using System;
using System.Globalization;

namespace AcDream.App;

/// <summary>
/// Typed bundle of startup-time configuration read from the process
/// environment. Built once in <c>Program.cs</c> and passed to
/// <c>GameWindow</c> so the rest of the app reads its config through
/// strongly-typed fields instead of scattered
/// <c>Environment.GetEnvironmentVariable</c> calls.
/// </summary>
/// <remarks>
/// <para>
/// <strong>Scope:</strong> startup-time only — values that don't change
/// once the window is up. Runtime diagnostic toggles
/// (e.g. <c>ACDREAM_DUMP_MOTION</c>, <c>ACDREAM_PROBE_*</c>) belong in
/// diagnostic owner classes (see <c>AcDream.Core.Physics.PhysicsDiagnostics</c>
/// for the template), not here.
/// </para>
/// <para>
/// See <c>docs/architecture/code-structure.md</c> §2 Rule 4 for the
/// rule that drove this extraction, and §4 Step 1 for the broader
/// extraction sequence this is the first cut of.
/// </para>
/// </remarks>
public sealed record RuntimeOptions(
    string DatDir,
    bool LiveMode,
    string LiveHost,
    int LivePort,
    string? LiveUser,
    string? LivePass,
    bool DevTools,
    bool DumpMoveTruth,
    bool NoAudio,
    bool EnableSkyPesDebug,
    int HidePartIndex,
    bool RetailCloseDegrades,
    bool DumpSceneryZ,
    int? LegacyStreamRadius)
{
    /// <summary>
    /// Build options from the process environment. Used by
    /// <c>Program.cs</c> at startup.
    /// </summary>
    public static RuntimeOptions FromEnvironment(string datDir)
        => Parse(datDir, Environment.GetEnvironmentVariable);

    /// <summary>
    /// Build options from a custom environment getter. Used by tests to
    /// inject controlled env values without touching the process
    /// environment.
    /// </summary>
    /// <param name="datDir">Resolved dat-file directory.</param>
    /// <param name="env">Function returning the value for an env-var
    /// name, or <c>null</c> when unset.</param>
    public static RuntimeOptions Parse(string datDir, Func<string, string?> env)
    {
        if (datDir is null) throw new ArgumentNullException(nameof(datDir));
        if (env    is null) throw new ArgumentNullException(nameof(env));

        return new RuntimeOptions(
            DatDir:              datDir,
            LiveMode:            IsExactlyOne(env("ACDREAM_LIVE")),
            LiveHost:            env("ACDREAM_TEST_HOST") ?? "127.0.0.1",
            LivePort:            TryParseInt(env("ACDREAM_TEST_PORT")) ?? 9000,
            LiveUser:            NullIfEmpty(env("ACDREAM_TEST_USER")),
            LivePass:            NullIfEmpty(env("ACDREAM_TEST_PASS")),
            DevTools:            IsExactlyOne(env("ACDREAM_DEVTOOLS")),
            DumpMoveTruth:       IsExactlyOne(env("ACDREAM_DUMP_MOVE_TRUTH")),
            NoAudio:             IsExactlyOne(env("ACDREAM_NO_AUDIO")),
            EnableSkyPesDebug:   IsExactlyOne(env("ACDREAM_ENABLE_SKY_PES")),
            HidePartIndex:       TryParseInt(env("ACDREAM_HIDE_PART")) ?? -1,
            // Default-on: any value other than the literal string "0" enables
            // retail close-detail degrades. Set ACDREAM_RETAIL_CLOSE_DEGRADES=0
            // only for before/after diagnostic comparisons.
            RetailCloseDegrades: !string.Equals(env("ACDREAM_RETAIL_CLOSE_DEGRADES"), "0", StringComparison.Ordinal),
            DumpSceneryZ:        IsExactlyOne(env("ACDREAM_DUMP_SCENERY_Z")),
            // Legacy override for ACDREAM_STREAM_RADIUS. Caller applies it on
            // top of the quality preset's radii. Null when unset or invalid.
            LegacyStreamRadius:  TryParseNonNegativeInt(env("ACDREAM_STREAM_RADIUS")));
    }

    /// <summary>True iff live-mode credentials are present and valid for connecting.</summary>
    public bool HasLiveCredentials =>
        LiveMode && !string.IsNullOrEmpty(LiveUser) && !string.IsNullOrEmpty(LivePass);

    private static bool IsExactlyOne(string? s)
        => string.Equals(s, "1", StringComparison.Ordinal);

    private static string? NullIfEmpty(string? s)
        => string.IsNullOrEmpty(s) ? null : s;

    private static int? TryParseInt(string? s)
        => int.TryParse(s, NumberStyles.Integer, CultureInfo.InvariantCulture, out var v) ? v : null;

    private static int? TryParseNonNegativeInt(string? s)
        => TryParseInt(s) is { } v && v >= 0 ? v : null;
}