Function available_chains 

pub fn available_chains(
    tables: &StartposTables,
    campaign: &str,
    faction: &FactionEntry,
) -> Result<Option<HashSet<String>>>

Returns the building chains available to a faction.

The chains are the ones of the availability sets of the faction’s rows if it has any, else of its subculture’s (rows without faction), else of its culture’s (rows without faction nor subculture), looking first at the campaign’s rows and then at the ones without campaign. The rows without culture, subculture nor faction add their sets to every faction.

Arguments

• tables - Tables with building_chain_availabilities and building_chain_availability_sets.
• campaign - Campaign key.
• faction - The faction.

Returns

The chain keys, or None if the tables don’t restrict chains.

Errors

Returns an error if a column is missing.