-- Macro: Generate a CTE that unions current and predecessor data for a given source

{% macro chain_lineage(source_ref, urn_col='urn', year_col='year') %}

with current_data as (
    select
        {{ urn_col }} as current_urn,
        {{ urn_col }} as source_urn,
        *
    from {{ source_ref }}
),

predecessor_data as (
    select
        lin.current_urn,
        src.{{ urn_col }} as source_urn,
        src.*
    from {{ source_ref }} src
    inner join {{ ref('int_school_lineage') }} lin
        on src.{{ urn_col }} = lin.predecessor_urn
    where not exists (
        select 1 from {{ source_ref }} curr
        where curr.{{ urn_col }} = lin.current_urn
          and curr.{{ year_col }} = src.{{ year_col }}
    )
),

combined as (
    select * from current_data
    union all
    select * from predecessor_data
)

select * from combined

{% endmacro %}