using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using ClawdDotNet.Core.Api.Models;

namespace ClawdDotNet.Core.Transcripts;

/// <summary>
/// Collects the transcript of one run while it happens (#660). The engine calls it at the
/// few points where something enters or leaves the conversation; nothing here talks to
/// the model or the database.
///
/// <para>Recording is bounded: tool results are clipped to <see cref="MaxToolResultChars"/>,
/// any single text to <see cref="MaxTextChars"/>, and the whole transcript to
/// <see cref="MaxTotalChars"/>. Beyond that only the entry heads are kept (who called what,
/// how many tokens), which is what an analysis of a runaway run needs anyway.</para>
///
/// <para>A disabled recorder (<see cref="Disabled"/>) accepts every call and keeps
/// nothing, so the engine never has to branch.</para>
/// </summary>
public sealed class RunTranscriptRecorder
{
    public const int MaxToolResultChars = 4_000;
    public const int MaxTextChars = 32_000;
    public const int MaxTotalChars = 256_000;

    private readonly Lock _lock = new();
    private readonly List<TranscriptEntry> _entries = [];
    private readonly TimeProvider _clock;
    private int _size;
    private bool _truncated;

    public static RunTranscriptRecorder Disabled { get; } = new(enabled: false);

    public bool Enabled { get; }
    public string? SystemPrompt { get; private set; }

    /// <summary>The message as sent by its author - without the time line the engine prepends.</summary>
    public string? PromptPreview { get; private set; }
    public DateTime StartedAt { get; }

    public RunTranscriptRecorder(bool enabled = true, TimeProvider? clock = null)
    {
        Enabled = enabled;
        _clock = clock ?? TimeProvider.System;
        StartedAt = _clock.GetUtcNow().UtcDateTime;
    }

    // ─── Engine hooks ───

    /// <param name="sentMessage">What the model received, including what the engine added.</param>
    /// <param name="originalMessage">The message as its author wrote it - the list preview.</param>
    public void Begin(string? systemPrompt, string sentMessage, string? originalMessage = null)
    {
        if (!Enabled) return;
        SystemPrompt = string.IsNullOrWhiteSpace(systemPrompt) ? null : SecretScrubber.Scrub(systemPrompt);
        PromptPreview = SecretScrubber.Scrub(originalMessage ?? sentMessage);
        Add(TranscriptEntryKind.User, sentMessage, MaxTextChars);
    }

    /// <summary>A message the engine sent on its own (follow-up after an empty answer etc.).</summary>
    public void EngineNote(string text)
    {
        if (!Enabled) return;
        Add(TranscriptEntryKind.EngineNote, text, MaxTextChars);
    }

    public void Event(string text)
    {
        if (!Enabled) return;
        Add(TranscriptEntryKind.Event, text, MaxTextChars);
    }

    /// <summary>One model response with the usage of exactly this request.</summary>
    public void ModelStep(ChatMessage response, Usage? usage, string? finishReason)
    {
        if (!Enabled) return;

        var calls = response.ToolCalls?
            .Select(c => new TranscriptToolCall(
                c.Id, c.Function.Name, Clip(SecretScrubber.Scrub(c.Function.Arguments ?? ""), MaxTextChars, out _)))
            .ToList();

        var (text, clipped) = Prepare(response.Content, MaxTextChars);

        lock (_lock)
        {
            var groesse = (text?.Length ?? 0) + (calls?.Sum(c => c.Arguments.Length + c.Name.Length) ?? 0);
            var ueber = _size + groesse > MaxTotalChars;
            if (ueber) _truncated = true;

            _entries.Add(new TranscriptEntry
            {
                Kind = TranscriptEntryKind.Assistant,
                At = _clock.GetUtcNow().UtcDateTime,
                Text = ueber ? null : text,
                ToolCalls = ueber ? calls?.Select(c => c with { Arguments = "" }).ToList() : calls,
                PromptTokens = usage?.PromptTokens,
                CompletionTokens = usage?.CompletionTokens,
                CachedTokens = usage?.CachedTokens,
                CostUsd = usage?.Cost,
                FinishReason = finishReason,
                Clipped = clipped || ueber
            });
            if (!ueber) _size += groesse;
        }
    }

    public void ToolResults(IReadOnlyList<ToolCall> calls, IReadOnlyList<string?> results)
    {
        if (!Enabled) return;
        for (var i = 0; i < calls.Count; i++)
        {
            Add(TranscriptEntryKind.ToolResult, results.ElementAtOrDefault(i) ?? "(no result)", MaxToolResultChars,
                calls[i].Id, calls[i].Function.Name);
        }
    }

