typedef struct {
    SV *self;
    PGconn *conn;
    UV prep_counter;
    UV cookie; /* currently active transaction object; 0 = none active */
} fupg_conn;


static SV *fupg_conn_errsv(PGconn *conn, const char *action) {
    dTHX;
    HV *hv = newHV();
    hv_stores(hv, "action", newSVpv(action, 0));
    hv_stores(hv, "severity", newSVpvs("FATAL")); /* Connection-related errors are always fatal */
    hv_stores(hv, "message", newSVpv(PQerrorMessage(conn), 0));
    return fu_croak_hv(hv, "FU::PG::error", "FATAL: %s", PQerrorMessage(conn));
}

static void fupg_conn_croak(fupg_conn *c, const char *action) {
    dTHX;
    croak_sv(fupg_conn_errsv(c->conn, action));
}

/* Takes ownership of the PGresult and croaks. */
static void fupg_result_croak(PGresult *r, const char *action, const char *query) {
    dTHX;
    HV *hv = newHV();
    hv_stores(hv, "action", newSVpv(action, 0));
    char *s = PQresultErrorField(r, PG_DIAG_SEVERITY_NONLOCALIZED);
    hv_stores(hv, "severity", newSVpv(s ? s : "FATAL", 0));
    if (query) hv_stores(hv, "query", newSVpv(query, 0));

    /* If the PGresult is not an error, assume it's an unexpected resultStatus */
    s = PQresultErrorField(r, PG_DIAG_MESSAGE_PRIMARY);
    hv_stores(hv, "message", s ? newSVpv(s, 0) : newSVpvf("unexpected status code '%s'", PQresStatus(PQresultStatus(r))));

    /* I like the verbose error messages. Doesn't include anything that's not
     * also fetched below, but saves me from having to do the formatting
     * manually. */
    char *verbose = NULL;
    if (s) {
        verbose = PQresultVerboseErrorMessage(r, PQERRORS_VERBOSE, PQSHOW_CONTEXT_ERRORS);
        if (s) {
            hv_stores(hv, "verbose_message", newSVpv(verbose, 0));
            PQfreemem(verbose);
        }
    }

    if ((s = PQresultErrorField(r, PG_DIAG_MESSAGE_DETAIL))) hv_stores(hv, "detail", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_MESSAGE_HINT))) hv_stores(hv, "hint", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_STATEMENT_POSITION))) hv_stores(hv, "statement_position", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_INTERNAL_POSITION))) hv_stores(hv, "internal_position", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_INTERNAL_QUERY))) hv_stores(hv, "internal_query", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_CONTEXT))) hv_stores(hv, "context", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_SCHEMA_NAME))) hv_stores(hv, "schema_name", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_TABLE_NAME))) hv_stores(hv, "table_name", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_COLUMN_NAME))) hv_stores(hv, "column_name", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_DATATYPE_NAME))) hv_stores(hv, "datatype_name", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_CONSTRAINT_NAME))) hv_stores(hv, "constraint_name", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_SOURCE_FILE))) hv_stores(hv, "source_file", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_SOURCE_LINE))) hv_stores(hv, "source_line", newSVpv(s, 0));
    if ((s = PQresultErrorField(r, PG_DIAG_SOURCE_FUNCTION))) hv_stores(hv, "source_function", newSVpv(s, 0));

    PQclear(r);
    croak_sv(verbose
        ? fu_croak_hv(hv, "FU::PG::error", "%s", SvPV_nolen(*hv_fetchs(hv, "verbose_message", 0)))
        : fu_croak_hv(hv, "FU::PG::error", "%s: %s",
            SvPV_nolen(*hv_fetchs(hv, "severity", 0)),
            SvPV_nolen(*hv_fetchs(hv, "message", 0))
        )
    );
}

static SV *fupg_connect(pTHX_ const char *str) {
    PGconn *conn = PQconnectdb(str);
    if (PQstatus(conn) != CONNECTION_OK) {
        SV *sv = fupg_conn_errsv(conn, "connect");
        PQfinish(conn);
        croak_sv(sv);
    }

