using System.Text;
using System.Text.Json;

namespace DevJsonDB.IO;

public class LocalStore<T> : IStore<T>
{
    private static Encoding DefaultEncoding = Encoding.UTF8;
    private string filePath;
    private List<T> items;
    private bool autoCommit;

    public LocalStore(string filePath, bool autoCommit)
    {
        this.filePath = filePath;
        this.items = new List<T>();
        this.autoCommit = autoCommit;

        this.InitDatabase();
    }

    public void Dispose()
    {
        this.Commit();
    }

    public void Commit()
    {
        try
        {
            using (FileStream fs = new FileStream(this.filePath, FileMode.OpenOrCreate))
            using (StreamWriter writer = new StreamWriter(fs, DefaultEncoding))
            {
                fs.Seek(0, SeekOrigin.Begin);
                fs.SetLength(0);

                for (int i = 0 ; i < items.Count; i++)
                {
                    T item = items[i];
                    string json = JsonSerializer.Serialize<T>(item);
                    writer.Write(json);
                    if (i != items.Count - 1)
                    {
                        writer.Write("\n");
                    }
                }
            }
        }
        catch (Exception ex)
        {
            throw new JsonDBException(ex.Message, ex);
        }
    }

    public bool Add(T item)
    {
        if (this.items.Contains(item))
        {
            return false;
        }

        this.items.Add(item);
        this.AutoCommit(FastMergeType.Add);
        return true;
    }

    public bool Has(T item)
    {
        return this.items.Contains(item);
    }

    public bool Remove(T item)
    {
        bool ret = this.items.Remove(item);
        this.AutoCommit(FastMergeType.Remove);
        return ret;
    }

    public IEnumerable<T> GetValues()
    {
        return this.items.ToList();
    }

    private void AutoCommit(FastMergeType mergeType)
    {
        if (!this.autoCommit) return;

        try
        {
            // Fast-Merge
            switch (mergeType)
            {
                case FastMergeType.Add:
                {
                    using (FileStream fs = new FileStream(this.filePath, FileMode.Append))
                    using (StreamWriter writer = new StreamWriter(fs, DefaultEncoding))
                    {
                        T lastItem = this.items.ElementAt(this.items.Count() - 1);
                        string json = JsonSerializer.Serialize<T>(lastItem);
                        if (fs.Length > 0)
                        {
                            writer.Write("\n");
                        }
                        writer.Write(json);
                    }
                    break;
                }
                case FastMergeType.Remove:
                {
                    this.Commit();
                    break;
                }
            }
        }
        catch (Exception ex)
        {
            throw new JsonDBException(ex.Message, ex);
        }
    }

    private void InitDatabase()
    {
        try
        {
            using (FileStream fs = new FileStream(this.filePath, FileMode.OpenOrCreate))
            using (StreamReader reader = new StreamReader(fs, DefaultEncoding))
            {
                string? line = null;
                while ((line = reader.ReadLine()) != null)
                {
                    T? value = JsonSerializer.Deserialize<T>(line);
                    if (value is object)
                    {
                        this.items.Add(value);
                    }
                }
            }
        }
        catch (Exception ex)
        {
            throw new JsonDBException(ex.Message, ex);
        }
    }
}