"""
SQL query building functions for employee workstation activity tracking.

This module contains functions for building SQL queries to calculate working durations.
"""
from datetime import datetime, timedelta  # Added timedelta

from flask import current_app

# Define timeout constants - consider moving to config if shared across modules
# This timeout is for capping session duration in reports if no explicit stop event is found soon after a start.
REPORT_QUERY_SESSION_TIMEOUT_SECONDS = 15 * 60  # 15 minutes


def calculate_duration_sql(
    time_period, user_filter=None, start_date_filter=None, end_date_filter=None
):
    """
    Generates the core SQL query to calculate working durations.
    Uses LEAD() window function to pair 'working' with the next event.
    Calculates duration in hours using PostgreSQL functions.

    Args:
        time_period (str): Time period to group by ('daily', 'weekly', or 'monthly').
        user_filter (str, optional): Username to filter results by (exact match).
        start_date_filter (str, optional): Start date for filtering events (YYYY-MM-DD).
        end_date_filter (str, optional): End date for filtering events (YYYY-MM-DD).

    Returns:
        str: SQL query for calculating durations.
        dict: Parameters for the SQL query.
    """
    params = {}
    date_conditions = []
    if start_date_filter:
        date_conditions.append("w_events.ts >= :start_date_param")
        params["start_date_param"] = start_date_filter
    if end_date_filter:
        # Add 1 day to end_date_filter to make it inclusive of the whole day
        # Or expect end_date_filter to be exclusive upper bound already.
        # Assuming YYYY-MM-DD means start of that day.
        # To include the entire end_date_filter day, we query < (end_date_filter + 1 day)
        # For simplicity, let's assume date filters are applied directly to DATE(ts)
        # or that ts is already a date for daily grouping if filters apply to period_start.
        # For now, let's filter the base events.
        # If end_date_filter is '2023-10-20', events up to '2023-10-20 23:59:59.999' should be included.
        # So ts < '2023-10-21'
        try:
            end_date_dt = datetime.strptime(end_date_filter, "%Y-%m-%d")
            exclusive_end_date_dt = end_date_dt + timedelta(days=1)
            params["end_date_param_exclusive"] = exclusive_end_date_dt.strftime(
                "%Y-%m-%d"
            )
            date_conditions.append("w_events.ts < :end_date_param_exclusive")
        except ValueError:
            current_app.logger.warning(
                f"Invalid end_date_filter format: {end_date_filter}. Ignoring."
            )

    event_selection_where_clause = ""
    if date_conditions:
        event_selection_where_clause = "WHERE " + " AND ".join(date_conditions)

    # For virtual event injection, also apply date filters if possible to limit scope
    # This part is tricky because virtual events are based on existing events.
    # If an event is just outside start_date_filter but its virtual stop is inside, how to handle?
    # For now, primary date filtering is on `public.work_events w_events`.

    user_where_clause_for_all_events = ""
    user_group_by_filter_final = ""
    if user_filter:
        user_where_clause_for_all_events = f"{'AND' if event_selection_where_clause else 'WHERE'} w_events.\"user\" = :user_param"
        user_group_by_filter_final = 'WHERE cd."user" = :user_param'
        params["user_param"] = user_filter

    # Conditional SQL parts for the 'w' alias in AllEvents UNION
    user_filter_condition_for_w = ""
    if user_filter:
        user_filter_condition_for_w = 'AND w."user" = :user_param'

    start_date_condition_for_w = ""
    if "start_date_param" in params:
        start_date_condition_for_w = "AND w.ts >= :start_date_param"

    end_date_condition_for_w = ""
    if "end_date_param_exclusive" in params:
        end_date_condition_for_w = "AND w.ts < :end_date_param_exclusive"

    period_grouping_options = {
        "daily": "DATE_TRUNC('day', start_time)",
        "weekly": "DATE_TRUNC('week', start_time)",
        "monthly": "DATE_TRUNC('month', start_time)",
    }
    period_grouping = period_grouping_options.get(time_period)
    if not period_grouping:
        current_app.logger.warning(
            f"Invalid time_period '{time_period}' in calculate_duration_sql, defaulting to 'daily'."
        )
        period_grouping = period_grouping_options["daily"]

    # SQL query structure
    sql_query = f"""
        WITH AllEvents AS (
            -- Select base events within the date range and for the specific user if provided
            SELECT
                w_events.\"user\",
                w_events.ts,
                w_events.state
            FROM public.work_events w_events
            {event_selection_where_clause}
            {user_where_clause_for_all_events}
            
