use brk_error::{OptionData, Result};
use brk_types::{Height, TimePeriod};
use vecdb::ReadableVec;

use crate::Query;

impl Query {
    /// First block height inside `period` looking back from the tip;
    /// genesis (`Height(0)`) for `All`. Errors `Internal` if the chosen
    /// lookback vec is stamped short of the tip - separating the
    /// "all-time" case from a transient stamp-lag dropout that would
    /// otherwise silently widen a windowed query to the full chain.
    pub(super) fn start_height(&self, period: TimePeriod) -> Result<Height> {
        let lookback = &self.computer().blocks.lookback;
        let tip = self.height();
        Ok(match period {
            TimePeriod::Day => lookback._24h.collect_one(tip).data()?,
            TimePeriod::ThreeDays => lookback._3d.collect_one(tip).data()?,
            TimePeriod::Week => lookback._1w.collect_one(tip).data()?,
            TimePeriod::Month => lookback._1m.collect_one(tip).data()?,
            TimePeriod::ThreeMonths => lookback._3m.collect_one(tip).data()?,
            TimePeriod::SixMonths => lookback._6m.collect_one(tip).data()?,
            TimePeriod::Year => lookback._1y.collect_one(tip).data()?,
            TimePeriod::TwoYears => lookback._2y.collect_one(tip).data()?,
            TimePeriod::ThreeYears => lookback._3y.collect_one(tip).data()?,
            TimePeriod::All => Height::from(0_usize),
        })
    }
}
