"""
    struct JSONModel <: MetabolicModel
        json::Dict{String,Any}
    end

A struct used to store the contents of a JSON model, i.e. a model read from a
file ending with `.json`. These model files typically store all the model
parameters in arrays of JSON objects (i.e. Julia dictionaries).

Usually, not all of the fields of the input JSON can be easily represented when
converting to other models, care should be taken to avoid losing information.

Direct work on this precise model type is not very efficient, as the accessor
functions need to repeatedly find the information in the JSON tree. This gets
very slow especially if calling many accessor functions sequentially. To avoid
that, convert to e.g. [`StandardModel`](@ref) as soon as possible.

# Example
````
model = load_json_model("some_model.json")
model.json # see the actual underlying JSON
reactions(model) # see the list of reactions
````
"""
struct JSONModel <: MetabolicModel
    json::Dict{String,Any}
end


# helper access macros, see examples below for usage
macro _json_sectionkey(namesConstant::Symbol, error)
    esc(:(
        begin
            _key = _guesskey(keys(model.json), _constants.keynames.$namesConstant)
            if isnothing(_key)
                $error
            end
            _key
        end
    ))
end

macro _json_section(namesConstant::Symbol, error)
    esc(:(
        begin
            _key = @_json_sectionkey $namesConstant ($error)
            model.json[_key]
        end
    ))
end

macro _json_section_firstid(namesConstant::Symbol, id::Symbol, error)
    return esc(:(
        begin
            _s = @_json_section $namesConstant ($error)
            _s[findfirst(x -> x["id"] == $id, _s)]
        end
    ))
end

function _parse_annotations(x)::Annotations
    Annotations([k => if typeof(v) == String
        [v]
    else
        convert(Vector{String}, v)
    end for (k, v) in x])
end

_parse_notes(x)::Notes = _parse_annotations(x)

"""
    reactions(model::JSONModel)

Extract reaction names (stored as `.id`) from JSON model.
"""
function reactions(model::JSONModel)
    rs = @_json_section rxns throw(
        DomainError(keys(model.json), "JSON model has no reaction keys"),
    )

    return [string(get(rs[i], "id", "rxn$i")) for i in eachindex(rs)]
end

"""
    metabolites(model::JSONModel)

Extract metabolite names (stored as `.id`) from JSON model.
"""
function metabolites(model::JSONModel)
    ms = @_json_section mets throw(
        DomainError(keys(model.json), "JSON model has no metabolite keys"),
    )

    return [string(get(ms[i], "id", "met$i")) for i in eachindex(ms)]
end

"""
    genes(model::JSONModel)

Extract gene names from a JSON model.
"""
function genes(model::JSONModel)
    gs = @_json_section genes return []

    return [string(get(gs[i], "id", "gene$i")) for i in eachindex(gs)]
end

"""
    stoichiometry(model::JSONModel)

Get the stoichiometry. Assuming the information is stored in reaction object
under key `.metabolites`.
"""
function stoichiometry(model::JSONModel)
    rxn_ids = reactions(model)
    met_ids = metabolites(model)

    rs = @_json_section rxns throw(
        DomainError(keys(model.json), "JSON model has no reaction keys"),
    )

    S = SparseArrays.spzeros(length(met_ids), length(rxn_ids))
    for (i, rid) in enumerate(rxn_ids)
        r = rs[findfirst(x -> x["id"] == rid, rs)]
        for (met_id, coeff) in r["metabolites"]
            j = findfirst(==(met_id), met_ids)
            if isnothing(j)
                throw(
                    DomainError(
                        met_id,
                        "Unknown metabolite found in stoichiometry of $(rxn_ids[i])",
                    ),
                )
            end
            S[j, i] = coeff
        end
    end
    return S
end

"""
    bounds(model::JSONModel)

Get the bounds for reactions, assuming the information is stored in
`.lower_bound` and `.upper_bound`.
"""
function bounds(model::JSONModel)
    rs = @_json_section rxns return (
        sparse(fill(-_constants.default_reaction_bound, n_reactions(model))),
        sparse(fill(_constants.default_reaction_bound, n_reactions(model))),
    )
    return (
        sparse([get(rxn, "lower_bound", -_constants.default_reaction_bound) for rxn in rs]),
        sparse([get(rxn, "upper_bound", _constants.default_reaction_bound) for rxn in rs]),
    )
end

"""
    objective(model::JSONModel)

Collect `.objective_coefficient` keys from model reactions.
"""
function objective(model::JSONModel)
    rs = @_json_section rxns return spzeros(n_reactions(model))

    return sparse([float(get(rxn, "objective_coefficient", 0.0)) for rxn in rs])
end

"""
    reaction_gene_associaton(model::JSONModel, rid::String)

Parses the `.gene_reaction_rule` from reactions.
"""
function reaction_gene_association(model::JSONModel, rid::String)
    rxn = @_json_section_firstid rxns rid return nothing
    return _maybemap(_parse_grr, get(rxn, "gene_reaction_rule", nothing))
end

"""
    reaction_subsystem(model::JSONModel, rid::String)

Parses the `.subsystem` out from reactions.
"""
function reaction_subsystem(model::JSONModel, rid::String)
    rxn = @_json_section_firstid rxns rid return nothing
    return get(rxn, "subsystem", nothing)
end

"""
    metabolite_formula(model::JSONModel, mid::String)

Parse and return the metabolite `.formula`
"""
function metabolite_formula(model::JSONModel, mid::String)
    met = @_json_section_firstid mets mid return nothing
    return _maybemap(_parse_formula, get(met, "formula", nothing))
end

