package de.srsoftware.widerhall.data;

import de.srsoftware.widerhall.Configuration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.*;

import static de.srsoftware.widerhall.Constants.*;
import static de.srsoftware.widerhall.Util.t;
import static de.srsoftware.widerhall.data.MailingList.HOLD_TIME;

/**
 * @author Stephan Richter, 2022
 * This class abstracts away all needed database operations
 */
public class Database {
    private static final Logger LOG = LoggerFactory.getLogger(Database.class);
    private static final String DB_VERSION = "db_version";
    private static Database singleton = null; // we only need one db handle ever. This will be it.
    private final Connection conn; // the actual db connection handle within the singleton

    /**
     * This class encapsulates a compiled request.
     * A compiled request is a ready-to execute sql string paired with a list of parameters
     */
    public class CompiledRequest{
        private final String sql;
        private final List<Object> args;

        /**
         * create new instance
         * @param sql final sql, ready to be executed
         * @param args arguments for the execution of the query
         */
        public CompiledRequest(String sql, List<Object> args){
            this.sql = sql;
            this.args = args;
        }

        /**
         * build the final SQL and execute the actual request (for SELECT statements)
         * @return the result set produced by the SELECT statement
         * @throws SQLException
         */
        public ResultSet exec() throws SQLException {
            LOG.debug("Executing {}",this);
            try {
                var stmt = conn.prepareStatement(sql);
                for (int i = 0; i < args.size(); i++) stmt.setObject(i+1, args.get(i));
                return stmt.executeQuery();
            } catch (SQLException sqle) { // add sql to the exception
                throw new SQLException(t("Query '{}' failed:",this),sqle);
            }
        }

        /**
         * build the final SQL and execure the actual request (for statements that generate no result)
         * @throws SQLException
         */
        public void run() throws SQLException {
            LOG.debug("Running {}",this);
            try {
                var stmt = conn.prepareStatement(sql);
                for (int i = 0; i < args.size(); i++) stmt.setObject(i+1, args.get(i));
                stmt.execute();
            } catch (SQLException sqle) {
                throw new SQLException(t("Query '{}' failed:",this),sqle);
            }
        }

        @Override
        public String toString() {
            var filled = sql;
            int pos = filled.indexOf('?');
            int idx = 0;
            while (pos>0){
                var fill = args.get(idx++);
                var s = fill == null ? "NULL" : (fill instanceof Number ? ""+fill : "'"+fill+"'");
                filled = filled.substring(0,pos)+s+filled.substring(pos+1);
                pos = filled.indexOf('?',pos+s.length());
            }
            return filled;
        }
    }

    /**
     * helper class to allow daisy-chaining request modifiers
     */
    public class Request{

        private String groupBy = null;
        private final StringBuilder sql; // buffer the sql to be built
        private final HashMap<String, List<Object>> where = new HashMap<>(); // buffer condition statements for select
        private final HashMap<String,Object> values = new HashMap<>(); // buffer values for insert/update statements
        private final List<String> sortFields = new ArrayList<>();

        /**
         * Start to create a new request with the initial SQL
         * @param sql initial sql for the request
         */
        public Request(StringBuilder sql) {
            this.sql = sql;
        }

        /**
         * conditions are assembled in the following form:
         * SELECT … FROM … WHERE [key] in ([values])
         * <values> are build as list of question marks, whose arguments are applied later
         * @param args
         */
        private void applyConditions(ArrayList<Object> args){
            if (!where.isEmpty()){
                var clauses = new ArrayList<String>();
                sql.append(" WHERE ");

                for (var entry : where.entrySet()){
                    { // build the list of question marks
                        var arr = new String[entry.getValue().size()];
                        Arrays.fill(arr, "?");
                        var marks = String.join(", ", arr);
                        clauses.add("(" + entry.getKey() + " IN (" + marks + "))");
                    }
                    args.addAll(entry.getValue()); // will be applied to the prepared statement later
                }
                sql.append(String.join(" AND ",clauses));
            }
        }

        private void applyGrouping(){
            if (groupBy != null && !groupBy.isBlank()) sql.append(" GROUP BY ").append(groupBy.trim());
        }

        private void applySorting(){
            if (!sortFields.isEmpty()) sql.append(" ORDER BY ").append(String.join(", ",sortFields));
        }

