'use strict'

const path = require('path')
const fs = require('../fs')
const { pathExists } = require('../path-exists')

const u = require('universalify').fromPromise

/**
 * Function that returns two types of paths, one relative to symlink, and one
 * relative to the current working directory. Checks if path is absolute or
 * relative. If the path is relative, this function checks if the path is
 * relative to symlink or relative to current working directory. This is an
 * initiative to find a smarter `srcpath` to supply when building symlinks.
 * This allows you to determine which path to use out of one of three possible
 * types of source paths. The first is an absolute path. This is detected by
 * `path.isAbsolute()`. When an absolute path is provided, it is checked to
 * see if it exists. If it does it's used, if not an error is returned
 * (callback)/ thrown (sync). The other two options for `srcpath` are a
 * relative url. By default Node's `fs.symlink` works by creating a symlink
 * using `dstpath` and expects the `srcpath` to be relative to the newly
 * created symlink. If you provide a `srcpath` that does not exist on the file
 * system it results in a broken symlink. To minimize this, the function
 * checks to see if the 'relative to symlink' source file exists, and if it
 * does it will use it. If it does not, it checks if there's a file that
 * exists that is relative to the current working directory, if does its used.
 * This preserves the expectations of the original fs.symlink spec and adds
 * the ability to pass in `relative to current working direcotry` paths.
 */

async function symlinkPaths (srcpath, dstpath) {
  if (path.isAbsolute(srcpath)) {
    try {
      await fs.lstat(srcpath)
    } catch (err) {
      err.message = err.message.replace('lstat', 'ensureSymlink')
      throw err
    }

    return {
      toCwd: srcpath,
      toDst: srcpath
    }
  }

  const dstdir = path.dirname(dstpath)
  const relativeToDst = path.join(dstdir, srcpath)

  const exists = await pathExists(relativeToDst)
  if (exists) {
    return {
      toCwd: relativeToDst,
      toDst: srcpath
    }
  }

  try {
    await fs.lstat(srcpath)
  } catch (err) {
    err.message = err.message.replace('lstat', 'ensureSymlink')
    throw err
  }

  return {
    toCwd: srcpath,
    toDst: path.relative(dstdir, srcpath)
  }
}

function symlinkPathsSync (srcpath, dstpath) {
  if (path.isAbsolute(srcpath)) {
    const exists = fs.existsSync(srcpath)
    if (!exists) throw new Error('absolute srcpath does not exist')
    return {
      toCwd: srcpath,
      toDst: srcpath
    }
  }

  const dstdir = path.dirname(dstpath)
  const relativeToDst = path.join(dstdir, srcpath)
  const exists = fs.existsSync(relativeToDst)
  if (exists) {
    return {
      toCwd: relativeToDst,
      toDst: srcpath
    }
  }

  const srcExists = fs.existsSync(srcpath)
  if (!srcExists) throw new Error('relative srcpath does not exist')
  return {
    toCwd: srcpath,
    toDst: path.relative(dstdir, srcpath)
  }
}

module.exports = {
  symlinkPaths: u(symlinkPaths),
  symlinkPathsSync
}