source: code/trunk/msgstore_memory.go@ 443

package soju

import (
        "fmt"
        "strconv"
        "time"

        "gopkg.in/irc.v3"
)

const messageRingBufferCap = 4096

func parseMemoryMsgID(s string) (netID int64, entity string, seq uint64, err error) {
        netID, entity, extra, err := parseMsgID(s)
        if err != nil {
                return 0, "", 0, err
        }
        seq, err = strconv.ParseUint(extra, 10, 64)
        if err != nil {
                return 0, "", 0, fmt.Errorf("failed to parse message ID %q: %v", s, err)
        }
        return netID, entity, seq, nil
}

func formatMemoryMsgID(netID int64, entity string, seq uint64) string {
        extra := strconv.FormatUint(seq, 10)
        return formatMsgID(netID, entity, extra)
}

type ringBufferKey struct {
        networkID int64
        entity    string
}

type memoryMessageStore struct {
        buffers map[ringBufferKey]*messageRingBuffer
}

func newMemoryMessageStore() *memoryMessageStore {
        return &memoryMessageStore{
                buffers: make(map[ringBufferKey]*messageRingBuffer),
        }
}

func (ms *memoryMessageStore) Close() error {
        ms.buffers = nil
        return nil
}

func (ms *memoryMessageStore) get(network *network, entity string) *messageRingBuffer {
        k := ringBufferKey{networkID: network.ID, entity: entity}
        if rb, ok := ms.buffers[k]; ok {
                return rb
        }
        rb := newMessageRingBuffer(messageRingBufferCap)
        ms.buffers[k] = rb
        return rb
}

func (ms *memoryMessageStore) LastMsgID(network *network, entity string, t time.Time) (string, error) {
        var seq uint64
        k := ringBufferKey{networkID: network.ID, entity: entity}
        if rb, ok := ms.buffers[k]; ok {
                seq = rb.cur
        }
        return formatMemoryMsgID(network.ID, entity, seq), nil
}

func (ms *memoryMessageStore) Append(network *network, entity string, msg *irc.Message) (string, error) {
        k := ringBufferKey{networkID: network.ID, entity: entity}
        rb, ok := ms.buffers[k]
        if !ok {
                rb = newMessageRingBuffer(messageRingBufferCap)
                ms.buffers[k] = rb
        }

        seq := rb.Append(msg)
        return formatMemoryMsgID(network.ID, entity, seq), nil
}

func (ms *memoryMessageStore) LoadLatestID(network *network, entity, id string, limit int) ([]*irc.Message, error) {
        _, _, seq, err := parseMemoryMsgID(id)
        if err != nil {
                return nil, err
        }

        k := ringBufferKey{networkID: network.ID, entity: entity}
        rb, ok := ms.buffers[k]
        if !ok {
                return nil, nil
        }

        return rb.LoadLatestSeq(seq, limit)
}

type messageRingBuffer struct {
        buf []*irc.Message
        cur    uint64
}

func newMessageRingBuffer(capacity int) *messageRingBuffer {
        return &messageRingBuffer{
                buf: make([]*irc.Message, capacity),
                cur: 1,
        }
}

func (rb *messageRingBuffer) cap() uint64 {
        return uint64(len(rb.buf))
}

func (rb *messageRingBuffer) Append(msg *irc.Message) uint64 {
        seq := rb.cur
        i := int(seq % rb.cap())
        rb.buf[i] = msg
        rb.cur++
        return seq
}

func (rb *messageRingBuffer) LoadLatestSeq(seq uint64, limit int) ([]*irc.Message, error) {
        if seq > rb.cur {
                return nil, fmt.Errorf("loading messages from sequence number (%v) greater than current (%v)", seq, rb.cur)
        } else if seq == rb.cur {
                return nil, nil
        }

        // The query excludes the message with the sequence number seq
        diff := rb.cur - seq - 1
        if diff > rb.cap() {
                // We dropped diff - cap entries
                diff = rb.cap()
        }
        if int(diff) > limit {
                diff = uint64(limit)
        }

        l := make([]*irc.Message, int(diff))
        for i := 0; i < int(diff); i++ {
                j := int((rb.cur - diff + uint64(i)) % rb.cap())
                l[i] = rb.buf[j]
        }

        return l, nil
}