//----------------------------------------------------------------------------//
//                           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 <kernel/term.h>

//----------------------------------------------------------//
//           Internal functions for VGA terminals           //
//           These DO NOT check input correctness           //
//----------------------------------------------------------//

//
// 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)

//
// Clears terminal
//
error_t VGA_ClearTermUnlocked(Terminal_t *term)
{
    const uchar  color   = VGA_ComputeColorCode(term->fgColor, term->bgColor);
    const ushort filler  = VGA_ComputeEntry(' ', color);
    const size_t bufsize = term->width * term->height;

    // Fill the buffer
    memsetw((ushort *)term->data, filler, bufsize);

    // XXX update cursor too
    term->currentX = term->currentY = 0;

    return EOK;
}

//
// Writes a single character on the terminal
//
error_t VGA_PutOnTermUnlocked(Terminal_t *term, char ch)
{
    uint i;
    size_t prevY;

    if (ch == '\r') {
        term->currentX = 0;
        return EOK;
    }

    // Line feed first takes us to the very end of the line
    // Later in this function we actually do the line feed
    else if (ch == '\n') {
        term->currentX = term->width - 1;
    }

    // Tabulations account for "term->tabSize" spaces
    else if (ch == '\t') {
        prevY = term->currentX;
        for (i = 0; i < term->tabSize; i++) {
            // Make sure tabulations can't spread over two lines
            if (term->currentX == prevY) {
                VGA_PutOnTermUnlocked(term, ' ');
            }
        }
    }

    else {
        ushort      *buffer  = (ushort *)term->data;
        const size_t offset = VGA_ComputeOffset(term, term->currentX, term->currentY);
        buffer[offset] = VGA_ComputeEntry(ch, VGA_ComputeColorCode(term->fgColor, term->bgColor));
    }

    // Did we reach the end of line?
    if (++term->currentX == term->width) {
        term->currentX = 0;

        // Did we reach the buffer's end?
        if (++term->currentY == term->height) {
            // XXX scroll up
            term->currentY = 0;
        }
    }

    // Nothing can go wrong
    return EOK;
}

//
// Prints string on terminal
//
error_t VGA_PrintOnTermUnlocked(Terminal_t *term, const char *str)
{
    error_t retcode = EOK;

    while (*str && retcode == EOK) {
        retcode = term->PutOnTermUnlocked(term, *str++);
    }

    return retcode;
}

//
// VGA output
// XXX custom sizes
//
Terminal_t VGA_Terminal = {
    .initDone   = FALSE,
    .lock       = INITLOCK(KLOCK_MUTEX),

    .name       = "VGA Output Terminal",
    .type       = "VGA",

    .data       = (void *)0xB8000,
    .width      = 80,
    .height     = 25,
    .currentX   = 0,
    .currentY   = 0,

    .tabSize    = KTABSIZE,
    .fgColor    = KTERM_COLOR_LGREY,
    .bgColor    = KTERM_COLOR_BLACK,

    .ClearTermUnlocked      = VGA_ClearTermUnlocked,
    .PutOnTermUnlocked      = VGA_PutOnTermUnlocked,
    .PrintOnTermUnlocked    = VGA_PrintOnTermUnlocked,
};


//
// Initialize VGA output
//
void VGA_Init(void)
{
    KalAssert(VGA_Terminal.initDone != INITOK);

    VGA_Terminal.initDone = INITOK;
}