import * as fs from "node:fs";
import * as path from "node:path";

export type AgentScope = "user" | "project" | "both";

export interface AgentConfig {
  name: string;
  description: string;
  tools?: string[];
  model?: string;
  systemPrompt: string;
  source: "user" | "project";
  filePath: string;
}

export interface AgentDiscoveryResult {
  agents: AgentConfig[];
  projectAgentsDir: string | null;
}

function getAgentDir(): string {
  const envDir = process.env.PI_AGENT_DIR;
  if (envDir) return envDir;
  return path.join(process.env.HOME ?? process.env.USERPROFILE ?? "/tmp", ".pi", "agent");
}

function parseFrontmatter<T>(content: string): { frontmatter: T; body: string } {
  const match = content.match(/^---\r?\n([\s\S]*?)\r?\n---\r?\n([\s\S]*)$/);
  if (!match) return { frontmatter: {} as T, body: content };
  const lines = match[1].split(/\r?\n/);
  const frontmatter: Record<string, string> = {};
  for (const line of lines) {
    const idx = line.indexOf(":");
    if (idx > 0) frontmatter[line.slice(0, idx).trim()] = line.slice(idx + 1).trim();
  }
  return { frontmatter: frontmatter as T, body: match[2] };
}

function loadAgentsFromDir(dir: string, source: "user" | "project"): AgentConfig[] {
  const agents: AgentConfig[] = [];
  if (!fs.existsSync(dir)) return agents;
  let entries: fs.Dirent[];
  try { entries = fs.readdirSync(dir, { withFileTypes: true }); } catch { return agents; }
  for (const entry of entries) {
    if (!entry.name.endsWith(".md")) continue;
    if (!entry.isFile() && !entry.isSymbolicLink()) continue;
    const filePath = path.join(dir, entry.name);
    let content: string;
    try { content = fs.readFileSync(filePath, "utf-8"); } catch { continue; }
    const { frontmatter, body } = parseFrontmatter<Record<string, string>>(content);
    if (!frontmatter.name || !frontmatter.description) continue;
    const tools = frontmatter.tools?.split(",").map((t: string) => t.trim()).filter(Boolean);
    agents.push({
      name: frontmatter.name,
      description: frontmatter.description,
      tools: tools && tools.length > 0 ? tools : undefined,
      model: frontmatter.model,
      systemPrompt: body,
      source,
      filePath,
    });
  }
  return agents;
}

function isDirectory(p: string): boolean {
  try { return fs.statSync(p).isDirectory(); } catch { return false; }
}

function findNearestProjectAgentsDir(cwd: string): string | null {
  let currentDir = cwd;
  while (true) {
    const candidate = path.join(currentDir, ".pi", "agents");
    if (isDirectory(candidate)) return candidate;
    const parentDir = path.dirname(currentDir);
    if (parentDir === currentDir) return null;
    currentDir = parentDir;
  }
}

export function discoverAgents(cwd: string, scope: AgentScope): AgentDiscoveryResult {
  const userDir = path.join(getAgentDir(), "agents");
  const projectAgentsDir = findNearestProjectAgentsDir(cwd);
  const userAgents = scope === "project" ? [] : loadAgentsFromDir(userDir, "user");
  const projectAgents = scope === "user" || !projectAgentsDir ? [] : loadAgentsFromDir(projectAgentsDir, "project");
  const agentMap = new Map<string, AgentConfig>();
  if (scope === "both") {
    for (const agent of userAgents) agentMap.set(agent.name, agent);
    for (const agent of projectAgents) agentMap.set(agent.name, agent);
  } else if (scope === "user") {
    for (const agent of userAgents) agentMap.set(agent.name, agent);
  } else {
    for (const agent of projectAgents) agentMap.set(agent.name, agent);
  }
  return { agents: Array.from(agentMap.values()), projectAgentsDir };
}