(* Copyright (c) 2008, Adam Chlipala
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * - Redistributions of source code must retain the above copyright notice,
 *   this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * - The names of contributors may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *)

(* Simplify a Core program algebraically, without unfolding definitions *)

structure ReduceLocal :> REDUCE_LOCAL = struct

open Core

structure IM = IntBinaryMap

fun multiLiftExpInExp n e =
    if n = 0 then
        e
    else
        multiLiftExpInExp (n - 1) (CoreEnv.liftExpInExp 0 e)

datatype env_item =
         Unknown
       | Known of exp

       | Lift of int

type env = env_item list

val deKnown = List.filter (fn Known _ => false
                            | _ => true)

datatype result = Yes of env | No | Maybe

fun match (env, p : pat, e : exp) =
    let
        val baseline = length env

        fun match (env, p, e) =
            case (#1 p, #1 e) of
                (PWild, _) => Yes env
              | (PVar (x, t), _) => Yes (Known (multiLiftExpInExp (length env - baseline) e) :: env)

              | (PPrim p, EPrim p') =>
                if Prim.equal (p, p') then
                    Yes env
                else
                    No

              | (PCon (_, PConVar n1, _, NONE), ECon (_, PConVar n2, _, NONE)) =>
                if n1 = n2 then
                    Yes env
                else
                    No

              | (PCon (_, PConVar n1, _, SOME p), ECon (_, PConVar n2, _, SOME e)) =>
                if n1 = n2 then
                    match (env, p, e)
                else
                    No

              | (PCon (_, PConFfi {mod = m1, con = con1, ...}, _, NONE),
                 ECon (_, PConFfi {mod = m2, con = con2, ...}, _, NONE)) =>
                if m1 = m2 andalso con1 = con2 then
                    Yes env
                else
                    No

              | (PCon (_, PConFfi {mod = m1, con = con1, ...}, _, SOME ep),
                 ECon (_, PConFfi {mod = m2, con = con2, ...}, _, SOME e)) =>
                if m1 = m2 andalso con1 = con2 then
                    match (env, p, e)
                else
                    No

              | (PRecord xps, ERecord xes) =>
                if List.exists (fn ((CName _, _), _, _) => false
                                 | _ => true) xes then
                    Maybe
                else
                    let
                        fun consider (xps, env) =
                            case xps of
                                [] => Yes env
                              | (x, p, _) :: rest =>
                                case List.find (fn ((CName x', _), _, _) => x' = x
                                                 | _ => false) xes of
                                    NONE => No
                                  | SOME (_, e, _) =>
                                    case match (env, p, e) of
                                        No => No
                                      | Maybe => Maybe
                                      | Yes env => consider (rest, env)
                    in
                        consider (xps, env)
                    end

              | _ => Maybe
    in
        match (env, p, e)
    end

fun exp env (all as (e, loc)) =
    case e of
        EPrim _ => all
      | ERel n =>
        let
            fun find (n', env, nudge, lift) =
                case env of
                    [] => (ERel (n + nudge), loc)
                  | Lift lift' :: rest => find (n', rest, nudge + lift', lift + lift')
                  | Unknown :: rest =>
                    if n' = 0 then
                        (ERel (n + nudge), loc)
                    else
                        find (n' - 1, rest, nudge, lift + 1)
                  | Known e :: rest =>
                    if n' = 0 then
                        ((*print "SUBSTITUTING\n";*)
                         exp (Lift lift :: rest) e)
                    else
                        find (n' - 1, rest, nudge - 1, lift)
        in
            find (n, env, 0, 0)
        end
      | ENamed _ => all
      | ECon (dk, pc, cs, eo) => (ECon (dk, pc, cs, Option.map (exp env) eo), loc)
      | EFfi _ => all
      | EFfiApp (m, f, es) => (EFfiApp (m, f, map (exp env) es), loc)

