nncmpp/nncmpp.c

/*
 * nncmpp -- the MPD client you never knew you needed
 *
 * Copyright (c) 2016 - 2023, Přemysl Eric Janouch <p@janouch.name>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "config.h"

// We "need" to have an enum for attributes before including liberty.
// Avoiding colours in the defaults here in order to support dumb terminals.
#define ATTRIBUTE_TABLE(XX)                              \
	XX( NORMAL,      normal,       -1, -1, 0           ) \
	XX( HIGHLIGHT,   highlight,    -1, -1, A_BOLD      ) \
	/* Gauge                                          */ \
	XX( ELAPSED,     elapsed,      -1, -1, A_REVERSE   ) \
	XX( REMAINS,     remains,      -1, -1, A_UNDERLINE ) \
	/* Tab bar                                        */ \
	XX( TAB_BAR,     tab_bar,      -1, -1, A_REVERSE   ) \
	XX( TAB_ACTIVE,  tab_active,   -1, -1, A_UNDERLINE ) \
	/* Listview                                       */ \
	XX( HEADER,      header,       -1, -1, A_UNDERLINE ) \
	XX( EVEN,        even,         -1, -1, 0           ) \
	XX( ODD,         odd,          -1, -1, 0           ) \
	XX( DIRECTORY,   directory,    -1, -1, 0           ) \
	XX( SELECTION,   selection,    -1, -1, A_REVERSE   ) \
	/* Cyan is good with both black and white.
	 * Can't use A_REVERSE because bold'd be bright.
	 * Unfortunately ran out of B&W attributes.       */ \
	XX( MULTISELECT, multiselect,  -1,  6, 0           ) \
	/* This ought to be indicative enough.            */ \
	XX( DEFOCUSED,   defocused,    -1, -1, A_UNDERLINE ) \
	XX( SCROLLBAR,   scrollbar,    -1, -1, 0           ) \
	/* These are for debugging only                   */ \
	XX( WARNING,     warning,       3, -1, 0           ) \
	XX( ERROR,       error,         1, -1, 0           ) \
	XX( INCOMING,    incoming,      2, -1, 0           ) \
	XX( OUTGOING,    outgoing,      4, -1, 0           )

enum
{
#define XX(name, config, fg_, bg_, attrs_) ATTRIBUTE_ ## name,
	ATTRIBUTE_TABLE (XX)
#undef XX
	ATTRIBUTE_COUNT
};

// My battle-tested C framework acting as a GLib replacement.  Its one big
// disadvantage is missing support for i18n but that can eventually be added
// as an optional feature.  Localised applications look super awkward, though.

// User data for logger functions to enable formatted logging
#define print_fatal_data    ((void *) ATTRIBUTE_ERROR)
#define print_error_data    ((void *) ATTRIBUTE_ERROR)
#define print_warning_data  ((void *) ATTRIBUTE_WARNING)

#define LIBERTY_WANT_POLLER
#define LIBERTY_WANT_ASYNC
#define LIBERTY_WANT_PROTO_HTTP
#define LIBERTY_WANT_PROTO_MPD
#include "liberty/liberty.c"
#include "liberty/liberty-tui.c"

#define HAVE_LIBERTY
#include "line-editor.c"

#include <dirent.h>
#include <locale.h>
#include <math.h>
#include <sys/ioctl.h>
#include <termios.h>

// ncurses is notoriously retarded for input handling, we need something
// different if only to receive mouse events reliably.
//
// 2021 update: ncurses is mostly reliable now, though rxvt-unicode only
// supports the 1006 mode that ncurses also supports mode starting with 9.25.
#include "termo.h"

// We need cURL to extract links from Internet stream playlists.  It'd be way
// too much code to do this all by ourselves, and there's nothing better around.
#include <curl/curl.h>

