from dataclasses import dataclass, field
from typing import List, Optional

@dataclass
class Packet:
    """
    Represents a single Teletext packet (Row).
    In T42, we have 42 bytes:
    Byte 0-1: Magazine and Row Address (Hamming 8/4 encoding)
    Byte 2-41: Data bytes (40 bytes)
    """
    original_data: bytes
    magazine: int = field(init=False)
    row: int = field(init=False)
    data: bytearray = field(init=False)

    def __post_init__(self):
        if len(self.original_data) != 42:
            raise ValueError(f"Packet must be 42 bytes, got {len(self.original_data)}")
        
        # Parse Magazine and Row from the first 2 bytes (Hamming 8/4)
        # MRAG (Magazine + Row Address Group)
        # Byte 0: P1 D1 P2 D2 P3 D3 P4 D4
        # Byte 1: P1 D1 P2 D2 P3 D3 P4 D4
        
        b1 = self.original_data[0]
        b2 = self.original_data[1]
        
        # De-interleave Hamming bits to get M (3 bits) and R (5 bits)
        # This is the "basic" interpretation. 
        # For a robust editor we assume the input T42 is valid or we just store bytes.
        # But we need Mag/Row to organize pages.
        
        # Decode Hamming 8/4 logic is complex to implementation from scratch correctly 
        # without a reference, but usually D1, D2, D3, D4 are at bit positions 1, 3, 5, 7 
        # (0-indexed, where 0 is LSB). 
        # Let's perform a simple extraction assuming no bit errors for now.
        
        def decode_hamming_8_4(byte_val):
            # Extract data bits: bits 1, 3, 5, 7
            return ((byte_val >> 1) & 1) | \
                   (((byte_val >> 3) & 1) << 1) | \
                   (((byte_val >> 5) & 1) << 2) | \
                   (((byte_val >> 7) & 1) << 3)

        d1 = decode_hamming_8_4(b1)
        d2 = decode_hamming_8_4(b2)
        
        # Magazine is 3 bits (Logic is specific: Mag 8 is encoded as 0)
        # Row is 5 bits.
        
        # According to Spec (ETSI EN 300 706):
        # b1 encoded: M1 M2 M3 R1
        # b2 encoded: R2 R3 R4 R5
        
        self.magazine = (d1 & 0b0111) 
        if self.magazine == 0:
            self.magazine = 8
            
        row_low_bit = (d1 >> 3) & 1
        row_high_bits = d2
        self.row = (row_high_bits << 1) | row_low_bit
        
        self.data = bytearray(self.original_data[2:])

    @property
    def is_header(self):
        return self.row == 0

@dataclass
class Page:
    """
    Represents a Teletext Page (e.g., 100).
    Can have multiple subpages.
    """
    magazine: int
    page_number: int  # 00-99
    sub_code: int = 0 # Subpage code (0000 to 3F7F hex usually, simplest is 0-99 equivalent)
    packets: List[Packet] = field(default_factory=list)
    
    @property
    def full_page_number(self):
        return f"{self.magazine}{self.page_number:02d}"

@dataclass
class TeletextService:
    """
    Container for all pages.
    """
    pages: List[Page] = field(default_factory=list)
    # We also keep a flat list of all packets to preserve order on save
    all_packets: List[Packet] = field(default_factory=list)