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

# Generate the converter's base intermediate database migration file from
# the core database state and YAML configuration in schema.yml
# Invoke from core root directory as `./migrations/scripts/generate_schema`
# It accepts an optional command line argument for the output file path which
# overrides the path configured in schema.yml

puts "Loading application..."
require_relative "../../config/environment"

module Migrations
  class SchemaGenerator
    def initialize(opts = {})
      config = YAML.load_file(File.join(__dir__, "schema.yml"), symbolize_names: true)

      @core_db_connection = ActiveRecord::Base.connection
      @output_stream = StringIO.new
      @indirectly_ignored_columns = Hash.new { |h, k| h[k] = [] }

      @output_file_path = opts[:output_file_path] || config[:output_file_path]

      @table_configs = config[:tables]
      @column_configs = config[:columns]

      @configured_table_names = @table_configs&.keys&.sort || []
      @global_column_ignore_list = @column_configs[:ignore] || []
    end

    def run
      puts "Generating base converter migration file for Discourse #{Discourse::VERSION::STRING}"

      generate_header
      generate_tables
      generate_indirectly_ignored_columns_log
      generate_migration_file

      puts "", "Done"
    end

    private

    def generate_header
      @output_stream.puts <<~HEADER
        /*
         This file is auto-generated from the Discourse core database schema. Instead of editing it directly,
         please update the `schema.yml` configuration file and re-run the `generate_schema` script to update it.
        */
      HEADER
    end

    def generate_tables
      puts "Generating tables..."

      @configured_table_names.each do |name|
        raise "Core table named '#{name}' not found" unless valid_table?(name)

        generate_table(name)
      end
    end

    def generate_indirectly_ignored_columns_log
      puts "Generating indirectly ignored column list..."

      @output_stream.puts "\n\n/*"

      @output_stream.puts <<~NOTE
        Core table columns implicitly excluded from the generated schema above via the `include` configuration option
        in `schema.yml`. This serves as an inventory of these columns, allowing new core additions to be tracked and,
        if necessary, synchronized with the intermediate database schema.\n
      NOTE

      @indirectly_ignored_columns.each_with_index do |(table_name, columns), index|
        next if virtual_table?(table_name) || columns.blank?

        @output_stream.puts "" if index.positive?
        @output_stream.puts "Table: #{table_name}"
        @output_stream.puts "--------#{"-" * table_name.length}"

        columns.each do |column|
          @output_stream.puts " #{column.name} #{column.type} #{column.null}"
        end
      end

      @output_stream.puts "*/"
    end

    def generate_migration_file
      file_path = File.expand_path(@output_file_path, __dir__)

      puts "Generating base migration file '#{file_path}'..."

      File.open(file_path, "w") { |f| f << @output_stream.string.chomp }
    end

    def generate_column_definition(column)
      definition = "  #{column.name} #{type(column)}"
      definition << " NOT NULL" unless column.null

      definition
    end

    def generate_index(table_name, index)
      @output_stream.print "CREATE "
      @output_stream.print "UNIQUE " if index[:unique]
      @output_stream.print "INDEX #{index[:name]} ON #{table_name} (#{index[:columns].join(", ")})"
      @output_stream.print " #{index[:condition]}" if index[:condition].present?
      @output_stream.puts ";"
    end

    def column_list_for(table_name)
      ignore_columns = @table_configs.dig(table_name, :ignore) || []
      include_columns = @table_configs.dig(table_name, :include) || []

      include_columns.present? ? [:include, include_columns] : [:ignore, ignore_columns]
    end

    def generate_table(name)
      puts "Generating #{name}..."

      column_definitions = []
      column_records = columns(name)
      mode, column_list = column_list_for(name)
      indexes = indexes(name)
      configured_primary_key = primary_key(name)

      primary_key, composite_key =
        if configured_primary_key.present?
          [configured_primary_key].flatten.each do |pk|
            if column_records.map(&:name).exclude?(pk)
              raise "Column named '#{pk}' does not exist in table '#{name}'"
            end
          end

          [
            configured_primary_key,
            configured_primary_key.is_a?(Array) && configured_primary_key.length > 1,
          ]
        else
          virtual_table?(name) ? [] : [@core_db_connection.primary_key(name), false]
        end

      @output_stream.puts ""
      @output_stream.puts "CREATE TABLE #{name} ("

      if !composite_key && primary_key.present?
        primary_key_column = column_records.find { |c| c.name == primary_key }

        if (mode == :include && column_list.include?(primary_key_column.name)) ||
             (mode == :ignore && column_list.exclude?(primary_key_column.name))
          column_definitions << "  #{primary_key_column.name} #{type(primary_key_column)} NOT NULL PRIMARY KEY"
        end
      end

      column_records.each do |column|
        next if @global_column_ignore_list.include?(column.name)
        next if (mode == :ignore) && column_list.include?(column.name)
        if !column.is_a?(CustomColumn) && (mode == :include) && column_list.exclude?(column.name)
          @indirectly_ignored_columns[name] << column

          next
        end
        next if !composite_key && (column.name == primary_key)

        column_definitions << generate_column_definition(column)
      end

      column_definitions << "  PRIMARY KEY (#{primary_key.join(", ")})" if composite_key

      @output_stream.puts column_definitions.join(",\n")
      @output_stream.puts ");"
      @output_stream.puts "" if indexes.present?

      indexes.each { |index| generate_index(name, index) }
    end

    class CustomColumn
      attr_reader :name

      def initialize(name, type, null)
        @name = name
        @raw_type = type
        @raw_null = null
      end

      def type
        @raw_type&.to_sym || :text
      end

      def null
        @raw_null.nil? ? true : @raw_null
      end

      def merge!(other_column)
        @raw_null = other_column.null if @raw_null.nil?
        @raw_type ||= other_column.type

        self
      end
    end

    def columns(name)
      extensions = column_extensions(name)

      return extensions if virtual_table?(name)

      default_columns = @core_db_connection.columns(name)

      return default_columns if extensions.blank?

      extended_columns =
        default_columns.map do |default_column|
          extension = extensions.find { |ext| ext.name == default_column.name }

          if extension
            extensions.delete(extension)

            extension.merge!(default_column)
          else
            default_column
          end
        end

      extended_columns + extensions
    end

    def column_extensions(name)
      extensions = @table_configs.dig(name, :extend)

      return [] if extensions.nil?

      extensions.map { |column| CustomColumn.new(column[:name], column[:type], column[:is_null]) }
    end

    def type(column)
      case column.type
      when :string, :inet
        "TEXT"
      else
        column.type.to_s.upcase
      end
    end

    def valid_table?(name)
      @core_db_connection.tables.include?(name.to_s) || virtual_table?(name)
    end

    def virtual_table?(name)
      !!@table_configs.dig(name, :virtual)
    end

    def indexes(table_name)
      @table_configs.dig(table_name, :indexes) || []
    end

    def primary_key(table_name)
      @table_configs.dig(table_name, :primary_key)
    end
  end
end

Migrations::SchemaGenerator.new(output_file_path: ARGV.first).run