use crate::base::*;
use crate::parser::*;
use crate::spans::*;
use crate::validator::FnInfo;
use crate::value::Value;
use chumsky::prelude::SimpleSpan;
use imbl::HashMap;
use imbl::Vector;
use std::cell::RefCell;
use std::rc::Rc;

#[derive(Debug)]
pub struct LErr {
    pub msg: String,
    pub trace: Vec<String>,
}

impl LErr {
    pub fn new(msg: String) -> LErr {
        LErr {
            msg: msg.to_string(),
            trace: vec![],
        }
    }

    pub fn add_trace(mut self, fn_name: String) -> LErr {
        self.trace.push(fn_name);
        self
    }
}

type LResult<'src> = Result<Value<'src>, LErr>;

#[derive(Debug)]
pub struct Process<'src> {
    pub locals: Vec<(String, Value<'src>)>,
    pub prelude: Vec<(String, Value<'src>)>,
    pub ast: &'src Ast,
    pub span: SimpleSpan,
    pub fn_info: std::collections::HashMap<*const Ast, FnInfo>,
}

impl<'src> Process<'src> {
    pub fn resolve(&self, word: &String) -> LResult<'src> {
        let resolved_local = self.locals.iter().rev().find(|(name, _)| word == name);

        match resolved_local {
            Some((_, value)) => Ok(value.clone()),
            None => {
                let resolved_prelude = self.prelude.iter().rev().find(|(name, _)| word == name);
                match resolved_prelude {
                    Some((_, value)) => Ok(value.clone()),
                    None => Err(LErr::new(format!("unbound name {word}"))),
                }
            }
        }
    }

    pub fn bind(&mut self, word: String, value: &Value<'src>) {
        self.locals.push((word, value.clone()));
    }

    pub fn match_eq<T>(&self, x: T, y: T) -> Option<&Process<'src>>
    where
        T: PartialEq,
    {
        if x == y {
            Some(self)
        } else {
            None
        }
    }

