using System.Diagnostics.CodeAnalysis;
using System.Text.Json.Serialization;

namespace MultiversalDiplomacy.Model;

/// <summary>
/// Represents a multiversal coordinate at which a state of the map exists.
/// </summary>
[JsonConverter(typeof(SeasonJsonConverter))]
public struct Season(string timeline, int turn)
{
    /// <summary>
    /// The root season of every game. This is defined to avoid any confusion about what the first turn or timeline
    /// should be or what season to use to key into a fresh <see cref="Timelines"/>.
    /// </summary>
    public static readonly Season First = new(Timelines.IntToString(0), 0);

    /// <summary>
    /// The timeline to which this season belongs.
    /// </summary>
    public string Timeline { get; } = timeline;

    /// <summary>
    /// The current turn, beginning at 0. Each season (spring and fall) is one turn.
    /// Phases that only occur after the fall phase occur when Turn % 2 == 1.
    /// The current year is (Turn / 2) + 1901.
    /// </summary>
    public int Turn { get; } = turn;

    /// <summary>
    /// The multiversal designation of this season.
    /// </summary>
    [JsonIgnore]
    public readonly string Key => $"{this.Timeline}{this.Turn}";

    /// <summary>
    /// Create a new season from a tuple coordinate.
    /// </summary>
    public Season((string timeline, int turn) coord) : this(coord.timeline, coord.turn) { }

    /// <summary>
    /// Create a new season from a combined string designation.
    /// </summary>
    /// <param name="designation"></param>
    public Season(string designation) : this(SplitKey(designation)) { }

    /// <summary>
    /// Extract the timeline and turn components of a season designation.
    /// </summary>
    /// <param name="seasonKey">A timeline-turn season designation.</param>
    /// <returns>The timeline and turn components.</returns>
    /// <exception cref="FormatException"></exception>
    public static (string timeline, int turn) SplitKey(string seasonKey)
    {
        int i = 1;
        for (; !char.IsAsciiDigit(seasonKey[i]) && i < seasonKey.Length; i++);
        return int.TryParse(seasonKey.AsSpan(i), out int turn)
            ? (seasonKey[..i], turn)
            : throw new FormatException($"Could not parse turn from {seasonKey}");
    }

    public override readonly string ToString() => Key;

    /// <remarks>
    /// Seasons are essentially 2D points, so they are equal when their components are equal.
    /// </remarks>
    public override readonly bool Equals([NotNullWhen(true)] object? obj)
        => obj is Season season
        && Timeline == season.Timeline
        && Turn == season.Turn;

    public static bool operator ==(Season one, Season two) => one.Equals(two);

    public static bool operator !=(Season one, Season two) => !(one == two);

    public override readonly int GetHashCode() => (Timeline, Turn).GetHashCode();
}