    // ─── Result ───

    public RunTranscript Build(string runId, string agentId, string model, string source, string? taskId, string status)
    {
        lock (_lock)
        {
            return new RunTranscript
            {
                RunId = runId,
                AgentId = agentId,
                Model = model,
                Source = source,
                TaskId = taskId,
                StartedAt = StartedAt,
                CompletedAt = _clock.GetUtcNow().UtcDateTime,
                Status = status,
                SystemPromptHash = SystemPrompt is null ? null : Hash(SystemPrompt),
                PromptPreview = PromptPreview,
                Entries = _entries.ToList(),
                SizeChars = _size,
                Truncated = _truncated
            };
        }
    }

    public static string Hash(string text)
        => Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(text)))[..32].ToLowerInvariant();

    // ─── Helpers ───

    private void Add(string kind, string? text, int max, string? toolCallId = null, string? toolName = null)
    {
        var (prepared, clipped) = Prepare(text, max);
        lock (_lock)
        {
            var ueber = _size + (prepared?.Length ?? 0) > MaxTotalChars;
            if (ueber) _truncated = true;
            _entries.Add(new TranscriptEntry
            {
                Kind = kind,
                At = _clock.GetUtcNow().UtcDateTime,
                Text = ueber ? null : prepared,
                ToolCallId = toolCallId,
                ToolName = toolName,
                Clipped = clipped || ueber
            });
            if (!ueber) _size += prepared?.Length ?? 0;
        }
    }

    private static (string? Text, bool Clipped) Prepare(string? text, int max)
    {
        if (string.IsNullOrEmpty(text)) return (text, false);
        var clipped = Clip(SecretScrubber.Scrub(text), max, out var wasClipped);
        return (clipped, wasClipped);
    }

    /// <summary>Keeps start and end — the end of a tool result is often the interesting part.</summary>
    internal static string Clip(string text, int max, out bool clipped)
    {
        clipped = text.Length > max;
        if (!clipped) return text;

        var head = max * 3 / 4;
        var tail = max - head;
        return text[..head] + $"\n[… {text.Length - max} characters omitted …]\n" + text[^tail..];
    }
}

/// <summary>
/// Removes the kinds of secrets that can end up in prompts or tool results before a
/// transcript is stored. Deliberately conservative: it targets recognisable secret
/// formats, not arbitrary text.
/// </summary>
public static partial class SecretScrubber
{
    public const string Mask = "«redacted»";

    public static string Scrub(string text)
    {
        if (string.IsNullOrEmpty(text)) return text;

        text = ApiKey().Replace(text, Mask);
        text = Bearer().Replace(text, "Bearer " + Mask);
        text = PasswordAssignment().Replace(text, m => m.Groups["key"].Value + m.Groups["sep"].Value + Mask);
        text = LicenseKey().Replace(text, Mask);
        return text;
    }

    [GeneratedRegex(@"\b(?:sk-or-v1-|sk-or-|sk-ant-|sk-proj-|sk-|ghp_|gho_|github_pat_|xox[baprs]-)[A-Za-z0-9_\-]{16,}")]
    private static partial Regex ApiKey();

    [GeneratedRegex(@"Bearer\s+[A-Za-z0-9._~+/\-]{16,}=*", RegexOptions.IgnoreCase)]
    private static partial Regex Bearer();

    [GeneratedRegex(@"(?<key>\b(?:password|passwort|pwd|secret|api[_-]?key|token)\b)(?<sep>\s*[=:]\s*""?)[^;\s""',}]+", RegexOptions.IgnoreCase)]
    private static partial Regex PasswordAssignment();

    [GeneratedRegex(@"\b[A-Z0-9]{5}(?:-[A-Z0-9]{5}){4}\b")]
    private static partial Regex LicenseKey();
}