/** @file
 * @brief HoneyValueManager class
 */
/* Copyright (C) 2008,2009,2010,2011,2012,2016,2017,2018 Olly Betts
 * Copyright (C) 2008,2009 Lemur Consulting Ltd
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see
 * <https://www.gnu.org/licenses/>.
 */

#include <config.h>

#include "honey_values.h"

#include "honey_cursor.h"
#include "honey_postlist.h"
#include "honey_postlisttable.h"
#include "honey_termlist.h"
#include "honey_termlisttable.h"

#include "bitstream.h"
#include "debuglog.h"
#include "backends/documentinternal.h"
#include "pack.h"

#include "xapian/error.h"
#include "xapian/valueiterator.h"

#include <algorithm>
#include <memory>

using namespace Honey;
using namespace std;

// FIXME:
//  * multi-values?
//  * values named instead of numbered?

void
ValueChunkReader::assign(const char* p_, size_t len, Xapian::docid last_did)
{
    p = p_;
    end = p_ + len;
    if (!unpack_uint(&p, end, &did))
        throw Xapian::DatabaseCorruptError("Failed to unpack docid delta");
    did = last_did - did;
    if (!unpack_string(&p, end, value))
        throw Xapian::DatabaseCorruptError("Failed to unpack first value");
}

void
ValueChunkReader::next()
{
    if (p == end) {
        p = NULL;
        return;
    }

    Xapian::docid delta;
    if (!unpack_uint(&p, end, &delta)) {
        throw Xapian::DatabaseCorruptError("Failed to unpack streamed value "
                                           "docid");
    }
    did += delta + 1;
    if (!unpack_string(&p, end, value))
        throw Xapian::DatabaseCorruptError("Failed to unpack streamed value");
}

void
ValueChunkReader::skip_to(Xapian::docid target)
{
    if (p == NULL || target <= did)
        return;

    size_t value_len;
    while (p != end) {
        // Get the next docid
        Xapian::docid delta;
        if (rare(!unpack_uint(&p, end, &delta))) {
            throw Xapian::DatabaseCorruptError("Failed to unpack streamed "
                                               "value docid");
        }
        did += delta + 1;

        // Get the length of the string
        if (rare(!unpack_uint(&p, end, &value_len))) {
            throw Xapian::DatabaseCorruptError("Failed to unpack streamed "
                                               "value length");
        }

        // Check that it's not too long
        if (rare(value_len > size_t(end - p))) {
            throw Xapian::DatabaseCorruptError("Failed to unpack streamed "
                                               "value");
        }

        // Assign the value and return only if we've reached the target
        if (did >= target) {
            value.assign(p, value_len);
            p += value_len;
            return;
        }
        p += value_len;
    }
    p = NULL;
}

void
HoneyValueManager::add_value(Xapian::docid did, Xapian::valueno slot,
                             const string& val)
{
    auto i = changes.find(slot);
    if (i == changes.end()) {
        i = changes.insert(make_pair(slot, map<Xapian::docid, string>())).first;
    }
    i->second[did] = val;
}

void
HoneyValueManager::remove_value(Xapian::docid did, Xapian::valueno slot)
{
    auto i = changes.find(slot);
    if (i == changes.end()) {
        i = changes.insert(make_pair(slot, map<Xapian::docid, string>())).first;
    }
    i->second[did] = string();
}

Xapian::docid
HoneyValueManager::get_chunk_containing_did(Xapian::valueno slot,
                                            Xapian::docid did,
                                            string& chunk) const
{
    LOGCALL(DB, Xapian::docid, "HoneyValueManager::get_chunk_containing_did", slot | did | chunk);
    if (!cursor)
        cursor.reset(postlist_table.cursor_get());
    if (!cursor) RETURN(0);

    bool exact = cursor->find_entry_ge(make_valuechunk_key(slot, did));
    if (!exact) {
        // The chunk doesn't end with docid did, so we need to get
        // the last docid in the chunk from the key to return.
        did = docid_from_key(slot, cursor->current_key);
    }

    cursor->read_tag();
    chunk = cursor->current_tag;
    // FIXME: fails, not sure why: swap(chunk, cursor->current_tag);

