use std::convert::Infallible;

use eoa_lib::fitness::FitnessFunction;
use itertools::Itertools;
use nalgebra::{allocator::Allocator, distance, Const, DefaultAllocator, Dim, Dyn, OMatrix, OVector, Point};
use plotters::prelude::*;

use crate::graph::{minimal_spanning_tree_kruskal, Edge, GenericGraph, Graph, WeightedEdge};

#[derive(PartialEq, Clone, Debug)]
pub struct TSPCity {
    point: Point<f64, 2>
}

#[derive(Debug)]
pub struct TSPEdge {
    from: usize,
    to: usize,
    distance: f64
}

impl Edge for TSPEdge {
    fn from_node(&self) -> usize {
        self.from
    }

    fn to_node(&self) -> usize {
        self.to
    }
}

impl WeightedEdge for TSPEdge {
    type Cost = f64;

    fn cost(&self) -> Self::Cost {
        self.distance
    }
}

#[derive(PartialEq, Clone, Debug)]
pub struct NodePermutation<D: Dim>
where
    DefaultAllocator: Allocator<D>
{
    pub permutation: OVector<usize, D>
}

/// An instance of TSP, a fully connected graph
/// with cities that connect to each other.
/// The D parameter represents the number of cities.
#[derive(PartialEq, Clone, Debug)]
pub struct TSPInstance<D>
where
    D: Dim,
    DefaultAllocator: Allocator<D, D>
{
    pub cities: Vec<TSPCity>,
    pub distances: OMatrix<f64, D, D>
}

impl TSPInstance<Dyn>
where
{
    pub fn new_dyn(cities: Vec<(f64, f64)>) -> Self {
        let dim = Dyn(cities.len());

        let cities = OMatrix::<f64, Dyn, Const<2>>::from_fn_generic(dim, Const::<2>, |i, j| if j == 0 { cities[i].0 } else { cities[i].1 });
        TSPInstance::new(cities)
    }
}

impl<const D: usize> TSPInstance<Const<D>>
where
{
    pub fn new_const(cities: Vec<(f64, f64)>) -> Self {
        let cities = OMatrix::<f64, Const<D>, Const<2>>::from_fn(|i, j| if j == 0 { cities[i].0 } else { cities[i].1 });
        TSPInstance::new(cities)
    }
}

impl<D> TSPInstance<D>
where
    D: Dim,
    DefaultAllocator: Allocator<D, D>,
    DefaultAllocator: Allocator<D>,
    DefaultAllocator: Allocator<D, Const<2>>,
{
    pub fn new(cities: OMatrix<f64, D, Const<2>>) -> Self {
        let dim = cities.shape_generic().0;

        let cities = cities.row_iter()
                .map(|position|
                     TSPCity { point: Point::<f64, 2>::new(position[0], position[1])  }
                )
                .collect::<Vec<_>>();

        let distances = OMatrix::from_fn_generic(
            dim,
            dim,
            |i, j| distance(&cities[i].point, &cities[j].point)
        );

        Self {
            cities,
            distances
        }
    }

    pub fn to_graph(self) -> GenericGraph<TSPCity, TSPEdge> {
        let cities = self.cities.len();
        let mut graph = GenericGraph::new(self.cities, false);

        for i in 0..cities {
            for j in i+1..cities {
                graph.add_generic_edge(TSPEdge {
                    from: i,
                    to: j,
                    distance: self.distances[(i, j)]
                });
            }
        }

        graph
    }
}

impl<D> TSPInstance<D>
where
    D: Dim,
    DefaultAllocator: Allocator<D, D>,
    DefaultAllocator: Allocator<D>,
{
    pub fn dimension(&self) -> D {
        self.distances.shape_generic().0
    }

    pub fn verify_solution(solution: &NodePermutation<D>) -> bool {
        let mut seen_vertices = OVector::from_element_generic(
            solution.permutation.shape_generic().0,
            solution.permutation.shape_generic().1,
            false
        );

        for &vertex in solution.permutation.iter() {
            // This vertex index is out of bounds
            if vertex >= solution.permutation.len() {
                return false;
            }

