/* vifm
 * Copyright (C) 2020 xaizek.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

#include "vcache.h"

#include <fcntl.h> /* F_GETFL F_SETFL O_NONBLOCK fcntl() */

#include <stdio.h> /* FILE */
#include <stdlib.h> /* free() */
#include <string.h> /* memmove() memset() strcmp() */
#include <time.h> /* time_t time() */

#include "cfg/config.h"
#include "compat/os.h"
#include "lua/vlua.h"
#include "ui/cancellation.h"
#include "ui/quickview.h"
#include "ui/ui.h"
#include "utils/darray.h"
#include "utils/file_streams.h"
#include "utils/filemon.h"
#include "utils/fs.h"
#include "utils/path.h"
#include "utils/selector.h"
#include "utils/str.h"
#include "utils/string_array.h"
#include "utils/test_helpers.h"
#include "background.h"
#include "filetype.h"
#include "status.h"

/* Maximum number of seconds to wait for data. */
enum { MAX_RUN_TIME_S = 60 };

/* Maximum number of seconds to wait for process to cancel. */
enum { MAX_KILL_DELAY_S = 2 };

/* Cached output of a specific previewer for a specific file. */
typedef struct vcache_entry_t
{
	char *path;        /* Full path to the file. */
	char *viewer;      /* Viewer of the file. */
	bg_job_t *job;     /* If not NULL, source of file contents. */
	filemon_t filemon; /* Timestamp for the file. */
	strlist_t lines;   /* Top lines of preview contents. */
	time_t started_at; /* Since when we're waiting for the data. */
	time_t kill_timer; /* Since when we're waiting for the job to die or zero. */
	size_t size;       /* Size taken up by this entry (lower bound). */
	int max_lines;     /* Number of lines requested. */

	/* Value of maxtreedepth for this entry. */
	int max_tree_depth;
	/* Whether cache contains complete output of the viewer. */
	unsigned int complete : 1;
	/* Whether last line is truncated. */
	unsigned int truncated : 1;
	/* Value of toptreestats for this entry. */
	unsigned int top_tree_stats : 1;
}
vcache_entry_t;

TSTATIC size_t vcache_entry_size(void);
static void wait_async_finish(vcache_entry_t *centry);
static vcache_entry_t * find_cache_entry(const char full_path[],
		const char viewer[], int max_lines);
static vcache_entry_t * alloc_cache_entry(void);
static void compact_cache(void);
static vcache_entry_t * new_cache_entry(void);
TSTATIC void vcache_reset(size_t max_size);
static void free_cache_entry(vcache_entry_t *centry);
static int is_cache_match(const vcache_entry_t *centry, const char path[],
		const char viewer[]);
static int is_cache_valid(const vcache_entry_t *centry, const char path[],
		const char viewer[], int max_lines);
static void update_cache_entry(vcache_entry_t *centry, const char path[],
		const char viewer[], MacroFlags flags, int max_lines, const char **error);
static void update_sizes(vcache_entry_t *centry);
static int pull_async(vcache_entry_t *centry);
static int read_async_output(vcache_entry_t *centry);
static void cancel_job(vcache_entry_t *centry);
static int is_ready_for_read(FILE *stream);
static int need_more_async_output(vcache_entry_t *centry);
static strlist_t view_entry(vcache_entry_t *centry, MacroFlags flags,
		const char **error);
static strlist_t view_builtin(vcache_entry_t *centry, const char **error);
static strlist_t view_plugin(vcache_entry_t *centry, const char **error);
static strlist_t view_external(vcache_entry_t *centry, MacroFlags flags,
		const char **error);
TSTATIC strlist_t read_lines(FILE *fp, int max_lines, int *complete);

/* Cache of viewers' output.  Ordered from least to most recently used. */
static vcache_entry_t **cache;
/* Declarations to enable use of DA_* on cache. */
static DA_INSTANCE(cache);
/* Amount of memory taken up by the cache (lower bound). */
static size_t cache_size;
/* Maximum size of the cache. */
static size_t max_cache_size = 3U*1024*1024;

void
vcache_finish(void)
{
	size_t i;
	for(i = 0U; i < DA_SIZE(cache); ++i)
	{
		if(cache[i]->job != NULL)
		{
			bg_job_cancel(cache[i]->job);
			bg_job_terminate(cache[i]->job);
			bg_job_decref(cache[i]->job);
			cache[i]->job = NULL;
		}
	}
}

size_t
vcache_size(void)
{
	return cache_size;
}

TSTATIC size_t
vcache_entry_size(void)
{
	return sizeof(vcache_entry_t);
}

int
vcache_check(vcache_is_previewed_cb is_previewed)
{
	int changed = 0;

