Cleanup: Split most code out of DataSets.jl (#36)

* Move DataSet related code into DataSet.jl
* Move DataProject related code into data_project.jl
* Move registry of storage drivers into storage_drivers.jl
* Remove link_dataset and unlink_dataset internal functions, and a buggy
  unwanted variant of load_project.

Author: c42f

src/DataSet.jl

@@ -0,0 +1,165 @@
+"""
+A `DataSet` is a metadata overlay for data held locally or remotely which is
+unopinionated about the underlying storage mechanism.
+
+The data in a `DataSet` has a type which implies an index; the index can be
+used to partition the data for processing.
+"""
+struct DataSet
+    # For now, the representation `conf` contains data read directly from the
+    # TOML. Once the design has settled we might get some explicit fields and
+    # do validation.
+    uuid::UUID     # Unique identifier for the dataset. Use uuid4() to create these.
+    conf
+
+    function DataSet(conf)
+        _check_keys(conf, DataSet, ["uuid"=>String, "storage"=>Dict, "name"=>String])
+        _check_keys(conf["storage"], DataSet, ["driver"=>String])
+        check_dataset_name(conf["name"])
+        new(UUID(conf["uuid"]), conf)
+    end
+
+    #=
+    name::String # Default name for convenience.
+                         # The binding to an actual name is managed by the data
+                         # project.
+    storage        # Storage config and driver definition
+    maps::Vector{DataMap}
+
+    # Generic dictionary of other properties... for now. Required properties
+    # will be moved
+    _other::Dict{Symbol,Any}
+
+    #storage_id     # unique identifier in storage backend, if it exists
+    #owner          # Project or user who owns the data
+    #description::String
+    #type           # Some representation of the type of data?
+    #               # An array, blob, table, tree, etc
+    #cachable::Bool # Can the data be cached?  It might not for data governance
+    #               # reasons or it might change commonly.
+    ## A set of identifiers
+    #tags::Set{String}
+    =#
+end
+
+_key_match(config, (k,T)::Pair) = haskey(config, k) && config[k] isa T
+_key_match(config, k::String) = haskey(config, k)
+
+function _check_keys(config, context, keys)
+    missed_keys = filter(k->!_key_match(config, k), keys)
+    if !isempty(missed_keys)
+        error("""
+              Missing expected keys in $context:
+              $missed_keys
+
+              In TOML fragment:
+              $(sprint(TOML.print,config))
+              """)
+    end
+end
+
+"""
+    check_dataset_name(name)
+
+Check whether a dataset name is valid. Valid names include start with a letter
+and may contain letters, numbers or `_`. Names may be hieracicial, with pieces
+separated with forward slashes. Examples:
+
+    my_data
+    my_data_1
+    username/data
+    organization/project/data
+"""
+function check_dataset_name(name::AbstractString)
+    # DataSet names disallow most punctuation for now, as it may be needed as
+    # delimiters in data-related syntax (eg, for the data REPL).
+    dataset_name_pattern = r"
+        ^
+        [[:alpha:]]
+        (?:
+            [[:alnum:]_]      |
+            / (?=[[:alpha:]])
+        )*
+        $
+        "x
+    if !occursin(dataset_name_pattern, name)
+        error("DataSet name \"$name\" is invalid. DataSet names must start with a letter and can contain only letters, numbers, `_` or `/`.")
+    end
+end
+
+# Hacky thing until we figure out which fields DataSet should actually have.
+function Base.getproperty(d::DataSet, name::Symbol)
+    if name in fieldnames(DataSet)
+        return getfield(d, name)
+    else
+        getfield(d, :conf)[string(name)]
+    end
+end
+
+Base.getindex(d::DataSet, name::AbstractString) = getindex(d.conf, name)
+Base.haskey(d::DataSet, name::AbstractString) = haskey(d.conf, name)
+
+# Split the fragment section as a '/' separated RelPath
+function dataspec_fragment_as_path(d::DataSet)
+    if haskey(d, "dataspec")
+        fragment = get(d.dataspec, "fragment", nothing)
+        if !isnothing(fragment)
+            return RelPath(split(fragment, '/'))
+        end
+    end
+    return nothing
+end
+
+function Base.show(io::IO, d::DataSet)
+    print(io, DataSet, "(name=$(repr(d.name)), uuid=$(repr(d.uuid)), #= … =#)")
+end
+
+function Base.show(io::IO, ::MIME"text/plain", d::DataSet)
+    TOML.print(io, d.conf)
+end
+
+
+#-------------------------------------------------------------------------------
+# Functions for opening datasets
+
+# do-block form of open()
+function Base.open(f::Function, as_type, dataset::DataSet)
+    storage_config = dataset.storage
+    driver = _find_driver(dataset)
+    driver(storage_config, dataset) do storage
+        open(f, as_type, storage)
+    end
+end
+
+# Contexts-based form of open()
+@! function Base.open(dataset::DataSet)
+    storage_config = dataset.storage
+    driver = _find_driver(dataset)
+    # Use `enter_do` because drivers don't yet use the ResourceContexts.jl mechanism
+    (storage,) = @! enter_do(driver, storage_config, dataset)
+    storage
+end
+
+@! function Base.open(as_type, dataset::DataSet)
+    storage = @! open(dataset)
+    @! open(as_type, storage)
+end
+
+# TODO:
+#  Consider making a distinction between open() and load().
+
+# Finalizer-based version of open()
+function Base.open(dataset::DataSet)
+    @context begin
+        result = @! open(dataset)
+        @! ResourceContexts.detach_context_cleanup(result)
+    end
+end
+
+function Base.open(as_type, dataset::DataSet)
+    @context begin
+        result = @! open(as_type, dataset)
+        @! ResourceContexts.detach_context_cleanup(result)
+    end
+end
+