// The spectrum analyser requires a DFT transform.  The FFTW library is fairly
// efficient, and doesn't have a requirement on the number of bins.
#ifdef WITH_FFTW
#include <fftw3.h>
#endif  // WITH_FFTW

// Remote MPD control needs appropriate volume controls.
#ifdef WITH_PULSE
#include "liberty/liberty-pulse.c"
#include <pulse/context.h>
#include <pulse/error.h>
#include <pulse/introspect.h>
#include <pulse/subscribe.h>
#include <pulse/sample.h>
#endif  // WITH_PULSE

// Elementary port of the TUI to X11.
#ifdef WITH_X11
#include <X11/Xatom.h>
#include <X11/Xlib.h>
#include <X11/keysym.h>
#include <X11/XKBlib.h>
#include <X11/Xft/Xft.h>
#endif  // WITH_X11

#define APP_TITLE  PROGRAM_NAME         ///< Left top corner

#include "nncmpp-actions.h"

// --- Utilities ---------------------------------------------------------------

static int64_t
clock_msec (clockid_t clock)
{
	struct timespec tp;
	hard_assert (clock_gettime (clock, &tp) != -1);
	return (int64_t) tp.tv_sec * 1000 + (int64_t) tp.tv_nsec / 1000000;
}

static void
shell_quote (const char *str, struct str *output)
{
	// See SUSv3 Shell and Utilities, 2.2.3 Double-Quotes
	str_append_c (output, '"');
	for (const char *p = str; *p; p++)
	{
		if (strchr ("`$\"\\", *p))
			str_append_c (output, '\\');
		str_append_c (output, *p);
	}
	str_append_c (output, '"');
}

static bool
xstrtoul_map (const struct str_map *map, const char *key, unsigned long *out)
{
	const char *field = str_map_find (map, key);
	return field && xstrtoul (out, field, 10);
}

static const char *
xbasename (const char *path)
{
	const char *last_slash = strrchr (path, '/');
	return last_slash ? last_slash + 1 : path;
}

static char *xstrdup0 (const char *s) { return s ? xstrdup (s) : NULL; }

static char *
latin1_to_utf8 (const char *latin1)
{
	struct str converted = str_make ();
	while (*latin1)
	{
		uint8_t c = *latin1++;
		if (c < 0x80)
			str_append_c (&converted, c);
		else
		{
			str_append_c (&converted, 0xC0 | (c >> 6));
			str_append_c (&converted, 0x80 | (c & 0x3F));
		}
	}
	return str_steal (&converted);
}

static void
str_enforce_utf8 (struct str *self)
{
	if (!utf8_validate (self->str, self->len))
	{
		char *sanitized = latin1_to_utf8 (self->str);
		str_reset (self);
		str_append (self, sanitized);
		free (sanitized);
	}
}

static void
cstr_uncapitalize (char *s)
{
	if (isupper (s[0]) && islower (s[1]))
		s[0] = tolower_ascii (s[0]);
}

static int
print_curl_debug (CURL *easy, curl_infotype type, char *data, size_t len,
	void *ud)
{
	(void) easy;
	(void) ud;
	(void) type;

	char copy[len + 1];
	for (size_t i = 0; i < len; i++)
	{
		uint8_t c = data[i];
		copy[i] = !iscntrl_ascii (c) || c == '\n' ? c : '.';
	}
	copy[len] = '\0';

	char *next;
	for (char *p = copy; p; p = next)
	{
		if ((next = strchr (p, '\n')))
			*next++ = '\0';
		if (!*p)
			continue;

		if (!utf8_validate (p, strlen (p)))
		{
			char *fixed = latin1_to_utf8 (p);
			print_debug ("cURL: %s", fixed);
			free (fixed);
		}
		else
			print_debug ("cURL: %s", p);
	}
	return 0;
}

static char *
mpd_parse_kv (char *line, char **value)
{
	char *key = mpd_client_parse_kv (line, value);
	if (!key)  print_debug ("%s: %s", "erroneous MPD output", line);
	return key;
}

