// 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;
using System.Diagnostics.CodeAnalysis;
using System.Text.Json.Serialization;
 
namespace Microsoft.Extensions.AI;
 
/// <summary>Represents a chat message used by an <see cref="IChatClient" />.</summary>
/// <related type="Article" href="https://learn.microsoft.com/dotnet/ai/quickstarts/build-chat-app">Build an AI chat app with .NET.</related>
[DebuggerDisplay("[{Role}] {ContentForDebuggerDisplay}{EllipsesForDebuggerDisplay,nq}")]
public class ChatMessage
{
    private IList<AIContent>? _contents;
    private string? _authorName;
 
    /// <summary>Initializes a new instance of the <see cref="ChatMessage"/> class.</summary>
    /// <remarks>The instance defaults to having a role of <see cref="ChatRole.User"/>.</remarks>
    [JsonConstructor]
    public ChatMessage()
    {
    }
 
    /// <summary>Initializes a new instance of the <see cref="ChatMessage"/> class.</summary>
    /// <param name="role">The role of the author of the message.</param>
    /// <param name="content">The text content of the message.</param>
    public ChatMessage(ChatRole role, string? content)
        : this(role, content is null ? [] : [new TextContent(content)])
    {
    }
 
    /// <summary>Initializes a new instance of the <see cref="ChatMessage"/> class.</summary>
    /// <param name="role">The role of the author of the message.</param>
    /// <param name="contents">The contents for this message.</param>
    public ChatMessage(ChatRole role, IList<AIContent>? contents)
    {
        Role = role;
        _contents = contents;
    }
 
    /// <summary>Clones the <see cref="ChatMessage"/> to a new <see cref="ChatMessage"/> instance.</summary>
    /// <returns>A shallow clone of the original message object.</returns>
    /// <remarks>
    /// This is a shallow clone. The returned instance is different from the original, but all properties
    /// refer to the same objects as the original.
    /// </remarks>
    public ChatMessage Clone() =>
        new()
        {
            AdditionalProperties = AdditionalProperties,
            _authorName = _authorName,
            _contents = _contents,
            CreatedAt = CreatedAt,
            RawRepresentation = RawRepresentation,
            Role = Role,
            MessageId = MessageId,
        };
 
    /// <summary>Gets or sets the name of the author of the message.</summary>
    public string? AuthorName
    {
        get => _authorName;
        set => _authorName = string.IsNullOrWhiteSpace(value) ? null : value;
    }
 
    /// <summary>Gets or sets a timestamp for the chat message.</summary>
    public DateTimeOffset? CreatedAt { get; set; }
 
    /// <summary>Gets or sets the role of the author of the message.</summary>
    public ChatRole Role { get; set; } = ChatRole.User;
 
    /// <summary>Gets the text of this message.</summary>
    /// <remarks>
    /// This property concatenates the text of all <see cref="TextContent"/> objects in <see cref="Contents"/>.
    /// </remarks>
    [JsonIgnore]
    public string Text => Contents.ConcatText();
 
    /// <summary>Gets or sets the chat message content items.</summary>
    [AllowNull]
    public IList<AIContent> Contents
    {
        get => _contents ??= [];
        set => _contents = value;
    }
 
    /// <summary>Gets or sets the ID of the chat message.</summary>
    public string? MessageId { get; set; }
 
    /// <summary>Gets or sets the raw representation of the chat message from an underlying implementation.</summary>
    /// <remarks>
    /// If a <see cref="ChatMessage"/> 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 any additional properties associated with the message.</summary>
    public AdditionalPropertiesDictionary? AdditionalProperties { get; set; }
 
    /// <inheritdoc/>
    public override string ToString() => Text;
 
    /// <summary>Gets a <see cref="AIContent"/> object to display in the debugger display.</summary>
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private AIContent? ContentForDebuggerDisplay
    {
        get
        {
            string text = Text;
            return
                !string.IsNullOrWhiteSpace(text) ? new TextContent(text) :
                _contents is { Count: > 0 } ? _contents[0] :
                null;
        }
    }
 
    /// <summary>Gets an indication for the debugger display of whether there's more content.</summary>
    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
    private string EllipsesForDebuggerDisplay => _contents is { Count: > 1 } ? ", ..." : string.Empty;
}