#! /usr/bin/env python3
# pyright: strict

# --------------------------------------------------------------------
# --- Cachegrind's differencer.                         cg_diff.in ---
# --------------------------------------------------------------------

# This file is part of Cachegrind, a high-precision tracing profiler
# built with Valgrind.
#
# Copyright (C) 2002-2023 Nicholas Nethercote
#    njn@valgrind.org
#
# This program 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 2 of the
# License, or (at your option) any later version.
#
# This program 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 this program; if not, see <http://www.gnu.org/licenses/>.
#
# The GNU General Public License is contained in the file COPYING.

# This script diffs Cachegrind output files.
#
# Use `make pydiff` to "build" this script every time it is changed. This runs
# the formatters, type-checkers, and linters on `cg_diff.in` and then generates
# `cg_diff`.
#
# This is a cut-down version of `cg_annotate.in`.

from __future__ import annotations

import re
import sys
from argparse import ArgumentParser, Namespace
from collections import defaultdict
from typing import Callable, DefaultDict, NewType, NoReturn

SearchAndReplace = Callable[[str], str]


# A typed wrapper for parsed args.
class Args(Namespace):
    # None of these fields are modified after arg parsing finishes.
    mod_filename: SearchAndReplace
    mod_funcname: SearchAndReplace
    cgout_filename1: str
    cgout_filename2: str

    @staticmethod
    def parse() -> Args:
        # We support Perl-style `s/old/new/flags` search-and-replace
        # expressions, because that's how this option was implemented in the
        # old Perl version of `cg_diff`. This requires conversion from
        # `s/old/new/` style to `re.sub`. The conversion isn't a perfect
        # emulation of Perl regexps (e.g. Python uses `\1` rather than `$1` for
        # using captures in the `new` part), but it should be close enough. The
        # only supported flags are `g` (global) and `i` (ignore case).
        def search_and_replace(regex: str | None) -> SearchAndReplace:
            if regex is None:
                return lambda s: s

            # Extract the parts of an `s/old/new/tail` regex. `(?<!\\)/` is an
            # example of negative lookbehind. It means "match a forward slash
            # unless preceded by a backslash".
            m = re.match(r"s/(.*)(?<!\\)/(.*)(?<!\\)/(g|i|gi|ig|)$", regex)
            if m is None:
                raise ValueError

            # Forward slashes must be escaped in an `s/old/new/` expression,
            # but we then must unescape them before using them with `re.sub`.
            pat = m.group(1).replace(r"\/", r"/")
            repl = m.group(2).replace(r"\/", r"/")
            tail = m.group(3)

            if "g" in tail:
                count = 0  # unlimited
            else:
                count = 1

            if "i" in tail:
                flags = re.IGNORECASE
            else:
                flags = re.RegexFlag(0)

            return lambda s: re.sub(re.compile(pat, flags=flags), repl, s, count=count)

        desc = (
            "Diff two Cachegrind output files. Deprecated; use "
            "`cg_annotate --diff` instead."
        )
        p = ArgumentParser(description=desc)

        p.add_argument("--version", action="version", version="%(prog)s-@VERSION@")

        p.add_argument(
            "--mod-filename",
            type=search_and_replace,
            metavar="REGEX",
            default=search_and_replace(None),
            help="a search-and-replace regex applied to filenames, e.g. "
            "`s/prog[0-9]/progN/`",
        )
        p.add_argument(
            "--mod-funcname",
            type=search_and_replace,
            metavar="REGEX",
            default=search_and_replace(None),
            help="like --mod-filename, but for function names",
        )

        p.add_argument(
            "cgout_filename1",
            nargs=1,
            metavar="cachegrind-out-file1",
            help="file produced by Cachegrind",
        )
        p.add_argument(
            "cgout_filename2",
            nargs=1,
            metavar="cachegrind-out-file2",
            help="file produced by Cachegrind",
        )

        return p.parse_args(namespace=Args())  # type: ignore [return-value]


# Args are stored in a global for easy access.
args = Args.parse()


# A single instance of this class is constructed, from `args` and the `events:`
# line in the cgout file.
class Events:
    # The event names.
    events: list[str]

    def __init__(self, text: str) -> None:
        self.events = text.split()
        self.num_events = len(self.events)

    # Raises a `ValueError` exception on syntax error.
    def mk_cc(self, str_counts: list[str]) -> Cc:
        # This is slightly faster than a list comprehension.
        counts = list(map(int, str_counts))

        if len(counts) == self.num_events:
            pass
        elif len(counts) < self.num_events:
            # Add zeroes at the end for any missing numbers.
            counts.extend([0] * (self.num_events - len(counts)))
        else:
            raise ValueError

        return counts

    def mk_empty_cc(self) -> Cc:
        # This is much faster than a list comprehension.
        return [0] * self.num_events


# A "cost centre", which is a dumb container for counts. Always the same length
# as `Events.events`, but it doesn't even know event names. `Events.mk_cc` and
# `Events.mk_empty_cc` are used for construction.
#
# This used to be a class with a single field `counts: list[int]`, but this
# type is very hot and just using a type alias is much faster.
Cc = list[int]


# Add the counts in `a_cc` to `b_cc`.
def add_cc_to_cc(a_cc: Cc, b_cc: Cc) -> None:
    for i, a_count in enumerate(a_cc):
        b_cc[i] += a_count


