// sample_usage.cpp — see sample_usage.h. Pure: standard library only.

#include "sample_usage.h"

#include <cctype>
#include <cstddef>
#include <limits>

namespace reasampler {

namespace {

constexpr const char* kMagic = "rsusage1";

// Append one length-prefixed field: <decimal-len> ':' <bytes>. The same wire idiom as
// assignment_request / provenance — one grammar across every ext-state seam.
void putField(std::string& out, const std::string& field) {
    out += std::to_string(field.size());
    out += ':';
    out += field;
}

// Bounds-checked cursor over the encoded string (the assignment_request Cursor, trimmed
// to the two field kinds this record needs). A short read latches ok_ false.
class Cursor {
public:
    explicit Cursor(const std::string& s) : s_(s) {}

    bool ok() const { return ok_; }
    bool atEnd() const { return pos_ >= s_.size(); }

    bool field(std::string& out) {
        if (!ok_) return false;
        const std::size_t colon = s_.find(':', pos_);
        if (colon == std::string::npos) return fail();
        if (colon == pos_) return fail();  // empty length token
        if (colon - pos_ > 20u) return fail();  // SIZE_MAX is 20 decimal digits
        std::size_t len = 0;
        for (std::size_t i = pos_; i < colon; ++i) {
            const char c = s_[i];
            if (c < '0' || c > '9') return fail();
            const std::size_t digit = static_cast<std::size_t>(c - '0');
            if (len > (std::numeric_limits<std::size_t>::max() - digit) / 10u)
                return fail();
            len = len * 10u + digit;
        }
        const std::size_t start = colon + 1;
        if (start > s_.size() || len > s_.size() - start) return fail();
        out.assign(s_, start, len);
        pos_ = start + len;
        return true;
    }

    // Consumes an exact literal at the cursor (the magic tag). Fails if absent.
    bool literal(const char* lit) {
        if (!ok_) return false;
        std::size_t i = 0;
        for (; lit[i] != '\0'; ++i) {
            if (pos_ + i >= s_.size() || s_[pos_ + i] != lit[i]) return fail();
        }
        pos_ += i;
        return true;
    }

    // A length-prefixed unsigned decimal (the hold count). Fails on empty, non-digit,
    // or a value past a sane ceiling (a record cannot hold more entries than bytes).
    bool fieldCount(std::size_t& out) {
        std::string f;
        if (!field(f)) return false;
        if (f.empty() || f.size() > 10u) return fail();
        std::size_t v = 0;
        for (const char c : f) {
            if (c < '0' || c > '9') return fail();
            v = v * 10u + static_cast<std::size_t>(c - '0');
        }
        out = v;
        return true;
    }

private:
    bool fail() {
        ok_ = false;
        return false;
    }

    const std::string& s_;
    std::size_t pos_ = 0;
    bool ok_ = true;
};

}  // namespace

std::string encodeUsageRecord(const UsageRecord& rec) {
    std::string out = kMagic;
    putField(out, rec.trackGuid);
    putField(out, rec.ownerNonce);
    putField(out, rec.unioned ? "1" : "0");
    putField(out, std::to_string(rec.holds.size()));
    for (const UsageHold& h : rec.holds) {
        putField(out, h.sampleId);
        putField(out, h.relativePath);
    }
    return out;
}

std::optional<UsageRecord> decodeUsageRecord(const std::string& wire) {
    Cursor c(wire);
    if (!c.literal(kMagic)) return std::nullopt;
    UsageRecord rec;
    if (!c.field(rec.trackGuid)) return std::nullopt;
    if (!c.field(rec.ownerNonce)) return std::nullopt;
    std::string unionedField;
    if (!c.field(unionedField)) return std::nullopt;
    if (unionedField == "1") rec.unioned = true;
    else if (unionedField == "0") rec.unioned = false;
    else return std::nullopt;  // anything else is corruption -> reject whole
    std::size_t count = 0;
    if (!c.fieldCount(count)) return std::nullopt;
    // Each hold needs at least 4 wire bytes ("0:0:"), so a count past wire.size()/4 is
    // provably bogus — reject before looping rather than iterating a crafted huge count.
    if (count > wire.size() / 4u + 1u) return std::nullopt;
    rec.holds.reserve(count);
    for (std::size_t i = 0; i < count; ++i) {
        UsageHold h;
        if (!c.field(h.sampleId)) return std::nullopt;
        if (!c.field(h.relativePath)) return std::nullopt;
        rec.holds.push_back(std::move(h));
    }
    if (!c.ok() || !c.atEnd()) return std::nullopt;  // trailing garbage -> reject whole
    return rec;
}

