#include "blockstore.h"

// Stabilize small write:
// 1) Copy data from the journal to the data device
//    Sync it before writing metadata if we want to keep metadata consistent
//    Overall it's optional because it can be replayed from the journal until
//    it's cleared, and reads are also fulfilled from the journal
// 2) Increase version on the metadata device and sync it
// 3) Advance clean_db entry's version, clear previous journal entries
//
// This makes 1 4K small write+sync look like:
// 512b+4K (journal) + sync + 512b (journal) + sync + 4K (data) [+ sync?] + 512b (metadata) + sync.
// WA = 2.375. It's not the best, SSD FTL-like redirect-write with defragmentation
// could probably be lower even with defragmentation. But it's fixed and it's still
// better than in Ceph. :)

// Stabilize big write:
// 1) Copy metadata from the journal to the metadata device
// 2) Move dirty_db entry to clean_db and clear previous journal entries
//
// This makes 1 128K big write+sync look like:
// 128K (data) + sync + 512b (journal) + sync + 512b (journal) + sync + 512b (metadata) + sync.
// WA = 1.012. Very good :)

// AND We must do it in batches, for the sake of reduced fsync call count
// AND We must know what we stabilize. Basic workflow is like:
// 1) primary OSD receives sync request
// 2) it determines his own unsynced writes from blockstore's information
//    just before submitting fsync
// 3) it submits syncs to blockstore and peers
// 4) after everyone acks sync it takes the object list and sends stabilize requests to everyone

int blockstore::dequeue_stable(blockstore_operation *op)
{
    obj_ver_id* v;
    int i, todo = 0;
    for (i = 0, v = (obj_ver_id*)op->buf; i < op->len; i++, v++)
    {
        auto dirty_it = dirty_db.find(*v);
        if (dirty_it == dirty_db.end())
        {
            auto clean_it = clean_db.find(v->oid);
            if (clean_it == clean_db.end() || clean_it->second.version < v->version)
            {
                // No such object version
                op->retval = EINVAL;
                op->callback(op);
                return 1;
            }
            else
            {
                // Already stable
            }
        }
        else if (IS_UNSYNCED(dirty_it->second.state))
        {
            // Object not synced yet. Caller must sync it first
            op->retval = EAGAIN;
            op->callback(op);
            return 1;
        }
        else if (!IS_STABLE(dirty_it->second.state))
        {
            todo++;
        }
    }
    if (!todo)
    {
        // Already stable
        op->retval = 0;
        op->callback(op);
        return 1;
    }
    // Check journal space
    blockstore_journal_check_t space_check(this);
    if (!space_check.check_available(op, todo, sizeof(journal_entry_stable), 0))
    {
        return 0;
    }
    // There is sufficient space. Get SQEs
    struct io_uring_sqe *sqe[space_check.sectors_required];
    for (i = 0; i < space_check.sectors_required; i++)
    {
        BS_SUBMIT_GET_SQE_DECL(sqe[i]);
    }
    // Prepare and submit journal entries
    int s = 0, cur_sector = -1;
    for (i = 0, v = (obj_ver_id*)op->buf; i < op->len; i++, v++)
    {
        journal_entry_stable *je = (journal_entry_stable*)
            prefill_single_journal_entry(journal, JE_STABLE, sizeof(journal_entry_stable));
        je->oid = v->oid;
        je->version = v->version;
        je->crc32 = je_crc32((journal_entry*)je);
        journal.crc32_last = je->crc32;
        if (cur_sector != journal.cur_sector)
        {
            if (cur_sector == -1)
                op->min_used_journal_sector = 1 + journal.cur_sector;
            cur_sector = journal.cur_sector;
            prepare_journal_sector_write(op, journal, sqe[s++]);
        }
    }
    op->max_used_journal_sector = 1 + journal.cur_sector;
    op->pending_ops = s;
    return 1;
}

