53 lines
2.3 KiB
C#
53 lines
2.3 KiB
C#
using System.Runtime.InteropServices;
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namespace CursorLang.Core.Services;
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/// <summary>
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/// Tells the agent that settings.json has changed.
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/// </summary>
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/// <remarks>
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/// The message carries nothing but the fact. The temptation to send the changed values
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/// along has to be resisted: the file would stop being the only source of truth, and
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/// the two would part company the first time somebody edits it by hand. Nothing else
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/// tells the agent — it does not watch the file — so a message that goes missing means
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/// settings it does not pick up until it is restarted.
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///
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/// Order is what makes it safe. The settings window writes the file whole, moves it
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/// into place in one step and only then signals, so by the time the agent reads there
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/// is nothing half-written to read.
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///
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/// A registered message rather than <c>WM_APP + n</c>: the identifier is unique across
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/// the system, so it cannot be confused with anything else that finds its way to that
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/// window.
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/// </remarks>
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internal static class SettingsSignal
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{
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/// <summary>The window class the agent registers for its hidden window.</summary>
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internal const string AgentWindowClass = "CursorLang.Agent.Window";
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/// <summary>The message both sides agree on.</summary>
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internal static uint Message { get; } = RegisterWindowMessage("CursorLang.SettingsChanged");
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/// <summary>
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/// Wakes the agent, if one is running in this session. Silence is a normal
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/// answer: the settings window is perfectly usable with no agent behind it.
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/// </summary>
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internal static void NotifyAgent()
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{
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IntPtr agent = FindWindow(AgentWindowClass, null);
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if (agent != IntPtr.Zero)
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{
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PostMessage(agent, Message, IntPtr.Zero, IntPtr.Zero);
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}
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}
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[DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "RegisterWindowMessageW")]
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private static extern uint RegisterWindowMessage(string lpString);
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[DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "FindWindowW")]
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private static extern IntPtr FindWindow(string lpClassName, string? lpWindowName);
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[DllImport("user32.dll", CharSet = CharSet.Unicode, EntryPoint = "PostMessageW")]
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private static extern bool PostMessage(IntPtr hWnd, uint message, IntPtr wParam, IntPtr lParam);
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}
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