"""Order-preserving, reversible storage for SQLite text containing NUL.

PostgreSQL text forbids U+0000. Encode it as SOH/SOH, and encode a literal
SOH as SOH/STX. All other characters stay unchanged. The mapping preserves
binary lexicographic order, including string prefixes and composite keys.
"""

CODEC = 'nul-soh-v1'
ESCAPE = '\x01'


def encode(value):
    if isinstance(value, str):
        return value.replace(ESCAPE, ESCAPE + '\x02').replace('\x00', ESCAPE + ESCAPE)
    return value


def decode(value):
    if not isinstance(value, str) or ESCAPE not in value:
        return value
    result = []
    start = 0
    while (position := value.find(ESCAPE, start)) >= 0:
        result.append(value[start:position])
        following = value[position + 1:position + 2]
        if following not in (ESCAPE, '\x02'):
            raise ValueError('Invalid nul-soh-v1 text escape')
        result.append('\x00' if following == ESCAPE else ESCAPE)
        start = position + 2
    result.append(value[start:])
    return ''.join(result)