//! This module contains the definitions for a Symbol.

use std::collections::HashSet;

use uuid::Uuid;

use crate::{model::module::ModuleId, symtab::SymbolTable};

/// Tuple struct for type safety. Has methods for fetching symbols by ID.
#[derive(Debug, PartialEq, Eq, Hash, Copy, Clone)]
pub struct SymbolId(Uuid);

impl From<Symbol> for SymbolId {
    fn from(sym: Symbol) -> Self {
        sym.id
    }
}

impl SymbolId {
    pub fn new() -> Self {
        Self(Uuid::new_v4())
    }

    /// Convenience method to get the [`Module`] from a [`ModuleId`].
    pub fn to_module<'s>(&self, registry: &'s SymbolTable) -> Option<&'s Symbol> {
        registry.get(self)
    }

    /// Convenience method to get the [`Module`] name from a [`ModuleId`].
    pub fn to_module_name<'m>(self, registry: &'m SymbolTable) -> Option<&'m str> {
        if let Some(module) = self.to_module(&registry) {
            Some(module.name.as_str())
        } else {
            None
        }
    }
}

/// A symbol is a named reference that may be resolved later to an address by a linker.
#[derive(Debug)]
pub struct Symbol {
    /// Stored cheaply instead of the name. Shall be stored in the symbol table under
    /// this key.
    pub id: SymbolId,

    /// The human-readable name for the symbol.
    pub name: String,

    pub visibility: Visibility,

    pub symbol_type: SymbolType,

    /// The id of the module the symbol is defined in. This will be different for symbols
    /// in different objects.
    pub module_id: ModuleId,

    /// Whether or not the symbol requires relocating.
    pub needs_relocation: bool,

    /// A list of the symbol's dependencies.
    ///
    /// e.g.
    ///
    /// ```dsa
    /// main:
    ///   call another_func
    ///
    /// another_func:
    ///   // Code goes here
    ///   ret
    /// ```
    ///
    /// Where `main` depends on `another_func`.
    pub dependencies: HashSet<SymbolId>,

    /// The address of the symbol.
    pub address: Option<u32>,
    /// The section the symbol is in.
    /// TODO: Perhaps make this a proper type?
    pub section: Option<String>,
    pub size: Option<u32>,
}

impl Symbol {
    pub fn new(
        name: String,
        module_id: ModuleId,
        visibility: Visibility,
        symbol_type: SymbolType,
    ) -> Self {
        Self {
            id: SymbolId::new(),
            name,
            module_id,
            address: None,
            section: None,
            size: None,
            visibility,
            symbol_type,
            needs_relocation: false,
            dependencies: HashSet::new(),
        }
    }

    /// Adds a dependency on another [`Symbol`].
    pub fn add_dependency(&mut self, dep: SymbolId) {
        if self.id == dep {
            return;
        }

        // We can resolve a lot of addresses at assembly time, but not really foreign
        // ones, since we aren't certain of their position.
        //
        /* TODO: Handle this for flat binary case i.e. no linker required. This may be
         *       done using a similar method to before, such as just concatenating all
         * of the files together and handling jumps and halts.
         *
         * > Ask Harry or read the initial code.
         */
        if self.dependencies.insert(dep) {
            self.needs_relocation = true;
        }
    }

    /// Returns whether a [`Symbol`] depends on `symbol_id`.
    pub fn depends_on(&self, symbol_id: &SymbolId) -> bool {
        self.dependencies.contains(symbol_id)
    }

    /// Removes a [`Symbol`] from the dependency set.
    pub fn remove_dependency(&mut self, symbol_id: &SymbolId) {
        self.dependencies.remove(symbol_id);

        if self.dependencies.is_empty() {
            self.needs_relocation = false;
        }
    }
}

#[derive(Debug, Copy, Clone)]
/// The visibility of the symbol in different object files.
pub enum Visibility {
    /// STB_PUBLIC under the ELF spec. Visible in all other object files. Shall be used
    /// for labels. Remember labels are namespaced in different files so they won't clash
    /// with one another.
    Public,
    /// Only visible within this object file. STB_LOCAL under ELF spec. Shall be used for
    /// data definitions unless they are marked public.
    Local,
    /// STB_WEAK under the ELF spec. Potentially unused.
    Weak,
}

#[derive(Debug)]
pub enum SymbolType {
    LabelOrFunction,
    Variable,
}