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+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Library: noscrypt
+* Package: noscrypt
+* File: noscrypt.h
+* 
+* noscrypt is free software: you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published
+* by the Free Software Foundation, either version 2 of the License,
+* or (at your option) any later version.
+*
+* noscrypt is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+* General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with noscrypt. If not, see http://www.gnu.org/licenses/.
+*/
+
+/*
+* noscrypt is a an open-source, strict C89 library that performs the basic 
+* cryptographic operations found in the Nostr protocol. It is designed to be
+* portable and easy to use in any C89 compatible environment. It is also designed
+*/
+
+#pragma once
+
+#ifndef NOSCRYPT_H
+#define NOSCRYPT_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+#if defined(_MSC_VER) || defined(WIN32) || defined(_WIN32)
+	#define IS_WINDOWS
+#endif
+
+//Set api export calling convention (allow used to override)
+#ifndef NC_CC
+	#ifdef IS_WINDOWS
+		//STD for importing to other languages such as .NET
+		#define NC_CC __stdcall
+	#else
+		#define NC_CC 
+	#endif
+#endif // !NC_CC
+
+#ifndef NC_EXPORT	//Allow users to disable the export/impoty macro if using source code directly
+	#ifdef NOSCRYPT_EXPORTING
+		#ifdef IS_WINDOWS
+			#define NC_EXPORT __declspec(dllexport)
+		#else
+			#define NC_EXPORT __attribute__((visibility("default")))
+		#endif // IS_WINDOWS
+	#else
+		#ifdef IS_WINDOWS
+			#define NC_EXPORT __declspec(dllimport)
+		#else
+			#define NC_EXPORT
+		#endif // IS_WINDOWS
+	#endif // !NOSCRYPT_EXPORTING
+#endif // !NC_EXPORT
+
+
+#ifndef IS_WINDOWS
+	#ifndef inline
+		#define inline __inline__
+	#endif // !inline
+#endif // !IS_WINDOWS
+
+//NULL
+#ifndef NULL
+	#define NULL ((void*)0)
+#endif // !NULL
+
+/*
+* CONSTANTS
+*/
+#define BIP340_PUBKEY_HEADER_BYTE 0x02
+#define NIP44_MESSAGE_KEY_SIZE 76
+#define NC_ENCRYPTION_NONCE_SIZE 32
+#define NC_SEC_KEY_SIZE 32
+#define NC_PUBKEY_SIZE 32
+#define NC_SHARED_SEC_SIZE 32
+#define NC_CONV_KEY_SIZE 32
+#define NC_MESSAGE_KEY_SIZE NIP44_MESSAGE_KEY_SIZE
+
+/*
+* From spec
+* https://github.com/nostr-protocol/nips/blob/master/44.md#decryption
+*/
+#define NIP44_MIN_ENC_MESSAGE_SIZE 1
+#define NIP44_MAX_ENC_MESSAGE_SIZE 65535
+#define NIP44_MIN_DEC_MESSAGE_SIZE 99
+#define NIP44_MAX_DEC_MESSAGE_SIZE 65603 
+
+/*
+* The Nip44 constant salt 
+* https://github.com/nostr-protocol/nips/blob/master/44.md#encryption
+*/
+static const uint8_t Nip44ConstantSalt[8] = { 0x6e, 0x69, 0x70, 0x34, 0x34, 0x2d, 0x76, 0x32 };
+
+/*
+*	ERROR CODES
+* 
+* Error codes are 64bit integers. The lower 8 bits are reserved for 
+* the error code, and the upper 8 bits are reserved for the argument 
+* position.
+* 
+* NCResult type is 64bit to also allow for positive return values for
+* operations that return a value count.
