using System;
using System.IO;

namespace ytLive.Helpers;

/// <summary>
/// Which run of LlamaCasty this process is, and where its private state lives.
/// <para><b>Dev-only affordance (creator directive, 2026-09-26).</b> Pre-1.0 the creator
/// needs two instances side by side: one streaming, one screen-capturing the other.
/// Two instances on one Windows profile collide on state, and two of those collisions
/// are hard failures rather than annoyances:
/// <list type="bullet">
/// <item><b>The SQLite layout DB.</b> The app's model is read-whole-scene / write-whole-scene,
/// so two instances saving different layouts clobber each other.</item>
/// <item><b>The WebView2 user data folder.</b> Chromium takes an exclusive lock on it; the
/// second instance of the same exe simply fails to start.</item>
/// <item><b>The auth token store.</b> A test instance would overwrite the real YouTube
/// sign-in.</item>
/// <item><b>startup.log.</b> Two appenders interleave into one file, so a crash in either
/// instance is ambiguous.</item>
/// </list>
/// So in <c>DEBUG</c> a process can claim an identity and gets its own private root
/// under <c>instances\&lt;id&gt;</c>: <c>$env:YTLIVE_INSTANCE=2; dotnet run</c>.
/// Recording, screen capture and the ffmpeg <c>tools\</c> cache are deliberately LEFT
/// shared — the cache should be shared, and the creator chooses the record folder.
/// Global hotkeys are also left alone: if both instances register the same one, Windows
/// refuses the second, which is the correct answer.</para>
/// <para><b>At 1.0 this disappears.</b> The whole implementation is inside
/// <c>#if DEBUG</c>; a Release build compiles to the two pass-throughs at the bottom —
/// no environment variable, no alternate folder, not even the variable's NAME in the
/// binary. Call sites are unconditional, so Release cannot accidentally diverge: it
/// always resolves the one real user profile.</para>
/// </summary>
public static class InstanceProfile
{
#if DEBUG
    /// <summary>Environment variable naming this instance. Absent or blank = the primary
    /// instance on the real user profile.</summary>
    public const string InstanceVariable = "YTLIVE_INSTANCE";

    /// <summary>This instance's id, or null for the primary instance.</summary>
    public static string? Id => Sanitize(Environment.GetEnvironmentVariable(InstanceVariable));

    /// <summary>Private state root: the real profile normally, a per-instance subfolder
    /// when an id is claimed.</summary>
    public static string DataRoot => Id is { } id
        ? Path.Combine(DefaultRoot, "instances", id)
        : DefaultRoot;

    /// <summary>Chromium's user data folder, or null to let WebView2 pick its default
    /// (which is what Release always does). Must be per-instance or the second
    /// instance dies on Chromium's exclusive lock.</summary>
    public static string? WebViewDataFolder => Id is null ? null : Path.Combine(DataRoot, "webview2");

    /// <summary>Reject anything that is not a plain path segment, so the variable can
    /// never be used to walk out of the profile directory or name a UNC path.</summary>
    private static string? Sanitize(string? raw)
    {
        if (string.IsNullOrWhiteSpace(raw)) return null;
        var trimmed = raw.Trim();
        foreach (var c in trimmed)
            if (!char.IsLetterOrDigit(c) && c != '-' && c != '_') return null;
        return trimmed;
    }
#else
    // Release: one profile, no alternate paths, no environment variable. Multi-instance
    // is a development affordance, not a shipping feature.
    public static string DataRoot => DefaultRoot;
    public static string? WebViewDataFolder => null;
#endif

    /// <summary>The one real user profile: <c>%APPDATA%\ytLlive</c>. Note the historical
    /// double-L — do not "fix" it, users already have their layouts there.</summary>
    public static string DefaultRoot => Path.Combine(
        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
        "ytLlive");
}