Futonizer/Services/FileNameHelper.cs

using System.IO;
using System.Text.RegularExpressions;

namespace Futonizer.Services;

/// <summary>
/// Pure static helpers for computing the final output filename from a source
/// file path, applying release-tag prefixing and show-name injection.
/// </summary>
public static class FileNameHelper
{
    // Folder suffix release tag:  "Show Name-TTGA"  →  tag = "TTGA"
    // All-uppercase, 2-8 chars, at end of folder name.
    private static readonly Regex FolderSuffixTagRegex =
        new(@"-([A-Z][A-Z0-9]{1,7})$", RegexOptions.Compiled);

    // File suffix release tag:  "…HEVC-DemiHuman"  →  tag = "DemiHuman"
    // Mixed case, 3-21 chars (no dots/spaces), at end of filename stem.
    // Min 3 chars avoids false-positives like "-v2" or "-HD".
    private static readonly Regex FileSuffixTagRegex =
        new(@"-([A-Za-z][A-Za-z0-9]{2,20})$", RegexOptions.Compiled);

    // Prefix release tag:  "[KAA] Show Name"  →  tag = "KAA"
    private static readonly Regex PrefixTagRegex =
        new(@"^\[(.+?)\]", RegexOptions.Compiled);

    // Episode-only filename (no tag prefix): starts with S01E01, S1E1, etc.
    private static readonly Regex EpisodeOnlyRegex =
        new(@"^S\d+E\d+", RegexOptions.IgnoreCase | RegexOptions.Compiled);

    // Episode start after a tag prefix is stripped: plain number OR S01E01 style.
    // e.g. "03 - Deus Vult ..." or "S01E01-Deep Blue"
    private static readonly Regex EpisodeStartRegex =
        new(@"^(\d+|S\d+E\d+)", RegexOptions.IgnoreCase | RegexOptions.Compiled);

    // Individual metadata-token patterns used to find where the show name ends
    // inside a folder name.
    private static readonly Regex[] MetadataPatterns =
    [
        new(@"^S\d+$",                                                              RegexOptions.IgnoreCase | RegexOptions.Compiled), // S01
        new(@"^S\d+E\d+",                                                          RegexOptions.IgnoreCase | RegexOptions.Compiled), // S01E01...
        new(@"^E[Pp]?\d+$",                                                        RegexOptions.IgnoreCase | RegexOptions.Compiled), // E01, EP01
        new(@"^\d{3,4}[pP]$",                                                      RegexOptions.Compiled),                           // 1080p, 720p
        new(@"^(4K|UHD|2160p)$",                                                   RegexOptions.IgnoreCase | RegexOptions.Compiled), // 4K, UHD
        new(@"^(BD|BluRay|Blu-Ray|WEB|WEB-DL|WEBRip|HDTV|AMZN|NF|DSNP|HULU|MAX)$",RegexOptions.IgnoreCase | RegexOptions.Compiled), // sources
        new(@"^(Remux|Encode)$",                                                   RegexOptions.IgnoreCase | RegexOptions.Compiled), // processing
        new(@"^(HEVC|AVC|x264|x265|H\.?264|H\.?265|VP9)$",                        RegexOptions.IgnoreCase | RegexOptions.Compiled), // video codecs
        new(@"^(FLAC|AAC|DTS|TrueHD|Atmos|AC3|EAC3|Opus|MP3)$",                  RegexOptions.IgnoreCase | RegexOptions.Compiled), // audio codecs
        new(@"^(HDR|SDR|10bit|8bit|HDR10|DV|DoVi)$",                              RegexOptions.IgnoreCase | RegexOptions.Compiled), // HDR / bit-depth
    ];

    // -------------------------------------------------------------------------

    /// <summary>
    /// Computes the final output filename for a given source file path, applying
    /// (in order):
    /// <list type="number">
    ///   <item>Filename suffix tag extraction — a trailing <c>-GroupName</c> on
    ///         the filename stem is stripped and promoted to a bracket prefix.
    ///         Takes priority over any folder-derived tag.</item>
    ///   <item>Show-name injection — if the (now tag-free) filename starts with
    ///         an episode code (e.g. S01E01) the show name is derived from the
    ///         parent folder and prepended.</item>
    ///   <item>Release-tag prefix — a <c>[TAG]</c> bracket prefix, sourced from
    ///         the filename suffix, the folder suffix, or the folder prefix,
    ///         in that priority order.</item>
    /// </list>
    /// Returns the original filename unchanged when no transformations apply.
    /// </summary>
    public static string ComputeOutputFileName(string sourceFilePath)
    {
        string fileName    = Path.GetFileName(sourceFilePath);
        string ext         = Path.GetExtension(fileName);
        string stemNoExt   = Path.GetFileNameWithoutExtension(fileName);
        string? folder     = Path.GetDirectoryName(sourceFilePath);
        string folderName  = string.IsNullOrEmpty(folder) ? "" : (Path.GetFileName(folder) ?? "");

