stack/apps/gateway/src/preferences/system-override.service.ts

import { Injectable, Logger } from '@nestjs/common';
import { createQueue, type QueueHandle } from '@mosaic/queue';

const SESSION_SYSTEM_KEY = (sessionId: string) => `mosaic:session:${sessionId}:system`;
const SESSION_SYSTEM_FRAGMENTS_KEY = (sessionId: string) =>
  `mosaic:session:${sessionId}:system:fragments`;
const SYSTEM_OVERRIDE_TTL_SECONDS = 604800; // 7 days

interface OverrideFragment {
  text: string;
  addedAt: number;
}

@Injectable()
export class SystemOverrideService {
  private readonly logger = new Logger(SystemOverrideService.name);
  private readonly handle: QueueHandle;

  constructor() {
    this.handle = createQueue();
  }

  async set(sessionId: string, override: string): Promise<void> {
    // Load existing fragments
    const existing = await this.handle.redis.get(SESSION_SYSTEM_FRAGMENTS_KEY(sessionId));
    const fragments: OverrideFragment[] = existing
      ? (JSON.parse(existing) as OverrideFragment[])
      : [];

    // Append new fragment
    fragments.push({ text: override, addedAt: Date.now() });

    // Condense fragments into one coherent override
    const texts = fragments.map((f) => f.text);
    const condensed = await this.condenseOverrides(texts);

    // Store both: fragments array and condensed result
    const pipeline = this.handle.redis.pipeline();
    pipeline.setex(
      SESSION_SYSTEM_FRAGMENTS_KEY(sessionId),
      SYSTEM_OVERRIDE_TTL_SECONDS,
      JSON.stringify(fragments),
    );
    pipeline.setex(SESSION_SYSTEM_KEY(sessionId), SYSTEM_OVERRIDE_TTL_SECONDS, condensed);
    await pipeline.exec();

    this.logger.debug(
      `Set system override for session ${sessionId} (${fragments.length} fragment(s), TTL=${SYSTEM_OVERRIDE_TTL_SECONDS}s)`,
    );
  }

  async get(sessionId: string): Promise<string | null> {
    return this.handle.redis.get(SESSION_SYSTEM_KEY(sessionId));
  }

  async renew(sessionId: string): Promise<void> {
    const pipeline = this.handle.redis.pipeline();
    pipeline.expire(SESSION_SYSTEM_KEY(sessionId), SYSTEM_OVERRIDE_TTL_SECONDS);
    pipeline.expire(SESSION_SYSTEM_FRAGMENTS_KEY(sessionId), SYSTEM_OVERRIDE_TTL_SECONDS);
    await pipeline.exec();
  }

  async clear(sessionId: string): Promise<void> {
    await this.handle.redis.del(
      SESSION_SYSTEM_KEY(sessionId),
      SESSION_SYSTEM_FRAGMENTS_KEY(sessionId),
    );
    this.logger.debug(`Cleared system override for session ${sessionId}`);
  }

  /**
   * Merge an array of override fragments into one coherent string.
   * If only one fragment exists, returns it as-is.
   * For multiple fragments, calls Haiku to produce a merged instruction.
   * Falls back to newline concatenation if the LLM call fails.
   */
  async condenseOverrides(fragments: string[]): Promise<string> {
    if (fragments.length === 0) return '';
    if (fragments.length === 1) return fragments[0]!;

    const numbered = fragments.map((f, i) => `${i + 1}. ${f}`).join('\n');
    const prompt =
      `Merge these system prompt instructions into one coherent paragraph. ` +
      `If instructions conflict, favor the most recently added (last in the list). ` +
      `Be concise — output only the merged instruction, nothing else.\n\n` +
      `Instructions (oldest first):\n${numbered}`;

    const apiKey = process.env['ANTHROPIC_API_KEY'];
    if (!apiKey) {
      this.logger.warn('ANTHROPIC_API_KEY not set — falling back to newline concatenation');
      return fragments.join('\n');
    }

    try {
      const response = await fetch('https://api.anthropic.com/v1/messages', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          'x-api-key': apiKey,
          'anthropic-version': '2023-06-01',
        },
        body: JSON.stringify({
          model: 'claude-haiku-4-5-20251001',
          max_tokens: 1024,
          messages: [{ role: 'user', content: prompt }],
        }),
      });

      if (!response.ok) {
        const errorText = await response.text();
        throw new Error(`Anthropic API error ${response.status}: ${errorText}`);
      }

      const data = (await response.json()) as {
        content: Array<{ type: string; text: string }>;
      };

      const textBlock = data.content.find((c) => c.type === 'text');
      if (!textBlock) {
        throw new Error('No text block in Anthropic response');
      }

      return textBlock.text.trim();
    } catch (err) {
      this.logger.error(
        `Condensation LLM call failed — falling back to newline concatenation: ${String(err)}`,
      );
      return fragments.join('\n');
    }
  }
}