/* SPDX-License-Identifier: Unlicense
 */

#define OPTPARSE_IMPLEMENTATION
#define OPTPARSE_API static
#ifdef __GNUC__
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wold-style-cast"
#pragma GCC diagnostic ignored "-Wshadow"
#endif
#include "optparse/optparse.h"
#ifdef __GNUC__
#pragma GCC diagnostic pop
#endif

#include "chardev.hpp"
#include "bus.hpp"
#include "graphics.hpp"
#include "vdp.hpp"
#include "io.hpp"
#include "m68k_debugging.hpp"
#include "gdbremote_parser.hpp"
#include "utils.hpp"
#include "musashi-m68k/m68k.h"
#include "musashi-m68k/m68kcpu.h"

#include <arpa/inet.h>
#include <cassert>
#include <cstdio>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <cstdarg>
#include <ctime>
#include <fcntl.h>
#include <sys/socket.h>
#include <unistd.h>
#include <signal.h>
#include <netdb.h>
#include <poll.h>

#if !defined(DEBUG_TRACE_INSTRUCTIONS)
#   define DEBUG_TRACE_INSTRUCTIONS 0
#endif

#if !defined(DEBUG_TRACE_GDB_REMOTE)
#   define DEBUG_TRACE_GDB_REMOTE 0
#endif

#define MESSAGE_BUFFER_SIZE 1024

unsigned char g_rom[ROM_SIZE] = {};
unsigned char g_ram[RAM_SIZE] = {};
unsigned char g_sound_ram[SOUND_RAM_SIZE] = {};
IO g_io1(IO1_START);
unsigned char g_psg[PSG_SIZE] = {};
VDP g_vdp(VDP_START);
std::vector<Breakpoint> code_bkpts{}, read_bkpts{}, write_bkpts{}, access_bkpts{};

uint64_t g_cycles_counter = 0;

bool quit{};

template<typename T, size_t S>
struct Backtrace {
    static_assert(S > 0, "Backtrace size cannot be zero");
    void Push(T value)
    {
        head = (head + 1) % S;
        buffer[head] = value;
    }
    void Normalize(void)
    {
        constexpr auto last_offset = S - 1;
        for (; head < last_offset; head++) {
            const T tmp = buffer[last_offset];
            memmove(&buffer[1], &buffer[0], (S - 1) * sizeof(buffer[0]));
            buffer[0] = tmp;
        }
    }
    static constexpr size_t Size(void) {
        return S;
    }
    T buffer[S]{};
    size_t head{};
};

static constexpr struct timespec kOneMillisecond{0, 1000000};
static constexpr struct timespec kIdleSleepTime{0, 10000000};
static char msg_buf[MESSAGE_BUFFER_SIZE];
static M68KDebuggingControl g_m68k_debug{};
static Backtrace<uint32_t, 10> g_pc_backtrace{};

static int set_socket_reuseaddr(const int socket_fd)
{
    const int val = 1;
    const socklen_t len = sizeof(val);
    return setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, (void*)&val, len);
}

static inline int SetNonblock(const int fd)
{
    const int flags = fcntl(fd, F_GETFL);
    if (flags == -1) {
        return errno;
    }
    const int ret = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
    if (ret == -1) {
        return errno;
    }
    return 0;
}

