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=head1 NAME

Database::Abstraction - Read-only Database Abstraction Layer (ORM)

=head1 VERSION

Version 0.36

=cut

=head1 DESCRIPTION

C<Database::Abstraction> is a read-only ORM for Perl that gives a uniform
interface over CSV, PSV, XML, SQLite, and BerkeleyDB files - without writing
any SQL.

Key features:

=over 4

=item *

B<No SQL required.>  Use plain Perl method calls for simple lookups and
scans; switch storage formats without changing application code.

=item *

B<Rich query criteria.>  Pass plain values, SQL wildcards, C<undef> (IS NULL),
comparison operators (C<< > >> C<< < >> C<< >= >> C<< <= >> C<!=>), pattern
operators (C<-like>, C<-not_like>), set operators (C<-in>, C<-not_in>,
C<-between>), and logical groupings (C<-or>, C<-and>).

=item *

B<Automatic joins.>  Add a C<join> parameter to any select method to
combine tables with INNER, LEFT, RIGHT, FULL, or CROSS joins.

=item *

B<Chained query builder.>  The C<query()> method returns a
L<Database::Abstraction::Query> object for fluent, composable queries:
C<< $db->query->where(...)->order_by(...)->limit(...)->all() >>.

=item *

B<Schema introspection.>  C<columns()> lists column names; C<schema()>
returns full type/nullability metadata, using native driver introspection
(C<PRAGMA table_info> for SQLite, C<column_info> for others).

=item *

B<DSN portability.>  Pass a C<dsn> (plus optional C<username>/C<password>)
to connect to any DBI-supported database (SQLite, PostgreSQL, MySQL, ...)
instead of pointing at a local file.

=item *

B<Performance.>  Small files are slurped into a RAM hash for sub-millisecond
lookups.  All DBI statement handles are cached with C<prepare_cached()>.
A CHI-compatible cache layer is also supported.

=back

=head1 SYNOPSIS

    # 1. Create a thin subclass for your table (e.g. Database/Foo.pm)
    package Database::Foo;
    use parent 'Database::Abstraction';

    # 2. Open the database - file is auto-detected from the class name
    #    (looks for foo.sql / foo.psv / foo.csv / foo.xml / foo.db)
    my $db = Database::Foo->new(directory => '/path/to/data');

    # 3. Simple lookups -----------------------------------------------

    # Fetch one row
    my $row = $db->fetchrow_hashref(entry => 'key1');

    # Fetch all rows matching a criterion
    my $rows = $db->selectall_arrayref(status => 'active');

    # Column shortcut via AUTOLOAD
    my $name = $db->name(entry => 'key1');

    # 4. Rich criteria ------------------------------------------------

    # Comparison operators
    my $high = $db->selectall_arrayref(score => { '>' => 90 });

    # Set membership
    my $selected = $db->selectall_arrayref(
        name => { -in => ['Alice', 'Bob'] }
    );

    # Range
    my $mid = $db->selectall_arrayref(
        score => { -between => [60, 80] }
    );

    # OR grouping
    my $either = $db->selectall_arrayref(
        -or => [
            { status => 'active'    },
            { score  => { '>' => 95 } },
        ]
    );

    # 5. Joins --------------------------------------------------------

    my $joined = $db->selectall_arrayref(
        join => { table => 'dept', on => 'foo.dept_id = dept.id', type => 'LEFT' }
    );

    # 6. Chained query builder ----------------------------------------

    my $results = $db->query
        ->where(status => 'active')
        ->where(score  => { '>=' => 80 })
        ->order_by('score DESC')
        ->limit(10)
        ->all();

    my $first = $db->query->where(name => 'Alice')->first();
    my $count = $db->query->where(status => 'active')->count();

    # 7. Connect via DSN (PostgreSQL, MySQL, SQLite, ...) ---------------

    my $db2 = Database::Foo->new(
        dsn      => 'dbi:Pg:dbname=mydb;host=db.example.com',
        username => 'myuser',
        password => 's3cret',
    );

    # 8. Schema introspection -----------------------------------------

    my $cols   = $db->columns();  # ['entry', 'name', 'score', ...]
    my $schema = $db->schema();   # { name => { type=>'TEXT', nullable=>1, ... }, ... }

=head1 QUICK START EXAMPLE

If F</var/dat/foo.csv> contains:

    "customer_id","name"
    "plugh","John"
    "xyzzy","Jane"

Create a driver in F<.../Database/foo.pm>:

    package Database::foo;
    use parent 'Database::Abstraction';

    # Regular CSV: no entry column, comma-separated
    sub new {
        my ($class, %args) = @_;
        return $class->SUPER::new(no_entry => 1, sep_char => ',', %args);
    }

Then query it:

    my $foo = Database::foo->new(directory => '/var/dat');

    # Prints "John"
    print 'Customer: ', $foo->name(customer_id => 'plugh'), "\n";

    # Returns { customer_id => 'xyzzy', name => 'Jane' }
    my $row = $foo->fetchrow_hashref(customer_id => 'xyzzy');

=head1 FILE FORMATS

The module probes the C<directory> for files in this priority order:

=over 4

=item 1. C<SQLite>

File ending C<.sql>

=item 2. C<PSV>

Pipe-separated file, ending C<.psv>

=item 3. C<CSV>

Comma (or custom) separated file, ending C<.csv> or C<.db>; can be
gzipped.  B<Note:> the default separator is C<!> not C<,> for historical
reasons - pass C<< sep_char => ',' >> for standard CSVs.

