Move metadata to BMI helper functions

[SouthEndMusic]

Issue addressed

Fixes #432

Explanation

I am working on some 'metaprogramming' functions to convert the metadata that is now present at the struct definitions into compact functions that can be used for the BMI:

function extract_metadata(line)
    metadata = split(line, "|")

    unit = if length(metadata) < 2
        "\"mm dt-1\""
    else
        metadata[2]
    end

    exchange = if length(metadata) < 3
        1
    else
        Int(metadata[3])
    end

    grid_type = if length(metadata) < 4
        "unstructured"
    else
        metadata[4]
    end

    grid_location = if length(metadata) < 5
        "node"
    else
        metadata[5]
    end

    (; unit, exchange, grid_type, grid_location)
end

function add_to_dict(dict, key, value)
    if key ∉ keys(dict)
        dict[key] = []
    end
    push!(dict[key], value)
end

function build_bmi_function(function_name, type, dict)
    function_code = "function $function_name(::$type, var_name, name)" 

    if_ = "if"

    for (value, var_names) in dict
        # A functional smiley, my life is complete
        names = "(:" * join(var_names, ", :")
        if length(var_names) == 1
            names *= ",)"
        else
            names *= ")"
        end
        function_code *= "\n  $if_ var_name in $names\n      $value"
        if_ = "elseif"
    end

    function_code *= "\n  else\n      var_error(name)\n  end\nend"

    return function_code
end

function build_bmi_functions(input)
    lines = split(input, "\n")
    type = match(r"struct (.*?){", first(lines))[1]

    unit_dict = Dict{String, Vector{String}}()
    grid_type_dict = Dict{String, Vector{String}}()
    grid_location_dict = Dict{String, Vector{String}}()

    for line in lines
        line = replace(line, r"\s" => "")
        var_name = split(line, "::")[1]
        (occursin("|0", line) || line == "" || !occursin("::", line)) && continue
        metadata = extract_metadata(line)
        add_to_dict(unit_dict, metadata.unit, var_name)
        add_to_dict(grid_type_dict, metadata.grid_type, var_name)
        add_to_dict(grid_location_dict, metadata.grid_location, var_name)
    end

    get_var_units = build_bmi_function("get_var_units", type, unit_dict)
    get_var_location = build_bmi_function("get_var_location", type, grid_location_dict)

    (; get_var_units, get_var_location)
end

function strip_metadata(input)
    output = ""
    for line in split(input, "\n")
        if occursin("::", line)
            first_bar_loc = findfirst("|", line)[1]
            output *= line[1:first_bar_loc-1] * "\n"
        else
            output *= line * "\n"
        end
    end
    output
end

Using the model from run_flextopo.jl, I get desired behavior:

BMI.get_var_units(model, "vertical.wb_snow") # "mmdt-1"
BMI.get_var_location(model, "vertical.wb_snow") # "node"

[SouthEndMusic]

@verseve before I refactor all relevant structs with this, let me know whether you this this is a good approach.

[verseve]

Hi @SouthEndMusic , thanks for looking into this and welcome to the wflow team 😃! I think this could be a nice approach if we want to stick to storing metadata in the structs. An alternative could be that we store this information somewhere else, also related to issue #481 (in that mapping we could also store metadata).

PR #486 has quite some struct changes (and removal of structs), so probably best to start implementing this (if we stick to metatdata in structs) when that PR has been reviewed and merged, I think.

[SouthEndMusic]

Thanks (: I don't fully oversee #481, but my approach here is to remove all metadata from the structs, and move that data to functions only called in the relevant BMI functions. I have only applied this to the FLEXTOPO struct as a proof of concept.

To be clear: the functions above are not meant to become part of the source code. They are only meant to automate the code changes for this PR, and I posted them to show what I am doing.