    fupg_conn *c = safecalloc(1, sizeof(fupg_conn));
    c->conn = conn;
    return fupg_selfobj(c, "FU::PG::conn");
}

static const char *fupg_status(fupg_conn *c) {
    if (PQstatus(c->conn) == CONNECTION_BAD) return "bad";
    switch (PQtransactionStatus(c->conn)) {
        case PQTRANS_IDLE: return c->cookie ? "txn_done" : "idle";
        case PQTRANS_ACTIVE: return "active"; /* can't happen, we don't do async */
        case PQTRANS_INTRANS: return "txn_idle";
        case PQTRANS_INERROR: return "txn_error";
        default: return "unknown";
    }
}

static void fupg_disconnect(fupg_conn *c) {
    PQfinish(c->conn);
    c->conn = NULL;
}

static void fupg_destroy(fupg_conn *c) {
    PQfinish(c->conn);
    safefree(c);
}

static SV *fupg_exec_result(pTHX_ PGresult *r) {
    SV *ret = &PL_sv_undef;
    char *tup = PQcmdTuples(r);
    if (tup && *tup) {
        ret = sv_2mortal(newSVpv(tup, 0));
        SvIV(ret);
        SvIOK_only(ret);
    }
    return ret;
}

static SV *fupg_exec(pTHX_ fupg_conn *c, const char *sql) {
    PGresult *r = PQexec(c->conn, sql);
    if (!r) fupg_conn_croak(c, "exec");
    switch (PQresultStatus(r)) {
        case PGRES_EMPTY_QUERY:
        case PGRES_COMMAND_OK:
        case PGRES_TUPLES_OK: break;
        default: fupg_result_croak(r, "exec", sql);
    }
    SV *ret = fupg_exec_result(r);
    PQclear(r);
    return ret;
}

/* Validate a FU::PG::txn object and extract the connection */
static fupg_conn *fupg_get_transaction(pTHX_ SV *sv) {
    if (!sv_derived_from(sv, "FU::PG::txn")) goto invalid;
    sv = SvRV(sv);
    if (SvTYPE(sv) != SVt_PVAV) goto invalid;
    AV *av = (AV *)sv;

    SV **v = av_fetch(av, 0, 0);
    if (!v || !*v) goto invalid;
    fupg_conn *c = (fupg_conn *)SvIVX(SvRV(*v));

    v = av_fetch(av, 1, 0);
    if (!v || !*v) goto invalid;
    if (!SvOK(*v)) fu_confess("Invalid attempt to run a query on a transaction that has already finished");
    if (c->cookie != SvUV(*v)) fu_confess("Invalid cross-transaction operation");
    return c;
invalid:
    fu_confess("invalid transaction object");
}

/* Read a Perl value from a PGresult.
 * Currently assumes text format and just creates a PV. */
static SV *fupg_val(pTHX_ const PGresult *r, int row, int col) {
    if (PQgetisnull(r, row, col)) return newSV(0);
    return newSVpvn_utf8(PQgetvalue(r, row, col), PQgetlength(r, row, col), 1);
}

typedef struct {
    /* Set in $conn->q() */
    SV *self;
    fupg_conn *conn; /* has a refcnt on conn->self */
    UV cookie;
    char *query;
    SV **bind;
    int bindn;
    /* Set during prepare */
    int prepared;
    char name[32];
    PGresult *describe;
    /* Set during execute */
    int paramn;
    char **param;
    PGresult *result;
} fupg_st;

static SV *fupg_q(pTHX_ fupg_conn *c, const char *query, I32 ax, I32 argc) {
    fupg_st *st = safecalloc(1, sizeof(fupg_st));
    st->conn = c;
    st->cookie = c->cookie;
    SvREFCNT_inc(c->self);

    st->query = savepv(query);
    if (argc > 2) {
        st->bind = safemalloc((argc-2) * sizeof(SV *));
        I32 i;
        for (i=2; i < argc; i++) {
            st->bind[st->bindn] = newSV(0);
            sv_setsv(st->bind[st->bindn], ST(i));
            st->bindn++;
        }
    }

    return fupg_selfobj(st, "FU::PG::st");
}

static void fupg_st_prepare(pTHX_ fupg_st *st) {
    if (st->describe) return;
    if (st->prepared) fu_confess("invalid attempt to re-prepare invalid statement");