+*/
+
+#define ARG_POSITION_OFFSET 8
+#define NC_ERROR_CODE_MASK 0xFF
+
+#define NC_SUCCESS 0
+#define E_NULL_PTR -1
+#define E_INVALID_ARG -2
+#define E_INVALID_CONTEXT -3
+#define E_ARGUMENT_OUT_OF_RANGE -4
+
+/*
+* Validation macros
+*/
+
+#define CHECK_NULL_PTR(ptr) if(ptr == NULL) return E_NULL_PTR;
+#define CHECK_INVALID_ARG(x) if(x == NULL) return E_INVALID_ARG;
+#define CHECK_NULL_ARG(x, argPos) if(x == NULL) return NCResultWithArgPosition(E_NULL_PTR, argPos);
+#define CHECK_ARG_RANGE(x, min, max, argPos) if(x < min || x > max) return NCResultWithArgPosition(E_ARGUMENT_OUT_OF_RANGE, argPos);
+
+#ifdef DEBUG
+
+//Must include assert.h for assertions
+#include <assert.h>
+
+#define DEBUG_ASSERT(x) assert(x);
+#define DEBUG_ASSERT2(x, message) assert(x && message);
+#else
+#define DEBUG_ASSERT(x)
+#define DEBUG_ASSERT2(x, message)
+#endif
+
+/* A compressed resul/return value, negative values 
+are failure, 0 is success and positive values are 
+defined by the operation. 
+*/
+typedef int64_t NCResult;
+
+/*
+ An secp256k1 secret key (aka 32byte private key buffer)
+*/
+typedef struct secret_key_struct {
+
+	uint8_t key[NC_SEC_KEY_SIZE];
+
+}NCSecretKey;
+
+/*
+  An x-only secp256k1 public key
+*/
+typedef struct xonly_pubkey_struct {
+
+	uint8_t key[NC_PUBKEY_SIZE];
+
+}NCPublicKey;
+
+/*
+	An opaque full library context object
+*/
+typedef struct ctx_struct {
+
+	void* secpCtx;
+
+}NCContext;
+
+/*
+* The encryption arguments structure. This structure is used to pass 
+arguments to the encryption and decryption functions. It stores the
+data buffers and required nonce used for the stream cipher.
+*/
+typedef struct nc_encryption_struct {
+
+	/*
+	* The nonce used for the stream cipher.
+	*/
+	uint8_t nonce[NC_ENCRYPTION_NONCE_SIZE];
+
+	/* The input data buffer to encrypt/decrypt */
+	const void* inputData;
+
+	/* The output data buffer to write data to */
+	void* outputData;
+
+	/* The size of the data buffers. Buffers must 
+	* be the same size or larger than this value
+	*/
+	uint32_t dataSize;
+
+} NCCryptoData;
+
+/*
+	API FUNCTIONS
+*/
+
+static inline NCSecretKey* NCToSecKey(uint8_t key[NC_SEC_KEY_SIZE])
+{
+	return (NCSecretKey*)key;
+}
+
+static inline NCPublicKey* NCToPubKey(uint8_t key[NC_PUBKEY_SIZE])
+{
+	return (NCPublicKey*)key;
+}
+
+static inline NCResult NCResultWithArgPosition(NCResult err, uint8_t argPosition) 
+{
+	//Store the error code in the lower 8 bits and the argument position in the upper 24 bits
+	return (err & NC_ERROR_CODE_MASK) | (((uint32_t)argPosition) << ARG_POSITION_OFFSET);
+}
+
+/*
+* Parses an error code and returns the error code and the argument position 
+that caused the error.
+* @param result The error code to parse
+* @param code A pointer to the error code to write to
+* @param argPosition A pointer to the argument position to write to
+*/
+NC_EXPORT void NC_CC NCParseErrorCode(NCResult result, int* code, int* argPosition)
+{
+	//Get the error code from the lower 8 bits and the argument position from the upper 8 bits
+	*code = result & NC_ERROR_CODE_MASK;
+	*argPosition = (result >> ARG_POSITION_OFFSET) & 0xFF;
+}
+
+/*--------------------------------------
+*		LIB CONTEXT API
+*/
+
+/*
+* Runtime check for the size of the context struct to allow 
+for dynamic allocation when context size structure is not known. 
