use futures::{TryStream, TryStreamExt as _};
use snafu::{OptionExt as _, ResultExt as _, Snafu};

use super::{CreateListerSnafu, ListError, RecordingDataManager, Year};

pub use time::Month;

#[derive(Debug, Snafu)]
pub enum TakeError {
    /// months are supposed to be directories, but this wasn't (because it didn't end with `/`)
    NotADirectory,

    /// could not parse the month as its name
    ParseMonthNameError { source: time::error::InvalidVariant },
}

pub fn take(s: &str) -> Result<(Month, &str), TakeError> {
    let (month, rest) = s.split_once('/').context(NotADirectorySnafu)?;

    let month = month.parse().context(ParseMonthNameSnafu)?;

    Ok((month, rest))
}

#[derive(Debug, Snafu)]
pub enum MonthEntryError {
    /// failed to get an entry from the storage operator's lister
    ReceiveEntryError { source: opendal::Error },

    /// failed to parse the entry as a month
    ParseError { source: TakeError },
}

impl RecordingDataManager {
    pub async fn months(
        &self,
        year: Year,
    ) -> Result<impl TryStream<Ok = Month, Error = MonthEntryError> + Unpin, ListError> {
        let lister = self
            .operator
            .lister(&format!("{year}/"))
            .await
            .context(CreateListerSnafu)?;

        Ok(lister
            .map_err(|error| MonthEntryError::ReceiveEntryError { source: error })
            .and_then(|entry| {
                std::future::ready(
                    take(entry.name())
                        .map(|(month, rest)| month)
                        .context(ParseSnafu),
                )
            }))
    }
}