use std::ptr::NonNull;

use crate::go;
use crate::lexer::{tokenize, LexerError, Token};
use crate::unknown_game;
use crate::{GameTree, GameType, SgfNode, SgfProp};

/// Returns the [`GameTree`] values parsed from the provided text.
///
/// # Errors
/// If the text can't be parsed as an SGF FF\[4\] collection, then an error is returned.
///
/// # Examples
/// ```
/// use sgf_parse::{parse, GameType};
///
/// let sgf = "(;SZ[9]C[Some comment];B[de];W[fe])(;B[de];W[ff])";
/// let gametrees = parse(sgf).unwrap();
/// assert!(gametrees.len() == 2);
/// assert!(gametrees.iter().all(|gametree| gametree.gametype() == GameType::Go));
/// ```
pub fn parse(text: &str) -> Result<Vec<GameTree>, SgfParseError> {
    let tokens = tokenize(text)
        .map(|result| match result {
            Err(e) => Err(SgfParseError::LexerError(e)),
            Ok((token, _span)) => Ok(token),
        })
        .collect::<Result<Vec<_>, _>>()?;
    split_by_gametree(&tokens)?
        .into_iter()
        .map(|tokens| match find_gametype(tokens)? {
            GameType::Go => parse_gametree::<go::Prop>(tokens),
            GameType::Unknown => parse_gametree::<unknown_game::Prop>(tokens),
        })
        .collect::<Result<_, _>>()
}

/// Error type for failures parsing sgf from text.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SgfParseError {
    LexerError(LexerError),
    UnexpectedGameTreeStart,
    UnexpectedGameTreeEnd,
    UnexpectedProperty,
    UnexpectedEndOfData,
    UnexpectedGameType,
}

impl From<LexerError> for SgfParseError {
    fn from(error: LexerError) -> Self {
        Self::LexerError(error)
    }
}

impl std::fmt::Display for SgfParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            SgfParseError::LexerError(e) => write!(f, "Error tokenizing: {}", e),
            SgfParseError::UnexpectedGameTreeStart => write!(f, "Unexpected start of game tree"),
            SgfParseError::UnexpectedGameTreeEnd => write!(f, "Unexpected end of game tree"),
            SgfParseError::UnexpectedProperty => write!(f, "Unexpected property"),
            SgfParseError::UnexpectedEndOfData => write!(f, "Unexpected end of data"),
            SgfParseError::UnexpectedGameType => write!(f, "Unexpected game type"),
        }
    }
}

impl std::error::Error for SgfParseError {}

// Split the tokens up into individual gametrees.
//
// This will let us easily scan each gametree for GM properties.
// Only considers StartGameTree/EndGameTree tokens.
fn split_by_gametree(tokens: &[Token]) -> Result<Vec<&[Token]>, SgfParseError> {
    let mut gametrees = vec![];
    let mut gametree_depth: u64 = 0;
    let mut slice_start = 0;
    for (i, token) in tokens.iter().enumerate() {
        match token {
            Token::StartGameTree => gametree_depth += 1,
            Token::EndGameTree => {
                if gametree_depth == 0 {
                    return Err(SgfParseError::UnexpectedGameTreeEnd);
                }
                gametree_depth -= 1;
                if gametree_depth == 0 {
                    gametrees.push(&tokens[slice_start..=i]);
                    slice_start = i + 1;
                }
            }
            _ => {}
        }
    }
    if gametree_depth != 0 {
        return Err(SgfParseError::UnexpectedEndOfData);
    }

