package DBIx::Custom::QueryBuilder;

use strict;

use warnings;

use base 'Object::Simple';

use Carp 'croak';

use DBIx::Custom::Query;

# Carp trust relationship

push @DBIx::Custom::CARP_NOT, __PACKAGE__;

push @DBIx::Custom::Where::CARP_NOT, __PACKAGE__;

# Attributes

__PACKAGE__->attr('tags' => sub { {} });

sub build_query {

    my ($self, $source)  = @_;

    # Parse

    my $tree = $self->_parse($source);

    # Build query

    my $query = $self->_build_query($tree);

    return $query;

}

sub register_tag {

    my $self = shift;

    # Merge tag

    my $tags = ref $_[0] eq 'HASH' ? $_[0] : {@_};

    $self->tags({%{$self->tags}, %$tags});

    return $self;

}

sub _build_query {

    my ($self, $tree) = @_;

    # SQL

    my $sql = '';

    # All Columns

    my $all_columns = [];

    # Tables

    my $tables = [];

    # Build SQL 

    foreach my $node (@$tree) {

        # Text

        if ($node->{type} eq 'text') { $sql .= $node->{value} }

        # Tag

        else {

            # Tag name

            my $tag_name = $node->{tag_name};

            # Tag arguments

            my $tag_args = $node->{tag_args};

            # Table

            if ($tag_name eq 'table') {

                my $table = $tag_args->[0];

                push @$tables, $table;

                $sql .= $table;

                next;

            }

            # Get tag

            my $tag = $self->tag_processors->{$tag_name}

                             || $self->tags->{$tag_name};

            # Tag is not registered

            croak qq{Tag "$tag_name" in "{a }" is not registered}

                . qq{ (DBIx::Custom::QueryBuilder::build_query)}

              unless $tag;

            # Tag not sub reference

            croak qq{Tag "$tag_name" must be sub reference}

                . qq{ (DBIx::Custom::QueryBuilder::build_query)}

              unless ref $tag eq 'CODE';

            # Execute tag

            my $r = $tag->(@$tag_args);

            # Check tag return value

            croak qq{Tag "$tag_name" must return [STRING, ARRAY_REFERENCE]}

                . qq{ (DBIx::Custom::QueryBuilder::build_query)}

              unless ref $r eq 'ARRAY' && defined $r->[0] && ref $r->[1] eq 'ARRAY';

            # Part of SQL statement and colum names

            my ($part, $columns) = @$r;

            # Add columns

            push @$all_columns, @$columns;

            # Join part tag to SQL

            $sql .= $part;

        }

    }

    # Check placeholder count

    my $placeholder_count = $self->_placeholder_count($sql);

    my $column_count      = @$all_columns;

    croak qq{Placeholder count in "$sql" must be same as column count $column_count}

        . qq{ (DBIx::Custom::QueryBuilder::build_query)}

      unless $placeholder_count eq @$all_columns;

    # Add semicolon

    $sql .= ';' unless $sql =~ /;$/;

    # Query

    my $query = DBIx::Custom::Query->new(

        sql => $sql,

        columns => $all_columns,

        tables => $tables

    );

    return $query;

}

sub _parse {

    my ($self, $source) = @_;

    # Source

    $source ||= '';

    # Tree

    my @tree;

    # Value

    my $value = '';

    # State

    my $state = 'text';

    # Before charactor

    my $before = '';

    # Position

    my $pos = 0;

    # Parse

    my $original = $source;

    while (defined(my $c = substr($source, $pos, 1))) {

        # Last

        last unless length $c;

        # State is text

        if ($state eq 'text') {

            # Tag start charactor

            if ($c eq '{') {

                # Escaped charactor

                if ($before eq "\\") {

                    substr($value, -1, 1, '');

                    $value .= $c;

                }

                # Tag start

                else {

                    # Change state

                    $state = 'tag';

                    # Add text

                    push @tree, {type => 'text', value => $value}

                      if $value;

                    # Clear

                    $value = '';

