# encoding: utf-8
# frozen_string_literal: true

module Carbon
  module Core
    module Pointer
      # Defines pointer arithmatic.  This allows for addition and subtraction,
      # as well as comparison.  This module defines the following functions:
      #
      # - `.+<N: Carbon::Numeric>(self, other: N): self`
      # - `.-<N: Carbon::Numeric>(self, other: N): self`
      # - `.<<N: Carbon::Numeric>(self, other: N): Carbon::Boolean`
      # - `.><N: Carbon::Numeric>(self, other: N): Carbon::Boolean`
      # - `.<=<N: Carbon::Numeric>(self, other: N): Carbon::Boolean`
      # - `.>=<N: Carbon::Numeric>(self, other: N): Carbon::Boolean`
      # - `.<=><N: Carbon::Numeric>(self, other: N): Carbon::Int8`
      # - `.<(self, other: self): Carbon::Boolean`
      # - `.>(self, other: self): Carbon::Boolean`
      # - `.<=(self, other: self): Carbon::Boolean`
      # - `.>=(self, other: self): Carbon::Boolean`
      # - `.<=>(self, other: self): Carbon::Int8`
      #
      # These are defined for all integers except boolean.
      module Math
        # The math operations that can be applied to pointers.
        #
        # @return [<::Symbol>]
        MATH_OPERATIONS = %i(+ -).freeze

        # The comparison operations that can be applied to pointers.
        #
        # @return [<::Symbol>]
        COMP_OPERATIONS = %i(< > <= >=).freeze

        # Comprehensively defines all of the math, comparison, and spaceship
        # operations for pointers.
        #
        # @see #define_math_function
        # @see #define_comp_function
        # @see #define_space_function
        # @see #define_comp_pointer_function
        # @see #define_space_pointer_function
        # @return [void]
        def define_math_functions
          Ints.each do |int|
            next if int.size == 1
            MATH_OPERATIONS.each { |op| define_math_function(int, op) }
            COMP_OPERATIONS.each { |op| define_comp_function(int, op) }
            define_space_function(int)
          end

          COMP_OPERATIONS.each { |op| define_comp_pointer_function(op) }
          define_space_pointer_function
        end

        # Defines the `<=>` function for two pointers.  This returns `-1`,
        # `0`, or `1`, if the receiver is less than, equal to, or greater than
        # the parameter, respectively.
        #
        # @return [void]
        def define_space_pointer_function
          function_name = PTYPE.call(:<=>, [PTYPE, PTYPE])
          Core.define(function: function_name) do |function|
            function[:return] = Carbon::Type("Carbon::Int8")
            define_space_pointer_definition(function[:definition])
          end
        end

        # Defines a comparison function for two pointers.
        #
        # @param op [::Symbol] The operation that the function performs.
        #   This should be one of {COMP_OPERATIONS}.
        # @return [void]
        def define_comp_pointer_function(op)
          function_name = PTYPE.call(op, [PTYPE, PTYPE])
          Core.define(function: function_name) do |function|
            function[:return] = Carbon::Boolean
            define_comp_pointer_definition(op, function[:definition])
          end
        end

        # Defines the space function (`<=>`) for a pointer and an integer.
        # It returns `-1`, `0`, or `1`, if the receiver is less than, equal to,
        # or greater than the parameter, respectively.
        #
        # @param int [Core::Int] The integer type to compare to.
        # @return [void]
        def define_space_function(int)
          function_name = PTYPE.call(:<=>, [PTYPE, int.name])
          Core.define(function: function_name) do |function|
            function[:return] = Carbon::Type("Carbon::Int8")
            define_space_definition(int, function[:definition])
          end
        end

        # Defines a given math function on a pointer.
        #
        # @param int [Core::Int] The integer type that the operation uses.
        # @param op [::Symbol] The math operation to perform.  This should be
        #   one of {MATH_OPERATIONS}.
        # @return [void]
        def define_math_function(int, op)
          function_name = PTYPE.call(op, [PTYPE, int.name])
          Core.define(function: function_name) do |function|
            function[:return] = PTYPE
            define_math_definition(int, op, function[:definition])
          end
        end

        # Defines a given comparison operation on a pointer.
        #
        # @param int [Core::Int] The integer type that the operation uses.
        # @param op [::Symbol] The comparison operation to perform.  This should
        #   be one of {COMP_OPERATIONS}.
        def define_comp_function(int, op)
          function_name = PTYPE.call(op, [PTYPE, int.name])
          Core.define(function: function_name) do |function|
            function[:return] = Carbon::Boolean
            define_comp_definition(int, op, function[:definition])
          end
        end

      private

        def perform_pointer_cast(entry, params, int)
          this, other = params
          this.name, other.name = %w(self other)
          fname = PTYPE.call(int.cast, [PTYPE])
          thisint = entry.call(fname, this)
          otherint = entry.call(fname, other)
          [thisint, otherint]
        end

        def define_space_pointer_definition(definition)
          entry = definition.add("entry").build
          params = definition.params
          int = Int.find(sign: :signed, size: 64)
          this, other = perform_pointer_cast(entry, params, int)

          fname = PTYPE.call(:<=>, [int.name, int.name])
          entry.ret(entry.call(fname, this, other))
        end

        def define_comp_pointer_definition(op, definition)
          entry = definition.add("entry").build
          params = definition.params
          int = Ints.find { |i| i.sign == :signed && i.size == 64 }
          this, other = perform_pointer_cast(entry, params, int)
          icmp = Integer::Math::COMP_OPERATIONS_MAP.fetch([:signed, op])

          entry.ret(entry.icmp(icmp, this, other))
        end

        def define_space_definition(int, definition)
          entry = definition.add("entry").build
          this, other = definition.params
          this.name, other.name = %w(self other)

          fname = PTYPE.call(int.cast, [PTYPE])
          intptr = entry.call(fname, this)
          fname = PTYPE.call(:<=>, [int.name, int.name])
          entry.ret(entry.call(fname, intptr, other))
        end

        def define_comp_definition(int, op, definition)
          entry = definition.add("entry").build
          this, other = definition.params
          this.name, other.name = %w(self other)

          fname = PTYPE.call(int.cast, [PTYPE])
          intptr = entry.call(fname, this)
          icmp = Integer::Math::COMP_OPERATIONS_MAP.fetch([int.sign, op])
          entry.ret(entry.icmp(icmp, intptr, other))
        end

        def define_math_definition(_int, op, definition)
          entry = definition.add("entry").build
          this, other = definition.params
          this.name, other.name = %w(self other)
          other = entry.mul(other, -1) if op == :-

          entry.ret(entry.gep(this, other))
        end
      end
    end
  end
end