<?php
    if (!isset($_REQUEST['asm'])) {
        echo "Stack Machine Assembler<br/>";
        echo "<form method=\"post\">";
        echo "<textarea name=\"asm\" rows=\"30\" cols=\"100\"></textarea><br>";
        echo "<input type=\"submit\" value=\"Assemble\">";
        echo "</form>";
    } else {
        $lines = explode("\n", $_REQUEST['asm']);
        if (count($lines) == 0) {
            echo "You need to supply input";
            die();
        }
        $SYMBOLTABLE = array('PSW' => 'FFFB',
                             'A' => 'FFFC',
                             'B' => 'FFFD',
                             'C' => 'FFFE',
                             'D' => 'FFFF');
        $FUNCTABLE = array('nop' => array('00', 0),
                           'halt' => array('01', 0),
                           'pushimm' => array('02', 1),
                           'pushext' => array('03', 2),
                           'popinh' => array('04', 0),
                           'popext' => array('05', 2),
                           'jnz' => array('06', 2),
                           'jnn' => array('0A', 2),
                           'add' => array('07', 0),
                           'sub' => array('08', 0),
                           'nor' => array('09', 0));

        // Pass 1, parse commands, throw symbols into tables.
        for ($i = 0; $i < count($lines); $i++) {
            $line = $lines[$i];

            // Find comment on line if it exists. Strip it from line.
            $commPos = strpos($line, '--'); // Find comment position (If it exists)
            $comment = '';
            if ($commPos === false) $commPos = strlen($line);
            else $comment = substr($line, $commPos); // Store comment
            $line = substr($line, 0, $commPos); // Strip comment.
            $line = trim($line); // Remove space from before/after command.
            if ($line== '') continue; // If line is blank, not a command, skip it.

            // Find if there's a label, add it to symbol table.
            $symPos = strpos($line, ':');
            $symbol = '';
            if ($symPos !== false) {
                $symbol = substr($line, 0, $symPos);
                $line = trim(substr($line, $symPos + 1));
                if ($line == '') continue;
                $SYMBOLTABLE[$symbol] = dechex(count($parse)); // Set symbol table entry to address.
            }

            // Replace the line in the list with the line minus symbol, and minus comment.
            $lines2[] = $line;

            // Check for function, replace. Make sure to leave room for operand
            $funcEnd = strpos($line, ' ');
            if ($funcEnd === false) $funcEnd = strlen($line);
            $func = substr($line, 0, $funcEnd);
            if (array_key_exists($func, $FUNCTABLE)) {
                $parse[] = str_pad(base_convert($FUNCTABLE[$func][0], 16, 2), 8, '0', STR_PAD_LEFT).' '.$line;
               if ($symbol != '') $parse[count($parse) - 1] .= ' ['.$symbol.' = 0x'.$SYMBOLTABLE[$symbol].']';
                // Create room for the added data in parse 2
                for ($j = 0; $j < $FUNCTABLE[$func][1]; $j++)
                    $parse[] = '';
            } else
                die("Problem parsing ASM, unknown function $func");
        }

        $pLoc = 0;
        for ($i = 0; $i < count($parse); $i++) {
            // Increase our internal pointer if this is a command. And skip over it.
            if ($parse[$i] != '') {
                $pLoc++;
                $parse2[] = $parse[$i];
                continue;
            }

            // Grab the current working line. This will be function and operand only
            $line = $lines2[$pLoc - 1];
            $funcEnd = strpos($line, ' ');
            if ($funcEnd === false) $funcEnd = strlen($line);
            $func = substr($line, 0, $funcEnd);
            $operand = substr($line, $funcEnd + 1);

            // Check if we have a symbol that matches this, a function, or a +/- operation. Otherwise it is a hex value.
            $fun = '';
            if (strpos($operand, "(") !== false) {
                $fun = $operand[0];
                if ($fun != 'L' && $fun != 'H') {
                    die("Invalid function call");
                }
                $operand = substr($operand, 2, -1);
            }
            if ($operand[0] == '+' || $operand[0] == '-') {
                if ($operand[strlen($operand)-1] == 'h') $base = 16;
                else $base = 10;
                $operand = $i + intval(substr($operand, 0, strlen($operand)-1), $base) - 1;
                $operand = base_convert($operand, 10, 2);
            } else if (@array_key_exists($operand, $SYMBOLTABLE)) {
                $operand = base_convert($SYMBOLTABLE[$operand], 16, 2);
            } else {
                $pos = strpos($operand, '+');
                if ($pos === false) $pos = strpos($operand, '-');
                if ($pos === false)
                    $operand = base_convert($operand, 16, 2);
                else {
                    $off = substr($operand, $pos + 1);
                    if (substr($off, -1) == 'h') $off = intval(base_convert(substr($off, 0, -1), 16, 10));
                    else if (substr($off, -1) == 'd') $off = intval(substr($off, 0, -1));
                    else $off = intval($off);
                    $operand = substr($operand, 0, $pos);
                    if (@array_key_exists($operand, $SYMBOLTABLE)) {
                        $operand = base_convert((hexdec($SYMBOLTABLE[$operand]) + $off), 10, 2);
                    } else
                        die("Can't offset constant value");
                }
            }
            if ($fun != '') {
                $operand = str_pad($operand, 16, '0', STR_PAD_LEFT);
                if ($fun == 'L')
                    $operand = substr($operand, 8, 8);
                else
                    $operand = substr($operand, 0, 8);
            } else
                $operand = str_pad($operand, $FUNCTABLE[$func][1]*8, '0', STR_PAD_LEFT);

            // Push the output value to parse2, the final machine code.
            for ($j = 0; $j < $FUNCTABLE[$func][1]; $j++) {
                $parse2[] = substr($operand, $j * 8, 8);
            }
            // We are on the first operand, so increase i by one less than the operand count.
            $i += $FUNCTABLE[$func][1] - 1;
        }

        // Output the machine code to console
        for ($i = 0; $i < count($parse2); $i++) {
            echo $parse2[$i]."\n";
        }
    }
?>