✨ support condition

src/struct/struct.ts

@@ -2,9 +2,11 @@ import { DataType } from "../dataType";
 import { definePackage } from "../package/definePackages";
 import { PackageType } from "../package/package";
 
-export type StructConf = Array<{ name: string; type: DataType<any>; default?: any }>;
+export type StructConf = Array<{ name: string; type: DataType<any>; default?: any; condition?: ItemCondition }>;
 export type StructData = { [row_name: string]: any };
 
+export type ItemCondition = (data: StructData) => boolean;
+
 export class Struct<T extends StructData> implements DataType<StructData & T> {
     readonly config: StructConf;
 
@@ -14,16 +16,18 @@ export class Struct<T extends StructData> implements DataType<StructData & T> {
 
     write(value: T): Buffer {
         const result: Buffer[] = [];
-        for (let { name, type, default: defaultValue } of this.config) {
-            const fixedValue = value[name];
-            result.push(type.write(fixedValue ?? defaultValue));
+        for (let { name, type, default: defaultValue, condition } of this.config) {
+            if (condition && !condition(value)) continue;
+            const itemValue = value[name] ?? defaultValue;
+            result.push(type.write(itemValue));
         }
         return Buffer.concat(result);
     }
     read(buffer: Buffer, offset: number): [T, number] {
         let structOffset = 0;
         let result: T = {} as T;
-        for (let { name, type } of this.config) {
+        for (let { name, type, condition } of this.config) {
+            if (condition && !condition(result)) continue;
             let [value, rowOffset] = type.read(buffer, offset + structOffset);
             (result as StructData)[name] = value;
             structOffset += rowOffset;

src/struct/structBuilder.ts

@@ -1,7 +1,7 @@
 import { BaseTypes } from "../baseTypes";
 import { DataType } from "../dataType";
 import { TypeGenerator } from "../defineType";
-import { Struct, StructConf, StructData } from "./struct";
+import { ItemCondition, Struct, StructConf, StructData } from "./struct";
 
 export class StructBuilder {
     static new() {
@@ -18,13 +18,31 @@ export class StructBuilder {
         this.structConf.push({ name, type, ...(default_value === undefined ? null : { default: default_value }) });
         return this;
     }
+
     generatorRow<C extends any[], T>(name: string, generator: TypeGenerator<C, T>, default_value?: T) {
         return (...param: C) => {
             this.row(name, generator(...param), default_value);
             return this;
         };
     }
 
+    setCondition(row_name: string, condition: ItemCondition): this;
+    setCondition(condition: ItemCondition): this;
+    setCondition(...args: [string, ItemCondition] | [ItemCondition]) {
+        if (typeof args[0] === "function") {
+            const [condition] = args;
+            this.structConf[this.structConf.length - 1].condition = condition;
+        } else {
+            const [row_name, condition] = args;
+            for (let [index, row] of this.structConf.entries())
+                if (row.name == row_name) {
+                    this.structConf[index].condition = condition;
+                    break;
+                }
+        }
+        return this;
+    }
+
     // Int8
 
     rowInt8(name: string, default_value?: number) {