package clientv3

import (
    "sync"

    pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
    "golang.org/x/net/context"
    "google.golang.org/grpc"
)

// Txn is the interface that wraps mini-transactions.
//
//     Tx.If(
//      Compare(Value(k1), ">", v1),
//      Compare(Version(k1), "=", 2)
//     ).Then(
//      OpPut(k2,v2), OpPut(k3,v3)
//     ).Else(
//      OpPut(k4,v4), OpPut(k5,v5)
//     ).Commit()
//
type Txn interface {
    // If takes a list of comparison. If all comparisons passed in succeed,
    // the operations passed into Then() will be executed. Or the operations
    // passed into Else() will be executed.
    If(cs ...Cmp) Txn

    // Then takes a list of operations. The Ops list will be executed, if the
    // comparisons passed in If() succeed.
    Then(ops ...Op) Txn

    // Else takes a list of operations. The Ops list will be executed, if the
    // comparisons passed in If() fail.
    Else(ops ...Op) Txn

    // Commit tries to commit the transaction.
    Commit() (*TxnResponse, error)

    // TODO: add a Do for shortcut the txn without any condition?
}

type txn struct {
    kv  *kv
    ctx context.Context

    mu    sync.Mutex
    cif   bool
    cthen bool
    celse bool

    isWrite bool

    cmps []*pb.Compare

    sus []*pb.RequestOp
    fas []*pb.RequestOp
}

func (txn *txn) If(cs ...Cmp) Txn {
    txn.mu.Lock()
    defer txn.mu.Unlock()

    if txn.cif {
        panic("cannot call If twice!")
    }

    if txn.cthen {
        panic("cannot call If after Then!")
    }

    if txn.celse {
        panic("cannot call If after Else!")
    }

    txn.cif = true

    for i := range cs {
        txn.cmps = append(txn.cmps, (*pb.Compare)(&cs[i]))
    }

    return txn
}

func (txn *txn) Then(ops ...Op) Txn {
    txn.mu.Lock()
    defer txn.mu.Unlock()

    if txn.cthen {
        panic("cannot call Then twice!")
    }
    if txn.celse {
        panic("cannot call Then after Else!")
    }

    txn.cthen = true

    for _, op := range ops {
        txn.isWrite = txn.isWrite || op.isWrite()
        txn.sus = append(txn.sus, op.toRequestOp())
    }

    return txn
}

func (txn *txn) Else(ops ...Op) Txn {
    txn.mu.Lock()
    defer txn.mu.Unlock()

    if txn.celse {
        panic("cannot call Else twice!")
    }

    txn.celse = true

    for _, op := range ops {
        txn.isWrite = txn.isWrite || op.isWrite()
        txn.fas = append(txn.fas, op.toRequestOp())
    }

    return txn
}

func (txn *txn) Commit() (*TxnResponse, error) {
    txn.mu.Lock()
    defer txn.mu.Unlock()
    for {
        resp, err := txn.commit()
        if err == nil {
            return resp, err
        }
        if isHaltErr(txn.ctx, err) {
            return nil, toErr(txn.ctx, err)
        }
        if txn.isWrite {
            return nil, toErr(txn.ctx, err)
        }
    }
}

func (txn *txn) commit() (*TxnResponse, error) {
    r := &pb.TxnRequest{Compare: txn.cmps, Success: txn.sus, Failure: txn.fas}

    var opts []grpc.CallOption
    if !txn.isWrite {
        opts = []grpc.CallOption{grpc.FailFast(false)}
    }
    resp, err := txn.kv.remote.Txn(txn.ctx, r, opts...)
    if err != nil {
        return nil, err
    }
    return (*TxnResponse)(resp), nil
}