static void
mpd_read_time (const char *value, int *sec, int *optional_msec)
{
	if (!value)
		return;

	char *end = NULL;
	long n = strtol (value, &end, 10);
	if (n < 0 || (*end && *end != '.'))
		return;

	int msec = 0;
	if (*end == '.')
	{
		// In practice, MPD always uses three decimal digits
		size_t digits = strspn (++end, "0123456789");
		if (end[digits])
			return;

		if (digits--) msec += (*end++ - '0') * 100;
		if (digits--) msec += (*end++ - '0') * 10;
		if (digits--) msec +=  *end++ - '0';
	}

	*sec = MIN (INT_MAX, n);
	if (optional_msec)
		*optional_msec = msec;
}

// --- cURL async wrapper ------------------------------------------------------

// You are meant to subclass this structure, no user_data pointers needed
struct poller_curl_task;

/// Receives notification for finished transfers
typedef void (*poller_curl_done_fn)
	(CURLMsg *msg, struct poller_curl_task *task);

struct poller_curl_task
{
	CURL *easy;                         ///< cURL easy interface handle
	char curl_error[CURL_ERROR_SIZE];   ///< cURL error info buffer
	poller_curl_done_fn on_done;        ///< Done callback
};

struct poller_curl_fd
{
	LIST_HEADER (struct poller_curl_fd)
	struct poller_fd fd;                ///< Poller FD
};

struct poller_curl
{
	struct poller *poller;              ///< Parent poller
	struct poller_timer timer;          ///< cURL timer
	CURLM *multi;                       ///< cURL multi interface handle
	struct poller_curl_fd *fds;         ///< List of all FDs

	// TODO: also make sure to dispose of them at the end of the program

	int registered;                     ///< Number of attached easy handles
};

static void
poller_curl_collect (struct poller_curl *self, curl_socket_t s, int ev_bitmask)
{
	int running = 0;
	CURLMcode res;
	// XXX: ignoring errors, in particular CURLM_CALL_MULTI_PERFORM
	if ((res = curl_multi_socket_action (self->multi, s, ev_bitmask, &running)))
		print_debug ("cURL: %s", curl_multi_strerror (res));

	CURLMsg *msg;
	while ((msg = curl_multi_info_read (self->multi, &running)))
		if (msg->msg == CURLMSG_DONE)
		{
			struct poller_curl_task *task = NULL;
			hard_assert (!curl_easy_getinfo
				(msg->easy_handle, CURLINFO_PRIVATE, &task));
			task->on_done (msg, task);
		}
}

static void
poller_curl_on_socket (const struct pollfd *pfd, void *user_data)
{
	int mask = 0;
	if (pfd->revents & POLLIN)  mask |= CURL_CSELECT_IN;
	if (pfd->revents & POLLOUT) mask |= CURL_CSELECT_OUT;
	if (pfd->revents & POLLERR) mask |= CURL_CSELECT_ERR;
	poller_curl_collect (user_data, pfd->fd, mask);
}

static int
poller_curl_on_socket_action (CURL *easy, curl_socket_t s, int what,
	void *user_data, void *socket_data)
{
	(void) easy;
	struct poller_curl *self = user_data;

	struct poller_curl_fd *fd;
	if (!(fd = socket_data))
	{
		set_cloexec (s);

		fd = xmalloc (sizeof *fd);
		LIST_PREPEND (self->fds, fd);

		fd->fd = poller_fd_make (self->poller, s);
		fd->fd.dispatcher = poller_curl_on_socket;
		fd->fd.user_data = self;
		curl_multi_assign (self->multi, s, fd);
	}
	if (what == CURL_POLL_REMOVE)
	{
		// Some annoying cURL bug.  Never trust libraries.
		fd->fd.closed = fcntl(fd->fd.fd, F_GETFL) < 0 && errno == EBADF;

