#ifndef EVSQL_H

#define EVSQL_H

/**

 * @file src/evsql.h

 *

 * A SQL library designed for use with libevent and PostgreSQL's libpq. Provides support for queueing non-transactional

 * requests, transaction support, parametrized queries and result iteration.

 *

 * Currently, the API does not expose the underlying libpq data structures, but since it is currently the only

 * underlying implementation, there is no guarantee that the same API will actually work with other databases' interface

 * libraries...

 *

 * The order of function calls and callbacks goes something like this:

 *

 *  -   evsql_new_pq()

 *

 *  -   evsql_trans()

 *      -   evsql_trans_abort()

 *      -   evsql_trans_error_cb()

 *      -   evsql_trans_ready_cb()

 *

 *  -   evsql_query(), \ref evsql_param_ + evsql_query_params(), evsql_query_exec()

 *      -   evsql_query_abort()

 *      -   evsql_query_cb()

 *          -   \ref evsql_result_

 *          -   evsql_result_free()

 *

 *  -   evsql_trans_commit()

 *      -   evsql_trans_done_cb()

 *

 */

/**

 * System includes

 */

#include <stdint.h>

#include <stdbool.h>

#include <event2/event.h>

/**

 * For err_t.

 */

#include "lib/err.h"

/**

 * @struct evsql

 *

 * The generic session handle used to manage a single "database connector" with multiple queries/transactions.

 *

 * @see \ref evsql_

 */

struct evsql;

/**

 * @struct evsql_trans

 *

 * Opaque transaction handle returned by evsql_trans() and used for the \ref evsql_query_ functions

 *

 * @see \ref evsql_trans_

 */

struct evsql_trans;

/**

 * @struct evsql_query

 *

 * Opaque query handle returned by the \ref evsql_query_ functions and used for evsql_query_abort()

 *

 * @see \ref evsql_query_

 */

struct evsql_query;

/**

 * @struct evsql_result

 *

 * Opaque result handle received by evsql_query_cb(), and used with the \ref evsql_result_ functions

 *

 * @see evsql_query_cb

 * @see \ref evsql_result_

 */

struct evsql_result;

/**

 * Various transaction isolation levels for conveniance

 *

 * @see evsql_trans

 */

enum evsql_trans_type {

    EVSQL_TRANS_DEFAULT,

    EVSQL_TRANS_SERIALIZABLE,

    EVSQL_TRANS_REPEATABLE_READ,

    EVSQL_TRANS_READ_COMMITTED,

    EVSQL_TRANS_READ_UNCOMMITTED,

};

/**

 * An item can be in different formats, the classical text-based format (i.e. snprintf "1234") or a more low-level

 * binary format (i.e uint16_t 0x04F9 in network-byte order).

 */

enum evsql_item_format {

    /** Format values as text strings */

    EVSQL_FMT_TEXT,

    /** Type-specific binary encoding */

    EVSQL_FMT_BINARY,

};

/**

 * An item has a specific type, these correspond somewhat to the native database types.

 */

enum evsql_item_type {

    /** End marker, zero */

    EVSQL_TYPE_INVALID,

    /** A SQL NULL */

    EVSQL_TYPE_NULL_,

    /** A `struct evsql_item_binary` */

    EVSQL_TYPE_BINARY,

    /** A NUL-terminated char* */

    EVSQL_TYPE_STRING,

    /** A uint16_t value */

    EVSQL_TYPE_UINT16,

    /** A uint32_t value */

    EVSQL_TYPE_UINT32,

    /** A uint64_t value */

    EVSQL_TYPE_UINT64,

    EVSQL_TYPE_MAX

};

/**

 * Value for use with EVSQL_TYPE_BINARY, this just a non-NUL-terminated char* and an explicit length

 */

struct evsql_item_binary {

    /** The binary data */

    const char *ptr;

    /** Number of bytes pointed to by ptr */

    size_t len;

};

/**

 * Metadata about the format and type of an item, this does not hold any actual value.

