Map-creating macro

Asset.hx

package;

class Asset
{
    public var locale : String;
    public var name : String;
    public var resource : String;
    public var type : String;
    
    public function new(locale : String, name : String, resource : String, type : String)
    {
        this.locale = locale;
        this.name = name;
        this.resource = resource;
        this.type = type;
    }
}

AssetData.hx

package;

typedef AssetData =
{
    var en : AssetLocaleData;
    var fr : AssetLocaleData;
}

typedef AssetLocaleData =
{
    var html : AssetPlatformData;
    var ios : AssetPlatformData;
    var android : AssetPlatformData;
}

typedef AssetPlatformData = Array<AssetEntryData>;

typedef AssetEntryData = 
{
    var name : String;
    var type : String;
    var resource : String;
    var isLoaded : Bool;
}

assets.json

{
  "en": {
    "html": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture.fbx",
         "isLoaded": false
      }
    ],
    "ios": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture_ios.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture_ios.fbx",
         "isLoaded": false
      }
    ],
    "android": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture_android.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture_android.fbx",
         "isLoaded": false
      }
    ]
  },
  "fr": {
    "html": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture.fbx",
         "isLoaded": false
      }
    ],
    "ios": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture_ios.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture_ios.fbx",
         "isLoaded": false
      }
    ],
    "android": [
      {
         "name": "textureA",
         "type": "texture",
         "resource": "some_url_to_a_texture_android.png",
         "isLoaded": false
      },
      {
         "name": "meshA",
         "type": "mesh",
         "resource": "some_url_to_a_texture_android.fbx",
         "isLoaded": false
      }
    ]
  }
}

AssetService.hx

package;

@:build(AssetServiceBuilder.build())
class AssetService
{
}

AssetServiceBuilder.hx

package;

import haxe.macro.Context;
import haxe.macro.Expr;
import haxe.macro.Type;

using haxe.macro.Tools;

class AssetServiceBuilder
{
    public static macro function build() : Array<Field>
    {
        // The build fields of the class being built
        var fields = Context.getBuildFields();
        // The asset data we want to store into a map
        var assetData : AssetData = haxe.Json.parse(sys.io.File.getContent("res/assets.json"));
        // The array of expressions representing the final map of assets
        var assets = [];
        
        // We use reflection to iterate through fields of the anonymous object that is assetData
        for (locale in Reflect.fields(assetData))
        {
            // This is akin to assetData[locale] or assetData.locale
            var l : AssetData.AssetLocaleData = Reflect.field(assetData, locale);
            // The array of expressions representing the internal map of assets per platform
            var localAssets = [];
            
            for (platform in Reflect.fields(l))
            {
                var p : AssetData.AssetPlatformData = Reflect.field(l, platform);
                // I'm only looking at the assets for a single platform to avoid duplicate keys
                if (platform == "ios")
                {
                    for (entry in p)
                    {
                        // Note the use of `macro` and expression reification (`$v{}`)
                        localAssets.push(macro $v{entry.name} => new Asset($v{locale}, $v{entry.name}, $v{entry.resource}, $v{entry.type}));
                    }
                }
            }
            // Note the use of `macro` and expression reification (`$a{}`)
            assets.push(macro $v{locale} => $a{localAssets});
        }
        
        // We "push" (add) a new field to the class
        fields.push({
            // Think of this as the line position that will be referenced on error
            pos: Context.currentPos(),
            // Field name
            name: "_assets",
            // We won't be adding any metadata
            meta: null,
            // The field will be a variable of the Map<String, Map<String, Asset>> type, and will contain the array of expressions making up a map
            kind: FieldType.FVar(macro : Map<String, Map<String, Asset>>, macro $a{assets}),
            // We won't be adding any documentation
            doc: null,
            // We'll give it private visibility
            access: [Access.APrivate]
        });
        
        // Once the build macro is done it needs to return the context's build fields
        return fields;
    }
}