#nullable enable

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Text.Json.Serialization;

namespace imm;

/// <summary>
/// Represents the base interface for versioned, immutable objects.
/// Provides access to metadata and potentially the previous version.
/// </summary>
public interface Obj
{
    /// <summary>
    /// Gets the base metadata associated with this version.
    /// </summary>
    Metadata_Versioned Meta { get; }

    /// <summary>
    /// Gets the previous version as a base object, if available.
    /// Returns null if this is the first version or if history is not tracked.
    /// </summary>
    Obj? Old { get; }

    /// <summary>
    /// Creates a new version without functional change.
    /// Returns the new version as an Obj.
    /// </summary>
    Obj Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 );
}


/// <summary>
/// Obj delegate for change notifications.
/// </summary>
public delegate void ChangeDelegate<T>( T? oldVersion, T newVersion );


/// <summary>
/// Represents a generic interface for immutable objects,
/// providing access to basic processing functions and change notifications.
/// </summary>
public interface Obj<T> : Obj where T : Obj<T>
{
    /// <summary>
    /// Gets the change delegate associated with this object.
    /// </summary>
    [JsonIgnore]
    ChangeDelegate<T> OnChange { get; set; }

    /// <summary>
    /// Applies a transformation and creates a new version using basic processing.
    /// </summary>
    T Process(
        Func<T, T> fn,
        string reason = "Processed",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0,
        [CallerArgumentExpression( "fn" )] string expStr = "" );


    /// <summary>
    /// Creates a new version without a functional change using basic processing.
    /// Uses 'new' to provide a type-safe return.
    /// </summary>
    new T Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 );
}


/*
static public class ObjExtensions
{
    /// <summary>
    /// Creates a new version of the object with the specified reason.
    /// </summary>
    public static T Record<T>( this T obj, string reason = "Recorded" ) where T : Obj
    {
        if( obj is Recorded<T> recorded )
        {
            return recorded.Record( reason );
        }
        else if( obj is Versioned<T> versioned )
        {
            return versioned.Record( reason );
        }
        else
        {
            // Dont care

            return obj;
        }
    }
}
*/

// --- Metadata Hierarchy ---

public interface VersionedMeta
{
    public uint Version { get; }
    public string Reason { get; }
}


/// <summary>
/// Obj metadata for version tracking.
/// </summary>
public record Metadata_Versioned
{
    public uint Version { get; init; } = 1;
    public string Reason { get; init; } = "Created";
}


public interface RecordedMeta : VersionedMeta
{
    public string MemberName { get; }
    public string FilePath { get; }
    public int LineNumber { get; }
    public string Expression { get; }
}


/// <summary>
/// Metadata for version and recording (debug/caller info, history).
/// </summary>
public record Metadata_Recorded : Metadata_Versioned, RecordedMeta
{
    internal object? OldObject { get; init; } = null;
    public string MemberName { get; init; } = "";
    public string FilePath { get; init; } = "";
    public int LineNumber { get; init; } = 0;
    public string Expression { get; init; } = "";
}

public interface TimedMeta : RecordedMeta
{
    public DateTime CreatedAt { get; }
    public DateTime TouchedAt { get; }
}


/// <summary>
/// Metadata for version, recording, and timing.
/// </summary>
public record Metadata_Timed : Metadata_Recorded, TimedMeta
{
    public DateTime CreatedAt { get; init; } = DateTime.UtcNow;
    public DateTime TouchedAt { get; init; } = DateTime.UtcNow;
}

// --- Record Hierarchy ---

/// <summary>
/// Level 1: Basic versioning. Implements Obj<T>.
/// </summary>
public record class Versioned<T> : Obj<T> where T : Versioned<T>
{
    public Metadata_Versioned Meta { get; init; } = new();

    [DebuggerBrowsable( DebuggerBrowsableState.Never )]
    [JsonIgnore]
    public ChangeDelegate<T> OnChange { get; set; } = ( o, n ) => { };

    public virtual Obj? Old => null;

    Metadata_Versioned Obj.Meta => this.Meta;
    [JsonIgnore]
    Obj? Obj.Old => this.Old;

    public Versioned() { }
    protected Versioned( Versioned<T> original )
    {
        OnChange = original.OnChange;
        Meta = original.Meta;
    }

    public virtual T Process(
        Func<T, T> fn,
        string reason = "Processed",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0,
        [CallerArgumentExpression( "fn" )] string expStr = "" )
    {
        var current = (T)this;
        var next = fn( current );

        if( ReferenceEquals( current, next ) )
            return current;

        var newVersion = next with
        {
            Meta = new Metadata_Versioned { /*...*/ },
            OnChange = current.OnChange
        };
        newVersion.OnChange( current, newVersion );
        return newVersion;
    }