                }

            }

            # Tag end charactor

            elsif ($c eq '}') {

                # Escaped charactor

                if ($before eq "\\") {

                    substr($value, -1, 1, '');

                    $value .= $c;

                }

                # Unexpected

                else {

                    croak qq{Parsing error. unexpected "\}". }

                        . qq{pos $pos of "$original"}

                        . qq{ (DBIx::Custom::QueryBuilder::build_query)};

                }

            }

            # Normal charactor

            else { $value .= $c }

        }

        # State is tags

        else {

            # Tag start charactor

            if ($c eq '{') {

                # Escaped charactor

                if ($before eq "\\") {

                    substr($value, -1, 1, '');

                    $value .= $c;

                }

                # Unexpected

                else {

                    croak qq{Parsing error. unexpected "\{". }

                        . qq{pos $pos of "$original"}

                        . qq{ (DBIx::Custom::QueryBuilder::build_query)};

                }

            }

            # Tag end charactor

            elsif ($c eq '}') {

                # Escaped charactor

                if ($before eq "\\") {

                    substr($value, -1, 1, '');

                    $value .= $c;

                }

                # Tag end

                else {

                    # Change state

                    $state = 'text';

                    # Add tag

                    my ($tag_name, @tag_args) = split /\s+/, $value;

                    push @tree, {type => 'tag', tag_name => $tag_name, 

                                 tag_args => \@tag_args};

                    # Clear

                    $value = '';

                }

            }

            # Normal charactor

            else { $value .= $c }

        }

        # Save before charactor

        $before = $c;

        # increment position

        $pos++;

    }

    # Tag not finished

    croak qq{Tag not finished. "$original"}

        . qq{ (DBIx::Custom::QueryBuilder::build_query)}

      if $state eq 'tag';

    # Add rest text

    push @tree, {type => 'text', value => $value}

      if $value;

    return \@tree;

}

sub _placeholder_count {

    my ($self, $expand) = @_;

    # Count

    $expand ||= '';

    my $count = 0;

    my $pos   = -1;

    while (($pos = index($expand, '?', $pos + 1)) != -1) {

        $count++;

    }

    return $count;

}

# DEPRECATED!

__PACKAGE__->attr('tag_processors' => sub { {} });

# DEPRECATED!

sub register_tag_processor {

    my $self = shift;

    # Merge tag

    my $tag_processors = ref $_[0] eq 'HASH' ? $_[0] : {@_};

    $self->tag_processors({%{$self->tag_processors}, %{$tag_processors}});

    return $self;

}

1;

=head1 NAME

DBIx::Custom::QueryBuilder - Query builder

=head1 SYNOPSIS

    my $builder = DBIx::Custom::QueryBuilder->new;

    my $query = $builder->build_query(

        "select from table {= k1} && {<> k2} || {like k3}"

    );

=head1 ATTRIBUTES

=head2 C<tags>

    my $tags = $builder->tags;

    $builder = $builder->tags(\%tags);

Tags.

=head1 METHODS

L<DBIx::Custom::QueryBuilder> inherits all methods from L<Object::Simple>

and implements the following new ones.

=head2 C<build_query>

    my $query = $builder->build_query($source);

Create a new L<DBIx::Custom::Query> object from SQL source.

SQL source contains tags, such as {= title}, {like author}.

C<{> and C<}> is reserved. If you use these charactors,

you must escape them using '\'. Note that '\' is

already perl escaped charactor, so you must write '\\'. 

    'select * from books \\{ something statement \\}'

B<Example:>

SQL source

      "select * from table where {= title} && {like author} || {<= price}"

Query

    {

        sql     => "select * from table where title = ? && author like ? price <= ?;"

        columns => ['title', 'author', 'price']

    }

=head2 C<register_tag>

    $builder->register_tag(\%tags);

    $builder->register_tag(%tags);

Register tag.

B<Example:>

    $builder->register_tag(

        '?' => sub {

            my $column = shift;

            return ['?', [$column]];

        }

    );

See also L<DBIx::Custom::Tag> to know tag.