formatter: add math

fixes #149
2020-11-02 12:59:09 -05:00
parent 14acf8f56d
commit 119d0a5879
3 changed files with 584 additions and 120 deletions
--- a/README.md
+++ b/README.md
@@ -89,7 +89,7 @@ playerctl metadata --format "Now playing: {{ artist }} - {{ album }} - {{ title
 # prints 'Now playing: Lana Del Rey - Born To Die - Video Games'
 ```

-Included in the template language are some built-in variables and helper functions for common formatting that you can call on template variables.
+Included in the template language are some built-in variables and helper functions for common formatting that you can call on template variables. It can also do basic math operations on numbers including `+`, `-`, `*`, `/`, and operation ordering with `()` parens.

 ```bash
 # Prints 'Total length: 3:23'
@@ -103,6 +103,12 @@ playerctl metadata --format "Artist in lowercase: {{ lc(artist) }}"

 # Prints 'STATUS: PLAYING'
 playerctl status --format "STATUS: {{ uc(status) }}"
+
+# Prints the time remaining in the track (e.g, 'Time remaining: 2:07')
+playerctl metadata --format "Time remaining: {{ duration(mpris:length - position) }}
+
+# Prints volume from 0 - 100
+playerctl metadata --format "Volume: {{ volume * 100 }}"
 ```

 | Function        | Argument         | Description                                                        |
--- a/playerctl/playerctl-formatter.c
+++ b/playerctl/playerctl-formatter.c
@@ -4,6 +4,7 @@
 #include <glib.h>
 #include <inttypes.h>
 #include <playerctl/playerctl-player.h>
+#include <stdio.h>

 #include "playerctl/playerctl-common.h"

@@ -11,6 +12,11 @@

 #define MAX_ARGS 32

+#define INFIX_ADD "+"
+#define INFIX_SUB "-"
+#define INFIX_MUL "*"
+#define INFIX_DIV "/"
+
 // clang-format off
 G_DEFINE_QUARK(playerctl-formatter-error-quark, playerctl_formatter_error);
 // clang-format on
@@ -19,11 +25,13 @@ enum token_type {
    TOKEN_VARIABLE,
    TOKEN_STRING,
    TOKEN_FUNCTION,
+    TOKEN_NUMBER,
 };

 struct token {
    enum token_type type;
    gchar *data;
+    gdouble numeric_data;
    GList *args;
 };

@@ -31,6 +39,13 @@ enum parser_state {
    STATE_EXPRESSION = 0,
    STATE_IDENTIFIER,
    STATE_STRING,
+    STATE_NUMBER,
+};
+
+enum parse_level {
+    PARSE_FULL = 0,
+    PARSE_NEXT_IDENT,
+    PARSE_MULT_DIV,
 };

 struct _PlayerctlFormatterPrivate {
@@ -86,28 +101,90 @@ static gboolean token_list_contains_key(GList *tokens, const gchar *key) {
    return FALSE;
 }

-static gboolean is_identifier_char(gchar c) {
-    return g_ascii_isalnum(c) || c == '_' || c == ':' || c == '-';
+static gboolean is_identifier_start_char(gchar c) {
+    return g_ascii_isalpha(c) || c == '_';
 }

-static struct token *tokenize_expression(const gchar *format, gint pos, gint *end, GError **error) {
+static gboolean is_identifier_char(gchar c) {
+    return g_ascii_isalnum(c) || c == '_' || c == ':';
+}
+
+static gboolean is_numeric_char(gchar c) {
+    return g_ascii_isdigit(c) || c == '.';
+}
+
+static gchar *infix_to_identifier(gchar infix) {
+    switch (infix) {
+    case '+':
+        return g_strdup(INFIX_ADD);
+    case '-':
+        return g_strdup(INFIX_SUB);
+    case '*':
+        return g_strdup(INFIX_MUL);
+    case '/':
+        return g_strdup(INFIX_DIV);
+    default:
+        assert(false && "not reached");
+    }
+}
+
+static struct token *tokenize_expression(const gchar *format, gint pos, gint *end,
+                                         enum parse_level level, GError **error) {
    GError *tmp_error = NULL;
    int len = strlen(format);
    char buf[1028];
    int buf_len = 0;
+    struct token *tok = NULL;

    enum parser_state state = STATE_EXPRESSION;

+    if (pos > len - 1) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1, "unexpected end of expression");
+        return NULL;
+    }
+
    for (int i = pos; i < len; ++i) {
        switch (state) {
        case STATE_EXPRESSION:
            if (format[i] == ' ') {
                continue;
+            } else if (format[i] == '(') {
+                // ordering parens
+                tok = tokenize_expression(format, i + 1, end, PARSE_FULL, &tmp_error);
+                if (tmp_error != NULL) {
+                    g_propagate_error(error, tmp_error);
+                    return NULL;
+                }
+
+                if (*end > len - 1 || format[*end] != ')') {
+                    g_set_error(error, playerctl_formatter_error_quark(), 1,