+* @return The size of the context struct in bytes
+*/
+NC_EXPORT uint32_t NC_CC NCGetContextStructSize(void);
+/*
+* Initializes a context struct with the given entropy
+* @param ctx A pointer to the context structure to initialize
+* @param entropy The 32byte entropy to initialize the context with
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCInitContext(
+	NCContext* ctx, 
+	const uint8_t entropy[32]
+);
+/*
+* Reinitializes a context struct with the given 
+* @param ctx A pointer to the context structure to initialize
+* @param entropy The 32byte entropy to initialize the context with
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCReInitContext(
+	NCContext* ctx, 
+	const uint8_t entropy[32]
+);
+
+/*
+* Destroys a context struct
+* @param ctx A pointer to the existing context structure to destroy
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCDestroyContext(NCContext* ctx);
+
+
+
+/*--------------------------------------
+*		HIGH LEVEL SIGNING API
+*/
+
+/*
+* Gets a 32byte x-only compressed public key from the given secret key
+* @param ctx A pointer to the existing library context
+* @param sk A pointer to the secret key
+* @param pk A pointer to the compressed public key buffer to write to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCGetPublicKey(
+	const NCContext* ctx, 
+	const NCSecretKey* sk, 
+	NCPublicKey* pk
+);
+/*
+* Validates that a given secret key is valid according to the secp256k1 curve. This 
+is functionally the same as calling secp256k1_ec_seckey_verify. 
+* @param ctx A pointer to the existing library context
+* @param sk A pointer to the secret key to verify 
+* @return NC_SUCCESS if the secret key is in a valid format, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCValidateSecretKey(
+	const NCContext* ctx, 
+	const NCSecretKey* sk
+);
+
+
+/*
+* Signs a raw message after computing the sha256 checksum using the
+given secret key and writes the signature to the sig64 buffer.
+* @param ctx A pointer to the existing library context
+* @param sk A pointer to the secret key to sign with
+* @param random32 A pointer to the 32byte random32 buffer to use for signing
+* @param data A pointer to the raw data buffer to sign
+* @param dataSize The size of the raw data buffer
+* @param sig64 A pointer to the 64byte buffer to write the signature to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCSignData(
+	const NCContext* ctx,
+	const NCSecretKey* sk,
+	const uint8_t random32[32],
+	const uint8_t* data,
+	const size_t dataSize,
+	uint8_t sig64[64]
+);
+
+/*
+* Verifies a signature of a raw data buffer matches the output using the given public key.
+* @param ctx A pointer to the existing library context
+* @param sig64 The 64byte signature to verify
+* @param data A pointer to the raw data buffer to verify
+* @param dataSize The size of the raw data buffer
+* @param pk A pointer to the the x-only compressed public key (x-only serialized public key)
+* @return NC_SUCCESS if the signature could be verified, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCVerifyData(
+	const NCContext* ctx,
+	const NCPublicKey* pk,
+	const uint8_t* data,
+	const size_t dataSize,
+	uint8_t sig64[64]
+);
+
+/*--------------------------------------
+*		EXTENDED SIGNING API
+*/
+
+/*
+* Signs a message using the given secret key and writes the signature to the sig64 buffer
+* @param ctx A pointer to the existing library context
+* @param sk A pointer to the secret key to sign with
+* @param random32 A pointer to the 32byte random32 buffer to use for signing
+* @param digest32 A pointer to 32byte sha256 digest32 to sign
+* @param sig64 A pointer to the 64byte buffer to write the signature to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCSignDigest(
+	const NCContext* ctx,
+	const NCSecretKey* sk,
+	const uint8_t random32[32],
+	const uint8_t digest32[32],
+	uint8_t sig64[64]
+);
+
+/*
+* Verifies a signature of a digest32 matches the output using the given public key.
+Equivalent to calling secp256k1_schnorrsig_verify.
+* @param ctx A pointer to the existing library context
+* @param sig64 The 64byte signature to verify
+* @param digest32 The 32byte digest32 to verify
+* @param pk A pointer to the the x-only compressed public key (x-only serialized public key)
+* @return NC_SUCCESS if the signature could be verified, otherwise an error code
+*/
+NC_EXPORT NCResult NC_CC NCVerifyDigest(
+	const NCContext* ctx,
+	const NCPublicKey* pk,
+	const uint8_t digest32[32],
+	const uint8_t sig64[64]
+);
+
+
+
+/*--------------------------------------
+*		HIGH LEVEL ENCRYPTION API
+*/
+
+/*
+*			NOTES
+* 
+*	NIP-44 requires that plaintext/ciphertext must be padded in powers of 2.
