use bigdecimal::{BigDecimal, Context, RoundingMode};
use std::sync::LazyLock;

static ROUNDING_MODE: RoundingMode = RoundingMode::HalfEven;
/// Will use default precision (either 100 or ${RUST_BIGDECIMAL_DEFAULT_PRECISION})
static DECIMAL_CONTEXT: LazyLock<Context> = std::sync::LazyLock::new(|| Context::default().with_rounding_mode(ROUNDING_MODE));

/// Represents an account that holds equity. An account may hold equity with
/// multiple equity symbols.
pub struct FiduciaryAccount {
    pub fiduciary_account_id: u8,
    pub fiduciary_account_number: usize,
    pub fiduciary_account_name: String,
    pub fiduciary_account_description: String,
    pub fiduciary_account_created_timestamp: chrono::DateTime<chrono::Utc>,
}

/// An atomic enum to describe for what element of equity a symbol tracks
/// (stock, fund, etc.)
pub enum EquityType {
    STOCK,
    ETF,
    CRYPTO
}

impl std::fmt::Display for EquityType {

    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", match self {
            EquityType::STOCK => "STOCK",
            EquityType::ETF => "ETF",
            EquityType::CRYPTO => "CRYPTO",
        })
    }

}

/// Represents a symbol used to ascribe speculative value
pub struct EquitySymbol {
    pub equity_symbol_id: usize,
    pub equity_symbol_name: String,
    pub equity_symbol_type: EquityType,
    pub equity_symbol_managing_company: String,
    pub equity_symbol_created_timestamp: chrono::DateTime<chrono::Utc>,
}

/// An atomic enum to describe the basic action of an equity change event
pub enum ChangeEventType {
    BUY,
    SELL
}

impl ChangeEventType {

    /// Relativizes the effect of a change event for numeration
    pub fn score(&self) -> i8 {
        match self {
            ChangeEventType::BUY => 1,
            ChangeEventType::SELL => -1,
        }
    }

}

impl std::fmt::Display for ChangeEventType {

    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", match self {
            ChangeEventType::BUY => "BUY",
            ChangeEventType::SELL => "SELL",
        })
    }

}

/// An immutable record describing a quantative change for a symbolized
/// equity attributed to an account.
pub struct EquityChangeEvent {
    pub equity_change_event_id: usize,
    pub fiduciary_account_id: u8,
    pub equity_symbol_id: usize,
    pub equity_change_quantity: BigDecimal,
    pub equity_change_cost_basis_usd: BigDecimal,
    pub equity_change_type: ChangeEventType,
    pub equity_change_timestamp: chrono::DateTime<chrono::Utc>,
}

impl EquityChangeEvent {

    /// Provides an estimate of the numerated change based on the cost basis
    /// of the equity and the quantity
    pub fn estimated_price(&self) -> BigDecimal {
        DECIMAL_CONTEXT.multiply(&self.equity_change_cost_basis_usd, &self.equity_change_quantity)
    }

}

mod tests {
    use super::*;
    use std::str::FromStr;

    fn nat(num: BigDecimal) -> BigDecimal {
        num.with_scale_round(2_i64, ROUNDING_MODE)
    }

    #[test]
    fn event_type_score_buy() {
        let eventType = ChangeEventType::BUY;

        assert_eq!(eventType.score(), 1_i8);
    }

    #[test]
    fn event_type_score_sell() {
        let eventType = ChangeEventType::SELL;

        assert_eq!(eventType.score(), -1_i8);
    }

    #[test]
    fn change_event_estimated_price() {
        let event = EquityChangeEvent {
            equity_change_event_id: 0,
            fiduciary_account_id: 0,
            equity_symbol_id: 0,
            equity_change_quantity: BigDecimal::from_str("0.125").unwrap(),
            equity_change_cost_basis_usd: BigDecimal::from_str("82.80").unwrap(),
            equity_change_type: ChangeEventType::BUY,
            equity_change_timestamp: chrono::Local::now().to_utc(),
        };

        assert_eq!(nat(event.estimated_price()).to_plain_string(), "10.35");
    }

    #[test]
    fn change_event_estimated_price_rounded() {
        let event = EquityChangeEvent {
            equity_change_event_id: 0,
            fiduciary_account_id: 0,
            equity_symbol_id: 0,
            equity_change_quantity: BigDecimal::from_str("87.12808").unwrap(),
            equity_change_cost_basis_usd: BigDecimal::from_str("14.91").unwrap(),
            equity_change_type: ChangeEventType::BUY,
            equity_change_timestamp: chrono::Local::now().to_utc(),
        };

        // actual: 1299.0796728
        assert_eq!(nat(event.estimated_price()).to_plain_string(), "1299.08");
    }
}