use crate::lex::lex;
use crate::SyntaxKind;
use crate::SyntaxKind::*;
use rowan::ast::AstNode;
use std::str::FromStr;

#[derive(Debug)]
pub enum Error {
    Io(std::io::Error),
    Parse(ParseError),
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match &self {
            Error::Io(e) => write!(f, "IO error: {}", e),
            Error::Parse(e) => write!(f, "Parse error: {}", e),
        }
    }
}

impl From<std::io::Error> for Error {
    fn from(e: std::io::Error) -> Self {
        Error::Io(e)
    }
}

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

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct ParseError(Vec<String>);

impl std::fmt::Display for ParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        for err in &self.0 {
            writeln!(f, "{}", err)?;
        }
        Ok(())
    }
}

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

impl From<ParseError> for Error {
    fn from(e: ParseError) -> Self {
        Error::Parse(e)
    }
}

/// Second, implementing the `Language` trait teaches rowan to convert between
/// these two SyntaxKind types, allowing for a nicer SyntaxNode API where
/// "kinds" are values from our `enum SyntaxKind`, instead of plain u16 values.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Lang {}
impl rowan::Language for Lang {
    type Kind = SyntaxKind;
    fn kind_from_raw(raw: rowan::SyntaxKind) -> Self::Kind {
        unsafe { std::mem::transmute::<u16, SyntaxKind>(raw.0) }
    }
    fn kind_to_raw(kind: Self::Kind) -> rowan::SyntaxKind {
        kind.into()
    }
}

/// GreenNode is an immutable tree, which is cheap to change,
/// but doesn't contain offsets and parent pointers.
use rowan::GreenNode;

/// You can construct GreenNodes by hand, but a builder
/// is helpful for top-down parsers: it maintains a stack
/// of currently in-progress nodes
use rowan::GreenNodeBuilder;

/// The parse results are stored as a "green tree".
/// We'll discuss working with the results later
#[derive(Debug)]
struct Parse {
    green_node: GreenNode,
    #[allow(unused)]
    errors: Vec<String>,
}

fn parse(text: &str) -> Parse {
    struct Parser {
        /// input tokens, including whitespace,
        /// in *reverse* order.
        tokens: Vec<(SyntaxKind, String)>,
        /// the in-progress tree.
        builder: GreenNodeBuilder<'static>,
        /// the list of syntax errors we've accumulated
        /// so far.
        errors: Vec<String>,
    }

    impl Parser {
        fn error(&mut self, msg: String) {
            self.builder.start_node(ERROR.into());
            if self.current().is_some() {
                self.bump();
            }
            self.errors.push(msg);
            self.builder.finish_node();
        }

        fn parse_expr(&mut self) {
            self.builder.start_node(EXPR.into());
            loop {
                match self.current() {
                    Some(NEWLINE) => {
                        break;
                    }
                    Some(_t) => {
                        self.bump();
                    }
                    None => {
                        break;
                    }
                }
            }
            self.builder.finish_node();
        }

        fn parse_recipe_line(&mut self) {
            self.builder.start_node(RECIPE.into());
            self.expect(INDENT);
            self.expect(TEXT);
            self.expect(NEWLINE);
            self.builder.finish_node();
        }

        fn parse_rule(&mut self) {
            self.builder.start_node(RULE.into());
            self.skip_ws();
            self.expect(IDENTIFIER);
            self.skip_ws();
            if self.tokens.pop().map(|(k, t)| (k, t)) == Some((OPERATOR, ":".to_string())) {
                self.builder.token(OPERATOR.into(), ":");
            } else {
                self.error("expected ':'".into());
            }
            self.skip_ws();
            self.parse_expr();
            self.expect(NEWLINE);
            loop {
                match self.current() {
                    Some(INDENT) => {
                        self.parse_recipe_line();
                    }
                    Some(NEWLINE) => {
                        self.bump();
                        break;
                    }
                    _ => {
                        break;
                    }
                }
            }
            self.builder.finish_node();
        }

        fn parse_assignment(&mut self) {
            self.builder.start_node(VARIABLE.into());
            self.skip_ws();
            self.expect(IDENTIFIER);
            self.skip_ws();
            self.expect(OPERATOR);
            self.skip_ws();
            self.parse_expr();
            self.expect(NEWLINE);
            self.builder.finish_node();
        }

        fn parse(mut self) -> Parse {
            self.builder.start_node(ROOT.into());
            loop {
                match self.find(|&&(k, _)| k == OPERATOR || k == NEWLINE || k == LPAREN) {
                    Some((OPERATOR, ":")) => {
                        self.parse_rule();
                    }
                    Some((OPERATOR, "?=")) | Some((OPERATOR, "=")) | Some((OPERATOR, ":=")) | Some((OPERATOR, "::=")) | Some((OPERATOR, ":::=")) | Some((OPERATOR, "+=")) | Some((OPERATOR, "!=")) => {
                        self.parse_assignment();
                    }
                    Some((NEWLINE, _)) => {
                        self.bump();
                    }
                    Some(_) | None => {
                        self.error(format!("unexpected token {:?}", self.current()));
                        if self.current().is_some() {
                            self.bump();
                        }
                    }
                }

                if self.current().is_none() {
                    break;
                }
            }
            // Close the root node.
            self.builder.finish_node();

