use std::collections::BTreeMap;

use crate::builtin_cells::get_builtins;
use crate::parser;
use crate::rtlil;

fn make_pubid(id: &str) -> String {
    "\\".to_owned() + id
}

#[derive(Debug)]
pub enum CompileErrorKind {
    UndefinedReference(String),
    BadArgCount{received: usize, expected: usize},
}

#[derive(Debug)]
pub struct CompileError {
    kind: CompileErrorKind,
}

impl CompileError {
    fn new(kind: CompileErrorKind) -> Self {
        Self { kind }
    }
}

pub enum GenericParam<T> {
    Unsolved,
    Solved(T),
}

pub enum Type {
    /// a wire of some width
    Wire(GenericParam<u32>),
}

impl Type {
    pub fn wire() -> Self {
        Self::Wire(GenericParam::Unsolved)
    }
}

pub struct CallArgument {
    pub name: String,
    pub atype: Type,
}

// module that can be instantiated like a function
pub struct Callable {
    pub name: String,
    pub args: Vec<CallArgument>,
    pub ret: Type,
    pub instantiate: Box<dyn Fn(&str, &[String], &str) -> rtlil::Cell>,
}

struct Context {
    callables: BTreeMap<String, Callable>,
}

fn lower_expression(
    ctx: &Context,
    module: &mut rtlil::Module,
    expr: &parser::Expression,
) -> Result<String, CompileError> {
    match expr {
        parser::Expression::Ident(ident) => Ok(make_pubid(ident)),
        parser::Expression::Call(call) => {
            let output_gen_id = module.make_genid("cell");
            module.add_wire(rtlil::Wire::new(&output_gen_id, 1, None));

            let args_resolved = call
                .args
                .iter()
                .map(|expr| lower_expression(ctx, module, expr))
                .collect::<Result<Vec<_>, _>>()?;

            let callable = ctx
                .callables
                .get(call.name.fragment() as &str)
                .ok_or_else(|| {
                    CompileError::new(CompileErrorKind::UndefinedReference(
                        call.name.fragment().to_string(),
                    ))
                })?;

            if args_resolved.len() != callable.args.len() {
                return Err(CompileError::new(CompileErrorKind::BadArgCount{
                    expected: callable.args.len(), received: args_resolved.len()
                }))
            }

            let cell_id = module.make_genid(&callable.name);

            let cell = (*callable.instantiate)(&cell_id, args_resolved.as_slice(), &output_gen_id);
            module.add_cell(cell);
            Ok(output_gen_id)
        }
        parser::Expression::Operation(_op) => todo!(),
    }
}

fn lower_assignment(
    ctx: &Context,
    module: &mut rtlil::Module,
    assignment: parser::Assign,
) -> Result<(), CompileError> {
    let target_id = make_pubid(assignment.lhs);
    let return_wire = lower_expression(ctx, module, &assignment.expr)?;
    module.add_connection(target_id, return_wire);
    Ok(())
}

pub fn lower_module(pa_module: parser::Module) -> Result<String, CompileError> {
    let mut writer = rtlil::ILWriter::new();
    let mut ir_module = rtlil::Module::new(make_pubid(pa_module.name));
    let context = Context {
        callables: get_builtins()
            .into_iter()
            .map(|clb| (clb.name.to_owned(), clb))
            .collect(),
    };
    writer.write_line("autoidx 1");
    for (idx, port) in pa_module.ports.iter().enumerate() {
        let dir_option = match port.direction {
            parser::PortDirection::Input => rtlil::PortOption::Input(idx as i32 + 1),
            parser::PortDirection::Output => rtlil::PortOption::Output(idx as i32 + 1),
        };
        let wire = rtlil::Wire::new(
            make_pubid(port.net.name),
            port.net.width.unwrap_or(1) as u32,
            Some(dir_option),
        );
        ir_module.add_wire(wire);
    }
    for stmt in pa_module.statements {
        match stmt {
            parser::Statement::Assign(assignment) => {
                lower_assignment(&context, &mut ir_module, assignment)?
            }
        }
    }
    ir_module.write_rtlil(&mut writer);
    Ok(writer.finish())
}