		poller_fd_reset (&fd->fd);
		LIST_UNLINK (self->fds, fd);
		free (fd);
	}
	else
	{
		short events = 0;
		if (what == CURL_POLL_IN)    events = POLLIN;
		if (what == CURL_POLL_OUT)   events =          POLLOUT;
		if (what == CURL_POLL_INOUT) events = POLLIN | POLLOUT;
		poller_fd_set (&fd->fd, events);
	}
	return 0;
}

static void
poller_curl_on_timer (void *user_data)
{
	poller_curl_collect (user_data, CURL_SOCKET_TIMEOUT, 0);
}

static int
poller_curl_on_timer_change (CURLM *multi, long timeout_ms, void *user_data)
{
	(void) multi;
	struct poller_curl *self = user_data;

	if (timeout_ms < 0)
		poller_timer_reset (&self->timer);
	else
		poller_timer_set (&self->timer, timeout_ms);
	return 0;
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

static bool
poller_curl_init (struct poller_curl *self, struct poller *poller,
	struct error **e)
{
	memset (self, 0, sizeof *self);
	if (!(self->multi = curl_multi_init ()))
		return error_set (e, "cURL setup failed");

	CURLMcode mres;
	if ((mres = curl_multi_setopt (self->multi,
			CURLMOPT_SOCKETFUNCTION, poller_curl_on_socket_action))
	 || (mres = curl_multi_setopt (self->multi,
			CURLMOPT_TIMERFUNCTION, poller_curl_on_timer_change))
	 || (mres = curl_multi_setopt (self->multi, CURLMOPT_SOCKETDATA, self))
	 || (mres = curl_multi_setopt (self->multi, CURLMOPT_TIMERDATA, self)))
	{
		curl_multi_cleanup (self->multi);
		self->multi = NULL;
		return error_set (e, "%s: %s",
			"cURL setup failed", curl_multi_strerror (mres));
	}

	self->timer = poller_timer_make ((self->poller = poller));
	self->timer.dispatcher = poller_curl_on_timer;
	self->timer.user_data = self;
	return true;
}

static void
poller_curl_free (struct poller_curl *self)
{
	curl_multi_cleanup (self->multi);
	poller_timer_reset (&self->timer);

	LIST_FOR_EACH (struct poller_curl_fd, iter, self->fds)
	{
		poller_fd_reset (&iter->fd);
		free (iter);
	}
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

/// Initialize a task with a new easy instance that can be used with the poller
static bool
poller_curl_spawn (struct poller_curl_task *task, struct error **e)
{
	CURL *easy;
	if (!(easy = curl_easy_init ()))
		return error_set (e, "cURL setup failed");

	// We already take care of SIGPIPE, and native DNS timeouts are only
	// a problem for people without the AsynchDNS feature.
	//
	// Unfortunately, cURL doesn't allow custom callbacks for DNS.
	// The most we could try is parse out the hostname and provide an address
	// override for it using CURLOPT_RESOLVE.  Or be our own SOCKS4A/5 proxy.

	CURLcode res;
	if ((res = curl_easy_setopt (easy, CURLOPT_NOSIGNAL,    1L))
	 || (res = curl_easy_setopt (easy, CURLOPT_ERRORBUFFER, task->curl_error))
	 || (res = curl_easy_setopt (easy, CURLOPT_PRIVATE,     task)))
	{
		curl_easy_cleanup (easy);
		return error_set (e, "%s", curl_easy_strerror (res));
	}

	task->easy = easy;
	return true;
}

static bool
poller_curl_add (struct poller_curl *self, CURL *easy, struct error **e)
{
	CURLMcode mres;
	// "CURLMOPT_TIMERFUNCTION [...] will be called from within this function"
	if ((mres = curl_multi_add_handle (self->multi, easy)))
		return error_set (e, "%s", curl_multi_strerror (mres));
	self->registered++;
	return true;
}

static bool
poller_curl_remove (struct poller_curl *self, CURL *easy, struct error **e)
{
	CURLMcode mres;
	if ((mres = curl_multi_remove_handle (self->multi, easy)))
		return error_set (e, "%s", curl_multi_strerror (mres));
	self->registered--;
	return true;
}

