// v1.12: extracted from inference.ts to give the prompt-assembly logic its
// own home + test surface. Adds the container-guidance layer (BOOCHAT.md
// baked into the Docker image, injected between the base prompt and the
// agent block).
//
// Resolution order, last-wins on conflicts:
//   base prompt
//   + container guidance (this layer, NEW in v1.12)
//   + agent.system_prompt          (resolved from data/AGENTS.md by getAgentById)
//   + session.system_prompt OR project.default_system_prompt

import { readFile, stat } from 'node:fs/promises';
import type { Agent, Project, Session } from '../types/api.js';

const BASE_SYSTEM_PROMPT = (projectPath: string) =>
  `You are BooCode Chat, a code investigation assistant. The user is working on a project located at ${projectPath}. Use the file-read tools (view_file, list_dir, grep, find_files) to investigate code when needed. Be concise. Cite file paths and line numbers when discussing code. Do not hallucinate file contents — read the file first. Tool results may be truncated; if so, narrow your query rather than guessing.`;

// v1.12 mtime-watch cache. Mirrors the safeStat pattern in services/agents.ts.
// On every call we stat the file; if the mtime matches the cached entry we
// return the cached content without re-reading. If the file is missing we
// cache { mtime: 0, content: null } so the not-found case still benefits
// from caching (one stat per call, no readFile attempt on a known-missing
// path). Because BOOCHAT.md is bind-mounted from the host, edits land
// immediately on the next chat turn — no container restart needed.
let cachedGuidance: { mtime: number; content: string | null } | null = null;

function resolveGuidancePath(): string {
  return process.env['CONTAINER_GUIDANCE_FILE'] ?? '/app/BOOCHAT.md';
}

export async function loadContainerGuidance(): Promise<string | null> {
  const path = resolveGuidancePath();
  try {
    return await readFile(path, 'utf8');
  } catch {
    return null;
  }
}

export async function getContainerGuidance(): Promise<string | null> {
  const path = resolveGuidancePath();
  let mtimeMs: number;
  try {
    const s = await stat(path);
    mtimeMs = s.mtimeMs;
  } catch {
    cachedGuidance = { mtime: 0, content: null };
    return null;
  }
  if (cachedGuidance && cachedGuidance.mtime === mtimeMs) {
    return cachedGuidance.content;
  }
  const content = await loadContainerGuidance();
  cachedGuidance = { mtime: mtimeMs, content };
  return content;
}

// Test-only: clear the cache so consecutive tests don't share state.
export function _resetContainerGuidanceCacheForTests(): void {
  cachedGuidance = null;
}

export async function buildSystemPrompt(
  project: Project,
  session: Session,
  agent: Agent | null
): Promise<string> {
  let out = BASE_SYSTEM_PROMPT(project.path);
  const guidance = await getContainerGuidance();
  if (guidance) {
    out += `\n\n--- Container guidance ---\n${guidance}\n--- end container guidance ---\n`;
  }
  if (agent && agent.system_prompt.trim().length > 0) {
    out += '\n\n' + agent.system_prompt.trim();
  }
  const sessionPrompt = session.system_prompt?.trim() ?? '';
  const projectPrompt = project.default_system_prompt?.trim() ?? '';
  const userPrompt = sessionPrompt || projectPrompt;
  if (userPrompt.length > 0) {
    out += '\n\n' + userPrompt;
  }
  return out;
}