=item 4. C<XML>

File ending C<.xml>

=item 5. C<BerkeleyDB>

Binary key-value file ending C<.db>

=back

Pass C<dsn> to bypass file detection entirely and connect via any DBI driver.

=head1 QUERY CRITERIA

All select methods (C<selectall_arrayref>, C<selectall_array>,
C<fetchrow_hashref>, C<count>) accept the same criteria syntax.

=head2 Plain value

    status => 'active'          # status = 'active'
    name   => undef             # name IS NULL

Values containing C<%> or C<_> are matched with C<LIKE>:

    name => 'A%'                # name LIKE 'A%'

=head2 Comparison operator hashref

    score => { '>'  => 90  }   # score > 90
    score => { '<'  => 50  }   # score < 50
    score => { '>=' => 80  }   # score >= 80
    score => { '<=' => 100 }   # score <= 100
    score => { '!=' => 0   }   # score != 0

Multiple operators on one column are ANDed:

    score => { '>' => 60, '<' => 90 }   # 60 < score < 90

=head2 Pattern matching

    name => { -like     => 'A%'  }   # name LIKE 'A%'
    name => { -not_like => 'Z%'  }   # name NOT LIKE 'Z%'

=head2 Set membership

    name => { -in     => ['Alice', 'Bob'] }   # name IN (...)
    name => { -not_in => ['Alice', 'Bob'] }   # name NOT IN (...)

=head2 Range

    score => { -between => [60, 90] }   # score BETWEEN 60 AND 90

=head2 Logical groupings

C<-or> and C<-and> take an arrayref of condition hashrefs:

    -or => [
        { status => 'active'        },
        { score  => { '>' => 95 }   },
    ]

    -and => [
        { status => 'active'        },
        { score  => { '>=' => 80 }  },
    ]

=head2 Joins

Any select method accepts a C<join> key with a hashref (or arrayref of
hashrefs) describing the join:

    join => {
        table => 'dept',
        on    => 'employees.dept_id = dept.id',
        type  => 'LEFT',    # INNER (default) | LEFT | RIGHT | FULL | CROSS
    }

    # Multiple joins
    join => [
        { table => 'dept',    on => 'e.dept_id   = dept.id'   },
        { table => 'country', on => 'e.country_id = country.id' },
    ]

=head1 SUBROUTINES/METHODS

=head2 init

Set class-level defaults shared by all instances.

    Database::Abstraction::init(directory => '../data');

Accepts the same parameters as L</new>.  Returns a reference to the
current defaults hash, so you can read them back:

    my $defaults = Database::Abstraction::init();
    print $defaults->{'directory'}, "\n";

=cut

=head2 import

The module can be initialised by the C<use> directive.

    use Database::Abstraction 'directory' => '/etc/data';

or

    use Database::Abstraction { 'directory' => '/etc/data' };

=cut

=head2 new

Create an object pointing to a read-only database.

Accepts arguments as a hash, a hashref, or - as a shortcut - a single bare
string which is taken to be C<directory>.

=head3 Connection parameters

=over 4

=item * C<directory>

Directory containing the data files.  The module probes this directory for
files named after the subclass (see L</FILE FORMATS>).  Required unless
C<dsn> is given.

=item * C<dsn>

A DBI data-source string (e.g. C<dbi:SQLite:dbname=/path/to/db> or
C<dbi:Pg:dbname=mydb;host=db.example.com>).  When present, file detection
is skipped entirely and the DSN is used directly.  The SQL dialect is
inferred from the DSN prefix (C<sqlite>, C<postgres>, C<mysql>).

=item * C<username>

Database username.  Used only with C<dsn>; ignored for file-based backends.

=item * C<password>

Database password.  Used only with C<dsn>; ignored for file-based backends.

=item * C<dbname>

Override the filename stem searched in C<directory> (default: the table
name derived from the class name).

=item * C<filename>

Override the full filename (relative to C<directory>).  Takes precedence
over C<dbname>.

=back

=head3 Behaviour parameters

=over 4

=item * C<no_entry>

Set to C<1> when the table has no key column (standard CSVs, for example).
Default is C<0> (keyed on C<entry>).

=item * C<id>

Name of the key column.  Default is C<entry>.

=item * C<sep_char>

Field separator for CSV/PSV files.
Default is C<!> - pass C<< sep_char => ',' >>
for standard comma-separated files.