            // Turn the builder into a GreenNode
            Parse {
                green_node: self.builder.finish(),
                errors: self.errors,
            }
        }
        /// Advance one token, adding it to the current branch of the tree builder.
        fn bump(&mut self) {
            let (kind, text) = self.tokens.pop().unwrap();
            self.builder.token(kind.into(), text.as_str());
        }
        /// Peek at the first unprocessed token
        fn current(&self) -> Option<SyntaxKind> {
            self.tokens.last().map(|(kind, _)| *kind)
        }

        fn find(&self, finder: impl FnMut(&&(SyntaxKind, String)) -> bool) -> Option<(SyntaxKind, &str)> {
            self.tokens.iter().rev().find(finder).map(|(kind, text)| (*kind, text.as_str()))
        }

        fn expect(&mut self, expected: SyntaxKind) {
            if self.current() != Some(expected) {
                self.error(format!("expected {:?}, got {:?}", expected, self.current()));
            } else {
                self.bump();
            }
        }
        fn skip_ws(&mut self) {
            while self.current() == Some(WHITESPACE) {
                self.bump()
            }
        }
    }

    let mut tokens = lex(text);
    tokens.reverse();
    Parser {
        tokens,
        builder: GreenNodeBuilder::new(),
        errors: Vec::new(),
    }
    .parse()
}

/// To work with the parse results we need a view into the
/// green tree - the Syntax tree.
/// It is also immutable, like a GreenNode,
/// but it contains parent pointers, offsets, and
/// has identity semantics.

type SyntaxNode = rowan::SyntaxNode<Lang>;
#[allow(unused)]
type SyntaxToken = rowan::SyntaxToken<Lang>;
#[allow(unused)]
type SyntaxElement = rowan::NodeOrToken<SyntaxNode, SyntaxToken>;

impl Parse {
    fn syntax(&self) -> SyntaxNode {
        SyntaxNode::new_root(self.green_node.clone())
    }

    fn root(&self) -> Makefile {
        Makefile::cast(self.syntax()).unwrap()
    }
}

macro_rules! ast_node {
    ($ast:ident, $kind:ident) => {
        #[derive(PartialEq, Eq, Hash)]
        #[repr(transparent)]
        pub struct $ast(SyntaxNode);

        impl AstNode for $ast {
            type Language = Lang;

            fn can_cast(kind: SyntaxKind) -> bool {
                kind == $kind
            }

            fn cast(syntax: SyntaxNode) -> Option<Self> {
                if Self::can_cast(syntax.kind()) {
                    Some(Self(syntax))
                } else {
                    None
                }
            }

            fn syntax(&self) -> &SyntaxNode {
                &self.0
            }
        }

        impl ToString for $ast {
            fn to_string(&self) -> String {
                self.0.text().to_string()
            }
        }
    };
}

ast_node!(Makefile, ROOT);
ast_node!(Rule, RULE);
ast_node!(Identifier, IDENTIFIER);
ast_node!(VariableDefinition, VARIABLE);

impl VariableDefinition {
    pub fn name(&self) -> Option<String> {
        self.syntax().children_with_tokens().find_map(|it| it.as_token().and_then(|it| {
            if it.kind() == IDENTIFIER {
                Some(it.text().to_string())
            } else {
                None
            }
        }))
    }

    pub fn raw_value(&self) -> Option<String> {
        self.syntax().children().find(|it| it.kind() == EXPR).map(|it| it.text().to_string())
    }
}

impl Makefile {
    pub fn new() -> Makefile {
        let mut builder = GreenNodeBuilder::new();

        builder.start_node(ROOT.into());
        builder.finish_node();

        let syntax = SyntaxNode::new_root(builder.finish());
        Makefile(syntax.clone_for_update())
    }

    /// Read a changelog file from a reader
    pub fn read<R: std::io::Read>(mut r: R) -> Result<Makefile, Error> {
        let mut buf = String::new();
        r.read_to_string(&mut buf)?;
        Ok(buf.parse()?)
    }

    pub fn read_relaxed<R: std::io::Read>(mut r: R) -> Result<Makefile, Error> {
        let mut buf = String::new();
        r.read_to_string(&mut buf)?;

        let parsed = parse(&buf);
        Ok(parsed.root().clone_for_update())
    }

    pub fn rules(&self) -> impl Iterator<Item = Rule> {
        self.syntax()
            .children()
            .filter_map(Rule::cast)
    }

    pub fn variable_definitions(&self) -> impl Iterator<Item = VariableDefinition> {
        self.syntax()
            .children()
            .filter_map(VariableDefinition::cast)
    }