"""
    metabolite_charge(model::JSONModel, mid::String)

Return the metabolite `.charge`
"""
function metabolite_charge(model::JSONModel, mid::String)
    met = @_json_section_firstid mets mid return nothing
    return get(met, "charge", 0)
end

"""
    metabolite_compartment(model::JSONModel, mid::String)

Return the metabolite `.compartment`
"""
function metabolite_compartment(model::JSONModel, mid::String)
    met = @_json_section_firstid mets mid return nothing
    return get(met, "compartment", nothing)
end

"""
    gene_annotations(model::JSONModel, gid::String)::Annotations

Gene annotations from the [`JSONModel`](@ref).
"""
function gene_annotations(model::JSONModel, gid::String)::Annotations
    gene = @_json_section_firstid genes gid return Dict()
    _maybemap(_parse_annotations, get(gene, "annotation", nothing))
end

"""
    gene_notes(model::JSONModel, gid::String)::Notes

Gene notes from the [`JSONModel`](@ref).
"""
function gene_notes(model::JSONModel, gid::String)::Notes
    gene = @_json_section_firstid genes gid return Dict()
    _maybemap(_parse_notes, get(gene, "notes", nothing))
end

"""
    reaction_annotations(model::JSONModel, rid::String)::Annotations

Reaction annotations from the [`JSONModel`](@ref).
"""
function reaction_annotations(model::JSONModel, rid::String)::Annotations
    rxn = @_json_section_firstid rxns rid return Dict()
    _maybemap(_parse_annotations, get(rxn, "annotation", nothing))
end

"""
    reaction_notes(model::JSONModel, rid::String)::Notes

Reaction notes from the [`JSONModel`](@ref).
"""
function reaction_notes(model::JSONModel, rid::String)::Notes
    rxn = @_json_section_firstid rxns rid return Dict()
    _maybemap(_parse_notes, get(rxn, "notes", nothing))
end

"""
    metabolite_annotations(model::JSONModel, mid::String)::Annotations

Metabolite annotations from the [`JSONModel`](@ref).
"""
function metabolite_annotations(model::JSONModel, mid::String)::Annotations
    met = @_json_section_firstid mets mid return Dict()
    _maybemap(_parse_annotations, get(met, "annotation", nothing))
end

"""
    metabolite_notes(model::JSONModel, mid::String)::Notes

Metabolite notes from the [`JSONModel`](@ref).
"""
function metabolite_notes(model::JSONModel, mid::String)::Notes
    met = @_json_section_firstid mets mid return Dict()
    _maybemap(_parse_notes, get(met, "notes", nothing))
end

"""
    reaction_stoichiometry(model::JSONModel, rxn_id::String)::Dict{String, Float64}

Return the reaction equation of reaction with id `rxn_id` in model. The reaction
equation maps metabolite ids to their stoichiometric coefficients.
"""
function reaction_stoichiometry(m::JSONModel, rxn_id::String)::Dict{String,Float64}
    ind = findfirst(x -> x["id"] == rxn_id, m.json["reactions"])
    m.json["reactions"][ind]["metabolites"]
end

"""
    Base.convert(::Type{JSONModel}, mm::MetabolicModel)

Convert any [`MetabolicModel`](@ref) to [`JSONModel`](@ref).
"""
function Base.convert(::Type{JSONModel}, mm::MetabolicModel)
    if typeof(mm) == JSONModel
        return mm
    end

    rxn_ids = reactions(mm)
    met_ids = metabolites(mm)
    gene_ids = genes(mm)
    S = stoichiometry(mm)
    lbs, ubs = bounds(mm)
    ocs = objective(mm)

    json_model = JSONModel(Dict{String,Any}())
    json = Dict{String,Any}()
    json["id"] = "model" # default

    #TODO: add notes, names and similar fun stuff when they are available

    json[first(_constants.keynames.genes)] = [
        Dict([
            "id" => gid,
            "annotation" => gene_annotations(mm, gid),
            "notes" => gene_notes(mm, gid),
        ],) for gid in gene_ids
    ]

    json[first(_constants.keynames.mets)] = [
        Dict([
            "id" => mid,
            "formula" => _maybemap(_unparse_formula, metabolite_formula(mm, mid)),
            "charge" => metabolite_charge(mm, mid),
            "compartment" => metabolite_compartment(mm, mid),
            "annotation" => metabolite_annotations(mm, mid),
            "notes" => metabolite_notes(mm, mid),
        ]) for mid in met_ids
    ]

    json[first(_constants.keynames.rxns)] = [
        begin
            res = Dict{String,Any}()
            res["id"] = rid
            res["subsystem"] = reaction_subsystem(mm, rid)
            res["annotation"] = reaction_annotations(mm, rid)
            res["notes"] = reaction_notes(mm, rid)

            grr = reaction_gene_association(mm, rid)
            if !isnothing(grr)
                res["gene_reaction_rule"] = _unparse_grr(String, grr)
            end

            res["lower_bound"] = lbs[ri]
            res["upper_bound"] = ubs[ri]
            res["objective_coefficient"] = ocs[ri]
            I, V = findnz(S[:, ri])
            res["metabolites"] =
                Dict{String,Float64}([met_ids[ii] => vv for (ii, vv) in zip(I, V)])
            res
        end for (ri, rid) in enumerate(rxn_ids)
    ]

    return JSONModel(json)
end