        /**
         * apply values (for insert or update statements)
         * @param args
         */
        private void applyValues(ArrayList<Object> args){
            if (values.isEmpty()) return;
            var currentSql = sql();
            if (currentSql.startsWith("INSERT")){
                var keys = new ArrayList<String>();
                for (var entry : values.entrySet()) {
                    keys.add(entry.getKey());
                    args.add(entry.getValue());
                }
                sql.append("(")
                        .append(String.join(", ",keys))
                        .append(")")
                        .append(" VALUES ");
                var arr = new String[args.size()];
                Arrays.fill(arr,"?");
                var marks = String.join(", ",arr);
                sql.append("(").append(marks).append(")");
            }
            if (currentSql.startsWith("UPDATE")){
                var expressions = new ArrayList<String>();
                for (var entry : values.entrySet()) {
                    expressions.add(entry.getKey()+" = ?");
                    args.add(entry.getValue());
                }
                sql.append(" SET ").append(String.join(", ",expressions));
            }
        }

        @Override
        protected Request clone() {
            Request clone = new Request(new StringBuilder(sql));
            clone.where.putAll(where);
            clone.values.putAll(values);
            return clone;
        }

        /**
         * finalize sql, save sql and arguments as compiled request
         * @return
         */
        public CompiledRequest compile(Object ...additionalArgs){
            var args = new ArrayList<>();
            applyValues(args);
            applyConditions(args);
            applyGrouping();
            applySorting();
            if (additionalArgs != null) {
                for (Object arg : additionalArgs) args.add(arg);
            }
            return new CompiledRequest(sql.toString(),args);
        }

        public Request groupBy(String column) {
            groupBy = column;
            return this;
        }

        public void run() throws SQLException {
            compile().run();
        }

        /**
         * set single value for a certain key
         * @param key
         * @param value
         * @return
         */
        public Request set(String key, Object value) {
            values.put(key,value);
            return this;
        }

        public Request sort(String field) {
            sortFields.add(field);
            return this;
        }

        /**
         * get the current (i.e. non-final) sql
         * @return
         */
        public String sql() {
            return sql.toString();
        }

        @Override
        public String toString() {
            return "Request("+clone().compile()+')';
        }

        /**
         * apply a map of values (for insert/update statements)
         * @param newValues
         * @return
         */
        public Request values(Map<String,Object> newValues) {
            values.putAll(newValues);
            return this;
        }

        /**
         * add a where condition in the form of … WHERE [key] in ([values])
         * @param key
         * @param values
         * @return
         */
        public Request where(String key, Object ... values) {
            for (var val : values) where(key,val);
            return this;
        }

        /**
         * add a where condition in the form of … WHERE [key] in ([values])
         * @param key
         * @param values
         * @return
         */
        public Request where(String key, Collection<? extends Object> values) {
            for (var val : values) where(key,val);
            return this;
        }

        /**
         * add a where condition in the form of … WHERE [key] in ([value])
         * @param key
         * @param value
         * @return
         */
        private Request where(String key, Object value) {
            var list = where.get(key);
            if (list == null) where.put(key,list = new ArrayList<>());
            list.add(value);
            return this;
        }
    }

    public Database(Connection connection) {
        this.conn = connection;
    }

    /**
     * take care of table creation, if required tables do not exist
     * @return
     * @throws SQLException
     */
    private Database assertTables() throws SQLException {
        if (!tableExists(User.TABLE_NAME)) User.createTable();
        if (!tableExists(MailingList.TABLE_NAME)) MailingList.createTable();
        if (!tableExists(ListMember.TABLE_NAME)) ListMember.createTable();
        if (!tableExists(Post.TABLE_NAME)) Post.createTable();
        if (!columnExists(MailingList.TABLE_NAME,HOLD_TIME)) MailingList.createHoldTimeColumn();
        return this;
    }

