import contextlib
import re
import typing

from parsing import StackEffect

UNUSED = "unused"


class Formatter:
    """Wraps an output stream with the ability to indent etc."""

    stream: typing.TextIO
    prefix: str
    emit_line_directives: bool = False
    lineno: int  # Next line number, 1-based
    filename: str  # Slightly improved stream.filename
    nominal_lineno: int
    nominal_filename: str

    def __init__(
            self, stream: typing.TextIO, indent: int,
                  emit_line_directives: bool = False, comment: str = "//",
    ) -> None:
        self.stream = stream
        self.prefix = " " * indent
        self.emit_line_directives = emit_line_directives
        self.comment = comment
        self.lineno = 1
        self.filename = prettify_filename(self.stream.name)
        self.nominal_lineno = 1
        self.nominal_filename = self.filename

    def write_raw(self, s: str) -> None:
        self.stream.write(s)
        newlines = s.count("\n")
        self.lineno += newlines
        self.nominal_lineno += newlines

    def emit(self, arg: str) -> None:
        if arg:
            self.write_raw(f"{self.prefix}{arg}\n")
        else:
            self.write_raw("\n")

    def set_lineno(self, lineno: int, filename: str) -> None:
        if self.emit_line_directives:
            if lineno != self.nominal_lineno or filename != self.nominal_filename:
                self.emit(f'#line {lineno} "{filename}"')
                self.nominal_lineno = lineno
                self.nominal_filename = filename

    def reset_lineno(self) -> None:
        if self.lineno != self.nominal_lineno or self.filename != self.nominal_filename:
            self.set_lineno(self.lineno + 1, self.filename)

    @contextlib.contextmanager
    def indent(self):
        self.prefix += "    "
        yield
        self.prefix = self.prefix[:-4]

    @contextlib.contextmanager
    def block(self, head: str, tail: str = ""):
        if head:
            self.emit(head + " {")
        else:
            self.emit("{")
        with self.indent():
            yield
        self.emit("}" + tail)

    def stack_adjust(
        self,
        input_effects: list[StackEffect],
        output_effects: list[StackEffect],
    ):
        shrink, isym = list_effect_size(input_effects)
        grow, osym = list_effect_size(output_effects)
        diff = grow - shrink
        if isym and isym != osym:
            self.emit(f"STACK_SHRINK({isym});")
        if diff < 0:
            self.emit(f"STACK_SHRINK({-diff});")
        if diff > 0:
            self.emit(f"STACK_GROW({diff});")
        if osym and osym != isym:
            self.emit(f"STACK_GROW({osym});")

    def declare(self, dst: StackEffect, src: StackEffect | None):
        if dst.name == UNUSED or dst.cond == "0":
            return
        typ = f"{dst.type}" if dst.type else "PyObject *"
        if src:
            cast = self.cast(dst, src)
            init = f" = {cast}{src.name}"
        elif dst.cond:
            init = " = NULL"
        else:
            init = ""
        sepa = "" if typ.endswith("*") else " "
        self.emit(f"{typ}{sepa}{dst.name}{init};")

    def assign(self, dst: StackEffect, src: StackEffect):
        if src.name == UNUSED:
            return
        if src.size:
            # Don't write sized arrays -- it's up to the user code.
            return
        cast = self.cast(dst, src)
        if re.match(r"^REG\(oparg(\d+)\)$", dst.name):
            self.emit(f"Py_XSETREF({dst.name}, {cast}{src.name});")
        else:
            stmt = f"{dst.name} = {cast}{src.name};"
            if src.cond and src.cond != "1":
                if src.cond == "0":
                    # It will not be executed
                    return
                stmt = f"if ({src.cond}) {{ {stmt} }}"
            self.emit(stmt)

    def cast(self, dst: StackEffect, src: StackEffect) -> str:
        return f"({dst.type or 'PyObject *'})" if src.type != dst.type else ""


def prettify_filename(filename: str) -> str:
    # Make filename more user-friendly and less platform-specific,
    # it is only used for error reporting at this point.
    filename = filename.replace("\\", "/")
    if filename.startswith("./"):
        filename = filename[2:]
    if filename.endswith(".new"):
        filename = filename[:-4]
    return filename


def list_effect_size(effects: list[StackEffect]) -> tuple[int, str]:
    numeric = 0
    symbolic: list[str] = []
    for effect in effects:
        diff, sym = effect_size(effect)
        numeric += diff
        if sym:
            symbolic.append(maybe_parenthesize(sym))
    return numeric, " + ".join(symbolic)


def effect_size(effect: StackEffect) -> tuple[int, str]:
    """Return the 'size' impact of a stack effect.

    Returns a tuple (numeric, symbolic) where:

    - numeric is an int giving the statically analyzable size of the effect
    - symbolic is a string representing a variable effect (e.g. 'oparg*2')

    At most one of these will be non-zero / non-empty.
    """
    if effect.size:
        assert not effect.cond, "Array effects cannot have a condition"
        return 0, effect.size
    elif effect.cond:
        if effect.cond in ("0", "1"):
            return int(effect.cond), ""
        return 0, f"{maybe_parenthesize(effect.cond)} ? 1 : 0"
    else:
        return 1, ""


def maybe_parenthesize(sym: str) -> str:
    """Add parentheses around a string if it contains an operator.

    An exception is made for '*' which is common and harmless
    in the context where the symbolic size is used.
    """
    if re.match(r"^[\s\w*]+$", sym):
        return sym
    else:
        return f"({sym})"


def string_effect_size(arg: tuple[int, str]) -> str:
    numeric, symbolic = arg
    if numeric and symbolic:
        return f"{numeric} + {symbolic}"
    elif symbolic:
        return symbolic
    else:
        return str(numeric)