    /* TODO: This is where we check for any cached prepared statements */

    snprintf(st->name, sizeof(st->name), "fupg%"UVuf, ++st->conn->prep_counter);

    /* TODO: Pipeline these two commands, no need for two round-trips with the server */
    PGresult *r = PQprepare(st->conn->conn, st->name, st->query, 0, NULL);
    if (!r) fupg_conn_croak(st->conn , "prepare");
    if (PQresultStatus(r) != PGRES_COMMAND_OK)
        fupg_result_croak(r, "prepare", st->query);
    PQclear(r);
    st->prepared = 1;

    r = PQdescribePrepared(st->conn->conn, st->name);
    if (!r) fupg_conn_croak(st->conn , "prepare");
    if (PQresultStatus(r) != PGRES_COMMAND_OK)
        fupg_result_croak(r, "prepare", st->query);
    st->describe = r;
}

static SV *fupg_st_params(pTHX_ fupg_st *st) {
    fupg_st_prepare(aTHX_ st);
    int i, nparams = PQnparams(st->describe);
    AV *av = newAV_alloc_x(nparams);
    for (i=0; i<nparams; i++) {
        HV *hv = newHV();
        hv_stores(hv, "oid", newSViv(PQparamtype(st->describe, i)));
        av_push_simple(av, newRV_noinc((SV *)hv));
    }
    return sv_2mortal(newRV_noinc((SV *)av));
}

static SV *fupg_st_columns(pTHX_ fupg_st *st) {
    fupg_st_prepare(aTHX_ st);
    int i, ncols = PQnfields(st->describe);
    AV *av = newAV_alloc_x(ncols);
    for (i=0; i<ncols; i++) {
        HV *hv = newHV();
        const char *name = PQfname(st->describe, i);
        hv_stores(hv, "name", newSVpvn_utf8(name, strlen(name), 1));
        hv_stores(hv, "oid", newSViv(PQftype(st->describe, i)));
        int tmod = PQfmod(st->describe, i);
        if (tmod >= 0) hv_stores(hv, "typemod", newSViv(tmod));
        av_push_simple(av, newRV_noinc((SV *)hv));
    }
    return sv_2mortal(newRV_noinc((SV *)av));
}

static void fupg_st_check_dupcols(pTHX_ PGresult *r) {
    HV *hv = newHV();
    int i, nfields = PQnfields(r);
    for (i=0; i<nfields; i++) {
        const char *key = PQfname(r, i);
        int len = -strlen(key);
        if (hv_exists(hv, key, len)) {
            SvREFCNT_dec((SV *)hv);
            fu_confess("Query returns multiple columns with the same name ('%s')", key);
        }
        hv_store(hv, key, len, &PL_sv_yes, 0);
    }
    SvREFCNT_dec((SV *)hv);
}

static void fupg_st_execute(pTHX_ fupg_st *st) {
    /* Disallow fetching the results more than once. I don't see a reason why
     * someone would need that and disallowing it leaves room for fetching the
     * results in a streaming fashion without breaking API compat. */
    if (st->result) fu_confess("Invalid attempt to execute statement multiple times");

    /* TODO: prepare can be skipped when prepared statement caching is disabled and (text-format queries or no bind params) */
    fupg_st_prepare(aTHX_ st);
    st->param = safemalloc(st->bindn * sizeof(char *));
    int i;
    for (i=0; i<st->bindn; i++) {
        st->param[i] = SvPVutf8_nolen(st->bind[i]);
        st->paramn++;
    }