	/* TODO: consider doing this in a separate thread. */

	size_t i;
	for(i = 0U; i < DA_SIZE(cache); ++i)
	{
		if(cache[i]->job != NULL)
		{
			changed |= (pull_async(cache[i]) && is_previewed(cache[i]->path));
		}
	}

	return changed;
}

strlist_t
vcache_lookup(const char full_path[], const char viewer[], MacroFlags flags,
		ViewerKind kind, int max_lines, int sync, const char **error)
{
	*error = NULL;

	/* Skip caching of data if we can't really cache it or when user doesn't want
	 * it to be cached. */
	if(kind == VK_GRAPHICAL || ma_flags_present(flags, MF_NO_CACHE))
	{
		static vcache_entry_t non_cache;
		free_cache_entry(&non_cache);

		non_cache.max_lines = max_lines;
		replace_string(&non_cache.path, full_path);
		update_string(&non_cache.viewer, viewer);

		non_cache.lines = view_entry(&non_cache, flags, error);
		wait_async_finish(&non_cache);

		return non_cache.lines;
	}

	vcache_entry_t *centry = find_cache_entry(full_path, viewer, max_lines);
	if(centry != NULL && is_cache_valid(centry, full_path, viewer, max_lines))
	{
		return centry->lines;
	}

	if(centry == NULL)
	{
		centry = alloc_cache_entry();
		if(centry == NULL)
		{
			*error = "Failed to allocate cache entry";
			strlist_t empty_list = {};
			return empty_list;
		}
	}

	update_cache_entry(centry, full_path, viewer, flags, max_lines, error);

	if(sync)
	{
		wait_async_finish(centry);
	}

	if(kind != VK_PASS_THROUGH && centry->lines.nitems == 0 &&
			centry->job != NULL)
	{
		/* TODO: consider printing time we're waiting for output. */
		static char *items[] = { "[...]" };
		static strlist_t stub = { .items = items, .nitems = 1 };
		return stub;
	}

	return centry->lines;
}

/* Waits for asynchronous job to be done. */
static void
wait_async_finish(vcache_entry_t *centry)
{
	bg_job_t *job = centry->job;
	if(job == NULL)
	{
		return;
	}

	ui_cancellation_push_on();

	do
	{
		wait_for_data_from(job->pid, job->output, 0, &ui_cancellation_info);

		if(ui_cancellation_requested())
		{
			break;
		}

		int read_result;
		do
		{
			read_result = read_async_output(centry);
		}
		while(read_result > 0);

		if(read_result < 0)
		{
			break;
		}
	}
	while(bg_job_is_running(job));

	while(read_async_output(centry) > 0)
	{
		/* Reading is performed in conditional expression. */
	}

	if(ui_cancellation_requested())
	{
		centry->lines.nitems = add_to_string_array(&centry->lines.items,
				centry->lines.nitems, "[cancelled]");
	}
	ui_cancellation_pop();

	bg_job_decref(centry->job);
	centry->job = NULL;
}

/* Looks up existing cache entry that matches specified set of parameters.
 * Returns the entry or NULL. */
static vcache_entry_t *
find_cache_entry(const char full_path[], const char viewer[], int max_lines)
{
	size_t i;
	for(i = 0U; i < DA_SIZE(cache); ++i)
	{
		if(is_cache_match(cache[i], full_path, viewer))
		{
			vcache_entry_t *centry = cache[i];

			/* Make the most recently used entry the last one. */
			memmove(cache + i, cache + i + 1,
					sizeof(*cache)*(DA_SIZE(cache) - 1U - i));
			cache[DA_SIZE(cache) - 1U] = centry;

			return centry;
		}
	}
	return NULL;
}

/* Allocates a zero-initialized cache entry.  When cache size limit is reached
 * older cache entries are reused.  Returns the entry or NULL. */
static vcache_entry_t *
alloc_cache_entry(void)
{
	if(max_cache_size == 0U)
	{
		return NULL;
	}

	compact_cache();
	return new_cache_entry();
}

/* Shrinks cache if its size is larger than the limit. */
static void
compact_cache(void)
{
	if(cache == NULL)
	{
		return;
	}