    pub fn match_pattern(&mut self, patt: &Ast, val: &Value<'src>) -> Option<&Process<'src>> {
        use Ast::*;
        match (patt, val) {
            (NilPattern, Value::Nil) => Some(self),
            (PlaceholderPattern, _) => Some(self),
            (NumberPattern(x), Value::Number(y)) => self.match_eq(x, y),
            (BooleanPattern(x), Value::Boolean(y)) => self.match_eq(x, y),
            (KeywordPattern(x), Value::Keyword(y)) => self.match_eq(x, y),
            (StringPattern(x), Value::InternedString(y)) => self.match_eq(x, y),
            (StringPattern(x), Value::AllocatedString(y)) => self.match_eq(&x.to_string(), y),
            (InterpolatedPattern(_, StringMatcher(matcher)), Value::InternedString(y)) => {
                match matcher(y.to_string()) {
                    Some(matches) => {
                        let mut matches = matches
                            .iter()
                            .map(|(word, string)| {
                                (
                                    word.clone(),
                                    Value::AllocatedString(Rc::new(string.clone())),
                                )
                            })
                            .collect::<Vec<_>>();
                        self.locals.append(&mut matches);
                        Some(self)
                    }
                    None => None,
                }
            }
            (WordPattern(w), val) => {
                self.bind(w.to_string(), val);
                Some(self)
            }
            (AsPattern(word, type_str), value) => {
                let ludus_type = r#type(value);
                let type_kw = Value::Keyword(type_str);
                if type_kw == ludus_type {
                    self.bind(word.to_string(), value);
                    Some(self)
                } else {
                    None
                }
            }
            (TuplePattern(x), Value::Tuple(y)) => {
                let has_splat = x.iter().any(|patt| matches!(patt, (Splattern(_), _)));
                if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                    return None;
                };
                let to = self.locals.len();
                for i in 0..x.len() {
                    if let Splattern(patt) = &x[i].0 {
                        let mut list = Vector::new();
                        for i in i..y.len() {
                            list.push_back(y[i].clone())
                        }
                        let list = Value::List(list);
                        self.match_pattern(&patt.0, &list);
                    } else if self.match_pattern(&x[i].0, &y[i]).is_none() {
                        self.locals.truncate(to);
                        return None;
                    }
                }
                Some(self)
            }
            (ListPattern(x), Value::List(y)) => {
                let has_splat = x.iter().any(|patt| matches!(patt, (Splattern(_), _)));
                if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                    return None;
                };
                let to = self.locals.len();
                for (i, (patt, _)) in x.iter().enumerate() {
                    if let Splattern(patt) = &patt {
                        let list = Value::List(y.skip(i));
                        self.match_pattern(&patt.0, &list);
                    } else if self.match_pattern(patt, y.get(i).unwrap()).is_none() {
                        self.locals.truncate(to);
                        return None;
                    }
                }
                Some(self)
            }
            // TODO: optimize this on several levels
            // - [ ] opportunistic mutation
            // - [ ] get rid of all the pointer indirection in word splats
            (DictPattern(x), Value::Dict(y)) => {
                let has_splat = x.iter().any(|patt| matches!(patt, (Splattern(_), _)));
                if x.len() > y.len() || (!has_splat && x.len() != y.len()) {
                    return None;
                };
                let to = self.locals.len();
                let mut matched = vec![];
                for (pattern, _) in x {
                    match pattern {
                        PairPattern(key, patt) => {
                            if let Some(val) = y.get(key) {
                                if self.match_pattern(&patt.0, val).is_none() {
                                    self.locals.truncate(to);
                                    return None;
                                } else {
                                    matched.push(key);
                                }
                            } else {
                                return None;
                            };
                        }
                        Splattern(pattern) => match pattern.0 {
                            WordPattern(w) => {
                                // TODO: find a way to take ownership
                                // this will ALWAYS make structural changes, because of this clone
                                // we want opportunistic mutation if possible
                                let mut unmatched = y.clone();
                                for key in matched.iter() {
                                    unmatched.remove(*key);
                                }
                                self.bind(w.to_string(), &Value::Dict(unmatched));
                            }
                            PlaceholderPattern => (),
                            _ => unreachable!(),
                        },
                        _ => unreachable!(),
                    }
                }
                Some(self)
            }
            _ => None,
        }
    }

    pub fn match_clauses(
        &mut self,
        value: &Value<'src>,
        clauses: &'src [Spanned<Ast>],
    ) -> LResult<'src> {
        {
            let root = self.ast;
            let to = self.locals.len();
            let mut clauses = clauses.iter();
            while let Some((Ast::MatchClause(patt, guard, body), _)) = clauses.next() {
                if self.match_pattern(&patt.0, value).is_some() {
                    let pass_guard = match guard.as_ref() {
                        None => true,
                        Some(guard_expr) => self.visit(guard_expr)?.bool(),
                    };
                    if !pass_guard {
                        self.locals.truncate(to);
                        continue;
                    }
                    let result = self.visit(body);
                    self.locals.truncate(to);
                    self.ast = root;
                    return result;
                }
            }
            Err(LErr::new("no match".to_string()))
        }
    }

