diff --git a/src/group.js b/src/group.js
new file mode 100644
index 0000000..9fda360
--- /dev/null
+++ b/src/group.js
@@ -0,0 +1,151 @@
+var DB; //container for database
+
+function addTag(floID, tag) {
+    return new Promise((resolve, reject) => {
+        DB.query("INSERT INTO Tags (floID, tag) VALUE (?,?)", [floID, tag])
+            .then(result => resolve(`Added ${floID} to ${tag}`))
+            .catch(error => {
+                if (error.code === "ER_DUP_ENTRY")
+                    reject(`${floID} already in ${tag}`);
+                else
+                    reject(error);
+            });
+    });
+}
+
+function getBest() {
+    return new Promise((resolve, reject) => {
+        DB.query("SELECT tag FROM TagList ORDER BY priority DESC").then(result => {
+            let tags = result.map(r => r.tag);
+            recursiveGetBest(tags)
+                .then(result => resolve(result))
+                .catch(error => reject(error))
+        })
+    })
+}
+
+function recursiveGetBest(tags) {
+    return new Promise((resolve, reject) => {
+        let tag = tags.shift();
+        getBestInTag(tag)
+            .then(result => resolve(result))
+            .catch(error => {
+                if (error !== false)
+                    return reject(error);
+                else
+                    recursiveGetBest(tags)
+                    .then(result => resolve(result))
+                    .catch(error => reject(error))
+            })
+    })
+}
+
+function getBestInTag(tag, cur_price) {
+    return new Promise((resolve, reject) => {
+        DB.query("SELECT SellOrder.id, SellOrder.floID, SellOrder.quantity FROM SellOrder" +
+            " INNER JOIN Tags ON Tags.floID = SellOrder.floID" +
+            " WHERE Tags.tag = ? AND minPrice <=? ORDER BY time_placed", [tag, cur_price]).then(orders => {
+            if (orders.length === 0)
+                reject(false);
+            else if (orders.length === 1)
+                checkMinimumGain(orders[0])
+                .then(result => resolve(result))
+                .catch(error => reject(error))
+            else
+                getPointsFromAPI(orders.map(o => o.floID)).then(points => {
+                    let orders_sorted = orders.map(o => [o, points[o.floID]])
+                        .sort((a, b) => a[1] < b[1] ? -1 : a[1] > b[1] ? 1 : 0) //sort by points (ascending)
+                        .map(x => x[0]);
+                    getTopValidOrder(orders_sorted)
+                        .then(result => resolve(result))
+                        .catch(error => reject(error))
+                }).catch(error => reject(error))
+        })
+    });
+}
+
+function getPointsFromAPI(floIDs) {
+    floIDs = Array.from(new Set(floIDs));
+    return new Promise((resolve, reject) => {
+        DB.query("SELECT api FROM TagList WHERE tag=?", [tag]).then(result => {
+            let api = result[0].api;
+            Promise.allSettled(floIDs.map(id => fetch_api(api, id))).then(result => {
+                let points = {};
+                for (let i in result)
+                    if (result[i].status === "fulfilled")
+                        points[floIDs[i]] = result[i];
+                resolve(points);
+            }).catch(error => reject(error))
+        }).catch(error => reject(error))
+    });
+}
+
+function fetch_api(api, id) {
+    return new Promise((resolve, reject) => {
+        //TODO: fetch data from API
+    })
+}
+
+function getTopValidOrder(orders) {
+    return new Promise((resolve, reject) => {
+        if (!orders.length)
+            return reject(false)
+        checkMinimumGain(orders.pop()) //pop: as the orders are sorted in ascending (highest point should be checked 1st)
+            .then(result => resolve(result))
+            .catch(error => {
+                if (error !== false)
+                    return reject(error);
+                else
+                    getTopValidOrder(orders)
+                    .then(result => resolve(result))
+                    .catch(error => reject(error));
+            });
+    });
+}
+
+function checkMinimumGain(sellOrder) {
+    return new Promise((resolve, reject) => {
+        DB.query("SELECT id, quantity, base FROM Vault WHERE floID=? ORDER BY base", [sellOrder.floID]).then(result => {
+            let rem = Math.min(sellOrder.quantity, maxQuantity),
+                sell_base = 0,
+                base_quantity = 0,
+                txQueries = [];
+            for (let i = 0; i < result.length && rem > 0; i++) {
+                if (rem < result[i].quantity) {
+                    txQueries.push(["UPDATE Vault SET quantity=quantity-? WHERE id=?", [rem, result[i].id]]);
+                    if (result[i].base) {
+                        sell_base += (rem * result[i].base);
+                        base_quantity += rem;
+                    }
+                    rem = 0;
+                } else {
+                    txQueries.push(["DELETE FROM Vault WHERE id=?", [result[i].id]]);
+                    if (result[i].base) {
+                        sell_base += (result[i].quantity * result[i].base);
+                        base_quantity += result[i].quantity;
+                    }
+                    rem -= result[i].quantity;
+                }
+            }
+            if (base_quantity)
+                sell_base = sell_base / base_quantity;
+            if (rem > 0 || sell_base > cur_price) {
+                //1st condition (rem>0) should not happen (sell order placement was success when insufficient FLO).
+                if (rem > 0)
+                    console.warn(`Sell order ${sellOrder.id} is active, but FLO is insufficient`);
+                reject(false);
+            } else
+                resolve({
+                    sellOrder,
+                    txQueries
+                });
+        }).catch(error => reject(error));
+    })
+
+}
+
+module.exports = {
+    set DB(db) {
+        DB = db;
+    }
+};
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