stack/apps/gateway/src/agent/skill-loader.service.ts

import { Inject, Injectable, Logger } from '@nestjs/common';
import type { ToolDefinition } from '@mariozechner/pi-coding-agent';
import { SkillsService } from '../skills/skills.service.js';
import { createSkillTools } from './tools/skill-tools.js';

export interface LoadedSkills {
  /** Meta-tools: skill_list + skill_invoke */
  metaTools: ToolDefinition[];
  /**
   * System prompt additions from enabled prompt-type skills.
   * Callers may prepend these to the session system prompt.
   */
  promptAdditions: string[];
}

/**
 * SkillLoaderService is responsible for:
 * 1. Providing the skill meta-tools (skill_list, skill_invoke) to agent sessions.
 * 2. Collecting system-prompt additions from enabled prompt-type skills.
 */
@Injectable()
export class SkillLoaderService {
  private readonly logger = new Logger(SkillLoaderService.name);

  constructor(@Inject(SkillsService) private readonly skillsService: SkillsService) {}

  /**
   * Load enabled skills and return tools + prompt additions for a new session.
   */
  async loadForSession(): Promise<LoadedSkills> {
    const metaTools = createSkillTools(this.skillsService);

    let promptAdditions: string[] = [];
    try {
      const enabledSkills = await this.skillsService.findEnabled();
      promptAdditions = enabledSkills.flatMap((skill) => {
        const config = (skill.config ?? {}) as Record<string, unknown>;
        const skillType = (config['type'] as string | undefined) ?? 'prompt';
        if (skillType === 'prompt') {
          const addition = (config['prompt'] as string | undefined) ?? skill.description;
          return addition ? [addition] : [];
        }
        return [];
      });

      this.logger.log(
        `Loaded ${enabledSkills.length} enabled skill(s), ` +
          `${promptAdditions.length} prompt addition(s)`,
      );
    } catch (err) {
      // Non-fatal: log and continue without prompt additions
      this.logger.warn(
        `Failed to load skill prompt additions: ${err instanceof Error ? err.message : String(err)}`,
      );
    }

    return { metaTools, promptAdditions };
  }
}