#
    This file contains definitions of operators like "+" and "and".

use "core/metaprogramming.nom"

# Indexing
immediately
    #   NOTE!!! It's critical that there are spaces around %key if it's a string,
        otherwise, Lua will get confused and interpret %obj[[[foo]]] as %obj("[foo]")
        instead of %obj[ "foo" ].
        It's also critical to have parens around %obj, otherwise Lua is too dumb to
        realize that {x=1}["x"] is the same as ({x=1})["x"] or that
        {x=1}.x is the same as ({x=1}).x
    parse [..]
        %obj' %key, %obj's %key, %key in %obj, %key'th in %obj, %key of %obj,
        %key st in %obj, %key nd in %obj, %key rd in %obj, %key th in %obj,
    ..as: %obj.%key

# Comparison Operators
immediately
    compile [%x < %y] to: Lua value "(\(%x as lua expr) < \(%y as lua expr))"
    compile [%x > %y] to: Lua value "(\(%x as lua expr) > \(%y as lua expr))"
    compile [%x <= %y] to: Lua value "(\(%x as lua expr) <= \(%y as lua expr))"
    compile [%x >= %y] to: Lua value "(\(%x as lua expr) >= \(%y as lua expr))"
    compile [%a is %b, %a = %b, %a == %b] to
        lua> ".."
            local safe = {Text=true, Number=true}
            local a_lua, b_lua = \(%a as lua), \(%b as lua)
            if safe[\%a.type] or safe[\%b.type] then
                return Lua.Value(tree.source, "(", a_lua, " == ", b_lua, ")")
            else
                return Lua.Value(tree.source, "utils.equivalent(", a_lua, ", ", b_lua, ")")
            end
    compile [%a isn't %b, %a is not %b, %a not= %b, %a != %b] to
        lua> ".."
            local safe = {Text=true, Number=true}
            local a_lua, b_lua = \(%a as lua), \(%b as lua)
            if safe[\%a.type] or safe[\%b.type] then
                return Lua.Value(tree.source, "(", a_lua, " ~= ", b_lua, ")")
            else
                return Lua.Value(tree.source, "(not utils.equivalent(", a_lua, ", ", b_lua, "))")
            end
    # For strict identity checking, use (%x's id) is (%y's id)
    compile [%'s id, id of %] to: Lua value "nomsu.ids[\(% as lua expr)]"

# Variable assignment operator
immediately
    compile [%var <- %value] to
        lua> "local \%var_lua = \(%var as lua)"
        assume %var_lua.is_value or barf "Invalid target for assignment: \%var"
        lua> ".."
            \%value = \%value:map(function(t)
                if Action:is_instance(t) and t.stub == "?" then
                    return \%var
                end
            end)
            local \%value_lua = \(%value as lua)

        assume %value_lua.is_value or barf "Invalid value for assignment: \%value"
        lua> ".."
            local lua = Lua(tree.source, \%var_lua, ' = ', \%value_lua, ';')
            if \%var.type == 'Var' then
                lua:add_free_vars({\%var})
            end
            return lua;

immediately
    # Simultaneous mutli-assignments like: x,y,z = 1,x,3;
    compile [<- %assignments] to
        assume ((%assignments' "type") is "Dict") or barf ".."
            Expected a Dict for the assignments part of '<- %' statement, not \%assignments
        lua> ".."
            local lhs, rhs = Lua(tree.source), Lua(tree.source)
            for i, item in ipairs(\%assignments) do
                local \%target, \%value = item[1], item[2]
                \%value = \%value:map(function(t)
                    if Action:is_instance(t) and t.stub == "?" then
                        return \%target
                    end
                end)
                local target_lua = \(%target as lua)
                if not target_lua.is_value then error("Invalid target for assignment: "..\(%target as text)) end
                local value_lua = \(%value as lua)
                if not value_lua.is_value then error("Invalid value for assignment: "..\(%value as text)) end
                if \%target.type == "Var" then
                    lhs:add_free_vars({\%target})
                end
                if i > 1 then
                    lhs:append(", ")
                    rhs:append(", ")
                end
                lhs:append(target_lua)
                rhs:append(value_lua)
            end
            return Lua(tree.source, lhs, " = ", rhs, ";")

immediately
    compile [external %var <- %value] to
        %var_lua <- (%var as lua)
        assume %var_lua.is_value or barf "Invalid target for assignment: \%var"
        %value_lua <- (%value as lua)
        assume %value_lua.is_value or barf "Invalid value for assignment: \%value"
        return: Lua "\%var_lua = \%value_lua;"

    compile [with external %externs %body] to
        %body_lua <- (%body as lua statements)
        lua> "\%body_lua:remove_free_vars(\%externs);"
        return %body_lua

