import pandas as pd
import glob
import os

def merge_parquets(input_dir, output_file):
    # find all .parquet files
    paths = glob.glob(os.path.join(input_dir, "*.parquet"))
    if not paths:
        print(f"No parquet files found in {input_dir}")
        return

    dfs = []
    for p in paths:
        try:
            df = pd.read_parquet(p)
            dfs.append(df)
        except Exception as e:
            print(f"  ⚠️  Skipping {p}: {e}")

    # concat will union all columns; missing columns → NaN
    merged = pd.concat(dfs, ignore_index=True, sort=False)

    merged.to_parquet(output_file, index=False)
    print(f"✅ Merged {len(dfs)} files → {output_file}")
    print(f"   Total rows: {len(merged)}, Total columns: {len(merged.columns)}")


merge_parquets("./checkpoints/","./checkpoints_merged/all_data_merged.parquet")