 */

struct evsql_item_info {

    /** The format */

    enum evsql_item_format format;

    /** The type type */

    enum evsql_item_type type;

    /** Various flags */

    struct evsql_item_flags {

        /** The value may be NULL @see evsql_result_next */

        bool null_ok : 1;

    } flags;

};

/**

 * An union to provide storage for the values of small types

 *

 * @see evsql_item

 */

union evsql_item_value {

    /** 16-bit unsigned integer */

    uint16_t uint16;

    /** 32-bit unsigned integer */

    uint32_t uint32;

    /** 64-bit unsigned integer */

    uint64_t uint64;

};

/**

 * A generic structure containing the type and value of a query parameter or a result field.

 *

 * @see evsql_query_info

 * @see evsql_query_params

 * @see evsql_result_info

 */

struct evsql_item {

    /** The "header" containing the type and format */

    struct evsql_item_info info;

    /**

     * Pointer to the raw databytes. 

     * Set to NULL for SQL NULLs, otherwise &value or an external buf 

     */

    const char *bytes;

    /**

     * Size of the byte array pointed to by bytes, zero for EVSQL_FMT_TEXT data.

     */

    size_t length;

    /**

     * Inline storage for small values

     */

    union evsql_item_value value;

    /** Internal flags */

    struct {

        /**

         * The item has a value stored in `value`

         */

        bool has_value : 1;

    } flags;

};

/**

 * Query meta-info, similar to a prepared statement.

 *

 * Contains the literal SQL query and the types of the parameters, but no more.

 *

 * @see evsql_query_exec

 */

struct evsql_query_info {

    /** The SQL query itself */

    const char *sql;

    /** 

     * A variable-length array of the item_info parameters, terminated by an EVSQL_TYPE_INVALID entry.

     */

    struct evsql_item_info params[];

};

/**

 * Contains the query parameter types and their actual values

 *

 * @see evsql_query_params

 */

struct evsql_query_params {

    /** Requested result format for this query. XXX: move elsewhere */

    enum evsql_item_format result_format;

    /**

     * A variable-length array of the item parameter-values, terminated by an EVSQL_TYPE_INVALID entry.

     */

    struct evsql_item list[];

};

/**

 * Result layout metadata. This contains the stucture needed to decode result rows.

 *

 * @see evsql_result_begin

 */

struct evsql_result_info {

    /** XXX: make up something useful to stick here */

    int _unused;

    /**

     * A variable-length array of the item_info column types.

     */

    struct evsql_item_info columns[];

};

/**

 * Magic macros for defining param/result info -lists

 *  

 * @code

 *  static struct evsql_query_params params = EVSQL_PARAMS(EVSQL_FMT_BINARY) {

 *      EVSQL_PARAM( UINT32 ),

 *      ...,

 *

 *      EVSQL_PARAMS_END

 *  };

 * @endcode

 *

 * @name EVSQL_TYPE/PARAM_*

 * @{

 */

/**

 * A `struct evsql_item_info` initializer, using FMT_BINARY and the given EVSQL_TYPE_ -suffix.

 *

 * @param typenam the suffix of an evsql_item_type name

 *

 * @see struct evsql_item_info

 * @see enum evsql_item_type

 */

#define EVSQL_TYPE(typenam)                     { EVSQL_FMT_BINARY, EVSQL_TYPE_ ## typenam  }

/**

 * End marker for a `struct evsql_item_info` array.

 *

 * @see struct evsql_item_info

 */

#define EVSQL_TYPE_END                          { EVSQL_FMT_BINARY, EVSQL_TYPE_INVALID      }

/**

 * Initializer block for an evsql_query_params struct

 */

#define EVSQL_PARAMS(result_fmt)            { result_fmt, 

/**

 * An evsql_item initializer

 */

#define EVSQL_PARAM(typenam)                    { EVSQL_TYPE(typenam) }

/**

 * Include the ending item and terminate the pseudo-block started using #EVSQL_PARAMS

 */

#define EVSQL_PARAMS_END                        { EVSQL_TYPE_END } \

                                              } // <<<

// @}

/**

 * Callback definitions

 *

 * @name evsql_*_cb

 * @{

 */

/**

 * Callback for handling query results.

 *

 * The query has completed, either succesfully or unsuccesfully.

 *

 * Use the \ref evsql_result_ functions to manipulate the results, and call evsql_result_free() (or equivalent) once done.

