package pkcs12

import (
	"crypto/sha1"
	"math/big"
)

var (
	deriveKeyByAlg = map[string]func(salt, password []byte, iterations int) []byte{
		pbeWithSHAAnd3KeyTripleDESCBC: func(salt, password []byte, iterations int) []byte {
			return pbkdf(sha1Sum, 20, 64, salt, password, iterations, 1, 24)
		},
		pbewithSHAAnd40BitRC2CBC: func(salt, password []byte, iterations int) []byte {
			return pbkdf(sha1Sum, 20, 64, salt, password, iterations, 1, 5)
		},
	}
	deriveIVByAlg = map[string]func(salt, password []byte, iterations int) []byte{
		pbeWithSHAAnd3KeyTripleDESCBC: func(salt, password []byte, iterations int) []byte {
			return pbkdf(sha1Sum, 20, 64, salt, password, iterations, 2, 8)
		},
		pbewithSHAAnd40BitRC2CBC: func(salt, password []byte, iterations int) []byte {
			return pbkdf(sha1Sum, 20, 64, salt, password, iterations, 2, 8)
		},
	}
)

func sha1Sum(in []byte) []byte {
	sum := sha1.Sum(in)
	return sum[:]
}

func pbkdf(hash func([]byte) []byte, u, v int, salt, password []byte, r int, ID byte, size int) (key []byte) {
	// implementation of https://tools.ietf.org/html/rfc7292#appendix-B.2 , RFC text verbatim in comments

	//    Let H be a hash function built around a compression function f:

	//       Z_2^u x Z_2^v -> Z_2^u

	//    (that is, H has a chaining variable and output of length u bits, and
	//    the message input to the compression function of H is v bits).  The
	//    values for u and v are as follows:

	//            HASH FUNCTION     VALUE u        VALUE v
	//              MD2, MD5          128            512
	//                SHA-1           160            512
	//               SHA-224          224            512
	//               SHA-256          256            512
	//               SHA-384          384            1024
	//               SHA-512          512            1024
	//             SHA-512/224        224            1024
	//             SHA-512/256        256            1024

	//    Furthermore, let r be the iteration count.

	//    We assume here that u and v are both multiples of 8, as are the
	//    lengths of the password and salt strings (which we denote by p and s,
	//    respectively) and the number n of pseudorandom bits required.  In
	//    addition, u and v are of course non-zero.

	//    For information on security considerations for MD5 [19], see [25] and
	//    [1], and on those for MD2, see [18].

	//    The following procedure can be used to produce pseudorandom bits for
	//    a particular "purpose" that is identified by a byte called "ID".
	//    This standard specifies 3 different values for the ID byte:

	//    1.  If ID=1, then the pseudorandom bits being produced are to be used
	//        as key material for performing encryption or decryption.

	//    2.  If ID=2, then the pseudorandom bits being produced are to be used
	//        as an IV (Initial Value) for encryption or decryption.

	//    3.  If ID=3, then the pseudorandom bits being produced are to be used
	//        as an integrity key for MACing.

	//    1.  Construct a string, D (the "diversifier"), by concatenating v/8
	//        copies of ID.
	D := []byte{}
	for i := 0; i < v; i++ {
		D = append(D, ID)
	}

	//    2.  Concatenate copies of the salt together to create a string S of
	//        length v(ceiling(s/v)) bits (the final copy of the salt may be
	//        truncated to create S).  Note that if the salt is the empty
	//        string, then so is S.

	S := []byte{}
	{
		s := len(salt)
		times := s / v
		if s%v > 0 {
			times++
		}
		for len(S) < times*v {
			S = append(S, salt...)
		}
		S = S[:times*v]
	}

	//    3.  Concatenate copies of the password together to create a string P
	//        of length v(ceiling(p/v)) bits (the final copy of the password
	//        may be truncated to create P).  Note that if the password is the
	//        empty string, then so is P.

	P := []byte{}
	{
		s := len(password)
		times := s / v
		if s%v > 0 {
			times++
		}
		for len(P) < times*v {
			P = append(P, password...)
		}
		password = nil
		P = P[:times*v]
	}

	//    4.  Set I=S||P to be the concatenation of S and P.
	I := append(S, P...)

	//    5.  Set c=ceiling(n/u).
	c := size / u
	if size%u > 0 {
		c++
	}

	//    6.  For i=1, 2, ..., c, do the following:
	A := make([]byte, c*20)
	for i := 0; i < c; i++ {

		//        A.  Set A2=H^r(D||I). (i.e., the r-th hash of D||1,
		//            H(H(H(... H(D||I))))
		Ai := hash(append(D, I...))
		for j := 1; j < r; j++ {
			Ai = hash(Ai[:])
		}
		copy(A[i*20:], Ai[:])

		if i < c-1 { // skip on last iteration

			//        B.  Concatenate copies of Ai to create a string B of length v
			//            bits (the final copy of Ai may be truncated to create B).
			B := []byte{}
			for len(B) < v {
				B = append(B, Ai[:]...)
			}
			B = B[:v]

			//        C.  Treating I as a concatenation I_0, I_1, ..., I_(k-1) of v-bit
			//            blocks, where k=ceiling(s/v)+ceiling(p/v), modify I by
			//            setting I_j=(I_j+B+1) mod 2^v for each j.
			{
				Bbi := new(big.Int)
				Bbi.SetBytes(B)

				one := big.NewInt(1)

				for j := 0; j < len(I)/v; j++ {
					Ij := new(big.Int)
					Ij.SetBytes(I[j*v : (j+1)*v])
					Ij.Add(Ij, Bbi)
					Ij.Add(Ij, one)
					Ijb := Ij.Bytes()
					if len(Ijb) > v {
						Ijb = Ijb[len(Ijb)-v:]
					}
					copy(I[j*v:(j+1)*v], Ijb)
				}
			}
		}
	}
	//    7.  Concatenate A_1, A_2, ..., A_c together to form a pseudorandom
	//        bit string, A.

	//    8.  Use the first n bits of A as the output of this entire process.
	A = A[:size]

	return A

	//    If the above process is being used to generate a DES key, the process
	//    should be used to create 64 random bits, and the key's parity bits
	//    should be set after the 64 bits have been produced.  Similar concerns
	//    hold for 2-key and 3-key triple-DES keys, for CDMF keys, and for any
	//    similar keys with parity bits "built into them".
}