import { accessSync, constants, statSync } from "node:fs";
import * as path from "node:path";

export type VerifierResourceSource = "project" | "package";

export interface ResolvedVerifierResource {
  path: string;
  source: VerifierResourceSource;
  attemptedPaths: string[];
}

interface ResourceCandidate {
  path: string;
  source: VerifierResourceSource;
}

export function resolveVerifierAgentPath(opts: {
  cwd: string;
  packageRoot: string;
  agentName: string;
}): ResolvedVerifierResource {
  return firstReadableResource([
    {
      source: "project",
      path: path.resolve(opts.cwd, ".pi", "agents", `${opts.agentName}.md`),
    },
    {
      source: "package",
      path: path.resolve(opts.packageRoot, "agents", `${opts.agentName}.md`),
    },
  ]);
}

export function resolveVerifierPromptPath(opts: {
  cwd: string;
  packageRoot: string;
  promptFileName: string;
}): ResolvedVerifierResource {
  return firstReadableResource([
    {
      source: "project",
      path: path.resolve(opts.cwd, ".pi", "verifier", "prompts", opts.promptFileName),
    },
    {
      source: "package",
      path: path.resolve(opts.packageRoot, "prompts", opts.promptFileName),
    },
  ]);
}

function firstReadableResource(candidates: ResourceCandidate[]): ResolvedVerifierResource {
  const attemptedPaths = candidates.map((candidate) => candidate.path);
  for (const candidate of candidates) {
    if (isReadableFile(candidate.path)) {
      return { ...candidate, attemptedPaths };
    }
  }

  const fallback = candidates[candidates.length - 1];
  if (!fallback) {
    return { path: "", source: "package", attemptedPaths };
  }
  return { ...fallback, attemptedPaths };
}

function isReadableFile(filePath: string): boolean {
  try {
    if (!statSync(filePath).isFile()) return false;
    accessSync(filePath, constants.R_OK);
    return true;
  } catch {
    return false;
  }
}