Migration tool for crystal web frameworks

pg_migrate.cr

# prosgres Migration tool for crystal frameworks
# just create a ./db folder and add some migrations files

# ./db/0.sql
# ./db/1.sql
# ...
# ./db/22.sql # and so on ...
#
# Usage :
# require "pg" # I use a modified version solisoft/crystal-pg for now until main repo deployed
# DB = PG.connect("postgres://#{ENV["db_user"]}:#{ENV["db_password"]}@#{ENV["db_host"]}:#{ENV["db_port"]}/#{ENV["db_name"]}")
# require "./pg_migrate"
# migration = PgMigrate.new(DB)
# migration.run


class PgMigrate

  def initialize(raw)
    @raw = raw
  end

  def run
    puts "Running migrations..."
    start = 0 # starting at migration 0
    if from_scratch?
      # If no versions table then create it
      @raw.exec("CREATE TABLE versions( last_version  INT )")
    else
      # Get latest migration's version
      start = @raw.exec("SELECT last_version FROM versions LIMIT 1").rows.first.first as Int32 rescue 0
    end
    m = false # Used to check if at least one migration was done
    files = Dir.entries("./db/") - [".", ".."]
    files = files.map {|l| l.split(".").first.to_i }.sort
    files.each do |f|
      if f > start # A new migration ?
        m = true
        puts ":: Migrating #{f}.sql"
        puts @raw.exec_all(File.open("./db/#{f}.sql").read())
        # set latest version
        @raw.exec_all("TRUNCATE versions; INSERT INTO versions VALUES (#{f});")
      end
    end
    puts ":: Nothing to migrate" unless m
    puts "Done"
  end

  # Check if versions table exists or not
  private def from_scratch?
    tables = @raw.exec("SELECT * FROM pg_catalog.pg_tables").rows
    tables = tables.select {|l| l[0] == "public"}
    tables = tables.map {|l| l[1]}
    tables.index("versions") == nil
  end
end