package SQL::Translator::Diff;


## SQLT schema diffing code
use strict;
use warnings;

use Data::Dumper;
use SQL::Translator::Schema::Constants;

use base 'Class::Accessor::Fast';

# Input/option accessors
__PACKAGE__->mk_accessors(qw/
  ignore_index_names ignore_constraint_names ignore_view_sql
  ignore_proc_sql output_db source_schema target_schema 
  case_insensitive no_batch_alters ignore_missing_methods producer_options
/);

my @diff_arrays = qw/
  tables_to_drop
  tables_to_create
/;

my @diff_hash_keys = qw/
  constraints_to_create
  constraints_to_drop
  indexes_to_create
  indexes_to_drop
  fields_to_create
  fields_to_alter
  fields_to_rename
  fields_to_drop
  table_options
  table_renamed_from
/;

__PACKAGE__->mk_accessors(@diff_arrays, 'table_diff_hash');

sub schema_diff {
    #  use Data::Dumper;
    ## we are getting instructions on how to turn the source into the target
    ## source == original, target == new (hmm, if I need to comment this, should I rename the vars again ??)
    ## _schema isa SQL::Translator::Schema
    ## _db is the name of the producer/db it came out of/into
    ## results are formatted to the source preferences

    my ($source_schema, $source_db, $target_schema, $output_db, $options) = @_;
    $options ||= {};

    my $obj = SQL::Translator::Diff->new( {
      %$options,
      source_schema => $source_schema,
      target_schema => $target_schema,
      output_db     => $output_db
    } );

    $obj->compute_differences->produce_diff_sql;
}

sub new {
  my ($class, $values) = @_;
  $values->{$_} ||= [] foreach @diff_arrays;
  $values->{table_diff_hash} = {};

  $values->{producer_options} ||= {};
  $values->{output_db} ||= $values->{source_db};
  return $class->SUPER::new($values);
}

sub compute_differences {
    my ($self) = @_;

    my $target_schema = $self->target_schema;
    my $source_schema = $self->source_schema;

    my $producer_class = "SQL::Translator::Producer::@{[$self->output_db]}";
    eval "require $producer_class";
    die $@ if $@;

    if (my $preprocess = $producer_class->can('preprocess_schema')) {
      $preprocess->($source_schema);
      $preprocess->($target_schema);
    }

    my %src_tables_checked = ();
    my @tar_tables = sort { $a->name cmp $b->name } $target_schema->get_tables;
    ## do original/source tables exist in target?
    for my $tar_table ( @tar_tables ) {
      my $tar_table_name = $tar_table->name;

      my $src_table;

      $self->table_diff_hash->{$tar_table_name} = {
        map {$_ => [] } @diff_hash_keys
      };

      if (my $old_name = $tar_table->extra('renamed_from')) {
        $src_table = $source_schema->get_table( $old_name, $self->case_insensitive );
        if ($src_table) {
          $self->table_diff_hash->{$tar_table_name}{table_renamed_from} = [ [$src_table, $tar_table] ];
        } else {
          delete $tar_table->extra->{renamed_from};
          warn qq#Renamed table can't find old table "$old_name" for renamed table\n#;
        }
      } else {
        $src_table = $source_schema->get_table( $tar_table_name, $self->case_insensitive );
      }

      unless ( $src_table ) {
        ## table is new
        ## add table(s) later. 
        push @{$self->tables_to_create}, $tar_table;
        next;
      }

      my $src_table_name = $src_table->name;
      $src_table_name = lc $src_table_name if $self->case_insensitive;
      $src_tables_checked{$src_table_name} = 1;


      $self->diff_table_options($src_table, $tar_table);

      ## Compare fields, their types, defaults, sizes etc etc
      $self->diff_table_fields($src_table, $tar_table);

      $self->diff_table_indexes($src_table, $tar_table);
      $self->diff_table_constraints($src_table, $tar_table);

    } # end of target_schema->get_tables loop

    for my $src_table ( $source_schema->get_tables ) {
      my $src_table_name = $src_table->name;

      $src_table_name = lc $src_table_name if $self->case_insensitive;

      push @{ $self->tables_to_drop}, $src_table
        unless $src_tables_checked{$src_table_name};
    }

    return $self;
}

sub produce_diff_sql {
    my ($self) = @_;

    my $target_schema = $self->target_schema;
    my $source_schema = $self->source_schema;
    my $tar_name  = $target_schema->name;
    my $src_name  = $source_schema->name;

    my $producer_class = "SQL::Translator::Producer::@{[$self->output_db]}";
    eval "require $producer_class";
    die $@ if $@;

