/*
 * Copyright (C) 2022  Aravinth Manivannan <realaravinth@batsense.net>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
use std::collections::HashMap;
use std::rc::Rc;

pub trait Purchasable {
    fn cost(&self) -> f64;
    fn name(&self) -> &str;
    fn paid_by(&self) -> &dyn Actor;
}

pub struct Split {
    purchase: Rc<dyn Purchasable>,
    split_strategy: SplitStrategy,
}

#[derive(Default)]
pub struct SplitHashMap {
    shares: HashMap<String, (Rc<dyn Actor>, f64)>,
}

impl SplitHashMap {
    pub fn iter(&self) -> SplitHashMapIter {
        let iter = self.shares.iter();
        SplitHashMapIter { iter }
    }

    pub fn insert(&mut self, actor: Rc<dyn Actor>, amount: f64) {
        let name = actor.name().to_owned();
        self.shares.insert(name, (actor, amount));
    }

    pub fn get(&mut self, actor: Rc<dyn Actor>) -> Option<f64> {
        if let Some((_actor, cost)) = self.shares.get(actor.name()) {
            Some(*cost)
        } else {
            None
        }
    }
}

pub struct SplitHashMapIter<'a> {
    iter: std::collections::hash_map::Iter<'a, String, (Rc<dyn Actor>, f64)>,
}

impl<'a> Iterator for SplitHashMapIter<'a> {
    type Item = (Rc<dyn Actor>, f64);

    fn next(&mut self) -> Option<Self::Item> {
        if let Some((_, (actor, cost))) = self.iter.next() {
            Some((actor.clone(), *cost))
        } else {
            None
        }
    }
}

impl Split {
    pub fn validate(&self) -> bool {
        self.split_strategy.validate(self.purchase.as_ref())
    }
}

/*
 * SPLITTING STRATEGIES:
 *  Unequal: Each actor's split is specified in specific amounts
 *  Shares: Each actor's split is specified in specific percentage
 *  Equal: Each actor's split is computed by splitting total expense among all participating actors
 */
pub enum SplitStrategy {
    Unequal(SplitHashMap),
    Shares(SplitHashMap),
    Equal(Vec<Rc<dyn Actor>>),
}

impl SplitStrategy {
    pub fn validate(&self, item: &dyn Purchasable) -> bool {
        match self {
            SplitStrategy::Unequal(config) => {
                let mut total = 0.00;
                for (_actor, share) in config.iter() {
                    total += share;
                }

                let cost = item.cost();
                println!("Unequal sharing: expected {cost} got {total}");
                total == cost
            }
            SplitStrategy::Shares(config) => {
                let mut total = 0.00;
                let cost = item.cost();
                let mut total_shares = 0.00;
                for (_actor, share) in config.iter() {
                    total_shares += share;
                    total += cost * share;
                }

                println!("Unequal sharing: expected shares 1 got {total_shares}");
                println!("Unequal sharing: expected {cost} got {total}");
                total_shares == 1.00 && total == cost
            }
            SplitStrategy::Equal(c) => !c.is_empty(),
        }
    }
}

pub trait Actor {
    fn spends(&mut self, i: Split);
    fn owes(&mut self, i: Split);
    // name must be unique in a namespace
    fn name(&self) -> &str;
}

pub struct Person {
    name: String,
    spent: Vec<Split>,
    owes: Vec<Split>,
}

impl Person {
    pub fn new(name: String) -> Self {
        let owes = Vec::default();
        let spent = Vec::default();

        Self { name, spent, owes }
    }
}

impl Actor for Person {
    fn spends(&mut self, split: Split) {
        if split.purchase.paid_by().name() == self.name() {
            self.spent.push(split);
        } else {
            unimplemented!("Raise error: Actor didn't pay for purchase")
        }
    }
    fn owes(&mut self, split: Split) {
        if split.purchase.paid_by().name() == self.name() {
            unimplemented!("Raise error: Actor didn't paid for purchase; can't own money")
        } else {
            self.owes.push(split);
        }
    }
    fn name(&self) -> &str {
        &self.name
    }
}

pub struct Item {
    cost: f64,
    name: String,
    payer: Rc<dyn Actor>,
}

impl Item {
    pub fn new(name: String, cost: f64, payer: Rc<dyn Actor>) -> Self {
        Self { cost, name, payer }
    }
}

impl Purchasable for Item {
    fn cost(&self) -> f64 {
        self.cost
    }
    fn name(&self) -> &str {
        &self.name
    }

    fn paid_by(&self) -> &dyn Actor {
        self.payer.as_ref()
    }
}

//impl Actor for Person {
//    fn spends<P: Purchasable>(&self, i: &I);
//    fn owes<T: Actor>(&self, amount: usize);
//}

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

    #[test]
    fn split_works() {
        let person1: Rc<dyn Actor> = Rc::new(Person::new("person1".into()));
        let person2: Rc<dyn Actor> = Rc::new(Person::new("person2".into()));
        let person3: Rc<dyn Actor> = Rc::new(Person::new("person3".into()));
        let person4: Rc<dyn Actor> = Rc::new(Person::new("person4".into()));

        let item = Item::new("test item".into(), 240.00, person1.clone());
        let actors = vec![
            person1.clone(),
            person2.clone(),
            person3.clone(),
            person4.clone(),
        ];

        // equal split
        let strategy = SplitStrategy::Equal(actors.clone());
        assert!(strategy.validate(&item));

        // share split
        let mut split = SplitHashMap::default();
        split.insert(person1.clone(), 0.3);
        split.insert(person2.clone(), 0.4);
        split.insert(person3.clone(), 0.2);
        split.insert(person4.clone(), 0.1);
        let strategy = SplitStrategy::Shares(split);
        assert!(strategy.validate(&item));

        // Unequal split
        let mut split = SplitHashMap::default();
        split.insert(person1.clone(), 0.3 * item.cost());
        split.insert(person2.clone(), 0.4 * item.cost());
        split.insert(person3.clone(), 0.2 * item.cost());
        split.insert(person4.clone(), 0.1 * item.cost());
        let strategy = SplitStrategy::Unequal(split);
        assert!(strategy.validate(&item));
    }
}