static int setup_socket(
        const char* host, uint16_t port, char* addrstr, size_t addrstr_size)
{
    struct addrinfo hints{}, * result{};
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;
    char port_str[6]{};
    snprintf(port_str, sizeof(port_str), "%u", port);
    const int gai_ret = getaddrinfo(host, port_str, &hints, &result);
    if (gai_ret != 0) {
        fprintf(stderr, "getaddrinfo(%s): %s\n", host, gai_strerror(gai_ret));
        return -1;
    }
    int socket_fd = -1;
    for (struct addrinfo* rp = result; rp != nullptr; rp = rp->ai_next) {
        socket_fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
        if (socket_fd == -1)
            continue;
        // Set O_NONBLOCK for the socket
        const int ret = SetNonblock(socket_fd);
        if (ret) {
            fprintf(stderr, "fcntl(socket_fd, F_SETFL O_NONBLOCK): %s\n", strerror(ret));
            close(socket_fd);
            socket_fd = -1;
            break;
        }
        // Make TCP port reusable in case of kill or crash.
        // Deliberate explanation: https://stackoverflow.com/a/3233022
        if (set_socket_reuseaddr(socket_fd) == -1) {
            perror("setsockopt failed");
            close(socket_fd);
            socket_fd = -1;
            break;
        }
        if (0 == bind(socket_fd, rp->ai_addr, rp->ai_addrlen)) {
            void* addr_ptr;
            if (rp->ai_addr->sa_family == AF_INET) {
                addr_ptr = reinterpret_cast<void*>(
                        &((struct sockaddr_in*)rp->ai_addr)->sin_addr);
            } else if (rp->ai_addr->sa_family == AF_INET6) {
                addr_ptr = reinterpret_cast<void*>(
                        &((struct sockaddr_in6*)rp->ai_addr)->sin6_addr);
            } else {
                assert(false);
            }
            inet_ntop(rp->ai_addr->sa_family, addr_ptr, addrstr, addrstr_size);
            addrstr[addrstr_size - 1] = '\0';
            break;
        }
        fprintf(stderr, "Binding to %s:%u failed\n", addrstr, port);
        close(socket_fd);
        socket_fd = -1;
    }
    freeaddrinfo(result);
    if (socket_fd == -1) {
        fprintf(stderr, "Could not bind or create socket: "
                "getaddrinfo did not give any suitable entry\n");
        return -1;
    }
    fprintf(stderr, "Binding to %s:%u done\n", addrstr, port);
    return socket_fd;
}

static inline bool IsReset(const std::string& command)
{
    if (command == "reset") return true;
    if (command == "reset halt") return true;
    if (command == "system_reset") return true;
    return false;
}

