lambdust 0.1.1

//! Advanced Monad and Applicative Algebra for Lambdust.
//!
//! This module extends the basic monad system with advanced monadic constructs
//! needed for R7RS-large compliance and sophisticated effect handling:
//! - Monad transformers (MonadT)
//! - Maybe, Either, List, IO, State, Reader, Writer monads
//! - Applicative functors and their laws
//! - do-notation syntax sugar support
//! - Free monads and extensible effects

#![allow(missing_docs)]

use super::MonadicValue;
use crate::diagnostics::Result;
use crate::eval::value::Value;
use std::fmt;
use std::marker::PhantomData;
use std::sync::Arc;

/// Simplified trait for monadic computations (without HKT).
/// This avoids Rust's higher-kinded type limitations.
pub trait MonadicOps<A> {
    /// The concrete monadic type
    type Output<B>;
    
    /// Monadic return operation.
    fn pure(value: A) -> Self;
    
    /// Monadic bind operation.
    fn bind<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> Self::Output<B>;
    
    /// Map a function over the monadic value.
    fn map<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> B;
}

/// Maybe monad for optional values.
#[derive(Debug, Clone, PartialEq)]
pub enum Maybe<A> {
    Nothing,
    Just(A),
}

/// Either monad for error handling.
#[derive(Debug, Clone, PartialEq)]
pub enum Either<L, R> {
    Left(L),
    Right(R),
}

/// List monad for non-deterministic computations.
#[derive(Debug, Clone, PartialEq)]
pub struct List<A> {
    items: Vec<A>,
}

/// IO monad for side effects.
#[derive(Clone)]
pub struct IO<A> {
    action: Arc<dyn Fn() -> Result<A> + Send + Sync>,
}

impl<A> std::fmt::Debug for IO<A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("IO")
            .field("action", &"<function>")
            .finish()
    }
}

/// State monad for stateful computations.
#[derive(Clone)]
pub struct State<S, A> {
    run_state: Arc<dyn Fn(S) -> Result<(A, S)> + Send + Sync>,
}

impl<S, A> std::fmt::Debug for State<S, A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("State")
            .field("run_state", &"<function>")
            .finish()
    }
}

/// Reader monad for environment access.
#[derive(Clone)]
pub struct Reader<R, A> {
    run_reader: Arc<dyn Fn(R) -> Result<A> + Send + Sync>,
}

impl<R, A> std::fmt::Debug for Reader<R, A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Reader")
            .field("run_reader", &"<function>")
            .finish()
    }
}

/// Writer monad for accumulating output.
#[derive(Clone)]
pub struct Writer<W, A> {
    run_writer: Arc<dyn Fn() -> Result<(A, W)> + Send + Sync>,
}

impl<W, A> std::fmt::Debug for Writer<W, A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Writer")
            .field("run_writer", &"<function>")
            .finish()
    }
}

/// Monad transformer trait (simplified).
pub trait MonadTrans<M> {
    type T<A>;
    
    /// Lift a computation from the base monad.
    fn lift<A>(ma: M) -> Self::T<A>;
}

/// Maybe transformer.
#[derive(Debug, Clone)]
pub struct MaybeT<M, A> {
    run_maybe_t: M, // M<Maybe<A>>
    phantom: PhantomData<A>,
}

/// Either transformer.
#[derive(Debug, Clone)]
pub struct EitherT<E, M, A> {
    run_either_t: M, // M<Either<E, A>>
    phantom: PhantomData<(E, A)>,
}

/// State transformer.
#[derive(Clone)]
pub struct StateT<S, M, A> {
    run_state_t: Arc<dyn Fn(S) -> M + Send + Sync>, // S -> M<(A, S)>
    phantom: PhantomData<A>,
}

impl<S, M, A> std::fmt::Debug for StateT<S, M, A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("StateT")
            .field("run_state_t", &"<function>")
            .field("phantom", &self.phantom)
            .finish()
    }
}

