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

namespace FastSeekWpf.Core;

[Serializable]
public class CachedEntry
{
    public ulong FileRef { get; set; }
    public ulong ParentRef { get; set; }
    public string Name { get; set; } = string.Empty;
    public FileKind Kind { get; set; }
}

[Serializable]
public class CacheData
{
    public List<CachedEntry> Entries { get; set; } = new();
    public string DriveRoot { get; set; } = string.Empty;
    public List<JournalCheckpoint> Checkpoints { get; set; } = new();
}

// Compact in-memory entry — matches Rust IndexEntry exactly
public struct IndexEntry
{
    public ulong FileRef;
    public ulong ParentRef;
    public uint NameOff;
    public uint NameLowerOff;
    public ushort NameLen;
    public ushort NameLowerLen;
    public byte Flags; // bit 0 = is_dir

    public readonly bool IsDir => (Flags & 1) != 0;
    public readonly FileKind Kind => IsDir ? FileKind.Directory : FileKind.File;
}

// Main index store — matches Rust IndexStore exactly (single drive_root)
public class IndexStore
{
    public List<IndexEntry> Entries = new();
    public List<byte> NameArena = new();        // UTF-8 name bytes
    public List<byte> NameLowerArena = new();   // UTF-8 lowercase name bytes
    public List<(ulong fileRef, int idx)> RefLookup = new(); // sorted by file_ref
    public string DriveRoot = string.Empty;
    public List<JournalCheckpoint> Checkpoints = new();

    public int Count => Entries.Count;

    // Arena accessors — matches Rust name() and name_lower()
    public string Name(IndexEntry e)
    {
        return Encoding.UTF8.GetString(NameArena.ToArray(), (int)e.NameOff, e.NameLen);
    }

    public string NameLower(IndexEntry e)
    {
        return Encoding.UTF8.GetString(NameLowerArena.ToArray(), (int)e.NameLowerOff, e.NameLowerLen);
    }

    // Ref lookup (binary search) — matches Rust lookup_idx()
    public uint? LookupIdx(ulong fileRef)
    {
        int lo = 0, hi = RefLookup.Count - 1;
        while (lo <= hi)
        {
            int mid = (lo + hi) >>> 1;
            var r = RefLookup[mid].fileRef;
            if (r == fileRef) return (uint)RefLookup[mid].idx;
            if (r < fileRef) lo = mid + 1;
            else hi = mid - 1;
        }
        return null;
    }

    private void RebuildRefLookup()
    {
        RefLookup.Clear();
        RefLookup.Capacity = Entries.Count;
        for (int i = 0; i < Entries.Count; i++)
            RefLookup.Add((Entries[i].FileRef, i));
        RefLookup.Sort((a, b) => a.fileRef.CompareTo(b.fileRef));
    }

    // Populate from MFT scan — matches Rust populate_from_scan()
    public void PopulateFromScan(ScanResult scan, string driveRoot)
    {
        this.DriveRoot = driveRoot;
        int count = scan.Records.Count;
        Entries.Capacity = count;
        NameArena.Capacity = count * 30;
        NameLowerArena.Capacity = count * 30;

        foreach (var r in scan.Records)
        {
            int start = (int)r.NameOff;
            int len = r.NameLen;
            var nameChars = new char[len];
            for (int i = 0; i < len; i++)
                nameChars[i] = scan.NameData[start + i];
            string name = new string(nameChars);
            string nameLower = name.ToLowerInvariant();

            uint nOff = (uint)NameArena.Count;
            ushort nLen = (ushort)name.Length;
            NameArena.AddRange(Encoding.UTF8.GetBytes(name));

            uint nlOff = (uint)NameLowerArena.Count;
            ushort nlLen = (ushort)nameLower.Length;
            NameLowerArena.AddRange(Encoding.UTF8.GetBytes(nameLower));

            Entries.Add(new IndexEntry
            {
                FileRef = r.FileRef,
                ParentRef = r.ParentRef,
                NameOff = nOff,
                NameLowerOff = nlOff,
                NameLen = nLen,
                NameLowerLen = nlLen,
                Flags = r.IsDir ? (byte)1 : (byte)0
            });
        }
    }

    // Sort entries by lowercase name and rebuild lookup — matches Rust finalize()
    public void Finalize()
    {
        // Rust uses sort_unstable_by with store_ptr for name_lower comparison.
        // We use a stable sort with proper key extraction.
        var indices = Enumerable.Range(0, Entries.Count).ToArray();
        Array.Sort(indices, (a, b) =>
        {
            var ea = Entries[a];
            var eb = Entries[b];
            return string.CompareOrdinal(
                Encoding.UTF8.GetString(NameLowerArena.ToArray(), (int)ea.NameLowerOff, ea.NameLowerLen),
                Encoding.UTF8.GetString(NameLowerArena.ToArray(), (int)eb.NameLowerOff, eb.NameLowerLen));
        });

        var sorted = new List<IndexEntry>(Entries.Count);
        foreach (var i in indices)
            sorted.Add(Entries[i]);
        Entries = sorted;

