HEAsoft is a unified release of the FTOOLS and XANADU software packages for high-energy astrophysics data analysis, including tools like XSPEC.

After installation, users must initialize the HEAsoft environment by running the following commands:

export HEADAS=$(ls -d "${CONDA_PREFIX}/x86_64-pc-linux-gnu-libc"*/ | head -n 1)
source "${HEADAS}/headas-init.sh"
export LHEAPERL="${CONDA_PREFIX}/bin/perl"

This setup configures several environment variables required for HEAsoft, including PATH, LD_LIBRARY_PATH, PFILES, PERL5LIB, PYTHONPATH, and component-specific variables such as PGPLOT_DIR, XANADU, and POW_LIBRARY.

Note: LHEAPERL must be manually set to point to your Conda environment's Perl interpreter after sourcing headas-init.sh.

For mission-specific functionality (e.g., Swift, NuSTAR, IXPE), additional environment setup may be required. Refer to the HEAsoft documentation for details.

Warning for XSPEC Users: The /spectral/modelData directory (~5.9GB) is excluded from this package to reduce its size, making XSPEC unusable without it.

To enable XSPEC, follow these steps:

Download the HEAsoft source tarball for the same version as this package (6.35.2):
```
wget https://heasarc.gsfc.nasa.gov/FTP/software/lheasoft/lheasoft6.35.2/heasoft-6.35.2src.tar.gz
```
Replace 6.35.2 by the actual the package version (e.g., 6.35.2).
Extract the tarball:
```
tar zxf heasoft-6.35.2src.tar.gz
```

Copy the modelData directory to the appropriate location:

mkdir -p "${CONDA_PREFIX}/spectral"
cp -r heasoft-6.35.2/Xspec/src/spectral/modelData "${CONDA_PREFIX}/spectral/"