UsagePublishPlan planUsagePublish(const std::optional<std::string>& existing,
                                  const UsageRecord& mine) {
    UsagePublishPlan plan;
    // The written form of "just mine": mine's identity + holds, unioned=false (the plan
    // computes the flag; a sole-writer record is un-poisoned).
    UsageRecord cleanMine = mine;
    cleanMine.unioned = false;
    plan.wire = encodeUsageRecord(cleanMine);

    if (!existing || existing->empty()) {
        // Fresh key — write mine.
        return plan;
    }
    const std::optional<UsageRecord> theirs = decodeUsageRecord(*existing);
    if (!theirs) {
        // Undecodable existing value under MY key: corruption (a sibling sharing
        // this key via copy always writes decodable records). REMINT rather than
        // overwrite: writing mine over the corrupt key would clear the prune-side
        // abort, but a same-key sibling B's holds would then be unprotected until
        // B publishes again. Leaving the corrupt key in place keeps the prune-side
        // abort firing (foldUsageRecords.abortPrune) so the window where B's holds
        // might be unprotected can never resolve toward delete. Mine is published
        // under the new key that remint produces.
        // NOTE (>16 MB gap): readReasamplerExtState returning nullopt for a value
        // larger than 16 MB is indistinguishable from "absent" at the publish site;
        // that narrow case takes the fresh-write branch above rather than remint.
        // Both outcomes are safe (fresh write is also correct for a truly absent key);
        // the gap is documented in the header's fail-safe list.
        plan.remint = true;
        return plan;
    }

    const bool nonceMatch =
        !mine.ownerNonce.empty() && theirs->ownerNonce == mine.ownerNonce;

    if (nonceMatch && !theirs->unioned) {
        // Exactly THIS incarnation wrote the key (the per-lifetime nonce is the exact
        // ownership proof — a same-track sibling's byte-identical hold set can NOT pass
        // this test, its nonce differs) AND no other writer has ever unioned into it,
        // so the content is provably all mine. Clean replace: released holds drop.
        if (plan.wire == *existing) plan.skipWrite = true;  // idle reload tick
        return plan;
    }

    if (theirs->trackGuid == mine.trackGuid || (nonceMatch && theirs->unioned)) {
        // A foreign writer on MY OWN track (a same-track copy-sibling, or my own
        // last-session record — indistinguishable by construction), or a record I
        // wrote last but that carries unioned holds from an earlier multi-writer
        // merge. Either way no hold in it may be dropped by me — union, existing-
        // first, de-duped, and the record is (or stays) POISONED unioned=true so no
        // future nonce-matching write can clean-replace a sibling's holds away.
        UsageRecord merged;
        merged.trackGuid = mine.trackGuid;
        merged.ownerNonce = mine.ownerNonce;
        merged.unioned = true;
        merged.holds = theirs->holds;
        for (const UsageHold& h : mine.holds) {
            bool dup = false;
            for (const UsageHold& e : merged.holds) {
                if (e == h) { dup = true; break; }
            }
            if (!dup) merged.holds.push_back(h);
        }
        if (theirs->unioned && merged.holds == theirs->holds) {
            // Already poisoned and the union adds nothing — the write would flip only
            // the ownerNonce. Skip the redundant ext-state churn. (A false->true
            // unioned flip is NEVER skipped: it is the poison that protects the other
            // writer's holds from the last writer's future clean replace.)
            plan.skipWrite = true;
        }
        plan.wire = encodeUsageRecord(merged);
        return plan;
    }