        RebuildRefLookup();
        NameArena.TrimExcess();
        NameLowerArena.TrimExcess();
    }

    // Cache serialization — matches Rust to_cache()
    public CacheData ToCache()
    {
        return new CacheData
        {
            Entries = Entries.Select(e => new CachedEntry
            {
                FileRef = e.FileRef,
                ParentRef = e.ParentRef,
                Name = Name(e),
                Kind = e.Kind
            }).ToList(),
            DriveRoot = DriveRoot,
            Checkpoints = new List<JournalCheckpoint>(Checkpoints)
        };
    }

    // Cache deserialization — matches Rust from_cache()
    public static IndexStore FromCache(CacheData cache)
    {
        int count = cache.Entries.Count;
        var store = new IndexStore
        {
            DriveRoot = cache.DriveRoot,
            Checkpoints = new List<JournalCheckpoint>(cache.Checkpoints)
        };
        store.Entries.Capacity = count;
        store.NameArena.Capacity = count * 30;
        store.NameLowerArena.Capacity = count * 30;

        foreach (var c in cache.Entries)
        {
            string nameLower = c.Name.ToLowerInvariant();

            uint nOff = (uint)store.NameArena.Count;
            ushort nLen = (ushort)c.Name.Length;
            store.NameArena.AddRange(Encoding.UTF8.GetBytes(c.Name));

            uint nlOff = (uint)store.NameLowerArena.Count;
            ushort nlLen = (ushort)nameLower.Length;
            store.NameLowerArena.AddRange(Encoding.UTF8.GetBytes(nameLower));

            store.Entries.Add(new IndexEntry
            {
                FileRef = c.FileRef,
                ParentRef = c.ParentRef,
                NameOff = nOff,
                NameLowerOff = nlOff,
                NameLen = nLen,
                NameLowerLen = nlLen,
                Flags = c.Kind == FileKind.Directory ? (byte)1 : (byte)0
            });
        }

        store.RebuildRefLookup();
        store.NameArena.TrimExcess();
        store.NameLowerArena.TrimExcess();
        return store;
    }

    // Live mutations — match Rust insert(), remove(), rename(), apply_move()

    public void Insert(FileRecord record)
    {
        string nameLower = record.Name.ToLowerInvariant();

        uint nOff = (uint)NameArena.Count;
        ushort nLen = (ushort)record.Name.Length;
        NameArena.AddRange(Encoding.UTF8.GetBytes(record.Name));

        uint nlOff = (uint)NameLowerArena.Count;
        ushort nlLen = (ushort)nameLower.Length;
        NameLowerArena.AddRange(Encoding.UTF8.GetBytes(nameLower));

        var entry = new IndexEntry
        {
            FileRef = record.FileRef,
            ParentRef = record.ParentRef,
            NameOff = nOff,
            NameLowerOff = nlOff,
            NameLen = nLen,
            NameLowerLen = nlLen,
            Flags = record.Kind == FileKind.Directory ? (byte)1 : (byte)0
        };

        // Rust: partition_point by name_lower comparison
        int pos = 0;
        string key = nameLower;
        for (; pos < Entries.Count; pos++)
        {
            var e = Entries[pos];
            string cmp = Encoding.UTF8.GetString(NameLowerArena.ToArray(), (int)e.NameLowerOff, e.NameLowerLen);
            if (string.CompareOrdinal(key, cmp) < 0)
                break;
        }
        Entries.Insert(pos, entry);
        RebuildRefLookup();
    }

    public void Remove(ulong fileRef)
    {
        // Name bytes left as dead space in arena (negligible for rare deletes)
        Entries.RemoveAll(e => e.FileRef == fileRef);
        RebuildRefLookup();
    }

    public void Rename(ulong oldRef, FileRecord newRecord)
    {
        Remove(oldRef);
        Insert(newRecord);
    }

    public void ApplyMove(ulong fileRef, ulong newParentRef, string name, FileKind kind)
    {
        Remove(fileRef);
        Insert(new FileRecord
        {
            FileRef = fileRef,
            ParentRef = newParentRef,
            Name = name,
            Kind = kind
        });
    }

    // Build path by walking parent chain — matches Rust build_path()
    public string BuildPath(ulong fileRef)
    {
        var components = new List<string>(16);
        ulong current = fileRef;

        for (int i = 0; i < 64; i++)
        {
            var idx = LookupIdx(current);
            if (idx == null) break;

            var entry = Entries[(int)idx];
            components.Add(Name(entry));
            if (entry.ParentRef == current) break;
            current = entry.ParentRef;
        }

        components.Reverse();
        var sb = new StringBuilder(DriveRoot);
        foreach (var comp in components)
        {
            if (sb.Length > 0 && sb[sb.Length - 1] != '\\' && sb[sb.Length - 1] != '/')
                sb.Append('\\');
            sb.Append(comp);
        }
        return sb.ToString();
    }
}