use nu_parser::{parse, parse_module_block};
use nu_protocol::report_error;
use nu_protocol::{engine::StateWorkingSet, Module, ShellError, Span};

fn add_file(
    working_set: &mut StateWorkingSet,
    name: &String,
    content: &[u8],
) -> (Module, Vec<Span>) {
    let file_id = working_set.add_file(name.clone(), content);
    let new_span = working_set.get_span_for_file(file_id);

    let (_, module, comments) = parse_module_block(working_set, new_span, name.as_bytes());

    if let Some(err) = working_set.parse_errors.first() {
        report_error(working_set, err);
    }

    parse(working_set, Some(name), content, true);

    if let Some(err) = working_set.parse_errors.first() {
        report_error(working_set, err);
    }

    (module, comments)
}

fn load_prelude(working_set: &mut StateWorkingSet, prelude: Vec<(&str, &str)>, module: &Module) {
    let mut decls = Vec::new();
    let mut errs = Vec::new();
    for (name, search_name) in prelude {
        if let Some(id) = module.decls.get(&search_name.as_bytes().to_vec()) {
            let decl = (name.as_bytes().to_vec(), id.to_owned());
            decls.push(decl);
        } else {
            errs.push(ShellError::GenericError(
                format!("could not load `{}` from `std`.", search_name),
                String::new(),
                None,
                None,
                Vec::new(),
            ));
        }
    }

    if !errs.is_empty() {
        report_error(
            working_set,
            &ShellError::GenericError(
                "Unable to load the prelude of the standard library.".into(),
                String::new(),
                None,
                Some("this is a bug: please file an issue in the [issue tracker](https://github.com/nushell/nushell/issues/new/choose)".to_string()),
                errs,
            ),
        );
    }

    working_set.use_decls(decls);
}

pub fn load_standard_library(
    engine_state: &mut nu_protocol::engine::EngineState,
) -> Result<(), miette::ErrReport> {
    let delta = {
        let name = "std".to_string();
        let content = include_str!("../lib/mod.nu");

        // these modules are loaded in the order they appear in this list
        #[rustfmt::skip]
        let submodules = vec![
            // helper modules that could be used in other parts of the library
            ("log", include_str!("../lib/log.nu")),

            // the rest of the library
            ("dirs", include_str!("../lib/dirs.nu")),
            ("iter", include_str!("../lib/iter.nu")),
            ("help", include_str!("../lib/help.nu")),
            ("testing", include_str!("../lib/testing.nu")),
            ("xml", include_str!("../lib/xml.nu")),
        ];

        // Define commands to be preloaded into the default (top level, unprefixed) namespace.
        // User can invoke these without having to `use std` beforehand.
        // Entries are: (name to add to default namespace, path under std to find implementation)
        //
        // Conventionally, for a command implemented as `std foo`, the name added
        // is either `std foo` or bare `foo`, not some arbitrary rename.

        let prelude = vec![
            ("std help", "help"),
            ("std help commands", "help commands"),
            ("std help aliases", "help aliases"),
            ("std help modules", "help modules"),
            ("std help externs", "help externs"),
            ("std help operators", "help operators"),
        ];

        let mut working_set = StateWorkingSet::new(engine_state);

        for (name, content) in submodules {
            let (module, comments) =
                add_file(&mut working_set, &name.to_string(), content.as_bytes());
            working_set.add_module(name, module, comments);
        }

        let (module, comments) = add_file(&mut working_set, &name, content.as_bytes());
        load_prelude(&mut working_set, prelude, &module);
        working_set.add_module(&name, module, comments);

        working_set.render()
    };

    engine_state.merge_delta(delta)?;

    Ok(())
}