use chrono::NaiveDate;
use indexmap::IndexMap;
use serde::Serialize;

use crate::data::{DataSet, DataSetError, PriceField};

#[derive(Debug, Clone)]
pub struct PositionLot {
    pub acquired_date: NaiveDate,
    pub quantity: u32,
    pub price: f64,
}

#[derive(Debug, Clone)]
pub struct Position {
    pub symbol: String,
    pub quantity: u32,
    pub average_cost: f64,
    pub last_price: f64,
    pub realized_pnl: f64,
    lots: Vec<PositionLot>,
}

impl Position {
    pub fn new(symbol: impl Into<String>) -> Self {
        Self {
            symbol: symbol.into(),
            quantity: 0,
            average_cost: 0.0,
            last_price: 0.0,
            realized_pnl: 0.0,
            lots: Vec::new(),
        }
    }

    pub fn is_flat(&self) -> bool {
        self.quantity == 0
    }

    pub fn buy(&mut self, date: NaiveDate, quantity: u32, price: f64) {
        if quantity == 0 {
            return;
        }

        self.lots.push(PositionLot {
            acquired_date: date,
            quantity,
            price,
        });
        self.quantity += quantity;
        self.last_price = price;
        self.recalculate_average_cost();
    }

    pub fn sell(&mut self, quantity: u32, price: f64) -> Result<f64, String> {
        if quantity > self.quantity {
            return Err(format!(
                "sell quantity {} exceeds current quantity {} for {}",
                quantity, self.quantity, self.symbol
            ));
        }

        let mut remaining = quantity;
        let mut realized = 0.0;

        while remaining > 0 {
            let Some(first_lot) = self.lots.first_mut() else {
                return Err(format!("position {} has no lots to sell", self.symbol));
            };

            let lot_sell = remaining.min(first_lot.quantity);
            realized += (price - first_lot.price) * lot_sell as f64;
            first_lot.quantity -= lot_sell;
            remaining -= lot_sell;

            if first_lot.quantity == 0 {
                self.lots.remove(0);
            }
        }

        self.quantity -= quantity;
        self.last_price = price;
        self.realized_pnl += realized;
        self.recalculate_average_cost();
        Ok(realized)
    }

    pub fn sellable_qty(&self, date: NaiveDate) -> u32 {
        self.lots
            .iter()
            .filter(|lot| lot.acquired_date < date)
            .map(|lot| lot.quantity)
            .sum()
    }

    pub fn market_value(&self) -> f64 {
        self.quantity as f64 * self.last_price
    }

    pub fn unrealized_pnl(&self) -> f64 {
        (self.last_price - self.average_cost) * self.quantity as f64
    }

    pub fn holding_return(&self, price: f64) -> Option<f64> {
        if self.quantity == 0 || self.average_cost <= 0.0 {
            None
        } else {
            Some((price / self.average_cost) - 1.0)
        }
    }

    fn recalculate_average_cost(&mut self) {
        if self.quantity == 0 {
            self.average_cost = 0.0;
            return;
        }

        let total_cost = self
            .lots
            .iter()
            .map(|lot| lot.price * lot.quantity as f64)
            .sum::<f64>();

        self.average_cost = total_cost / self.quantity as f64;
    }

    pub fn apply_cash_dividend(&mut self, dividend_per_share: f64) -> f64 {
        if self.quantity == 0 || !dividend_per_share.is_finite() || dividend_per_share == 0.0 {
            return 0.0;
        }

        for lot in &mut self.lots {
            lot.price -= dividend_per_share;
        }
        self.average_cost -= dividend_per_share;
        self.last_price -= dividend_per_share;
        self.quantity as f64 * dividend_per_share
    }

    pub fn apply_split_ratio(&mut self, ratio: f64) -> i32 {
        if self.quantity == 0 || !ratio.is_finite() || ratio <= 0.0 || (ratio - 1.0).abs() < 1e-9 {
            return 0;
        }

        let old_quantity = self.quantity;
        let mut scaled_lots = self
            .lots
            .iter()
            .map(|lot| PositionLot {
                acquired_date: lot.acquired_date,
                quantity: round_half_up_u32(lot.quantity as f64 * ratio),
                price: lot.price / ratio,
            })
            .collect::<Vec<_>>();