// --- Compact map -------------------------------------------------------------

// MPD provides us with a hefty amount of little key-value maps.  The overhead
// of str_map for such constant (string -> string) maps is too high and it's
// much better to serialize them (mainly cache locality and memory efficiency).
//
// This isn't intended to be reusable and has case insensitivity built-in.

typedef uint8_t *compact_map_t;         ///< Compacted (string -> string) map

static compact_map_t
compact_map (struct str_map *map)
{
	struct str s = str_make ();
	struct str_map_iter iter = str_map_iter_make (map);

	char *value;
	static const size_t zero = 0, alignment = sizeof zero;
	while ((value = str_map_iter_next (&iter)))
	{
		size_t entry_len = iter.link->key_length + 1 + strlen (value) + 1;
		size_t padding_len = (alignment - entry_len % alignment) % alignment;
		entry_len += padding_len;

		str_append_data (&s, &entry_len, sizeof entry_len);
		str_append_printf (&s, "%s%c%s%c", iter.link->key, 0, value, 0);
		str_append_data (&s, &zero, padding_len);
	}
	str_append_data (&s, &zero, sizeof zero);
	return (compact_map_t) str_steal (&s);
}

static char *
compact_map_find (compact_map_t data, const char *needle)
{
	size_t entry_len;
	while ((entry_len = *(size_t *) data))
	{
		data += sizeof entry_len;
		if (!strcasecmp_ascii (needle, (const char *) data))
			return (char *) data + strlen (needle) + 1;
		data += entry_len;
	}
	return NULL;
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

struct item_list
{
	compact_map_t *items;               ///< Compacted (string -> string) maps
	size_t len;                         ///< Length
	size_t alloc;                       ///< Allocated items
};

static struct item_list
item_list_make (void)
{
	struct item_list self = {};
	self.items = xcalloc (sizeof *self.items, (self.alloc = 16));
	return self;
}

static void
item_list_free (struct item_list *self)
{
	for (size_t i = 0; i < self->len; i++)
		free (self->items[i]);
	free (self->items);
}

static bool
item_list_set (struct item_list *self, int i, struct str_map *item)
{
	if (i < 0 || (size_t) i >= self->len)
		return false;

	free (self->items[i]);
	self->items[i] = compact_map (item);
	return true;
}

static compact_map_t
item_list_get (struct item_list *self, int i)
{
	if (i < 0 || (size_t) i >= self->len || !self->items[i])
		return NULL;
	return self->items[i];
}

static void
item_list_resize (struct item_list *self, size_t len)
{
	// Make the allocated array big enough but not too large
	size_t new_alloc = self->alloc;
	while (new_alloc < len)
		new_alloc <<= 1;
	while ((new_alloc >> 1) >= len
		&& (new_alloc - len) >= 1024)
		new_alloc >>= 1;

	for (size_t i = len; i < self->len; i++)
		free (self->items[i]);
	if (new_alloc != self->alloc)
		self->items = xreallocarray (self->items,
			sizeof *self->items, (self->alloc = new_alloc));
	for (size_t i = self->len; i < len; i++)
		self->items[i] = NULL;

	self->len = len;
}

// --- Spectrum analyzer -------------------------------------------------------

// See http://www.zytrax.com/tech/audio/equalization.html
// for a good write-up about this problem domain