/// Reader transformer.
#[derive(Clone)]
pub struct ReaderT<R, M, A> {
    run_reader_t: Arc<dyn Fn(R) -> M + Send + Sync>, // R -> M<A>
    phantom: PhantomData<A>,
}

impl<R, M, A> std::fmt::Debug for ReaderT<R, M, A> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("ReaderT")
            .field("run_reader_t", &"<function>")
            .field("phantom", &self.phantom)
            .finish()
    }
}

/// Writer transformer.
#[derive(Debug, Clone)]
pub struct WriterT<W, M, A> {
    run_writer_t: M, // M<(A, W)>
    phantom: PhantomData<(W, A)>,
}

/// Free monad for extensible effects.
#[derive(Debug, Clone)]
pub enum Free<F, A> {
    Pure(A),
    Free(F), // F<Free<F, A>>
}

/// do-notation support structure.
#[derive(Debug, Clone)]
pub struct DoNotation {
    /// Sequence of monadic bindings
    bindings: Vec<DoBinding>,
    /// Final expression
    result: String, // Simplified: store as string
}

/// A single binding in do-notation.
#[derive(Debug, Clone)]
pub struct DoBinding {
    /// Variable name (if any)
    var: Option<String>,
    /// Monadic expression
    expr: String, // Simplified: store as string
}

/// Advanced monad operations.
pub struct MonadOps;

impl<A> Maybe<A> {
    /// Creates a Just value.
    pub fn just(value: A) -> Self {
        Maybe::Just(value)
    }
    
    /// Creates a Nothing value.
    pub fn nothing() -> Self {
        Maybe::Nothing
    }
    
    /// Checks if this is Nothing.
    pub fn is_nothing(&self) -> bool {
        matches!(self, Maybe::Nothing)
    }
    
    /// Checks if this is Just.
    pub fn is_just(&self) -> bool {
        matches!(self, Maybe::Just(_))
    }
    
    /// Converts to Option.
    pub fn to_option(self) -> Option<A> {
        match self {
            Maybe::Just(a) => Some(a),
            Maybe::Nothing => None,
        }
    }
    
    /// Converts from Option.
    pub fn from_option(opt: Option<A>) -> Self {
        match opt {
            Some(a) => Maybe::Just(a),
            None => Maybe::Nothing,
        }
    }
}

impl<L, R> Either<L, R> {
    /// Creates a Left value.
    pub fn left(value: L) -> Self {
        Either::Left(value)
    }
    
    /// Creates a Right value.
    pub fn right(value: R) -> Self {
        Either::Right(value)
    }
    
    /// Checks if this is Left.
    pub fn is_left(&self) -> bool {
        matches!(self, Either::Left(_))
    }
    
    /// Checks if this is Right.
    pub fn is_right(&self) -> bool {
        matches!(self, Either::Right(_))
    }
    
    /// Maps over the Right value.
    pub fn map_right<R2, F>(self, f: F) -> Either<L, R2>
    where
        F: FnOnce(R) -> R2,
    {
        match self {
            Either::Left(l) => Either::Left(l),
            Either::Right(r) => Either::Right(f(r)),
        }
    }
    
    /// Maps over the Left value.
    pub fn map_left<L2, F>(self, f: F) -> Either<L2, R>
    where
        F: FnOnce(L) -> L2,
    {
        match self {
            Either::Left(l) => Either::Left(f(l)),
            Either::Right(r) => Either::Right(r),
        }
    }
}

impl<A> List<A> {
    /// Creates an empty list.
    pub fn empty() -> Self {
        List { items: Vec::new() }
    }
    
    /// Creates a singleton list.
    pub fn singleton(item: A) -> Self {
        List { items: vec![item] }
    }
    
    /// Creates a list from a vector.
    pub fn from_vec(items: Vec<A>) -> Self {
        List { items }
    }
    
    /// Converts to a vector.
    pub fn to_vec(self) -> Vec<A> {
        self.items
    }
    
    /// Checks if the list is empty.
    pub fn is_empty(&self) -> bool {
        self.items.is_empty()
    }
    
    /// Gets the length of the list.
    pub fn len(&self) -> usize {
        self.items.len()
    }
}

impl<A> IO<A> {
    /// Creates a new IO action.
    pub fn new<F>(action: F) -> Self
    where
        F: Fn() -> Result<A> + Send + Sync + 'static,
    {
        IO {
            action: Arc::new(action),
        }
    }
    