        let expected_total = round_half_up_u32(old_quantity as f64 * ratio);
        let scaled_total = scaled_lots.iter().map(|lot| lot.quantity).sum::<u32>();
        if let Some(last_lot) = scaled_lots.last_mut() {
            if scaled_total < expected_total {
                last_lot.quantity += expected_total - scaled_total;
            } else if scaled_total > expected_total {
                last_lot.quantity = last_lot
                    .quantity
                    .saturating_sub(scaled_total - expected_total);
            }
        }
        scaled_lots.retain(|lot| lot.quantity > 0);

        self.lots = scaled_lots;
        self.quantity = self.lots.iter().map(|lot| lot.quantity).sum();
        self.last_price /= ratio;
        self.recalculate_average_cost();
        self.quantity as i32 - old_quantity as i32
    }
}

#[derive(Debug, Clone)]
pub struct PortfolioState {
    cash: f64,
    positions: IndexMap<String, Position>,
    cash_receivables: Vec<CashReceivable>,
}

#[derive(Debug, Clone)]
pub(crate) struct SuccessorConversionOutcome {
    pub old_symbol: String,
    pub new_symbol: String,
    pub old_quantity: u32,
    pub new_quantity_delta: i32,
    pub new_quantity_after: u32,
    pub new_average_cost_after: f64,
    pub cash_delta: f64,
}

impl PortfolioState {
    pub fn new(initial_cash: f64) -> Self {
        Self {
            cash: initial_cash,
            positions: IndexMap::new(),
            cash_receivables: Vec::new(),
        }
    }

    pub fn cash(&self) -> f64 {
        self.cash
    }

    pub fn positions(&self) -> &IndexMap<String, Position> {
        &self.positions
    }

    pub fn position(&self, symbol: &str) -> Option<&Position> {
        self.positions.get(symbol)
    }

    pub fn position_mut_if_exists(&mut self, symbol: &str) -> Option<&mut Position> {
        self.positions.get_mut(symbol)
    }

    pub fn position_mut(&mut self, symbol: &str) -> &mut Position {
        self.positions
            .entry(symbol.to_string())
            .or_insert_with(|| Position::new(symbol))
    }

    pub fn apply_cash_delta(&mut self, delta: f64) {
        self.cash += delta;
    }

    pub fn prune_flat_positions(&mut self) {
        self.positions.retain(|_, position| !position.is_flat());
    }

    pub fn add_cash_receivable(&mut self, receivable: CashReceivable) {
        self.cash_receivables.push(receivable);
    }

    pub fn settle_cash_receivables(&mut self, date: NaiveDate) -> Vec<CashReceivable> {
        let mut settled = Vec::new();
        let mut pending = Vec::new();
        for receivable in self.cash_receivables.drain(..) {
            if receivable.payable_date <= date {
                self.cash += receivable.amount;
                settled.push(receivable);
            } else {
                pending.push(receivable);
            }
        }
        self.cash_receivables = pending;
        settled
    }

    pub fn cash_receivables(&self) -> &[CashReceivable] {
        &self.cash_receivables
    }

    pub fn update_prices(
        &mut self,
        date: NaiveDate,
        data: &DataSet,
        field: PriceField,
    ) -> Result<(), DataSetError> {
        for position in self.positions.values_mut() {
            let price = data.price(date, &position.symbol, field).ok_or_else(|| {
                DataSetError::MissingSnapshot {
                    kind: match field {
                        PriceField::DayOpen => "day open price",
                        PriceField::Open => "open price",
                        PriceField::Close => "close price",
                        PriceField::Last => "last price",
                    },
                    date,
                    symbol: position.symbol.clone(),
                }
            })?;
            position.last_price = price;
        }
        Ok(())
    }

    pub fn market_value(&self) -> f64 {
        self.positions.values().map(Position::market_value).sum()
    }

    pub fn total_equity(&self) -> f64 {
        self.cash + self.market_value()
    }

    pub fn holdings_summary(&self, date: NaiveDate) -> Vec<HoldingSummary> {
        self.positions
            .values()
            .filter(|position| position.quantity > 0)
            .map(|position| HoldingSummary {
                date,
                symbol: position.symbol.clone(),
                quantity: position.quantity,
                average_cost: position.average_cost,
                last_price: position.last_price,
                market_value: position.market_value(),
                unrealized_pnl: position.unrealized_pnl(),
                realized_pnl: position.realized_pnl,
            })
            .collect()
    }