 *

 * @param res The result handle that must be result_free'd after use

 * @param arg The void* passed to \ref evsql_query_

 *

 * @see evsql_query

 */

typedef void (*evsql_query_cb)(struct evsql_result *res, void *arg);

/**

 * Callback for handling global-level errors.

 *

 * The evsql is not useable anymore.

 *

 * XXX: this is not actually called yet, as no retry logic is implemented, so an evsql itself never fails.

 *

 * @see evsql_new_pq

 */

typedef void (*evsql_error_cb)(struct evsql *evsql, void *arg);

/**

 * Callback for handling transaction-level errors. This may be called at any time during a transaction's lifetime,

 * including from within the \ref evsql_query_ functions (but not always).

 *

 * The transaction is not useable anymore.

 *

 * @param trans the transaction in question

 * @param arg the void* passed to evsql_trans

 *

 * @see evsql_trans

 */

typedef void (*evsql_trans_error_cb)(struct evsql_trans *trans, void *arg);

/**

 * Callback for handling evsql_trans/evsql_query_abort completion. The transaction is ready for use with \ref evsql_query_.

 *

 * @param trans the transaction in question

 * @param arg the void* passed to evsql_trans

 *

 * @see evsql_trans

 * @see evsql_query_abort

 */

typedef void (*evsql_trans_ready_cb)(struct evsql_trans *trans, void *arg);

/**

 * Callback for handling evsql_trans_commit completion. The transaction was commited, and should not be used anymore.

 *

 * @param trans the transaction in question

 * @param arg the void* passed to evsql_trans

 *

 * @see evsql_trans

 * @see evsql_trans_commit

 */

typedef void (*evsql_trans_done_cb)(struct evsql_trans *trans, void *arg);

// @}

/**

 * Session functions

 *

 * @defgroup evsql_* Session interface

 * @see evsql.h

 * @{

 */

/**

 * Session creation functions

 *

 * @defgroup evsql_new_* Session creation interface

 * @see evsql.h

 * @{

 */

/**

 * Create a new PostgreSQL/libpq (evpq) -based evsql using the given conninfo.

 *

 * The given \a pq_conninfo pointer must stay valid for the duration of the evsql's lifetime.

 *

 * See the libpq reference manual for the syntax of pq_conninfo

 *

 * @param ev_base the libevent base to use

 * @param pq_conninfo the libpq connection information

 * @param error_fn XXX: not used, may be NULL

 * @param cb_arg: XXX: not used, argument for error_fn

 * @return the evsql context handle for use with other functions

 */

struct evsql *evsql_new_pq (struct event_base *ev_base, const char *pq_conninfo, 

    evsql_error_cb error_fn, 

    void *cb_arg

);

// @}

/**

 * Close a connection. Callbacks for waiting queries will not be run.

 *

 * XXX: not implemented yet.

 *

 * @param evsql the context handle from \ref evsql_new_

 */

void evsql_close (struct evsql *evsql);

// @}

/**

 * Query API

 *

 * @defgroup evsql_query_* Query interface

 * @see evsql.h

 * @{

 */

/**

 * Queue the given query for execution.

 *

 * If \a trans is given (i.e. not NULL), then the transaction must be idle, and the query will be executed in that

 * transaction's context. Otherwise, the query will be executed without a transaction using an idle connection, or

 * enqueued for later execution.

 *

 * Once the query is complete (got a result, got an error, the connection failed), then \a query_fn will be called.

 * The callback can use the \ref evsql_result_ functions to manipulate the query results.

 *

 * The returned evsql_query handle can be passed to evsql_query_abort at any point before \a query_fn being called. 

 *

 * @param evsql the context handle from \ref evsql_new_

 * @param trans the optional transaction handle from evsql_trans

 * @param command the raw SQL command itself

 * @param query_fn the evsql_query_cb() to call once the query is complete

 * @param cb_arg the void* passed to the above

 * @return the evsql_query handle that can be used to abort the query

 */

struct evsql_query *evsql_query (struct evsql *evsql, struct evsql_trans *trans, const char *command, evsql_query_cb query_fn, void *cb_arg);

/**

 * Execute the given SQL query using the list of parameter types/values given via evsql_query_params.