    pub fn apply(&mut self, callee: Value<'src>, caller: Value<'src>) -> LResult<'src> {
        use Value::*;
        match (callee, caller) {
            (Keyword(kw), Dict(dict)) => {
                if let Some(val) = dict.get(kw) {
                    Ok(val.clone())
                } else {
                    Ok(Nil)
                }
            }
            (Dict(dict), Keyword(kw)) => {
                if let Some(val) = dict.get(kw) {
                    Ok(val.clone())
                } else {
                    Ok(Nil)
                }
            }
            (Fn(f), Tuple(args)) => {
                let args = Tuple(args);
                let to = self.locals.len();
                let mut enclosing = f.enclosing.clone();
                self.locals.append(&mut enclosing);
                let result = self.match_clauses(&args, f.body);
                self.locals.truncate(to);
                result
            }
            // TODO: partially applied functions shnould work! In #15
            (Fn(_f), Args(_args)) => todo!(),
            (_, Keyword(_)) => Ok(Nil),
            (_, Args(_)) => Err(LErr::new("you may only call a function".to_string())),
            (Base(f), Tuple(args)) => match f {
                BaseFn::Nullary(f) => {
                    let num_args = args.len();
                    if num_args != 0 {
                        Err(LErr::new(format!(
                            "wrong arity: expected 0 arguments, got {num_args}"
                        )))
                    } else {
                        Ok(f())
                    }
                }
                BaseFn::Unary(f) => {
                    let num_args = args.len();
                    if num_args != 1 {
                        Err(LErr::new(format!(
                            "wrong arity: expected 1 argument, got {num_args}"
                        )))
                    } else {
                        Ok(f(&args[0]))
                    }
                }
                BaseFn::Binary(r#fn) => {
                    let num_args = args.len();
                    if num_args != 2 {
                        Err(LErr::new(format!(
                            "wrong arity: expected 2 arguments, got {num_args}"
                        )))
                    } else {
                        Ok(r#fn(&args[0], &args[1]))
                    }
                }
                BaseFn::Ternary(f) => {
                    let num_args = args.len();
                    if num_args != 3 {
                        Err(LErr::new(format!(
                            "wrong arity: expected 3 arguments, got {num_args}"
                        )))
                    } else {
                        Ok(f(&args[0], &args[1], &args[2]))
                    }
                }
            },
            _ => unreachable!(),
        }
    }

    pub fn visit(&mut self, node: &'src Spanned<Ast>) -> LResult<'src> {
        let (expr, span) = node;
        self.ast = expr;
        self.span = *span;
        self.eval()
    }