+*	Since this library operates on data at the binary level, and does not do 
+*	ANY runtime heap allocation, it is up to the user to ensure that the 
+*	plaintext/ciphertext buffers are padded properly in The NCryptoData struct
+*   before calling the encryption/decryption functions.
+*/
+
+/*
+* High level api for encrypting nostr messages using a secret key and a public key. Use
+the NCEncryptEx functions for extended encryption functionality
+* @param ctx The library context
+* @param sk The secret key (the local private key)
+* @param pk The 32byte compressed public key (x-only serialized public key) the other user's public key
+* @param args The encryption arguments
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCEncrypt(
+	const NCContext* ctx, 
+	const NCSecretKey* sk, 
+	const NCPublicKey* pk, 
+	NCCryptoData* args
+);
+
+/*
+* High level api for decrypting nostr messages using a secret key and a public key. Use
+the NCDecryptEx functions for extended decryption functionality.
+* @param ctx The library context
+* @param sk The secret key (the local private key)
+* @param pk The 32byte compressed public key (x-only serialized public key) the other user's public key
+* @param args The decryption arguments
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCDecrypt(
+	const NCContext* ctx, 
+	const NCSecretKey* sk, 
+	const NCPublicKey* pk, 
+	NCCryptoData* args
+);
+
+
+/*--------------------------------------
+*		EXTENDED ENCRYPTION API
+*/
+
+/*
+* Computes a NIP-44 shared secret from a secret key and a public key and 
+stores it in the sharedPoint buffer.
+* @param ctx A pointer to the existing library context
+* @param sk The secret key
+* @param pk The 32byte compressed public key (x-only serialized public key)
+* @param sharedPoint The 32byte buffer to store write the secret data to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCGetSharedSecret(
+	const NCContext* ctx, 
+	const NCSecretKey* sk, 
+	const NCPublicKey* pk, 
+	uint8_t sharedPoint[NC_SHARED_SEC_SIZE]
+);
+
+/*
+* Computes a NIP-44 conversation key from the local secret key and the remote 
+public key, and stores it in the conversationKey buffer.
+* @param ctx A pointer to the existing library context
+* @param sk A pointer to the 32byte the secret key
+* @param pk A pointer to the 32byte compressed public key (x-only serialized public key)
+* @param conversationKey The 32byte buffer to store write the conversation key to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCGetConversationKey(
+	const NCContext* ctx, 
+	const NCSecretKey* sk, 
+	const NCPublicKey* pk, 
+	uint8_t conversationKey[NC_CONV_KEY_SIZE]
+);
+/*
+* Computes a NIP-44 conversation key a shared secret/point, and stores it in the 
+conversationKey buffer.
+* @param ctx A pointer to the existing library context
+* @param sharedPoint A pointer to the 32byte shared secret/point
+* @param conversationKey The 32byte buffer to store write the conversation key to
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error
+*/
+NC_EXPORT NCResult NC_CC NCGetConversationKeyEx(
+	const NCContext* ctx, 
+	const uint8_t sharedPoint[NC_SHARED_SEC_SIZE], 
+	uint8_t conversationKey[NC_CONV_KEY_SIZE]
+);
+
+/*
+* Encrypts a message using the given conversation key and writes the encrypted message to the
+* output buffer. The output buffer must be at least 99 bytes in size.
+* @param ctx A pointer to the existing library context
+* @param conversationKey A pointer to the 32byte conversation key
+* @param args A pointer to the encryption arguments structure
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error.
+*/
+NC_EXPORT NCResult NC_CC NCEncryptEx(
+	const NCContext* ctx, 
+	const uint8_t conversationKey[NC_CONV_KEY_SIZE],
+	NCCryptoData* args
+);
+
+/*
+* Decrypts a message using the given conversation key and writes the decrypted message to the
+* output buffer. 
+* @param ctx A pointer to the existing library context
+* @param conversationKey A pointer to the 32byte conversation key
+* @param args A pointer to the decryption arguments structure
+* @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
+the error code and positional argument that caused the error.
+*/
+NC_EXPORT NCResult NC_CC NCDecryptEx(
+	const NCContext* ctx, 
+	const uint8_t conversationKey[NC_CONV_KEY_SIZE], 
+	NCCryptoData* args
+);
+
+#endif // !NOSCRYPT_H