static std::string CreateResponse(
        M68KDebuggingControl& m68k_debug,
        const GDBRemote::Packet& packet)
{
    using namespace GDBRemote;
    switch (packet.type) {
    case PacketType::kNone:
        break;
    case PacketType::kQuerySupported:
        return "PacketSize=400000" // PacketSize number is in HEX
            // These commented-out options are from OpenOCD
            // TODO ";qXfer:memory-map:read+"
            // TODO ";qXfer:features:read+"
            // TODO ";qXfer:threads:read+"
            ";QStartNoAckMode+" // It makes GDB shit fast!
            ";vContSupported+" // We support "vCont?" packet
            ;
    case PacketType::kQueryHaltReason:
        return "S05"; // TODO real reason
    case PacketType::kQueryC:
        break;
    case PacketType::kQueryFThreadInfo:
        break;
    case PacketType::kQuerySThreadInfo:
        break;
    case PacketType::kQueryRTOSThreadInfo:
        break;
    case PacketType::kQueryAttached:
        return "1";
    case PacketType::kQueryTraceStatus:
        break;
    case PacketType::kQueryRcmd:
        {
            const auto * const packet_data =
                static_cast<const PacketDataRcmd*>(packet.data.get());
            if (IsReset(packet_data->data)) {
                m68k_pulse_reset();
                // I don't want to skip reset cycles here, because GDB does not
                // re-read registers every time, and if we skip reset cycles
                // here, the consequent "stepi" in gdb will end up on second
                // instruction of reset handler. If we don't skip reset cycles,
                // the first "stepi" after "monitor reset" will land us on the
                // first instruction in reset handler - I'd prefer this exact
                // behavior for now.
                return "OK";
            }
        }
        break;
    case PacketType::kQStartNoAckMode:
        m68k_debug.SetNoAckMode(true);
        return "OK";
    case PacketType::kSetThreadForCont:
        return "OK";
    case PacketType::kSetThreadForOps:
        break;
    case PacketType::kVMustReplyEmpty:
        break;
    case PacketType::kEnableExtendedMode:
        break;
    case PacketType::kInterrupt:
        m68k_debug.RaiseBreakpoint();
        return "S05"; // TODO real reason
    case PacketType::kContinue:
        m68k_debug.SetRunning(true);
        return "OK";
    case PacketType::kContinueAskSupported:
        return "vCont:c:s";
    case PacketType::kReadGeneralRegisters:
        {
            const M68KCPUState state = m68k_debug.GetCPUState();
            std::string result{};
            for (size_t i = 0; i < state.registers_count; i++)
            {
                constexpr size_t value_size = std::string_view("12345678").length();
                char value[value_size + 1]{};
                const int ret = snprintf(value, value_size + 1, "%08x", state.registers[i]);
                (void) ret;
                assert(ret == value_size);
                result += std::string(value, value_size);
            }
            return result;
        }
    case PacketType::kWriteGeneralRegisters:
        {
            const auto * const data =
                static_cast<const PacketDataWriteGeneralRegisters*>(packet.data.get());
            const auto& registers = data->registers;
            for (size_t i = 0; i < registers.size(); i++) {
                m68k_debug.SetRegister(static_cast<M68KRegister>(i), registers[i]);
            }
            return "OK";
        }
        break;
    case PacketType::kReadRegister:
        {
            const auto * const data =
                static_cast<const PacketDataReadRegister*>(packet.data.get());
            const auto reg_id = static_cast<M68KRegister>(data->reg_id);
            if (reg_id >= M68KRegister::kRegistersCount) {
                return "E00";
            }
            const uint32_t value = m68k_debug.GetRegister(reg_id);
            constexpr size_t value_size = std::string_view("12345678").length();
            char value_str[value_size + 1]{};
            const int ret = snprintf(value_str, value_size + 1, "%08x", value);
            (void) ret;
            assert(ret == value_size);
            return std::string(value_str, value_size);
        }
        break;
    case PacketType::kWriteRegister:
        {
            const auto * const data =
                static_cast<const PacketDataWriteRegister*>(packet.data.get());
            const auto reg_id = static_cast<M68KRegister>(data->reg_id);
            const auto value = data->value;
            if (reg_id >= M68KRegister::kRegistersCount) {
                return "E00";
            }
            m68k_debug.SetRegister(reg_id, value);
            return "OK";
        }
        break;
    case PacketType::kReadMemory:
        {
            const auto * const data =
                static_cast<const PacketDataReadMemory*>(packet.data.get());
            const uint32_t offset = data->offset;
            const uint32_t length = data->length;
            auto ret_data = std::string(length * 2, '\0');
            for (uint32_t i = 0; i < length; i++) {
                const uint8_t byte = m68k_debug.Read8(i + offset);
                Utils::ConvertByteToHex(byte, &ret_data[i*2]);
            }
            return ret_data;
        }
    case PacketType::kWriteMemory:
        {
            const auto * const packet_data =
                static_cast<const PacketDataWriteMemory*>(packet.data.get());
            const uint32_t offset = packet_data->offset;
            const uint32_t length = packet_data->length;
            const auto write_data = packet_data->data;
            for (uint32_t i = 0; i < length; i++) {
                m68k_debug.Write8(i + offset, write_data[i]);
            }
            return "OK";
        }
    case PacketType::kStep:
        g_cycles_counter += m68k_execute(1);
        return "S05"; // TODO real reason
    case PacketType::kSetBreakpoint:
        {
            const auto * const bkpt_data =
                static_cast<const PacketDataBreakpoint*>(packet.data.get());
            m68k_debug.SetBreakpoint(bkpt_data->type, bkpt_data->offset, bkpt_data->length);
            return "OK";
        }
    case PacketType::kDeleteBreakpoint:
        {
            const auto * const bkpt_data =
                static_cast<const PacketDataBreakpoint*>(packet.data.get());
            m68k_debug.RemoveBreakpoint(bkpt_data->type, bkpt_data->offset, bkpt_data->length);
            return "OK";
        }
    }
    return "";
}

static void exit_error(const char* fmt, ...)
{
    va_list args;
    va_start(args, fmt);
    vfprintf(stderr, fmt, args);
    va_end(args);
    fprintf(stderr, "\n");
    exit(EXIT_FAILURE);
}

/* Called when the CPU pulses the RESET line */
void m68k_reset_callback(void)
{
    g_vdp.Reset();
}