    pub fn eval(&mut self) -> LResult<'src> {
        use Ast::*;
        let (root_node, root_span) = (self.ast, self.span);
        let result = match root_node {
            Nil => Ok(Value::Nil),
            Boolean(b) => Ok(Value::Boolean(*b)),
            Number(n) => Ok(Value::Number(*n)),
            Keyword(k) => Ok(Value::Keyword(k)),
            String(s) => Ok(Value::InternedString(s)),
            Interpolated(parts) => {
                let mut interpolated = std::string::String::new();
                for part in parts {
                    match &part.0 {
                        StringPart::Data(s) => interpolated.push_str(s.as_str()),
                        StringPart::Word(w) => {
                            let val = self.resolve(w)?;
                            interpolated.push_str(val.interpolate().as_str())
                        }
                        StringPart::Inline(_) => unreachable!(),
                    }
                }
                Ok(Value::AllocatedString(Rc::new(interpolated)))
            }
            Block(exprs) => {
                let to = self.locals.len();
                let mut result = Value::Nil;
                for expr in exprs {
                    result = self.visit(expr)?;
                }
                self.locals.truncate(to);
                Ok(result)
            }
            If(cond, if_true, if_false) => {
                let truthy = self.visit(cond)?;
                let to_visit = if truthy.bool() { if_true } else { if_false };
                self.visit(to_visit)
            }
            List(members) => {
                let mut vect = Vector::new();
                for member in members {
                    let member_value = self.visit(member)?;
                    match member.0 {
                        Ast::Splat(_) => match member_value {
                            Value::List(list) => vect.append(list),
                            _ => {
                                return Err(LErr::new(
                                    "only lists may be splatted into lists".to_string(),
                                ))
                            }
                        },
                        _ => vect.push_back(member_value),
                    }
                }
                Ok(Value::List(vect))
            }
            Tuple(members) => {
                let mut vect = Vec::new();
                for member in members {
                    vect.push(self.visit(member)?);
                }
                Ok(Value::Tuple(Rc::new(vect)))
            }
            Word(w) | Ast::Splat(w) => {
                let val = self.resolve(&w.to_string())?;
                Ok(val)
            }
            Let(patt, expr) => {
                let val = self.visit(expr)?;
                let result = match self.match_pattern(&patt.0, &val) {
                    Some(_) => Ok(val),
                    None => Err(LErr::new("no match".to_string())),
                };
                result
            }
            Placeholder => Ok(Value::Placeholder),
            Arguments(a) => {
                let mut args = vec![];
                for arg in a.iter() {
                    args.push(self.visit(arg)?)
                }
                let result = if args.iter().any(|arg| matches!(arg, Value::Placeholder)) {
                    Ok(Value::Args(Rc::new(args)))
                } else {
                    Ok(Value::Tuple(Rc::new(args)))
                };
                result
            }
            Dict(terms) => {
                let mut dict = HashMap::new();
                for term in terms {
                    match term {
                        (Ast::Pair(key, value), _) => {
                            dict.insert(*key, self.visit(value)?);
                        }
                        (Ast::Splat(_), _) => {
                            let resolved = self.visit(term)?;
                            let Value::Dict(to_splat) = resolved else {
                                return Err(LErr::new(
                                    "cannot splat non-dict into dict".to_string(),
                                ));
                            };
                            dict = to_splat.union(dict);
                        }
                        _ => unreachable!(),
                    }
                }
                Ok(Value::Dict(dict))
            }
            LBox(name, expr) => {
                let val = self.visit(expr)?;
                let boxed = Value::Box(name, Rc::new(RefCell::new(val)));
                self.bind(name.to_string(), &boxed);
                Ok(boxed)
            }
            Synthetic(root, first, rest) => {
                let root_val = self.visit(root)?;
                let first_val = self.visit(first)?;
                let mut curr = self.apply(root_val, first_val)?;
                for term in rest.iter() {
                    let next = self.visit(term)?;
                    curr = self.apply(curr, next)?;
                }
                Ok(curr)
            }
            When(clauses) => {
                for clause in clauses.iter() {
                    let WhenClause(cond, body) = &clause.0 else {
                        unreachable!()
                    };
                    if self.visit(cond)?.bool() {
                        return self.visit(body);
                    };
                }
                Err(LErr::new("no match".to_string()))
            }
            Match(scrutinee, clauses) => {
                let value = self.visit(scrutinee)?;
                self.match_clauses(&value, clauses)
            }
            Fn(name, clauses, doc) => {
                let doc = doc.map(|s| s.to_string());
                let ptr: *const Ast = root_node;
                let info = self.fn_info.get(&ptr).unwrap();
                let FnInfo::Defined(_, _, enclosing) = info else {
                    unreachable!()
                };
                let enclosing = enclosing
                    .iter()
                    .filter(|binding| binding != name)
                    .map(|binding| (binding.clone(), self.resolve(binding).unwrap().clone()))
                    .collect();
                let the_fn = Value::Fn::<'src>(Rc::new(crate::value::Fn::<'src> {
                    name: name.to_string(),
                    body: clauses,
                    doc,
                    enclosing,
                }));
                self.bind(name.to_string(), &the_fn);
                Ok(the_fn)
            }
            FnDeclaration(_name) => Ok(Value::Nil),
            Panic(msg) => {
                let msg = self.visit(msg)?;
                Err(LErr::new(format!("{msg}")))
            }
            Repeat(times, body) => {
                let times_num = match self.visit(times) {
                    Ok(Value::Number(n)) => n as usize,
                    _ => return Err(LErr::new("`repeat` may only take numbers".to_string())),
                };
                for _ in 0..times_num {
                    self.visit(body)?;
                }
                Ok(Value::Nil)
            }
            Do(terms) => {
                let mut result = self.visit(&terms[0])?;
                for term in terms.iter().skip(1) {
                    let next = self.visit(term)?;
                    let arg = Value::Tuple(Rc::new(vec![result]));
                    result = self.apply(next, arg)?;
                }
                Ok(result)
            }
            Loop(init, clauses) => {
                let mut args = self.visit(init)?;
                loop {
                    let result = self.match_clauses(&args, clauses)?;
                    if let Value::Recur(recur_args) = result {
                        args = Value::Tuple(Rc::new(recur_args));
                    } else {
                        return Ok(result);
                    }
                }
            }
            Recur(args) => {
                let mut vect = Vec::new();
                for arg in args {
                    vect.push(self.visit(arg)?);
                }
                Ok(Value::Recur(vect))
            }
            _ => unreachable!(),
        };
        self.ast = root_node;
        self.span = root_span;
        result
    }
}