    RETURN(did);
}

static const size_t CHUNK_SIZE_THRESHOLD = 2000;

namespace Honey {

class ValueUpdater {
    HoneyPostListTable& table;

    Xapian::valueno slot;

    string ctag;

    ValueChunkReader reader;

    string tag;

    Xapian::docid prev_did;

    Xapian::docid last_did;

    Xapian::docid new_last_did;

    Xapian::docid last_allowed_did;

    void append_to_stream(Xapian::docid did, const string& value) {
        Assert(did);
        if (!tag.empty()) {
            AssertRel(did,>,prev_did);
            pack_uint(tag, did - prev_did - 1);
        }
        prev_did = did;
        new_last_did = did;
        pack_string(tag, value);
        if (tag.size() >= CHUNK_SIZE_THRESHOLD) write_tag();
    }

    void write_tag() {
        // If the last docid has changed, delete the old entry.
        if (last_did && new_last_did != last_did) {
            table.del(make_valuechunk_key(slot, last_did));
        }
        if (!tag.empty()) {
            table.add(make_valuechunk_key(slot, new_last_did), tag);
        }
        last_did = 0;
        tag.resize(0);
    }

  public:
    ValueUpdater(HoneyPostListTable& table_, Xapian::valueno slot_)
        : table(table_), slot(slot_), last_did(0), last_allowed_did(0) { }

    ~ValueUpdater() {
        while (!reader.at_end()) {
            // FIXME: use skip_to and some splicing magic instead?
            append_to_stream(reader.get_docid(), reader.get_value());
            reader.next();
        }
        write_tag();
    }

    void update(Xapian::docid did, const string& value) {
        if (last_allowed_did && did > last_allowed_did) {
            // The next change needs to go in a later existing chunk than the
            // one we're currently updating, so we copy over the rest of the
            // entries from the current chunk, write out the updated chunk and
            // drop through to the case below will read in that later chunk.
            // FIXME: use some string splicing magic instead of this loop.
            while (!reader.at_end()) {
                // last_allowed_did should be an upper bound for this chunk.
                AssertRel(reader.get_docid(),<=,last_allowed_did);
                append_to_stream(reader.get_docid(), reader.get_value());
                reader.next();
            }
            write_tag();
            last_allowed_did = 0;
        }
        if (last_allowed_did == 0) {
            last_allowed_did = HONEY_MAX_DOCID;
            Assert(tag.empty());
            new_last_did = 0;
            unique_ptr<HoneyCursor> cursor(table.cursor_get());
            if (cursor->find_entry_ge(make_valuechunk_key(slot, did))) {
                // We found an exact match, so the last docid is the one
                // we looked for.
                last_did = did;
            } else {
                Assert(!cursor->after_end());
                // Otherwise we need to unpack it from the key we found.
                // We may have found a non-value-chunk entry in which case
                // docid_from_key() returns 0.
                last_did = docid_from_key(slot, cursor->current_key);
            }

            // If there are no further chunks, then the last docid that can go
            // in this chunk is the highest valid docid.  If there are further
            // chunks then it's one less than the first docid of the next
            // chunk.
            if (last_did) {
                // We found a value chunk.
                cursor->read_tag();
                // FIXME:swap(cursor->current_tag, ctag);
                ctag = cursor->current_tag;
                reader.assign(ctag.data(), ctag.size(), last_did);
            }
            if (cursor->next()) {
                const string& key = cursor->current_key;
                Xapian::docid next_last_did = docid_from_key(slot, key);
                if (next_last_did) {
                    cursor->read_tag();
                    Xapian::docid delta;
                    const char* p = cursor->current_tag.data();
                    const char* e = p + cursor->current_tag.size();
                    if (!unpack_uint(&p, e, &delta)) {
                        throw Xapian::DatabaseCorruptError("Failed to unpack "
                                                           "docid delta");
                    }
                    Xapian::docid next_first_did = next_last_did - delta;
                    last_allowed_did = next_first_did - 1;
                }
                Assert(last_allowed_did);
                AssertRel(last_allowed_did,>=,last_did);
            }
        }