+                                "expected \")\" (position  %d)", *end);
+                    token_destroy(tok);
+                    return NULL;
+                }
+                *end += 1;
+
+                goto loop_out;
+            } else if (format[i] == '+' || format[i] == '-') {
+                // unary + or -
+                struct token *operand =
+                    tokenize_expression(format, i + 1, end, PARSE_NEXT_IDENT, &tmp_error);
+                if (tmp_error != NULL) {
+                    g_propagate_error(error, tmp_error);
+                    return NULL;
+                }
+                tok = token_create(TOKEN_FUNCTION);
+                tok->data = infix_to_identifier(format[i]);
+                tok->args = g_list_append(tok->args, operand);
+                goto loop_out;
            } else if (format[i] == '"') {
                state = STATE_STRING;
                continue;
-            } else if (!is_identifier_char(format[i])) {
-                // TODO return NULL to indicate there is no expression
+            } else if (is_numeric_char(format[i])) {
+                state = STATE_NUMBER;
+                buf[buf_len++] = format[i];
+                continue;
+            } else if (!is_identifier_start_char(format[i])) {
                g_set_error(error, playerctl_formatter_error_quark(), 1,
                            "unexpected \"%c\", expected expression (position  %d)", format[i], i);
                return NULL;
@@ -120,17 +197,42 @@ static struct token *tokenize_expression(const gchar *format, gint pos, gint *en

        case STATE_STRING:
            if (format[i] == '"') {
-                struct token *ret = token_create(TOKEN_STRING);
+                tok = token_create(TOKEN_STRING);
                buf[buf_len] = '\0';
-                ret->data = g_strdup(buf);
+                tok->data = g_strdup(buf);

                i++;
                while (i < len && format[i] == ' ') {
                    i++;
                }
                *end = i;
-                // printf("string: '%s'\n", ret->data);
-                return ret;
+                // printf("string: '%s'\n", tok->data);
+                goto loop_out;
+            } else {
+                buf[buf_len++] = format[i];
+            }
+            break;
+
+        case STATE_NUMBER:
+            if (!is_numeric_char(format[i]) || i == len - 2) {
+                tok = token_create(TOKEN_NUMBER);
+                buf[buf_len] = '\0';
+                tok->data = g_strdup(buf);
+                char *endptr = NULL;
+                gdouble number = strtod(tok->data, &endptr);
+                if (endptr == NULL || *endptr != '\0') {
+                    g_set_error(error, playerctl_formatter_error_quark(), 1,
+                                "invalid number: \"%s\" (position %d)", tok->data, i);
+                    token_destroy(tok);
+                    return NULL;
+                }
+                tok->numeric_data = number;
+                while (i < len && format[i] == ' ') {
+                    i++;
+                }
+                *end = i;
+                // printf("number: '%f'\n", tok->numeric_data);
+                goto loop_out;
            } else {
                buf[buf_len++] = format[i];
            }
@@ -138,28 +240,28 @@ static struct token *tokenize_expression(const gchar *format, gint pos, gint *en

        case STATE_IDENTIFIER:
            if (format[i] == '(') {
-                struct token *ret = token_create(TOKEN_FUNCTION);
+                tok = token_create(TOKEN_FUNCTION);
                buf[buf_len] = '\0';
-                ret->data = g_strdup(buf);
+                tok->data = g_strdup(buf);
                i += 1;
-                // printf("function: '%s'\n", ret->data);
+                // printf("function: '%s'\n", tok->data);

                int nargs = 0;
                while (TRUE) {
-                    ret->args =
-                        g_list_append(ret->args, tokenize_expression(format, i, end, &tmp_error));
+                    tok->args = g_list_append(
+                        tok->args, tokenize_expression(format, i, end, PARSE_FULL, &tmp_error));

                    nargs++;

                    if (nargs > MAX_ARGS) {
                        g_set_error(error, playerctl_formatter_error_quark(), 1,
                                    "maximum args of %d exceeded", MAX_ARGS);