    # Map of name we store under => producer method name
    my %func_map = (
      constraints_to_create => 'alter_create_constraint',
      constraints_to_drop   => 'alter_drop_constraint',
      indexes_to_create     => 'alter_create_index',
      indexes_to_drop       => 'alter_drop_index',
      fields_to_create      => 'add_field',
      fields_to_alter       => 'alter_field',
      fields_to_rename      => 'rename_field',
      fields_to_drop        => 'drop_field',
      table_options         => 'alter_table',
      table_renamed_from    => 'rename_table',
    );
    my @diffs;
  
    if (!$self->no_batch_alters && 
        (my $batch_alter = $producer_class->can('batch_alter_table')) ) 
    {
      # Good - Producer supports batch altering of tables.
      foreach my $table ( sort keys %{$self->table_diff_hash} ) {
        my $tar_table = $target_schema->get_table($table)
                     || $source_schema->get_table($table);

        push @diffs, $batch_alter->($tar_table,
          { map {
              $func_map{$_} => $self->table_diff_hash->{$table}{$_}
            } keys %func_map 
          }, 
          $self->producer_options
        );
      }
    } else {

      # If we have any table renames we need to do those first;
      my %flattened_diffs;
      foreach my $table ( sort keys %{$self->table_diff_hash} ) {
        my $table_diff = $self->table_diff_hash->{$table};
        for (@diff_hash_keys) {
          push( @{ $flattened_diffs{ $func_map{$_} } ||= [] }, @{ $table_diff->{$_} } );
        }
      }

      push @diffs, map( {
          if (@{ $flattened_diffs{$_} || [] }) {
            my $meth = $producer_class->can($_);
            
            $meth ? map { 
                    my $sql = $meth->( (ref $_ eq 'ARRAY' ? @$_ : $_), $self->producer_options );
                    $sql ?  ("$sql") : (); 
                  } @{ $flattened_diffs{$_} }
                  : $self->ignore_missing_methods
                  ? "-- $producer_class cant $_"
                  : die "$producer_class cant $_";
          } else { () }

        } qw/rename_table
             alter_drop_constraint
             alter_drop_index
             drop_field
             add_field
             alter_field
             rename_field
             alter_create_index
             alter_create_constraint
             alter_table/),
    }

    if (my @tables = @{ $self->tables_to_create } ) {
      my $translator = new SQL::Translator(
        producer_type => $self->output_db,
        add_drop_table => 0,
        no_comments => 1,
        # TODO: sort out options
        %{ $self->producer_options }
      );
      $translator->producer_args->{no_transaction} = 1;
      my $schema = $translator->schema;

      $schema->add_table($_) for @tables;

      unshift @diffs, 
        # Remove begin/commit here, since we wrap everything in one.
        grep { $_ !~ /^(?:COMMIT|START(?: TRANSACTION)?|BEGIN(?: TRANSACTION)?)/ } $producer_class->can('produce')->($translator);
    }

    if (my @tables_to_drop = @{ $self->{tables_to_drop} || []} ) {
      my $meth = $producer_class->can('drop_table');
      
      push @diffs, $meth ? ( map { $meth->($_, $self->producer_options) } @tables_to_drop)
                         : $self->ignore_missing_methods
                         ? "-- $producer_class cant drop_table"
                         : die "$producer_class cant drop_table";
    }

    if (@diffs) {
      unshift @diffs, "BEGIN";
      push    @diffs, "\nCOMMIT";
    } else {
      @diffs = ("-- No differences found");
    }

    if ( @diffs ) {
      if ( $self->output_db !~ /^(?:MySQL|SQLite|PostgreSQL)$/ ) {
        unshift(@diffs, "-- Output database @{[$self->output_db]} is untested/unsupported!!!");
      }

      my @return = 
        map { $_ ? ( $_ =~ /;$/xms ? $_ : "$_;\n\n" ) : "\n" }
        ("-- Convert schema '$src_name' to '$tar_name':", @diffs);

      return wantarray ? @return : join('', @return);
    }
    return undef;