        // Copy over entries until we get to the one we want to
        // add/modify/delete.
        // FIXME: use skip_to and some splicing magic instead?
        while (!reader.at_end() && reader.get_docid() < did) {
            append_to_stream(reader.get_docid(), reader.get_value());
            reader.next();
        }
        if (!reader.at_end() && reader.get_docid() == did) reader.next();
        if (!value.empty()) {
            // Add/update entry for did.
            append_to_stream(did, value);
        }
    }
};

}

void
HoneyValueManager::merge_changes()
{
    for (auto&& i : changes) {
        Xapian::valueno slot = i.first;
        Honey::ValueUpdater updater(postlist_table, slot);
        for (auto&& j : i.second) {
            updater.update(j.first, j.second);
        }
    }
    changes.clear();
}

string
HoneyValueManager::add_document(Xapian::docid did, const Xapian::Document& doc,
                                map<Xapian::valueno, ValueStats>& val_stats)
{
    Xapian::ValueIterator it = doc.values_begin();
    if (it == doc.values_end()) {
        // No document values.
        auto i = slots.find(did);
        if (i != slots.end()) {
            // Document's values already added or modified in this batch.
            i->second = string();
        }
        return string();
    }

    Xapian::valueno count = doc.internal->values_count();
    Xapian::VecCOW<Xapian::termpos> slotvec(count);

    Xapian::valueno first_slot = it.get_valueno();
    Xapian::valueno last_slot = first_slot;
    while (it != doc.values_end()) {
        Xapian::valueno slot = it.get_valueno();
        slotvec.push_back(slot);
        const string& value = *it;

        // Update the statistics.
        auto i = val_stats.insert(make_pair(slot, ValueStats()));
        ValueStats& stats = i.first->second;
        if (i.second) {
            // There were no statistics stored already, so read them.
            get_value_stats(slot, stats);
        }

        // Now, modify the stored statistics.
        if ((stats.freq)++ == 0) {
            // If the value count was previously zero, set the upper and lower
            // bounds to the newly added value.
            stats.lower_bound = value;
            stats.upper_bound = value;
        } else {
            // Otherwise, simply make sure they reflect the new value.
            //
            // Check the upper bound first, as for some common uses of value
            // slots (dates) the values will tend to get larger not smaller
            // over time.
            int cmp = value.compare(stats.upper_bound);
            if (cmp >= 0) {
                if (cmp > 0) stats.upper_bound = value;
            } else if (value < stats.lower_bound) {
                stats.lower_bound = value;
            }
        }

        add_value(did, slot, value);
        last_slot = slot;
        ++it;
    }

    if (!termlist_table.is_open()) {
        return string();
    }

    string enc;
    pack_uint(enc, last_slot);
    BitWriter slots_used(enc);
    if (count > 1) {
        slots_used.encode(first_slot, last_slot);
        slots_used.encode(count - 2, last_slot - first_slot);
        slots_used.encode_interpolative(slotvec, 0, slotvec.size() - 1);
    }

    return slots_used.freeze();
}

void
HoneyValueManager::delete_document(Xapian::docid did,
                                   map<Xapian::valueno, ValueStats>& val_stats)
{
    Assert(termlist_table.is_open());
    auto it = slots.find(did);
    string s;
    if (it != slots.end()) {
        swap(s, it->second);
    } else {
        // Get from table, making a swift exit if this document has no terms or
        // values.
        if (!termlist_table.get_exact_entry(termlist_table.make_key(did), s))
            return;
        slots.insert(make_pair(did, string()));
    }