-                        token_destroy(ret);
+                        token_destroy(tok);
                        return NULL;
                    }

                    if (tmp_error != NULL) {
-                        token_destroy(ret);
+                        token_destroy(tok);
                        g_propagate_error(error, tmp_error);
                        return NULL;
                    }
@@ -177,22 +279,21 @@ static struct token *tokenize_expression(const gchar *format, gint pos, gint *en
                    } else {
                        g_set_error(error, playerctl_formatter_error_quark(), 1,
                                    "expecting \")\" (position %d)", *end);
-                        token_destroy(ret);
+                        token_destroy(tok);
                        return NULL;
                    }
                }
-
-                return ret;
+                goto loop_out;
            } else if (!is_identifier_char(format[i])) {
-                struct token *ret = token_create(TOKEN_VARIABLE);
+                tok = token_create(TOKEN_VARIABLE);
                buf[buf_len] = '\0';
-                ret->data = g_strdup(buf);
+                tok->data = g_strdup(buf);
                while (i < len && format[i] == ' ') {
                    i++;
                }
                *end = i;
-                // printf("variable: '%s' end='%c'\n", ret->data, format[*end]);
-                return ret;
+                // printf("variable: '%s' end='%c'\n", tok->data, format[*end]);
+                goto loop_out;
            } else {
                buf[buf_len] = format[i];
                ++buf_len;
@@ -201,8 +302,63 @@ static struct token *tokenize_expression(const gchar *format, gint pos, gint *en
        }
    }

-    g_set_error(error, playerctl_formatter_error_quark(), 1, "unexpected end of format string");
+loop_out:
+
+    if (tok == NULL) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1, "unexpected end of expression");
        return NULL;
+    }
+    while (*end < len && format[*end] == ' ') {
+        *end += 1;
+    }
+    if (level == PARSE_NEXT_IDENT || *end >= len - 1) {
+        return tok;
+    }
+
+    gchar infix_id = format[*end];
+    while (infix_id == '*' || infix_id == '/' || infix_id == '+' || infix_id == '-') {
+        while (infix_id == '*' || infix_id == '/') {
+            struct token *operand =
+                tokenize_expression(format, *end + 1, end, PARSE_NEXT_IDENT, &tmp_error);
+            if (tmp_error != NULL) {
+                token_destroy(tok);
+                g_propagate_error(error, tmp_error);
+                return NULL;
+            }
+
+            struct token *operation = token_create(TOKEN_FUNCTION);
+            operation->data = infix_to_identifier(infix_id);
+            operation->args = g_list_append(operation->args, tok);
+            operation->args = g_list_append(operation->args, operand);
+
+            tok = operation;
+            infix_id = format[*end];
+        }
+
+        if (level == PARSE_MULT_DIV) {
+            return tok;
+        }
+
+        if (infix_id == '+' || infix_id == '-') {
+            struct token *operand =
+                tokenize_expression(format, *end + 1, end, PARSE_MULT_DIV, &tmp_error);
+            if (tmp_error != NULL) {
+                token_destroy(tok);
+                g_propagate_error(error, tmp_error);
+                return NULL;
+            }
+
+            struct token *operation = token_create(TOKEN_FUNCTION);
+            operation->data = infix_to_identifier(infix_id);
+            operation->args = g_list_append(operation->args, tok);
+            operation->args = g_list_append(operation->args, operand);
+
+            tok = operation;
+            infix_id = format[*end];
+        }
+    }
+
+    return tok;
 }

 static GList *tokenize_format(const char *format, GError **error) {
@@ -236,7 +392,7 @@ static GList *tokenize_format(const char *format, GError **error) {

            i += 2;
            int end = 0;
-            struct token *token = tokenize_expression(format, i, &end, &tmp_error);
+            struct token *token = tokenize_expression(format, i, &end, PARSE_FULL, &tmp_error);
            if (tmp_error != NULL) {
                token_list_destroy(tokens);
                g_propagate_error(error, tmp_error);
@@ -272,7 +428,7 @@ static GList *tokenize_format(const char *format, GError **error) {