    /// Runs the IO action.
    pub fn run(self) -> Result<A> {
        (self.action)()
    }
}

impl<S, A> State<S, A> {
    /// Creates a new state computation.
    pub fn new<F>(f: F) -> Self
    where
        F: Fn(S) -> Result<(A, S)> + Send + Sync + 'static,
    {
        State {
            run_state: Arc::new(f),
        }
    }
    
    /// Runs the state computation.
    pub fn run(self, initial_state: S) -> Result<(A, S)> {
        (self.run_state)(initial_state)
    }
    
    /// Gets the current state.
    pub fn get<St>() -> State<St, St>
    where
        St: Clone + Send + Sync + 'static,
    {
        State::new(|s: St| Ok((s.clone(), s)))
    }
    
    /// Sets the state.
    pub fn put(new_state: S) -> State<S, ()>
    where
        S: Clone + Send + Sync + 'static,
    {
        State::new(move |_| Ok(((), new_state.clone())))
    }
    
    /// Modifies the state.
    pub fn modify<F>(f: F) -> State<S, ()>
    where
        F: Fn(S) -> S + Send + Sync + 'static,
    {
        State::new(move |s| Ok(((), f(s))))
    }
}

impl<R, A> Reader<R, A> {
    /// Creates a new reader computation.
    pub fn new<F>(f: F) -> Self
    where
        F: Fn(R) -> Result<A> + Send + Sync + 'static,
    {
        Reader {
            run_reader: Arc::new(f),
        }
    }
    
    /// Runs the reader computation.
    pub fn run(self, environment: R) -> Result<A> {
        (self.run_reader)(environment)
    }
    
    /// Asks for the environment.
    pub fn ask<Rd>() -> Reader<Rd, Rd>
    where
        Rd: Clone + Send + Sync + 'static,
    {
        Reader::new(|r: Rd| Ok(r.clone()))
    }
    
    /// Asks for a part of the environment.
    pub fn asks<F, B>(f: F) -> Reader<R, B>
    where
        F: Fn(R) -> B + Send + Sync + 'static,
    {
        Reader::new(move |r| Ok(f(r)))
    }
}

impl<W, A> Writer<W, A> {
    /// Creates a new writer computation.
    pub fn new<F>(f: F) -> Self
    where
        F: Fn() -> Result<(A, W)> + Send + Sync + 'static,
    {
        Writer {
            run_writer: Arc::new(f),
        }
    }
    
    /// Runs the writer computation.
    pub fn run(self) -> Result<(A, W)> {
        (self.run_writer)()
    }
    
    /// Writes a value to the log.
    pub fn tell(w: W) -> Writer<W, ()>
    where
        W: Clone + Send + Sync + 'static,
    {
        Writer::new(move || Ok(((), w.clone())))
    }
}

// Simplified monadic instances

impl<A> MonadicOps<A> for Maybe<A> {
    type Output<B> = Maybe<B>;
    
    fn pure(value: A) -> Self {
        Maybe::Just(value)
    }
    
    fn bind<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> Self::Output<B>,
    {
        match self {
            Maybe::Just(a) => f(a),
            Maybe::Nothing => Maybe::Nothing,
        }
    }
    
    fn map<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> B,
    {
        match self {
            Maybe::Just(a) => Maybe::Just(f(a)),
            Maybe::Nothing => Maybe::Nothing,
        }
    }
}

impl<L, R> MonadicOps<R> for Either<L, R> {
    type Output<B> = Either<L, B>;
    
    fn pure(value: R) -> Self {
        Either::Right(value)
    }
    
    fn bind<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(R) -> Self::Output<B>,
    {
        match self {
            Either::Right(r) => f(r),
            Either::Left(l) => Either::Left(l),
        }
    }
    
    fn map<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(R) -> B,
    {
        match self {
            Either::Right(r) => Either::Right(f(r)),
            Either::Left(l) => Either::Left(l),
        }
    }
}

