# frozen_string_literal: true

require_relative '../phonetics'
require 'json'

module Phonetics
  class CodeGenerator
    attr_reader :writer

    def initialize(writer = STDOUT)
      @writer = writer
    end

    def generate_phonetic_cost_c_code
      generator = PhoneticCost.new(writer)
      generator.generate
      writer.flush
    end

    def generate_next_phoneme_length_c_code
      generator = NextPhonemeLength.new(writer)
      generator.generate
      writer.flush
    end

    private

    def binary(str)
      "0b#{str.bytes.map { |byte| byte.to_s(2).rjust(8, '0') }.join}"
    end

    # Turn the bytes of all phonemes into a lookup trie where a sequence of
    # bytes can find a phoneme in linear time.
    def phoneme_byte_trie
      phoneme_byte_trie_for(Phonetics.phonemes)
    end

    def phoneme_byte_trie_for(phonemes)
      phonemes.each_with_object({}) do |phoneme, trie|
        phoneme.bytes.each_with_index.reduce(trie) do |subtrie, (byte, idx)|
          subtrie[byte] ||= {}

          # If we've reached the end of the byte string
          if phoneme.bytes.length - 1 == idx
            # Check if this is a duplicate lookup path. If there's a collision
            # then this whole approach makes no sense.
            if subtrie[byte].key?(:source)
              source = subtrie[byte][:source]
              raise "Duplicate byte sequence on #{phoneme.inspect} & #{source.inspect} (#{phoneme.bytes.inspect})"
            else
              subtrie[byte][:source] = phoneme
            end
          end
          subtrie[byte]
        end
      end
    end

    def describe(phoneme, depth = 0)
      indent depth, "// Phoneme: '#{phoneme}', bytes: #{phoneme.bytes.inspect}"
      if Phonetics::Consonants.features.key?(phoneme)
        indent depth, "// consonant features: #{Phonetics::Consonants.features[phoneme].to_json}"
      else
        indent depth, "// vowel features: #{Phonetics::Vowels::FormantFrequencies[phoneme].to_json}"
      end
    end

    def ruby_source
      location = caller_locations.first
      "#{location.path.split('/')[-4..-1].join('/')}:#{location.lineno}"
    end

    def indent(depth, line)
      write "    #{' ' * depth}#{line}"
    end

    def write(line)
      writer.puts line
    end
  end

  class PhoneticCost < CodeGenerator
    # We find the phonetic distance between two phonemes using a compiled
    # lookup table. This is implemented as a set of nested switch statements.
    # Hard to read when compiled, but simple to generate and fast at runtime.
    #
    # We generate a `phonetic_cost` function that takes four arguments: Two
    # strings, and the lengths of those strings. Each string should be exactly
    # one valid phoneme, which is possible thanks to the (also generated)
    # next_phoneme_length() function.
    #
    # This will print a C code file with a function that implements a multil-level C
    # switch like the following:
    #
    #    switch (phoneme1) {
    #      case 'ɪ': // two bytes: [201, 170]
    #                // vowel features: {"F1":300,"F2":2100,"rounded":false}
    #
    #         switch(phoneme2) {
    #            'i': // one byte: [105]
    #                 // vowel features: {"F1":240,"F2":2400,"rounded":false}
    #              return (float) 0.14355381904337383;
    #              break;
    #
    #  the distance of ("ɪ", "i")2 is therefore 0.14355
    #
    def generate
      write(<<-HEADER.gsub(/^ {6}/, ''))

      // This is compiled from Ruby, in #{ruby_source}
      #include <stdint.h>
      #include <stdio.h>
      #include <inttypes.h>
      float phonetic_cost(int64_t phoneme1, int64_t phoneme2) {
        if (phoneme1 == phoneme2) {
          return (float) 0.0;
        }

      HEADER

      write '  switch (phoneme1) {'
      Phonetics.phonemes.each do |phoneme1|
        write "    case #{binary(phoneme1)}:"
        describe(phoneme1, 2)
        write '      switch(phoneme2) {'
        Phonetics.distance_map[phoneme1].each do |phoneme2, distance|
          write "        case #{binary(phoneme2)}:"
          describe(phoneme2, 6)
          write "          return (float) #{distance};"
          write '          break;'
        end
        write '      }'
        write '      break;'
      end
      write '  }'
      write '  return (float) 1.0;'
      write '};'
      write ''
    end
  end

  class NextPhonemeLength < CodeGenerator
    # There's no simple way to break a string of IPA characters into phonemes.
    # We do it by generating a function that, given a string of IPA characters,
    # the starting index in that string, and the length of the string, returns
    # the length of the next phoneme, or zero if none is found.
    #
    # Pseudocode:
    #   - return 0 if length - index == 0
    #   - switch on first byte, matching on possible first bytes of phonemes
    #     within the selected case statement:
    #     - return 1 if length - index == 1
    #     - switch on second byte, matching on possible second bytes of phonemes
    #       within the selected case statement:
    #       - return 2 if length - index == 1
    #       ...
    #       - default case: return 2 iff a phoneme terminates here
    #     - default case: return 1 iff a phoneme terminates here
    #   - return 0
    #
    def generate
      write(<<-HEADER.gsub(/^ {6}/, ''))
      // This is compiled from Ruby, in #{ruby_source}
      #include <stdio.h>
      int next_phoneme_length(int *string, int cursor, int length) {

        int max_length;
        max_length = length - cursor;

      HEADER

      next_phoneme_switch(phoneme_byte_trie, 0)

      # If we fell through all the cases, return 0
      write '  return 0;'
      write '}'
    end

    private

    # Recursively build switch statements for the body of next_phoneme_length
    def next_phoneme_switch(trie, depth)
      # switch (string[cursor + depth]) {
      #   case N: // for N in subtrie.keys
      #     // if a case statement matches the current byte AND there's chance
      #     // that a longer string might match, recurse.
      #     if (max_length >= depth) {
      #       // recurse
      #     }
      #     break;
      #   // if there's a :source key here then a phoneme terminates at this
      #   // point and this depth is a valid return value.
      #   default:
      #     return depth;
      #     break;
      # }
      indent depth, "switch(string[cursor + #{depth}]) {"
      write ''
      trie.each do |key, subtrie|
        next if key == :source
        next if subtrie.empty?

        indent depth, "case #{key}:"

        # Add a comment to help understand the dataset
        describe(subtrie[:source], depth + 1) if subtrie[:source]

        if subtrie.keys == [:source]
          indent depth, " return #{depth + 1};"
        else
          indent depth, " if (max_length > #{depth + 1}) {"
          next_phoneme_switch(subtrie, depth + 1)
          indent depth, ' } else {'
          indent depth, "   return #{depth + 1};"
          indent depth, ' }'
        end

        indent depth, '    break;'
      end

      if trie.key?(:source)
        indent depth, '  default:'
        indent depth, "    return #{depth};"
      end
      indent depth, '}'
    end
  end
end