	size_t i;
	size_t j = 0U;
	for(i = 0U; i < DA_SIZE(cache) && cache_size >= max_cache_size; ++i)
	{
		vcache_entry_t *centry = cache[i];
		if(centry->job != NULL)
		{
			cache[j++] = centry;
			/* Give it a chance to finish gracefully. */
			cancel_job(centry);
			continue;
		}

		cache_size -= centry->size;
		free_cache_entry(centry);
		free(centry);
	}

	memmove(cache + j, cache + i, sizeof(*cache)*(DA_SIZE(cache) - i));
	DA_REMOVE_AFTER(cache, cache + j + DA_SIZE(cache) - i);
}

/* Allocates a new cache entry unconditionally.  Returns the entry. */
static vcache_entry_t *
new_cache_entry(void)
{
	vcache_entry_t **centry = DA_EXTEND(cache);
	if(centry == NULL)
	{
		return NULL;
	}

	*centry = calloc(1, sizeof(**centry));
	if(*centry == NULL)
	{
		return NULL;
	}

	DA_COMMIT(cache);
	return *centry;
}

/* Invalidates all cache entries and changes size limit. */
TSTATIC void
vcache_reset(size_t max_size)
{
	size_t i;
	for(i = 0U; i < DA_SIZE(cache); ++i)
	{
		free_cache_entry(cache[i]);
		free(cache[i]);
	}
	DA_REMOVE_ALL(cache);

	max_cache_size = max_size;
	cache_size = 0;
}

/* Frees resources of a cache entry. */
static void
free_cache_entry(vcache_entry_t *centry)
{
	update_string(&centry->path, NULL);
	update_string(&centry->viewer, NULL);

	free_string_array(centry->lines.items, centry->lines.nitems);
	centry->lines.items = NULL;
	centry->lines.nitems = 0;

	if(centry->job != NULL)
	{
		bg_job_cancel(centry->job);
		bg_job_terminate(centry->job);
		bg_job_decref(centry->job);
		centry->job = NULL;
	}
}

/* Checks whether cache entry matches specified file and viewer.  Returns
 * non-zero if so, otherwise zero is returned. */
static int
is_cache_match(const vcache_entry_t *centry, const char path[],
		const char viewer[])
{
	int same_viewer = (centry->viewer == NULL && viewer == NULL)
	               || (centry->viewer != NULL && viewer != NULL &&
	                   strcmp(centry->viewer, viewer) == 0);
	return same_viewer
	    && centry->path != NULL
	    && paths_are_equal(centry->path, path);
}

/* Checks whether data in the cache entry is up to date with the file on disk
 * and contains enough lines.  Returns non-zero if so, otherwise zero is
 * returned. */
static int
is_cache_valid(const vcache_entry_t *centry, const char path[],
		const char viewer[], int max_lines)
{
	filemon_t filemon;
	(void)filemon_from_file(path, FMT_MODIFIED, &filemon);
	if(!filemon_equal(&centry->filemon, &filemon))
	{
		/* Error before and error now make a match, so we don't fail in that
		 * case. */
		if(filemon_is_set(&filemon) || filemon_is_set(&centry->filemon))
		{
			return 0;
		}
	}

	if((centry->top_tree_stats != cfg.top_tree_stats ||
			centry->max_tree_depth != cfg.max_tree_depth) && is_dir(path))
	{
		return 0;
	}

	return (centry->complete || centry->lines.nitems >= max_lines);
}

/* Setups cache entry for a specific file and viewer replacing its previous
 * state in the process.  *error is set either to NULL or an error code on
 * failure. */
static void
update_cache_entry(vcache_entry_t *centry, const char path[],
		const char viewer[], MacroFlags flags, int max_lines, const char **error)
{
	(void)filemon_from_file(path, FMT_MODIFIED, &centry->filemon);
	centry->max_lines = max_lines;

	replace_string(&centry->path, path);
	update_string(&centry->viewer, viewer);

	if(centry->job == NULL)
	{
		free_string_array(centry->lines.items, centry->lines.nitems);
		centry->lines = view_entry(centry, flags, error);

		update_sizes(centry);
	}
	else
	{
		(void)pull_async(centry);
	}
}

/* Computes size occupied by the entry updating total cache size too. */
static void
update_sizes(vcache_entry_t *centry)
{
	cache_size -= centry->size;

