// HAL serial output endpoint. This file owns polling COM1 writes and subscribes serial to HAL text streams.

#include <stdint.h>
#include <intrin.h>
#include <ntlite/ddi/hal_api.h>
#include <kernel/hal/hal_output.h>

#define HAL_COM1_DATA_PORT   0x03F8u
#define HAL_COM1_STATUS_PORT 0x03FDu
#define HAL_COM1_TX_READY    0x20u

static volatile long gSerialWriteLock;

// Waits until COM1 can accept one byte.
static void HalSerialWaitForTransmit(void) {
    while ((__inbyte(HAL_COM1_STATUS_PORT) & HAL_COM1_TX_READY) == 0)
        _mm_pause();
}

// Writes one byte to COM1.
static void HalSerialWriteByte(uint8_t value) {
    HalSerialWaitForTransmit();
    __outbyte(HAL_COM1_DATA_PORT, value);
}

// Acquires the normal serial writer lock.
static void HalSerialAcquireWriteLock(void) {
    while (_InterlockedCompareExchange(&gSerialWriteLock, 1, 0) != 0)
        _mm_pause();
}

// Releases the normal serial writer lock.
static void HalSerialReleaseWriteLock(void) {
    _InterlockedExchange(&gSerialWriteLock, 0);
}

// Writes one output record through polling COM1.
static void HalSerialWriteRecord(void* context, const HAL_OUTPUT_RECORD* record) {
    (void)context;
    if (!record || !record->Buffer)
        return;

    bool emergency = (record->Flags & HAL_OUTPUT_WRITE_EMERGENCY) != 0;
    uintptr_t interruptFlags = 0;
    if (!emergency) {
        interruptFlags = HalDisableInterrupts();
        HalSerialAcquireWriteLock();
    }

    for (size_t i = 0; i < record->Length; i++) {
        char c = record->Buffer[i];
        if (c == '\n')
            HalSerialWriteByte('\r');
        HalSerialWriteByte((uint8_t)c);
    }

    if (!emergency) {
        HalSerialReleaseWriteLock();
        HalRestoreInterrupts(interruptFlags);
    }
}

// Registers the polling serial endpoint.
void HalSerialInitialize(HAL_OUTPUT_ROUTER* output) {
    if (!output || !output->RegisterEndpoint)
        return;

    HAL_OUTPUT_ENDPOINT endpoint;
    endpoint.Name = "serial0";
    endpoint.StreamMask = HAL_OUTPUT_STREAM_ALL;
    endpoint.Capabilities = HAL_OUTPUT_ENDPOINT_PANIC_SAFE;
    endpoint.Write = HalSerialWriteRecord;
    endpoint.Context = 0;

    uint32_t endpointId = HAL_OUTPUT_ENDPOINT_INVALID;
    if (KSUCCESS(output->RegisterEndpoint(&endpoint, &endpointId)))
        output->SerialEndpointId = endpointId;
}