// Copyright (c) 2016-2021 Fabian Schuiki

//! An implementation of lazy compiler passes.

// #![deny(missing_docs)]

use std;
use std::cell::RefCell;
use std::collections::HashMap;
use std::fmt;

use crate::hir;
use crate::score::*;
use crate::score::{ScoreBoard, ScoreContext};
use crate::ty::Ty;
use crate::typeck::TypeckContext;
use moore_common::score::{NodeStorage, Result};
use moore_common::NodeId;

/// A lazily evaluated node.
pub enum LazyNode<F> {
    /// Evaluation is currently running.
    Running,
    /// The callback which will provide the desired output.
    Pending(F),
}

impl<F> fmt::Debug for LazyNode<F> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            LazyNode::Running => write!(f, "running"),
            LazyNode::Pending(_) => write!(f, "pending"),
        }
    }
}

/// A table of lazy compiler phases.
pub struct LazyPhaseTable<'sb, 'ast: 'sb, 'ctx: 'sb> {
    /// The score board.
    pub sb: &'sb ScoreBoard<'ast, 'ctx>,
    /// The lazy HIR table.
    pub hir: LazyPhase<LazyHirTable<'sb, 'ast, 'ctx>>,
    /// The lazy typeck table.
    pub typeck: RefCell<LazyTypeckTable<'sb, 'ast, 'ctx>>,
    /// The lazy typeval table.
    pub typeval: RefCell<LazyTypevalTable<'sb, 'ast, 'ctx>>,
}

impl<'sb, 'ast, 'ctx> LazyPhaseTable<'sb, 'ast, 'ctx> {
    /// Create a new phase table.
    pub fn new(sb: &'sb ScoreBoard<'ast, 'ctx>) -> LazyPhaseTable<'sb, 'ast, 'ctx> {
        LazyPhaseTable {
            sb: sb,
            hir: LazyPhase::new(),
            typeck: RefCell::new(HashMap::new()),
            typeval: RefCell::new(HashMap::new()),
        }
    }
}

/// A table of tasks needed to perform a compiler phase.
pub struct LazyPhase<T> {
    pub table: RefCell<T>,
}

impl<T: Default> LazyPhase<T>
where
    T: Default,
{
    /// Create a new lazy phase.
    pub fn new() -> LazyPhase<T> {
        LazyPhase {
            table: RefCell::new(Default::default()),
        }
    }

    /// Schedule a task to be lazily executed.
    pub fn schedule<I, F>(&self, id: I, f: F)
    where
        T: NodeStorage<I, Node = LazyNode<F>>,
    {
        self.table.borrow_mut().set(id, LazyNode::Pending(f));
    }

    /// Run a task.
    pub fn run<'lazy, 'sb, 'ast, 'ctx, I, R>(
        &self,
        id: I,
        ctx: &ScoreContext<'lazy, 'sb, 'ast, 'ctx>,
    ) -> Result<R>
    where
        I: Copy + fmt::Debug,
        T: NodeStorage<
            I,
            Node = LazyNode<
                Box<for<'a, 'b> Fn(&'a ScoreContext<'b, 'sb, 'ast, 'ctx>) -> Result<R> + 'sb>,
            >,
        >,
    {
        let task = self.table.borrow_mut().set(id, LazyNode::Running);
        match task {
            Some(LazyNode::Pending(f)) => f(ctx),
            Some(LazyNode::Running) => panic!("recursion when running task for {:?}", id),
            None => panic!("no task scheduled for {:?}", id),
        }
    }
}

/// A callback to lazily lower a node to HIR.
pub type LazyHir<'sb, 'ast, 'ctx, R> =
    Box<for<'a, 'b> Fn(&'a ScoreContext<'b, 'sb, 'ast, 'ctx>) -> Result<R> + 'sb>;

/// A callback to lazily typeck a node.
pub type LazyTypeck<'sb, 'ast, 'ctx> =
    Box<for<'a, 'b, 'c> Fn(&'a TypeckContext<'b, 'c, 'sb, 'ast, 'ctx>) -> Result<()> + 'sb>;

/// A callback to lazily evaluate the type of a node.
pub type LazyTypeval<'sb, 'ast, 'ctx> =
    Box<for<'a, 'b, 'c> Fn(&'a TypeckContext<'b, 'c, 'sb, 'ast, 'ctx>) -> Result<&'ctx Ty> + 'sb>;

/// A table of pending or running HIR lowerings.
node_storage!(LazyHirTable<'sb, 'ast, 'ctx> where ('ast: 'sb, 'ctx: 'sb):
    // Miscellaneous
    subtype_inds:     SubtypeIndRef    => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::SubtypeInd>>,

    // Expressions
    exprs:            ExprRef          => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Expr>>,
    aggregates:       AggregateRef     => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Aggregate>>,

    // Declarations
    const_decls:      ConstDeclRef     => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Decl<hir::ConstDecl>>>,
    signal_decls:     SignalDeclRef    => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Decl<hir::SignalDecl>>>,
    var_decls:        VarDeclRef       => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Decl<hir::VarDecl>>>,
    file_decls:       FileDeclRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Decl<hir::FileDecl>>>,
    type_decls:       TypeDeclRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::TypeDecl>>,

    // Sequential statements
    wait_stmts:       WaitStmtRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::WaitStmt>>>,
    assert_stmts:     AssertStmtRef    => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::AssertStmt>>>,
    report_stmts:     ReportStmtRef    => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::ReportStmt>>>,
    sig_assign_stmts: SigAssignStmtRef => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::SigAssignStmt>>>,
    var_assign_stmts: VarAssignStmtRef => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::VarAssignStmt>>>,
    call_stmt:        CallStmtRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::CallStmt>>>,
    if_stmt:          IfStmtRef        => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::IfStmt>>>,
    case_stmt:        CaseStmtRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::CaseStmt>>>,
    loop_stmt:        LoopStmtRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::LoopStmt>>>,
    nexit_stmt:       NexitStmtRef     => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::NexitStmt>>>,
    return_stmt:      ReturnStmtRef    => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::ReturnStmt>>>,
    null_stmt:        NullStmtRef      => LazyNode<LazyHir<'sb, 'ast, 'ctx, hir::Stmt<hir::NullStmt>>>,
);

impl<'sb, 'ast, 'ctx> Default for LazyHirTable<'sb, 'ast, 'ctx> {
    fn default() -> LazyHirTable<'sb, 'ast, 'ctx> {
        LazyHirTable::new()
    }
}

/// A table of pending or running type checks.
pub type LazyTypeckTable<'sb, 'ast, 'ctx> = HashMap<NodeId, LazyNode<LazyTypeck<'sb, 'ast, 'ctx>>>;

/// A table of pending or running type evaluations.
pub type LazyTypevalTable<'sb, 'ast, 'ctx> =
    HashMap<NodeId, LazyNode<LazyTypeval<'sb, 'ast, 'ctx>>>;