ExtModel cannot handle path formats from different OS

[SCLaan]

Is your feature request related to a problem? Please describe.
When working on Windows ExtModel (and maybe other functions) cannot read Unix paths (and probably vice-versa). With many quick pre- and post-processing steps on Windows machines and the larger simulations on a Linux cluster an automatic conversion of path formats when reading data will be necessary. Also for saving it will be a good feature to be able to choose the output format (Windows/Unix).

To Reproduce

1. Make an external forcings file (dummy.ext) with the content:

[boundary]
quantity=waterlevelbnd
locationfile=/p/11203669-004-kpp-morfwad-krw-slib/Waddenzee_model_hydro/04_Boundary_conditions/east_v05_part2.pli
forcingfile=/p/11203669-004-kpp-morfwad-krw-slib/Waddenzee_model_hydro/04_Boundary_conditions/east_part2_wl_20151222_20180101.bc
return_time=0.0000000e+000

2. Open external forcings file in python on Windows:

from pathlib import Path
from hydrolib.core.io.ext.models import ExtModel
extFile = Path(r'dummy.ext')
extData = ExtModel(extFile)

3. This causes an error like:

DWSM-FM_bc.ext -> boundary -> 19 -> forcingFile
  File: `\\directory.intra\Project\p\11203669-004-kpp-morfwad-krw-slib\Waddenzee_model_hydro\04_Boundary_conditions\south_temp_20151222_20180101.bc` not found, skipped parsing. (type=value_error)

Describe the solution you'd like

• ExtModel to automatically determine the format of paths and to be be able to read the data regardless of the used OS.
• ExtModel to include an option for saving in a different format (e.g. save as Unix on Windows). Ideally this is set based on the format already used.

Technical design
(Proposal by @arthurvd)

• Implementation in the FileModel class is probably enough and as high as possible.
• It should support optional configuration of the path-style (Windows or Unix-like) during model load()
• A similar optional argument should support a custom path-style upon save() of a model
• By default, the current OS style must be detected and used.
• Path style options can become a small Enum class.
• Probably this must become a data attribute in the FileModel class, such that it can also be set while creating models from scratch, e.g.:

fmmodel = FMModel()
extmodel = ExtModel()
extmodel.filepath = '/p/foo/forcing.ext`
extmodel.path_style = PathStyle.UNIXLIKE   # or do we even autodetect this in set_attribute or so?

• For absolute paths, no translation is possible (we don't know which Windows driveletter corresponds with which leading root dir on Linux). OR: should the user be able to supply some mapping table of absolute path parts?
• Final remark: before making all of this: INVESTIGATE whether pathlib or some other package already has some built-in features for this.

[veenstrajelmer]

Suggestion: always write forward slashes (windows also supports this), then the only issue that remains are the hardcoded drive letters

[priscavdsluis]

I put this is back in TODO for now, since I would like to discuss this with the rest of the team:

• Resolving absolute paths from posix to windows will indeed be a challenge. For example, in this, case /p has to be converted to p:. This in itself is not difficult, but it will become trial and error code: if the converted path can be found, it was apparently an absolute path, otherwise it must be a relative path. From windows to posix, will be easier.
• I agree with @veenstrajelmer, that we could always write forward slashes. This way, all relative paths that were written with hydrolib-core can be correctly read with hydrolib-core on any OS. However, what about models that already exist with backward slashes?

[priscavdsluis]

@SCLaan, thanks for your feedback! Good to hear it works.

[arthurvd]

@SCLaan : wil jij deze nieuwe functionaliteit testen?
Het staat in @priscavdsluis's branch #361 (feat/339-handle-path-format-different-OS), en je gebruikt het bijvoorbeeld zo (op Windows verwijzend naar files met Linux /p/enzovoort paden.

inputmdu=Path(r"p:/model/flowfm.mdu")
fmmodel = FMModel(filepath=inputmdu, path_style="unix")

# [..]
outputmdu=Path(r"p:/model/flowfm_modified.mdu")
fmmodel.filepath = outputmdu
fmmodel.save(path_style="unix")

[priscavdsluis]

#474 can be merged once this issue is merged (should make tests green for that issue)

[SCLaan]

@SCLaan : wil jij deze nieuwe functionaliteit testen? Het staat in @priscavdsluis's branch #361 (feat/339-handle-path-format-different-OS), en je gebruikt het bijvoorbeeld zo (op Windows verwijzend naar files met Linux /p/enzovoort paden.

inputmdu=Path(r"p:/model/flowfm.mdu")
fmmodel = FMModel(filepath=inputmdu, path_style="unix")

# [..]
outputmdu=Path(r"p:/model/flowfm_modified.mdu")
fmmodel.filepath = outputmdu
fmmodel.save(path_style="unix")

I did some quick tests and this seems to be working fine. I think this issue can now be closed.