refactor: implement AI Client (#36)

This implements the guts of the AI client, including fetching Model
configuration, interpolation, and tests.

pkgs/sdk/server-ai/README.md

@@ -22,7 +22,7 @@ The .NET build tools should automatically load the most appropriate build of the
 
 ## Getting started
 
-Refer to the [SDK documentation](https://docs.launchdarkly.com/sdk/server-side/dotnet#getting-started) for instructions on getting started with using the SDK.
+Refer to the [SDK documentation](https://docs.launchdarkly.com/sdk/ai/dotnet) for instructions on getting started with using the SDK.
 
 ## Signing
 

pkgs/sdk/server-ai/src/Adapters/LdClientAdapter.cs

@@ -0,0 +1,32 @@
+using LaunchDarkly.Logging;
+using LaunchDarkly.Sdk.Server.Ai.Interfaces;
+
+namespace LaunchDarkly.Sdk.Server.Ai.Adapters;
+
+/// <summary>
+/// Adapts an <see cref="LdClient"/> to the requirements of <see cref="LdAiClient"/>.
+/// </summary>
+public class LdClientAdapter : ILaunchDarklyClient
+{
+    private readonly LdClient _client;
+
+    /// <summary>
+    /// Constructs the adapter from an existing client.
+    /// </summary>
+    /// <param name="client">the adapter</param>
+    public LdClientAdapter(LdClient client)
+    {
+        _client = client;
+    }
+
+    /// <inheritdoc/>
+    public LdValue JsonVariation(string key, Context context, LdValue defaultValue)
+        => _client.JsonVariation(key, context, defaultValue);
+
+    /// <inheritdoc/>
+    public void Track(string name, Context context, LdValue data, double metricValue)
+        => _client.Track(name, context, data, metricValue);
+
+    /// <inheritdoc/>
+    public ILogger GetLogger() => new LoggerAdapter(_client.GetLogger());
+}

pkgs/sdk/server-ai/src/Adapters/LoggerAdapter.cs

@@ -0,0 +1,28 @@
+using LaunchDarkly.Logging;
+using LaunchDarkly.Sdk.Server.Ai.Interfaces;
+
+namespace LaunchDarkly.Sdk.Server.Ai.Adapters;
+
+/// <summary>
+/// Adapts a <see cref="Logger"/> to the requirements of the <see cref="LdAiClient"/>'s
+/// logger.
+/// </summary>
+internal class LoggerAdapter : ILogger
+{
+    private readonly Logger _logger;
+
+    /// <summary>
+    /// Creates a new adapter.
+    /// </summary>
+    /// <param name="logger">the existing logger</param>
+    public LoggerAdapter(Logger logger)
+    {
+        _logger = logger;
+    }
+
+    /// <inheritdoc/>
+    public void Error(string format, params object[] allParams) => _logger.Error(format, allParams);
+
+    /// <inheritdoc/>
+    public void Warn(string format, params object[] allParams) => _logger.Warn(format, allParams);
+}

