feat: add predicates

fixes #1

Author: luxass

src/loom.ts

@@ -8,12 +8,28 @@ export interface LoomConfig<
   TInputSchema extends z.ZodType,
   TOptionsSchema extends z.ZodType,
 > {
+  /**
+   * The schema of the input data.
+   */
   inputSchema: TInputSchema;
+
+  /**
+   * The schema of the options.
+   */
   optionsSchema: TOptionsSchema;
+
+  /**
+   * The template function.
+   */
   template: (
     ctx: LoomContext<TOptionsSchema>,
     item: TInputSchema["_input"]
   ) => string;
+
+  /**
+   * The predicate function.
+   */
+  predicate?: (ctx: LoomContext<TOptionsSchema>, item: TInputSchema["_input"]) => boolean;
 }
 
 export interface LoomInstance<
@@ -43,6 +59,11 @@ export function createLoom<
     const lines: string[] = [];
 
     for (const item of validatedInput) {
+      // if predicate is defined, and returns false, skip this item
+      if (config.predicate && !config.predicate(ctx, item)) {
+        continue;
+      }
+
       lines.push(config.template(ctx, item));
     }