// source: A data source to read and edit
//
// This header provides the main definitions for data sources, which back the
// data that is shown and edited in the application. Data sources implement a
// base interface for reading and writing chunks, with some optional features
// being defined by capabilities.

#pragma once
#include <stdbool.h>
#include <sys/types.h>
#include "buffer.h"

// Data source capabilities //

/* The data source is writable and can be modified by API. */
#define SOURCE_WRITE 0x01
/* The data source can by resized, adding or removing new bytes. */
#define SOURCE_RESIZE 0x02
/* The data source can save to an external file */
#define SOURCE_SAVEAS 0x04

// Interface to data sources //

typedef struct {
    /* Interface name */
    char const *name;
    /* Whether the source should be closed before we return to menu */
    bool close_on_return_to_menu;
    /* Load a chunk from the data source into a buffer. */
    ssize_t (*read)(void *_cookie, void *buf, off_t offset, size_t size);
    /* Write from a buffer into a segment of the data source. If the interface
       has the SOURCE_RESIZE capability, the buffer might be of a different
       size than the segment. */
    bool (*write)(void *_cookie, void *buf, size_t buf_size, off_t offset,
        size_t segment_size);
    /* Current source data size. */
    size_t (*size)(void *_cookie);
    /* Whether the source is currently dirty (ie. requires a save). */
    bool (*dirty)(void *_cookie);
    /* Save the data to its original medium, or, if the  SOURCE_SAVEAS
       capability is available and outfile is not NULL, a file. */
    bool (*save)(void *_cookie, char const *outfile);
    /* Close the data source. */
    void (*close)(void *_cookie);

} source_intf_t;

// An open data source //

typedef struct {
    /* Interface identifier, and opaque interface data */
    source_intf_t *intf;
    void *cookie;
    /* Source capabilities */
    int cap;
    /* Source name. Can be any string: file path, "memory at X", etc. */
    char *origin;
    /* If set, there is no origin and the "SAVE" button is disabled (only
       useful if "SAVE AS" is enabled) */
    bool no_origin;
    /* Front buffer for edition */
    buffer_t *buf;
    /* Address of the front buffer in the source */
    off_t buf_offset;
    /* Length of the front buffer in the source */
    int buf_segment_size;

} source_t;

/* Open a data source; this is a low-level function used by source-specific
   opening functions. */
source_t *source_open(source_intf_t *intf, void *cookie, char const *origin);

/* Size of the source's data. Might be inaccurate if the front buffer has been
   expanded */
size_t source_size(source_t *s);

/* Whether the source has been modified and needs a save. */
bool source_dirty(source_t *s);

/* Replace the source's buffer's contents with data read from the source. */
ssize_t source_load(source_t *s, off_t offset, size_t segment_size);

/* Determine whether the `n` bytes following `offset` are currently loaded in
   the front buffer. */
bool source_requires_load(source_t *s, off_t offset, int n);

/* Make sure that the `n` bytes following `offset` are loaded in the front
   buffer. If not, load the region around there. Returns true if the region
   changed, otherwise false. */
void source_ensure_loaded(source_t *s, off_t offset, int n);

/* Push the front buffer into the data source. */
bool source_save_front_buffer(source_t *s);

/* Save the source. The `outfile` is NULL for the current origin, or a file
   path to save as (if supported). */
bool source_save(source_t *s, char const *outfile);

/* Free a source and its data. */
void source_free(source_t *s);

// Supported data sources //

#include "source-loaded-file.h"
#include "source-lazy-file.h"
#include "source-memory.h"