#ifdef WITH_FFTW

struct spectrum
{
	int sampling_rate;                  ///< Number of samples per seconds
	int channels;                       ///< Number of sampled channels
	int bits;                           ///< Number of bits per sample
	int bars;                           ///< Number of output vertical bars

	int bins;                           ///< Number of DFT bins
	int useful_bins;                    ///< Bins up to the Nyquist frequency
	int samples;                        ///< Number of windows to average
	float accumulator_scale;            ///< Scaling factor for accum. values
	int *top_bins;                      ///< Top DFT bin index for each bar
	char *rendered;                     ///< String buffer for the "render"
	float *spectrum;                    ///< The "render" as normalized floats

	void *buffer;                       ///< Input buffer
	size_t buffer_len;                  ///< Input buffer fill level
	size_t buffer_size;                 ///< Input buffer size

	/// Decode the respective part of the buffer into the second half of data
	void (*decode) (struct spectrum *, int sample);

	float *data;                        ///< Normalized audio data
	float *window;                      ///< Sampled window function
	float *windowed;                    ///< data * window
	fftwf_complex *out;                 ///< DFT output
	fftwf_plan p;                       ///< DFT plan/FFTW configuration
	float *accumulator;                 ///< Accumulated powers of samples
};

// - - Windows - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

// Out: float[n] of 0..1
static void
window_hann (float *coefficients, size_t n)
{
	for (size_t i = 0; i < n; i++)
	{
		float sine = sin (M_PI * i / n);
		coefficients[i] = sine * sine;
	}
}

// In: float[n] of -1..1, float[n] of 0..1; out: float[n] of -1..1
static void
window_apply (const float *in, const float *coefficients, float *out, size_t n)
{
	for (size_t i = 0; i < n; i++)
		out[i] = in[i] * coefficients[i];
}

// In: float[n] of 0..1; out: float 0..n, describing the coherent gain
static float
window_coherent_gain (const float *in, size_t n)
{
	float sum = 0;
	for (size_t i = 0; i < n; i++)
		sum += in[i];
	return sum;
}

// - - Decoding  - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

static void
spectrum_decode_8 (struct spectrum *s, int sample)
{
	size_t n = s->useful_bins;
	float *data = s->data + n;
	for (int8_t *p = (int8_t *) s->buffer + sample * n * s->channels;
		n--; p += s->channels)
	{
		int32_t acc = 0;
		for (int ch = 0; ch < s->channels; ch++)
			acc += p[ch];
		*data++ = (float) acc / s->channels / -INT8_MIN;
	}
}

static void
spectrum_decode_16 (struct spectrum *s, int sample)
{
	size_t n = s->useful_bins;
	float *data = s->data + n;
	for (int16_t *p = (int16_t *) s->buffer + sample * n * s->channels;
		n--; p += s->channels)
	{
		int32_t acc = 0;
		for (int ch = 0; ch < s->channels; ch++)
			acc += p[ch];
		*data++ = (float) acc / s->channels / -INT16_MIN;
	}
}

static void
spectrum_decode_16_2 (struct spectrum *s, int sample)
{
	size_t n = s->useful_bins;
	float *data = s->data + n;
	for (int16_t *p = (int16_t *) s->buffer + sample * n * 2; n--; p += 2)
		*data++ = ((int32_t) p[0] + p[1]) / 2. / -INT16_MIN;
}

// - - Spectrum analysis - - - - - - - - - - - - - - - - - - - - - - - - - - - -

static const char *spectrum_bars[] =
	{ " ", "▁", "▂", "▃", "▄", "▅", "▆", "▇", "█" };

/// Assuming the input buffer is full, updates the rendered spectrum
static void
spectrum_sample (struct spectrum *s)
{
	memset (s->accumulator, 0, sizeof *s->accumulator * s->useful_bins);

