# This file assumes that the output of the generator will be placed
# within a module or a class.  However, the module/class requires a
# `type` method, which takes a terminal and gives its type, as a
# symbol.  These types should line up with the terminals that were
# defined in the original grammar.

# The actions to take during parsing.  In every state, there are a
# set of acceptable peek tokens; this table tells the parser what
# to do on each acceptable peek token.  The possible actions include
# `:accept`, `:reduce`, and `:state`; `:accept` means to accept the
# input and return the value of the pasing.  `:reduce` means to
# reduce the top of the stack into a given nonterminal.  `:state`
# means to transition to another state.
#
# @return [Array<Hash<(Symbol, Array<(Symbol, Numeric)>)>>]
ACTION_TABLE = {{= generate_action_table }}.freeze

# A list of all of the productions.  Only includes the left-hand side,
# the number of tokens on the right-hand side, and the block to call
# on reduction.
#
# @return [Array<Array<(Symbol, Numeric, Proc)>>]
PRODUCTIONS  = {{= generate_productions_list }}.freeze

# Runs the parser.
#
# @param input [Array<Object>] the input to run the parser over.
# @return [Object] the result of the accept.
def parse(input)
  stack = []
  stack.push([nil, 0])
  input = input.dup
  last  = nil

  until stack.empty? do
    last = parse_action(stack, input)
  end

  last

end

# Actually performs the parsing action on the given stack on input.
# If you want to implement a push parser, than messing with this
# method is probably the way to go.
#
# @param stack [Array<Array<(Object, Numeric)>>] the stack of the
#   parser.  The actual order of the stack is important.
# @param input [Array<Object>] the input to run the parser over.
#   The elements of this may be passed to the `type` method.
# @return [Object] the result of the last accepting reduction.
def parse_action(stack, input)
  last = nil
  peek_token = if input.empty?
    :$end
  else
    type(input.first)
  end

  action = ACTION_TABLE[stack.last.last].fetch(peek_token) do
    ACTION_TABLE[stack.last.last].fetch(:$default)
  end
  case action.first
  when :accept
    production = PRODUCTIONS[action.last]
    last       = stack.pop(production[1]).first.first
    stack.pop
  when :reduce
    production = PRODUCTIONS[action.last]
    removing   = stack.pop(production[1])
    value = instance_exec(*removing.map(&:first), &production[2])
    goto  = ACTION_TABLE[stack.last.last][production[0]]
    stack.push([value, goto.last])
  when :state
    stack.push([input.shift, action.last])
  else
    raise NotImplementedError, "Unknown action #{action.first}"
  end

  last

rescue KeyError => e
  if handle_error(
    { :stack     => stack,
      :peek      => peek_token,
      :remaining => input,
      :error     => e,
      :expected  => ACTION_TABLE[stack.last.last].keys
    })
    retry
  end
end

{{ if define_own_handler? }}
def handle_error(data, _ = false)
{{   if panic_mode? }}
  if _ || data[:peek] == :$end # we can't recover if
                              # we're at the end
{{   end }}
    raise {{= error_class }},
      "Unexpected token #{data[:peek]}; " \
      "expected one of #{data[:expected].join(', ')}",
      data[:error].backtrace
{{   if panic_mode? }}
  end

  new_peek = :$error
  acceptable_state = false
  state = nil

  until data[:stack].empty? or acceptable_state
    state = data[:stack].last.last

    if ACTION_TABLE[state].key?(new_peek)
      acceptable_state = true
    else
      data[:stack].pop # discard
    end
  end

  return handle_error(data, true) unless acceptable_state

  action = ACTION_TABLE[state][new_peek]
  lookaheads = nil

  until lookaheads
    if action[0] == :state
      lookaheads = ACTION_TABLE[action.last].keys
    elsif action[0] == :reduce
      rule   = PRODUCTIONS[action.last]
      action = ACTION_TABLE[stack[-rule[1]].last][rule[0]]
    end
  end

  until data[:remaining].empty? || lookaheads.
    include?(data[:remaining][0].first)
    data[:remaining].shift
  end

  data[:remaining].unshift([new_peek, data[:error]])
  true

{{   end }}
end
{{ end }}