#! /usr/bin/env ruby

# Inspired by
# https://gist.github.com/jeromedalbert/afab24e80102b41d75d5f5538f1459c4
#
# This requires the following setup in a relevant Git attributes file:
#
#     db/schema.rb merge=railsschema
#
# And then the following setup in a relevant Git config file:
#
#     [merge "railsschema"]
#       name = Rails schema.db merge driver
#       driver = "path/to/this/script" %O %A %B %L %P
#
# (For further details, 'git help gitattributes', section 'Defining a custom
# merge driver')

ancestor, current, other, marker_size, final_path = ARGV

current_name = %x(git name-rev --name-only HEAD).strip
other_name = %x(git name-rev --name-only ORIG_HEAD).strip
ancestor_ref = %x(git merge-base HEAD ORIG_HEAD).strip
ancestor_name = %x(git name-rev --name-only #{ancestor_ref}).strip

MARKER = 'ActiveRecord::Schema\\.define\\(version: ([0-9_]+)\\)\\s+do'
REGEX = %r(^<{#{marker_size}} .*\n#{MARKER}\n={#{marker_size}}\n#{MARKER}\n>{#{marker_size}} .*)

system 'git', 'merge-file', "--marker-size=#{marker_size}", "-L #{current_name}", "-L #{ancestor_name}", "-L #{other_name}", current, ancestor, other
source = File.read(current)
modified = source.sub(REGEX) { "ActiveRecord::Schema.define(version: #{[$1, $2].max}) do" }

if source != modified
  File.open(current, 'w') { |f| f.write modified }
end

# Indicate leftover conflicts, if any
exit 1 if modified.include?('<' * marker_size.to_i)

# Otherwise mark auto-addition and stage it!
system 'git', 'add', final_path