}

sub diff_table_indexes {
  my ($self, $src_table, $tar_table) = @_;

  my (%checked_indices);
  INDEX_CREATE:
  for my $i_tar ( $tar_table->get_indices ) {
    for my $i_src ( $src_table->get_indices ) {
      if ( $i_tar->equals($i_src, $self->case_insensitive, $self->ignore_index_names) ) {
        $checked_indices{$i_src} = 1;
        next INDEX_CREATE;
      }
    }
    push @{$self->table_diff_hash->{$tar_table}{indexes_to_create}}, $i_tar;
  }

  INDEX_DROP:
  for my $i_src ( $src_table->get_indices ) {
    next if !$self->ignore_index_names && $checked_indices{$i_src};
    for my $i_tar ( $tar_table->get_indices ) {
      next INDEX_DROP if $i_src->equals($i_tar, $self->case_insensitive, $self->ignore_index_names);
    }
    push @{$self->table_diff_hash->{$tar_table}{indexes_to_drop}}, $i_src;
  }
}


sub diff_table_constraints {
  my ($self, $src_table, $tar_table) = @_;

  my(%checked_constraints);
  CONSTRAINT_CREATE:
  for my $c_tar ( $tar_table->get_constraints ) {
    for my $c_src ( $src_table->get_constraints ) {

      # This is a bit of a hack - needed for renaming tables to work
      local $c_src->{table} = $tar_table;

      if ( $c_tar->equals($c_src, $self->case_insensitive, $self->ignore_constraint_names) ) {
        $checked_constraints{$c_src} = 1;
        next CONSTRAINT_CREATE;
      }
    }
    push @{ $self->table_diff_hash->{$tar_table}{constraints_to_create} }, $c_tar;
  }


  CONSTRAINT_DROP:
  for my $c_src ( $src_table->get_constraints ) {

    # This is a bit of a hack - needed for renaming tables to work
    local $c_src->{table} = $tar_table;

    next if !$self->ignore_constraint_names && $checked_constraints{$c_src};
    for my $c_tar ( $tar_table->get_constraints ) {
      next CONSTRAINT_DROP if $c_src->equals($c_tar, $self->case_insensitive, $self->ignore_constraint_names);
    }

    push @{ $self->table_diff_hash->{$tar_table}{constraints_to_drop} }, $c_src;
  }

}

sub diff_table_fields {
  my ($self, $src_table, $tar_table) = @_;

  # List of ones ew've renamed from so we dont drop them
  my %renamed_source_fields;

  for my $tar_table_field ( $tar_table->get_fields ) {
    my $f_tar_name      = $tar_table_field->name;

    if (my $old_name = $tar_table_field->extra->{renamed_from}) {
      my $src_table_field = $src_table->get_field( $old_name, $self->case_insensitive );
      unless ($src_table_field) {
        warn qq#Renamed column can't find old column "@{[$src_table->name]}.$old_name" for renamed column\n#;
        delete $tar_table_field->extra->{renamed_from};
      } else {
        push @{$self->table_diff_hash->{$tar_table}{fields_to_rename} }, [ $src_table_field, $tar_table_field ];
        $renamed_source_fields{$old_name} = 1;
        next;
      }
    }

    my $src_table_field = $src_table->get_field( $f_tar_name, $self->case_insensitive );

    unless ( $src_table_field ) {
      push @{$self->table_diff_hash->{$tar_table}{fields_to_create}}, $tar_table_field;
      next;
    }

    # field exists, something changed. This is a bit complex. Parsers can 
    # normalize types, but only some of them do, so compare the normalized and
    # parsed types for each field to each other
    if ( !$tar_table_field->equals($src_table_field, $self->case_insensitive) &&
         !$tar_table_field->equals($src_table_field->parsed_field, $self->case_insensitive) && 
         !$tar_table_field->parsed_field->equals($src_table_field, $self->case_insensitive) && 
         !$tar_table_field->parsed_field->equals($src_table_field->parsed_field, $self->case_insensitive) ) {

      # Some producers might need src field to diff against
      push @{$self->table_diff_hash->{$tar_table}{fields_to_alter}}, [ $src_table_field, $tar_table_field ];
      next;
    }
  }


