using System.Text;

namespace ClawdDotNet.Core.Organisation;

/// <summary>
/// #683: The "Organisation" section of an agent's system prompt — its unit, its lead, whom it
/// can reach, and what changed recently.
///
/// <para><b>Why the code writes it and not the agent's own texts.</b> The concept demands
/// that agents are told when they move, and warns: an agent that has to infer its lead from
/// a prompt escalates to the wrong place. A section generated from the tree is always true —
/// a move changes it by itself, for the agent that moved and for both leads.</para>
///
/// <para><b>Without units there is no section</b>, so instances without a structure keep
/// exactly the prompt they had — and the prompt cache that goes with it.</para>
/// </summary>
public static class OrgBriefing
{
    /// <summary>Starts the section; also how an existing chat context finds it to replace it.</summary>
    public const string Heading = "# Organisation";

    /// <summary>How long a move or a new colleague is pointed out.</summary>
    public static readonly TimeSpan RecentChange = TimeSpan.FromDays(7);

    private const int MaxDescription = 120;

    public static string? For(OrgChart org, string agentId, DateTime nowUtc)
    {
        if (!org.HasUnits || org.Agent(agentId) is not { } agent)
            return null;

        var sb = new StringBuilder();
        sb.AppendLine(Heading);

        var unit = org.UnitOf(agentId);
        if (unit is null)
        {
            sb.AppendLine("You are on the top level of this instance, above all units.");
        }
        else
        {
            sb.Append($"You belong to the unit \"{unit.Name}\" ({org.PathOf(unit.Id)})");
            if (agent.UnitSinceUtc is { } since)
            {
                sb.Append($", since {since:yyyy-MM-dd}");
                if (nowUtc - since < RecentChange)
                    sb.Append(" — this is recent: your lead, your colleagues and possibly your tools changed");
            }
            sb.AppendLine(".");

            if (!string.IsNullOrWhiteSpace(unit.Goal))
                sb.AppendLine($"Goal of your unit: {unit.Goal.Trim()}");
        }

        var lead = org.EffectiveLeaderOf(agentId);
        if (lead is not null)
            sb.AppendLine($"Your lead: {Name(lead)}. Questions, problems and anything outside your unit go to your lead.");
        else
            sb.AppendLine("There is no lead agent above you. What you cannot decide goes to a human: create a task for @human.");

        if (org.LedBy(agentId) is { } led)
        {
            sb.AppendLine($"You lead the unit \"{led.Name}\". Delegate within it, and hand what goes beyond it to your own lead.");
            var subUnits = org.Children(led.Id);
            if (subUnits.Count > 0)
            {
                sb.AppendLine("Its sub-units: " + string.Join("; ", subUnits.Select(u =>
                    org.LeaderOf(u.Id) is { } l ? $"{u.Name} (lead: {l.AgentId})" : $"{u.Name} (no lead — its members report to you)")) + ".");
            }

            var joined = org.MembersOf(led.Id)
                .Where(m => m.AgentId != agentId && m.UnitSinceUtc is { } s && nowUtc - s < RecentChange)
                .ToList();
            if (joined.Count > 0)
                sb.AppendLine("New in your unit: " + string.Join(", ", joined.Select(m => $"{m.AgentId} since {m.UnitSinceUtc:yyyy-MM-dd}")) + ".");

            // The lead that was left is told as well as the one that was joined.
            var left = org.Agents
                .Where(a => string.Equals(a.PreviousUnitId, led.Id, StringComparison.OrdinalIgnoreCase)
                            && a.UnitSinceUtc is { } s && nowUtc - s < RecentChange)
                .ToList();
            if (left.Count > 0)
                sb.AppendLine("Left your unit recently: " + string.Join(", ", left.Select(a =>
                    $"{a.AgentId} (now in {(org.UnitOf(a.AgentId) is { } u ? u.Name : "the top level")})")) +
                    ". Hand over what is still open with them.");
        }

        var contacts = org.AddressBook(agentId)
            .Where(id => lead is null || !string.Equals(id, lead.AgentId, StringComparison.OrdinalIgnoreCase))
            .Select(id => org.Agent(id)!)
            .OrderBy(a => a.AgentId, StringComparer.OrdinalIgnoreCase)
            .ToList();

        if (contacts.Count > 0)
        {
            sb.AppendLine("You can also reach:");
            foreach (var contact in contacts)
                sb.AppendLine($"- {Name(contact)}{Describe(contact.Description)}");
        }

        sb.Append("Agents not named here cannot be reached from your position — go through your lead.");
        return sb.ToString();
    }

    /// <summary>
    /// Replaces the organisation section of a system prompt, appends it, or removes it —
    /// leaving everything before it untouched. Existing chat contexts keep their system
    /// prompt otherwise (#193); only this section follows the structure.
    /// </summary>
    public static string WithSection(string systemPrompt, string? section)
    {
        var start = systemPrompt.IndexOf("\n\n" + Heading + "\n", StringComparison.Ordinal);
        var basePrompt = start >= 0 ? systemPrompt[..start] : systemPrompt;
        if (start < 0 && systemPrompt.StartsWith(Heading + "\n", StringComparison.Ordinal))
            basePrompt = "";

        if (string.IsNullOrWhiteSpace(section))
            return basePrompt;
        return basePrompt.Length == 0 ? section : basePrompt + "\n\n" + section;
    }

    private static string Name(Config.AgentConfig agent)
        => string.IsNullOrWhiteSpace(agent.DisplayName) || agent.DisplayName == agent.AgentId
            ? agent.AgentId
            : $"{agent.DisplayName} ({agent.AgentId})";

    private static string Describe(string? description)
    {
        if (string.IsNullOrWhiteSpace(description))
            return "";
        var line = description.ReplaceLineEndings(" ").Trim();
        return " — " + (line.Length > MaxDescription ? line[..MaxDescription] + "…" : line);
    }
}