#!/usr/bin/env ruby
# frozen_string_literal: true

# Step 1: Direct Mapping from relational database to RDF
# Implements the W3C Direct Mapping (https://www.w3.org/TR/rdb-direct-mapping/)

require 'sequel'
require 'rdf'
require 'rdf/turtle'

BASE_IRI = 'http://example.org/migrants/'

DB = Sequel.mysql2(host: '127.0.0.1', port: 3306, user: 'migrants', database: 'migrants', password: '1234')

# Foreign key definitions: table -> { column -> [referenced_table, referenced_column] }
FOREIGN_KEYS = {
  migration_table: {
    IDPerson:     [:person,       :IDPerson],
    IDStartPlace: [:location,     :IDLocation],
    IDDestPlace:  [:location,     :IDLocation]
  },
  organisation: {
    IDLocation: [:location, :IDLocation]
  },
  person: {
    IDBirthPlace: [:location, :IDLocation],
    IDDeathPlace: [:location, :IDLocation]
  },
  personnames: {
    IDPerson: [:person, :IDPerson]
  },
  person_profession: {
    IDPerson: [:person, :IDPerson]
  },
  relationship: {
    IDPerson_active:  [:person,       :IDPerson],
    IDPerson_passive: [:person,       :IDPerson],
    IDLocation:       [:location,     :IDLocation],
    IDOrganisation:   [:organisation, :IDOrganisation]
  },
  religions: {
    IDPerson: [:person, :IDPerson]
  },
  work: {
    IDPerson:        [:person,       :IDPerson],
    IDLocation:      [:location,     :IDLocation],
    IDOrganisation:  [:organisation, :IDOrganisation],
    IDOrganisation2: [:organisation, :IDOrganisation]
  }
}.freeze

# Primary keys for each table
PRIMARY_KEYS = {
  location:           :IDLocation,
  migration_table:    :IDMig,
  organisation:       :IDOrganisation,
  person:             :IDPerson,
  person_profession:  :IDProfPerson,
  personnames:        :IDPersonname,
  relationship:       :IDRel,
  religions:          :IDReligion,
  work:               :IDWork
}.freeze

def row_iri(table, pk_value)
  RDF::URI.new("#{BASE_IRI}#{table}/#{URI.encode_www_form_component(pk_value.to_s)}")
end

def column_iri(table, column)
  RDF::URI.new("#{BASE_IRI}#{table}##{column}")
end

def class_iri(table)
  RDF::URI.new("#{BASE_IRI}#{table}")
end

def ref_iri(table, fk_col)
  RDF::URI.new("#{BASE_IRI}#{table}#ref-#{fk_col}")
end

def to_rdf_literal(value)
  case value
  when Integer
    RDF::Literal.new(value, datatype: RDF::XSD.integer)
  when Float
    RDF::Literal.new(value, datatype: RDF::XSD.double)
  when Date
    RDF::Literal.new(value.to_s, datatype: RDF::XSD.date)
  when Time, DateTime
    RDF::Literal.new(value.to_s, datatype: RDF::XSD.dateTime)
  when TrueClass, FalseClass
    RDF::Literal.new(value, datatype: RDF::XSD.boolean)
  else
    RDF::Literal.new(value.to_s)
  end
end

graph = RDF::Graph.new

PRIMARY_KEYS.each do |table, pk_col|
  fk_defs = FOREIGN_KEYS.fetch(table, {})

  DB[table].each do |row|
    pk_value = row[pk_col]
    subject = row_iri(table, pk_value)

    # rdf:type
    graph << [subject, RDF.type, class_iri(table)]

    row.each do |col, value|
      next if value.nil?

      col_sym = col.to_sym

      if fk_defs.key?(col_sym)
        # Foreign key -> object property linking to referenced row
        ref_table, _ref_col = fk_defs[col_sym]
        graph << [subject, ref_iri(table, col), row_iri(ref_table, value)]
      else
        # Regular column -> datatype property
        graph << [subject, column_iri(table, col), to_rdf_literal(value)]
      end
    end
  end
end

output_path = File.expand_path('../graph-01.ttl', __dir__)
RDF::Turtle::Writer.open(output_path, prefixes: {
  rdf:  RDF.to_uri,
  xsd:  RDF::XSD.to_uri,
  base: RDF::URI.new(BASE_IRI)
}) do |writer|
  graph.each_statement { |stmt| writer << stmt }
end

puts "Written #{graph.count} triples to #{output_path}"