    Ok(gametrees)
}

// Parse a single gametree of a known type.
fn parse_gametree<Prop: SgfProp>(tokens: &[Token]) -> Result<GameTree, SgfParseError>
where
    SgfNode<Prop>: std::convert::Into<GameTree>,
{
    // TODO: Rewrite this without `unsafe`
    let mut collection: Vec<SgfNode<Prop>> = vec![];
    // //// Pointer to the `Vec` of children we're currently building.
    let mut current_node_list_ptr = NonNull::new(&mut collection).unwrap();
    // Stack of pointers to incomplete `Vec`s of children.
    let mut incomplete_child_lists: Vec<NonNull<Vec<SgfNode<Prop>>>> = vec![];
    //// Using pointers involves some unsafe calls, but should be ok here.
    //// Since pointers are always initialized from real structs, and those structs
    //// live for the whole function body, our only safety concern is dangling pointers.
    ////
    //// Since we build the tree traversing depth-first those structs shouldn't be
    //// modified while the pointer is live. Heap-allocated contents of their
    //// `children` may be modified, but that shouldn't change anything.

    let mut tokens = tokens.iter().peekable();
    while let Some(token) = tokens.next() {
        match token {
            Token::StartGameTree => {
                // SGF game trees must have a root node.
                if let Some(node_list_ptr) = incomplete_child_lists.last() {
                    let node_list = unsafe { node_list_ptr.as_ref() };
                    if node_list.is_empty() {
                        return Err(SgfParseError::UnexpectedGameTreeStart);
                    }
                }
                incomplete_child_lists.push(current_node_list_ptr);
            }
            Token::EndGameTree => match incomplete_child_lists.pop() {
                Some(node_list) => current_node_list_ptr = node_list,
                None => return Err(SgfParseError::UnexpectedGameTreeEnd),
            },
            Token::StartNode => {
                let mut new_node = SgfNode::default();
                let mut prop_tokens = vec![];
                while let Some(Token::Property(_)) = tokens.peek() {
                    prop_tokens.push(tokens.next().unwrap());
                }
                for token in prop_tokens {
                    match token {
                        // TODO: Consider refactoring to consume tokens and avoid clones.
                        Token::Property((identifier, values)) => new_node
                            .properties
                            .push(Prop::new(identifier.clone(), values.clone())),
                        _ => unreachable!(),
                    }
                }
                let node_list = unsafe { current_node_list_ptr.as_mut() };
                node_list.push(new_node);
                current_node_list_ptr =
                    NonNull::new(&mut node_list.last_mut().unwrap().children).unwrap();
            }
            Token::Property(_) => return Err(SgfParseError::UnexpectedProperty),
        }
    }

    if !incomplete_child_lists.is_empty() || collection.len() != 1 {
        return Err(SgfParseError::UnexpectedEndOfData);
    }
    let mut root_node = collection.into_iter().next().unwrap();
    root_node.is_root = true;
    Ok(root_node.into())
}

// Figure out which game to parse from a slice of tokens.
//
// This function is necessary because we need to know the game before we can do the parsing.
fn find_gametype(tokens: &[Token]) -> Result<GameType, SgfParseError> {
    let gm_props: Vec<_> = tokens
        .iter()
        .filter_map(|token| match token {
            Token::Property((prop_ident, prop_values)) => {
                if prop_ident == "GM" {
                    Some(prop_values)
                } else {
                    None
                }
            }
            _ => None,
        })
        .collect();
    match gm_props.len() {
        0 => Ok(GameType::Go),
        1 => {
            let props = gm_props[0];
            if props.len() != 1 {
                return Ok(GameType::Unknown);
            }
            match props[0].as_str() {
                "1" => Ok(GameType::Go),
                _ => Ok(GameType::Unknown),
            }
        }
        _ => Err(SgfParseError::UnexpectedProperty),
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::{go, serialize};

    fn load_test_sgf() -> Result<String, Box<dyn std::error::Error>> {
        // See https://www.red-bean.com/sgf/examples/
        let mut sgf_path = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
        sgf_path.push("resources/test/ff4_ex.sgf");
        let data = std::fs::read_to_string(sgf_path)?;

        Ok(data)
    }

    fn get_go_nodes() -> Result<Vec<SgfNode<go::Prop>>, Box<dyn std::error::Error>> {
        let data = load_test_sgf()?;

