"""Row hashing, diff classification, and sync state tracking.

Used by push/pull commands to detect which rows have been modified locally
since the last pull, and to detect conflicts with server-side changes.
"""

import hashlib
import json
from typing import Any, Dict, List, Optional, Tuple

from . import sheet_format as sf

# Row statuses
STATUS_SYNCED = "synced"
STATUS_MODIFIED = "modified"
STATUS_NEW = "new"
STATUS_ERROR = "error"
STATUS_CONFLICT = "conflict"


def compute_row_hash(cells: List[str]) -> str:
    """SHA-256 hash of the visible + property columns of a row.

    Only the data columns are hashed (not sync tracking columns).
    Blank/empty cells are normalised to the empty string.
    """
    # Use columns 0..COL_PROP_END-1 (visible + properties, not sync cols)
    data_cells = cells[: sf.COL_PROP_END]
    # Normalise
    normalised = [str(c).strip() if c else "" for c in data_cells]
    raw = "\t".join(normalised).encode("utf-8")
    return hashlib.sha256(raw).hexdigest()


def classify_row(cells: List[str]) -> str:
    """Return the sync status of a single row.

    Reads the stored hash and current cell values to determine whether
    the row is synced, modified, new, or in an error state.
    """
    # Ensure we have enough columns
    while len(cells) < sf.BOM_TOTAL_COLS:
        cells.append("")

    stored_hash = cells[sf.COL_ROW_HASH].strip() if cells[sf.COL_ROW_HASH] else ""
    stored_status = cells[sf.COL_ROW_STATUS].strip() if cells[sf.COL_ROW_STATUS] else ""

    # No hash -> new row (never pulled from server)
    if not stored_hash:
        # Check if there's any data in the row
        has_data = any(
            cells[i].strip()
            for i in range(sf.COL_PROP_END)
            if i < len(cells) and cells[i]
        )
        return STATUS_NEW if has_data else ""

    # Compute current hash and compare
    current_hash = compute_row_hash(cells)
    if current_hash == stored_hash:
        return STATUS_SYNCED
    return STATUS_MODIFIED


def classify_rows(all_rows: List[List[str]]) -> List[Tuple[int, str, List[str]]]:
    """Classify every row in a sheet.

    Returns list of ``(row_index, status, cells)`` for rows that have data.
    Blank separator rows and the header row (index 0) are skipped.
    """
    results = []
    for i, cells in enumerate(all_rows):
        if i == 0:
            continue  # header row
        status = classify_row(list(cells))
        if status:
            results.append((i, status, list(cells)))
    return results


def build_push_diff(
    classified: List[Tuple[int, str, List[str]]],
    server_timestamps: Optional[Dict[str, str]] = None,
) -> Dict[str, List[Dict[str, Any]]]:
    """Build a push diff from classified rows.

    *server_timestamps* maps part numbers to their server ``updated_at``
    values, used for conflict detection.

    Returns a dict with keys ``new``, ``modified``, ``conflicts``, and
    the count of ``unchanged`` rows.
    """
    server_ts = server_timestamps or {}
    new_rows = []
    modified_rows = []
    conflicts = []
    unchanged = 0

    for row_idx, status, cells in classified:
        if status == STATUS_SYNCED:
            unchanged += 1
            continue

        pn = cells[sf.COL_PN].strip() if len(cells) > sf.COL_PN else ""
        stored_ts = (
            cells[sf.COL_UPDATED_AT].strip()
            if len(cells) > sf.COL_UPDATED_AT and cells[sf.COL_UPDATED_AT]
            else ""
        )

        row_info = {
            "row_index": row_idx,
            "part_number": pn,
            "description": cells[sf.COL_DESCRIPTION].strip()
            if len(cells) > sf.COL_DESCRIPTION
            else "",
            "cells": cells[: sf.COL_PROP_END],
        }

        if status == STATUS_NEW:
            new_rows.append(row_info)
        elif status == STATUS_MODIFIED:
            # Check for conflict: server changed since we pulled
            server_updated = server_ts.get(pn, "")
            if stored_ts and server_updated and server_updated != stored_ts:
                row_info["local_ts"] = stored_ts
                row_info["server_ts"] = server_updated
                conflicts.append(row_info)
            else:
                modified_rows.append(row_info)

    return {
        "new": new_rows,
        "modified": modified_rows,
        "conflicts": conflicts,
        "unchanged": unchanged,
    }


def update_row_sync_state(
    cells: List[str],
    status: str,
    updated_at: str = "",
    parent_pn: str = "",
) -> List[str]:
    """Set the sync tracking columns on a row and return it.

    Recomputes the row hash from current visible+property data.
    """
    while len(cells) < sf.BOM_TOTAL_COLS:
        cells.append("")

    cells[sf.COL_ROW_HASH] = compute_row_hash(cells)
    cells[sf.COL_ROW_STATUS] = status
    if updated_at:
        cells[sf.COL_UPDATED_AT] = updated_at
    if parent_pn:
        cells[sf.COL_PARENT_PN] = parent_pn

    return cells