impl<A> MonadicOps<A> for List<A> {
    type Output<B> = List<B>;
    
    fn pure(value: A) -> Self {
        List::singleton(value)
    }
    
    fn bind<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> Self::Output<B>,
    {
        let mut result = Vec::new();
        for item in self.items {
            let mapped = f(item);
            result.extend(mapped.items);
        }
        List::from_vec(result)
    }
    
    fn map<B, F>(self, f: F) -> Self::Output<B>
    where
        F: Fn(A) -> B,
    {
        let mut result = Vec::new();
        for item in self.items {
            result.push(f(item));
        }
        List::from_vec(result)
    }
}

impl MonadOps {
    /// Monadic when - conditional execution for Maybe.
    pub fn when_maybe(condition: bool, action: Maybe<()>) -> Maybe<()> {
        if condition {
            action
        } else {
            Maybe::Just(())
        }
    }
    
    /// Monadic unless - conditional execution (negated) for Maybe.
    pub fn unless_maybe(condition: bool, action: Maybe<()>) -> Maybe<()> {
        Self::when_maybe(!condition, action)
    }
    
    /// Sequence two Maybe computations.
    pub fn sequence_maybe<A, B>(ma: Maybe<A>, mb: Maybe<B>) -> Maybe<(A, B)>
    where
        A: Clone,
        B: Clone,
    {
        ma.bind(|a| mb.clone().map(|b| (a.clone(), b)))
    }
    
    /// Map a function over Maybe values.
    pub fn map_maybe<A, B, F>(f: F, items: Vec<A>) -> Maybe<Vec<B>>
    where
        F: Fn(A) -> Maybe<B>,
    {
        let mut results = Vec::new();
        for item in items {
            match f(item) {
                Maybe::Just(b) => results.push(b),
                Maybe::Nothing => return Maybe::Nothing,
            }
        }
        Maybe::Just(results)
    }
}

impl DoNotation {
    /// Creates a new do-notation block.
    pub fn new() -> Self {
        Self {
            bindings: Vec::new(),
            result: String::new(),
        }
    }
    
    /// Adds a binding to the do-block.
    pub fn bind(mut self, var: Option<String>, expr: String) -> Self {
        self.bindings.push(DoBinding { var, expr });
        self
    }
    
    /// Sets the result expression.
    pub fn result(mut self, expr: String) -> Self {
        self.result = expr;
        self
    }
    
    /// Compiles the do-notation to monadic bind operations.
    pub fn compile(&self) -> String {
        // Simplified compilation
        // A proper implementation would generate proper monadic code
        format!("do {{ {} }}", self.result)
    }
}

// Integration with existing Lambdust effect system

/// Converts a Maybe to a MonadicValue.
pub fn maybe_to_monadic<A>(maybe: Maybe<A>) -> MonadicValue
where
    A: Into<Value>,
{
    match maybe {
        Maybe::Just(a) => MonadicValue::pure(a.into()),
        Maybe::Nothing => MonadicValue::pure(Value::Nil),
    }
}

/// Converts an Either to a MonadicValue.
pub fn either_to_monadic<L, R>(either: Either<L, R>) -> MonadicValue
where
    L: Into<Value>,
    R: Into<Value>,
{
    match either {
        Either::Right(r) => MonadicValue::pure(r.into()),
        Either::Left(l) => MonadicValue::error(super::monad::ErrorAction::Return(l.into())),
    }
}

/// Converts a List to a MonadicValue.
pub fn list_to_monadic<A>(list: List<A>) -> MonadicValue
where
    A: Into<Value>,
{
    let values: Vec<Value> = list.items.into_iter().map(|a| a.into()).collect();
    MonadicValue::pure(Value::list(values))
}

impl fmt::Display for DoNotation {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        writeln!(f, "do")?;
        for binding in &self.bindings {
            if let Some(var) = &binding.var {
                writeln!(f, "  {} <- {}", var, binding.expr)?;
            } else {
                writeln!(f, "  {}", binding.expr)?;
            }
        }
        writeln!(f, "  {}", self.result)
    }
}

impl Default for DoNotation {
    fn default() -> Self {
        Self::new()
    }
}