  # Now check to see if any fields from src_table need to be dropped
  for my $src_table_field ( $src_table->get_fields ) {
    my $f_src_name      = $src_table_field->name;
    next if $renamed_source_fields{$f_src_name};

    my $tar_table_field = $tar_table->get_field( $f_src_name, $self->case_insensitive );

    unless ( $tar_table_field ) {
      push @{$self->table_diff_hash->{$tar_table}{fields_to_drop}}, $src_table_field;
      next;
    }
  }
}

sub diff_table_options {
  my ($self, $src_table, $tar_table) = @_;

  my $cmp = sub {
    my ($a_name, undef, $b_name, undef) = ( %$a, %$b );
    $a_name cmp $b_name;
  };
  # Need to sort the options so we dont get supruious diffs.
  my (@src_opts, @tar_opts);
  @src_opts = sort $cmp $src_table->options;
  @tar_opts = sort $cmp $tar_table->options;


  # If there's a difference, just re-set all the options
  push @{ $self->table_diff_hash->{$tar_table}{table_options} }, $tar_table
    unless $src_table->_compare_objects( \@src_opts, \@tar_opts );
}

1;

__END__

=head1 NAME

SQL::Translator::Diff

=head1 DESCRIPTION

Takes two input SQL::Translator::Schemas (or SQL files) and produces ALTER 
statments to make them the same

=head1 SNYOPSIS

Simplest usage:

 use SQL::Translator::Diff;
 my $sql = SQL::Translator::Diff::schema_diff($source_schema, 'MySQL', $target_schema, 'MySQL', $options_hash)

OO usage:

 use SQL::Translator::Diff;
 my $diff = SQL::Translator::Diff->new({
   output_db     => 'MySQL',
   source_schema => $source_schema,
   target_schema => $target_schema,
   %$options_hash,
 })->compute_differences->produce_diff_sql;

=head1 OPTIONS

=over

=item B<ignore_index_names>

Match indexes based on types and fields, ignoring name.

=item B<ignore_constraint_names>

Match constrains based on types, fields and tables, ignoring name.

=item B<output_db>

Which producer to use to produce the output.

=item B<case_insensitive>

Ignore case of table, field, index and constraint names when comparing

=item B<no_batch_alters>

Produce each alter as a distinct C<ALTER TABLE> statement even if the producer
supports the ability to do all alters for a table as one statement.

=item B<ignore_missing_methods>

If the diff would need a method that is missing from the producer, just emit a
comment showing the method is missing, rather than dieing with an error

=back

=head1 PRODUCER FUNCTIONS

The following producer functions should be implemented for completeness. If
any of them are needed for a given diff, but not found, an error will be 
thrown.

=over

=item * C<alter_create_constraint($con)>

=item * C<alter_drop_constraint($con)>

=item * C<alter_create_index($idx)>

=item * C<alter_drop_index($idx)>

=item * C<add_field($fld)>

=item * C<alter_field($old_fld, $new_fld)>

=item * C<rename_field($old_fld, $new_fld)>

=item * C<drop_field($fld)>

=item * C<alter_table($table)>

=item * C<drop_table($table)>

=item * C<rename_table($old_table, $new_table)> (optional)

=item * C<batch_alter_table($table, $hash)> (optional)

If the producer supports C<batch_alter_table>, it will be called with the 
table to alter and a hash, the keys of which will be the method names listed
above; values will be arrays of fields or constraints to operate on. In the 
case of the field functions that take two arguments this will appear as a hash.

I.e. the hash might look something like the following:

 {
   alter_create_constraint => [ $constraint1, $constraint2 ],
   add_field   => [ $field ],
   alter_field => [ [$old_field, $new_field] ]
 }


=item * C<preprocess_schema($class, $schema)> (optional)

C<preprocess_schema> is called by the Diff code to allow the producer to
normalize any data it needs to first. For example, the MySQL producer uses
this method to ensure that FK contraint names are unique.

Basicaly any changes that need to be made to produce the SQL file for the
schema should be done here, so that a diff between a parsed SQL file and (say)
a parsed DBIx::Class::Schema object will be sane.

(As an aside, DBIx::Class, for instance, uses the presence of a 
C<preprocess_schema> function on the producer to know that it can diff between
the previous SQL file and its own internal representation. Without this method
on th producer it will diff the two SQL files which is slower, but known to 
work better on old-style producers.)

=back


=head1 AUTHOR

Original Author(s) unknown.

Refactor/re-write and more comprehensive tests by Ash Berlin C<< ash@cpan.org >>.

Redevelopment sponsored by Takkle Inc.

=cut