/* Called when the CPU acknowledges an interrupt */
int m68k_irq_ack(int level)
{
    (void) level;
    CPU_INT_LEVEL = 0;
    return M68K_INT_ACK_AUTOVECTOR;
}

static void make_hex(char* buff, unsigned int pc, unsigned int length)
{
    char* ptr = buff;

    for (;length>0;length -= 2)
    {
        sprintf(ptr, "%04x", m68k_read_disassembler_16(pc));
        pc += 2;
        ptr += 4;
        if (length > 2)
            *ptr++ = ' ';
    }
}

static void PrintInstructionTrace(const uint32_t pc)
{
    char buff[100];
    const unsigned int instr_size =
        m68k_disassemble(buff, pc, M68K_CPU_TYPE_68000);
    char buff2[100];
    make_hex(buff2, pc, instr_size);
    printf("  %08x: %-20s: %s\n", pc, buff2, buff);
    fflush(stdout);
}

// TODO m68k_set_illg_instr_callback for true software breakpoint "4e4f"

int m68k_instr_callback(const int pc)
{
    g_pc_backtrace.Push(pc);
    for (size_t bi = 0; bi < code_bkpts.size(); bi++) {
        if (code_bkpts[bi].offset == static_cast<uint32_t>(pc)) {
            g_m68k_debug.RaiseBreakpoint();
            m68k_end_timeslice();
            printf("Breakpoint @ 0x%08x\n", pc);
            g_pc_backtrace.Normalize();
            printf("PC backtrace (size=%zu):\n", g_pc_backtrace.Size());
            for (size_t i = 0; i < g_pc_backtrace.Size(); i++) {
                PrintInstructionTrace(g_pc_backtrace.buffer[i]);
            }
            return 1;
        }
    }
    if (DEBUG_TRACE_INSTRUCTIONS) {
        PrintInstructionTrace(pc);
    }
    return 0;
}

void m68k_breakpoint_callback(void)
{
    g_pc_backtrace.Normalize();
    printf("PC backtrace (size=%zu):\n", g_pc_backtrace.Size());
    for (size_t i = 0; i < g_pc_backtrace.Size(); i++)
    {
        PrintInstructionTrace(g_pc_backtrace.buffer[i]);
    }
    g_m68k_debug.RaiseBreakpoint();
    m68k_end_timeslice();
}

void ParseAndReact(
        const int conn_fd,
        GDBRemote::ExchangeContext& exchange_ctx,
        M68KDebuggingControl& m68k_debug,
        const char* const msg_data,
        const size_t msg_data_len)
{
    for (size_t i = 0; i < static_cast<size_t>(msg_data_len); i++) {
        const auto res = exchange_ctx.Consume(msg_data[i]);
        if (res == nullptr) continue;
        if (DEBUG_TRACE_GDB_REMOTE && res->packet.length() > 0) {
            printf("<- \"%s\"\n", exchange_ctx.GetLastPacket().c_str());
            const auto packet = GDBRemote::Packet::Parse(res->packet);
            printf(
                    "   Packet type: \"%s\"\n",
                    GDBRemote::Packet::PacketTypeToString(packet.type));
        }
        if (res->ack.length() > 0 && !m68k_debug.IsNoAckModeEnabled()) {
            if (DEBUG_TRACE_GDB_REMOTE)
                printf("-> \"%s\"\n", res->ack.c_str());
            if (send(conn_fd, &res->ack[0], res->ack.length(), 0) == -1)
                perror("Send failed (ack/nak)");
        }
        if (res->packet.length() > 0) {
            const auto packet = GDBRemote::Packet::Parse(res->packet);
            const auto response =
                exchange_ctx.WrapDataToSend(CreateResponse(m68k_debug, packet));
            if (DEBUG_TRACE_GDB_REMOTE)
                printf("-> \"%s\"\n", response.c_str());
            if (send(conn_fd, &response[0], response.length(), 0) == -1)
                perror("Send failed (response)");
        }
    }
}

