/******************************************************************************
 * File:        MCU_USB_prg.c
 * Component:   MCU_USB
 * Description: USB-CDC driver. TX via putchar_raw (fire-and-forget).
 *              RX via internal ring buffer, lazily drained from the SDK's
 *              stdio layer on every ReadByte / ReadBuffer / IsDataAvailable
 *              call. No separate RX task or interrupt needed — the SDK's
 *              TinyUSB background task fills stdio internally, and we pull
 *              from stdio into our ring buffer on demand.
 *
 * Layer:       MCU (hardware abstraction)
 *****************************************************************************/

#include "STD_TYPES.h"

#include "pico/stdio_usb.h"
#include "pico/stdio.h"
#include "pico/time.h"

#include "MCU_USB.h"
#include "MCU_USB_priv.h"
#include "MCU_USB_cfg.h"

/* ------------------------------------------------------------------------ */
/*                    RX RING BUFFER                                         */
/* ------------------------------------------------------------------------ */

/** @brief  RX ring buffer size — must be power of 2. */
#define USB_RX_BUFFER_SIZE_BITS   6U
#define USB_RX_BUFFER_SIZE        (1U << USB_RX_BUFFER_SIZE_BITS)
#define USB_RX_BUFFER_MASK        (USB_RX_BUFFER_SIZE - 1U)

static u8  au8RxBuffer[USB_RX_BUFFER_SIZE];
static u16 u16RxHead = 0U;
static u16 u16RxTail = 0U;

/**
 * @brief  Drain any available bytes from the SDK's stdio into our ring buffer.
 *
 * Called lazily from ReadByte, ReadBuffer, and bIsRxDataAvailable.
 * getchar_timeout_us(0) is non-blocking — returns PICO_ERROR_TIMEOUT (-1)
 * immediately if no data. We keep pulling until the SDK has nothing left
 * or our ring buffer is full.
 */
static void vDrainStdio(void)
{
    s32 s32ByteLoc;
    u16 u16NextHeadLoc;

    s32ByteLoc = (s32)getchar_timeout_us(0);

    while (s32ByteLoc >= 0)
    {
        u16NextHeadLoc = (u16RxHead + 1U) & USB_RX_BUFFER_MASK;

        /* If the ring buffer is full, stop draining (oldest data preserved,
         * newest data from SDK is lost). Caller should read faster. */
        if (u16NextHeadLoc == u16RxTail)
        {
            /* Buffer full — can't store this byte. Break out. */
            break;
        }

        au8RxBuffer[u16RxHead] = (u8)s32ByteLoc;
        u16RxHead = u16NextHeadLoc;

        s32ByteLoc = (s32)getchar_timeout_us(0);
    }
}

/* ========================================================================= */
/*                           INIT                                            */
/* ========================================================================= */

STD_tenuResult MCU_USB_enuInit(void)
{
    STD_tenuResult enuResultLoc = STD_OK;
    STD_tBool bSdkInitSuccess = STD_FALSE;

    bSdkInitSuccess = (stdio_usb_init() != 0) ? STD_TRUE : STD_FALSE;

    if (bSdkInitSuccess == STD_FALSE)
    {
        enuResultLoc = STD_NOK;
    }
    else
    {
        #if MCU_USB_WAIT_FOR_CONNECTION == MCU_USB_WAIT_FOR_CONNECTION_ENABLED
        absolute_time_t absTimeout = make_timeout_time_ms(MCU_USB_CONNECTION_TIMEOUT_MS);
        STD_tBool bHostOpen = STD_FALSE;
        STD_tBool bTimeoutReached = STD_FALSE;
        do
        {
            sleep_ms(10);
            bHostOpen = (stdio_usb_connected() != 0) ? STD_TRUE : STD_FALSE;
            bTimeoutReached = (time_reached(absTimeout) != 0) ? STD_TRUE : STD_FALSE;
        } while ((bHostOpen == STD_FALSE) && (bTimeoutReached == STD_FALSE));

        if (bHostOpen == STD_FALSE)
        {
            enuResultLoc = STD_NOK;
        }
        #endif
    }

    return enuResultLoc;
}

/* ========================================================================= */
/*                           SEND BYTE                                       */
/* ========================================================================= */

STD_tenuResult MCU_USB_enuSendByte(u8 u8Byte)
{
    STD_tenuResult enuResultLoc = STD_OK;

    putchar_raw(u8Byte);

    return enuResultLoc;
}

/* ========================================================================= */
/*                           SEND BUFFER                                     */
/* ========================================================================= */

STD_tenuResult MCU_USB_enuSendBuffer(const u8 *pu8Data, u16 u16Length)
{
    STD_tenuResult enuResultLoc = STD_OK;
    u16 u16IndexLoc;

    if (pu8Data == STD_NULL)
    {
        enuResultLoc = STD_NULL_POINTER_ERROR;
    }
    else
    {
        for (u16IndexLoc = 0U; u16IndexLoc < u16Length; u16IndexLoc++)
        {
            putchar_raw(pu8Data[u16IndexLoc]);
        }
    }

    return enuResultLoc;
}

/* ========================================================================= */
/*                     READ BYTE (NON-BLOCKING)                              */
/* ========================================================================= */

STD_tenuResult MCU_USB_enuReadByte(u8 *pu8Byte)
{
    STD_tenuResult enuResultLoc = STD_OK;

    if (pu8Byte == STD_NULL)
    {
        enuResultLoc = STD_NULL_POINTER_ERROR;
    }
    else
    {
        /* Pull any pending data from SDK into our ring buffer */
        vDrainStdio();

        if (u16RxHead == u16RxTail)
        {
            enuResultLoc = STD_NOK;
        }
        else
        {
            *pu8Byte = au8RxBuffer[u16RxTail];
            u16RxTail = (u16RxTail + 1U) & USB_RX_BUFFER_MASK;
        }
    }

    return enuResultLoc;
}

/* ========================================================================= */
/*                     READ BUFFER (NON-BLOCKING)                            */
/* ========================================================================= */

STD_tenuResult MCU_USB_enuReadBuffer(u8 *pu8Data, u16 u16MaxLength, u16 *pu16Read)
{
    STD_tenuResult enuResultLoc = STD_OK;

    if ((pu8Data == STD_NULL) || (pu16Read == STD_NULL))
    {
        enuResultLoc = STD_NULL_POINTER_ERROR;
    }
    else
    {
        vDrainStdio();

        u16 u16CountLoc = 0U;

        while ((u16RxHead != u16RxTail) && (u16CountLoc < u16MaxLength))
        {
            pu8Data[u16CountLoc] = au8RxBuffer[u16RxTail];
            u16RxTail = (u16RxTail + 1U) & USB_RX_BUFFER_MASK;
            u16CountLoc++;
        }

        *pu16Read = u16CountLoc;

        if (u16CountLoc == 0U)
        {
            enuResultLoc = STD_NOK;
        }
    }

    return enuResultLoc;
}

/* ========================================================================= */
/*                        RX DATA AVAILABLE CHECK                            */
/* ========================================================================= */

STD_tBool MCU_USB_bIsRxDataAvailable(void)
{
    STD_tBool bResultLoc = STD_FALSE;

    vDrainStdio();

    if (u16RxHead != u16RxTail)
    {
        bResultLoc = STD_TRUE;
    }

    return bResultLoc;
}