// Copyright 2024-2025 the libevm authors.
//
// The libevm additions to go-ethereum are free software: you can redistribute
// them and/or modify them under the terms of the GNU Lesser General Public License
// as published by the Free Software Foundation, either version 3 of the License,
// or (at your option) any later version.
//
// The libevm additions are distributed in the hope that they will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser
// General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see
// <http://www.gnu.org/licenses/>.

package params

import (
	"math/big"

	"github.com/ava-labs/libevm/common"
	"github.com/ava-labs/libevm/libevm"
)

// ChainConfigHooks are required for all types registered as [Extras] for
// [ChainConfig] payloads.
type ChainConfigHooks interface {
	CheckConfigForkOrder() error
	CheckConfigCompatible(newcfg *ChainConfig, headNumber *big.Int, headTimestamp uint64) *ConfigCompatError
	Description() string
}

// TODO(arr4n): given the choice of whether a hook should be defined on a
// ChainConfig or on the Rules, what are the guiding principles? A ChainConfig
// carries the most general information while Rules benefit from "knowing" the
// block number and timestamp. I am leaning towards the default choice being
// on Rules (as it's trivial to copy information from ChainConfig to Rules in
// [Extras.NewRules]) unless the call site only has access to a ChainConfig.

// RulesHooks are required for all types registered as [Extras] for [Rules]
// payloads.
type RulesHooks interface {
	RulesAllowlistHooks
	// PrecompileOverride signals whether or not the EVM interpreter MUST
	// override its treatment of the address when deciding if it is a
	// precompiled contract. If PrecompileOverride returns `true` then the
	// interpreter will treat the address as a precompile i.f.f the
	// [PrecompiledContract] is non-nil. If it returns `false` then the default
	// precompile behaviour is honoured.
	PrecompileOverride(common.Address) (_ libevm.PrecompiledContract, override bool)
	// ActivePrecompiles receives the addresses that would usually be returned
	// by a call to [vm.ActivePrecompiles] and MUST return the value to be
	// returned by said function, which will be propagated. It MAY alter the
	// received slice. The value it returns MUST be consistent with the
	// behaviour of the PrecompileOverride hook.
	ActivePrecompiles([]common.Address) []common.Address
	// MinimumGasConsumption receives a transaction's gas limit and returns the
	// minimum quantity of gas units to be charged for said transaction. If the
	// returned value is greater than the transaction's limit, the minimum spend
	// will be capped at the limit. The minimum spend will be applied _after_
	// refunds, if any.
	MinimumGasConsumption(txGasLimit uint64) (gas uint64)
}

// RulesAllowlistHooks are a subset of [RulesHooks] that gate actions, signalled
// by returning a nil (allowed) or non-nil (blocked) error.
type RulesAllowlistHooks interface {
	// CanCreateContract is called after the deployer's nonce is incremented but
	// before all other state-modifying actions. The [libevm.AddressContext.Raw]
	// field will always be nil.
	CanCreateContract(_ *libevm.AddressContext, gas uint64, _ libevm.StateReader) (gasRemaining uint64, _ error)
	CanExecuteTransaction(from common.Address, to *common.Address, _ libevm.StateReader) error
}

// Hooks returns the hooks registered with [RegisterExtras], or [NOOPHooks] if
// none were registered.
func (c *ChainConfig) Hooks() ChainConfigHooks {
	if e := registeredExtras; e.Registered() {
		return e.Get().payloads.hooksFromChainConfig(c)
	}
	return NOOPHooks{}
}

// Hooks returns the hooks registered with [RegisterExtras], or [NOOPHooks] if
// none were registered.
func (r *Rules) Hooks() RulesHooks {
	if e := registeredExtras; e.Registered() {
		return e.Get().payloads.hooksFromRules(r)
	}
	return NOOPHooks{}
}

// NOOPHooks implements both [ChainConfigHooks] and [RulesHooks] such that every
// hook is a no-op. This allows it to be returned instead of a nil interface,
// which would otherwise require every usage site to perform a nil check. It can
// also be embedded in structs that only wish to implement a sub-set of hooks.
// Use of a NOOPHooks is equivalent to default Ethereum behaviour.
type NOOPHooks struct{}

var _ interface {
	ChainConfigHooks
	RulesHooks
} = NOOPHooks{}

// CheckConfigForkOrder verifies all (otherwise valid) fork orders.
func (NOOPHooks) CheckConfigForkOrder() error {
	return nil
}

// CheckConfigCompatible verifies all (otherwise valid) new configs.
func (NOOPHooks) CheckConfigCompatible(*ChainConfig, *big.Int, uint64) *ConfigCompatError {
	return nil
}

// Description returns the empty string.
func (NOOPHooks) Description() string {
	return ""
}

// CanExecuteTransaction allows all (otherwise valid) transactions.
func (NOOPHooks) CanExecuteTransaction(_ common.Address, _ *common.Address, _ libevm.StateReader) error {
	return nil
}

// CanCreateContract allows all (otherwise valid) contract deployment, not
// consuming any more gas.
func (NOOPHooks) CanCreateContract(_ *libevm.AddressContext, gas uint64, _ libevm.StateReader) (uint64, error) {
	return gas, nil
}

// PrecompileOverride instructs the EVM interpreter to use the default
// precompile behaviour.
func (NOOPHooks) PrecompileOverride(common.Address) (libevm.PrecompiledContract, bool) {
	return nil, false
}

// ActivePrecompiles echoes the active addresses unchanged.
func (NOOPHooks) ActivePrecompiles(active []common.Address) []common.Address {
	return active
}

// MinimumGasConsumption always returns 0.
func (NOOPHooks) MinimumGasConsumption(uint64) uint64 {
	return 0
}