    // Foreign value from ANOTHER track: this instance is a cross-track copy (or was
    // moved). Take a fresh identity; never overwrite the other's record.
    plan.remint = true;
    return plan;
}

std::vector<std::string> usageHeldPaths(
    const std::vector<UsageRecord>& records,
    const std::unordered_set<std::string>& liveTrackGuids,
    bool anyInstanceLive) {
    std::vector<std::string> out;
    std::unordered_set<std::string> seen;
    // FAIL-SAFE NET: records exist but not one instance was identified live anywhere —
    // indistinguishable from an identity-matcher failure, so protect EVERY record's
    // paths rather than none (zero-identified must never degrade toward delete).
    const bool protectAll = !records.empty() && !anyInstanceLive;
    for (const UsageRecord& rec : records) {
        const bool live = protectAll ||
                          (rec.trackGuid.empty()
                               ? anyInstanceLive
                               : (liveTrackGuids.count(rec.trackGuid) != 0));
        if (!live) continue;
        for (const UsageHold& h : rec.holds) {
            if (h.relativePath.empty()) continue;
            if (seen.insert(h.relativePath).second) out.push_back(h.relativePath);
        }
    }
    return out;
}

UsageFoldResult foldUsageRecords(
    const std::vector<std::optional<UsageRecord>>& decoded,
    const std::unordered_set<std::string>& liveTrackGuids,
    bool anyInstanceLive) {
    UsageFoldResult result;
    std::vector<UsageRecord> records;
    records.reserve(decoded.size());
    for (const std::optional<UsageRecord>& rec : decoded) {
        if (!rec) {
            // A present-but-unreadable record: it may protect ANYTHING, so the prune
            // must halt outright. Belt-and-braces: return the PROTECT-ALL set (all
            // readable records' paths) so the fail-safe holds even under a future
            // caller that forgets to check abortPrune before using heldPaths. The
            // abort flag is still the authoritative signal; heldPaths is the
            // maximum-protection fallback.
            result.abortPrune = true;
            // Collect EVERY path from EVERY readable record, bypassing the liveness
            // filter entirely (on abort the protected set is unknowable, so every
            // decoded hold must be included regardless of track-guid membership).
            std::unordered_set<std::string> seen;
            for (const std::optional<UsageRecord>& r : decoded) {
                if (!r) continue;
                for (const UsageHold& h : r->holds) {
                    if (h.relativePath.empty()) continue;
                    if (seen.insert(h.relativePath).second)
                        result.heldPaths.push_back(h.relativePath);
                }
            }
            return result;
        }
        records.push_back(*rec);
    }
    result.heldPaths = usageHeldPaths(records, liveTrackGuids, anyInstanceLive);
    return result;
}

std::string toUpperAscii(const std::string& s) {
    std::string out = s;
    for (char& c : out)
        c = static_cast<char>(std::toupper(static_cast<unsigned char>(c)));
    return out;
}

bool identityMatches(const std::string& identity, const std::string& uidHexUpper,
                     const std::string& nameUpper,
                     const std::string& outputNameUpper) {
    if (identity.empty()) return false;
    const std::string up = toUpperAscii(identity);
    // Primary: the 32-hex class UID embedded in REAPER's fx_ident rendering. Not
    // guaranteed on every platform/REAPER build (byte-order of the rendered FUID vs
    // REAPER's hex is unverified on Windows COM layout), hence the two name nets below
    // — and the protect-all fold above them (see usageHeldPaths).
    if (!uidHexUpper.empty() && up.find(uidHexUpper) != std::string::npos) return true;
    // The module filename base ("REASAMPLER_9000") — fx_ident carries the .vst3 module
    // path, so this is the alternative that works in the common case (the display name
    // "REASAMPLER 9000", space-separated, can never match the filename form).
    if (!outputNameUpper.empty() && up.find(outputNameUpper) != std::string::npos)
        return true;
    // The factory display name — matches original_name / renamed-instance renderings.
    // Beta-substring over-protect is deliberate (see the header note): stable needles
    // are substrings of beta ones, widening protection only — never a delete.
    return !nameUpper.empty() && up.find(nameUpper) != std::string::npos;
}

}  // namespace reasampler