.TH ARIF_SET_ENGINE 3 "Jan 02, 2023" 0.1.0 "ARIF User Manual"
.
.SH NAME
arif_set_engine - set input method engine
.
.SH SYNOPSIS
.EX
.B #include <arif.h>
.PP
.B void
.B arif_set_engine (
.BI "    struct arif_ctx          *" ctx ,
.BI "    struct arif_engine const *" engine ,
.BI "    void                     *" engine_data
.B );
.EE
.
.SH DESCRIPTION
The
.BR arif_set_engine ()
function changes the input context
.IR ctx 's
current input method engine and its associated data pointer to
.I \%engine
and
.IR \%engine_data .
It also resets the internal state of
.IR ctx .
.PP
Passing NULL
to
.I engine
is allowed.
See the "Input context without engine" subsection in NOTES for details.
.SS Input method engines
The
.B struct arif_engine
type defines a few functions for ARIF to communicate with an
input method engine.
.PP
.in +4n
.EX
struct arif_engine {
    arif_engine_init_func     *init;
    arif_engine_finalize_func *finalize;
    arif_engine_info_func     *info;
    arif_engine_query_func    *query;
};
.EE
.in
.PP
Only the
.I query
function is used by the ARIF library.
It's up to the library user to call the other functions when needed.
.SS Engine initialization
If an input method engine needs to be initialized before use, the
.I init
function must be implemented.
Otherwise, it should be NULL.
.PP
.in +4n
.EX
typedef int (arif_engine_init_func) (
    void const  *args,
    void       **engine_data_ptr
);
.EE
.in
.PP
Extra info can be passed into the initializer function through
.IR args .
.PP
If initialization is successful, the function must return 0.
Optionally, it can store a pointer to
.IR engine_data_ptr ,
which will be passed as an argument on subsequent engine function calls.
.PP
If initialization fails, the function must return a non-zero value.
.SS Engine finalization
If not NULL, the
.I finalize
function is used for cleaning up resources for an engine, when the engine is
no longer in use.
.PP
.in +4n
.EX
typedef void (arif_engine_finalize_func) (
    void *engine_data
);
.EE
.in
.PP
The
.I engine_data
argument is the pointer stored to
.I engine_data_ptr
during initialization.
.SS Engine info
If not NULL, the
.I info
function is used for retrieving information of an engine.
.PP
.in +4n
.EX
typedef void (arif_engine_info_func) (
    void        *engine_data,
    char const **name_ptr,
    char const **description_ptr
);
.EE
.in
.PP
The
.I engine_data
argument is the pointer stored to
.I engine_data_ptr
during initialization.
.PP
The function can store a NUL-terminated string that identifies an engine
to
.IR name_ptr .
It's preferably a short and memorable word (like "pinyin" and "rime").
.PP
The function can store another NUL-terminated string to
.IR description_ptr ,
to provide additional information of the engine, such as version,
copyright notice, homepage URL, etc.
.SS Query engine for candidates
The
.I query
function is used for asking the engine for candidates of an input text.
It must not be NULL.
.PP
.in +4n
.EX
typedef int (arif_engine_query_func) (
    void                    *engine_data,
    char const              *line,
    int                      offset,
    int                      len,
    int                      num_candidates,
    struct arif_cand const **candidates_ptr
);
.EE
.in
.PP
The
.I engine_data
argument is the pointer stored to
.I engine_data_ptr
during initialization.
.PP
The
.IR line ,
.I offset
and
.I len
arguments correspond to the arguments of function
.BR arif_query ()
with the same name.
If
.I line
is NULL, it means that the caller is asking for more candidates for the
previous input text.
.PP
The
.I num_candidates
argument is the minimum number of candidates required from the engine.
The engine should store the pointer of an array containing at least that many
candidates to
.IR candidates_ptr ,
and return the number of candidates.
If returning less than
.IR num_candidates ,
it indicates that the entire list of candidates is exhausted.
The engine should ensure that the memory location referenced by those
candidates are valid until the next
.I query
call with non-NULL
.IR line .
.PP
The engine is not responsible for specifying the display text for a candidate,
however, it may reuse the
.I display
and
.I display_len
members to store descriptive information regarding the candidate.
This information will be passed to the display function of the input context
through the
.I comment
and
.I comment_len
arguments (see
.BR \%arif_ctx_create ()).
.PP
Both
.I line
and
.I candidates_ptr
can be NULL, in which case the caller is indicating that a candidate at
.I offset
is selected with inlined candidate selection (see
.BR \%arif_query ()),
and the return value is ignored.
The engine may make use of this information for purposes like analytics.
.
.SH NOTES
.SS Input context without engine
For an input context, when
.BR arif_set_engine ()
is not yet called, or last called with a NULL
.I engine
argument, the input context does not have an associated input method engine.
.PP
In such input contexts, functions other than
.BR arif_set_engine ()
or
.BR arif_ctx_destroy ()
must not be called.
.
.SH COPYRIGHT
Copyright (C) 2023  CismonX <admin@cismon.net>
.PP
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
.PP
You should have received a copy of the license along with this document.
If not, see <https://www.gnu.org/licenses/fdl-1.3.html>.
.
.SH SEE ALSO
.BR arif_ctx_create (3),
.BR arif_ctx_destroy (3),
.BR arif_fetch (3),
.BR arif_query (3)