// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it 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 go-ethereum library is distributed in the hope that it 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 bloombits

import (
	"errors"

	"github.com/ethereum/go-ethereum/core/types"
)

// errSectionOutOfBounds is returned if the user tried to add more bloom filters
// to the batch than available space, or if tries to retrieve above the capacity,
var errSectionOutOfBounds = errors.New("section out of bounds")

// Generator takes a number of bloom filters and generates the rotated bloom bits
// to be used for batched filtering.
type Generator struct {
	blooms   [types.BloomBitLength][]byte // Rotated blooms for per-bit matching
	sections uint                         // Number of sections to batch together
	nextBit  uint                         // Next bit to set when adding a bloom
}

// NewGenerator creates a rotated bloom generator that can iteratively fill a
// batched bloom filter's bits.
func NewGenerator(sections uint) (*Generator, error) {
	if sections%8 != 0 {
		return nil, errors.New("section count not multiple of 8")
	}
	b := &Generator{sections: sections}
	for i := 0; i < types.BloomBitLength; i++ {
		b.blooms[i] = make([]byte, sections/8)
	}
	return b, nil
}

// AddBloom takes a single bloom filter and sets the corresponding bit column
// in memory accordingly.
func (b *Generator) AddBloom(index uint, bloom types.Bloom) error {
	// Make sure we're not adding more bloom filters than our capacity
	if b.nextBit >= b.sections {
		return errSectionOutOfBounds
	}
	if b.nextBit != index {
		return errors.New("bloom filter with unexpected index")
	}
	// Rotate the bloom and insert into our collection
	byteIndex := b.nextBit / 8
	bitMask := byte(1) << byte(7-b.nextBit%8)

	for i := 0; i < types.BloomBitLength; i++ {
		bloomByteIndex := types.BloomByteLength - 1 - i/8
		bloomBitMask := byte(1) << byte(i%8)

		if (bloom[bloomByteIndex] & bloomBitMask) != 0 {
			b.blooms[i][byteIndex] |= bitMask
		}
	}
	b.nextBit++

	return nil
}

// Bitset returns the bit vector belonging to the given bit index after all
// blooms have been added.
func (b *Generator) Bitset(idx uint) ([]byte, error) {
	if b.nextBit != b.sections {
		return nil, errors.New("bloom not fully generated yet")
	}
	if idx >= b.sections {
		return nil, errSectionOutOfBounds
	}
	return b.blooms[idx], nil
}