    pub fn add_rule(&mut self, target: &str) -> Rule {
        let mut builder = GreenNodeBuilder::new();
        builder.start_node(RULE.into());
        builder.token(IDENTIFIER.into(), target);
        builder.token(OPERATOR.into(), ":");
        builder.token(NEWLINE.into(), "\n");
        builder.finish_node();

        let syntax = SyntaxNode::new_root(builder.finish()).clone_for_update();
        let pos = self.0.children().count();
        self.0.splice_children(pos..pos, vec![syntax.clone().into()]);
        Rule(syntax)
    }
}

impl Rule {
    pub fn targets(&self) -> impl Iterator<Item = String> {
        self.syntax()
            .children_with_tokens()
            .take_while(|it| it.as_token().map_or(true, |t| t.kind() != OPERATOR))
            .filter_map(|it| it.as_token().map(|t| t.text().to_string()))
    }

    pub fn prerequisites(&self) -> impl Iterator<Item = String> {
        self.syntax()
            .children()
            .find(|it| it.kind() == EXPR)
            .into_iter().flat_map(|it| it.children_with_tokens().filter_map(|it| it.as_token().and_then(|t| if t.kind() == IDENTIFIER { Some(t.text().to_string()) } else { None })))
    }
}

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

impl FromStr for Makefile {
    type Err = ParseError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let parsed = parse(s);
        if parsed.errors.is_empty() {
            Ok(parsed.root().clone_for_update())
        } else {
            Err(ParseError(parsed.errors))
        }
    }
}

#[test]
fn test_parse_simple() {
    const SIMPLE: &str = r#"VARIABLE = value

rule: dependency
	command
"#;
    let parsed = parse(SIMPLE);
    assert_eq!(parsed.errors, Vec::<String>::new());
    let node = parsed.syntax();
    assert_eq!(
        format!("{:#?}", node),
        r#"ROOT@0..44
  VARIABLE@0..17
    IDENTIFIER@0..8 "VARIABLE"
    WHITESPACE@8..9 " "
    OPERATOR@9..10 "="
    WHITESPACE@10..11 " "
    EXPR@11..16
      IDENTIFIER@11..16 "value"
    NEWLINE@16..17 "\n"
  NEWLINE@17..18 "\n"
  RULE@18..44
    IDENTIFIER@18..22 "rule"
    OPERATOR@22..23 ":"
    WHITESPACE@23..24 " "
    EXPR@24..34
      IDENTIFIER@24..34 "dependency"
    NEWLINE@34..35 "\n"
    RECIPE@35..44
      INDENT@35..36 "\t"
      TEXT@36..43 "command"
      NEWLINE@43..44 "\n"
"#
    );

    let root = parsed.root().clone_for_update();

    let mut rules = root.rules().collect::<Vec<_>>();
    assert_eq!(rules.len(), 1);
    let rule = rules.pop().unwrap();
    assert_eq!(rule.targets().collect::<Vec<_>>(), vec!["rule"]);
    assert_eq!(rule.prerequisites().collect::<Vec<_>>(), vec!["dependency"]);

    let mut variables = root.variable_definitions().collect::<Vec<_>>();
    assert_eq!(variables.len(), 1);
    let variable = variables.pop().unwrap();
    assert_eq!(variable.name(), Some("VARIABLE".to_string()));
    assert_eq!(variable.raw_value(), Some("value".to_string()));
}

#[test]
fn test_parse_multiple_prerequisites() {
    const MULTIPLE_PREREQUISITES: &str = r#"rule: dependency1 dependency2
	command

"#;
    let parsed = parse(MULTIPLE_PREREQUISITES);
    assert_eq!(parsed.errors, Vec::<String>::new());
    let node = parsed.syntax();
    assert_eq!(
        format!("{:#?}", node),
        r#"ROOT@0..40
  RULE@0..40
    IDENTIFIER@0..4 "rule"
    OPERATOR@4..5 ":"
    WHITESPACE@5..6 " "
    EXPR@6..29
      IDENTIFIER@6..17 "dependency1"
      WHITESPACE@17..18 " "
      IDENTIFIER@18..29 "dependency2"
    NEWLINE@29..30 "\n"
    RECIPE@30..39
      INDENT@30..31 "\t"
      TEXT@31..38 "command"
      NEWLINE@38..39 "\n"
    NEWLINE@39..40 "\n"
"#);
    let root = parsed.root().clone_for_update();

    let rule = root.rules().next().unwrap();
    assert_eq!(rule.targets().collect::<Vec<_>>(), vec!["rule"]);
    assert_eq!(
        rule.prerequisites().collect::<Vec<_>>(),
        vec!["dependency1", "dependency2"]
    );
}

#[test]
fn test_add_rule() {
    let mut makefile = Makefile::new();
    let rule = makefile.add_rule("rule");
    assert_eq!(rule.targets().collect::<Vec<_>>(), vec!["rule"]);
    assert_eq!(rule.prerequisites().collect::<Vec<_>>(), Vec::<String>::new());

    assert_eq!(makefile.to_string(), "rule:\n");
}