 *

 * Use the EVSQL_PARAMS macros to declare \a params, and the \ref evsql_param_ functions to populate the values.

 *

 * See evsql_query() for more info about behaviour.

 *

 * See the <a href="http://www.postgresql.org/docs/8.3/static/libpq-exec.html#LIBPQ-EXEC-MAIN">libpq PQexecParams tip</a>

 * for the parameter syntax to use.

 *

 * @param evsql the context handle from \ref evsql_new_

 * @param trans the optional transaction handle from evsql_trans

 * @param command the SQL command to bind the parameters to

 * @param params the parameter types and values

 * @param query_fn the evsql_query_cb() to call once the query is complete

 * @param cb_arg the void* passed to the above

 * @see evsql_query

 */

struct evsql_query *evsql_query_params (struct evsql *evsql, struct evsql_trans *trans, 

    const char *command, const struct evsql_query_params *params, 

    evsql_query_cb query_fn, void *cb_arg

);

/**

 * Execute the given \a query_info's SQL query with the values given as variable arguments, using the \a query_info to

 * resolve the types.

 *

 * See evsql_query() for more info about behaviour.

 *

 * @param evsql the context handle from \ref evsql_new_

 * @param trans the optional transaction handle from evsql_trans

 * @param query_info the SQL query information

 * @param query_fn the evsql_query_cb() to call once the query is complete

 * @param cb_arg the void* passed to the above

 * @see evsql_query

 */

struct evsql_query *evsql_query_exec (struct evsql *evsql, struct evsql_trans *trans, 

    const struct evsql_query_info *query_info,

    evsql_query_cb query_fn, void *cb_arg,

    ...

);

/**

 * Abort a \a query returned by \ref evsql_query_ that has not yet completed (query_fn has not been called yet).

 *

 * The actual query itself may or may not be aborted (and hence may or may not be executed on the server), but \a query_fn

 * will not be called anymore, and the query will dispose of itself and any results returned.

 *

 * If the \a query is part of a transaction, then \a trans must be given, and the query must be the query that is currently

 * executing on that trans. The transaction's \a ready_fn will be called once the query has been aborted and the

 * transaction is now idle again.

 *

 * @param trans if the query is part of a transaction, then it MUST be given here

 * @param query the in-progress query to abort

 */

void evsql_query_abort (struct evsql_trans *trans, struct evsql_query *query);

/**

 * Print out a textual dump of the given \a sql query and \a params using DEBUG

 *

 * @param sql the SQL query command

 * @param params the list of parameter types and values

 */

void evsql_query_debug (const char *sql, const struct evsql_query_params *params);

// @}

/**

 * Transaction API

 *

 * @defgroup evsql_trans_* Transaction interface

 * @see evsql.h

 * @{

 */

/**

 * Create a new transaction.

 *

 * A transaction will be allocated its own connection, and the "BEGIN TRANSACTION ..." query will be sent (use the

 * \a type argument to specify this). 

 *

 * Once the transaction has been opened, the given \a ready_fn will be triggered, and the transaction can then

 * be used (see \ref evsql_query_).

 *

 * If, at any point, the transaction-connection fails, any pending query will be forgotten (i.e. the query callback

 * will NOT be called), and the given \a error_fn will be called. Note that this includes some, but not all,

 * cases where \ref evsql_query_ returns an error.

 *

 * Once you are done with the transaction, call either evsql_trans_commit() or evsql_trans_abort().

 *

 * @param evsql the context handle from \ref evsql_new_

 * @param type the type of transaction to create

 * @param error_fn the evsql_trans_error_cb() to call if this transaction fails

 * @param ready_fn the evsql_trans_ready_cb() to call once this transaction is ready for use

 * @param done_fn the evsql_trans_done_cb() to call once this transaction has been commmited

 * @param cb_arg the void* to pass to the above

 * @return the evsql_trans handle for use with other functions

 */

struct evsql_trans *evsql_trans (struct evsql *evsql, enum evsql_trans_type type, 

    evsql_trans_error_cb error_fn, 

    evsql_trans_ready_cb ready_fn, 

    evsql_trans_done_cb done_fn, 

    void *cb_arg

);

/**

 * Commit a transaction using "COMMIT TRANSACTION".

