"""
Port conflict detection for PIC.

Maps each service section to the port field names it exposes, and provides
detect_conflicts() to find cases where two distinct (section, field) slots
resolve to the same integer port value.
"""

# Maps section → list of port field names within that section's config dict.
# Must stay in sync with the _port_fields dict in app.py's update_config().
PORT_FIELDS = {
    'network':   ['dns_port'],
    'wireguard': ['port'],
    'email':     ['smtp_port', 'submission_port', 'imap_port', 'webmail_port'],
    'calendar':  ['port'],
    'files':     ['port', 'manager_port'],
}


def detect_conflicts(effective_config, incoming_patch):
    """
    Detect port conflicts across all tracked service sections.

    Parameters
    ----------
    effective_config : dict
        The current full config as stored (e.g. config_manager.configs).
        Each key is a section name; the value is a dict of that section's
        config fields.
    incoming_patch : dict
        The partial update the user is trying to save.  Values here override
        whatever is in effective_config for the purpose of conflict checking.

    Returns
    -------
    list of dict
        Each element is {'port': <int>, 'conflicts': [(section, field), ...]}.
        Only entries where 2+ (section, field) pairs share the same port are
        included.  Returns an empty list when there are no conflicts.
    """
    # Build merged view: start from stored config, overlay the patch
    merged = {}
    for section in PORT_FIELDS:
        stored = effective_config.get(section, {}) or {}
        patch = incoming_patch.get(section, {}) or {}
        merged[section] = {**stored, **patch}

    # Collect port → [(section, field)] mapping
    port_map = {}
    for section, fields in PORT_FIELDS.items():
        for field in fields:
            raw = merged[section].get(field)
            if raw is None or raw == '':
                continue
            try:
                port_val = int(raw)
            except (ValueError, TypeError):
                continue
            port_map.setdefault(port_val, []).append((section, field))

    # Return only entries that have more than one (section, field) slot
    conflicts = []
    for port_val, slots in port_map.items():
        if len(slots) >= 2:
            conflicts.append({'port': port_val, 'conflicts': slots})

    return conflicts