feat: 实现 PromptBuilder 段落构建器

src/core/prompt-builder.ts

@@ -0,0 +1,62 @@
+import type { PromptSection, SectionKind } from "./prompt-sections";
+
+export class PromptBuilder {
+  private sections: PromptSection[] = [];
+
+  head(text: string): this {
+    const existing = this.sections.findIndex((s) => s.kind === "head");
+    if (existing !== -1) {
+      this.sections[existing] = { kind: "head", content: text };
+    } else {
+      this.sections.push({ kind: "head", content: text });
+    }
+    return this;
+  }
+
+  context(text: string): this {
+    this.sections.push({ kind: "context", content: text });
+    return this;
+  }
+
+  prompt(text: string): this {
+    const existing = this.sections.findIndex((s) => s.kind === "prompt");
+    if (existing !== -1) {
+      this.sections[existing] = { kind: "prompt", content: text };
+    } else {
+      this.sections.push({ kind: "prompt", content: text });
+    }
+    return this;
+  }
+
+  guide(text: string): this {
+    this.sections.push({ kind: "guide", content: text });
+    return this;
+  }
+
+  warn(text: string): this {
+    this.sections.push({ kind: "warn", content: text });
+    return this;
+  }
+
+  build(): string {
+    const order: SectionKind[] = ["head", "context", "prompt", "guide", "warn"];
+    const groups: string[][] = order.map(() => []);
+
+    for (const section of this.sections) {
+      if (section.content.trim() === "") continue;
+      const idx = order.indexOf(section.kind);
+      if (idx !== -1) {
+        groups[idx].push(section.content);
+      }
+    }
+
+    const rendered: string[] = [];
+    for (const group of groups) {
+      if (group.length > 0) {
+        rendered.push(group.join("\n\n"));
+      }
+    }
+
+    return rendered.join("\n\n");
+  }
+}