use std::{collections::HashMap, fs, path::PathBuf, rc::Rc};

use compiler::compile;
use parser::parse;
use semantics::{check, Error, ImportRecord, Semantics};
use vm::{eval, Context};

pub mod compiler;
pub mod parser;
pub mod semantics;
pub mod tokens;
pub mod vm;

pub enum ModuleSource {
    SourceText(String),
}

#[derive(Debug)]
pub enum ModuleLoadError {
    IO(String, std::io::Error),
}

pub trait ModuleLoader {
    fn normalize_module_name(&self, source: &str, name: String) -> String;
    fn load_module(&self, name: &String) -> Result<ModuleSource, ModuleLoadError>;
}

pub struct StandardModuleLoader {
    base_path: PathBuf,
}

impl StandardModuleLoader {
    pub fn new(base_path: PathBuf) -> Self {
        StandardModuleLoader { base_path }
    }
}

impl ModuleLoader for StandardModuleLoader {
    fn normalize_module_name(&self, source: &str, name: String) -> String {
        let p = self.base_path.join(source).join(name.clone());
        let result = match std::fs::canonicalize(&p) {
            Ok(p) => match p.into_os_string().into_string() {
                Ok(s) => s,
                Err(_e) => name.clone(),
            },
            Err(_e) => name.clone(),
        };
        result
    }

    fn load_module(&self, name: &String) -> Result<ModuleSource, ModuleLoadError> {
        match fs::read_to_string(name) {
            Ok(c) => Ok(ModuleSource::SourceText(c)),
            Err(e) => Err(ModuleLoadError::IO(name.clone(), e)),
        }
    }
}

pub struct Module {
    id: u64,
    semantics: Rc<Semantics>,
}

impl Module {
    pub fn id(&self) -> u64 {
        self.id
    }

    pub fn semantics(&self) -> Rc<Semantics> {
        self.semantics.clone()
    }
}

pub struct Runtime {
    next_module_id: u64,
    modules: HashMap<String, Rc<Module>>,
    loader: Box<dyn ModuleLoader>,
}

impl Runtime {
    pub fn new(loader: Box<dyn ModuleLoader>) -> Self {
        Runtime {
            next_module_id: 0,
            modules: HashMap::new(),
            loader,
        }
    }

    pub fn load_module(&mut self, name: &str) -> Result<(Vec<Error>, Rc<Module>), ModuleLoadError> {
        let mut init_pending = HashMap::new();
        let mut names = Vec::new();
        let name = self.loader.normalize_module_name("", name.to_string());
        names.push(name.clone());

        let mut id_assign = self.next_module_id;

        while let Some(name) = names.pop() {
            if self.modules.contains_key(&name) || init_pending.contains_key(&name) {
                // Either already loaded or pending load.
                continue;
            }

            // TODO: Errors here are bad! Remember, run everything!
            match self.loader.load_module(&name)? {
                ModuleSource::SourceText(source) => {
                    let source: Rc<str> = source.into();
                    let (tree, lines) = parse(&source);
                    let semantics =
                        Rc::new(Semantics::new(name.clone().into(), source, tree, lines));

                    let mut normalized_imports = Vec::new();
                    for import in semantics.imports() {
                        let normalized = self.loader.normalize_module_name(&name, import.clone());

                        names.push(normalized.clone());
                        normalized_imports.push((import, normalized));
                    }

                    init_pending.insert(name, (id_assign, normalized_imports, semantics));
                    id_assign += 1;
                }
            }
        }

        for (_, (_, imports, semantics)) in init_pending.iter() {
            let mut import_table = HashMap::new();
            for (import, normalized) in imports.iter() {
                // NOTE: We look up the load(ed|ing) module here by normalized name, because that's how
                //       we track it...
                let target = if let Some(module) = self.modules.get(&*normalized) {
                    ImportRecord {
                        name: normalized.clone(),
                        module_id: module.id(),
                        semantics: Rc::downgrade(&module.semantics),
                    }
                } else {
                    let (module_id, _, semantics) = init_pending.get(&*normalized).unwrap();
                    ImportRecord {
                        name: normalized.clone(),
                        module_id: *module_id,
                        semantics: Rc::downgrade(semantics),
                    }
                };

                // ...but we set it into the import table here with the name
                // that the source code used, for more better binding.
                import_table.insert(import.clone(), target);
            }
            semantics.set_imports(import_table);
        }

        let mut errors = Vec::new();
        for (name, (id, _, semantics)) in init_pending.into_iter() {
            check(&semantics);
            errors.append(&mut semantics.snapshot_errors());
            self.modules.insert(name, Rc::new(Module { id, semantics }));
        }
        self.next_module_id = id_assign;

        let result = self.modules.get(&name).unwrap().clone();
        Ok((errors, result))
    }
}

pub fn process_file(file: &str) {
    let mut runtime = Runtime::new(Box::new(StandardModuleLoader::new(PathBuf::from("."))));

    let (errors, module) = match runtime.load_module(file) {
        Ok(r) => r,
        Err(_) => {
            eprintln!("Error loading module");
            return;
        }
    };

    // OK now there might be errors.
    if errors.len() > 0 {
        for e in errors {
            eprintln!("{file}: {}:{}: {}", e.start.0, e.start.1, e.message);
        }
        return;
    }

    // shrug
    let semantics = module.semantics();
    let module = compile(&semantics);
    let main_function = module.functions[module.init].clone();

    let mut context = Context::new(module.clone());
    match eval(&mut context, main_function, vec![]) {
        Ok(v) => {
            println!("{:?}", v);
        }
        Err(e) => {
            eprintln!("{:?}", e);
        }
    }
}