//! Output of synthetic spectrum.
//!
//! Translated from SYNSPEC `OUTPRI` subroutine (synspec54.f:3343).
//!
//! Outputs synthetic spectrum to file units, computes equivalent widths.

/// Physical constants
const CAS: f64 = 1.0 / 2.997925e18;
const EQWC: f64 = 1.19917e22;

/// Parameters for OUTPRI calculation
pub struct OutpriParams {
    /// Number of frequencies
    pub nfreq: usize,
    /// Frequency array (Hz)
    pub freq: Vec<f64>,
    /// Wavelength array (Angstroms)
    pub wlam: Vec<f64>,
    /// Emergent flux at each frequency [nfreq]
    pub flux: Vec<f64>,
    /// Frequency weights for equivalent width [nfreq]
    pub w: Vec<f64>,
    /// Print level
    pub iprin: i32,
    /// Blank flag
    pub iblank: i32,
    /// Number of blanks
    pub nblank: i32,
    /// Window mode flag
    pub ifwin: i32,
    /// Number of observed frequencies (window mode)
    pub nfrobs: usize,
    /// Observed frequencies (window mode)
    pub frqobs: Vec<f64>,
    /// Observed wavelengths (window mode)
    pub wlobs: Vec<f64>,
}

/// Result of OUTPRI calculation
pub struct OutpriResult {
    /// Equivalent width for this set (mA)
    pub eqw: f64,
    /// Positive equivalent width for this set (mA)
    pub eqwp: f64,
    /// Total equivalent width (mA)
    pub eqwt: f64,
    /// Total positive equivalent width (mA)
    pub eqwtp: f64,
    /// Spectrum data: (wavelength, flux_lambda) pairs
    pub spectrum: Vec<(f64, f64)>,
    /// Continuum data: (wavelength, flux_lambda) pairs
    pub continuum: Vec<(f64, f64)>,
}

/// Output of synthetic spectrum.
///
/// Computes emergent flux in lambda units, writes spectrum and continuum,
/// and calculates equivalent widths.
pub fn outpri(params: &OutpriParams, eqwt_in: f64, eqwtp_in: f64) -> OutpriResult {
    let nfreq = params.nfreq;
    let freq = &params.freq;
    let wlam = &params.wlam;
    let flux = &params.flux;
    let w = &params.w;

    let mut spectrum = Vec::new();
    let mut continuum = Vec::new();
    let mut eqw = 0.0;
    let mut eqwp = 0.0;
    let mut eqwt = eqwt_in;
    let mut eqwtp = eqwtp_in;

    if params.ifwin <= 0 {
        // Output synthetic spectrum
        for ij in 2..nfreq - 1 {
            let flam = flux[ij] * freq[ij] * freq[ij] * CAS;
            spectrum.push((wlam[ij], flam));
        }

        // Output continuum flux
        let flam = flux[0] * freq[0] * freq[0] * CAS;
        continuum.push((wlam[0], flam));
        if params.iblank == params.nblank {
            let flam = flux[nfreq - 1] * freq[nfreq - 1] * freq[nfreq - 1] * CAS;
            spectrum.push((wlam[nfreq - 1], flam));
            let flam = flux[1] * freq[1] * freq[1] * CAS;
            continuum.push((wlam[1], flam));
        }
    } else {
        // Window mode
        for ij in 0..params.nfrobs {
            let flam = flux[ij] * params.frqobs[ij] * params.frqobs[ij] * CAS * 0.5;
            let flam = flam.max(1.0e-40);
            spectrum.push((params.wlobs[ij], flam));
        }
    }

    // Compute equivalent widths
    if params.iprin >= 3 {
        let xx = 1.0 / (freq[1] - freq[0]);
        let xxx = 1.0 / (freq[0] + freq[1]) / (freq[0] + freq[1]);

        if params.ifwin <= 0 {
            for ij in 0..nfreq {
                let _flam = flux[ij] * freq[ij] * freq[ij] * CAS;
                let cont = ((freq[ij] - freq[0]) * flux[1]
                    + (freq[1] - freq[ij]) * flux[0])
                    * xx;
                let re0 = flux[ij] / cont;
                eqw += (1.0 - re0) * w[ij];
                let rep = re0.min(1.0);
                eqwp += (1.0 - rep) * w[ij];
            }
        } else {
            for ij in 0..params.nfrobs {
                let _flam = flux[ij] * freq[ij] * freq[ij] * CAS;
                let cont = ((params.frqobs[ij] - freq[0]) * flux[1]
                    + (freq[1] - params.frqobs[ij]) * flux[0])
                    * xx;
                let re0 = flux[ij] / cont;
                eqw += (1.0 - re0) * w[ij];
                let rep = re0.min(1.0);
                eqwp += (1.0 - rep) * w[ij];
            }
        }

        eqw = eqw * EQWC * xxx;
        eqwt += eqw;
        eqwp = eqwp * EQWC * xxx;
        eqwtp += eqwp;
    }

    OutpriResult {
        eqw,
        eqwp,
        eqwt,
        eqwtp,
        spectrum,
        continuum,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_outpri_basic() {
        let nfreq = 5;
        let params = OutpriParams {
            nfreq,
            freq: vec![1.0e15, 2.0e15, 3.0e15, 4.0e15, 5.0e15],
            wlam: vec![3000.0, 2000.0, 1500.0, 1200.0, 1000.0],
            flux: vec![1.0e-10, 2.0e-10, 3.0e-10, 4.0e-10, 5.0e-10],
            w: vec![0.1, 0.2, 0.3, 0.4, 0.5],
            iprin: 0,
            iblank: 1,
            nblank: 1,
            ifwin: 0,
            nfrobs: 0,
            frqobs: vec![],
            wlobs: vec![],
        };

        let result = outpri(&params, 0.0, 0.0);
        // When iblank == nblank, extra points are added:
        // spectrum: ij=2,3 from loop + nfreq-1=4 from iblank==nblank
        assert_eq!(result.spectrum.len(), 3);
        // continuum: ij=0 from main path + ij=1 from iblank==nblank
        assert_eq!(result.continuum.len(), 2);
    }

    #[test]
    fn test_outpri_flux_conversion() {
        // Verify FLAM = FLUX * FREQ^2 * CAS
        let flux_val = 1.0e-10;
        let freq_val = 3.0e15;
        let expected_flam = flux_val * freq_val * freq_val * CAS;

        let nfreq = 3;
        let params = OutpriParams {
            nfreq,
            freq: vec![1.0e15, 2.0e15, 3.0e15],
            wlam: vec![3000.0, 2000.0, 1500.0],
            flux: vec![flux_val, flux_val, flux_val],
            w: vec![0.1, 0.2, 0.3],
            iprin: 0,
            iblank: 1,
            nblank: 1,
            ifwin: 0,
            nfrobs: 0,
            frqobs: vec![],
            wlobs: vec![],
        };

        let result = outpri(&params, 0.0, 0.0);
        // Check that flux conversion is correct
        if let Some((_, flam)) = result.spectrum.first() {
            assert!((flam - expected_flam).abs() / expected_flam < 1.0e-10);
        }
    }
}