static void RunSingleVideoCycle(M68KDebuggingControl& m68k_debug, Graphics& graphics)
{
    do {
        g_cycles_counter += m68k_execute(4000);
        if (m68k_debug.HasBreakpoint()) {
            return;
        }
    } while (!g_vdp.Scanline());
    graphics.Render(g_vdp);
    g_cycles_counter += m68k_execute(400000);
}

static int emulator(M68KDebuggingControl& m68k_debug, Graphics& graphics, CharDev &gdb_chardev)
{
    if (gdb_chardev.type == CharDevType::kUndefined) {
        while (!quit) {
            RunSingleVideoCycle(m68k_debug, graphics);
        }
        return EXIT_SUCCESS;
    }
    constexpr size_t addrstr_size = 160;
    char addrstr[addrstr_size]{};
    const int port = gdb_chardev.port ? gdb_chardev.port : 3333;
    int socket_fd;
    if (gdb_chardev.path_len) {
        char *host = new (std::nothrow) char[gdb_chardev.path_len + 1];
        assert(host);
        memcpy(host, gdb_chardev.path, gdb_chardev.path_len);
        host[gdb_chardev.path_len] = '\0';
        socket_fd = setup_socket(host, port, addrstr, addrstr_size);
        delete [] host;
    } else {
        socket_fd = setup_socket("0.0.0.0", port, addrstr, addrstr_size);
    }
    if (socket_fd == -1)
        return EXIT_FAILURE;
    // Mark socket as listener
    if (listen(socket_fd, 4) == -1 ) {
        perror("Listen failed");
        close(socket_fd);
        return EXIT_FAILURE;
    }
    printf("Listening TCP %s:%u\n", addrstr, port);
    while (!quit) {
        struct sockaddr client_address{};
        socklen_t address_len{};
        const int conn_fd = accept(socket_fd, &client_address, &address_len);
        if (conn_fd == -1) {
            gdb_chardev.fd = conn_fd;
            if (errno == EWOULDBLOCK) {
                if (m68k_debug.IsRunning()) {
                    RunSingleVideoCycle(m68k_debug, graphics);
                    if (m68k_debug.HasBreakpoint()) {
                        m68k_debug.SetRunning(false);
                        printf("ResetPendingBreakpoint\n");
                        m68k_debug.ResetPendingBreakpoint();
                    }
                } else {
                    struct pollfd fds[1] = {
                        {/*.fd = */socket_fd, /*.events = */POLLIN, /*.revents = */0}};
                    const int timeout_msecs = 200;
                    if (0 == poll(fds, 1, timeout_msecs)) {
                        graphics.ReRender();
                    }
                }
                continue;
            }
            perror("Accept failed");
            close(socket_fd);
            return EXIT_FAILURE;
        }
        printf("Connection accepted\n");
        // Set O_NONBLOCK for connection
        const int ret = SetNonblock(conn_fd);
        if (ret == -1) {
            perror("fcntl(conn_fd, F_SETFL O_NONBLOCK)");
            return -1;
        }
        GDBRemote::ExchangeContext exchange_ctx{};
        while (!quit) {
            const ssize_t read_size = recv(conn_fd, msg_buf, MESSAGE_BUFFER_SIZE, 0);
            const int err = errno;
            if (read_size > 0) {
                ParseAndReact(conn_fd, exchange_ctx, m68k_debug, msg_buf, read_size);
                continue;
            } else if (read_size == 0) {
                printf("Client disconnected\n");
                break;
            } else if (read_size == -1 && err != EWOULDBLOCK) {
                perror("Recv failed");
                break;
            }
            if (m68k_debug.IsRunning()) {
                RunSingleVideoCycle(m68k_debug, graphics);
                if (m68k_debug.HasBreakpoint()) {
                    m68k_debug.SetRunning(false);
                    printf("ResetPendingBreakpoint\n");
                    m68k_debug.ResetPendingBreakpoint();
                    const auto response =
                        exchange_ctx.WrapDataToSend("S05");
                    if (DEBUG_TRACE_GDB_REMOTE)
                        printf("-> \"%s\"\n", response.c_str());
                    if (send(conn_fd, &response[0], response.length(), 0) == -1)
                        perror("Send failed (response)");
                }
            } else if (err == EWOULDBLOCK) {
                struct pollfd fds[1] = {
                    {/*.fd = */conn_fd, /*.events = */POLLIN, /*.revents = */0}};
                const int timeout_msecs = 200;
                if (0 == poll(fds, 1, timeout_msecs)) {
                    graphics.ReRender();
                }
            }
        }
        close(conn_fd);
        gdb_chardev.fd = -1;
        m68k_debug.SetNoAckMode(false);
    }
    close(socket_fd);
    return 0;
}

