Logging for D

module log;

import std.stdio;
import std.array;
import std.conv;
import std.string;
import std.datetime;

class Log
{
    string recordTemplate = `$t - $m`;// if not empty, then used as a template for output record;
    public LogEngine[] engines;
    bool IsEnabled = true;// Set to false if logging is not needed

    public this(LogEngine[] eng ...)
    {
        engines = eng;
        if (engines.length == 0) {
            engines.length = 1;
            engines[0] = new LogEngine();
        }
    }

    void opCall(T...)(string msg, T args)
    {
        if (!IsEnabled) return;

        if (recordTemplate != ``) {
            msg = replace(recordTemplate, `$m`,
                (args.length > 0 ? format(msg, args) : msg)
            );
            msg = replace(msg, `$t`, (cast(DateTime)Clock.currTime()).toSimpleString());
        }
        foreach(eng; engines)
            eng.Write(msg);
    }
}

class LogEngine
{
    public void Write(string msg)
    {
        writeln(msg);// default implementation, just output to console
    }
}

class FileLogEngine : LogEngine
{
    File f;
    public this(string FileName)
    {
        f = File(FileName, `a`);
    }

    override public void Write(string msg)
    {
        f.write(msg ~ "\n");
        f.flush();
    }
}

class DBLogEngine : LogEngine
{
    public this(string ConnectionString)
    {
        // open database connection
    }

    override public void Write(string msg)
    {
        // write record
    }
}

class EmailLogEngine : LogEngine
{
    public this(string host, int port = 25)
    {
        // initialize mail server structures
    }

    override public void Write(string msg)
    {
        // send message
    }
}