    return tokens;
 }

-static gchar *helperfn_lc(struct token *token, GVariant **args, int nargs, GError **error) {
+static GVariant *helperfn_lc(struct token *token, GVariant **args, int nargs, GError **error) {
    if (nargs != 1) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
                    "function lc takes exactly one argument (got %d)", nargs);
@@ -281,16 +437,18 @@ static gchar *helperfn_lc(struct token *token, GVariant **args, int nargs, GErro

    GVariant *value = args[0];
    if (value == NULL) {
-        return g_strdup("");
+        return g_variant_new("s", "");
    }

    gchar *printed = pctl_print_gvariant(value);
    gchar *printed_lc = g_utf8_strdown(printed, -1);
+    GVariant *ret = g_variant_new("s", printed_lc);
    g_free(printed);
-    return printed_lc;
+    g_free(printed_lc);
+    return ret;
 }

-static gchar *helperfn_uc(struct token *token, GVariant **args, int nargs, GError **error) {
+static GVariant *helperfn_uc(struct token *token, GVariant **args, int nargs, GError **error) {
    if (nargs != 1) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
                    "function uc takes exactly one argument (got %d)", nargs);
@@ -299,16 +457,19 @@ static gchar *helperfn_uc(struct token *token, GVariant **args, int nargs, GErro

    GVariant *value = args[0];
    if (value == NULL) {
-        return g_strdup("");
+        return g_variant_new("s", "");
    }

    gchar *printed = pctl_print_gvariant(value);
    gchar *printed_uc = g_utf8_strup(printed, -1);
+    GVariant *ret = g_variant_new("s", printed_uc);
    g_free(printed);
-    return printed_uc;
+    g_free(printed_uc);
+    return ret;
 }

-static gchar *helperfn_duration(struct token *token, GVariant **args, int nargs, GError **error) {
+static GVariant *helperfn_duration(struct token *token, GVariant **args, int nargs,
+                                   GError **error) {
    if (nargs != 1) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
                    "function uc takes exactly one argument (got %d)", nargs);
@@ -317,7 +478,7 @@ static gchar *helperfn_duration(struct token *token, GVariant **args, int nargs,

    GVariant *value = args[0];
    if (value == NULL) {
-        return g_strdup("");
+        return g_variant_new("s", "");
    }

    // mpris durations are represented as int64 in microseconds
@@ -341,12 +502,16 @@ static gchar *helperfn_duration(struct token *token, GVariant **args, int nargs,
        g_string_append_printf(formatted, "%" PRId64 ":%02" PRId64, minutes, seconds);
    }

-    return g_string_free(formatted, FALSE);
+    gchar *formatted_inner = g_string_free(formatted, FALSE);
+    GVariant *ret = g_variant_new("s", formatted_inner);
+    g_free(formatted_inner);
+
+    return ret;
 }

 /* Calls g_markup_escape_text to replace the text with appropriately escaped
 characters for XML */
-static gchar *helperfn_markup_escape(struct token *token, GVariant **args, int nargs,
+static GVariant *helperfn_markup_escape(struct token *token, GVariant **args, int nargs,
                                        GError **error) {
    if (nargs != 1) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
@@ -356,16 +521,18 @@ static gchar *helperfn_markup_escape(struct token *token, GVariant **args, int n

    GVariant *value = args[0];
    if (value == NULL) {
-        return g_strdup("");
+        return g_variant_new("s", "");
    }

    gchar *printed = pctl_print_gvariant(value);
    gchar *escaped = g_markup_escape_text(printed, -1);
+    GVariant *ret = g_variant_new("s", escaped);
+    g_free(escaped);
    g_free(printed);
-    return escaped;
+    return ret;
 }

-static gchar *helperfn_default(struct token *token, GVariant **args, int nargs, GError **error) {
+static GVariant *helperfn_default(struct token *token, GVariant **args, int nargs, GError **error) {
    if (nargs != 2) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
                    "function default takes exactly two arguments (got %d)", nargs);
@@ -373,22 +540,24 @@ static gchar *helperfn_default(struct token *token, GVariant **args, int nargs,
    }

    if (args[0] == NULL && args[1] == NULL) {
-        return g_strdup("");
+        return NULL;
    }

    if (args[0] == NULL) {
-        return pctl_print_gvariant(args[1]);
+        g_variant_ref(args[1]);
+        return args[1];
    } else {
-        gchar *printed = pctl_print_gvariant(args[0]);
