use std::collections::{HashMap, HashSet};

use num_traits::identities::{One, Zero};
use num_traits::sign::Signed;
use yolol_number::YololNumber;

use crate::ast::{InfixOp, PrefixOp, YololNode};
use crate::environment::Context;
use crate::graph::DepGraph;

/// Optimizes Yolol assign statements.
///
/// Optimization is idempotent when given the same context.
///
/// # Panics
///
/// Panics if any of the statements are malformed.
pub fn optimize(stmts: &[YololNode], context: &Context) -> Vec<YololNode> {
    let mut curr = stmts.to_vec();
    let mut next = reduce_constants(&curr);
    while curr != next {
        curr = next;
        next = reduce_constants(&curr);
    }
    eliminate_dead_code(&next, &context.exported())
}

fn reduce_constants(stmts: &[YololNode]) -> Vec<YololNode> {
    let mut reduced = Vec::new();
    let mut variables: HashMap<String, YololNode> = HashMap::new();
    for stmt in stmts.iter() {
        if let YololNode::AssignStmt { ident, expr } = stmt {
            variables.insert(ident.to_string(), *expr.clone());
            reduced.push(reduce_node(&variables, stmt));
        } else {
            panic!("expected Yolol statement, but got: {:?}", stmt);
        }
    }
    reduced
}

fn reduce_node(vars: &HashMap<String, YololNode>, node: &YololNode) -> YololNode {
    let zero = YololNumber::zero();
    let one = YololNumber::one();
    match node {
        YololNode::AssignStmt { ident, expr } => YololNode::AssignStmt {
            ident: ident.to_string(),
            expr: Box::new(reduce_node(vars, expr)),
        },
        YololNode::PrefixExpr { op, expr } => match (op, *expr.clone()) {
            // Fold literals
            (op, YololNode::Literal(y)) => match op {
                PrefixOp::Neg => YololNode::Literal(-y),
                PrefixOp::Not => YololNode::Literal(!y),
                PrefixOp::Abs => YololNode::Literal(y.abs()),
                PrefixOp::Sqrt if y >= zero => YololNode::Literal(y.sqrt()),
                PrefixOp::Sin => YololNode::Literal(y.sin()),
                PrefixOp::Cos => YololNode::Literal(y.cos()),
                PrefixOp::Tan if y.cos() != zero => YololNode::Literal(y.tan()),
                PrefixOp::Asin if y.abs() <= one => YololNode::Literal(y.asin()),
                PrefixOp::Acos if y.abs() <= one => YololNode::Literal(y.acos()),
                PrefixOp::Atan => YololNode::Literal(y.atan()),
                _ => node.clone(),
            },
            _ => YololNode::PrefixExpr {
                op: *op,
                expr: Box::new(reduce_node(vars, expr)),
            },
        },
        YololNode::InfixExpr { lhs, op, rhs } => match (*lhs.clone(), op, *rhs.clone()) {
            // Fold `0 + n` and `n + 0` to `n`
            (YololNode::Literal(y), InfixOp::Add, _) if y == zero => *rhs.clone(),
            (_, InfixOp::Add, YololNode::Literal(y)) if y == zero => *lhs.clone(),
            // Fold `n - 0` to `n`
            (_, InfixOp::Sub, YololNode::Literal(y)) if y == zero => *lhs.clone(),
            // Fold `0 * n` and `n * 0` to `0`
            (YololNode::Literal(y), InfixOp::Mul, _) if y == zero => *lhs.clone(),
            (_, InfixOp::Mul, YololNode::Literal(y)) if y == zero => *rhs.clone(),
            // Fold `1 * n` and `n * 1` to `n`
            (YololNode::Literal(y), InfixOp::Mul, _) if y == one => *rhs.clone(),
            (_, InfixOp::Mul, YololNode::Literal(y)) if y == one => *lhs.clone(),
            // Fold `n / 1` to `n`
            (_, InfixOp::Div, YololNode::Literal(y)) if y == one => *lhs.clone(),
            // Fold `1 ^ n` to `1`
            (YololNode::Literal(y), InfixOp::Exp, _) if y == one => *lhs.clone(),
            // Fold `n ^ 1` to `n`
            (_, InfixOp::Exp, YololNode::Literal(y)) if y == one => *lhs.clone(),
            // Fold literals
            (YololNode::Literal(y), op, YololNode::Literal(z)) => match op {
                InfixOp::Add => YololNode::Literal(y + z),
                InfixOp::Sub => YololNode::Literal(y - z),
                InfixOp::Mul => YololNode::Literal(y * z),
                InfixOp::Div if !z.is_zero() => YololNode::Literal(y / z),
                InfixOp::Mod if !z.is_zero() => YololNode::Literal(y % z),
                InfixOp::Exp if !(y.is_zero() && z.is_zero()) => YololNode::Literal(y.pow(z)),
                InfixOp::LessThan => YololNode::Literal(YololNumber::from(y < z)),
                InfixOp::LessEqual => YololNode::Literal(YololNumber::from(y <= z)),
                InfixOp::GreaterThan => YololNode::Literal(YololNumber::from(y > z)),
                InfixOp::GreaterEqual => YololNode::Literal(YololNumber::from(y >= z)),
                InfixOp::Equal => YololNode::Literal(YololNumber::from(y == z)),
                InfixOp::NotEqual => YololNode::Literal(YololNumber::from(y != z)),
                InfixOp::And => YololNode::Literal(YololNumber::from((y != zero) && (z != zero))),
                InfixOp::Or => YololNode::Literal(YololNumber::from((y != zero) || (z != zero))),
                _ => node.clone(),
            },
            _ => YololNode::InfixExpr {
                lhs: Box::new(reduce_node(vars, lhs)),
                op: *op,
                rhs: Box::new(reduce_node(vars, rhs)),
            },
        },
        // Propagate literals
        YololNode::Ident(s) => match vars.get(s) {
            Some(YololNode::Literal(y)) => YololNode::Literal(y.clone()),
            Some(node) => reduce_node(vars, node),
            // Ignore imported variable
            None => node.clone(),
        },
        YololNode::Literal(_) => node.clone(),
    }
}

fn eliminate_dead_code(stmts: &[YololNode], exported: &HashSet<String>) -> Vec<YololNode> {
    let graph = DepGraph::from_statements(stmts);
    let exported = graph.search_from(exported);
    let mut living = Vec::new();
    for stmt in stmts.iter() {
        if let YololNode::AssignStmt { ident, expr: _ } = stmt {
            if exported.contains(ident) {
                living.push(stmt.clone());
            }
        } else {
            panic!("expected Yolol statement, but got: {:?}", stmt)
        }
    }
    living
}