parameterized template</summary>
    public class FileNamingTemplate
    {
        /// <summary>Proposed full file path. May contain optional html-styled template tags. Eg: &lt;name&gt;</summary>
        public string Template { get; }

        /// <param name="template">Proposed file name with optional html-styled template tags.</param>
        public FileNamingTemplate(string template) => Template = ArgumentValidator.EnsureNotNullOrWhiteSpace(template, nameof(template));

        /// <summary>Optional step 1: Replace html-styled template tags with parameters. Eg {"name", "Bill Gates"} => /&lt;name&gt;/ => /Bill Gates/</summary>
        public Dictionary<string, object> ParameterReplacements { get; } = new Dictionary<string, object>();

        /// <summary>Convenience method</summary>
        public void AddParameterReplacement(string key, object value)
            // using .Add() instead of "[key] = value" will make unintended overwriting throw exception
            => ParameterReplacements.Add(key, value);

        /// <summary>Optional step 2: Replace all illegal characters with this. Default=<see cref="string.Empty"/></summary>
        public string IllegalCharacterReplacements { get; set; }

        /// <summary>Generate a valid path for this file or directory</summary>
        public LongPath GetFilePath(bool returnFirstExisting = false)
        {
            int lastSlash = Template.LastIndexOf('\\');

            var directoryName = lastSlash >= 0 ? Template[..(lastSlash + 1)] : string.Empty;
            var filename = lastSlash >= 0 ? Template[(lastSlash + 1)..] : Template;

            List<StringBuilder> filenameParts = new();

            var paramReplacements = ParameterReplacements.ToDictionary(r => $"<{formatKey(r.Key)}>", r => formatValue(r.Value));

            //Build the filename in parts, replacing replacement parameters with
            //their values, and storing the parts in a list.
            while(!string.IsNullOrEmpty(filename))
			{
                int openIndex = filename.IndexOf('<');
                int closeIndex = filename.IndexOf('>');

                if (openIndex == 0 && closeIndex > 0)
				{
                    var key = filename[..(closeIndex + 1)];

                    if (paramReplacements.ContainsKey(key))
                        filenameParts.Add(new StringBuilder(paramReplacements[key]));
                    else
                        filenameParts.Add(new StringBuilder(key));

                    filename = filename[(closeIndex + 1)..];
                }
                else if (openIndex > 0 && closeIndex > openIndex)
				{
                    var other = filename[..openIndex];
                    filenameParts.Add(new StringBuilder(other));
                    filename = filename[openIndex..];
                }
                else
				{
                    filenameParts.Add(new StringBuilder(filename));
                    filename = string.Empty;
                }
			}

            //Remove 1 character from the end of the longest filename part until
            //the total filename is less than max filename length
            while(filenameParts.Sum(p => p.Length) > LongPath.MaxFilenameLength)
			{
                int maxLength = filenameParts.Max(p => p.Length);
                var maxEntry = filenameParts.First(p => p.Length == maxLength);

                maxEntry.Remove(maxLength - 1, 1);
            }

            filename = string.Join("", filenameParts);

            return FileUtility.GetValidFilename(directoryName + filename, IllegalCharacterReplacements, returnFirstExisting);
        }

        private static string formatKey(string key)
            => key
            .Replace("<", "")
            .Replace(">", "");

        private string formatValue(object value)
        {
            if (value is null)
                return "";

            // Other illegal characters will be taken care of later. Must take care of slashes now so params can't introduce new folders.
            // Esp important for file templates.
            return value
                .ToString()
                .Replace($"{System.IO.Path.DirectorySeparatorChar}", IllegalCharacterReplacements)
                .Replace($"{System.IO.Path.AltDirectorySeparatorChar}", IllegalCharacterReplacements);
        }
    }
}