import re
import enum
import datetime

from email.utils  import parsedate_to_datetime
from email.header import decode_header

from nntp.tiny.db import DatabaseTable

def decode(text: str):
    decoded = decode_header(text)[0]

    if decoded[1] is None:
        if decoded[0] == b'':
            return ''

        return str(decoded[0])

    try:
        return str(decoded[0], decoded[1])
    except:
        if decoded[0] == b'':
            return ''

        return str(decoded[0])

def each_line(text: str):
    start = 0
    end   = len(text)

    while True:
        try:
            index = text.index('\n', start, end)

            yield text[start:index+1]

            start = index + 1

            if start == end:
                break
        except ValueError:
            yield text[start:end]
            break

def parse_timestamp(timestamp: str):
    if timestamp is None or timestamp == '':
        return datetime.datetime.fromtimestamp(0)

    return parsedate_to_datetime(timestamp)

class MessageState(enum.Enum):
    EMPTY  = 0
    HEADER = 1
    BODY   = 2

class Message(DatabaseTable):
    __slots__ = (
        '_cache',
        '_headers',
        '_body',
        '_key',
        'id',
        'newsgroup_id',
        'state',
        'line',
        'content',
    )

    name    = 'newsgroup_message'
    key     = 'id'
    columns = (
        'id',
        'newsgroup_id',
        'created_on',
        'message_id',
        'parent_id',
        'sender',
        'subject',
        'content'
    )

    RE_HEADER = re.compile(r'^([A-Za-z0-9\-]+): (.*)$')

    def __init__(self):
        self._cache       = dict()
        self._headers     = None
        self._body        = None
        self._key         = None
        self.id           = None
        self.newsgroup_id = None
        self.state        = MessageState.EMPTY
        self.line         = None
        self.content      = ''

    @staticmethod
    def __from_row__(row):
        message = Message()

        #
        # Defer parsing the message content until a specific header not already
        # assigned to a dedcicated property, or the message body, is required.
        #
        message.content = row['content']

        message.id           = row['id']
        message.newsgroup_id = row['newsgroup_id']
        message.created_on   = row['created_on']
        message.message_id   = row['message_id']
        message.parent_id    = row['parent_id']
        message.sender       = row['sender']

        return message

    def __values__(self) -> tuple:
        return (
            self.newsgroup_id,
            self.created_on,
            self.message_id,
            self.parent_id,
            self.sender,
            self.subject,
            self.content
        )

    @property
    def headers(self):
        if self._headers is None:
            self.read(self.content)

        return self._headers

    @property
    def body(self):
        if self._body is None:
            self.read(self.content)

        return self._body

    def header(self, key: str):
        if self._headers is None:
            self.read(self.content)

        return self.headers.get(key.lower())

    @property
    def created_on(self):
        value = self._cache.get('created_on')

        if value is not None:
            return datetime.datetime.fromisoformat(value)

        timestamp = self.header('Date')

        ret = parse_timestamp(timestamp)

        self._cache['created_on'] = str(ret)

        return ret

    @created_on.setter
    def created_on(self, value):
        if self._headers is not None:
            self._headers['date'] = str(value)

        self._cache['created_on'] = str(value)

    @property
    def message_id(self) -> str:
        if self._headers is None:
            return self._cache.get('message_id')

        return self.header('Message-ID')

    @message_id.setter
    def message_id(self, value):
        if self._headers is None:
            self._cache['message_id'] = value
        else:
            self.headers['message-id'] = value

    @property
    def parent_id(self) -> str:
        if self._headers is None:
            return self._cache.get('parent_id')

        return self.header('References')

    @parent_id.setter
    def parent_id(self, value):
        if self._headers is None:
            self._cache['parent_id'] = value
        else:
            self.headers['references'] = value

    @property
    def sender(self) -> str:
        if self._headers is None:
            return self._cache.get('sender')

        return self.headers.get('from', 'Unknown')

    @sender.setter
    def sender(self, value):
        if self._headers is None:
            self._cache['sender'] = value
        else:
            self.headers['from'] = value

    @property
    def subject(self) -> str:
        if self._headers is None:
            return self._cache.get('subject', '(no subject)')

        return self.headers.get('subject', '(no subject)')

    @subject.setter
    def subject(self, value):
        if self._headers is None:
            self._cache['subject'] = value
        else:
            self.headers['subject'] = value

    def is_first_line(self):
        return len(self.headers) == 1 and (self._body == '' or self._body is None)

    def read_line(self, line: str):
        if self.line is not None:
            self.content += self.line

        if self.state is MessageState.EMPTY:
            self.state    = MessageState.HEADER
            self._headers = dict()

        if self.state is MessageState.HEADER:
            if line == '\n' or line == '\r\n':
                self.state = MessageState.BODY
            elif line[0] == ' ' or line[0] == '\t':
                self._headers[self._key] += ' ' + decode(line.strip())
            else:
                match = self.RE_HEADER.match(line)

                if match:
                    self._key = match[1].lower()

                    self._headers[self._key] = decode(match[2].rstrip())
        elif self.state is MessageState.BODY:
            if self._body is None:
                self._body = ''
            else:
                self._body += self.line

        self.line = line

    def read(self, text: str):
        for line in each_line(text):
            self.read_line(line)

    @staticmethod
    def from_text(text: str):
        message = Message()

        for line in each_line(text):
            message.read_line(line)

        return message