"""Slack Block Kit message builders for shift schedule display."""

from datetime import datetime, timedelta
from zoneinfo import ZoneInfo

EASTERN = ZoneInfo("America/New_York")

DAY_ORDER = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]


def _format_shift_line(date: datetime, ext: str, name: str, source: str, is_today: bool) -> str:
    day_label = date.strftime("%a %b %-d")
    if is_today:
        day_label = f"*{day_label} (today)*"

    if source == "available":
        return f":large_yellow_circle:  {day_label} — *Available*"
    if source == "override":
        return f":large_blue_circle:  {day_label} — {name} (Ext {ext}) _[picked up]_"
    return f":white_circle:  {day_label} — {name} (Ext {ext})"


def build_week_schedule(schedule, start_date: datetime | None = None) -> list[dict]:
    """Build Block Kit blocks showing the two-week schedule.

    Args:
        schedule: ShiftSchedule instance
        start_date: Monday of the first week to show. Defaults to current week's Monday.
    """
    now = datetime.now(EASTERN)
    if start_date is None:
        start_date = now - timedelta(days=now.weekday())  # Monday of this week
    start_date = start_date.replace(hour=0, minute=0, second=0, microsecond=0)

    today_str = now.strftime("%Y-%m-%d")
    start_label = start_date.strftime("%b %-d")
    end_label = (start_date + timedelta(days=13)).strftime("%b %-d")

    # Build lines for both weeks, separated by a blank line
    lines = []
    open_dates = []
    for i in range(14):
        if i == 7:
            lines.append("")  # visual separator between weeks
        date = start_date + timedelta(days=i)
        date_str = date.strftime("%Y-%m-%d")
        day_name = DAY_ORDER[i % 7]
        ext, name, source = schedule.resolve_shift(date_str, day_name)
        is_today = date_str == today_str
        lines.append(_format_shift_line(date, ext, name, source, is_today))
        if source == "available":
            open_dates.append(date_str)

    blocks = [
        {
            "type": "header",
            "text": {"type": "plain_text", "text": f"After-Hours Schedule — {start_label} to {end_label}"},
        },
        {
            "type": "section",
            "text": {"type": "mrkdwn", "text": "\n".join(lines)},
        },
    ]

    # Add pickup buttons for open shifts (Slack max 5 per actions block)
    if open_dates:
        blocks.append({"type": "divider"})
        elements = []
        for date_str in open_dates:
            dt = datetime.strptime(date_str, "%Y-%m-%d")
            elements.append(
                {
                    "type": "button",
                    "text": {"type": "plain_text", "text": f"Pick up {dt.strftime('%a %b %-d')}"},
                    "action_id": f"pickup_{date_str}",
                    "style": "primary",
                }
            )
        # Slack allows max 5 buttons per actions block — use multiple blocks
        for chunk_start in range(0, len(elements), 5):
            blocks.append({"type": "actions", "elements": elements[chunk_start:chunk_start + 5]})

    return blocks


def build_shift_change_message(
    user_id: str, date_str: str, action: str, ext: str, name: str
) -> list[dict]:
    """Build a channel notification for a shift change."""
    dt = datetime.strptime(date_str, "%Y-%m-%d")
    day_label = dt.strftime("%A, %b %-d")

    if action == "picked_up":
        text = f":white_check_mark: <@{user_id}> picked up the shift for *{day_label}* (Ext {ext})"
    elif action == "dropped":
        text = f":warning: <@{user_id}> dropped the shift for *{day_label}* — it's now *Available*"
    elif action == "swapped":
        text = f":arrows_counterclockwise: <@{user_id}> swapped into the shift for *{day_label}* (Ext {ext})"
    else:
        text = f"Shift updated for *{day_label}*: {name} (Ext {ext})"

    return [{"type": "section", "text": {"type": "mrkdwn", "text": text}}]


def build_help_blocks() -> list[dict]:
    """Build help message blocks."""
    text = (
        "*After-Hours Shift Manager*\n\n"
        "`/oncall` — Show the two-week schedule\n"
        "`/oncall next` — Show the following two weeks\n"
        "`/oncall pick <date>` — Pick up a shift\n"
        "`/oncall drop <date>` — Drop your shift (marks it open)\n"
        "`/oncall swap <date> @person` — Swap your shift with someone\n"
        "`/oncall register <extension>` — Link your Slack account to your extension\n"
        "`/oncall roster` — Show all registered employees\n"
        "`/oncall help` — Show this help message\n\n"
        "_Dates can be: today, tomorrow, monday, friday, 4/5, 2026-04-05_"
    )
    return [{"type": "section", "text": {"type": "mrkdwn", "text": text}}]


def build_roster_blocks(roster: list[dict]) -> list[dict]:
    """Build roster display blocks."""
    if not roster:
        return [{"type": "section", "text": {"type": "mrkdwn", "text": "No employees in the roster."}}]

    lines = ["*On-Call Roster*\n"]
    for emp in sorted(roster, key=lambda x: x["SK"]):
        slack = f"<@{emp['slack_user_id']}>" if emp.get("slack_user_id") else "_not linked_"
        lines.append(f"Ext {emp['SK']} — {emp.get('name', 'Unknown')} ({slack})")

    return [{"type": "section", "text": {"type": "mrkdwn", "text": "\n".join(lines)}}]