    private void createVersionTable() throws SQLException {
            var sql = "CREATE TABLE %s (%s %s NOT NULL PRIMARY KEY);".formatted(DB_VERSION,DB_VERSION,INT);
            var db = Database.open();
            db.query(sql).compile().run();
            sql = "INSERT INTO %s VALUES (1)".formatted(DB_VERSION);
            db.query(sql).compile().run();
    }

    private boolean columnExists(String tableName, String columnName) throws SQLException {
        var rs = Database.open().select("pragma_table_info('"+tableName+"')","COUNT(*) AS num").where("name",columnName).compile().exec();
        try {
            if (rs.next()) return rs.getInt("num") > 0;
        } finally {
            rs.close();
        }
        return false;
    }

    public void createColumn(String tableName, String colName, String...typeArgs) throws SQLException {
        var sql = new StringBuilder("ALTER TABLE ")
                .append(tableName)
                .append(" ADD COLUMN ")
                .append(colName)
                .append(" ")
                .append(String.join(" ",typeArgs));
        new Request(sql).compile().run();
    }

    /**
     * prepare a deletion statement
     * @param tableName
     * @return
     */
    public Request deleteFrom(String tableName){
        return new Request(new StringBuilder("DELETE FROM ").append(tableName).append(" "));
    }

    /**
     * prepare an insertion statement
     * @param tableName
     * @return
     */
    public Request insertInto(String tableName){
        return new Request(new StringBuilder("INSERT INTO ").append(tableName).append(" "));
    }

    /**
     * check if we have an active db connection
     * @return
     */
    public boolean isOpen() {
        return conn instanceof Connection;
    }

    /**
     * Open the database, if it is not open.
     * Will create the singleton on first call.
     * Consecutive calls will just return the singleton.
     * @return
     */
    public static Database open() {
        if (singleton == null){
            Configuration config = Configuration.instance();
            var dbFile = config.dbFile();
            String url = "jdbc:sqlite:"+dbFile;
            LOG.debug("Opening {}",url);
            dbFile.getParentFile().mkdirs();
            try {
                singleton = new Database(DriverManager.getConnection(url));
                singleton.assertTables(); // must not be concatenated to exception above (assertTables accesses singleton)!
                singleton.update202405();
            } catch (SQLException sqle) {
                sqle.printStackTrace();
            }
        }
        return singleton;
    }

    /**
     * Create a query from a pre-set StringBuilder
     * @param sql
     * @return
     */
    public Request query(StringBuilder sql) {
        return new Request(sql);
    }

    public Request query(String sql) {
        return new Request(new StringBuilder(sql));
    }

    /**
     * create a SELECT [flields] FROM [table] request.
     * If no fields are supplied, a request in the form SELECT * FROM [table] will be generated.
     * @param tableName
     * @param fields
     * @return
     */
    public Request select(String tableName,String ... fields) {
        StringBuilder sql = new StringBuilder("SELECT ");
        if (fields == null || fields.length == 0){
            sql.append("*");
        } else {
            sql.append(String.join(", ",fields));
        }
        return new Request(sql.append(" FROM ").append(tableName));
    }

    /**
     * check, whether a table with the provided name exists
     * @param tbName
     * @return
     * @throws SQLException
     */
    public boolean tableExists(String tbName) throws SQLException {
        try {
            var sql = new StringBuilder("SELECT EXISTS (SELECT name FROM sqlite_schema WHERE type='table' AND name='")
                    .append(tbName)
                    .append("')");
            ResultSet rs = query(sql).compile().exec();
            int val = 0;
            if (rs.next()) val = rs.getInt(1);
            rs.close();
            return val > 0;
        } catch (SQLException e) {
            throw new SQLException(t("Was not able to check existence of table {}!",tbName),e);
        }
    }

    /**
     * create an UPDATE [tableName] query
     * @param tableName
     * @return
     */
    public Request update(String tableName) {
        return new Request(new StringBuilder("UPDATE ").append(tableName));
    }

    private Database update202405() throws SQLException {
        if (!tableExists(Database.DB_VERSION)) {
            createVersionTable();
            User.addTokenColumn();
        }
        return this;
    }
}