# snapshot_logic.py
import hashlib
import json
import logging
import shutil
import uuid
from datetime import datetime
from pathlib import Path

import pandas as pd
import requests

# Configure logging
logging.basicConfig(level=logging.INFO)
log = logging.getLogger(__name__)

CHUNK_SIZE = 65536
ALLOWED_EXT = {".csv", ".xls", ".xlsx"}

# --- Fingerprinting and Data Loading ---

def sha256_of_file(path: Path) -> str:
    h = hashlib.sha256()
    with path.open("rb") as f:
        while True:
            chunk = f.read(CHUNK_SIZE)
            if not chunk:
                break
            h.update(chunk)
    return h.hexdigest()

def load_first_sheet(path: Path) -> pd.DataFrame:
    ext = path.suffix.lower()
    if ext == ".csv":
        return pd.read_csv(path)
    elif ext in {".xls", ".xlsx"}:
        return pd.read_excel(path, sheet_name=0, engine='openpyxl')
    else:
        raise ValueError(f"Unsupported file extension: {ext}")

def canonicalize_df_for_fingerprint(df: pd.DataFrame) -> bytes:
    df2 = df.copy()
    df2.columns = [str(c) for c in df2.columns]
    df2 = df2.astype(str).fillna("")
    df2 = df2.reindex(sorted(df2.columns), axis=1)
    try:
        df2 = df2.sort_values(by=list(df2.columns), kind="mergesort").reset_index(drop=True)
    except Exception:
        df2 = df2.reset_index(drop=True)
    return df2.to_csv(index=False).encode("utf-8")

def fingerprint_from_file(path: Path) -> dict:
    file_hash = sha256_of_file(path)
    df = load_first_sheet(path)
    csv_bytes = canonicalize_df_for_fingerprint(df)
    df_hash = hashlib.sha256(csv_bytes).hexdigest()
    rows, cols = df.shape
    colnames = [str(c) for c in df.columns]
    return {
        "file_hash": file_hash,
        "data_hash": df_hash,
        "rows": int(rows),
        "cols": int(cols),
        "colnames": colnames,
    }

# --- Snapshot Management ---

def ensure_outdir(outdir: Path):
    (outdir / "snapshots").mkdir(parents=True, exist_ok=True)

def load_index(outdir: Path) -> dict:
    idx_path = outdir / "index.json"
    if idx_path.exists():
        try:
            return json.loads(idx_path.read_text(encoding="utf-8"))
        except (json.JSONDecodeError, IOError):
            return {}
    return {}

def save_index(outdir: Path, index: dict):
    idx_path = outdir / "index.json"
    idx_path.write_text(json.dumps(index, indent=2), encoding="utf-8")

def find_matching_snapshot(index: dict, file_hash: str, data_hash: str):
    # Priority 1: Exact file byte match
    for sid, meta in index.items():
        if meta.get("file_hash") == file_hash:
            return sid
    # Priority 2: Canonical data content match (handles renamed files)
    for sid, meta in index.items():
        if meta.get("data_hash") == data_hash:
            return sid
    return None

def save_snapshot_bundle(outdir: Path, snapshot_id: str, api_response: dict, src_path: Path, metadata: dict):
    snapshot_dir = outdir / "snapshots" / snapshot_id
    snapshot_dir.mkdir(parents=True, exist_ok=True)

    # Copy original file
    shutil.copy2(src_path, snapshot_dir / src_path.name)

    # Save metadata and responses
    (snapshot_dir / "api_response.json").write_text(json.dumps(api_response, indent=2), encoding="utf-8")
    (snapshot_dir / "metadata.json").write_text(json.dumps(metadata, indent=2), encoding="utf-8")

    # Generate and save preprocessed data and column stats
    preprocessed_df = preprocess_dataframe_locally(src_path)
    preprocessed_df.to_csv(snapshot_dir / "preprocessed.csv", index=False)
    
    col_stats = generate_column_stats(preprocessed_df)
    (snapshot_dir / "column_stats.json").write_text(json.dumps(col_stats, indent=2), encoding="utf-8")
    
    log.info(f"Saved new snapshot bundle to {snapshot_dir}")
    return snapshot_dir

# --- Data Processing & API Calls ---

def preprocess_dataframe_locally(file_path: Path) -> pd.DataFrame:
    """A simplified local preprocessing pipeline, mirroring the logic in the original script."""
    df = load_first_sheet(file_path)
    df.columns = [str(c).strip().lower().replace(" ", "_") for c in df.columns]
    df = df.loc[:, df.isnull().mean() < 0.5]
    for col in df.columns:
        if pd.api.types.is_numeric_dtype(df[col]):
            df[col] = df[col].fillna(df[col].median())
        elif pd.api.types.is_datetime64_any_dtype(df[col]):
            df[col] = df[col].fillna(pd.Timestamp("1970-01-01"))
        else:
            df[col] = df[col].fillna("Unknown")
        if df[col].dtype == "object":
            df[col] = pd.to_numeric(df[col], errors='ignore')
    df = df.drop_duplicates().reset_index(drop=True)
    return df

def generate_column_stats(df: pd.DataFrame) -> dict:
    col_stats = {}
    for col in df.columns:
        series = df[col]
        try:
            col_stats[col] = {
                "dtype": str(series.dtype),
                "n_unique": int(series.nunique(dropna=True)),
                "n_missing": int(series.isna().sum()),
                "sample_values": [str(v) for v in series.dropna().head(5).unique()]
            }
        except Exception:
            col_stats[col] = {"dtype": "unknown", "n_unique": None, "n_missing": None, "sample_values": []}
    return col_stats

def post_file_to_endpoint(endpoint: str, file_path: Path, timeout: int = 300) -> dict:
    log.info(f"Posting file {file_path.name} to {endpoint}")
    with file_path.open("rb") as f:
        files = {"file": (file_path.name, f)}
        resp = requests.post(endpoint, files=files, timeout=timeout)
    resp.raise_for_status()
    log.info("API request successful.")
    return resp.json()