# MIT License
#
# Copyright (c) 2023 Neil Webber
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# FUNCTIONALITY DISCLAIMER:
#   This is NOT meant to recreate the entire idea of a PDP-11 assembler.
#   Rather, it is meant as an ad-hoc assistance for creating and
#   debugging small test programs, of the sort that are found in pdptest.
#   As such, the methods here are written on an "as-needed" basis and
#   are focused around helping to create hand-constructed test code.
#

class PDP11InstructionAssembler:
    B6MODES = {}
    _rnames = [(f"R{_i}", _i) for _i in range(8)] + [("SP", 6), ("PC", 7)]
    for _rn, _i in _rnames:
        B6MODES[f"{_rn}"] = _i              # register direct
        B6MODES[f"({_rn})"] = 0o10 | _i     # register indirect
        B6MODES[f"({_rn})+"] = 0o20 | _i    # autoincrement
        B6MODES[f"@({_rn})+"] = 0o30 | _i   # autoincr deferred
        B6MODES[f"-({_rn})"] = 0o40 | _i    # autodecrement
        B6MODES[f"@-({_rn})"] = 0o50 | _i   # autodecr deferred
    del _i, _rn, _rnames

    def __init__(self):
        self.activeblock = None

    def startblock(self):
        self.activeblock = []

    def addtoblock(self, insts):
        if self.activeblock is not None:
            self.activeblock += insts
        return insts

    def endblock(self):
        insts, self.activeblock = self.activeblock, None
        return insts

    def immediate_value(self, s):
        base = 8
        if s[-1] == '.':
            base = 10
            s = s[:-1]
        val = int(s, base)

        # as a convenience, allow negative values and convert them
        if val < 0 and val >= -32768:
            val += 65536
        if val > 65535 or val < 0:
            raise ValueError(f"illegal value '{s}' = {val}")
        return val

    # this is a notational convenience to create a f'*${i].' string
    # for an operand that is an immediate deferred (i.e., numeric pointer)
    def ptr(self, i):
        return f'*${i}.'

    def operand_parser(self, operand_string, /):
        """Parse operand_string ('r1', '-(sp)', '4(r5)', $177776, etc).

        Returns: sequence: [6 bit code, additional words ...]

        Raises ValueError for syntax errors.

        Literals that should become (pc)+ (mode 0o27) must start with '$'
        They will be octal unless they end with a '.'

        Literals that are pointers and should become @(pc)+ must
        start with '*$' and will be octal unless they end with a '.'

        An integer, i, can be passed in directly; it is becomes f"${i}."
        """
        # NOTE: Not all forms implemented yet. See FUNCTIONALITY DISCLAIMER.

        # for convenience
        def valerr():
            return ValueError(f"cannot parse '{operand_string}'")

        # normalize the operand, upper case for strings, turn ints back
        # into their corresponding string (roundabout, but easiest)
        try:
            operand = operand_string.upper()
        except AttributeError:
            operand = f"${operand_string}."

        # bail out if spaces in middle, and remove spaces at ends
        s = operand.split()
        if len(s) > 1:
            raise valerr()
        operand = s[0]

        # operand now fully normalized: upper case, no spaces.

        # the first/easiest to try is to see if it is an immediate.
        # It will (must) start with either '$', or '*$' if so.
        try:
            if operand[0] == '$':
                return [0o27, self.immediate_value(operand[1:])]
            elif operand.startswith('*$'):
                return [0o37, self.immediate_value(operand[2:])]
        except ValueError:
            raise valerr() from None

        # wasn't immediate, see if it matches the precomputed modes
        try:
            return [self.B6MODES[operand]]
        except KeyError:
            pass
        
        # last chance: X(Rn) and @X(rn)

        # see if X(Rn) or @X(Rn)...
        if operand[0] == '@':
            mode = 0o70
            operand = operand[1:]
        else:
            mode = 0o60

        # for starters, it must contain one '(' so should split to 2
        s = operand.split('(')
        if len(s) != 2:
            raise valerr()
        idxval = self.immediate_value(s[0])

        # the back end of this, with the '(' put back on,
        # must end with ')' and must parse
        if s[1][-1] != ')':
            raise valerr()
        try:
            b6 = self.B6MODES['(' + s[1]]
        except KeyError:
            raise valerr() from None

        return [mode | (b6 & 0o07), idxval]

    def _2op(self, operation, src, dst):
        src6, *src_i = self.operand_parser(src)
        dst6, *dst_i = self.operand_parser(dst)
        return [ operation | src6 << 6 | dst6, *src_i, *dst_i ]

    def _1op(self, operation, dst):
        dst6, *dst_i = self.operand_parser(dst)
        return [ operation | dst6, *dst_i ]

    def mov(self, src, dst):
        return self.addtoblock(self._2op(0o010000, src, dst))

    def clr(self, dst):
        return self.addtoblock(self._1op(0o005000, dst))

    def inc(self, dst):
        return self.addtoblock(self._1op(0o005200, dst))

    def halt(self):
        return self.addtoblock([0])

        xxx = """
        
            0o012706, 0o20000,       # put system stack at 8k and works down

            0o012737, 0o22222, 0o20000,
            0o012737, 0o33333, 0o20002,
            0o012737, 0o44444, 0o40000,

            # point both kernel seg 0 PARs to physical zero
            0o005037, cn.KISA0,         # CLR $KISA0
            0o005037, cn.KDSA0,         # CLR $KDSA0

            # kernel seg 7 D space PAR to I/O page (at 22-bit location)
            0o012737, 0o017760000 >> 6, cn.KDSA0 + (7 * 2),

            # user I seg 0 to 0o20000, user D seg 0 to 0o40000
            0o012737, 0o20000 >> 6, cn.UISA0,
            0o012737, 0o40000 >> 6, cn.UDSA0,

            # set the PDRs for segment zero

            0o012703, 0o077406,      # MOV #77406,R3
            # 77406 = PDR<2:0> = ACF = 0o110 = read/write
            #         PLF<14:8> =0o0774 = full length (128*64 bytes = 8K)
            0o010337, cn.KISD0,         # MOV R3,KISD0 ...
            0o010337, cn.KDSD0,
            0o010337, cn.UISD0,
            0o010337, cn.UDSD0,
            # PDR for segment 7
            0o010337, cn.KDSD0 + (7 * 2),


            # set previous mode to USER, keeping current mode KERNEL, pri 7
            0o012737, (p.KERNEL << 14) | (p.USER << 12) | (7 << 5),
            self.ioaddr(p, p.PS_OFFS),

            # turn on 22-bit mode, unibus mapping, and I/D sep for k & u
            0o012737, 0o000065, self.ioaddr(p, p.mmu.MMR3_OFFS),

            # turn on relocation mode ... yeehah! (MMR0 known zero here)
            0o005237, self.ioaddr(p, p.mmu.MMR0_OFFS),   # INC MMR0
            )

"""