pkgs/sdk/server-ai/src/Config/LdAiConfig.cs

@@ -0,0 +1,191 @@
+using System.Collections.Generic;
+using System.Linq;
+using LaunchDarkly.Sdk.Server.Ai.DataModel;
+
+namespace LaunchDarkly.Sdk.Server.Ai.Config;
+
+/// <summary>
+/// Represents an AI configuration, which contains model parameters and prompt messages.
+/// </summary>
+public record LdAiConfig
+{
+
+    /// <summary>
+    /// Represents a single message, which is part of a prompt.
+    /// </summary>
+    public record Message
+    {
+        /// <summary>
+        /// The content of the message, which may contain Mustache templates.
+        /// </summary>
+        public readonly string Content;
+
+        /// <summary>
+        /// The role of the message.
+        /// </summary>
+        public readonly Role Role;
+
+        internal Message(string content, Role role)
+        {
+            Content = content;
+            Role = role;
+        }
+    }
+
+    /// <summary>
+    /// Builder for constructing an LdAiConfig instance, which can be passed as the default
+    /// value to the AI Client's <see cref="LdAiClient.ModelConfig"/> method.
+    /// </summary>
+    public class Builder
+    {
+        private bool _enabled;
+        private readonly List<Message> _prompt;
+        private readonly Dictionary<string, object> _modelParams;
+
+        internal Builder()
+        {
+            _enabled = false;
+            _prompt = new List<Message>();
+            _modelParams = new Dictionary<string, object>();
+        }
+
+        /// <summary>
+        /// Adds a prompt message with the given content and role. The default role is <see cref="Role.User"/>.
+        /// </summary>
+        /// <param name="content">the content, which may contain Mustache templates</param>
+        /// <param name="role">the role</param>
+        /// <returns>a new builder</returns>
+        public Builder AddPromptMessage(string content, Role role = Role.User)
+        {
+            _prompt.Add(new Message(content, role));
+            return this;
+        }
+
+        /// <summary>
+        /// Disables the config.
+        /// </summary>
+        /// <returns>the builder</returns>
+        public Builder Disable() => SetEnabled(false);
+
+        /// <summary>
+        /// Enables the config.
+        /// </summary>
+        /// <returns>the builder</returns>
+        public Builder Enable() => SetEnabled(true);
+
+        /// <summary>
+        /// Sets the enabled state of the config based on a boolean.
+        /// </summary>
+        /// <param name="enabled">whether the config is enabled</param>
+        /// <returns>the builder</returns>
+        public Builder SetEnabled(bool enabled)
+        {
+            _enabled = enabled;
+            return this;
+        }
+
+        /// <summary>
+        /// Sets a parameter for the model. The value may be any object.
+        /// </summary>
+        /// <param name="name">the parameter name</param>
+        /// <param name="value">the parameter value</param>
+        /// <returns>the builder</returns>
+        public Builder SetModelParam(string name, object value)
+        {
+            _modelParams[name] = value;
+            return this;
+        }
+
+        /// <summary>
+        /// Builds the LdAiConfig instance.
+        /// </summary>
+        /// <returns>a new LdAiConfig</returns>
+        public LdAiConfig Build()
+        {
+            return new LdAiConfig(_enabled, _prompt, new Meta(), _modelParams);
+        }
+    }
+
+    /// <summary>
+    /// The prompts associated with the config.
+    /// </summary>
+    public readonly IReadOnlyList<Message> Prompt;
+
+    /// <summary>
+    /// The model parameters associated with the config.
+    /// </summary>
+    public readonly IReadOnlyDictionary<string, object> Model;
+
+
+
+    internal LdAiConfig(bool enabled, IEnumerable<Message> prompt, Meta meta, IReadOnlyDictionary<string, object> model)
+    {
+        Model = model ?? new Dictionary<string, object>();
+        Prompt = prompt?.ToList() ?? new List<Message>();
+        VersionKey = meta?.VersionKey ?? "";
+        Enabled = enabled;
+    }
+
+    private static LdValue ObjectToValue(object obj)
+    {
+        if (obj == null)
+        {
+            return LdValue.Null;
+        }
+
+        return obj switch
+        {
+            bool b => LdValue.Of(b),
+            double d => LdValue.Of(d),
+            string s => LdValue.Of(s),
+            IEnumerable<object> list => LdValue.ArrayFrom(list.Select(ObjectToValue)),
+            IDictionary<string, object> dict => LdValue.ObjectFrom(dict.ToDictionary(kv => kv.Key,
+                kv => ObjectToValue(kv.Value))),
+            _ => LdValue.Null
+        };
+    }
+
+    internal LdValue ToLdValue()
+    {
+        return LdValue.ObjectFrom(new Dictionary<string, LdValue>
+        {
+            { "_ldMeta", LdValue.ObjectFrom(
+                new Dictionary<string, LdValue>
+                {
+                    { "versionKey", LdValue.Of(VersionKey) },
+                    { "enabled", LdValue.Of(Enabled) }
+                }) },
+            { "prompt", LdValue.ArrayFrom(Prompt.Select(m => LdValue.ObjectFrom(new Dictionary<string, LdValue>
+            {
+                { "content", LdValue.Of(m.Content) },
+                { "role", LdValue.Of(m.Role.ToString()) }
+            }))) },
+            { "model", ObjectToValue(Model) }
+        });
+    }
+
+    /// <summary>
+    /// Creates a new LdAiConfig builder.
+    /// </summary>
+    /// <returns>a new builder</returns>
+    public static Builder New() => new();
+
+    /// <summary>
+    /// Returns true if the config is enabled.
+    /// </summary>
+    /// <returns>true if enabled</returns>
+    public bool Enabled { get; }
+
+
+    /// <summary>
+    /// This field meant for internal LaunchDarkly usage.
+    /// </summary>
+    public string VersionKey { get; }
+
+    /// <summary>
+    /// Convenient helper that returns a disabled LdAiConfig.
+    /// </summary>
+    public static LdAiConfig Disabled = New().Disable().Build();
+
+
+}

