# This file was extracted from the HV SDK Docusaurus examples.
# It is intended as a downloadable, runnable companion to the documentation.
# Set HSI_EXAMPLE_BASE_DIR and related env vars to use your own data.
# Source page: /hsi/hv_sdk/examples/basics#band-selection

# region: setup
import os
from pathlib import Path

import numpy as np
import qtec_hv_sdk as hs
from qtec_hv_sdk.preprocessing import make_reference
from qtec_hv_sdk.preprocessing import reflectance_calibration


BASE_DIR = Path(os.environ.get("HSI_EXAMPLE_BASE_DIR", "/path/to/HSI_data/nuts"))
if not BASE_DIR.exists():
    raise SystemExit(
        "Run: 'export HSI_EXAMPLE_BASE_DIR=/path/to/HSI_data/' to setup the "
        "folder containing the example datacubes."
    )
CUBE = os.environ.get("HSI_EXAMPLE_CUBE", "mix1.pam")
DARK_REF = os.environ.get("HSI_EXAMPLE_DARK_REF", "dark_ref.pam")
WHITE_REF = os.environ.get("HSI_EXAMPLE_WHITE_REF", "white_ref.pam")

WAVELENGTH_MIN_NM = 430.0
WAVELENGTH_MAX_NM = 1700.0


def make_references():
    dark = hs.open(str(BASE_DIR / DARK_REF))
    white = hs.open(str(BASE_DIR / WHITE_REF))
    return make_reference(dark), make_reference(white)


def add_camera_wavelengths(img):
    # Example PAM cubes may not include wavelengths; attach them so downstream
    # wavelength-based code can use img.meta.spectral.wavelengths.
    if img.meta.spectral.wavelengths is not None:
        return img

    meta = img.meta
    meta.spectral = hs.SpectralMeta(
        wavelengths=hs.WavelengthMeta(
            np.linspace(WAVELENGTH_MIN_NM, WAVELENGTH_MAX_NM, img.meta.shape.bands),
            hs.WavelengthUnit.Nanometer,
        )
    )
    return img.with_meta(meta)


def open_reflectance_cube(cube_name=CUBE):
    dark_ref, white_ref = make_references()
    img = add_camera_wavelengths(hs.open(str(BASE_DIR / cube_name)))
    return reflectance_calibration(img, white_ref, dark_ref, clip=True)


def wavelengths_for_image(img):
    wavelengths = img.meta.spectral.wavelengths
    if wavelengths is None:
        raise ValueError("This image does not contain wavelength metadata.")
    if wavelengths.unit != hs.WavelengthUnit.Nanometer:
        raise ValueError(f"Expected wavelengths in nm, got {wavelengths.unit}.")
    return np.array(wavelengths.band_data)


def band_index_for_wavelength(wavelength_nm, img):
    wavelengths = wavelengths_for_image(img)
    return int(np.argmin(np.abs(wavelengths - wavelength_nm)))
# end region

# region: example
reflectance = open_reflectance_cube()

start_nm = 500
stop_nm = 1000

start_band = band_index_for_wavelength(start_nm, reflectance)
stop_band = band_index_for_wavelength(stop_nm, reflectance)

selected_range = reflectance[:, :, start_band:stop_band + 1]
every_fourth_band = reflectance[:, :, ::4]
rgb_band_indices = sorted([
    band_index_for_wavelength(650, reflectance),
    band_index_for_wavelength(550, reflectance),
    band_index_for_wavelength(460, reflectance),
])
selected_rgb_bands = reflectance.select_bands(rgb_band_indices)

print(f"Selected band range: {start_band}:{stop_band + 1}")
print(f"Selected range shape: {selected_range.shape}")
print(f"Every fourth band shape: {every_fourth_band.shape}")
print(f"Explicit band selection shape: {selected_rgb_bands.shape}")
# end region