use crate::Error;

use crate::token::{Id, Index};

use std::collections::HashMap;

#[derive(Default)]

pub struct Namespace<'a> {

    names: HashMap<Id<'a>, u32>,

    count: u32,

}

impl<'a> Namespace<'a> {

    pub fn register(&mut self, name: Option<Id<'a>>, desc: &str) -> Result<u32, Error> {

        let index = self.alloc();

        if let Some(name) = name {

            if let Some(_prev) = self.names.insert(name, index) {

                return Err(Error::new(

                    name.span(),

                    format!("duplicate {desc} identifier"),

                ));

            }

        }

        Ok(index)

    }

    pub fn alloc(&mut self) -> u32 {

        let index = self.count;

        self.count += 1;

        index

    }

    pub fn register_specific(&mut self, name: Id<'a>, index: u32, desc: &str) -> Result<(), Error> {

        if let Some(_prev) = self.names.insert(name, index) {

            return Err(Error::new(

                name.span(),

                format!(

                    "duplicate identifier: duplicate {desc} named `{}`",

                    name.name()

                ),

            ));

        }

        Ok(())

    }

    pub fn resolve(&self, idx: &mut Index<'a>, desc: &str) -> Result<u32, Error> {

        self.try_resolve(idx).ok_or_else(|| match idx {

            Index::Num(..) => unreachable!(),

            Index::Id(id) => resolve_error(*id, desc),

        })

    }

    pub fn try_resolve(&self, idx: &mut Index<'a>) -> Option<u32> {

        let id = match idx {

            Index::Num(n, _) => return Some(*n),

            Index::Id(id) => id,

        };

        if let Some(&n) = self.names.get(id) {

            *idx = Index::Num(n, id.span());

            return Some(n);

        }

        None

    }

}

pub fn resolve_error(id: Id<'_>, ns: &str) -> Error {

    assert!(

        !id.is_gensym(),

        "symbol generated by `wast` itself cannot be resolved {id:?}"

    );

    Error::new(

        id.span(),

        format!("unknown {ns}: failed to find name `${}`", id.name()),

    )

}