    pub(crate) fn apply_successor_conversion(
        &mut self,
        old_symbol: &str,
        new_symbol: &str,
        ratio: f64,
        cash_per_old_share: f64,
    ) -> Option<SuccessorConversionOutcome> {
        if !ratio.is_finite() || ratio <= 0.0 {
            return None;
        }
        let old_symbol_owned = old_symbol.to_string();
        let old_position = self.positions.shift_remove(old_symbol)?;
        if old_position.quantity == 0 {
            return None;
        }

        let old_quantity = old_position.quantity;
        let last_price = old_position.last_price;
        let realized_pnl = old_position.realized_pnl;
        let mut converted_lots = old_position
            .lots
            .into_iter()
            .map(|lot| PositionLot {
                acquired_date: lot.acquired_date,
                quantity: round_half_up_u32(lot.quantity as f64 * ratio),
                price: lot.price / ratio,
            })
            .collect::<Vec<_>>();
        let expected_total = round_half_up_u32(old_quantity as f64 * ratio);
        let scaled_total = converted_lots.iter().map(|lot| lot.quantity).sum::<u32>();
        if let Some(last_lot) = converted_lots.last_mut() {
            if scaled_total < expected_total {
                last_lot.quantity += expected_total - scaled_total;
            } else if scaled_total > expected_total {
                last_lot.quantity = last_lot
                    .quantity
                    .saturating_sub(scaled_total - expected_total);
            }
        }
        converted_lots.retain(|lot| lot.quantity > 0);
        let converted_quantity = converted_lots.iter().map(|lot| lot.quantity).sum::<u32>();
        let converted_last_price = if last_price > 0.0 {
            last_price / ratio
        } else {
            0.0
        };

        let successor = self
            .positions
            .entry(new_symbol.to_string())
            .or_insert_with(|| Position::new(new_symbol));
        successor.lots.extend(converted_lots);
        successor.quantity = successor.lots.iter().map(|lot| lot.quantity).sum();
        successor.realized_pnl += realized_pnl;
        if converted_last_price > 0.0 {
            successor.last_price = converted_last_price;
        }
        successor.recalculate_average_cost();

        Some(SuccessorConversionOutcome {
            old_symbol: old_symbol_owned,
            new_symbol: new_symbol.to_string(),
            old_quantity,
            new_quantity_delta: converted_quantity as i32,
            new_quantity_after: successor.quantity,
            new_average_cost_after: successor.average_cost,
            cash_delta: if cash_per_old_share.is_finite() {
                old_quantity as f64 * cash_per_old_share
            } else {
                0.0
            },
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn positions_preserve_insertion_order() {
        let date = NaiveDate::from_ymd_opt(2025, 1, 2).unwrap();
        let mut portfolio = PortfolioState::new(10_000.0);
        portfolio.position_mut("603657.SH").buy(date, 100, 10.0);
        portfolio.position_mut("001266.SZ").buy(date, 100, 10.0);
        portfolio.position_mut("601798.SH").buy(date, 100, 10.0);

        let symbols = portfolio.positions().keys().cloned().collect::<Vec<_>>();
        assert_eq!(
            symbols,
            vec![
                "603657.SH".to_string(),
                "001266.SZ".to_string(),
                "601798.SH".to_string()
            ]
        );
    }
}

#[derive(Debug, Clone, Serialize)]
pub struct HoldingSummary {
    #[serde(with = "date_format")]
    pub date: NaiveDate,
    pub symbol: String,
    pub quantity: u32,
    pub average_cost: f64,
    pub last_price: f64,
    pub market_value: f64,
    pub unrealized_pnl: f64,
    pub realized_pnl: f64,
}

#[derive(Debug, Clone)]
pub struct CashReceivable {
    pub symbol: String,
    pub ex_date: NaiveDate,
    pub payable_date: NaiveDate,
    pub amount: f64,
    pub reason: String,
}

mod date_format {
    use chrono::NaiveDate;
    use serde::Serializer;

    const FORMAT: &str = "%Y-%m-%d";

    pub fn serialize<S>(date: &NaiveDate, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(&date.format(FORMAT).to_string())
    }
}

fn round_half_up_u32(value: f64) -> u32 {
    if !value.is_finite() || value <= 0.0 {
        0
    } else {
        value.round() as u32
    }
}