//! Hatter comes with a few built-in functions to help make your life
//! easier, all defined in this module.

// Each built-in Hatter functions comes in one of two flavors of
// function: `Native` or `Special`. A `Native` function is a regular
// function that takes an `Args` struct and returns a
// `Result<Value>`, but `Special` is more like a macro (or fexpr):
// its arguments are not evaluated, but instead passed to the
// function as syntax. The scope of the caller is also passed to the
// special function. This means the function can then decide how,
// when, and if to evaluate arguments or not. We use this to
// implement short circuiting in `&&` and `||`, but it could have
// other applications, too.

use {
    crate::{Args, Env, Native, Result, Special, Stmt, Symbol, Value},
    std::{collections::HashMap, rc::Rc},
};

/// Return the builtin Special functions that come with Hatter.
/// Ideally we build this at compile time, at least in release mode,
/// instead of creating them all at runtime.
pub(crate) fn specials() -> HashMap<String, Rc<Special>> {
    let mut map: HashMap<String, Rc<Special>> = HashMap::new();

    map.insert("&&".into(), rc!(and));
    map.insert("||".into(), rc!(or));

    map
}

/// Return the builtin Native functions that come with Hatter.
pub(crate) fn natives() -> HashMap<String, Rc<Native>> {
    let mut map: HashMap<String, Rc<Native>> = HashMap::new();

    macro_rules! native {
        ($name:expr => $fn:expr) => {
            map.insert($name.to_string(), rc!($fn));
        };
    }

    native!("type" => r#type);
    native!("when" => when);
    native!("==" => eq);
    native!("!=" => neq);
    native!("not" => not);
    native!("!" => not);
    native!("concat" => concat);
    native!("index" => index);
    native!("set_index" => set_index);
    native!("<<" => push);
    native!("push" => push);
    native!("pop" => pop);
    native!("." => index);
    native!(".." => range);
    native!("..=" => range_inclusive);
    native!("+" => add);
    native!("-" => sub);
    native!("*" => mul);
    native!("/" => div);
    native!("%" => r#mod);
    native!(">" => gt);
    native!(">=" => gte);
    native!("<" => lt);
    native!("<=" => lte);
    native!("print" => print);
    native!("puts" => puts);
    native!("to-uppercase" => to_uppercase);
    native!("to-lowercase" => to_lowercase);
    native!("replace" => replace);
    native!("contains?" => contains_);
    native!("split" => split);
    native!("count" => count);
    native!("len" => len);
    native!("empty?" => empty_);

    map
}

//////////////////////////////////////////////////////////////////////
// Internal Functions

/// Combine several Values into a String.
/// Used internally by String interpolation.
///
/// `concat("hi", "-", 23) #=> "hi-23"`
pub fn concat(args: Args) -> Result<Value> {
    let mut sum = String::new();
    for arg in args {
        sum.push_str(&arg.to_string());
    }
    Ok(sum.into())
}

/// Returns a Value if a condition is true.
/// Used internally by tag attributes.
///
/// ```ignore
/// when(true, "yep")   #=> "yep"
/// when(false, "nope") #=> None
/// ```
pub fn when(args: Args) -> Result<Value> {
    let fst = args.need(0)?;
    if matches!(fst, Value::None | Value::Bool(false)) {
        Ok(Value::None)
    } else {
        Ok(args.need(1)?)
    }
}

/// Returns the String name of a Value's type.
///
/// ```ignore
/// type('heyo')  #=> "String"
/// type(123)     #=> "Number"
/// ```
pub fn r#type(args: Args) -> Result<Value> {
    Value::String(args.need(0)?.typename().into()).ok()
}

//////////////////////////////////////////////////////////////////////
// Boolean Operators

/// Special: Short-circuiting `&&` operator.
pub fn and(env: &mut Env, args: &[Stmt]) -> Result<Value> {
    if args.len() != 2 {
        return error!("Expected 2 args, got {}", 2);
    }
    Ok((env.eval(&args[0])?.to_bool() && env.eval(&args[1])?.to_bool()).into())
}

/// Special: Short-circuiting `||` operator.
pub fn or(env: &mut Env, args: &[Stmt]) -> Result<Value> {
    if args.len() != 2 {
        return error!("Expected 2 args, got {}", 2);
    }
    Ok((env.eval(&args[0])?.to_bool() || env.eval(&args[1])?.to_bool()).into())
}

/// `==` operator: check if two Values are equal.
pub fn eq(args: Args) -> Result<Value> {
    if let Some(val) = args.get(0) {
        match val {
            Value::None => matches!(args.get(1), Some(Value::None)),
            Value::Bool(b1) => match args.get(1) {
                Some(Value::Bool(b2)) => b1 == b2,
                _ => false,
            },
            Value::Number(n1) => match args.get(1) {
                Some(Value::Number(n2)) => n1 == n2,
                _ => false,
            },
            Value::String(s1) => match args.get(1) {
                Some(Value::String(s2)) => s1 == s2,
                _ => false,
            },
            _ => false,
        }
        .into()
    } else {
        Value::None
    }
    .ok()
}

