use core::{
    error::Error,
    fmt::{self, Display},
};

use alloc::vec::Vec;

use crate::{
    bytecode::Chunk,
    value::Value,
    vm::{Exception, FnArgs, Vm},
};

pub type SystemFn = fn(&mut Vm, FnArgs) -> Result<Value, Exception>;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ChunkId(u32);

#[derive(Debug, Clone)]
pub struct System {
    /// Resolves a system function name to an index into `fn`s.
    pub resolve_fn: fn(&str) -> Option<u8>,
    pub fns: [Option<SystemFn>; 256],
    pub chunks: Vec<Chunk>,
}

#[derive(Debug, Clone, Copy)]
pub struct SystemImage {
    chunks: usize,
}

macro_rules! def_fns {
    ($($index:tt $name:tt => $fnref:expr),* $(,)?) => {
        pub(crate) fn init_fns(system: &mut System) {
            $(
                debug_assert!(system.fns[$index].is_none());
                system.fns[$index] = Some($fnref);
            )*
        }

        pub(crate) fn resolve(name: &str) -> Option<u8> {
            match name {
                $($name => Some($index),)*
                _ => None,
            }
        }
    };
}

impl System {
    pub fn new(max_chunks: usize) -> Self {
        assert!(max_chunks < u32::MAX as usize);

        let mut system = Self {
            resolve_fn: Self::resolve,
            fns: [None; 256],
            chunks: Vec::with_capacity(max_chunks),
        };
        Self::init_fns(&mut system);
        system
    }

    pub fn add_chunk(&mut self, chunk: Chunk) -> Result<ChunkId, ChunkError> {
        if self.chunks.len() >= self.chunks.capacity() {
            return Err(ChunkError);
        }

        let id = ChunkId(self.chunks.len() as u32);
        self.chunks.push(chunk);
        Ok(id)
    }

    pub fn chunk(&self, id: ChunkId) -> &Chunk {
        &self.chunks[id.0 as usize]
    }

    pub fn image(&self) -> SystemImage {
        SystemImage {
            chunks: self.chunks.len(),
        }
    }

    pub fn restore_image(&mut self, image: &SystemImage) {
        self.chunks.resize_with(image.chunks, || {
            panic!("image must be a subset of the current system")
        });
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct ChunkError;

impl Display for ChunkError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("too many chunks")
    }
}

impl Error for ChunkError {}

pub mod fns {
    use alloc::vec::Vec;

    use crate::{
        value::{Fill, List, Ref, Rgba, Scribble, Shape, Stroke, Value, Vec2, Vec4},
        vm::{Exception, FnArgs, Vm},
    };

    use super::System;

    impl System {
        def_fns! {
            0x00 "+" => add,
            0x01 "-" => sub,
            0x02 "*" => mul,
            0x03 "/" => div,

            0x40 "not" => not,
            0x41 "=" => eq,
            0x42 "<>" => neq,
            0x43 "<" => lt,
            0x44 "<=" => leq,
            0x45 ">" => gt,
            0x46 ">=" => geq,

            0x80 "vec" => vec,
            0x81 ".x" => vec_x,
            0x82 ".y" => vec_y,
            0x83 ".z" => vec_z,
            0x84 ".w" => vec_w,

            0x85 "rgba" => rgba,
            0x86 ".r" => rgba_r,
            0x87 ".g" => rgba_g,
            0x88 ".b" => rgba_b,
            0x89 ".a" => rgba_a,

            0x90 "list" => list,

            0xc0 "to-shape" => to_shape_f,
            0xc1 "line" => line,
            0xc2 "rect" => rect,
            0xc3 "circle" => circle,
            0xe0 "stroke" => stroke,
            0xe1 "fill" => fill,
        }
    }

    pub fn add(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        let mut result = 0.0;
        for i in 0..args.num() {
            result += args.get_number(vm, i, "arguments to (+) must be numbers")?;
        }
        Ok(Value::Number(result))
    }

    pub fn sub(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() < 1 {
            return Err(vm.create_exception("(-) requires at least one argument to subtract from"));
        }

        static ERROR: &str = "arguments to (-) must be numbers";

        if args.num() == 1 {
            Ok(Value::Number(-args.get_number(vm, 0, ERROR)?))
        } else {
            let mut result = args.get_number(vm, 0, ERROR)?;
            for i in 1..args.num() {
                result -= args.get_number(vm, i, ERROR)?;
            }

            Ok(Value::Number(result))
        }
    }

    pub fn mul(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        let mut result = 1.0;
        for i in 0..args.num() {
            result *= args.get_number(vm, i, "arguments to (*) must be numbers")?;
        }

