# Copyright (c) 2024, Felix Fontein <felix@fontein.de>
# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
# SPDX-License-Identifier: GPL-3.0-or-later

# Note that this module util is **PRIVATE** to the collection. It can have breaking changes at any time.
# Do not use this from other collections or standalone plugins/modules!

"""
Parse go logfmt messages.

See https://pkg.go.dev/github.com/kr/logfmt?utm_source=godoc for information on the format.
"""

from __future__ import annotations


# The format is defined in https://pkg.go.dev/github.com/kr/logfmt?utm_source=godoc
# (look for "EBNFish")


class InvalidLogFmt(Exception):
    pass


class _Mode:
    GARBAGE = 0
    KEY = 1
    EQUAL = 2
    IDENT_VALUE = 3
    QUOTED_VALUE = 4


_ESCAPE_DICT = {
    '"': '"',
    "\\": "\\",
    "'": "'",
    "/": "/",
    "b": "\b",
    "f": "\f",
    "n": "\n",
    "r": "\r",
    "t": "\t",
}

_HEX_DICT = {
    "0": 0,
    "1": 1,
    "2": 2,
    "3": 3,
    "4": 4,
    "5": 5,
    "6": 6,
    "7": 7,
    "8": 8,
    "9": 9,
    "a": 0xA,
    "b": 0xB,
    "c": 0xC,
    "d": 0xD,
    "e": 0xE,
    "f": 0xF,
    "A": 0xA,
    "B": 0xB,
    "C": 0xC,
    "D": 0xD,
    "E": 0xE,
    "F": 0xF,
}


def _is_ident(cur):
    return cur > " " and cur not in ('"', "=")


class _Parser:
    def __init__(self, line):
        self.line = line
        self.index = 0
        self.length = len(line)

    def done(self):
        return self.index >= self.length

    def cur(self):
        return self.line[self.index]

    def next(self):
        self.index += 1

    def prev(self):
        self.index -= 1

    def parse_unicode_sequence(self):
        if self.index + 6 > self.length:
            raise InvalidLogFmt("Not enough space for unicode escape")
        if self.line[self.index : self.index + 2] != "\\u":
            raise InvalidLogFmt("Invalid unicode escape start")
        v = 0
        for i in range(self.index + 2, self.index + 6):
            v <<= 4
            try:
                v += _HEX_DICT[self.line[self.index]]
            except KeyError:
                raise InvalidLogFmt(
                    f"Invalid unicode escape digit {self.line[self.index]!r}"
                )
        self.index += 6
        return chr(v)


def parse_line(line, logrus_mode=False):
    result = {}
    parser = _Parser(line)
    key = []
    value = []
    mode = _Mode.GARBAGE

    def handle_kv(has_no_value=False):
        k = "".join(key)
        v = None if has_no_value else "".join(value)
        result[k] = v
        del key[:]
        del value[:]

    def parse_garbage(cur):
        if _is_ident(cur):
            return _Mode.KEY
        parser.next()
        return _Mode.GARBAGE

    def parse_key(cur):
        if _is_ident(cur):
            key.append(cur)
            parser.next()
            return _Mode.KEY
        if cur == "=":
            parser.next()
            return _Mode.EQUAL
        if logrus_mode:
            raise InvalidLogFmt('Key must always be followed by "=" in logrus mode')
        handle_kv(has_no_value=True)
        parser.next()
        return _Mode.GARBAGE

    def parse_equal(cur):
        if _is_ident(cur):
            value.append(cur)
            parser.next()
            return _Mode.IDENT_VALUE
        if cur == '"':
            parser.next()
            return _Mode.QUOTED_VALUE
        handle_kv()
        parser.next()
        return _Mode.GARBAGE

    def parse_ident_value(cur):
        if _is_ident(cur):
            value.append(cur)
            parser.next()
            return _Mode.IDENT_VALUE
        handle_kv()
        parser.next()
        return _Mode.GARBAGE

    def parse_quoted_value(cur):
        if cur == "\\":
            parser.next()
            if parser.done():
                raise InvalidLogFmt("Unterminated escape sequence in quoted string")
            cur = parser.cur()
            if cur in _ESCAPE_DICT:
                value.append(_ESCAPE_DICT[cur])
            elif cur != "u":
                es = f"\\{cur}"
                raise InvalidLogFmt(f"Unknown escape sequence {es!r}")
            else:
                parser.prev()
                value.append(parser.parse_unicode_sequence())
            parser.next()
            return _Mode.QUOTED_VALUE
        if cur == '"':
            handle_kv()
            parser.next()
            return _Mode.GARBAGE
        if cur < " ":
            raise InvalidLogFmt("Control characters in quoted string are not allowed")
        value.append(cur)
        parser.next()
        return _Mode.QUOTED_VALUE

    parsers = {
        _Mode.GARBAGE: parse_garbage,
        _Mode.KEY: parse_key,
        _Mode.EQUAL: parse_equal,
        _Mode.IDENT_VALUE: parse_ident_value,
        _Mode.QUOTED_VALUE: parse_quoted_value,
    }
    while not parser.done():
        mode = parsers[mode](parser.cur())
    if mode == _Mode.KEY and logrus_mode:
        raise InvalidLogFmt('Key must always be followed by "=" in logrus mode')
    if mode in (_Mode.KEY, _Mode.EQUAL):
        handle_kv(has_no_value=True)
    elif mode == _Mode.IDENT_VALUE:
        handle_kv()
    elif mode == _Mode.QUOTED_VALUE:
        raise InvalidLogFmt("Unterminated quoted string")
    return result