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// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// go-ethereum 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 core

import (
    "sync"

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

// BlockCache implements a caching mechanism specifically for blocks and uses FILO to pop
type BlockCache struct {
    size int

    hashes []common.Hash
    blocks map[common.Hash]*types.Block

    mu sync.RWMutex
}

// Creates and returns a `BlockCache` with `size`. If `size` is smaller than 1 it will panic
func NewBlockCache(size int) *BlockCache {
    if size < 1 {
        panic("block cache size not allowed to be smaller than 1")
    }

    bc := &BlockCache{size: size}
    bc.Clear()
    return bc
}

func (bc *BlockCache) Clear() {
    bc.blocks = make(map[common.Hash]*types.Block)
    bc.hashes = nil

}

func (bc *BlockCache) Push(block *types.Block) {
    bc.mu.Lock()
    defer bc.mu.Unlock()

    if len(bc.hashes) == bc.size {
        delete(bc.blocks, bc.hashes[0])

        // XXX There are a few other options on solving this
        // 1) use a poller / GC like mechanism to clean up untracked objects
        // 2) copy as below
        // re-use the slice and remove the reference to bc.hashes[0]
        // this will allow the element to be garbage collected.
        copy(bc.hashes, bc.hashes[1:])
    } else {
        bc.hashes = append(bc.hashes, common.Hash{})
    }

    hash := block.Hash()
    bc.blocks[hash] = block
    bc.hashes[len(bc.hashes)-1] = hash
}

func (bc *BlockCache) Delete(hash common.Hash) {
    bc.mu.Lock()
    defer bc.mu.Unlock()

    if _, ok := bc.blocks[hash]; ok {
        delete(bc.blocks, hash)
        for i, h := range bc.hashes {
            if hash == h {
                bc.hashes = bc.hashes[:i+copy(bc.hashes[i:], bc.hashes[i+1:])]
                // or ? => bc.hashes = append(bc.hashes[:i], bc.hashes[i+1]...)

                break
            }
        }
    }
}

func (bc *BlockCache) Get(hash common.Hash) *types.Block {
    bc.mu.RLock()
    defer bc.mu.RUnlock()

    if block, haz := bc.blocks[hash]; haz {
        return block
    }

    return nil
}

func (bc *BlockCache) Has(hash common.Hash) bool {
    bc.mu.RLock()
    defer bc.mu.RUnlock()

    _, ok := bc.blocks[hash]
    return ok
}

func (bc *BlockCache) Each(cb func(int, *types.Block)) {
    bc.mu.Lock()
    defer bc.mu.Unlock()

    i := 0
    for _, block := range bc.blocks {
        cb(i, block)
        i++
    }
}