"""Pipe-length-weighted demand allocation.

This module deliberately accepts plain topology data and performs no database
or file access. Application services are responsible for loading topology.
"""

from typing import Any, Mapping


def allocate_demand_by_pipe_length(
    demand: float,
    topology_nodes: Mapping[str, Mapping[str, Any]],
    topology_links: Mapping[str, Mapping[str, Any]],
) -> dict[str, float]:
    """Allocate total demand to junctions by half of each incident link length."""

    if not topology_nodes or not topology_links or demand == 0.0:
        return {}

    total_link_length = sum(
        abs(float(link["length"])) for link in topology_links.values()
    )
    if total_link_length <= 0.0:
        return {}

    demand_per_length = demand / total_link_length
    result: dict[str, float] = {}
    for node_id, node in topology_nodes.items():
        if node["type"] != "junction":
            continue
        incident_length = sum(
            abs(float(topology_links[link_id]["length"]))
            for link_id in node["links"]
        )
        result[node_id] = incident_length * demand_per_length * 0.5
    return result