        Ok(Value::Number(result))
    }

    pub fn div(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() < 1 {
            return Err(vm.create_exception("(/) requires at least one argument to divide"));
        }

        static ERROR: &str = "arguments to (/) must be numbers";
        let mut result = args.get_number(vm, 0, ERROR)?;
        for i in 1..args.num() {
            result /= args.get_number(vm, i, ERROR)?;
        }

        Ok(Value::Number(result))
    }

    pub fn not(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(not) expects a single argument to negate"));
        }

        let value = args.get(vm, 0);
        Ok(Value::from(value.is_falsy()))
    }

    pub fn eq(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(=) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a == b))
    }

    pub fn neq(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(<>) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a != b))
    }

    pub fn lt(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(<) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a < b))
    }

    pub fn leq(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(<=) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a <= b))
    }

    pub fn gt(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(>) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a > b))
    }

    pub fn geq(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(>=) expects two arguments to compare"));
        }

        let a = args.get(vm, 0);
        let b = args.get(vm, 1);
        Ok(Value::from(a >= b))
    }

    pub fn vec(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        static ERROR: &str = "arguments to (vec) must be numbers (vec x y z w)";
        match args.num() {
            0 => Ok(Value::Vec4(Vec4 {
                x: 0.0,
                y: 0.0,
                z: 0.0,
                w: 0.0,
            })),
            1 => {
                let x = args.get_number(vm, 0, ERROR)?;
                Ok(Value::Vec4(Vec4 {
                    x,
                    y: 0.0,
                    z: 0.0,
                    w: 0.0,
                }))
            }
            2 => {
                let x = args.get_number(vm, 0, ERROR)?;
                let y = args.get_number(vm, 1, ERROR)?;
                Ok(Value::Vec4(Vec4 {
                    x,
                    y,
                    z: 0.0,
                    w: 0.0,
                }))
            }
            3 => {
                let x = args.get_number(vm, 0, ERROR)?;
                let y = args.get_number(vm, 1, ERROR)?;
                let z = args.get_number(vm, 2, ERROR)?;
                Ok(Value::Vec4(Vec4 { x, y, z, w: 0.0 }))
            }
            4 => {
                let x = args.get_number(vm, 0, ERROR)?;
                let y = args.get_number(vm, 1, ERROR)?;
                let z = args.get_number(vm, 2, ERROR)?;
                let w = args.get_number(vm, 3, ERROR)?;
                Ok(Value::Vec4(Vec4 { x, y, z, w }))
            }
            _ => Err(vm.create_exception("(vec) expects 0-4 arguments (vec x y z w)")),
        }
    }

    pub fn vec_x(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.x) expects a single argument (.x vec)"));
        }

        let vec = args.get_vec4(vm, 0, "argument to (.x vec) must be a (vec)")?;
        Ok(Value::Number(vec.x))
    }

    pub fn vec_y(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.y) expects a single argument (.y vec)"));
        }

        let vec = args.get_vec4(vm, 0, "argument to (.y vec) must be a (vec)")?;
        Ok(Value::Number(vec.y))
    }

    pub fn vec_z(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.z) expects a single argument (.z vec)"));
        }

        let vec = args.get_vec4(vm, 0, "argument to (.z vec) must be a (vec)")?;
        Ok(Value::Number(vec.z))
    }

    pub fn vec_w(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.w) expects a single argument (.w vec)"));
        }

        let vec = args.get_vec4(vm, 0, "argument to (.w vec) must be a (vec)")?;
        Ok(Value::Number(vec.w))
    }

    pub fn rgba(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 4 {
            return Err(vm.create_exception("(rgba) expects four arguments (rgba r g b a)"));
        }

        static ERROR: &str = "arguments to (rgba r g b a) must be numbers";
        let r = args.get_number(vm, 0, ERROR)?;
        let g = args.get_number(vm, 1, ERROR)?;
        let b = args.get_number(vm, 2, ERROR)?;
        let a = args.get_number(vm, 3, ERROR)?;

        Ok(Value::Rgba(Rgba { r, g, b, a }))
    }

    pub fn rgba_r(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.r) expects a single argument (.r rgba)"));
        }

        let rgba = args.get_rgba(vm, 0, "argument to (.r rgba) must be an (rgba)")?;
        Ok(Value::Number(rgba.r))
    }

    pub fn rgba_g(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.g) expects a single argument (.g rgba)"));
        }

        let rgba = args.get_rgba(vm, 0, "argument to (.g rgba) must be an (rgba)")?;
        Ok(Value::Number(rgba.g))
    }

    pub fn rgba_b(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.b) expects a single argument (.b rgba)"));
        }

        let rgba = args.get_rgba(vm, 0, "argument to (.b rgba) must be an (rgba)")?;
        Ok(Value::Number(rgba.r))
    }

    pub fn rgba_a(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(.a) expects a single argument (.a rgba)"));
        }