/// `!=` operator: check if two Values are not equal.
pub fn neq(args: Args) -> Result<Value> {
    Value::Bool(match eq(args)? {
        Value::Bool(b) => !b,
        _ => false,
    })
    .ok()
}

/// `!` operator: return the opposite Bool of a Value
pub fn not(args: Args) -> Result<Value> {
    if let Some(val) = args.get(0) {
        match val {
            Value::None | Value::Bool(false) => Value::Bool(true),
            _ => Value::Bool(false),
        }
    } else {
        Value::None
    }
    .ok()
}

/// `>` operator: check if a number is greater than another.
pub fn gt(args: Args) -> Result<Value> {
    Value::Bool(args.need_number(0)? > args.need_number(1)?).ok()
}

/// `>=` operator: check if a number is greater than or equal to another.
pub fn gte(args: Args) -> Result<Value> {
    Value::Bool(args.need_number(0)? >= args.need_number(1)?).ok()
}

/// `<` operator: check if a number is less than another.
pub fn lt(args: Args) -> Result<Value> {
    Value::Bool(args.need_number(0)? < args.need_number(1)?).ok()
}

/// `<=` operator: check if a number is less than or equal to another.
pub fn lte(args: Args) -> Result<Value> {
    Value::Bool(args.need_number(0)? <= args.need_number(1)?).ok()
}

//////////////////////////////////////////////////////////////////////
// Math Functions

/// `+` operator: add two numbers.
pub fn add(args: Args) -> Result<Value> {
    if let Some(Value::Number(_)) = args.get(0) {
        let mut sum = 0.0;
        let mut iter = args.iter();
        while let Some(Value::Number(x)) = iter.next() {
            sum += x;
        }
        return Value::Number(sum).ok();
    } else if let Some(Value::String(_)) = args.get(0) {
        let mut sum = String::new();
        let mut iter = args.iter();
        while let Some(Value::String(x)) = iter.next() {
            sum += x;
        }
        return Value::String(sum.into()).ok();
    }
    Value::None.ok()
}

/// `-` operator: subtract one number from another.
pub fn sub(args: Args) -> Result<Value> {
    Value::Number(args.need_number(0)? - args.need_number(1)?).ok()
}

/// `*` operator: multiply two numbers.
pub fn mul(args: Args) -> Result<Value> {
    Value::Number(args.need_number(0)? * args.need_number(1)?).ok()
}

/// `/` operator: divide one number by another.
pub fn div(args: Args) -> Result<Value> {
    Value::Number(args.need_number(0)? / args.need_number(1)?).ok()
}

/// `%` operator: find the remainder of dividing one number by anohter.
pub fn r#mod(args: Args) -> Result<Value> {
    Value::Number(args.need_number(0)? % args.need_number(1)?).ok()
}

//////////////////////////////////////////////////////////////////////
// String Functions

/// Rust's `String::to_uppercase(&self)`
pub fn to_uppercase(args: Args) -> Result<Value> {
    Value::String(args.need_string(0)?.to_uppercase().into()).ok()
}

/// Rust's `String::to_lowercase(&self)`
pub fn to_lowercase(args: Args) -> Result<Value> {
    Value::String(args.need_string(0)?.to_lowercase().into()).ok()
}

/// Does the string contain a substring?
/// `contains?("Mr Rogers", "Mr") #=> true`
pub fn contains_(args: Args) -> Result<Value> {
    Value::Bool(args.need_string(0)?.contains(args.need_string(1)?)).ok()
}

/// Count occurences of substring in string.
/// `count("Mr Rogers", "r") #=> 2`
pub fn count(args: Args) -> Result<Value> {
    Value::from(args.need_string(0)?.matches(args.need_string(1)?).count()).ok()
}

/// Split a string into a List by a separator.
/// `split("Mr Rogers", " ")` #=> ["Mr", "Rogers"]`
pub fn split(args: Args) -> Result<Value> {
    Value::from(
        args.need_string(0)?
            .split(args.need_string(1)?)
            .collect::<Vec<_>>(),
    )
    .ok()
}

/// Find and replace all matches in a target string.
///
/// `replace("Mr Rogers", "Ro", "Dod") #=> "Mr Dodgers"`
pub fn replace(args: Args) -> Result<Value> {
    let s = args.need_string(0)?;
    let search = args.need_string(1)?;
    let replace = args.need_string(2)?;
    Value::String(s.replace(search, replace).into()).ok()
}

//////////////////////////////////////////////////////////////////////
// Container (Map, List, Object) Functions