            // A node is repeating
            if seen_vertices[vertex] {
                return false;
            }

            seen_vertices[vertex] = true;
        }

        true
    }

    pub fn solution_cost(&self, solution: &NodePermutation<D>) -> f64 {
        solution.permutation
            .iter()
            .circular_tuple_windows()
            .map(|(&node1, &node2): (&usize, &usize)| self.distances(node1, node2))
            .sum()
    }

    pub fn distances(&self, city_a: usize, city_b: usize) -> f64 {
        self.distances[(city_a, city_b)]
    }

    fn plot_internal(&self, solution: Option<&NodePermutation<D>>, filename: &str) -> Result<(), Box<dyn std::error::Error>> {
        let root = BitMapBackend::new(filename, (800, 600)).into_drawing_area();
        root.fill(&WHITE)?;

        let x_coords: Vec<f64> = self.cities.iter().map(|city| city.point.x).collect();
        let y_coords: Vec<f64> = self.cities.iter().map(|city| city.point.y).collect();

        let x_min = x_coords.iter().fold(f64::INFINITY, |a, &b| a.min(b));
        let x_max = x_coords.iter().fold(f64::NEG_INFINITY, |a, &b| a.max(b));
        let y_min = y_coords.iter().fold(f64::INFINITY, |a, &b| a.min(b));
        let y_max = y_coords.iter().fold(f64::NEG_INFINITY, |a, &b| a.max(b));

        let x_padding = (x_max - x_min) * 0.1;
        let y_padding = (y_max - y_min) * 0.1;

        let x_range = (x_min - x_padding)..(x_max + x_padding);
        let y_range = (y_min - y_padding)..(y_max + y_padding);

        let title = if let Some(sol) = solution {
            format!("TSP Solution (Cost: {:.2})", self.solution_cost(sol))
        } else {
            "TSP Instance".to_string()
        };

        let mut chart = ChartBuilder::on(&root)
            .caption(&title, ("sans-serif", 40))
            .margin(10)
            .x_label_area_size(40)
            .y_label_area_size(40)
            .build_cartesian_2d(x_range, y_range)?;

        chart.configure_mesh().draw()?;

        if let Some(sol) = solution {
            chart.draw_series(
                sol.permutation.iter().circular_tuple_windows().map(|(&city1_idx, &city2_idx)| {
                    let city1 = &self.cities[city1_idx];
                    let city2 = &self.cities[city2_idx];
                    PathElement::new(vec![(city1.point.x, city1.point.y), (city2.point.x, city2.point.y)], BLUE)
                })
            )?;
        }

        chart.draw_series(
            self.cities.iter().map(|city| {
                Circle::new((city.point.x, city.point.y), 5, RED.filled())
            })
        )?;

        root.present()?;
        Ok(())
    }

    pub fn plot(&self, filename: &str) -> Result<(), Box<dyn std::error::Error>> {
        self.plot_internal(None, filename)
    }

    pub fn draw_solution(&self, solution: &NodePermutation<D>, filename: &str) -> Result<(), Box<dyn std::error::Error>> {
        self.plot_internal(Some(solution), filename)
    }
}

impl<D> FitnessFunction for TSPInstance<D>
where
    D: Dim,
    DefaultAllocator: Allocator<D, D>,
    DefaultAllocator: Allocator<D>,
{
    type In = NodePermutation<D>;
    type Out = f64;
    type Err = Infallible;

    fn fit(self: &Self, inp: &Self::In) -> Result<Self::Out, Self::Err> {
        assert_eq!(inp.permutation.len(), self.cities.len());
        assert!(TSPInstance::verify_solution(inp));
        Ok(self.solution_cost(inp))
    }
}

#[cfg(test)]
mod tests {
    use nalgebra::{Const, SVector};
    use rand::seq::SliceRandom;

    use super::{NodePermutation, TSPInstance};

    #[test]
    fn test_verify_solution() {
        let mut rng = rand::rng();
        let rng = &mut rng;
        let mut chromosome = NodePermutation::<Const<6>> {
            permutation: SVector::from_vec(vec![0, 1, 2, 3, 4, 5])
        };

        for _ in 0..100 {
            chromosome.permutation.as_mut_slice().shuffle(rng);
            assert!(TSPInstance::verify_solution(&chromosome));
        }

        // Out of bounds
        chromosome.permutation[0] = 6;
        assert!(!TSPInstance::verify_solution(&chromosome));
        chromosome.permutation[0] = 7;
        assert!(!TSPInstance::verify_solution(&chromosome));
        chromosome.permutation[0] = 8;
        assert!(!TSPInstance::verify_solution(&chromosome));

        // Repeating
        chromosome.permutation[0] = 5;
        chromosome.permutation[1] = 5;
        assert!(!TSPInstance::verify_solution(&chromosome));

        let chromosome = NodePermutation::<Const<6>> {
            permutation: SVector::from_vec(vec![0, 1, 2, 3, 1, 5])
        };
        assert!(!TSPInstance::verify_solution(&chromosome));
    }


}