// Copyright 2011 Xing Xing <mikespook@gmail.com> All rights reserved.
// Use of this source code is governed by a MIT
// license that can be found in the LICENSE file.

package worker

import (
    "time"
    "github.com/mikespook/gearman-go/common"
)

const (
    Unlimited = 0
    OneByOne = 1

    Immediately = 0
)

var (
    ErrConnection = common.ErrConnection
)
// Job handler
type JobHandler func(*Job) error

type JobFunc func(*Job) ([]byte, error)

// The definition of the callback function.
type jobFunc struct {
    f JobFunc
    timeout uint32
}

// Map for added function.
type JobFuncs map[string]*jobFunc

/*
Worker side api for gearman

usage:
w = worker.New(worker.Unlimited)
w.AddFunction("foobar", foobar)
w.AddServer("127.0.0.1:4730")
w.Work() // Enter the worker's main loop

The definition of the callback function 'foobar' should suit for the type 'JobFunction'.
It looks like this:

func foobar(job *Job) (data []byte, err os.Error) {
    //sth. here
    //plaplapla...
    return
}
*/
type Worker struct {
    agents  []*agent
    funcs   JobFuncs
    in chan *Job
    running bool
    limit chan bool

    Id string
    // assign a ErrFunc to handle errors
    ErrHandler common.ErrorHandler
    JobHandler JobHandler
}

// Get a new worker
func New(l int) (worker *Worker) {
    worker = &Worker{
        agents: make([]*agent, 0),
        funcs: make(JobFuncs),
        in:  make(chan *Job, common.QUEUE_SIZE),
    }
    if l != Unlimited {
        worker.limit = make(chan bool, l)
    }
    return
}

// 
func (worker *Worker)err(e error) {
    if worker.ErrHandler != nil {
        worker.ErrHandler(e)
    }
}

// Add a server. The addr should be 'host:port' format.
// The connection is established at this time.
func (worker *Worker) AddServer(addr string) (err error) {
    // Create a new job server's client as a agent of server
    server, err := newAgent(addr, worker)
    if err != nil {
        return err
    }
    worker.agents = append(worker.agents, server)
    return
}

// Write a job to job server.
// Here, the job's mean is not the oraginal mean.
// Just looks like a network package for job's result or tell job server, there was a fail.
func (worker *Worker) broadcast(job *Job) {
    for _, v := range worker.agents {
        v.WriteJob(job)
    }
}

// Add a function.
// Plz added job servers first, then functions.
// The API will tell every connected job server that 'I can do this'
func (worker *Worker) AddFunc(funcname string,
f JobFunc, timeout uint32) (err error) {
    if _, ok := worker.funcs[funcname]; ok {
        return common.Errorf("The function already exists: %s", funcname)
    }
    worker.funcs[funcname] = &jobFunc{f: f, timeout: timeout}

    if worker.running {
        worker.addFunc(funcname, timeout)
    }
    return
}

// inner add function
func (worker *Worker) addFunc(funcname string, timeout uint32) {
    var datatype uint32
    var data []byte
    if timeout == 0 {
        datatype = common.CAN_DO
        data = []byte(funcname)
    } else {
        datatype = common.CAN_DO_TIMEOUT
        data = []byte(funcname + "\x00")
        t := common.Uint32ToBytes(timeout)
        data = append(data, t[:]...)
    }
    job := newJob(common.REQ, datatype, data)
    worker.broadcast(job)

}

// Remove a function.
// Tell job servers 'I can not do this now' at the same time.
func (worker *Worker) RemoveFunc(funcname string) (err error) {
    if _, ok := worker.funcs[funcname]; !ok {
        return common.Errorf("The function does not exist: %s", funcname)
    }
    delete(worker.funcs, funcname)
    if worker.running {
        worker.removeFunc(funcname)
    }
    return
}

