// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json.Serialization;
 
namespace Microsoft.Extensions.AI;
 
/// <summary>
/// Represents a single streaming response chunk from an <see cref="IChatClient"/>.
/// </summary>
/// <remarks>
/// <para>
/// Conceptually, this combines the roles of <see cref="ChatCompletion"/> and <see cref="ChatMessage"/>
/// in streaming output. For ease of consumption, it also flattens the nested structure you see on
/// streaming chunks in some AI service, so instead of a dictionary of choices, each update represents a
/// single choice (and hence has its own role, choice ID, etc.).
/// </para>
/// <para>
/// <see cref="StreamingChatCompletionUpdate"/> is so named because it represents streaming updates
/// to a single chat completion. As such, it is considered erroneous for multiple updates that are part
/// of the same completion to contain competing values. For example, some updates that are part of
/// the same completion may have a <see langword="null"/> <see cref="StreamingChatCompletionUpdate.Role"/>
/// value, and others may have a non-<see langword="null"/> value, but all of those with a non-<see langword="null"/>
/// value must have the same value (e.g. <see cref="ChatRole.Assistant"/>. It should never be the case, for example,
/// that one <see cref="StreamingChatCompletionUpdate"/> in a completion has a role of <see cref="ChatRole.Assistant"/>
/// while another has a role of "AI".
/// </para>
/// <para>
/// The relationship between <see cref="ChatCompletion"/> and <see cref="StreamingChatCompletionUpdate"/> is
/// codified in the <see cref="StreamingChatCompletionUpdateExtensions.ToChatCompletionAsync"/> and
/// <see cref="ChatCompletion.ToStreamingChatCompletionUpdates"/>, which enable bidirectional conversions
/// between the two. Note, however, that the conversion may be slightly lossy, for example if multiple updates
/// all have different <see cref="StreamingChatCompletionUpdate.RawRepresentation"/> objects whereas there's
/// only one slot for such an object available in <see cref="ChatCompletion.RawRepresentation"/>.
/// </para>
/// </remarks>
public class StreamingChatCompletionUpdate
{
    /// <summary>The completion update content items.</summary>
    private IList<AIContent>? _contents;
 
    /// <summary>The name of the author of the update.</summary>
    private string? _authorName;
 
    /// <summary>Gets or sets the name of the author of the completion update.</summary>
    public string? AuthorName
    {
        get => _authorName;
        set => _authorName = string.IsNullOrWhiteSpace(value) ? null : value;
    }
 
    /// <summary>Gets or sets the role of the author of the completion update.</summary>
    public ChatRole? Role { get; set; }
 
    /// <summary>
    /// Gets or sets the text of the first <see cref="TextContent"/> instance in <see cref="Contents" />.
    /// </summary>
    /// <remarks>
    /// If there is no <see cref="TextContent"/> instance in <see cref="Contents" />, then the getter returns <see langword="null" />,
    /// and the setter will add new <see cref="TextContent"/> instance with the provided value.
    /// </remarks>
    [JsonIgnore]
    public string? Text
    {
        get => Contents.FindFirst<TextContent>()?.Text;
        set
        {
            if (Contents.FindFirst<TextContent>() is { } textContent)
            {
                textContent.Text = value;
            }
            else if (value is not null)
            {
                Contents.Add(new TextContent(value));
            }
        }
    }
 
    /// <summary>Gets or sets the chat completion update content items.</summary>
    [AllowNull]
    public IList<AIContent> Contents
    {
        get => _contents ??= [];
        set => _contents = value;
    }
 
    /// <summary>Gets or sets the raw representation of the completion update from an underlying implementation.</summary>
    /// <remarks>
    /// If a <see cref="StreamingChatCompletionUpdate"/> is created to represent some underlying object from another object
    /// model, this property can be used to store that original object. This can be useful for debugging or
    /// for enabling a consumer to access the underlying object model if needed.
    /// </remarks>
    [JsonIgnore]
    public object? RawRepresentation { get; set; }
 
    /// <summary>Gets or sets additional properties for the update.</summary>
    public AdditionalPropertiesDictionary? AdditionalProperties { get; set; }
 
    /// <summary>Gets or sets the ID of the completion of which this update is a part.</summary>
    public string? CompletionId { get; set; }
 
    /// <summary>Gets or sets a timestamp for the completion update.</summary>
    public DateTimeOffset? CreatedAt { get; set; }
 
    /// <summary>Gets or sets the zero-based index of the choice with which this update is associated in the streaming sequence.</summary>
    public int ChoiceIndex { get; set; }
 
    /// <summary>Gets or sets the finish reason for the operation.</summary>
    public ChatFinishReason? FinishReason { get; set; }
 
    /// <summary>Gets or sets the model ID using in the creation of the chat completion of which this update is a part.</summary>
    public string? ModelId { get; set; }
 
    /// <inheritdoc/>
    public override string ToString() => Contents.ConcatText();
}