'use strict'

const secp256k1 = require('secp256k1')
const multihashing = require('multihashing-async')
const setImmediate = require('async/setImmediate')

const HASH_ALGORITHM = 'sha2-256'

module.exports = (randomBytes) => {
  const privateKeyLength = 32

  function generateKey (callback) {
    const done = (err, res) => setImmediate(() => callback(err, res))

    let privateKey
    do {
      privateKey = randomBytes(32)
    } while (!secp256k1.privateKeyVerify(privateKey))

    done(null, privateKey)
  }

  function hashAndSign (key, msg, callback) {
    const done = (err, res) => setImmediate(() => callback(err, res))

    multihashing.digest(msg, HASH_ALGORITHM, (err, digest) => {
      if (err) { return done(err) }

      try {
        const sig = secp256k1.sign(digest, key)
        const sigDER = secp256k1.signatureExport(sig.signature)
        return done(null, sigDER)
      } catch (err) { done(err) }
    })
  }

  function hashAndVerify (key, sig, msg, callback) {
    const done = (err, res) => setImmediate(() => callback(err, res))

    multihashing.digest(msg, HASH_ALGORITHM, (err, digest) => {
      if (err) { return done(err) }
      try {
        sig = secp256k1.signatureImport(sig)
        const valid = secp256k1.verify(digest, sig, key)
        return done(null, valid)
      } catch (err) { done(err) }
    })
  }

  function compressPublicKey (key) {
    if (!secp256k1.publicKeyVerify(key)) {
      throw new Error('Invalid public key')
    }
    return secp256k1.publicKeyConvert(key, true)
  }

  function decompressPublicKey (key) {
    return secp256k1.publicKeyConvert(key, false)
  }

  function validatePrivateKey (key) {
    if (!secp256k1.privateKeyVerify(key)) {
      throw new Error('Invalid private key')
    }
  }

  function validatePublicKey (key) {
    if (!secp256k1.publicKeyVerify(key)) {
      throw new Error('Invalid public key')
    }
  }

  function computePublicKey (privateKey) {
    validatePrivateKey(privateKey)
    return secp256k1.publicKeyCreate(privateKey)
  }

  return {
    generateKey: generateKey,
    privateKeyLength: privateKeyLength,
    hashAndSign: hashAndSign,
    hashAndVerify: hashAndVerify,
    compressPublicKey: compressPublicKey,
    decompressPublicKey: decompressPublicKey,
    validatePrivateKey: validatePrivateKey,
    validatePublicKey: validatePublicKey,
    computePublicKey: computePublicKey
  }
}