// Thread safety markers
unsafe impl<A: Send> Send for Maybe<A> {}
unsafe impl<A: Sync> Sync for Maybe<A> {}

unsafe impl<L: Send, R: Send> Send for Either<L, R> {}
unsafe impl<L: Sync, R: Sync> Sync for Either<L, R> {}

unsafe impl<A: Send> Send for List<A> {}
unsafe impl<A: Sync> Sync for List<A> {}

unsafe impl<A: Send> Send for IO<A> {}
unsafe impl<A: Sync> Sync for IO<A> {}

unsafe impl<S: Send, A: Send> Send for State<S, A> {}
unsafe impl<S: Sync, A: Sync> Sync for State<S, A> {}

unsafe impl<R: Send, A: Send> Send for Reader<R, A> {}
unsafe impl<R: Sync, A: Sync> Sync for Reader<R, A> {}

unsafe impl<W: Send, A: Send> Send for Writer<W, A> {}
unsafe impl<W: Sync, A: Sync> Sync for Writer<W, A> {}

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

    #[test]
    fn test_maybe_monad_ops() {
        let just_5 = Maybe::just(5);
        let nothing = Maybe::<i32>::nothing();
        
        assert!(just_5.is_just());
        assert!(nothing.is_nothing());
        
        // Test bind
        let result = just_5.bind(|x| Maybe::just(x * 2));
        assert_eq!(result, Maybe::just(10));
        
        let result = nothing.bind(|x| Maybe::just(x * 2));
        assert_eq!(result, Maybe::nothing());
        
        // Test map
        let result = Maybe::just(5).map(|x| x * 2);
        assert_eq!(result, Maybe::just(10));
    }
    
    #[test]
    fn test_either_monad_ops() {
        let right_5 = Either::<String, i32>::right(5);
        let left_err = Either::<String, i32>::left("error".to_string());
        
        assert!(right_5.is_right());
        assert!(left_err.is_left());
        
        // Test bind
        let result = right_5.bind(|x| Either::right(x * 2));
        assert_eq!(result, Either::right(10));
        
        let result = left_err.bind(|x| Either::right(x * 2));
        assert!(result.is_left());
        
        // Test map
        let result = Either::<String, i32>::right(5).map(|x| x * 2);
        assert_eq!(result, Either::right(10));
    }
    
    #[test]
    fn test_list_monad() {
        let list = List::from_vec(vec![1, 2, 3]);
        assert_eq!(list.len(), 3);
        assert!(!list.is_empty());
        
        let empty = List::<i32>::empty();
        assert!(empty.is_empty());
        
        let singleton = List::singleton(42);
        assert_eq!(singleton.len(), 1);
    }
    
    #[test]
    fn test_state_monad() {
        let computation = State::new(|s: i32| Ok((s + 1, s * 2)));
        let result = computation.run(5).unwrap();
        assert_eq!(result, (6, 10));
        
        let get_state = State::<i32, i32>::get();
        let result = get_state.run(42).unwrap();
        assert_eq!(result, (42, 42));
    }
    
    #[test]
    fn test_reader_monad() {
        let reader = Reader::new(|env: String| Ok(env.len()));
        let result = reader.run("hello".to_string()).unwrap();
        assert_eq!(result, 5);
        
        let ask = Reader::<String, String>::ask();
        let result = ask.run("world".to_string()).unwrap();
        assert_eq!(result, "world");
    }
    
    #[test]
    fn test_writer_monad() {
        let writer = Writer::new(|| Ok((42, "logged".to_string())));
        let result = writer.run().unwrap();
        assert_eq!(result, (42, "logged".to_string()));
    }
    
    #[test]
    fn test_do_notation() {
        let do_block = DoNotation::new()
            .bind(Some("x".to_string()), "getValue()".to_string())
            .bind(Some("y".to_string()), "getAnother()".to_string())
            .bind(None, "sideEffect()".to_string())
            .result("return (x + y)".to_string());
        
        assert_eq!(do_block.bindings.len(), 3);
        assert_eq!(do_block.result, "return (x + y)");
    }
}