        // 1. Extract in-filename suffix tag and remove it from the stem.
        //    e.g. "...HEVC-DemiHuman" → tag="DemiHuman", stem="...HEVC"
        string? fileTag = null;
        var fileSuffixMatch = FileSuffixTagRegex.Match(stemNoExt);
        if (fileSuffixMatch.Success)
        {
            fileTag  = fileSuffixMatch.Groups[1].Value;
            stemNoExt = stemNoExt[..fileSuffixMatch.Index];
            fileName  = stemNoExt + ext;
        }

        // 2. Determine the release tag: filename suffix > folder tag.
        string? tag = fileTag;
        if (string.IsNullOrEmpty(tag) && !string.IsNullOrEmpty(folderName))
            tag = ExtractReleaseTag(folderName);

        // 3. Check for episode-only patterns and inject show name if needed.
        if (!string.IsNullOrEmpty(folderName))
        {
            // Pattern A: untagged stem starts with S01E01 (e.g. "S01E01-Deep Blue.mkv")
            if (EpisodeOnlyRegex.IsMatch(stemNoExt))
            {
                string showName = ExtractShowName(folderName);
                if (!string.IsNullOrEmpty(showName))
                    fileName = showName + " " + fileName;
            }
            // Pattern B: file already carries [TAG] but episode number follows directly.
            //   e.g. "[WBDP] 03 - Deus Vult ..." → insert show name after the tag.
            else if (!string.IsNullOrEmpty(tag))
            {
                string tagPfx = $"[{tag}] ";
                if (stemNoExt.StartsWith(tagPfx, StringComparison.OrdinalIgnoreCase))
                {
                    string afterTag = stemNoExt[tagPfx.Length..];
                    if (EpisodeStartRegex.IsMatch(afterTag))
                    {
                        string showName = ExtractShowName(folderName);
                        if (!string.IsNullOrEmpty(showName))
                        {
                            // Strip the tag, inject show name; tag is re-prepended in step 4.
                            fileName = showName + " " + fileName[tagPfx.Length..];
                        }
                    }
                }
            }
        }

        // 4. Prepend release tag if not already present.
        if (!string.IsNullOrEmpty(tag))
        {
            string tagPrefix = $"[{tag}]";
            if (!fileName.StartsWith(tagPrefix, StringComparison.OrdinalIgnoreCase))
                fileName = tagPrefix + " " + fileName;
        }

        return fileName;
    }

    /// <summary>
    /// Extracts the release tag string (without brackets) from a folder name.
    /// Suffix pattern (<c>-TAG</c>) takes priority over prefix pattern
    /// (<c>[TAG]</c>).  Returns <c>null</c> when neither is present.
    /// </summary>
    public static string? ExtractReleaseTag(string folderName)
    {
        var suffixMatch = FolderSuffixTagRegex.Match(folderName);
        if (suffixMatch.Success) return suffixMatch.Groups[1].Value;

        var prefixMatch = PrefixTagRegex.Match(folderName);
        if (prefixMatch.Success) return prefixMatch.Groups[1].Value;

        return null;
    }

    /// <summary>
    /// Derives the show name from a folder name by stripping any release tag
    /// (prefix or suffix) and then:
    /// <list type="bullet">
    ///   <item>If the remainder contains brackets (e.g. <c>[BD][1080p-FLAC]</c>),
    ///         returns the text that precedes the first bracket.</item>
    ///   <item>Otherwise splits on spaces and collects words up to the first
    ///         recognised metadata token (season, quality, source, codec, etc.).</item>
    /// </list>
    /// </summary>
    public static string ExtractShowName(string folderName)
    {
        // Strip release tags first.
        string name = FolderSuffixTagRegex.Replace(folderName, "").Trim();
        name = PrefixTagRegex.Replace(name, "").Trim();

        // Nothing left, or what remains immediately starts with a bracket — no show name.
        if (string.IsNullOrEmpty(name) || name[0] == '[') return string.Empty;

        // Bracket-style metadata: "The Saga of Tanya the Evil [BD][1080p-FLAC][HEVC]"
        int bracketIdx = name.IndexOf('[');
        if (bracketIdx > 0)
            return name[..bracketIdx].Trim();

        // Space-separated metadata: "Grand Blue Dreaming S01 1080p BD Remux FLAC"
        var words     = name.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        var showWords = new List<string>();
        foreach (var word in words)
        {
            if (IsMetadataToken(word)) break;
            showWords.Add(word);
        }

        return string.Join(" ", showWords).Trim();
    }

    private static bool IsMetadataToken(string token)
    {
        foreach (var pattern in MetadataPatterns)
            if (pattern.IsMatch(token)) return true;
        return false;
    }
}