transform = require './transform'
SRP = require './srp'

# This is a high-level client interface for the SRP protocol.
class Server

	init: (options, callback) ->
		@vBuf = Buffer.from options.verifier, 'hex'
		@saltBuf = Buffer.from options.salt, 'hex'

		length = options.length || 4096;
		@srp = new SRP length

		if options.b
			bBuf = Buffer.from options.b, 'hex'
			@bInt = transform.buffer.toBigInteger bBuf
			@BBuf = @srp.B b: @bInt, v: transform.buffer.toBigInteger @vBuf
			callback()
		else
			@srp.b (err, b) =>
				@bInt = b
				@BBuf = @srp.B b: @bInt, v: transform.buffer.toBigInteger @vBuf

				callback()

	getPublicKey: () ->
		return @BBuf.toString 'hex'

	getPrivateKey: () ->
		bBuf = transform.bigInt.toBuffer @bInt
		return bBuf.toString 'hex'

	getSalt: () ->
		return @saltBuf.toString 'hex'

	setClientPublicKey: (hexA) ->
		@ABuf = Buffer.from hexA, 'hex'

		ABigInt = transform.buffer.toBigInteger @ABuf

		if @srp.isZeroWhenModN ABigInt
			throw Error 'Invalid A value, abort'

		# We have been given B, which means we can calculate u.
		@uInt = @srp.u A: @ABuf, B: @BBuf

		# We can also calculate our secret.
		@SBuf = @srp.serverS
					A: transform.buffer.toBigInteger @ABuf
					v: transform.buffer.toBigInteger @vBuf
					u: @uInt
					b: @bInt

		# Once we have the secret, we can calculate K.
		@KBuf = @srp.K S: @SBuf

	getSharedKey: () ->
		return @KBuf.toString 'hex'

	checkClientProof: (M1hex) ->
		clientM1Buf = Buffer.from M1hex, 'hex'
		@M1Buf = @srp.M1 A: @ABuf, B: @BBuf, K: @KBuf

		result = @M1Buf.toString('hex') is clientM1Buf.toString('hex')
		return result

	getProof: () ->
		@M2Buf = @srp.M2 A: @ABuf, M: @M1Buf, K: @KBuf

		result = @M2Buf.toString('hex')
		return result

module.exports = Server