package lite

import (
	"bytes"
	"errors"
	"fmt"

	"github.com/tendermint/tendermint/types"
)

// FullCommit contains a SignedHeader (the block's header and a commit that
// signs it), the validator set which signed the commit, and the next validator
// set. The next validator set (which is proven from the block header) allows
// us to revert to block-by-block updating of lite Verifier's latest validator
// set, even in the face of arbitrarily large power changes.
type FullCommit struct {
	SignedHeader   types.SignedHeader  `json:"signed_header"`
	Validators     *types.ValidatorSet `json:"validator_set"`
	NextValidators *types.ValidatorSet `json:"next_validator_set"`
}

// NewFullCommit returns a new FullCommit.
func NewFullCommit(signedHeader types.SignedHeader, valset, nextValset *types.ValidatorSet) FullCommit {
	return FullCommit{
		SignedHeader:   signedHeader,
		Validators:     valset,
		NextValidators: nextValset,
	}
}

// ValidateFull validates the components and ensures consistency.
// It also checks that Validators actually signed the SignedHeader.Commit.
// If > 2/3 did not sign the Commit from fc.Validators, it is not a valid
// commit!
func (fc FullCommit) ValidateFull(chainID string) error {
	if fc.Validators.Size() == 0 {
		return errors.New("empty FullCommit.Validators")
	}

	if !bytes.Equal(fc.SignedHeader.ValidatorsHash, fc.Validators.Hash()) {
		return fmt.Errorf("header has ValidatorsHash %X but valset hash is %X",
			fc.SignedHeader.ValidatorsHash,
			fc.Validators.Hash(),
		)
	}

	if fc.NextValidators.Size() == 0 {
		return errors.New("empty FullCommit.NextValidators")
	}

	if !bytes.Equal(fc.SignedHeader.NextValidatorsHash, fc.NextValidators.Hash()) {
		return fmt.Errorf("header has next ValidatorsHash %X but next valset hash is %X",
			fc.SignedHeader.NextValidatorsHash,
			fc.NextValidators.Hash(),
		)
	}

	err := fc.SignedHeader.ValidateBasic(chainID)
	if err != nil {
		return err
	}

	// Validate the signatures on the commit.
	hdr, cmt := fc.SignedHeader.Header, fc.SignedHeader.Commit
	return fc.Validators.VerifyCommit(hdr.ChainID, cmt.BlockID, hdr.Height, cmt)
}

// Height returns the height of the header.
func (fc FullCommit) Height() int64 {
	if fc.SignedHeader.Header == nil {
		panic("should not happen")
	}

	return fc.SignedHeader.Height
}

// ChainID returns the chainID of the header.
func (fc FullCommit) ChainID() string {
	if fc.SignedHeader.Header == nil {
		panic("should not happen")
	}

	return fc.SignedHeader.ChainID
}