-        if (g_strcmp0(printed, "") == 0) {
-            g_free(printed);
-            return pctl_print_gvariant(args[1]);
+        if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_STRING) &&
+            strlen(g_variant_get_string(args[0], NULL)) == 0) {
+            g_variant_ref(args[1]);
+            return args[1];
        }
-        return printed;
+        g_variant_ref(args[0]);
+        return args[0];
    }
 }

-static gchar *helperfn_emoji(struct token *token, GVariant **args, int nargs, GError **error) {
+static GVariant *helperfn_emoji(struct token *token, GVariant **args, int nargs, GError **error) {
    if (nargs != 1) {
        g_set_error(error, playerctl_formatter_error_quark(), 1,
                    "function emoji takes exactly one argument (got %d)", nargs);
@@ -397,7 +566,7 @@ static gchar *helperfn_emoji(struct token *token, GVariant **args, int nargs, GE

    GVariant *value = args[0];
    if (value == NULL) {
-        return g_strdup("");
+        return g_variant_new("s", "");
    }

    struct token *arg_token = g_list_first(token->args)->data;
@@ -416,38 +585,255 @@ static gchar *helperfn_emoji(struct token *token, GVariant **args, int nargs, GE
        if (pctl_parse_playback_status(status_str, &status)) {
            switch (status) {
            case PLAYERCTL_PLAYBACK_STATUS_PLAYING:
-                return g_strdup("▶️");
+                return g_variant_new("s", "▶️");
            case PLAYERCTL_PLAYBACK_STATUS_STOPPED:
-                return g_strdup("⏹️");
+                return g_variant_new("s", "⏹️");
            case PLAYERCTL_PLAYBACK_STATUS_PAUSED:
-                return g_strdup("⏸️");
+                return g_variant_new("s", "⏸️");
            }
        }
    } else if (g_strcmp0(key, "volume") == 0 &&
               g_variant_is_of_type(value, G_VARIANT_TYPE_DOUBLE)) {
        const gdouble volume = g_variant_get_double(value);
        if (volume < 0.3333) {
-            return g_strdup("🔈");
+            return g_variant_new("s", "🔈");
        } else if (volume < 0.6666) {
-            return g_strdup("🔉");
+            return g_variant_new("s", "🔉");
        } else {
-            return g_strdup("🔊");
+            return g_variant_new("s", "🔊");
        }
    }

-    return pctl_print_gvariant(value);
+    g_variant_ref(value);
+    return value;
 }

-struct template_helper {
+static gboolean is_valid_numeric_type(GVariant *value) {
+    // This is all the types we know about for numeric operations. May be
+    // expanded at a later time.
+    if (value == NULL) {
+        return FALSE;
+    }
+
+    if (g_variant_is_of_type(value, G_VARIANT_TYPE_INT64)) {
+        return TRUE;
+    } else if (g_variant_is_of_type(value, G_VARIANT_TYPE_DOUBLE)) {
+        return TRUE;
+    }
+
+    return FALSE;
+}
+
+static gdouble get_double_value(GVariant *value) {
+    if (g_variant_is_of_type(value, G_VARIANT_TYPE_INT64)) {
+        return (gdouble)g_variant_get_int64(value);
+    } else if (g_variant_is_of_type(value, G_VARIANT_TYPE_DOUBLE)) {
+        return g_variant_get_double(value);
+    } else {
+        assert(FALSE && "not reached");
+    }
+    return 0.0;
+}
+
+static GVariant *infixfn_add(struct token *token, GVariant **args, int nargs, GError **error) {
+    if (nargs == 1) {
+        // unary addition
+        if (!is_valid_numeric_type(args[0])) {
+            g_set_error(error, playerctl_formatter_error_quark(), 1,
+                        "Got unsupported operand type for unary +: '%s'",
+                        g_variant_get_type_string(args[0]));
+            return NULL;
+        }
+        g_variant_ref(args[0]);
+        return args[0];
+    }
+
+    if (nargs != 2) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Addition takes two arguments (got %d). This is a bug in Playerctl.", nargs);
+        return NULL;
+    }
+
+    if (args[0] == NULL || args[1] == NULL) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand type for +: NULL");
+        return NULL;
+    }
+
+    if (!is_valid_numeric_type(args[0]) || !is_valid_numeric_type(args[1])) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand types for +: '%s' and '%s'",
+                    g_variant_get_type_string(args[0]), g_variant_get_type_string(args[1]));
+        return NULL;
+    }
+
+    if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_INT64) &&
+        g_variant_is_of_type(args[1], G_VARIANT_TYPE_INT64)) {