        let rgba = args.get_rgba(vm, 0, "argument to (.a rgba) must be an (rgba)")?;
        Ok(Value::Number(rgba.r))
    }

    pub fn list(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        let elements: Vec<_> = (0..args.num()).map(|i| args.get(vm, i)).collect();
        vm.track_array(&elements)?;
        let id = vm.create_ref(Ref::List(List { elements }))?;
        Ok(Value::Ref(id))
    }

    fn to_shape(value: Value, vm: &Vm) -> Option<Shape> {
        match value {
            Value::Nil | Value::False | Value::True | Value::Number(_) | Value::Rgba(_) => None,
            Value::Ref(id) => {
                if let Ref::Shape(shape) = vm.get_ref(id) {
                    Some(shape.clone())
                } else {
                    None
                }
            }
            Value::Vec4(vec) => Some(Shape::Point(vec.into())),
        }
    }

    pub fn to_shape_f(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 1 {
            return Err(vm.create_exception("(shape) expects 1 argument (shape value)"));
        }

        if let Some(shape) = to_shape(args.get(vm, 0), vm) {
            let id = vm.create_ref(Ref::Shape(shape))?;
            Ok(Value::Ref(id))
        } else {
            Ok(Value::Nil)
        }
    }

    pub fn line(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(line) expects 2 arguments (line start end)"));
        }

        static ERROR: &str = "arguments to (line) must be (vec)";
        let start = args.get_vec4(vm, 0, ERROR)?;
        let end = args.get_vec4(vm, 1, ERROR)?;

        let id = vm.create_ref(Ref::Shape(Shape::Line(start.into(), end.into())))?;
        Ok(Value::Ref(id))
    }

    pub fn rect(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        static ARGS2: &str = "arguments to 2-argument (rect) must be (vec)";
        static ARGS4: &str = "arguments to 4-argument (rect) must be numbers";

        let (position, size) = match args.num() {
            2 => (args.get_vec4(vm, 0, ARGS2)?.into(), args.get_vec4(vm, 1, ARGS2)?.into()),
            4 => (
                Vec2 {
                    x: args.get_number(vm, 0, ARGS4)?,
                    y: args.get_number(vm, 1, ARGS4)?,
                },
                Vec2 {
                    x: args.get_number(vm, 2, ARGS4)?,
                    y: args.get_number(vm, 3, ARGS4)?,
                },
            ),
            _ => return Err(vm.create_exception("(rect) expects 2 arguments (rect position size) or 4 arguments (rect x y width height)"))
        };

        let id = vm.create_ref(Ref::Shape(Shape::Rect(position, size)))?;
        Ok(Value::Ref(id))
    }

    pub fn circle(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        static ARGS2: &str = "arguments to 2-argument (circle) must be (vec) and a number";
        static ARGS3: &str = "arguments to 3-argument (circle) must be numbers";

        let (position, radius) = match args.num() {
            2 => (args.get_vec4(vm, 0, ARGS2)?.into(), args.get_number(vm, 1, ARGS2)?),
            3 => (
                Vec2 {
                    x: args.get_number(vm, 0, ARGS3)?,
                    y: args.get_number(vm, 1, ARGS3)?,
                },
                args.get_number(vm, 2, ARGS3)?
            ),
            _ => return Err(vm.create_exception("(circle) expects 2 arguments (circle position radius) or 3 arguments (circle x y radius)"))
        };

        let id = vm.create_ref(Ref::Shape(Shape::Circle(position, radius)))?;
        Ok(Value::Ref(id))
    }

    pub fn stroke(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 3 {
            return Err(
                vm.create_exception("(stroke) expects 3 arguments (stroke thickness color shape)")
            );
        }

        let thickness = args.get_number(
            vm,
            0,
            "1st argument to (stroke) must be a thickness in pixels (number)",
        )?;
        let color = args.get_rgba(vm, 1, "2nd argument to (stroke) must be a color (rgba)")?;
        if let Some(shape) = to_shape(args.get(vm, 2), vm) {
            let id = vm.create_ref(Ref::Scribble(Scribble::Stroke(Stroke {
                thickness,
                color,
                shape,
            })))?;
            Ok(Value::Ref(id))
        } else {
            Ok(Value::Nil)
        }
    }

    pub fn fill(vm: &mut Vm, args: FnArgs) -> Result<Value, Exception> {
        if args.num() != 2 {
            return Err(vm.create_exception("(fill) expects 2 arguments (fill color shape)"));
        }

        let color = args.get_rgba(vm, 0, "1st argument to (fill) must be a color (rgba)")?;
        if let Some(shape) = to_shape(args.get(vm, 1), vm) {
            let id = vm.create_ref(Ref::Scribble(Scribble::Fill(Fill { color, shape })))?;
            Ok(Value::Ref(id))
        } else {
            Ok(Value::Nil)
        }
    }
}