 *

 * The transaction must be idle, just like for evsql_query. Once the transaction has been commited, the transaction's

 * \a done_fn will be called, after which the transaction must not be used anymore.

 *

 * You cannot abort a COMMIT, calling trans_abort() on trans after a succesful trans_commit is an error.

 *

 * Note that \a done_fn will never be called directly, always indirectly via the event loop.

 *

 * @param trans the transaction handle from evsql_trans to commit

 * @see evsql_trans

 */

int evsql_trans_commit (struct evsql_trans *trans);

/**

 * Abort a transaction, using "ROLLBACK TRANSACTION".

 *

 * No more transaction callbacks will be called. If there was a query running, it will be aborted, and the transaction

 * then rollback'd.

 *

 * You cannot abort a COMMIT, calling trans_abort on \a trans after a call to trans_commit is an error.

 * 

 * Do not call evsql_trans_abort from within evsql_trans_error_cb()!

 *

 * @param trans the transaction from evsql_trans to abort

 * @see evsql_trans

 */

void evsql_trans_abort (struct evsql_trans *trans);

/** 

 * Retrieve the transaction-specific error message from the underlying engine.

 *

 * Intended to be called from evsql_trans_error_cb()

 */

const char *evsql_trans_error (struct evsql_trans *trans);

// @}

/**

 * Parameter-building functions.

 *

 * These manipulate the value of the given parameter index.

 *

 * @defgroup evsql_param_* Parameter interface

 * @see evsql.h

 * @{

 */

/**

 * Sets the value of the parameter at the given index

 *

 * @param params the evsql_query_params struct

 * @param param the parameter index

 * @param ptr pointer to the binary data

 * @param len size of the binary data in bytes

 * @return zero on success, <0 on error

 */

int evsql_param_binary (struct evsql_query_params *params, size_t param, const char *ptr, size_t len);

/** @see evsql_param_binary */

int evsql_param_string (struct evsql_query_params *params, size_t param, const char *ptr);

/** @see evsql_param_binary */

int evsql_param_uint16 (struct evsql_query_params *params, size_t param, uint16_t uval);

/** @see evsql_param_binary */

int evsql_param_uint32 (struct evsql_query_params *params, size_t param, uint32_t uval);

/**

 * Sets the given parameter to NULL

 *

 * @param params the evsql_query_params struct

 * @param param the parameter index

 * @return zero on success, <0 on error

 */

int evsql_param_null (struct evsql_query_params *params, size_t param);

/**

 * Clears all the parameter values (sets them to NULL)

 *

 * @param params the evsql_query_params struct

 * @return zero on success, <0 on error

 */

int evsql_params_clear (struct evsql_query_params *params);

// @}

/**

 * Result-handling functions

 *

 * @defgroup evsql_result_* Result interface

 * @see evsql.h

 * @see evsql_result

 * @{

 */

/**

 * Check the result for errors. Intended for use with non-data queries, i.e. CREATE, etc.

 *

 * Returns zero if the query was OK, err otherwise. EIO indicates an SQL error, the error message can be retrived

 * using evsql_result_error.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @return zero on success, EIO on SQL error, positive error code otherwise

 */

err_t evsql_result_check (struct evsql_result *res);

/**

 * The iterator-based interface results interface.

 *

 * Define an evsql_result_info struct that describes the columns returned by the query, and call evsql_result_begin on

 * the evsql_result. This verifies the query result, and then prepares it for iteration using evsql_result_next.

 *

 * Call evsql_result_end once you've stopped iteration.

 *

 * Returns zero if the evsql_result is ready for iteration, err otherwise. EIO indicates an SQL error, the error

 * message can be retreived using evsql_result_error. The result must be released in both cases.

 *

 * Note: currently the iterator state is simply stored in evsql_result, so only one iterator at a time per evsql_result.

 *

 * @param info the metadata to use to handle the result row columns

 * @param res the result handle passed to evsql_query_cb()

 * @return zero on success, +err on error

 */

err_t evsql_result_begin (struct evsql_result_info *info, struct evsql_result *res);

/**

 * Reads the next result row from the result prepared using evsql_result_begin. Stores the field values into to given

 * pointer arguments based on the evsql_result_info given to evsql_result_begin.

