nim-confutils/confutils/envvar/reader.nim

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2020-10-22 07:18:08 +00:00
import
tables, typetraits, options, os,
serialization/[object_serialization, errors],
./utils
type
EnvvarReader* = object
prefix: string
key: seq[string]
EnvvarError* = object of SerializationError
EnvvarReaderError* = object of EnvvarError
GenericEnvvarReaderError* = object of EnvvarReaderError
deserializedField*: string
innerException*: ref CatchableError
proc handleReadException*(r: EnvvarReader,
Record: type,
fieldName: string,
field: auto,
err: ref CatchableError) =
var ex = new GenericEnvvarReaderError
ex.deserializedField = fieldName
ex.innerException = err
raise ex
proc init*(T: type EnvvarReader, prefix: string): T =
result.prefix = prefix
template getUnderlyingType*[T](_: Option[T]): untyped = T
proc readValue*[T](r: var EnvvarReader, value: var T)
{.raises: [SerializationError, ValueError, Defect].} =
mixin readValue
# TODO: reduce allocation
when T is (SomePrimitives or range or string):
let key = constructKey(r.prefix, r.key)
getValue(key, value)
elif T is Option:
let key = constructKey(r.prefix, r.key)
if existsEnv(key):
var outVal: getUnderlyingType(value)
getValue(key, outVal)
value = some(outVal)
elif T is (seq or array):
when uTypeIsPrimitives(T):
let key = constructKey(r.prefix, r.key)
getValue(key, value)
elif uTypeIsRecord(T):
let key = r.key[^1]
for i in 0..<value.len:
r.key[^1] = key & $i
r.readValue(value[i])
else:
const typeName = typetraits.name(T)
{.fatal: "Failed to convert from Envvar array an unsupported type: " & typeName.}
elif T is (object or tuple):
type T = type(value)
when T.totalSerializedFields > 0:
let fields = T.fieldReadersTable(EnvvarReader)
var expectedFieldPos = 0
r.key.add ""
value.enumInstanceSerializedFields(fieldName, field):
when T is tuple:
r.key[^1] = $expectedFieldPos
var reader = fields[][expectedFieldPos].reader
expectedFieldPos += 1
else:
r.key[^1] = fieldName
var reader = findFieldReader(fields[], fieldName, expectedFieldPos)
if reader != nil:
reader(value, r)
discard r.key.pop()
else:
const typeName = typetraits.name(T)
{.fatal: "Failed to convert from Envvar an unsupported type: " & typeName.}