    compile [with %assignments %body] to
        %lua <- (%body as lua statements)
        lua> ".."
            local lhs, rhs = Lua(tree.source), Lua(tree.source)
            local vars = {}
            for i, item in ipairs(\%assignments) do
                local \%target, \%value = item[1], item[2]
                if not \%target.type == "Var" then
                    error("Invalid target for 'with' assignment: "..tostring(\%target))
                end
                local target_lua = \(%target as lua)
                local value_lua = \(%value as lua)
                if not value_lua.is_value then
                    error("Invalid value for assignment: "..tostring(\%value))
                end
                if \%target.type == "Var" then
                    lhs:add_free_vars({\%target})
                end
                if i > 1 then
                    lhs:append(", ")
                    rhs:append(", ")
                end
                lhs:append(target_lua)
                rhs:append(value_lua)
                vars[i] = \%target
            end
            \%lua:remove_free_vars(vars)
            \%lua:prepend("local ", lhs, " = ", rhs, ";\n")
        return
            Lua ".."
                do
                    \%lua
                end -- 'with' block

immediately
    # Math Operators
    compile [%x wrapped around %y, %x mod %y] to: Lua value "(\(%x as lua expr) % \(%y as lua expr))"

    # 3-part chained comparisons
    # (uses a lambda to avoid re-evaluating middle value, while still being an expression)
    parse [%x <  %y <  %z] as: =lua "(function(x,y,z) return x <  y and y <  z; end)(\%x,\%y,\%z)"
    parse [%x <= %y <  %z] as: =lua "(function(x,y,z) return x <= y and y <  z; end)(\%x,\%y,\%z)"
    parse [%x <  %y <= %z] as: =lua "(function(x,y,z) return x <  y and y <= z; end)(\%x,\%y,\%z)"
    parse [%x <= %y <= %z] as: =lua "(function(x,y,z) return x <= y and y <= z; end)(\%x,\%y,\%z)"
    parse [%x >  %y >  %z] as: =lua "(function(x,y,z) return x >  y and y >  z; end)(\%x,\%y,\%z)"
    parse [%x >= %y >  %z] as: =lua "(function(x,y,z) return x >= y and y >  z; end)(\%x,\%y,\%z)"
    parse [%x >  %y >= %z] as: =lua "(function(x,y,z) return x >  y and y >= z; end)(\%x,\%y,\%z)"
    parse [%x >= %y >= %z] as: =lua "(function(x,y,z) return x >= y and y >= z; end)(\%x,\%y,\%z)"
    # TODO: optimize for common case where x,y,z are all either variables or number literals

    # Boolean Operators
    compile [%x and %y] to: Lua value "(\(%x as lua expr) and \(%y as lua expr))"
    compile [%x or %y] to: Lua value "(\(%x as lua expr) or \(%y as lua expr))"

    # Bitwise Operators
    compile [%a OR %b, %a | %b] to: Lua value "bit32.bor(\(%a as lua expr), \(%b as lua expr))"
    compile [%a XOR %b] to: Lua value "bit32.bxor(\(%a as lua expr), \(%b as lua expr))"
    compile [%a AND %b, %a & %b] to: Lua value "bit32.band(\(%a as lua expr), \(%b as lua expr))"
    compile [NOT %, ~ %] to: Lua value "bit32.bnot(\(% as lua expr))"
    compile [%x LSHIFT %shift, %x << %shift] to: Lua value "bit32.lshift(\(%x as lua expr), \(%shift as lua expr))"
    compile [%x RSHIFT %shift, %x >>> %shift] to: Lua value "bit32.rshift(\(%x as lua expr), \(%shift as lua expr))"
    compile [%x ARSHIFT %shift, %x >> %shift] to: Lua value "bit32.arshift(\(%x as lua expr), \(%shift as lua expr))"
    # TODO: implement OR, XOR, AND for multiple operands?

    # Unary operators
    compile [- %] to: Lua value "(- \(% as lua expr))"
    compile [not %] to: Lua value "(not \(% as lua expr))"
    # Using custom "len()" instead of Lua's "#" operator for compatibility with luajit.
    compile [length of %list] to: Lua value "len(\(%list as lua expr))"

# Update operators
immediately
    parse [%var + <- %, %var +<- %] as: %var <- (%var + %)
    parse [%var - <- %, %var -<- %] as: %var <- (%var - %)
    parse [%var * <- %, %var *<- %] as: %var <- (%var * %)
    parse [%var / <- %, %var /<- %] as: %var <- (%var / %)
    parse [%var ^ <- %, %var ^<- %] as: %var <- (%var ^ %)
    parse [%var and <- %] as: %var <- (%var and %)
    parse [%var or <- %] as: %var <- (%var or %)
    parse [wrap %var around %] as: %var <- (%var wrapped around %)