/// `.` operator and `[]` operator
/// Look up a List item by number or a Map item by key.
/// Returns None or the Value.
pub fn index(args: Args) -> Result<Value> {
    if args.len() != 2 {
        return Value::None.ok();
    }
    let subject = args.need(0)?;

    match subject {
        Value::Map(map) => map
            .borrow()
            .get(Symbol::from(args.need_string(1)?))
            .unwrap_or(&Value::None)
            .clone(),
        Value::List(list) => {
            let mut idx = args.need_number(1)? as isize;
            if idx < 0 {
                let len = list.borrow().len();
                if (idx.abs() as usize) <= len {
                    idx += list.borrow().len() as isize;
                }
            }
            list.borrow()
                .get(idx as usize)
                .unwrap_or(&Value::None)
                .clone()
        }
        Value::Object(o) => o.get(args.need_string(1)?).unwrap_or(Value::None),
        _ => Value::None,
    }
    .ok()
}

/// Set a specific index in a List or Map.
/// If List, must be equal to or below the length.
///
/// ```ignore
/// a[1] = 2
/// map[key] = val
/// ```
fn set_index(args: Args) -> Result<Value> {
    match args.need(0)? {
        Value::Map(map) => {
            map.borrow_mut()
                .insert(Symbol::from(args.need_string(1)?), args.need(2)?.into());
        }
        Value::List(list) => {
            let mut idx = args.need_number(1)? as isize;
            if idx < 0 {
                let len = list.borrow().len();
                if (idx.abs() as usize) < len {
                    idx += list.borrow().len() as isize;
                }
            }
            let idx = idx as usize;
            if idx > list.borrow().len() {
                return Value::None.ok();
            }
            list.borrow_mut().insert(idx, args.need(2)?.into());
        }
        Value::Object(o) => {
            o.set(args.need_string(1)?, args.need(2)?);
        }
        _ => {}
    }
    Value::None.ok()
}

/// Get the length of a Map, List, or String. Returns 0 for all
/// other values.
///
/// ```ignore
/// len([])            #=> 0
/// len([5])           #=> 1
/// len('hi')          #=> 2
/// len({name:'Ra'})   #=> 1
/// ```
pub fn len(args: Args) -> Result<Value> {
    match args.need(0)? {
        Value::List(list) => list.borrow().len().into(),
        Value::Map(map) => map.borrow().len().into(),
        Value::String(s) => s.len().into(),
        _ => Value::Number(0.0),
    }
    .ok()
}

/// True if the length of a Map, List, or String is `0`.
///
/// ```ignore
/// empty?([])  #=> true
/// empty?([1]) #=> false
/// ```
pub fn empty_(args: Args) -> Result<Value> {
    Value::Bool(len(args)?.to_f64() == 0.0).ok()
}

//////////////////////////////////////////////////////////////////////
// List Functions

/// Add a Value to a List. Modifies the List.
///
/// ```ignore
/// a := 1..=3  #=> [1,2,3]
/// push(a, 4)
/// a           #=> [1,2,3,4]
/// ```
pub fn push(args: Args) -> Result<Value> {
    if let Value::List(list) = args.need(0)? {
        list.borrow_mut().push(args.need(1)?);
    }
    Value::None.ok()
}

/// Remove the last Value from a List. Modifies the List.
/// ```ignore
/// a := 1..=3  #=> [1,2,3]
/// pop(a)      #=> 3
/// len(a)      #=> 2
/// ```
pub fn pop(args: Args) -> Result<Value> {
    if let Value::List(list) = args.need(0)? {
        Value::from(list.borrow_mut().pop())
    } else {
        Value::None
    }
    .ok()
}

//////////////////////////////////////////////////////////////////////
// Range Functions

/// `..` operator
///
/// `1..5  #=> [1,2,3,4]`
pub fn range(args: Args) -> Result<Value> {
    let start = args.need_number(0)? as i32;
    let end = args.need_number(1)? as i32;
    Ok((start..end).collect::<Vec<_>>().into())
}

/// `..=` operator
///
/// `1..=5  #=> [1,2,3,4,5]`
pub fn range_inclusive(args: Args) -> Result<Value> {
    let start = args.need_number(0)? as i32;
    let end = args.need_number(1)? as i32;
    Ok((start..=end).collect::<Vec<_>>().into())
}

//////////////////////////////////////////////////////////////////////
// I/O Functions

/// Print one or more Values, without newline.
pub fn print(mut args: Args) -> Result<Value> {
    while !args.is_empty() {
        let arg = args.remove(0);
        if args.is_empty() {
            args.env.print(format!("{}", arg));
        } else {
            args.env.print(format!("{} ", arg));
        }
    }
    Value::None.ok()
}

/// Print one or more Values, wit newlines.
pub fn puts(mut args: Args) -> Result<Value> {
    while !args.is_empty() {
        let arg = args.remove(0);
        if args.is_empty() {
            args.env.print(format!("{}", arg));
        } else {
            args.env.print(format!("{} ", arg));
        }
    }
    args.env.print("\n");
    Value::None.ok()
}