package main

import (
	"context"
	"fmt"
	"time"

	"github.com/filecoin-project/go-address"
	"github.com/filecoin-project/go-state-types/abi"
	"github.com/filecoin-project/lotus/api"
	"github.com/filecoin-project/lotus/build"
	"github.com/filecoin-project/lotus/chain/types"
	"github.com/filecoin-project/lotus/node/impl/full"
	"github.com/ipfs/go-cid"
)

const (
	LookbackCap            = time.Hour
	stateWaitLookbackLimit = abi.ChainEpoch(20)
)

var (
	ErrLookbackTooLong = fmt.Errorf("lookbacks of more than %s are disallowed", LookbackCap)
)

type rpcAPI interface {
	ChainHead(ctx context.Context) (*types.TipSet, error)
	ChainGetTipSet(ctx context.Context, tsk types.TipSetKey) (*types.TipSet, error)
	ChainGetTipSetByHeight(ctx context.Context, h abi.ChainEpoch, tsk types.TipSetKey) (*types.TipSet, error)
	GasEstimateMessageGas(ctx context.Context, msg *types.Message, spec *api.MessageSendSpec, tsk types.TipSetKey) (*types.Message, error)
	MpoolPushUntrusted(ctx context.Context, sm *types.SignedMessage) (cid.Cid, error)
	StateAccountKey(ctx context.Context, addr address.Address, tsk types.TipSetKey) (address.Address, error)
	StateGetActor(ctx context.Context, actor address.Address, ts types.TipSetKey) (*types.Actor, error)
	StateLookupID(ctx context.Context, addr address.Address, tsk types.TipSetKey) (address.Address, error)
	StateWaitMsgLimited(ctx context.Context, msg cid.Cid, confidence uint64, h abi.ChainEpoch) (*api.MsgLookup, error)
}

type GatewayAPI struct {
	rpc rpcAPI
}

func (a *GatewayAPI) checkTipsetKey(ctx context.Context, tsk types.TipSetKey) error {
	if tsk.IsEmpty() {
		return nil
	}

	ts, err := a.rpc.ChainGetTipSet(ctx, tsk)
	if err != nil {
		return err
	}

	return a.checkTipset(ts)
}

func (a *GatewayAPI) checkTipset(ts *types.TipSet) error {
	at := time.Unix(int64(ts.Blocks()[0].Timestamp), 0)
	if err := a.checkTimestamp(at); err != nil {
		return fmt.Errorf("bad tipset: %w", err)
	}
	return nil
}

func (a *GatewayAPI) checkTipsetHeight(ts *types.TipSet, h abi.ChainEpoch) error {
	tsBlock := ts.Blocks()[0]
	heightDelta := time.Duration(uint64(tsBlock.Height-h)*build.BlockDelaySecs) * time.Second
	timeAtHeight := time.Unix(int64(tsBlock.Timestamp), 0).Add(-heightDelta)

	if err := a.checkTimestamp(timeAtHeight); err != nil {
		return fmt.Errorf("bad tipset height: %w", err)
	}
	return nil
}

func (a *GatewayAPI) checkTimestamp(at time.Time) error {
	if time.Since(at) > LookbackCap {
		return ErrLookbackTooLong
	}

	return nil
}

func (a *GatewayAPI) ChainHead(ctx context.Context) (*types.TipSet, error) {
	// TODO: cache and invalidate cache when timestamp is up (or have internal ChainNotify)

	return a.rpc.ChainHead(ctx)
}

func (a *GatewayAPI) ChainGetTipSet(ctx context.Context, tsk types.TipSetKey) (*types.TipSet, error) {
	return a.rpc.ChainGetTipSet(ctx, tsk)
}

func (a *GatewayAPI) ChainGetTipSetByHeight(ctx context.Context, h abi.ChainEpoch, tsk types.TipSetKey) (*types.TipSet, error) {
	ts, err := a.rpc.ChainGetTipSet(ctx, tsk)
	if err != nil {
		return nil, err
	}

	// Check if the tipset key refers to a tipset that's too far in the past
	if err := a.checkTipset(ts); err != nil {
		return nil, err
	}

	// Check if the height is too far in the past
	if err := a.checkTipsetHeight(ts, h); err != nil {
		return nil, err
	}

	return a.rpc.ChainGetTipSetByHeight(ctx, h, tsk)
}

func (a *GatewayAPI) GasEstimateMessageGas(ctx context.Context, msg *types.Message, spec *api.MessageSendSpec, tsk types.TipSetKey) (*types.Message, error) {
	if err := a.checkTipsetKey(ctx, tsk); err != nil {
		return nil, err
	}

	return a.rpc.GasEstimateMessageGas(ctx, msg, spec, tsk)
}

func (a *GatewayAPI) MpoolPush(ctx context.Context, sm *types.SignedMessage) (cid.Cid, error) {
	// TODO: additional anti-spam checks
	return a.rpc.MpoolPushUntrusted(ctx, sm)
}

func (a *GatewayAPI) StateAccountKey(ctx context.Context, addr address.Address, tsk types.TipSetKey) (address.Address, error) {
	if err := a.checkTipsetKey(ctx, tsk); err != nil {
		return address.Undef, err
	}

	return a.rpc.StateAccountKey(ctx, addr, tsk)
}

func (a *GatewayAPI) StateGetActor(ctx context.Context, actor address.Address, tsk types.TipSetKey) (*types.Actor, error) {
	if err := a.checkTipsetKey(ctx, tsk); err != nil {
		return nil, err
	}

	return a.rpc.StateGetActor(ctx, actor, tsk)
}

func (a *GatewayAPI) StateLookupID(ctx context.Context, addr address.Address, tsk types.TipSetKey) (address.Address, error) {
	if err := a.checkTipsetKey(ctx, tsk); err != nil {
		return address.Undef, err
	}

	return a.rpc.StateLookupID(ctx, addr, tsk)
}

func (a *GatewayAPI) StateWaitMsg(ctx context.Context, msg cid.Cid, confidence uint64) (*api.MsgLookup, error) {
	return a.rpc.StateWaitMsgLimited(ctx, msg, confidence, stateWaitLookbackLimit)
}

var _ api.GatewayAPI = (*GatewayAPI)(nil)
var _ full.ChainModuleAPI = (*GatewayAPI)(nil)
var _ full.GasModuleAPI = (*GatewayAPI)(nil)
var _ full.MpoolModuleAPI = (*GatewayAPI)(nil)
var _ full.StateModuleAPI = (*GatewayAPI)(nil)