/*
 * Ed25519Utils.hpp — Ed25519 cryptographic primitives for Antheos auth.
 *
 * Thin wrapper around OpenSSL 3.0 EVP API. Keygen, sign, verify,
 * key serialization (hex), trusted key store, random nonce generation.
 *
 * All keys and signatures are hex-encoded strings. Private keys are
 * 64 hex chars (32-byte Ed25519 seed), public keys are 64 hex chars
 * (32 bytes), signatures are 128 hex chars (64 bytes).
 *
 * Copyright (c) 2026 Are Bjørby <are.bjorby@langsyn.org>
 * SPDX-License-Identifier: MIT
 */

#pragma once

#include <cstddef>
#include <cstdint>
#include <string>
#include <string_view>
#include <vector>

namespace antpeer {
namespace crypto {

/* ── Key types ────────────────────────────────────────────────────── */

struct KeyPair {
    std::string private_key;   /* 64 hex chars (32-byte Ed25519 seed) */
    std::string public_key;    /* 64 hex chars (32 bytes) */
    std::string key_id;        /* 32 hex chars (16-byte random identifier) */
};

struct TrustedKey {
    std::string oid;
    std::string key_id;        /* 32 hex chars */
    std::string public_key;    /* 64 hex chars */
};

/* ── Key generation ───────────────────────────────────────────────── */

/** Generate a fresh Ed25519 keypair with random key_id. */
KeyPair keygen();

/* ── Sign / Verify ────────────────────────────────────────────────── */

/** Sign data with Ed25519 private key. Returns signature as 128 hex chars. */
std::string sign(const void* data, size_t len,
                 const std::string& private_key_hex);
std::string sign(std::string_view data, const std::string& private_key_hex);

/** Verify Ed25519 signature against public key. */
bool verify(const void* data, size_t len,
            const std::string& signature_hex,
            const std::string& public_key_hex);
bool verify(std::string_view data,
            const std::string& signature_hex,
            const std::string& public_key_hex);

/* ── Nonce ────────────────────────────────────────────────────────── */

/** Generate cryptographically random nonce as hex string. */
std::string nonce(size_t bytes = 32);

/* ── Key I/O ──────────────────────────────────────────────────────── */

/**
 * Save keypair to file. Format:
 *   private_key = <hex>
 *   public_key  = <hex>
 *   key_id      = <hex>
 */
void save_key(const KeyPair& kp, const char* path);

/** Load keypair from file (same format as save_key). */
KeyPair load_key(const char* path);

/* ── Trusted key store ────────────────────────────────────────────── */

/**
 * Load trusted keys from config file. Format (one per line):
 *   OID  key_id  public_key_hex
 * Lines starting with # are comments. Empty lines are skipped.
 */
std::vector<TrustedKey> load_trusted_keys(const char* path);

/**
 * Look up public key for an OID in a trusted key set.
 * If key_id is non-empty, matches both OID and key_id.
 * Returns nullptr if not found.
 */
const TrustedKey* find_trusted_key(const std::vector<TrustedKey>& keys,
                                   std::string_view oid,
                                   std::string_view key_id = {});

/* ── Hex utilities ────────────────────────────────────────────────── */

std::string to_hex(const uint8_t* data, size_t len);
bool from_hex(const std::string& hex, uint8_t* out, size_t max_len);

} // namespace crypto
} // namespace antpeer