    /// <summary>
    /// Basic Record. Made virtual. Implements Obj<T>.Record.
    /// </summary>
    public virtual T Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 ) => Process( t => t, reason, dbgName, dbgPath, dbgLine );

    /// <summary>
    /// Implements Obj.Record by calling the virtual T Record.
    /// </summary>
    Obj Obj.Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 ) => this.Record( reason, dbgName, dbgPath, dbgLine );


}

/// <summary>
/// Level 2: Adds history and caller info.
/// </summary>
public record class Recorded<T> : Versioned<T> where T : Recorded<T>
{
    new public Metadata_Recorded Meta { get; init; } = new();

    [JsonIgnore]
    new public T? Old => Meta.OldObject as T;

    //public override Obj? Old => this.Old;
    //Metadata_Versioned Obj.Meta => this.Meta;

    public Recorded() { }
    protected Recorded( Recorded<T> original ) : base( original ) { Meta = original.Meta; }

    public override T Process(
        Func<T, T> fn,
        string reason = "",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0,
        [CallerArgumentExpression( "fn" )] string expStr = "" )
    {
        var current = (T)this;
        var next = fn( current );

        if( ReferenceEquals( current, next ) )
            return current;

        var newMeta = current.Meta with {
            Version = current.Meta.Version + 1,
            Reason = reason,
            MemberName = dbgName,
            FilePath = dbgPath,
            LineNumber = dbgLine,
            Expression = expStr,
            OldObject = current,
        };

        var newVersion = next with { Meta = newMeta, OnChange = current.OnChange };
        newVersion.OnChange( current, newVersion );
        return newVersion;
    }

    public new T Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 )
    {
        return Process( t => t, reason, dbgName, dbgPath, dbgLine );
    }

}

/// <summary>
/// Level 3: Adds timestamps.
/// </summary>
public record class Timed<T> : Recorded<T> where T : Timed<T>
{
    new public Metadata_Timed Meta { get; init; } = new();
    //Metadata_Versioned Obj.Meta => this.Meta;
    public TimeSpan SinceLastTouch => Meta.TouchedAt - ( Old?.Meta as Metadata_Timed )?.TouchedAt ?? TimeSpan.Zero;
    public TimeSpan TotalAge => Meta.TouchedAt - Meta.CreatedAt;

    public Timed() { }
    protected Timed( Timed<T> original ) : base( original ) { Meta = original.Meta; }


    public override T Process(
        Func<T, T> fn,
        string reason = "",
        [CallerMemberName] string dbgMethod = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0,
        [CallerArgumentExpression( "fn" )] string dbgExpStr = "" )
    {
        var current = (T)this;
        var next = fn( current );

        if( ReferenceEquals( current, next ) )
            return current;

        /*
        var newMeta = new Metadata_Timed
        {
            Version = current.Meta.Version + 1,
            Reason = reason,
            MemberName = dbgMethod,
            FilePath = dbgPath,
            LineNumber = dbgLine,
            Expression = dbgExpression,
            OldObject = current,
            CreatedAt = current.Meta.CreatedAt,
            TouchedAt = DateTime.UtcNow
        };
        */

        var newMeta = current.Meta with
        {
            Version = current.Meta.Version + 1,
            Reason = reason,
            MemberName = dbgMethod,
            FilePath = dbgPath,
            LineNumber = dbgLine,
            Expression = dbgExpStr,
            OldObject = current,
            TouchedAt = DateTime.UtcNow
        };

        // Testing: Shouldnt need the OnChange
        var newVersion = next with { Meta = newMeta };
        newVersion.OnChange( current, newVersion );
        return newVersion;
    }

    public new T Record(
        string reason = "Recorded",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0 )
    {
        return Process( t => t, reason, dbgName, dbgPath, dbgLine );
    }
}

/*
public static class TimedExt
{
    public static T Process<T>(
        ref T obj,
        Func<T, T> fn,
        string reason = "",
        [CallerMemberName] string dbgName = "",
        [CallerFilePath] string dbgPath = "",
        [CallerLineNumber] int dbgLine = 0,
        [CallerArgumentExpression( "fn" )] string dbgExpression = ""
    ) where T : imm.Timed<T>
    {
        obj = obj.Process( fn, reason, dbgName, dbgPath, dbgLine, dbgExpression );
        return obj;
    }
}
*/