=item * C<max_slurp_size>

Files smaller than this (in bytes) are loaded entirely into memory for fast
lookups.  Default is 16 KB.  Set to C<0> to force SQL mode for all sizes.

=item * C<no_fixate>

Set to C<1> to return mutable arrays.  Default is C<0> (arrays are made
read-only via L<Data::Reuse>).

=item * C<auto_load>

Set to C<0> to disable the AUTOLOAD column shortcut.  Default is C<1>
(enabled).

=back

=head3 Caching and logging

=over 4

=item * C<cache>

A L<CHI>-compatible cache object.  When set, query results are stored and
retrieved from the cache.

=item * C<cache_duration> / C<expires_in>

TTL for cached results.  Default is C<'1 hour'>.  C<expires_in> is a
synonym for compatibility with L<CHI>.

=item * C<logger>

An object that understands C<warn()> and C<trace()> (e.g.
L<Log::Log4perl>, L<Log::Any>), a code reference, or a filename.

=item * C<config_file>

Path to a YAML, XML, or INI configuration file whose keys are merged into
the constructor arguments.  Loaded via L<Object::Configure>.

=back

=head3 Notes

=over 4

=item *

If no arguments are set, class-level defaults set via C<init()> or C<use>
are used.

=item *

Slurp mode assumes the key column (C<entry>) is unique.  If it is not,
searches will be incomplete - disable slurp mode by setting
C<< max_slurp_size => 0 >>.

=item *

Passing an existing object as C<$class> clones it, merging any new
arguments.

=back

=cut

=head2  set_logger

Sets the class, code reference, or file that will be used for logging.

=cut

=head2 selectall_arrayref

Returns a reference to an array of hash references for every row that
matches the given criteria, or C<undef> when there are no matches.

    my $rows = $db->selectall_arrayref();                    # all rows
    my $rows = $db->selectall_arrayref(status => 'active');  # exact match
    my $rows = $db->selectall_arrayref(score => { '>' => 8 });  # operator

The full criteria syntax is described in L</QUERY CRITERIA>.

Pass a C<join> key to combine with another table:

    my $rows = $db->selectall_arrayref(
        dept_name => 'Engineering',
        join      => { table => 'dept', on => 'e.dept_id = dept.id' },
    );

Results are returned in the cache (if configured) and the returned array
reference is made read-only unless C<no_fixate> was set.

B<Note:> this always returns all matching rows.  Use L</selectall_array>
in scalar context, or C<< $db->query->limit(1)->all() >>, to fetch just one row.

=head3 PSEUDOCODE

    1. Parse criteria; extract and build any JOIN clause.
    2. If data is slurped AND no joins AND criteria are simple:
       a. No criteria -> return all rows as arrayref.
       b. entry-only lookup -> return [$data{entry}].
       c. Otherwise -> scan rows in-memory with _match_criterion.
    3. Otherwise build SQL: SELECT * FROM table [JOIN] [WHERE] ORDER BY id.
    4. Check cache; return cached arrayref on HIT.
    5. prepare_cached + execute; fetch all rows.
    6. Store result in cache; fixate the array; return arrayref.

=cut

=head2 selectall_hashref

Deprecated alias for L</selectall_arrayref>.  Use C<selectall_arrayref> in
new code.

=cut

=head2 selectall_array

Similar to L</selectall_arrayref> but returns a list of hash references
rather than a reference to an array.

    my @rows = $db->selectall_array(status => 'active');

In B<scalar context> it applies C<LIMIT 1> and returns just the first
matching hash reference - making it more efficient than C<selectall_arrayref>
when you only need one row.  In B<list context> all matching rows are returned.

Accepts the same criteria and C<join> parameter as L</selectall_arrayref>.

=cut

=head2 selectall_hash

Deprecated alias for L</selectall_array>.  Use C<selectall_array> in new
code.

=cut

=head2 count

Returns the number of rows matching the given criteria.

    my $total  = $db->count();
    my $active = $db->count(status => 'active');
    my $high   = $db->count(score  => { '>' => 90 });

Accepts the full criteria syntax described in L</QUERY CRITERIA>.

=cut

=head2 fetchrow_hashref

Returns a hash reference for the first row matching the given criteria,
or C<undef> when there is no match.  Always applies C<LIMIT 1>.

    my $row = $db->fetchrow_hashref(entry => 'key1');
    my $row = $db->fetchrow_hashref(score => { '>=' => 10 });

When C<no_entry> is B<not> set you may pass a single bare value and it is
used as the C<entry> key:

    my $row = $db->fetchrow_hashref('key1');    # same as entry => 'key1'

Accepts the full criteria syntax described in L</QUERY CRITERIA>, including
the C<join> parameter:

    my $row = $db->fetchrow_hashref(
        name => 'Alice',
        join => { table => 'dept', on => 'e.dept_id = dept.id' },
    );

Pass C<< table => $other_table >> to query a table other than the one
derived from the class name.

=cut