            UNION ALL
            
            -- Add virtual "stopped" events for users who have been inactive for more than REPORT_QUERY_SESSION_TIMEOUT_SECONDS
            -- This part needs to be mindful of the user_filter and date_filter as well.
            -- We select from work_events `w` here. If `w` is filtered by user/date, this UNION part is also filtered.
            SELECT 
                w.\"user\",
                w.ts + INTERVAL '{REPORT_QUERY_SESSION_TIMEOUT_SECONDS} seconds' AS ts,
                'stopped' AS state
            FROM public.work_events w
            -- Ensure the base 'working' event for virtual stop also respects date and user filters
            -- The primary selection for `w` is implicitly filtered if `w_events` in the top part of UNION is filtered.
            -- However, to be explicit or if `w` needs its own alias for clarity:
            -- Let's assume `w` here implicitly respects the outer scope if it was part of a larger subquery, 
            -- but in a UNION, it's a separate SELECT. So, `w` also needs filtering.
            -- Re-applying filters here to `w` to ensure virtual stops are only for relevant events.
            WHERE w.state = 'working'
            {user_filter_condition_for_w} 
            {start_date_condition_for_w}
            {end_date_condition_for_w}
            AND NOT EXISTS (
                SELECT 1
                FROM public.work_events w2
                WHERE w2.\"user\" = w.\"user\"
                AND w2.ts > w.ts
                AND w2.ts <= w.ts + INTERVAL '{REPORT_QUERY_SESSION_TIMEOUT_SECONDS} seconds'
            )
            AND NOT EXISTS (
                SELECT 1
                FROM public.work_events w3
                WHERE w3.\"user\" = w.\"user\"
                AND w3.state = 'stopped'
                AND w3.ts = w.ts + INTERVAL '{REPORT_QUERY_SESSION_TIMEOUT_SECONDS} seconds'
            )
        ),
        EventPairs AS (
            -- Pair events using LEAD function
            SELECT
                \"user\",
                ts AS start_time,
                state,
                LEAD(ts) OVER (PARTITION BY \"user\" ORDER BY ts) AS next_event_time,
                LEAD(state) OVER (PARTITION BY \"user\" ORDER BY ts) AS next_event_state
            FROM AllEvents
            -- No user filter here, it's applied in AllEvents and final select
            ORDER BY \"user\", ts
        ),
        TimeoutAdjusted AS (
            -- Adjust end time for sessions exceeding timeout
            SELECT
                \"user\",
                start_time,
                state,
                CASE
                    WHEN state = 'working' AND next_event_time IS NOT NULL 
                         AND EXTRACT(EPOCH FROM (next_event_time - start_time)) > {REPORT_QUERY_SESSION_TIMEOUT_SECONDS}
                    THEN start_time + INTERVAL '{REPORT_QUERY_SESSION_TIMEOUT_SECONDS} seconds'
                    WHEN state = 'working' AND next_event_time IS NULL -- Dangling working event, cap at timeout from start_time or now
                    THEN LEAST(start_time + INTERVAL '{REPORT_QUERY_SESSION_TIMEOUT_SECONDS} seconds', NOW() AT TIME ZONE 'UTC') 
                    ELSE next_event_time
                END AS adjusted_end_time,
                next_event_state
            FROM EventPairs
        ),
        CalculatedDurations AS (
            -- Calculate duration for each working session and find first login time
            SELECT
                \"user\",
                {period_grouping} AS period_start,
                SUM(
                    CASE
                        WHEN state = 'working' AND adjusted_end_time IS NOT NULL THEN
                            GREATEST(0, EXTRACT(EPOCH FROM (adjusted_end_time - start_time)) / 3600.0) -- Ensure non-negative
                        ELSE 0
                    END
                ) AS total_hours,
                MIN(CASE WHEN state = 'working' THEN start_time END) AS first_login_time
            FROM TimeoutAdjusted
            WHERE state = 'working'
            GROUP BY \"user\", period_start
        )
        -- Final aggregation and user filtering if applicable
        SELECT 
            cd.\"user\",
            cd.period_start,
            SUM(cd.total_hours) AS total_hours,
            MIN(cd.first_login_time) AS first_login_time
        FROM CalculatedDurations cd
        {user_group_by_filter_final}
        GROUP BY cd.\"user\", cd.period_start
        ORDER BY cd.\"user\", cd.period_start DESC;
    """

    current_app.logger.debug(f"Generated SQL query for reports: {sql_query}")
    current_app.logger.debug(f"SQL query parameters: {params}")

    return sql_query, params


# The filter_sql_by_user function is now obsolete and has been removed.