    /* I'm not super fond of this approach. Storing the full query results in a
     * PGresult involves unnecessary parsing, memory allocation and copying.
     * The wire protocol is sufficiently simple that I could parse the query
     * results directly from the network buffers without much additional code,
     * and that would be much more efficient. Alas, libpq doesn't let me do
     * that.
     * There is the option of fetching results in chunked mode, but from what I
     * gather that just saves a bit of memory in exchange for more and smaller
     * malloc()/free()'s. Performance-wise, it probably won't be much of an
     * improvement */
    PGresult *r = PQexecPrepared(st->conn->conn, st->name, st->paramn, (const char * const*)st->param, NULL, NULL, 0);
    if (!r) fupg_conn_croak(st->conn , "exec");
    switch (PQresultStatus(r)) {
        case PGRES_COMMAND_OK:
        case PGRES_TUPLES_OK: break;
        default: fupg_result_croak(r, "exec", st->query);
    }
    st->result = r;
}

static SV *fupg_st_exec(pTHX_ fupg_st *st) {
    fupg_st_execute(aTHX_ st);
    return fupg_exec_result(st->result);
}

static SV *fupg_st_val(pTHX_ fupg_st *st) {
    fupg_st_prepare(aTHX_ st);
    if (PQnfields(st->describe) > 1) fu_confess("Invalid use of $st->val() on query returning more than one column");
    if (PQnfields(st->describe) == 0) fu_confess("Invalid use of $st->val() on query returning no data");
    fupg_st_execute(aTHX_ st);
    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->val() on query returning more than one row");
    SV *sv = PQntuples(st->result) == 0 ? newSV(0) : fupg_val(aTHX_ st->result, 0, 0);
    return sv_2mortal(sv);
}

static I32 fupg_st_rowl(pTHX_ fupg_st *st, I32 ax) {
    dSP;
    fupg_st_execute(aTHX_ st);
    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowl() on query returning zero rows");
    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowl() on query returning more than one row");
    if (GIMME_V != G_LIST) {
        ST(0) = sv_2mortal(newSViv(PQnfields(st->result)));
        return 1;
    }
    int i, nfields = PQnfields(st->result);
    (void)POPs;
    EXTEND(SP, nfields);
    for (i=0; i<nfields; i++) mPUSHs(fupg_val(aTHX_ st->result, 0, i));
    return nfields;
}

static SV *fupg_st_rowa(pTHX_ fupg_st *st) {
    fupg_st_execute(aTHX_ st);
    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowl() on query returning zero rows");
    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowl() on query returning more than one row");
    int i, nfields = PQnfields(st->result);
    AV *av = newAV_alloc_x(nfields);
    SV *sv = sv_2mortal(newRV_noinc((SV *)av));
    for (i=0; i<nfields; i++) av_push_simple(av, fupg_val(aTHX_ st->result, 0, i));
    return sv;
}

static SV *fupg_st_rowh(pTHX_ fupg_st *st) {
    fupg_st_prepare(aTHX_ st);
    fupg_st_check_dupcols(aTHX_ st->describe);
    fupg_st_execute(aTHX_ st);
    if (PQntuples(st->result) == 0) fu_confess("Invalid use of $st->rowh() on query returning zero rows");
    if (PQntuples(st->result) > 1) fu_confess("Invalid use of $st->rowh() on query returning more than one row");
    int i, nfields = PQnfields(st->result);
    HV *hv = newHV();
    SV *sv = sv_2mortal(newRV_noinc((SV *)hv));
    for (i=0; i<nfields; i++) {
        const char *key = PQfname(st->result, i);
        hv_store(hv, key, -strlen(key), fupg_val(aTHX_ st->result, 0, i), 0);
    }
    return sv;
}

static void fupg_st_destroy(fupg_st *st) {
    int i;
    /* Ignore failure, this is just a best-effort attempt to free up resources on the backend */
    if (st->prepared) PQclear(PQclosePrepared(st->conn->conn, st->name));

    if (st->query) safefree(st->query);
    for (i=0; i < st->bindn; i++) SvREFCNT_dec(st->bind[i]);
    if (st->bind) safefree(st->bind);
    /* XXX: These point into bind SVs (for now): for (i=0; i < st->paramn; i++) safefree(st->param[i]); */
    if (st->param) safefree(st->param);
    PQclear(st->describe);
    PQclear(st->result);
    SvREFCNT_dec(st->conn->self);
    safefree(st);
}


/* TODO: $st->alla, allh, flat, kvv, kva, kvh */
/* TODO: Prepared statement caching */
/* TODO: Binary format fetching & type handling */