#!/usr/bin/perl
# 
# take apart a mysql dump.gz to into compressed table.zstd files
#
# cc-by_sa / GPLv3+ by Peter 'grin' Gervai, 2023
#

use warnings;
use strict;
use IO::File;

# the dump file
my $fn = "db_dump.sql.gz";

# skip these tables
my %skip = ( 'stupid_table' => 1, 'dont_need_either' => 1 );

# target dir
my $dir = "d_split_tables";
`mkdir -p ${dir}`			# that's the laziest way, highly unportable, yadda-yadda

# cat a compressed file
my $gzip_cat = "pigz -dcf";		# or 'gz' if you wish single threaded
my $zstd_cat = "zstd -T0 -dcf";		# or 'gz -dcf' or whatever
# store it compressed
my $zstd_store = "zstd -T0 - -o";	# or 'gz - -o' or even 'cat >'

# globals are okay
my $table='';	# actually processing table name (convenience)
my $skip=0;	# are we skipping a table now?

# write prelude into this file
my $fout = IO::File->new( "| ${zstd_store} prelude.sql" ) or die "cannot create prelude.sql: $!";

my $cnt=0; 	# count tables for fun

# read the compressed dump (usually .gz)
$f = IO::File->new( "${gzip_cat} $fn |" ) or die "cannot read pipe: $!";
while( <$f> ) {
    if( $skip ) {			# we are actively skipping this table
        if( /^UNLOCK TABLES;/ ) {	# that's the end of a table dump (for me, if it isn't for you... tough luck)
            $skip = 0;			# end of skip mode
        }
        next;				# skip, get next line
    }
    
    if( /^DROP TABLE.+`([^`]+)`;/ ) {	# start of a new table (again, for me)
        $table = $1;			# better readability: get table name
        if( $skip{$table} ) {		# this could be rewritten as a regex, for example
            print "SKIP $table!\n";	# skip stuff in %skip hash
            $skip = 1;			# entering skip mode
            next;
        }
        $fout->close;			# let's start a new file for a new table
        $fout = IO::File->new( "| ${zstd_store} ${dir}/table_${table}.sql.zst" ) or die "Cannot pipe for table_${table}.sql: $!";
        $cnt++;
        print "Created table_${table} as #${cnt}...         \r";
    }
    
    print $fout $_;			# no skip, we have a file already open, so write the line there
}

print "\n\nDone. ($cnt)\n\n";		# sayonara.