static void sigint_handler(int sig)
{
    printf("Signal %d received, exiting\n",sig);
    quit = true;
}

static void PrintUsage(FILE *s, const char *argv0)
{
    // Please, keep all lines in 80 columns range when printed.
    fprintf(s,
    "Usage: %s [options] <program-file-name>\n"
    "Options:\n"
    "  -h, --help            Show this message.\n"
    "  -g, --gdb[=DEV]       Accept GDB connection on DEV (default: 'tcp::3333').\n"
    "  -S, --stop            Freeze CPU at startup (use 'c' in GDB to start\n"
    "                        execution).\n"
    , argv0);
}

int main(int, char* argv[])
{
    struct optparse_long longopts[] = {
        {"help", 'h', OPTPARSE_NONE},
        {"gdb", 'g', OPTPARSE_OPTIONAL},
        {"stop", 'S', OPTPARSE_NONE},
        {},
    };
    struct CharDev gdb_chardev{};
    const char *program_file_name = nullptr;
    bool stop = false;
    struct optparse options;
    optparse_init(&options, argv);
    // Parse opts
    int option;
    while ((option = optparse_long(&options, longopts, nullptr)) != -1) {
        switch (option) {
        case 'h':
            PrintUsage(stdout, argv[0]);
            return EXIT_SUCCESS;
            break;
        case 'g':
            {
                const char *path = options.optarg ? options.optarg : "tcp::3333";
                gdb_chardev = CharDev::Parse(path);
                if (gdb_chardev.type == CharDevType::kPty) {
                    fprintf(stderr, "main: PTY chardev currently is not supported\n");
                    return EXIT_FAILURE;
                } else if (gdb_chardev.type == CharDevType::kUndefined) {
                    fprintf(stderr, "invalid chardev specified: \"%s\"\n", path);
                    return EXIT_FAILURE;
                }
            }
            break;
        case 'S':
            stop = true;
            printf("stop=%s\n", stop ? "true" : "false");
            break;
        case '?':
            fprintf(stderr, "main: optparse_long: Error: \"%s\"\n", options.errmsg);
            return EXIT_FAILURE;
        }
    }
    // Parse input file name
    char *arg;
    while ((arg = optparse_arg(&options))) {
        if (program_file_name == nullptr) {
            program_file_name = arg;
        } else {
            fprintf(stderr, "error: too many free arguments provided\n");
            return EXIT_FAILURE;
        }
    }
    if (program_file_name == nullptr) {
        fprintf(stderr, "main: Error: no program file name specified, see usage below.\n");
        PrintUsage(stderr, argv[0]);
        return EXIT_FAILURE;
    }
    FILE* const fhandle = fopen(program_file_name, "rb");
    if (fhandle == nullptr) {
        exit_error("Unable to open %s", argv[1]);
    }
    const size_t fread_ret = fread(g_rom, 1, ROM_SIZE, fhandle);
    if (fread_ret <= 0) {
        exit_error("Error reading %s", argv[1]);
    }
    printf("Read into ROM %zu bytes\n", fread_ret);
    struct sigaction sa;
    sa.sa_handler = sigint_handler;
    sigaction(SIGINT, &sa, nullptr);
    Graphics graphics{};
    if (!graphics.IsOk()) {
        return EXIT_FAILURE;
    }
    m68k_init();
    m68k_set_cpu_type(M68K_CPU_TYPE_68000);
    m68k_pulse_reset();
    g_cycles_counter += m68k_execute(1); // Skip reset cycles
    g_m68k_debug.SetRunning(!stop);
    emulator(g_m68k_debug, graphics, gdb_chardev);
    return EXIT_SUCCESS;
}