Message Handler(handler)

package stake
​
import (
    "bytes"
​
    sdk "github.com/cosmos/cosmos-sdk/types"
    abci "github.com/tendermint/abci/types"
)
​
//nolint
const (
    GasDeclareCandidacy int64 = 20
    GasEditCandidacy    int64 = 20
    GasDelegate         int64 = 20
    GasUnbond           int64 = 20
)
​
func NewHandler(k Keeper) sdk.Handler {
    return func(ctx sdk.Context, msg sdk.Msg) sdk.Result {
        // NOTE msg already has validate basic run
        switch msg := msg.(type) {
        case MsgDeclareCandidacy:
            return handleMsgDeclareCandidacy(ctx, msg, k)
        case MsgEditCandidacy:
            return handleMsgEditCandidacy(ctx, msg, k)
        case MsgDelegate:
            return handleMsgDelegate(ctx, msg, k)
        case MsgUnbond:
            return handleMsgUnbond(ctx, msg, k)
        default:
            return sdk.ErrTxDecode("invalid message parse in staking module").Result()
        }
    } 
}

// now we just perform action and save
func handleMsgDeclareCandidacy(ctx sdk.Context, msg MsgDeclareCandidacy, k Keeper) sdk.Result {
​
    // check to see if the pubkey or sender has been registered before
    _, found := k.GetCandidate(ctx, msg.CandidateAddr)
    if found {
        return ErrCandidateExistsAddr(k.codespace).Result()
    }
    if msg.Bond.Denom != k.GetParams(ctx).BondDenom {
        return ErrBadBondingDenom(k.codespace).Result()
    }
    if ctx.IsCheckTx() {
        return sdk.Result{
            GasUsed: GasDeclareCandidacy,
        }
    }
​
    candidate := NewCandidate(msg.CandidateAddr, msg.PubKey, msg.Description)
    k.setCandidate(ctx, candidate)
    tags := sdk.NewTags("action", []byte("declareCandidacy"), "candidate", msg.CandidateAddr.Bytes(), "moniker", []byte(msg.Description.Moniker), "identity", []byte(msg.Description.Identity))
​
    // move coins from the msg.Address account to a (self-bond) delegator account
    // the candidate account and global shares are updated within here
    delegateTags, err := delegate(ctx, k, msg.CandidateAddr, msg.Bond, candidate)
    if err != nil {
        return err.Result()
    }
    tags = tags.AppendTags(delegateTags)
    return sdk.Result{
        Tags: tags,
    }
}