(**
 * The phase applies the transformations shown below. These transformations are
 * required because the CiviC VM does not offer instructions that perform these
 * operations. Another reason is that conjunction and disjunction require
 * short-circuit evaluation. In the examples below, `b1` and `b2` are
 * expressions of type boolean, `i` is of type int and `f` is of type float.
 *
 * > b1 == b2   ==>   (int)b1 == (int)b2
 * > b1 != b2   ==>   (int)b1 != (int)b2
 * > b1 && b2   ==>   b1 ? b2 : false
 * > b1 || b2   ==>   b1 ? true : b2
 * > b1 + b2    ==>   (bool)((int)b1 + (int)b2)
 * > b1 * b2    ==>   (bool)((int)b1 * (int)b2)
 * > (bool)i    ==>   i != 0
 * > (bool)f    ==>   f != 0.0
 * > (int)b1    ==>   b1 ? 1 : 0
 * > (float)b1  ==>   b1 ? 1.0 : 0.0
 *)
open Ast
open Util

let cast ctype node = Type (TypeCast (ctype, node, noloc), ctype)

let boolconst  value = Type (BoolConst  (value, noloc), Bool)
let intconst   value = Type (IntConst   (value, noloc), Int)
let floatconst value = Type (FloatConst (value, noloc), Float)

let rec trav_binop = function
    | ((Eq | Ne) as op, left, right, loc) ->
        Binop (op, cast Int left, cast Int right, loc)

    | (And, left, right, loc) ->
        Cond (left, right, boolconst false, loc)

    | (Or, left, right, loc) ->
        Cond (left, boolconst true, right, loc)

    | ((Add | Mul) as op, left, right, loc) ->
        cast Bool (Binop (op, cast Int left, cast Int right, loc))

    | (op, left, right, loc) ->
        Binop (op, left, right, loc)

and bool_op = function
    | Binop (op, (Type (_, Bool) as left), (Type (_, Bool) as right), loc) ->
        trav_binop (op, left, right, loc)

    | TypeCast (Bool, (Type (_, Int) as value), loc) ->
        Binop (Ne, value, intconst 0, loc)

    | TypeCast (Bool, (Type (_, Float) as value), loc) ->
        Binop (Ne, value, floatconst 0.0, loc)

    | TypeCast (Int, (Type (_, Bool) as value), loc) ->
        Cond (value, intconst 1, intconst 0, loc)

    | TypeCast (Float, (Type (_, Bool) as value), loc) ->
        Cond (value, floatconst 1.0, floatconst 0.0, loc)

    | node -> transform_children bool_op node

let rec phase input =
    prerr_endline "- Convert bool operations";
    match input with
    | Ast node -> Ast (bool_op node)
    | _ -> raise (InvalidInput "bool operations")