// inner remove function
func (worker *Worker) removeFunc(funcname string) {
    job := newJob(common.REQ, common.CANT_DO, []byte(funcname))
    worker.broadcast(job)
}

func (worker *Worker) dealJob(job *Job) {
    defer func() {
        job.Close()
        if worker.running && worker.limit != nil {
            <-worker.limit
        }
    }()
    switch job.DataType {
    case common.ERROR:
        _, err := common.GetError(job.Data)
        worker.err(err)
    case common.JOB_ASSIGN, common.JOB_ASSIGN_UNIQ:
        if err := worker.exec(job); err != nil {
            worker.err(err)
        }
    default:
        worker.handleJob(job)
    }
}

// Main loop
func (worker *Worker) Work() {
    defer func() {
        for _, v := range worker.agents {
            v.Close()
        }
    }()
    worker.running = true
    for _, v := range worker.agents {
        go v.Work()
    }
    for funcname, f := range worker.funcs {
        worker.addFunc(funcname, f.timeout)
    }
    ok := true
    for ok {
        var job *Job
        if job, ok = <-worker.in; ok {
            go worker.dealJob(job)
        }
    }
}

// job handler
func (worker *Worker) handleJob(job *Job) {
    if worker.JobHandler != nil {
        if err := worker.JobHandler(job); err != nil {
            worker.err(err)
        }
    }
}

// Close.
func (worker *Worker) Close() {
    worker.running = false
    close(worker.in)
    if worker.limit != nil {
        close(worker.limit)
    }
}

// Send a something out, get the samething back.
func (worker *Worker) Echo(data []byte) {
    job := newJob(common.REQ, common.ECHO_REQ, data)
    worker.broadcast(job)
}

// Remove all of functions.
// Both from the worker or job servers.
func (worker *Worker) Reset() {
    job := newJob(common.REQ, common.RESET_ABILITIES, nil)
    worker.broadcast(job)
    worker.funcs = make(JobFuncs)
}

// Set the worker's unique id.
func (worker *Worker) SetId(id string) {
    worker.Id = id
    job := newJob(common.REQ, common.SET_CLIENT_ID, []byte(id))
    worker.broadcast(job)
}

// Execute the job. And send back the result.
func (worker *Worker) exec(job *Job) (err error) {
    defer func() {
        if r := recover(); r != nil {
            if e, ok := r.(error); ok {
                err = e
            } else {
                err = common.ErrUnknown
            }
        }
    } ()
    f, ok := worker.funcs[job.Fn]
    if !ok {
        return common.Errorf("The function does not exist: %s", job.Fn)
    }
    var r *result
    if f.timeout == 0 {
        d, e := f.f(job)
        r = &result{data:d, err: e}
    } else {
        r = execTimeout(f.f, job, time.Duration(f.timeout) * time.Second)
    }
    var datatype uint32
    if r.err == nil {
        datatype = common.WORK_COMPLETE
    } else {
        if r.data == nil {
            datatype = common.WORK_FAIL
        } else {
            datatype = common.WORK_EXCEPTION
        }
        err = r.err
    }

    job.magicCode = common.REQ
    job.DataType = datatype
    job.Data = r.data
    if worker.running {
        job.agent.WriteJob(job)
    }
    return
}

func (worker *Worker) removeAgent(a *agent) {
    for k, v := range worker.agents {
        if v == a {
            worker.agents = append(worker.agents[:k], worker.agents[k + 1:] ...)
        }
    }
    if len(worker.agents) == 0 {
        worker.err(common.ErrNoActiveAgent)
    }
}

type result struct {
    data []byte
    err error
}

func execTimeout(f JobFunc, job *Job, timeout time.Duration) (r *result) {
    rslt := make(chan *result)
    defer close(rslt)
    go func() {
        defer func() {recover()}()
        d, e := f(job)
        rslt <- &result{data: d, err: e}
    }()
    select {
    case r = <-rslt:
    case <-time.After(timeout):
        go job.cancel()
        return &result{err:common.ErrTimeOut}
    }
    return r
}