{{/*
    Gets the previous leaf section of a page / section.

    "Leaf section" means "section without sub-sections".

    "Previous" is regarding default ordering, respecting each
    intermediate section ordering.

    Expects a page or a section as argument.

    Returns a Section if it exists, 'false' if there is no such section.

    Here is a small example of what this function would return :

    - comic/             -> return false
        - ACT_1/         -> return false
            - chapter_1/ -> return false
                - P01    -> return false
                - P02    -> return false
            - chapter_2/ -> return `chapter_1/`
                - P03    -> return `chapter_2/`
                - P04    -> return `chapter_2/`
        - ACT_2/         -> return `chapter_2/`
            - chapter_3/ -> return `chapter_2/`
                - P05    -> return `chapter_2/`
                - P06    -> return `chapter_2/`
            - chapter_4/ -> return `chapter_3/`
                - P07    -> return `chapter_3/`
                - P08    -> return `chapter_3/`

    Example usage: {{ partial "func/PrevLeafSection.html" . }}
*/}}

{{ $prev_leaf_section := false }}
{{ $current_section := . }}

{{/* A regular page can ve given as argument instead of a section */}}
{{ if .IsPage }}
    {{ $current_section = .Parent }}
{{ end }}

{{/* if the root was reached, there is no possible previous section */}}
{{ if not ($current_section.FirstSection.Eq $current_section) }}

    {{/*
        Get the previous sibling section.
        We need to actually reverse the ordering because because
        Next / Prev use *descending* weight ordering.
    */}}

    {{ $sibling_sections := $current_section.Parent.Sections.Reverse }}

    {{ with $sibling_sections.Prev $current_section }}

        {{/* Sibling found, get the last leaf section in case there is more than one level of depth */}}
        {{ $prev_leaf_section = partial "func/LastSectionRecursive.html" . }}

    {{ else }}

        {{/* No sibling found, try again with parent */}}
        {{ $prev_leaf_section = partial "func/PrevLeafSection.html" $current_section.Parent }}

    {{ end }}
{{ end }}

{{ return $prev_leaf_section }}