//----------------------------------------------------------------------------//
//                           GNU GPL OS/K                                     //
//                                                                            //
//  Desc:       VGA terminal functions                                        //
//                                                                            //
//                                                                            //
//  Copyright © 2018-2019 The OS/K Team                                       //
//                                                                            //
//  This file is part of OS/K.                                                //
//                                                                            //
//  OS/K 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 3 of the License, or         //
//  any later version.                                                        //
//                                                                            //
//  OS/K 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 OS/K.  If not, see <https://www.gnu.org/licenses/>.            //
//----------------------------------------------------------------------------//

#include <extras/buf.h>
#include <kernel/boot.h>
#include <kernel/cursor.h>

//
// VGA-related macros
//
#define VGA_ComputeColorCode(fg, bg)    ((fg) | (bg) << 4)
#define VGA_ComputeOffset(term, x, y)   ((y) * (term)->width + (x))
#define VGA_ComputeEntry(ch, cl)        (((ushort)(ch)) | (ushort)(cl) << 8)

static uint bscroll = 0;

//
// VGA Buffer Flusher
//
error_t bvgaflusher(Buffer_t *buf)
{
    ushort *fbp = BtVideoInfo.framebufferAddr;
    uchar color = 0xf;

    uchar *currentLine = buf->wp - buf->lineLen - buf->lastLF;
    uchar *bufStart = (uchar *)lmax((size_t)buf->buf,
                            (size_t)currentLine
                            - (buf->nLines - 2 + bscroll) * buf->lineLen);

    uchar *ptr = bufStart;

    // Writes the buffer's content

    for (; ptr < buf->wp ; ptr++) {
        *fbp++ = VGA_ComputeEntry(*ptr, color);
    }
    

    // Update the cursor
    size_t curX = ((size_t)ptr - (size_t)bufStart) % buf->lineLen;
    size_t curY = ((size_t)ptr - (size_t)bufStart) / buf->lineLen;
    
    IoUpdateCursor(curX, curY);

    // Empty the rest of the buffer

    const size_t bufSize = buf->nLines * buf->lineLen;
    ushort *fbe = BtVideoInfo.framebufferAddr
                                     + (bufSize * sizeof(ushort));

    if (fbp < fbe) {
        const ushort filler = VGA_ComputeEntry(' ', color);
        while (fbp < fbe) *fbp++ = filler;
    }

    return EOK;
}

void IoScrollDown(void)
{
    if (bscroll > 0)
        bscroll--;
    bvgaflusher(BStdOut);
}


void IoScrollUp(void)
{
    // Keep the 8 below the 10 given to BOpenTermBufEx
    if (bscroll < BtVideoInfo.framebufferHeight * 8 && bscroll < BStdOut->nLines)
        bscroll++;
    bvgaflusher(BStdOut);
}


//
// Initialize VGA buffer
//
error_t IoInitVGABuffer(void)
{
    static char bvgabufsrc[1 * MB];
    static Buffer_t bvgabufstruct;
    
    BStdOut = &bvgabufstruct;

    BOpenTermBufEx(&BStdOut,
              bvgabufsrc, BS_WRONLY,
              BtVideoInfo.framebufferWidth,
              BtVideoInfo.framebufferHeight,
              10, bvgaflusher);

    BEnableAutoScroll(BStdOut);

    BStdDbg = BStdOut;

    return EOK;
}