import { existsSync, readdirSync, readFileSync, statSync } from "node:fs";
import { dirname, join } from "node:path";
import { getAgentDir, parseFrontmatter } from "@mariozechner/pi-coding-agent";

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

export interface SubagentPresetDiscoveryResult {
  presets: SubagentPreset[];
  projectPresetsDir: string | null;
}

function findNearestProjectPresetsDir(cwd: string): string | null {
  let current = cwd;
  while (true) {
    const candidate = join(current, ".pi", "subagents");
    try {
      if (statSync(candidate).isDirectory()) return candidate;
    } catch (_err) {
      // ignore
    }
    const parent = dirname(current);
    if (parent === current) return null;
    current = parent;
  }
}

function loadPresetDir(dir: string, source: "global" | "project"): SubagentPreset[] {
  if (!existsSync(dir)) return [];
  const entries = readdirSync(dir, { withFileTypes: true });
  const presets: SubagentPreset[] = [];

  for (const entry of entries) {
    if (!entry.name.endsWith(".md")) continue;
    if (!entry.isFile() && !entry.isSymbolicLink()) continue;
    const filePath = join(dir, entry.name);
    let content: string;
    try {
      content = readFileSync(filePath, "utf8");
    } catch (_err) {
      continue;
    }

    const parsed = parseFrontmatter<Record<string, unknown>>(content);
    const frontmatter = parsed.frontmatter ?? {};
    const body = parsed.body ?? "";

    if (typeof frontmatter.name !== "string") continue;
    if (typeof frontmatter.description !== "string") continue;

    const tools = typeof frontmatter.tools === "string"
      ? frontmatter.tools.split(",").map((t) => t.trim()).filter(Boolean)
      : undefined;

    presets.push({
      name: frontmatter.name,
      description: frontmatter.description,
      model: typeof frontmatter.model === "string" ? frontmatter.model : undefined,
      tools: tools && tools.length > 0 ? tools : undefined,
      systemPrompt: body.trim(),
      source,
      filePath,
    });
  }

  return presets;
}

export function discoverSubagentPresets(cwd: string, options: { homeDir?: string } = {}): SubagentPresetDiscoveryResult {
  const globalAgentDir = options.homeDir ? join(options.homeDir, ".pi", "agent") : getAgentDir();
  const globalDir = join(globalAgentDir, "subagents");
  const projectPresetsDir = findNearestProjectPresetsDir(cwd);

  const map = new Map<string, SubagentPreset>();

  for (const preset of loadPresetDir(globalDir, "global")) {
    map.set(preset.name, preset);
  }

  if (projectPresetsDir) {
    for (const preset of loadPresetDir(projectPresetsDir, "project")) {
      // project overrides global by name
      map.set(preset.name, preset);
    }
  }

  return { presets: Array.from(map.values()), projectPresetsDir };
}