using Microsoft.Extensions.AI;
using System.Text.Json;

namespace AnchorCli;

internal sealed class ChatSession
{
    private readonly IChatClient _agent;
    public ContextCompactor Compactor { get; }
    public List<ChatMessage> History { get; }

    public ChatSession(IChatClient innerClient)
    {
        Compactor = new ContextCompactor(innerClient);

        var tools = ToolRegistry.GetTools();
        _agent = new ChatClientBuilder(innerClient)
            .UseFunctionInvocation()
            .Build();

        History = new List<ChatMessage>
        {
            new(ChatRole.System, $$"""
                You are anchor, a coding assistant that edits files using the Hashline technique.

                ## Reading files
                When you read a file, lines are returned in the format: lineNumber:hash|content
                The "lineNumber:hash|" prefix is METADATA for anchoring — it is NOT part of the file.

                ## Editing files
                To edit, reference anchors as "lineNumber:hash" in startAnchor/endAnchor parameters.
                The newLines/initialLines parameter must contain RAW SOURCE CODE ONLY.
                ❌ WRONG: ["5:a3|    public void Foo()"]
                ✅ RIGHT: ["    public void Foo()"]
                Never include the "lineNumber:hash|" prefix in content you write — it will corrupt the file.

                ## Workflow
                1. ALWAYS call GrepFile before ReadFile on any source file.
                   Use patterns like "public|func|function|class|interface|enum|def|fn " to get a structural
                   outline of the file and identify the exact line numbers of the section you need.
                   Only then call ReadFile with a targeted startLine/endLine range.
                   ❌ WRONG: ReadFile("Foo.cs") — reads blindly without knowing the structure.
                   ✅ RIGHT: GrepFile("Foo.cs", "public|class|interface") → ReadFile("Foo.cs", 42, 90)
                2. After reading, edit the file before verifying the returned fingerprint.
                3. Edit from bottom to top so line numbers don't shift.
                4. If an anchor fails validation, re-read the relevant range to get fresh anchors.

                Keep responses concise. You have access to the current working directory.
                You are running on: {{System.Runtime.InteropServices.RuntimeInformation.OSDescription}}
            """)
        };
    }
    public void Reset()
    {
        // Keep only the system message
        var systemMessage = History[0];
        History.Clear();
        History.Add(systemMessage);
    }


    public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
        [System.Runtime.CompilerServices.EnumeratorCancellation] CancellationToken cancellationToken = default)
    {
        var options = new ChatOptions { Tools = ToolRegistry.GetTools() };
        var stream = _agent.GetStreamingResponseAsync(History, options, cancellationToken);

        await foreach (var update in stream.WithCancellation(cancellationToken))
        {
            yield return update;
        }
    }

    public async Task SaveAsync(string filePath, CancellationToken cancellationToken = default)
    {
        // Skip the system message when saving (it will be recreated on load)
        var messagesToSave = History.Skip(1).ToList();
        
        var options = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = true
        };
        
        var json = JsonSerializer.Serialize(messagesToSave, AppJsonContext.Default.ListChatMessage);
        await File.WriteAllTextAsync(filePath, json, cancellationToken);
    }

    public async Task LoadAsync(string filePath, CancellationToken cancellationToken = default)
    {
        var json = await File.ReadAllTextAsync(filePath, cancellationToken);
        
        var options = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
        };
        
        var messages = JsonSerializer.Deserialize<List<ChatMessage>>(json, AppJsonContext.Default.ListChatMessage)
            ?? new List<ChatMessage>();
        
        // Keep the system message and append loaded messages
        var systemMessage = History[0];
        History.Clear();
        History.Add(systemMessage);
        History.AddRange(messages);
    }
}