use std::fmt;

pub type Name = string_interner::DefaultSymbol;

pub struct ASTArena {
    strings: string_interner::StringInterner,
}

pub struct Debuggable<'a, T> {
    arena: &'a ASTArena,
    value: &'a T,
}

impl<'a> std::fmt::Debug for Debuggable<'a, Stmt> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.arena.show_stmt(self.value, f)
    }
}

impl ASTArena {
    pub fn new() -> ASTArena {
        ASTArena {
            strings: string_interner::StringInterner::new(),
        }
    }

    pub fn add_string(&mut self, s: &str) -> Name {
        self.strings.get_or_intern(s)
    }

    pub fn show_stmt(&self, stmt: &Stmt, f: &mut fmt::Formatter) -> fmt::Result {
        match stmt {
            Stmt::Puts(expr) => {
                write!(f, "Puts ")?;
                self.show_expr(&expr, f, 0)
            }
            Stmt::Fix(name) =>
                writeln!(f, "Fix({})", &self[*name]),
            Stmt::Assn(name, expr) => {
                write!(f, "Assn {} ", &self[*name])?;
                self.show_expr(&expr, f, 0)
            }
            Stmt::LitAssn(name, strs) => {
                write!(f, "LitAssn({}, [ ", &self[*name])?;
                for str in strs.iter() {
                    write!(f, " {} ", str)?;
                }
                writeln!(f, "]")
            }
        }
    }

    fn indent(&self, f: &mut fmt::Formatter, depth: usize) -> fmt::Result {
        for _ in 0..depth {
            write!(f, " ")?;
        }
        Ok(())
    }

    fn show_expr(&self, expr: &Expr, f: &mut fmt::Formatter, depth: usize) -> fmt::Result {
        match expr {
            Expr::Var(v) => writeln!(f, "Var({})", &self[*v]),
            Expr::Lit(Literal::Atom(n)) => writeln!(f, "Lit(Atom({}))", &self[*n]),
            Expr::Lit(lit) => writeln!(f, "{:?}", lit),
            Expr::Range(from, to) => {
                writeln!(f, "Range(")?;
                self.indent(f, depth + 2)?;
                self.show_expr(from, f, depth + 2)?;
                self.indent(f, depth + 2)?;
                self.show_expr(to, f, depth + 2)?;
                self.indent(f, depth)?;
                writeln!(f, ")")
            }

            Expr::Ap(func, arg) => {
                writeln!(f, "Ap(")?;
                self.indent(f, depth + 2)?;
                self.show_expr(func, f, depth + 2)?;
                self.indent(f, depth + 2)?;
                self.show_expr(arg, f, depth + 2)?;
                self.indent(f, depth)?;
                writeln!(f, ")")
            }

            Expr::Tup(expr) => {
                writeln!(f, "Tup(")?;
                for e in expr {
                    self.indent(f, depth + 2)?;
                    self.show_expr(e, f, depth + 2)?;
                }
                self.indent(f, depth)?;
                writeln!(f, ")")
            }

            Expr::Cat(expr) => {
                writeln!(f, "Cat(")?;
                for e in expr {
                    self.indent(f, depth + 2)?;
                    self.show_expr(e, f, depth + 2)?;
                }
                self.indent(f, depth)?;
                writeln!(f, ")")
            }

            Expr::Chc(expr) => {
                writeln!(f, "Chc(")?;
                for e in expr {
                    if let Some(s) = e.weight {
                        self.indent(f, depth + 2)?;
                        writeln!(f, "{}:", s)?;
                        self.indent(f, depth + 4)?;
                        self.show_expr(&e.value, f, depth + 4)?;
                    } else {
                        self.indent(f, depth + 2)?;
                        self.show_expr(&e.value, f, depth + 2)?;
                    }
                }
                self.indent(f, depth)?;
                writeln!(f, ")")
            }
            _ => writeln!(f, "[???]"),
        }
    }
}

impl std::ops::Index<string_interner::DefaultSymbol> for ASTArena {
    type Output = str;

    fn index(&self, sf: string_interner::DefaultSymbol) -> &str {
        self.strings.resolve(sf).unwrap()
    }
}

#[derive(Debug, Clone)]
pub enum Stmt {
    Puts(Expr),
    Fix(Name),
    Assn(Name, Expr),
    LitAssn(Name, Vec<String>),
}

impl Stmt {
    pub fn show<'a>(&'a self, ast: &'a ASTArena) -> Debuggable<'a, Stmt> {
        Debuggable {
            arena: ast,
            value: self,
        }
    }
}

#[derive(Debug, Clone)]
pub enum Expr {
    Var(Name),
    Cat(Vec<Expr>),
    Chc(Vec<Choice>),
    Rep(i64, Box<Expr>),
    Lit(Literal),
    Ap(Box<Expr>, Box<Expr>),
    Tup(Vec<Expr>),
    Let(Name, Box<Expr>, Box<Expr>),
    Fun(Vec<Case>),
    Case(Box<Expr>, Vec<Case>),
    Range(Box<Expr>, Box<Expr>),
}

#[derive(Debug, Clone)]
pub struct Case {
    pub pat: Pat,
    pub expr: Expr,
}

#[derive(Debug, Clone)]
pub enum Pat {
    Var(Name),
    Lit(Literal),
    Tup(Vec<Pat>),
}

#[derive(Debug, Clone)]
pub struct Choice {
    pub weight: Option<i64>,
    pub value: Expr,
}

impl Choice {
    pub fn weight(&self) -> i64 {
        self.weight.unwrap_or(1)
    }
}

#[derive(Debug, Clone)]
pub enum Literal {
    Str(String),
    Atom(Name),
    Num(i64),
}