pkgs/sdk/server-ai/src/DataModel/DataModel.cs

@@ -0,0 +1,86 @@
+using System.Collections.Generic;
+using System.Text.Json.Serialization;
+
+namespace  LaunchDarkly.Sdk.Server.Ai.DataModel;
+
+/// <summary>
+/// Represents the role of the prompt message.
+/// </summary>
+public enum Role
+{
+    /// <summary>
+    /// User role.
+    /// </summary>
+    User,
+    /// <summary>
+    /// System role.
+    /// </summary>
+    System,
+    /// <summary>
+    /// Assistant role.
+    /// </summary>
+    Assistant
+}
+
+/// <summary>
+/// Represents the JSON serialization of the Meta field.
+/// </summary>
+public class Meta
+{
+    /// <summary>
+    /// The version key.
+    /// </summary>
+    [JsonPropertyName("versionKey")]
+    public string VersionKey { get; set; }
+
+    /// <summary>
+    /// If the config is enabled.
+    /// </summary>
+    [JsonPropertyName("enabled")]
+    public bool Enabled { get; set; }
+}
+
+/// <summary>
+/// Represents the JSON serialization of a Message.
+/// </summary>
+public class Message
+{
+    /// <summary>
+    /// The content.
+    /// </summary>
+    [JsonPropertyName("content")]
+    public string Content { get; set; }
+
+    /// <summary>
+    /// The role.
+    /// </summary>
+    [JsonPropertyName("role")]
+    [JsonConverter(typeof(JsonStringEnumConverter))]
+    public Role Role { get; set; }
+}
+
+
+/// <summary>
+/// Represents the JSON serialization of an AiConfig.
+/// </summary>
+
+public class AiConfig
+{
+    /// <summary>
+    /// The prompt.
+    /// </summary>
+    [JsonPropertyName("prompt")]
+    public List<Message> Prompt { get; set; }
+
+    /// <summary>
+    /// LaunchDarkly metadata.
+    /// </summary>
+    [JsonPropertyName("_ldMeta")]
+    public Meta Meta { get; set; }
+
+    /// <summary>
+    /// The model params;
+    /// </summary>
+    [JsonPropertyName("model")]
+    public Dictionary<string, object> Model { get; set; }
+}

pkgs/sdk/server-ai/src/Interfaces/ILaunchDarklyClient.cs

@@ -0,0 +1,32 @@
+namespace LaunchDarkly.Sdk.Server.Ai.Interfaces;
+
+/// <summary>
+/// Interface representing capabilities needed by the AI Client. These are usually provided
+/// by the LaunchDarkly Server SDK.
+/// </summary>
+public interface ILaunchDarklyClient
+{
+    /// <summary>
+    /// Returns a JSON variation.
+    /// </summary>
+    /// <param name="key">the flag key</param>
+    /// <param name="context">the context</param>
+    /// <param name="defaultValue">the default value</param>
+    /// <returns>the evaluation result</returns>
+    LdValue JsonVariation(string key, Context context, LdValue defaultValue);
+
+    /// <summary>
+    /// Tracks a metric.
+    /// </summary>
+    /// <param name="name">metric name</param>
+    /// <param name="context">context</param>
+    /// <param name="data">associated data</param>
+    /// <param name="metricValue">metric value</param>
+    void Track(string name, Context context, LdValue data, double metricValue);
+
+    /// <summary>
+    /// Returns a logger.
+    /// </summary>
+    /// <returns>a logger</returns>
+    ILogger GetLogger();
+}