Daniel Dybing
4b7b73e9a3
- Refactored to parse page numbers as nibbles ((T<<4)|U) instead of decimal, preventing collisions between hex and decimal pages. - Updated to format page IDs as Hex. - Updated to display page IDs as Hex in the list. - Ensures filler/housekeeping pages are correctly isolated.
96 lines
3.1 KiB
Python
96 lines
3.1 KiB
Python
from dataclasses import dataclass, field
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from typing import List, Optional
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@dataclass
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class Packet:
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"""
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Represents a single Teletext packet (Row).
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In T42, we have 42 bytes:
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Byte 0-1: Magazine and Row Address (Hamming 8/4 encoding)
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Byte 2-41: Data bytes (40 bytes)
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"""
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original_data: bytes
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magazine: int = field(init=False)
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row: int = field(init=False)
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data: bytearray = field(init=False)
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def __post_init__(self):
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if len(self.original_data) != 42:
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raise ValueError(f"Packet must be 42 bytes, got {len(self.original_data)}")
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# Parse Magazine and Row from the first 2 bytes (Hamming 8/4)
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# MRAG (Magazine + Row Address Group)
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# Byte 0: P1 D1 P2 D2 P3 D3 P4 D4
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# Byte 1: P1 D1 P2 D2 P3 D3 P4 D4
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b1 = self.original_data[0]
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b2 = self.original_data[1]
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# De-interleave Hamming bits to get M (3 bits) and R (5 bits)
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# This is the "basic" interpretation.
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# For a robust editor we assume the input T42 is valid or we just store bytes.
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# But we need Mag/Row to organize pages.
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# Decode Hamming 8/4 logic is complex to implementation from scratch correctly
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# without a reference, but usually D1, D2, D3, D4 are at bit positions 1, 3, 5, 7
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# (0-indexed, where 0 is LSB).
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# Let's perform a simple extraction assuming no bit errors for now.
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def decode_hamming_8_4(byte_val):
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# Extract data bits: bits 1, 3, 5, 7
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return ((byte_val >> 1) & 1) | \
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(((byte_val >> 3) & 1) << 1) | \
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(((byte_val >> 5) & 1) << 2) | \
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(((byte_val >> 7) & 1) << 3)
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d1 = decode_hamming_8_4(b1)
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d2 = decode_hamming_8_4(b2)
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# Magazine is 3 bits (Logic is specific: Mag 8 is encoded as 0)
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# Row is 5 bits.
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# According to Spec (ETSI EN 300 706):
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# b1 encoded: M1 M2 M3 R1
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# b2 encoded: R2 R3 R4 R5
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self.magazine = (d1 & 0b0111)
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if self.magazine == 0:
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self.magazine = 8
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row_low_bit = (d1 >> 3) & 1
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row_high_bits = d2
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self.row = (row_high_bits << 1) | row_low_bit
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self.data = bytearray(self.original_data[2:])
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@property
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def is_header(self):
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return self.row == 0
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@dataclass
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class Page:
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"""
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Represents a Teletext Page (e.g., 100).
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Can have multiple subpages.
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"""
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magazine: int
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page_number: int # 00-99
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sub_code: int = 0 # Subpage code (0000 to 3F7F hex usually, simplest is 0-99 equivalent)
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language: int = 0 # National Option (0-7)
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packets: List[Packet] = field(default_factory=list)
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@property
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def full_page_number(self):
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# Format as Hex to support A-F pages
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return f"{self.magazine}{self.page_number:02X}"
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@dataclass
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class TeletextService:
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"""
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Container for all pages.
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"""
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pages: List[Page] = field(default_factory=list)
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# We also keep a flat list of all packets to preserve order on save
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all_packets: List[Packet] = field(default_factory=list)
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