using System.Text.Json;
using System.Text.Json.Serialization;

namespace MrGameEng.Atlases;

/// <summary>
/// Serializable description of one packed atlas: its page image files and the source-relative
/// region keys with their pixel rectangles. Stored as a JSON <c>.atlas</c> file next to the pages.
/// </summary>
public sealed class AtlasMetadata
{
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        WriteIndented = true,
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
    };

    /// <summary>Format version, bumped on breaking metadata changes.</summary>
    public int Version { get; init; } = 1;

    /// <summary>Atlas name (group key with '/' replaced by '.').</summary>
    public string Name { get; init; } = "";

    /// <summary>Maximum page size the atlas was built with (staleness check input).</summary>
    public int PageSize { get; init; }

    /// <summary>Padding in pixels the atlas was built with (staleness check input).</summary>
    public int Padding { get; init; }

    /// <summary>Page image files (relative to the metadata file), in page-index order.</summary>
    public List<AtlasPage> Pages { get; init; } = [];

    /// <summary>Packed regions, sorted by key.</summary>
    public List<AtlasRegion> Regions { get; init; } = [];

    /// <summary>Serializes this metadata to indented JSON.</summary>
    public string ToJson() => JsonSerializer.Serialize(this, JsonOptions);

    /// <summary>Parses metadata from JSON produced by <see cref="ToJson"/>.</summary>
    public static AtlasMetadata FromJson(string json) =>
        JsonSerializer.Deserialize<AtlasMetadata>(json, JsonOptions)
        ?? throw new InvalidDataException("Atlas metadata JSON deserialized to null.");
}

/// <summary>One page image of an atlas.</summary>
public sealed class AtlasPage
{
    /// <summary>Image file name, relative to the metadata file.</summary>
    public string File { get; init; } = "";

    /// <summary>Page width in pixels.</summary>
    public int Width { get; init; }

    /// <summary>Page height in pixels.</summary>
    public int Height { get; init; }
}

/// <summary>One packed source texture inside an atlas.</summary>
public sealed class AtlasRegion
{
    /// <summary>
    /// Region key: the source path relative to the build source root, forward slashes,
    /// without the file extension (e.g. <c>Things/Pawn/Animal/Fox</c>).
    /// </summary>
    public string Key { get; init; } = "";

    /// <summary>Index of the page containing this region.</summary>
    public int Page { get; init; }

    /// <summary>X of the region in page pixels.</summary>
    public int X { get; init; }

    /// <summary>Y of the region in page pixels.</summary>
    public int Y { get; init; }

    /// <summary>Region width in pixels.</summary>
    [JsonPropertyName("w")]
    public int Width { get; init; }

    /// <summary>Region height in pixels.</summary>
    [JsonPropertyName("h")]
    public int Height { get; init; }
}