use anyhow::{Result, anyhow};
use chrono::{DateTime, Duration, Utc};

pub fn parse_ttl_spec(ttl: &str) -> Result<Duration> {
    let ttl = ttl.trim();
    if ttl.is_empty() {
        return Err(anyhow!("ttl must not be empty"));
    }

    let (value, multiplier_seconds) = match ttl.chars().last() {
        Some('s') | Some('S') => (&ttl[..ttl.len() - 1], 1i64),
        Some('m') | Some('M') => (&ttl[..ttl.len() - 1], 60i64),
        Some('h') | Some('H') => (&ttl[..ttl.len() - 1], 60i64 * 60),
        Some('d') | Some('D') => (&ttl[..ttl.len() - 1], 60i64 * 60 * 24),
        Some('w') | Some('W') => (&ttl[..ttl.len() - 1], 60i64 * 60 * 24 * 7),
        _ => {
            return Err(anyhow!(
                "invalid ttl '{ttl}'. Use a positive duration like 30s, 15m, 1h, 7d, or 2w"
            ));
        }
    };

    let value: i64 = value
        .trim()
        .parse()
        .map_err(|_| anyhow!("invalid ttl '{ttl}'. Duration value must be a positive integer"))?;
    if value <= 0 {
        return Err(anyhow!("invalid ttl '{ttl}'. Duration value must be greater than zero"));
    }

    let total_seconds = value
        .checked_mul(multiplier_seconds)
        .ok_or_else(|| anyhow!("invalid ttl '{ttl}'. Duration is too large"))?;

    Ok(Duration::seconds(total_seconds))
}

pub fn expires_at_from_ttl(ttl: Option<&str>) -> Result<Option<DateTime<Utc>>> {
    match ttl {
        Some(ttl) => {
            let duration = parse_ttl_spec(ttl)?;
            Utc::now()
                .checked_add_signed(duration)
                .map(Some)
                .ok_or_else(|| anyhow!("ttl '{ttl}' overflows supported timestamp range"))
        }
        None => Ok(None),
    }
}