int blockstore::continue_stable(blockstore_operation *op)
{
    return 0;
}

void blockstore::handle_stable_event(ring_data_t *data, blockstore_operation *op)
{
    if (data->res < 0)
    {
        // sync error
        // FIXME: our state becomes corrupted after a write error. maybe do something better than just die
        throw new std::runtime_error("write operation failed. in-memory state is corrupted. AAAAAAAaaaaaaaaa!!!111");
    }
    op->pending_ops--;
    if (op->pending_ops == 0)
    {
        // First step: mark dirty_db entries as stable, acknowledge op completion
        obj_ver_id* v;
        int i;
        for (i = 0, v = (obj_ver_id*)op->buf; i < op->len; i++, v++)
        {
            // Mark all dirty_db entries up to op->version as stable
            auto dirty_it = dirty_db.find(*v);
            if (dirty_it != dirty_db.end())
            {
                do
                {
                    if (dirty_it->second.state == ST_J_SYNCED)
                    {
                        dirty_it->second.state = ST_J_STABLE;
                    }
                    else if (dirty_it->second.state == ST_D_META_SYNCED)
                    {
                        dirty_it->second.state = ST_D_STABLE;
                    }
                    else if (IS_STABLE(dirty_it->second.state))
                    {
                        break;
                    }
                    dirty_it--;
                } while (dirty_it != dirty_db.begin() && dirty_it->first.oid == v->oid);
                flusher.flush_queue.push_back(*v);
            }
        }
        // Acknowledge op
        op->retval = 0;
        op->callback(op);
    }
}

struct copy_buffer_t
{
    uint64_t offset, len;
    void *buf;
};

struct meta_sector_t
{
    uint64_t offset, len;
    int state;
    void *buf;
    int usage_count;
};

class journal_flusher_t
{
    blockstore *bs;
    int wait_state, wait_count;
    struct io_uring_sqe *sqe;
    struct ring_data_t *data;
    bool skip_copy;
    obj_ver_id cur;
    std::map<obj_ver_id, dirty_entry>::iterator dirty_it;
    std::vector<copy_buffer_t> v;
    std::vector<copy_buffer_t>::iterator it;
    uint64_t offset, len, submit_len, clean_loc, meta_sector, meta_pos;
    std::map<uint64_t, meta_sector_t>::iterator meta_it;

public:
    journal_flusher_t(int flush_count);
    std::map<uint64_t, meta_sector_t> meta_sectors;
    std::deque<obj_ver_id> flush_queue;
    void loop();
};