        Ok(go::parse(&data)?)
    }

    fn node_depth(mut sgf_node: &SgfNode<go::Prop>) -> u64 {
        let mut depth = 1;
        while sgf_node.children().count() > 0 {
            depth += 1;
            sgf_node = sgf_node.children().next().unwrap();
        }
        depth
    }

    #[test]
    fn sgf_has_two_gametrees() {
        let sgf_nodes = get_go_nodes().unwrap();
        assert_eq!(sgf_nodes.len(), 2);
    }

    #[test]
    fn gametree_one_has_five_variations() {
        let sgf_nodes = get_go_nodes().unwrap();
        let sgf_node = &sgf_nodes[0];
        assert_eq!(sgf_node.children().count(), 5);
    }

    #[test]
    fn gametree_one_has_size_19() {
        let sgf_nodes = get_go_nodes().unwrap();
        let sgf_node = &sgf_nodes[0];
        match sgf_node.get_property("SZ") {
            Some(go::Prop::SZ(size)) => assert_eq!(size, &(19, 19)),
            _ => unreachable!("Expected size property"),
        }
    }

    #[test]
    fn gametree_variation_depths() {
        let sgf_nodes = get_go_nodes().unwrap();
        let sgf_node = &sgf_nodes[0];
        let children: Vec<_> = sgf_node.children().collect();
        assert_eq!(node_depth(children[0]), 13);
        assert_eq!(node_depth(children[1]), 4);
        assert_eq!(node_depth(children[2]), 4);
    }

    #[test]
    fn gametree_two_has_one_variation() {
        let sgf_nodes = get_go_nodes().unwrap();
        let sgf_node = &sgf_nodes[1];
        assert_eq!(sgf_node.children().count(), 1);
    }

    #[test]
    fn serialize_then_parse() {
        let data = load_test_sgf().unwrap();
        let gametrees = parse(&data).unwrap();
        let text = serialize(&gametrees);
        assert_eq!(gametrees, parse(&text).unwrap());
    }

    #[test]
    fn invalid_property() {
        let input = "(;GM[1]W[rp.pmonpoqprpsornqmpm])";
        let sgf_nodes = go::parse(input).unwrap();
        let expected = vec![
            go::Prop::GM(1),
            go::Prop::Invalid("W".to_string(), vec!["rp.pmonpoqprpsornqmpm".to_string()]),
        ];

        assert_eq!(sgf_nodes.len(), 1);
        let sgf_node = &sgf_nodes[0];
        assert_eq!(sgf_node.properties().cloned().collect::<Vec<_>>(), expected);
    }

    #[test]
    fn unknown_game() {
        let input = "(;GM[37]W[rp.pmonpoqprpsornqmpm])";
        let gametrees = parse(input).unwrap();
        assert_eq!(gametrees.len(), 1);
        assert_eq!(gametrees[0].gametype(), GameType::Unknown);
        let sgf_node = match &gametrees[0] {
            GameTree::Unknown(node) => node,
            _ => panic!("Unexpected game type"),
        };
        let expected = vec![
            unknown_game::Prop::GM(37),
            unknown_game::Prop::W("rp.pmonpoqprpsornqmpm".into()),
        ];

        assert_eq!(sgf_node.properties().cloned().collect::<Vec<_>>(), expected);
    }

    #[test]
    fn mixed_games() {
        let input = "(;GM[1];W[dd])(;GM[37]W[rp.pmonpoqprpsornqmpm])";
        let gametrees = parse(input).unwrap();
        assert_eq!(gametrees.len(), 2);
        assert_eq!(gametrees[0].gametype(), GameType::Go);
        assert_eq!(gametrees[1].gametype(), GameType::Unknown);
    }

    #[test]
    fn stack_overflow() {
        // This input generated a stack overflow with the old code
        let input = "(;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;)";
        let result = parse(&input);
        assert!(result.is_ok());
    }
}