	/* This isn't zero to make even empty preview result take up space. */
	centry->size = sizeof(*centry);

	int i;
	for(i = 0; i < centry->lines.nitems; ++i)
	{
		centry->size += strlen(centry->lines.items[i]);
	}

	cache_size += centry->size;
}

/* Updates single entry backed by an asynchronous job.  Returns non-zero if
 * entry was updated, otherwise zero is returned. */
static int
pull_async(vcache_entry_t *centry)
{
	int changed = 0;

	if(centry->kill_timer != 0)
	{
		if(time(NULL) - centry->kill_timer > MAX_KILL_DELAY_S)
		{
			bg_job_terminate(centry->job);
		}
	}
	else if(time(NULL) - centry->started_at > MAX_RUN_TIME_S)
	{
		/* This job is running for too long. */
		cancel_job(centry);
	}
	else
	{
		if(!need_more_async_output(centry))
		{
			cancel_job(centry);
			return 0;
		}

		while(need_more_async_output(centry) && read_async_output(centry) > 0)
		{
			changed = 1;
		}
	}

	if(!bg_job_is_running(centry->job))
	{
		centry->complete = (read_async_output(centry) <= 0)
		                && (centry->kill_timer == 0 ||
		                    !bg_job_was_killed(centry->job));
		bg_job_decref(centry->job);
		centry->job = NULL;
		changed = 1;
	}

	return changed;
}

/* Cancels the job giving it some time to finish before forceful termination. */
static void
cancel_job(vcache_entry_t *centry)
{
	centry->kill_timer = time(NULL);
	bg_job_cancel(centry->job);
}

/* Populates entry with more data from an asynchronous job if it's available.
 * Returns zero if nothing was read, positive integer if something was read and
 * negative integer on reaching EOF. */
static int
read_async_output(vcache_entry_t *centry)
{
	if(!is_ready_for_read(centry->job->output))
	{
		return 0;
	}

	char piece[4096];
	size_t to_read = sizeof(piece) - 1;

#ifdef _WIN32
	/* Simulate asynchronous reading by not reading more than stream has. */
	HANDLE hpipe = (HANDLE)_get_osfhandle(fileno(centry->job->output));
	DWORD bytes_available = 0;
	if(!PeekNamedPipe(hpipe, NULL, 0, NULL, &bytes_available, NULL))
	{
		return -1;
	}
	if(bytes_available == 0)
	{
		return 0;
	}
	if(bytes_available < to_read)
	{
		to_read = bytes_available;
	}
#endif

	size_t len = fread(piece, 1, to_read, centry->job->output);
	piece[len] = '\0';

	if(len == 0)
	{
		return -1;
	}

	clearerr(centry->job->output);
	centry->size += len;
	cache_size += len;

	int new_truncated = (len > 0)
	                 && (piece[len - 1] != '\r' && piece[len - 1] != '\n');

	int nlines;
	char **lines = break_into_lines(piece, len, &nlines, 0);

	if(centry->truncated)
	{
		char **last = &centry->lines.items[centry->lines.nitems - 1];
		size_t last_len = strlen(*last);
		strappend(last, &last_len, lines[0]);
		free(lines[0]);
	}

	int i = (centry->truncated ? 1 : 0);
	while(i < nlines)
	{
		centry->lines.nitems = put_into_string_array(&centry->lines.items,
				centry->lines.nitems, lines[i]);
		++i;
	}
	free(lines);

	centry->truncated = new_truncated;
	return 1;
}

/* Checks whether stream contains data to be read.  Returns non-zero if so,
 * otherwise zero is returned. */
static int
is_ready_for_read(FILE *stream)
{
	selector_t *selector = selector_alloc();
	if(selector == NULL)
	{
		return 0;
	}

	int fd = fileno(stream);
#ifndef _WIN32
	selector_add(selector, fd);
#else
	HANDLE handle = (HANDLE)_get_osfhandle(fd);
	selector_add(selector, handle);
#endif

	int has_data = selector_wait(selector, 0);
	selector_free(selector);
	return has_data;
}