      | EApp ((ECApp ((ECAbs (_, _, (EAbs (_, (CRel 0, _), _,
                                           (ECon (dk, pc, [(CRel 0, loc)], SOME (ERel 0, _)), _)), _)), _),
                      t), _), e) =>
        (ECon (dk, pc, [t], SOME (exp env e)), loc)

      | EApp (e1, e2) =>
        let
            val e1 = exp env e1
            val e2 = exp env e2
        in
            case #1 e1 of
                EAbs (_, _, _, b) => exp (Known e2 :: deKnown env) b
              | _ => (EApp (e1, e2), loc)
        end

      | EAbs (x, dom, ran, e) => (EAbs (x, dom, ran, exp (Unknown :: env) e), loc)

      | ECApp ((ECAbs (_, _, (ECon (dk, pc, [(CRel 0, loc)], NONE), _)), _), t) =>
        (ECon (dk, pc, [t], NONE), loc)

      | ECApp (e, c) => (ECApp (exp env e, c), loc)
      | ECAbs (x, k, e) => (ECAbs (x, k, exp env e), loc)

      | EKApp (e, k) => (EKApp (exp env e, k), loc)
      | EKAbs (x, e) => (EKAbs (x, exp env e), loc)

      | ERecord xcs => (ERecord (map (fn (x, e, t) => (x, exp env e, t)) xcs), loc)
      | EField (e, c, others) =>
        let
            val e = exp env e

            fun default () = (EField (e, c, others), loc)
        in
            case (#1 e, #1 c) of
                (ERecord xcs, CName x) =>
                (case List.find (fn ((CName x', _), _, _) => x' = x | _ => false) xcs of
                     NONE => default ()
                   | SOME (_, e, _) => e)
              | _ => default ()
        end

      | EConcat (e1, c1, e2, c2) => (EConcat (exp env e1, c1, exp env e2, c2), loc)
      | ECut (e, c, others) => (ECut (exp env e, c, others), loc)
      | ECutMulti (e, c, others) => (ECutMulti (exp env e, c, others), loc)

      | ECase (e, pes, others) =>
        let
            fun patBinds (p, _) =
                case p of
                    PWild => 0
                  | PVar _ => 1
                  | PPrim _ => 0
                  | PCon (_, _, _, NONE) => 0
                  | PCon (_, _, _, SOME p) => patBinds p
                  | PRecord xpts => foldl (fn ((_, p, _), n) => n + patBinds p) 0 xpts

            fun push () =
                (ECase (exp env e,
                        map (fn (p, e) => (p,
                                           exp (List.tabulate (patBinds p,
                                                            fn _ => Unknown) @ env) e))
                            pes, others), loc)

            fun search pes =
                case pes of
                    [] => push ()
                  | (p, body) :: pes =>
                    case match (env, p, e) of
                        No => search pes
                      | Maybe => push ()
                      | Yes env' => exp env' body
        in
            search pes
        end

      | EWrite e => (EWrite (exp env e), loc)
      | EClosure (n, es) => (EClosure (n, map (exp env) es), loc)

      | ELet (x, t, e1, e2) => (ELet (x, t, exp env e1, exp (Unknown :: env) e2), loc)

      | EServerCall (n, es, t) => (EServerCall (n, map (exp env) es, t), loc)

fun reduce file =
    let
        fun doDecl (d as (_, loc)) =
            case #1 d of
                DCon _ => d
              | DDatatype _ => d
              | DVal (x, n, t, e, s) =>
                let
                    val e = exp [] e
                in
                    (DVal (x, n, t, e, s), loc)
                end
              | DValRec vis =>
                (DValRec (map (fn (x, n, t, e, s) => (x, n, t, exp [] e, s)) vis), loc)
              | DExport _ => d
              | DTable _ => d
              | DSequence _ => d
              | DView _ => d
              | DDatabase _ => d
              | DCookie _ => d
              | DStyle _ => d
              | DTask (e1, e2) => (DTask (exp [] e1, exp [] e2), loc)
    in
        map doDecl file
    end

val reduceExp = exp []

end