Revert "remove pg from vlib"

This reverts commit 15c5f671f0.

vlib/pg/pg.v

@@ -0,0 +1,124 @@
+module pg
+
+import os
+import time
+
+#flag -lpq
+#flag linux -I/usr/include/postgresql
+#flag darwin -I/opt/local/include/postgresql11
+#include <libpq-fe.h>
+
+struct DB {
+mut:
+	conn *C.PGconn
+}
+
+struct Row {
+pub:
+	vals []string
+}
+
+import const (
+	CONNECTION_OK
+) 
+
+struct C.PGResult { }
+
+fn C.PQconnectdb(a byteptr) *C.PGconn
+fn C.PQerrorMessage(voidptr) byteptr 
+fn C.PQgetvalue(voidptr, int, int) byteptr
+fn C.PQstatus(voidptr) int 
+
+pub fn connect(dbname, user string) DB {
+	conninfo := 'host=localhost user=$user dbname=$dbname'
+	conn:=C.PQconnectdb(conninfo.str)
+	status := C.PQstatus(conn)
+	if status != CONNECTION_OK { 
+		error_msg := C.PQerrorMessage(conn) 
+		eprintln('Connection to a PG database failed: ' + string(error_msg)) 
+		exit(1) 
+	}
+	return DB {conn: conn} 
+}
+
+fn res_to_rows(res voidptr) []pg.Row {
+	nr_rows := C.PQntuples(res) 
+	nr_cols := C.PQnfields(res) 
+	mut rows := []pg.Row
+	for i := 0; i < nr_rows; i++ {
+		mut row := Row{}
+		for j := 0; j < nr_cols; j++ {
+			val := C.PQgetvalue(res, i, j) 
+			row.vals << string(val)
+		}
+		rows << row
+	}
+	return rows
+}
+
+pub fn (db DB) q_int(query string) int {
+	rows := db.exec(query)
+	if rows.len == 0 {
+		println('q_int "$query" not found')
+		return 0
+	}
+	row := rows[0]
+	if row.vals.len == 0 {
+		return 0
+	}
+	val := row.vals[0]
+	return val.int() 
+}
+
+pub fn (db DB) q_string(query string) string {
+	rows := db.exec(query)
+	if rows.len == 0 {
+		println('q_string "$query" not found')
+		return ''
+	}
+	row := rows[0]
+	if row.vals.len == 0 {
+		return ''
+	}
+	val := row.vals[0]
+	return val
+}
+
+pub fn (db DB) q_strings(query string) []pg.Row {
+	return db.exec(query)
+}
+
+pub fn (db DB) exec(query string) []pg.Row {
+	res := C.PQexec(db.conn, query.str)
+	e := string(C.PQerrorMessage(db.conn))
+	if e != '' {
+		println('pg exec error:')
+		println(e)
+		return res_to_rows(res)
+	}
+	return res_to_rows(res)
+}
+
+
+// 
+pub fn (db DB) exec_param2(query string, param, param2 string) []pg.Row {
+	mut param_vals := [2]byteptr 
+	param_vals[0] = param.str 
+	param_vals[1] = param2.str 
+	res := C.PQexecParams(db.conn, query.str, 2, 0, param_vals, 0, 0, 0)  
+	e := string(C.PQerrorMessage(db.conn))
+	if e != '' {
+		println('pg exec2 error:')
+		println(e)
+		return res_to_rows(res)
+	}
+	return res_to_rows(res)
+}
+
+pub fn (db DB) exec_param(query string, param string) []pg.Row {
+	mut param_vals := [1]byteptr 
+	param_vals[0] = param.str 
+	res := C.PQexecParams(db.conn, query.str, 1, 0, param_vals, 0, 0, 0)  
+	return res_to_rows(res)
+}
+