# Subtract the counts in `a_cc` from `b_cc`.
def sub_cc_from_cc(a_cc: Cc, b_cc: Cc) -> None:
    for i, a_count in enumerate(a_cc):
        b_cc[i] -= a_count


# A paired filename and function name.
Flfn = NewType("Flfn", tuple[str, str])

# Per-function CCs.
DictFlfnCc = DefaultDict[Flfn, Cc]


def die(msg: str) -> NoReturn:
    print("cg_diff: error:", msg, file=sys.stderr)
    sys.exit(1)


def read_cgout_file(cgout_filename: str) -> tuple[str, Events, DictFlfnCc, Cc]:
    # The file format is described in Cachegrind's manual.
    try:
        cgout_file = open(cgout_filename, "r", encoding="utf-8")
    except OSError as err:
        die(f"{err}")

    with cgout_file:
        cgout_line_num = 0

        def parse_die(msg: str) -> NoReturn:
            die(f"{cgout_file.name}:{cgout_line_num}: {msg}")

        def readline() -> str:
            nonlocal cgout_line_num
            cgout_line_num += 1
            return cgout_file.readline()

        # Read "desc:" lines.
        while line := readline():
            if m := re.match(r"desc:\s+(.*)", line):
                # The "desc:" lines are unused.
                pass
            else:
                break

        # Read "cmd:" line. (`line` is already set from the "desc:" loop.)
        if m := re.match(r"cmd:\s+(.*)", line):
            cmd = m.group(1)
        else:
            parse_die("missing a `command:` line")

        # Read "events:" line.
        line = readline()
        if m := re.match(r"events:\s+(.*)", line):
            events = Events(m.group(1))
        else:
            parse_die("missing an `events:` line")

        fl = ""
        flfn = Flfn(("", ""))

        # Different places where we accumulate CC data.
        dict_flfn_cc: DictFlfnCc = defaultdict(events.mk_empty_cc)
        summary_cc = None

        # Line matching is done in order of pattern frequency, for speed.
        while line := readline():
            if line[0].isdigit():
                split_line = line.split()
                try:
                    # The line_num isn't used.
                    cc = events.mk_cc(split_line[1:])
                except ValueError:
                    parse_die("malformed or too many event counts")

                # Record this CC at the function level.
                add_cc_to_cc(cc, dict_flfn_cc[flfn])

            elif line.startswith("fn="):
                flfn = Flfn((fl, args.mod_funcname(line[3:-1])))

            elif line.startswith("fl="):
                # A longstanding bug: the use of `--mod-filename` makes it
                # likely that some files won't be found when annotating. This
                # doesn't matter much, because we use line number 0 for all
                # diffs anyway. It just means we get "This file was unreadable"
                # for modified filenames rather than a single "<unknown (line
                # 0)>" CC.
                fl = args.mod_filename(line[3:-1])
                # A `fn=` line should follow, overwriting the "???".
                flfn = Flfn((fl, "???"))

            elif m := re.match(r"summary:\s+(.*)", line):
                try:
                    summary_cc = events.mk_cc(m.group(1).split())
                except ValueError:
                    parse_die("malformed or too many event counts")

            elif line == "\n" or line.startswith("#"):
                # Skip empty lines and comment lines.
                pass

            else:
                parse_die(f"malformed line: {line[:-1]}")

    # Check if summary line was present.
    if not summary_cc:
        parse_die("missing `summary:` line, aborting")

    # Check summary is correct.
    total_cc = events.mk_empty_cc()
    for flfn_cc in dict_flfn_cc.values():
        add_cc_to_cc(flfn_cc, total_cc)
    if summary_cc != total_cc:
        msg = (
            "`summary:` line doesn't match computed total\n"
            f"- summary: {summary_cc}\n"
            f"- total:   {total_cc}"
        )
        parse_die(msg)

    return (cmd, events, dict_flfn_cc, summary_cc)


def main() -> None:
    filename1 = args.cgout_filename1[0]
    filename2 = args.cgout_filename2[0]

    (cmd1, events1, dict_flfn_cc1, summary_cc1) = read_cgout_file(filename1)
    (cmd2, events2, dict_flfn_cc2, summary_cc2) = read_cgout_file(filename2)

    if events1.events != events2.events:
        die("events in data files don't match")

    # Subtract file 1's CCs from file 2's CCs, at the Flfn level.
    for flfn, flfn_cc1 in dict_flfn_cc1.items():
        flfn_cc2 = dict_flfn_cc2[flfn]
        sub_cc_from_cc(flfn_cc1, flfn_cc2)
    sub_cc_from_cc(summary_cc1, summary_cc2)

    print(f"desc: Files compared:   {filename1}; {filename2}")
    print(f"cmd: {cmd1}; {cmd2}")
    print("events:", *events1.events, sep=" ")

    # Sort so the output is deterministic.
    def key(flfn_and_cc: tuple[Flfn, Cc]) -> Flfn:
        return flfn_and_cc[0]

    for flfn, flfn_cc2 in sorted(dict_flfn_cc2.items(), key=key):
        # Use `0` for the line number because we don't try to give line-level
        # CCs, due to the possibility of code changes causing line numbers to
        # move around.
        print(f"fl={flfn[0]}")
        print(f"fn={flfn[1]}")
        print("0", *flfn_cc2, sep=" ")

    print("summary:", *summary_cc2, sep=" ")


if __name__ == "__main__":
    main()