	// Credit for the algorithm goes to Audacity's /src/SpectrumAnalyst.cpp,
	// apparently Welch's method
	for (int sample = 0; sample < s->samples; sample++)
	{
		// We use 50% overlap and start with data from the last run (if any)
		memmove (s->data, s->data + s->useful_bins,
			sizeof *s->data * s->useful_bins);
		s->decode (s, sample);

		window_apply (s->data, s->window, s->windowed, s->bins);
		fftwf_execute (s->p);

		for (int bin = 0; bin < s->useful_bins; bin++)
		{
			// out[0][0] is the DC component, not useful to us
			float re = s->out[bin + 1][0];
			float im = s->out[bin + 1][1];
			s->accumulator[bin] += re * re + im * im;
		}
	}

	int last_bin = 0;
	char *p = s->rendered;
	for (int bar = 0; bar < s->bars; bar++)
	{
		int top_bin = s->top_bins[bar];

		// Think of this as accumulating energies within bands,
		// so that it matches our non-linear hearing--there's no averaging.
		// For more precision, we could employ an "equal loudness contour".
		float acc = 0;
		for (int bin = last_bin; bin < top_bin; bin++)
			acc += s->accumulator[bin];

		last_bin = top_bin;
		float db = 10 * log10f (acc * s->accumulator_scale);
		if (db > 0)
			db = 0;

		// Assuming decibels are always negative (i.e., properly normalized).
		// The division defines the cutoff: 8 * 7 = 56 dB of range.
		int height = N_ELEMENTS (spectrum_bars) - 1 + (int) (db / 7);
		p += strlen (strcpy (p, spectrum_bars[MAX (height, 0)]));

		// Even with slightly the higher display resolutions provided by X11,
		// 60 dB roughly covers the useful range.
		s->spectrum[bar] = MAX (0, 1 + db / 60);
	}
}

static bool
spectrum_init (struct spectrum *s, char *format, int bars, int fps,
	struct error **e)
{
	errno = 0;

	long sampling_rate, bits, channels;
	if (!format
	 || (sampling_rate = strtol (format, &format, 10), *format++ != ':')
	 || (bits          = strtol (format, &format, 10), *format++ != ':')
	 || (channels      = strtol (format, &format, 10), *format)
	 || errno != 0)
		return error_set (e, "invalid format, expected RATE:BITS:CHANNELS");

	if (sampling_rate < 20000 || sampling_rate > INT_MAX)
		return error_set (e, "unsupported sampling rate (%ld)", sampling_rate);
	if (bits != 8 && bits != 16)
		return error_set (e, "unsupported bit count (%ld)", bits);
	if (channels < 1 || channels > INT_MAX)
		return error_set (e, "no channels to sample (%ld)", channels);
	if (bars < 1 || bars > 12)
		return error_set (e, "requested too few or too many bars (%d)", bars);

	// All that can fail henceforth is memory allocation
	*s = (struct spectrum)
	{
		.sampling_rate = sampling_rate,
		.bits          = bits,
		.channels      = channels,
		.bars          = bars,
	};

	// The number of bars is always smaller than that of the samples (bins).
	// Let's start with the equation of the top FFT bin to use for a given bar:
	//   top_bin = (num_bins + 1) ^ (bar / num_bars) - 1
	// N.b. if we didn't subtract, the power function would make this ≥ 1.
	// N.b. we then also need to extend the range by the same amount.
	//
	// We need the amount of bins for the first bar to be at least one:
	//         1 ≤ (num_bins + 1) ^   (1 / num_bars) - 1
	//
	// Solving with Wolfram Alpha gives us:
	//   num_bins ≥ (2 ^ num_bars) - 1  [for y > 0]
	//
	// And we need to remember that half of the FFT bins are useless/missing--
	// FFTW skips useless points past the Nyquist frequency.
	int necessary_bins = 2 << s->bars;