journal_flusher_t::journal_flusher_t(int flusher_count)
{
}

void journal_flusher_t::loop()
{
    // This is much better than implementing the whole function as an FSM
    // Maybe I should consider a coroutine library like https://github.com/hnes/libaco ...
    if (wait_state == 1)
        goto resume_1;
    else if (wait_state == 2)
        goto resume_2;
    else if (wait_state == 3)
        goto resume_3;
    else if (wait_state == 4)
        goto resume_4;
    else if (wait_state == 5)
        goto resume_5;
    else if (wait_state == 6)
        goto resume_6;
    else if (wait_state == 7)
        goto resume_7;
    if (!flush_queue.size())
        return;
    cur = flush_queue.front();
    flush_queue.pop_front();
    dirty_it = bs->dirty_db.find(cur);
    if (dirty_it != bs->dirty_db.end())
    {
        v.clear();
        wait_count = 0;
        clean_loc = UINT64_MAX;
        skip_copy = false;
        do
        {
            if (dirty_it->second.state == ST_J_STABLE)
            {
                // First we submit all reads
                offset = dirty_it->second.offset;
                len = dirty_it->second.size;
                it = v.begin();
                while (1)
                {
                    for (; it != v.end(); it++)
                        if (it->offset >= offset)
                            break;
                    if (it == v.end() || it->offset > offset)
                    {
                        submit_len = it->offset >= offset+len ? len : it->offset-offset;
                    resume_1:
                        sqe = bs->get_sqe();
                        if (!sqe)
                        {
                            // Can't submit read, ring is full
                            wait_state = 1;
                            return;
                        }
                        v.insert(it, (copy_buffer_t){ .offset = offset, .len = submit_len, .buf = memalign(512, submit_len) });
                        data = ((ring_data_t*)sqe->user_data);
                        data->iov = (struct iovec){ v.end()->buf, (size_t)submit_len };
                        data->op = this;
                        io_uring_prep_readv(
                            sqe, bs->journal.fd, &data->iov, 1, bs->journal.offset + dirty_it->second.location + offset
                        );
                        wait_count++;
                    }
                    if (it == v.end() || it->offset+it->len >= offset+len)
                    {
                        break;
                    }
                }
                // So subsequent stabilizers don't flush the entry again
                dirty_it->second.state = ST_J_MOVE_READ_SUBMITTED;
            }
            else if (dirty_it->second.state == ST_D_STABLE)
            {
                // Copy last STABLE entry metadata
                if (!skip_copy)
                {
                    clean_loc = dirty_it->second.location;
                }
                skip_copy = true;
            }
            else if (IS_STABLE(dirty_it->second.state))
            {
                break;
            }
            dirty_it--;
        } while (dirty_it != bs->dirty_db.begin() && dirty_it->first.oid == cur.oid);
        if (clean_loc == UINT64_MAX)
        {
            // Find it in clean_db
            auto clean_it = bs->clean_db.find(cur.oid);
            if (clean_it == bs->clean_db.end())
            {
                // Object not present at all. This is a bug.
                throw new std::runtime_error("BUG: Object we are trying to flush not allocated on the data device");
            }
            else
                clean_loc = clean_it->second.location;
        }
        // Also we need to submit the metadata read. We do a read-modify-write for every operation.
        // But we must check if the same sector is already in memory.
        // Another option is to keep all raw metadata in memory all the time. Maybe I'll do it sometime...
        // And yet another option is to use LSM trees for metadata, but it sophisticates everything a lot,
        // so I'll avoid it as long as I can.
        meta_sector = (clean_loc / (512 / sizeof(clean_disk_entry))) * 512;
        meta_pos = (clean_loc % (512 / sizeof(clean_disk_entry)));
        meta_it = meta_sectors.find(meta_sector);
        if (meta_it == meta_sectors.end())
        {
            // Not in memory yet, read it
            meta_it = meta_sectors.emplace(meta_sector, (meta_sector_t){
                .offset = meta_sector,
                .len = 512,
                .state = 0, // 0 = not read yet
                .buf = memalign(512, 512),
                .usage_count = 1,
            }).first;
        resume_2:
            sqe = bs->get_sqe();
            if (!sqe)
            {
                wait_state = 2;
                return;
            }
            data = ((ring_data_t*)sqe->user_data);
            data->iov = (struct iovec){ meta_it->second.buf, 512 };
            data->op = this;
            io_uring_prep_writev(
                sqe, bs->meta_fd, &data->iov, 1, bs->meta_offset + meta_sector
            );
            wait_count++;
        }
        else
            meta_it->second.usage_count++;
        wait_state = 3;
    resume_3:
        // After reads complete we submit writes
        if (wait_count == 0)
        {
            for (it = v.begin(); it != v.end(); it++)
            {
            resume_4:
                sqe = bs->get_sqe();
                if (!sqe)
                {
                    // Can't submit a write, ring is full
                    wait_state = 4;
                    return;
                }
                data = ((ring_data_t*)sqe->user_data);
                data->iov = (struct iovec){ it->buf, (size_t)it->len };
                data->op = this;
                io_uring_prep_writev(
                    sqe, bs->data_fd, &data->iov, 1, bs->data_offset + clean_loc + it->offset
                );
                wait_count++;
            }
            // And a metadata write
        resume_5:
            if (meta_it->second.state == 0)
            {
                // metadata sector is still being read, wait for it
                wait_state = 5;
                return;
            }
            *((clean_disk_entry*)meta_it->second.buf + meta_pos) = {
                .oid = cur.oid,
                .version = cur.version,
                .flags = DISK_ENTRY_STABLE,
            };
        resume_6:
            sqe = bs->get_sqe();
            if (!sqe)
            {
                // Can't submit a write, ring is full
                wait_state = 6;
                return;
            }
            data = ((ring_data_t*)sqe->user_data);
            data->iov = (struct iovec){ meta_it->second.buf, 512 };
            data->op = this;
            io_uring_prep_writev(
                sqe, bs->meta_fd, &data->iov, 1, bs->meta_offset + meta_sector
            );
            wait_count++;
            wait_state = 7;
        resume_7:
            // Done, free all buffers
            if (wait_count == 0)
            {
                meta_it->second.usage_count--;
                if (meta_it->second.usage_count == 0)
                {
                    free(meta_it->second.buf);
                    meta_sectors.erase(meta_it);
                }
                for (it = v.begin(); it != v.end(); it++)
                {
                    free(it->buf);
                }
                v.clear();
                wait_state = 0;
            }
            // FIXME Now sync everything
        }
    }
}