    const char* p = s.data();
    const char* end = p + s.size();
    size_t slot_enc_size;
    if (!unpack_uint(&p, end, &slot_enc_size)) {
        throw Xapian::DatabaseCorruptError("Termlist encoding corrupt");
    }
    if (slot_enc_size == 0)
        return;

    end = p + slot_enc_size;
    Xapian::valueno last_slot;
    if (!unpack_uint(&p, end, &last_slot)) {
        throw Xapian::DatabaseCorruptError("Slots used data corrupt");
    }

    if (p != end) {
        BitReader rd(p, end);
        Xapian::valueno first_slot = rd.decode(last_slot);
        Xapian::valueno slot_count = rd.decode(last_slot - first_slot) + 2;
        rd.decode_interpolative(0, slot_count - 1, first_slot, last_slot);

        Xapian::valueno slot = first_slot;
        while (slot != last_slot) {
            auto i = val_stats.insert(make_pair(slot, ValueStats()));
            ValueStats& stats = i.first->second;
            if (i.second) {
                // There were no statistics stored already, so read them.
                get_value_stats(slot, stats);
            }

            // Now, modify the stored statistics.
            AssertRelParanoid(stats.freq, >, 0);
            if (--(stats.freq) == 0) {
                stats.lower_bound.resize(0);
                stats.upper_bound.resize(0);
            }

            remove_value(did, slot);

            slot = rd.decode_interpolative_next();
        }
    }

    Xapian::valueno slot = last_slot;
    {
        {
            // FIXME: share code with above
            auto i = val_stats.insert(make_pair(slot, ValueStats()));
            ValueStats& stats = i.first->second;
            if (i.second) {
                // There were no statistics stored already, so read them.
                get_value_stats(slot, stats);
            }

            // Now, modify the stored statistics.
            AssertRelParanoid(stats.freq, >, 0);
            if (--(stats.freq) == 0) {
                stats.lower_bound.resize(0);
                stats.upper_bound.resize(0);
            }

            remove_value(did, slot);
        }
    }
}

string
HoneyValueManager::replace_document(Xapian::docid did,
                                    const Xapian::Document& doc,
                                    map<Xapian::valueno, ValueStats>& val_stats)
{
    if (doc.get_docid() == did) {
        // If we're replacing a document with itself, but the optimisation for
        // this higher up hasn't kicked in (e.g. because we've added/replaced
        // a document since this one was read) and the values haven't changed,
        // then the call to delete_document() below will remove the values
        // before the subsequent add_document() can read them.
        //
        // The simplest way to handle this is to force the document to read its
        // values, which we only need to do this is the docid matches.  Note
        // that this check can give false positives as we don't also check the
        // database, so for example replacing document 4 in one database with
        // document 4 from another will unnecessarily trigger this, but forcing
        // the values to be read is fairly harmless, and this is unlikely to be
        // a common case.  (Currently we will end up fetching the values
        // anyway, but there's scope to change that in the future).
        doc.internal->ensure_values_fetched();
    }
    delete_document(did, val_stats);
    return add_document(did, doc, val_stats);
}

string
HoneyValueManager::get_value(Xapian::docid did, Xapian::valueno slot) const
{
    auto i = changes.find(slot);
    if (i != changes.end()) {
        auto j = i->second.find(did);
        if (j != i->second.end()) return j->second;
    }

    // Read it from the table.
    string chunk;
    Xapian::docid last_did;
    last_did = get_chunk_containing_did(slot, did, chunk);
    if (last_did == 0) return string();

    ValueChunkReader reader(chunk.data(), chunk.size(), last_did);
    reader.skip_to(did);
    if (reader.at_end() || reader.get_docid() != did) return string();
    return reader.get_value();
}

void
HoneyValueManager::get_all_values(map<Xapian::valueno, string>& values,
                                  Xapian::docid did) const
{
    Assert(values.empty());
    if (!termlist_table.is_open()) {
        // Either the database has been closed, or else there's no termlist
        // table.  Check if the postlist table is open to determine which is
        // the case.
        if (!postlist_table.is_open())
            HoneyTable::throw_database_closed();
        throw Xapian::FeatureUnavailableError("Database has no termlist");
    }

