import { access, mkdir, readdir, rm, stat, writeFile } from 'node:fs/promises';
import { constants } from 'node:fs';
import { extname, isAbsolute, join, normalize, parse, resolve, sep } from 'node:path';

export interface KnowledgeDocMetadata {
  name: string;
  size: number;
  modifiedAt: string;
  type: string;
}

export interface KnowledgeDocUploadInput {
  base64: string;
  fileName: string;
}

export const KNOWLEDGE_DOCS_DIR_ENV_NAME = 'ZN_AI_KNOWLEDGE_DOCS_DIR';

function getConfiguredDocsDir(): string {
  const override = process.env[KNOWLEDGE_DOCS_DIR_ENV_NAME]?.trim();
  if (override) {
    return resolve(override);
  }

  return resolve(process.cwd(), 'docs');
}

async function fileExists(filePath: string): Promise<boolean> {
  try {
    await access(filePath, constants.F_OK);
    return true;
  } catch {
    return false;
  }
}

export function getKnowledgeDocsDir(): string {
  return getConfiguredDocsDir();
}

export function isSafeKnowledgeDocName(fileName: string): boolean {
  const trimmed = fileName.trim();
  if (!trimmed) return false;
  if (trimmed === '.' || trimmed === '..') return false;
  if (isAbsolute(trimmed)) return false;
  return normalize(trimmed) === trimmed && parse(trimmed).base === trimmed;
}

export function resolveKnowledgeDocPath(fileName: string): string {
  if (!isSafeKnowledgeDocName(fileName)) {
    throw new Error('Invalid file name');
  }

  const docsDir = getKnowledgeDocsDir();
  const docsRoot = resolve(docsDir);
  const candidate = resolve(docsDir, fileName.trim());
  const rootWithSep = `${docsRoot}${docsRoot.endsWith(sep) ? '' : sep}`;

  if (candidate !== docsRoot && !candidate.startsWith(rootWithSep)) {
    throw new Error('Invalid file path');
  }

  return candidate;
}

async function ensureKnowledgeDocsDir(): Promise<void> {
  await mkdir(getKnowledgeDocsDir(), { recursive: true });
}

function getDocType(fileName: string, isDirectory: boolean): string {
  if (isDirectory) return 'directory';
  return extname(fileName).slice(1).toLowerCase() || 'file';
}

async function resolveAvailableFileName(fileName: string): Promise<string> {
  const docsDir = getKnowledgeDocsDir();
  const parsed = parse(fileName);
  let candidate = fileName;
  let counter = 1;

  while (await fileExists(join(docsDir, candidate))) {
    candidate = `${parsed.name}-${counter}${parsed.ext}`;
    counter += 1;
  }

  return candidate;
}

export async function listKnowledgeDocs(): Promise<KnowledgeDocMetadata[]> {
  await ensureKnowledgeDocsDir();
  const entries = await readdir(getKnowledgeDocsDir(), { withFileTypes: true });
  const results: KnowledgeDocMetadata[] = [];

  for (const entry of entries) {
    if (!entry.isFile() && !entry.isDirectory()) {
      continue;
    }

    const entryPath = join(getKnowledgeDocsDir(), entry.name);
    const info = await stat(entryPath);
    results.push({
      name: entry.name,
      size: info.size,
      modifiedAt: info.mtime.toISOString(),
      type: getDocType(entry.name, entry.isDirectory()),
    });
  }

  return results.sort((left, right) => {
    const leftTime = new Date(left.modifiedAt).getTime() || 0;
    const rightTime = new Date(right.modifiedAt).getTime() || 0;
    return rightTime - leftTime;
  });
}

export async function uploadKnowledgeDoc(input: KnowledgeDocUploadInput): Promise<KnowledgeDocMetadata> {
  await ensureKnowledgeDocsDir();

  if (!isSafeKnowledgeDocName(input.fileName)) {
    throw new Error('Invalid file name');
  }

  const buffer = Buffer.from(String(input.base64 || ''), 'base64');
  if (!buffer.length && String(input.base64 || '').trim()) {
    throw new Error('Invalid base64 payload');
  }

  const fileName = await resolveAvailableFileName(input.fileName.trim());
  const filePath = join(getKnowledgeDocsDir(), fileName);
  await writeFile(filePath, buffer);
  const info = await stat(filePath);

  return {
    name: fileName,
    size: info.size,
    modifiedAt: info.mtime.toISOString(),
    type: getDocType(fileName, false),
  };
}

export async function deleteKnowledgeDoc(fileName: string): Promise<void> {
  await ensureKnowledgeDocsDir();
  const filePath = resolveKnowledgeDocPath(fileName);
  await rm(filePath, { force: true });
}