/* Checks whether entry is full with data already.  Returns non-zero if so,
 * otherwise zero is returned. */
static int
need_more_async_output(vcache_entry_t *centry)
{
	int effective_lines = centry->lines.nitems;
	if(centry->truncated)
	{
		--effective_lines;
	}

	return (effective_lines < centry->max_lines);
}

/* Processes cache entry to get preview of a file.  Might spawn job for the
 * viewer and return. *error is set to an error message on failure.  Returns
 * output. */
static strlist_t
view_entry(vcache_entry_t *centry, MacroFlags flags, const char **error)
{
	if(is_null_or_empty(centry->viewer))
	{
		return view_builtin(centry, error);
	}

	if(vlua_handler_cmd(curr_stats.vlua, centry->viewer))
	{
		return view_plugin(centry, error);
	}

	return view_external(centry, flags, error);
}

/* Generates view via builtin means.  *error is set to an error message on
 * failure.  Returns output. */
static strlist_t
view_builtin(vcache_entry_t *centry, const char **error)
{
	ui_cancellation_push_on();

	int dir = is_dir(centry->path);

	FILE *fp = NULL;
	if(dir)
	{
		centry->top_tree_stats = cfg.top_tree_stats;
		centry->max_tree_depth = cfg.max_tree_depth;
		fp = qv_view_dir(centry->path, centry->max_lines);
	}
	else
	{
		/* Binary mode is important on Windows. */
		fp = os_fopen(centry->path, "rb");
	}

	strlist_t lines = {};
	if(fp != NULL)
	{
		int complete;
		lines = read_lines(fp, centry->max_lines, &complete);
		centry->complete = complete;
		fclose(fp);
	}
	else
	{
		*error = dir ? "Failed to list directory's contents"
		             : "Failed to read file's contents";
	}

	ui_cancellation_pop();
	return lines;
}

/* Calls a plugin to view a file.  *error is set to an error message on failure.
 * Returns output. */
static strlist_t
view_plugin(vcache_entry_t *centry, const char **error)
{
	return vlua_view_file(curr_stats.vlua, centry->viewer, centry->path,
			curr_stats.preview_hint);
}

/* Invokes viewer of a file to get its output.  *error is set to an error
 * message on failure.  Returns output. */
static strlist_t
view_external(vcache_entry_t *centry, MacroFlags flags, const char **error)
{
	strlist_t lines = {};

	BgJobFlags bg_flags = BJF_CAPTURE_OUT | BJF_MERGE_STREAMS;
	if(ma_flags_present(flags, MF_PIPE_FILE_LIST) ||
			ma_flags_present(flags, MF_PIPE_FILE_LIST_Z))
	{
		bg_flags |= BJF_SUPPLY_INPUT;
	}

	if(ma_flags_present(flags, MF_KEEP_IN_FG))
	{
		bg_flags |= BJF_KEEP_IN_FG;
	}

	centry->job = bg_run_external_job(centry->viewer, bg_flags, /*descr=*/NULL);
	if(centry->job == NULL)
	{
		*error = "Failed to start a viewer";
		return lines;
	}

	centry->kill_timer = 0;
	centry->started_at = time(NULL);
	centry->complete = 0;
	centry->truncated = 0;

	if(centry->job->input != NULL)
	{
		FILE *input = centry->job->input;
		centry->job->input = NULL;

		const int null_sep = ma_flags_present(flags, MF_PIPE_FILE_LIST_Z);
		write_marked_paths(input, curr_view, null_sep);
		fclose(input);
	}

#ifndef _WIN32
	/* Enable non-blocking read from output pipe.  On Windows we read the
	 * exact amount of data present in the stream. */
	int fd = fileno(centry->job->output);
	int file_flags = fcntl(fd, F_GETFL, 0);
	fcntl(fd, F_SETFL, file_flags | O_NONBLOCK);
#endif

	return lines;
}

/* Reads at most max_lines from the stream ignoring BOM.  Returns the lines
 * read. */
TSTATIC strlist_t
read_lines(FILE *fp, int max_lines, int *complete)
{
	strlist_t lines = {};
	skip_bom(fp);

	char *next_line = NULL;
	while(lines.nitems < max_lines && (next_line = read_line(fp, NULL)) != NULL)
	{
		const int old_len = lines.nitems;
		lines.nitems = put_into_string_array(&lines.items, lines.nitems, next_line);
		if(lines.nitems == old_len)
		{
			free(next_line);
			break;
		}
	}

	*complete = (next_line == NULL);
	return lines;
}

/* vim: set tabstop=2 softtabstop=2 shiftwidth=2 noexpandtab cinoptions-=(0 : */
/* vim: set cinoptions+=t0 : */