 *

 * If a field is NULL, and the result_info's evsql_item_type has flags.null_ok set, the given pointer is left

 * untouched, otherwise, an error is returned.

 *

 * @param res the result handle previous prepared using evsql_result_begin

 * @param ... a set of pointers corresponding to the evsql_result_info specified using evsql_result_begin

 * @return >0 when a row was read, zero when there are no more rows left, and -err on error

 */

int evsql_result_next (struct evsql_result *res, ...);

/**

 * Ends the result iteration, releasing any associated resources and the result itself.

 *

 * The result should not be iterated or accessed anymore.

 *

 * Note: this does the same thing as evsql_result_free, and works regardless of evsql_result_begin returning

 * succesfully or not.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @see evsql_result_free

 */

void evsql_result_end (struct evsql_result *res);

/**

 * Get the error message associated with the result, intended for use after evsql_result_check/begin return an error

 * code.

 * 

 * @param res the result handle passed to evsql_query_cb()

 * @return a char* containing the NUL-terminated error string. Valid until evsql_result_free is called.

 */

const char *evsql_result_error (const struct evsql_result *res);

/**

 * Get the number of data rows returned by the query

 *

 * @param res the result handle passed to evsql_query_cb()

 * @return the number of rows, >= 0

 */

size_t evsql_result_rows (const struct evsql_result *res);

/**

 * Get the number of columns in the data results from the query

 *

 * @param res the result handle passed to evsql_query_cb()

 * @return the number of columns, presumeably zero if there were no results

 */

size_t evsql_result_cols (const struct evsql_result *res);

/**

 * Get the number of rows affected by an UPDATE/INSERT/etc query.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @return the number of rows affected, >= 0

 */

size_t evsql_result_affected (const struct evsql_result *res);

/**

 * Fetch the raw binary value for the given field, returning it via ptr/size.

 *

 * The given row/col must be within bounds as returned by evsql_result_rows/cols.

 *

 * *ptr will point to *size bytes of read-only memory allocated internally.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @param row the row index to access

 * @param col the column index to access

 * @param ptr where to store a pointer to the read-only field data, free'd upon evsql_result_free

 * @param size updated to the size of the field value pointed to by ptr

 * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

 * @return zero on success, <0 on error

 */

int evsql_result_binary (const struct evsql_result *res, size_t row, size_t col, const char **ptr, size_t *size, bool nullok);

/**

 * Fetch the textual value of the given field, returning it via ptr.

 *

 * The given row/col must be within bounds as returned by evsql_result_rows/cols.

 *

 * *ptr will point to a NUL-terminated string allocated internally.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @param row the row index to access

 * @param col the column index to access

 * @param ptr where to store a pointer to the read-only field data, free'd upon evsql_result_free

 * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

 * @return zero on success, <0 on error

 */

int evsql_result_string (const struct evsql_result *res, size_t row, size_t col, const char **ptr, int nullok);

/**

 * Use evsql_result_binary to read a binary field value, and then convert it using ntoh[slq], storing the value in

 * *val.

 *

 * The given row/col must be within bounds as returned by evsql_result_rows/cols.

 *

 * @param res the result handle passed to evsql_query_cb()

 * @param row the row index to access

 * @param col the column index to access

 * @param uval where to store the decoded value

 * @param nullok when true and the field value is NULL, *ptr and *size are not modified, otherwise NULL means an error

 * @return zero on success, <0 on error

 */

int evsql_result_uint16 (const struct evsql_result *res, size_t row, size_t col, uint16_t *uval, int nullok);

/** @see evsql_result_uint16 */

int evsql_result_uint32 (const struct evsql_result *res, size_t row, size_t col, uint32_t *uval, int nullok);

/** @see evsql_result_uint16 */

int evsql_result_uint64 (const struct evsql_result *res, size_t row, size_t col, uint64_t *uval, int nullok);

/**

 * Every result handle passed to evsql_query_cb() MUST be released by the user, using this function.

 *

 * @param res the result handle passed to evsql_query_cb()

 */

void evsql_result_free (struct evsql_result *res);

// @}

#endif /* EVSQL_H */