    string s;
    if (!termlist_table.get_exact_entry(termlist_table.make_key(did), s))
        return;

    const char* p = s.data();
    const char* end = p + s.size();
    size_t slot_enc_size = *p++;

    if ((slot_enc_size & 0x80) == 0) {
        // If the top bit is clear we have a 7-bit bitmap of slots used.
        Xapian::valueno slot = 0;
        while (slot_enc_size) {
            if (slot_enc_size & 1) {
                values.insert(make_pair(slot, get_value(did, slot)));
            }
            ++slot;
            slot_enc_size >>= 1;
        }
        return;
    }

    slot_enc_size &= 0x7f;
    if (slot_enc_size == 0) {
        if (!unpack_uint(&p, end, &slot_enc_size)) {
            throw Xapian::DatabaseCorruptError("Termlist encoding corrupt");
        }
    }

    end = p + slot_enc_size;
    Xapian::valueno last_slot;
    if (!unpack_uint(&p, end, &last_slot)) {
        throw Xapian::DatabaseCorruptError("Slots used data corrupt");
    }

    if (p != end) {
        BitReader rd(p, end);
        Xapian::valueno first_slot = rd.decode(last_slot);
        Xapian::valueno slot_count = rd.decode(last_slot - first_slot) + 2;
        rd.decode_interpolative(0, slot_count - 1, first_slot, last_slot);

        Xapian::valueno slot = first_slot;
        while (slot != last_slot) {
            values.insert(make_pair(slot, get_value(did, slot)));
            slot = rd.decode_interpolative_next();
        }
    }
    values.insert(make_pair(last_slot, get_value(did, last_slot)));
}

void
HoneyValueManager::get_value_stats(Xapian::valueno slot) const
{
    LOGCALL_VOID(DB, "HoneyValueManager::get_value_stats", slot);
    // Invalidate the cache first in case an exception is thrown.
    mru_slot = Xapian::BAD_VALUENO;
    get_value_stats(slot, mru_valstats);
    mru_slot = slot;
}

void
HoneyValueManager::get_value_stats(Xapian::valueno slot,
                                   ValueStats& stats) const
{
    LOGCALL_VOID(DB, "HoneyValueManager::get_value_stats", slot | Literal("[stats]"));

    string tag;
    if (postlist_table.get_exact_entry(Honey::make_valuestats_key(slot), tag)) {
        const char* pos = tag.data();
        const char* end = pos + tag.size();

        if (!unpack_uint(&pos, end, &(stats.freq))) {
            if (pos == 0) {
                throw Xapian::DatabaseCorruptError("Incomplete stats item in "
                                                   "value table");
            }
            throw Xapian::RangeError("Frequency statistic in value table is "
                                     "too large");
        }
        if (!unpack_string(&pos, end, stats.lower_bound)) {
            if (pos == 0) {
                throw Xapian::DatabaseCorruptError("Incomplete stats item in "
                                                   "value table");
            }
            throw Xapian::RangeError("Lower bound in value table is too "
                                     "large");
        }
        size_t len = end - pos;
        if (len == 0) {
            stats.upper_bound = stats.lower_bound;
        } else {
            stats.upper_bound.assign(pos, len);
        }
    } else {
        stats.clear();
    }
}

void
HoneyValueManager::set_value_stats(map<Xapian::valueno, ValueStats>& val_stats)
{
    LOGCALL_VOID(DB, "HoneyValueManager::set_value_stats", val_stats);
    for (auto&& i : val_stats) {
        string key = Honey::make_valuestats_key(i.first);
        const ValueStats& stats = i.second;
        if (stats.freq != 0) {
            postlist_table.add(key, encode_valuestats(stats.freq,
                                                      stats.lower_bound,
                                                      stats.upper_bound));
        } else {
            postlist_table.del(key);
        }
    }
    val_stats.clear();
    mru_slot = Xapian::BAD_VALUENO;
}
