Add tint override to texture packs

src/main/kotlin/features/texturepack/TintOverrides.kt

@@ -0,0 +1,75 @@
+package moe.nea.firmament.features.texturepack
+
+import com.google.gson.JsonObject
+import com.google.gson.JsonPrimitive
+import moe.nea.firmament.util.ErrorUtil
+import moe.nea.firmament.util.assertNotNullOr
+
+data class TintOverrides(
+	val layerMap: Map<Int, TintOverride> = mapOf()
+) {
+	val hasOverrides by lazy { layerMap.values.any { it !is Reset } }
+
+	companion object {
+		val EMPTY = TintOverrides()
+		private val threadLocal = object : ThreadLocal<TintOverrides>() {}
+		fun enter(overrides: TintOverrides?) {
+			ErrorUtil.softCheck("Double entered tintOverrides") {
+				threadLocal.get() == null
+			}
+			threadLocal.set(overrides ?: EMPTY)
+		}
+
+		fun exit(overrides: TintOverrides?) {
+			ErrorUtil.softCheck("Exited with non matching enter tintOverrides") {
+				threadLocal.get() == (overrides ?: EMPTY)
+			}
+			threadLocal.remove()
+		}
+
+		fun getCurrentOverrides() =
+			assertNotNullOr(threadLocal.get(), "Got current tintOverrides without entering") { EMPTY }
+
+		fun parse(jsonObject: JsonObject): TintOverrides {
+			val map = mutableMapOf<Int, TintOverride>()
+			for ((key, value) in jsonObject.entrySet()) {
+				val layerIndex =
+					ErrorUtil.notNullOr(key.toIntOrNull(),
+					                    "Unknown layer index $value. Should be integer") { continue }
+				if (value.isJsonNull) {
+					map[layerIndex] = Reset
+					continue
+				}
+				val override = (value as? JsonPrimitive)
+					?.takeIf(JsonPrimitive::isNumber)
+					?.asInt
+					?.let(::Fixed)
+				if (override == null) {
+					ErrorUtil.softError("Invalid tint override for a layer: $value")
+					continue
+				}
+				map[layerIndex] = override
+			}
+			return TintOverrides(map)
+		}
+	}
+
+	fun mergeWithParent(parent: TintOverrides): TintOverrides {
+		val mergedMap = parent.layerMap.toMutableMap()
+		mergedMap.putAll(this.layerMap)
+		return TintOverrides(mergedMap)
+	}
+
+	fun hasOverrides(): Boolean = hasOverrides
+	fun getOverride(tintIndex: Int): Int? {
+		return when (val tint = layerMap[tintIndex]) {
+			is Reset -> null
+			is Fixed -> tint.color
+			null -> null
+		}
+	}
+
+	sealed interface TintOverride
+	data object Reset : TintOverride
+	data class Fixed(val color: Int) : TintOverride
+}