	// Discard frequencies above 20 kHz, which take up a constant ratio
	// of all bins, given by the sampling rate.  A more practical/efficient
	// solution would be to just handle 96/192/... kHz rates as bitshifts.
	//
	// Filtering out sub-20 Hz frequencies would be even more wasteful than
	// this wild DFT size, so we don't even try.  While we may just shift
	// the lowest used bin easily within the extra range provided by this
	// extension (the Nyquist is usually above 22 kHz, and it hardly matters
	// if we go a bit beyond 20 kHz in the last bin), for a small number of bars
	// the first bin already includes audible frequencies, and even for larger
	// numbers it wouldn't be too accurate.  An exact solution would require
	// having the amount of bins be strictly a factor of Nyquist / 20 (stemming
	// from the equation 20 = Nyquist / bins).  Since log2(44100 / 2 / 20) > 10,
	// it would be fairly expensive, and somewhat slowly updating.  Always.
	// (Note that you can increase window overlap to get smoother framerates,
	// but it would remain laggy.)
	double audible_ratio = s->sampling_rate / 2. / 20000;
	s->bins = ceil (necessary_bins * MAX (audible_ratio, 1));
	s->useful_bins = s->bins / 2;

	int used_bins = necessary_bins / 2;
	s->rendered = xcalloc (sizeof *s->rendered, s->bars * 3 + 1);
	s->spectrum = xcalloc (sizeof *s->spectrum, s->bars);
	s->top_bins = xcalloc (sizeof *s->top_bins, s->bars);
	for (int bar = 0; bar < s->bars; bar++)
	{
		int top_bin = floor (pow (used_bins + 1, (bar + 1.) / s->bars)) - 1;
		s->top_bins[bar] = MIN (top_bin, used_bins);
	}

	s->samples = s->sampling_rate / s->bins * 2 / MAX (fps, 1);
	if (s->samples < 1)
		s->samples = 1;

	// XXX: we average the channels but might want to average the DFT results
	if (s->bits == 8)   s->decode = spectrum_decode_8;
	if (s->bits == 16)  s->decode = spectrum_decode_16;

	// Micro-optimize to achieve some piece of mind; it's weak but measurable
	if (s->bits == 16 && s->channels == 2)
		s->decode = spectrum_decode_16_2;

	s->buffer_size = s->samples * s->useful_bins * s->bits / 8 * s->channels;
	s->buffer = xcalloc (1, s->buffer_size);

	// Prepare the window
	s->window = xcalloc (sizeof *s->window, s->bins);
	window_hann (s->window, s->bins);

	// Multiply by 2 for only using half of the DFT's result, then adjust to
	// the total energy of the window.  Both squared, because the accumulator
	// contains squared values.  Compute the average, and convert to decibels.
	// See also the mildly confusing https://dsp.stackexchange.com/a/14945.
	float coherent_gain = window_coherent_gain (s->window, s->bins);
	s->accumulator_scale = 2 * 2 / coherent_gain / coherent_gain / s->samples;

	s->data = xcalloc (sizeof *s->data, s->bins);
	s->windowed = fftw_malloc (sizeof *s->windowed * s->bins);
	s->out = fftw_malloc (sizeof *s->out * (s->useful_bins + 1));
	s->p = fftwf_plan_dft_r2c_1d (s->bins, s->windowed, s->out, FFTW_MEASURE);
	s->accumulator = xcalloc (sizeof *s->accumulator, s->useful_bins);
	return true;
}

static void
spectrum_free (struct spectrum *s)
{
	free (s->accumulator);
	fftwf_destroy_plan (s->p);
	fftw_free (s->out);
	fftw_free (s->windowed);
	free (s->data);
	free (s->window);
#if 0
	// We don't particularly want to discard wisdom.
	fftwf_cleanup ();
#endif

	free (s->rendered);
	free (s->spectrum);
	free (s->top_bins);
	free (s->buffer);

	memset (s, 0, sizeof *s);
}

#endif  // WITH_FFTW

// --- PulseAudio --------------------------------------------------------------

#ifdef WITH_PULSE

struct pulse
{
	struct poller_timer make_context;   ///< Event to establish connection
	pa_mainloop_api *api;               ///< PulseAudio event loop proxy
	pa_context *context;                ///< PulseAudio connection context