"""Convert simple commented-header .dat files (Ahmed Body, Faith Hill PIV/PSP/FISF
formats) to flat CSV.

Different from the NASA Tecplot zone parser (Extended_2D_Dataset/dat_to_csv.py).
These .dat files are:
    - Header: any number of '#'-prefixed lines
    - The last '#' line contains the column names, possibly with units in brackets
    - Data: whitespace-separated floats, one row per measurement point

Usage:
    python commented_dat_to_csv.py <dir_or_file> [<dir_or_file> ...]
"""

import sys
import os
import re
import glob
import numpy as np
import pandas as pd


# Match e.g. "x[mm]" or "U[m/s]" -> capture name and unit
_NAMED_UNIT_RE = re.compile(r'(\S+?)\[([^\]]+)\]')


def _parse_columns_from_header_line(line):
    """Parse a header line like '# x[mm] y[mm] z[mm] U[m/s] ...' -> list of column names.

    Spatial coords gain a unit suffix ("x_mm", "y_in", "z_m") so downstream tooling
    can map experiment coords to the OF mesh scale unambiguously. Non-spatial
    columns retain their original names.
    """
    s = line.lstrip('#').strip()
    out = []
    for tok in s.split():
        m = _NAMED_UNIT_RE.match(tok)
        if not m:
            out.append(tok)
            continue
        name, unit = m.group(1), m.group(2).strip()
        # only attach unit suffix to spatial coordinate columns
        if name.lower() in ('x', 'y', 'z') and unit in ('mm', 'm', 'in', 'cm'):
            out.append(f'{name}_{unit}')
        else:
            out.append(name)
    return out


def read_commented_dat(path):
    """Read a commented-header .dat file -> pandas DataFrame.

    The last header line beginning with '#' is treated as the column-name line.
    All other '#' lines are skipped. Data rows are whitespace-separated floats.
    """
    with open(path) as f:
        lines = f.readlines()

    last_header_idx = -1
    for i, line in enumerate(lines):
        if line.lstrip().startswith('#'):
            last_header_idx = i
        else:
            if line.strip():
                break

    if last_header_idx < 0:
        raise ValueError(f'{path}: no commented header found')

    columns = _parse_columns_from_header_line(lines[last_header_idx])
    data = np.genfromtxt(path, comments='#')
    if data.ndim == 1:
        data = data.reshape(1, -1)

    if data.shape[1] != len(columns):
        # Some files have variables labeled with extra '*' or unusual chars;
        # fall back to generic col_N names if mismatch
        columns = [f'col_{i}' for i in range(data.shape[1])]

    return pd.DataFrame(data, columns=columns)


def convert_path(path):
    if os.path.isdir(path):
        for dat in sorted(glob.glob(os.path.join(path, '*.dat'))):
            convert_path(dat)
        return
    if not path.lower().endswith('.dat'):
        return
    try:
        df = read_commented_dat(path)
    except Exception as exc:
        print(f'  FAILED {path}: {exc}')
        return
    csv_path = path[:-4] + '.csv'
    df.to_csv(csv_path, index=False)
    print(f'  {os.path.basename(path)} -> {os.path.basename(csv_path)}'
          f'  ({len(df)} rows, {len(df.columns)} cols)')


if __name__ == '__main__':
    if len(sys.argv) < 2:
        print(__doc__)
        sys.exit(1)
    for arg in sys.argv[1:]:
        print(f'\n[{arg}]')
        convert_path(arg)