+        gint64 val0 = g_variant_get_int64(args[0]);
+        gint64 val1 = g_variant_get_int64(args[1]);
+        gint64 result = val0 + val1;
+
+        if ((val0 > 0 && val1 > 0 && result < 0) || (val0 < 0 && val1 < 0 && result > 0)) {
+            g_set_error(error, playerctl_formatter_error_quark(), 1, "Numeric overflow detected");
+            return NULL;
+        }
+
+        return g_variant_new("x", result);
+    }
+
+    gdouble val0 = get_double_value(args[0]);
+    gdouble val1 = get_double_value(args[1]);
+    gdouble result = val0 + val1;
+
+    return g_variant_new("d", result);
+}
+
+static GVariant *infixfn_sub(struct token *token, GVariant **args, int nargs, GError **error) {
+    if (nargs == 1) {
+        // unary addition
+        if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_INT64)) {
+            gint64 value = g_variant_get_int64(args[0]);
+            return g_variant_new("x", value * -1);
+        } else if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_DOUBLE)) {
+            gdouble value = g_variant_get_double(args[0]);
+            return g_variant_new("d", value * -1);
+        } else {
+            g_set_error(error, playerctl_formatter_error_quark(), 1,
+                        "Got unsupported operand type for unary -: '%s'",
+                        g_variant_get_type_string(args[0]));
+            return NULL;
+        }
+    }
+
+    if (nargs != 2) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Subtraction takes two arguments (got %d). This is a bug in Playerctl.", nargs);
+        return NULL;
+    }
+
+    if (args[0] == NULL || args[1] == NULL) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand type for -: NULL");
+        return NULL;
+    }
+
+    if (!is_valid_numeric_type(args[0]) || !is_valid_numeric_type(args[1])) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand types for -: '%s' and '%s'",
+                    g_variant_get_type_string(args[0]), g_variant_get_type_string(args[1]));
+        return NULL;
+    }
+
+    if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_INT64) &&
+        g_variant_is_of_type(args[1], G_VARIANT_TYPE_INT64)) {
+        gint64 val0 = g_variant_get_int64(args[0]);
+        gint64 val1 = g_variant_get_int64(args[1]);
+        gint64 result = val0 - val1;
+
+        if ((val0 > 0 && val1 < 0 && result < 0) || (val0 < 0 && val1 > 0 && result > 0)) {
+            g_set_error(error, playerctl_formatter_error_quark(), 1, "Numeric overflow detected");
+            return NULL;
+        }
+
+        return g_variant_new("x", result);
+    }
+
+    gdouble val0 = get_double_value(args[0]);
+    gdouble val1 = get_double_value(args[1]);
+    gdouble result = val0 - val1;
+
+    return g_variant_new("d", result);
+}
+
+static GVariant *infixfn_mul(struct token *token, GVariant **args, int nargs, GError **error) {
+    if (nargs != 2) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Multiplication takes two arguments (got %d). This is a bug in Playerctl.",
+                    nargs);
+        return NULL;
+    }
+    if (!is_valid_numeric_type(args[0]) || !is_valid_numeric_type(args[1])) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand types for *: '%s' and '%s'",
+                    g_variant_get_type_string(args[0]), g_variant_get_type_string(args[1]));
+        return NULL;
+    }
+    if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_INT64) &&
+        g_variant_is_of_type(args[1], G_VARIANT_TYPE_INT64)) {
+        gint64 val0 = g_variant_get_int64(args[0]);
+        gint64 val1 = g_variant_get_int64(args[1]);
+        gint64 result = val0 * val1;
+
+        if (val0 != 0 && val1 / val0 != val1) {
+            g_set_error(error, playerctl_formatter_error_quark(), 1, "Numeric overflow detected");
+            return NULL;
+        }
+
+        return g_variant_new("x", result);
+    }
+
+    gdouble val0 = get_double_value(args[0]);
+    gdouble val1 = get_double_value(args[1]);
+    gdouble result = val0 * val1;
+
+    return g_variant_new("d", result);
+}
+
+static GVariant *infixfn_div(struct token *token, GVariant **args, int nargs, GError **error) {
+    if (nargs != 2) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Division takes two arguments (got %d). This is a bug in Playerctl.", nargs);
+        return NULL;
+    }
+    if (!is_valid_numeric_type(args[0]) || !is_valid_numeric_type(args[1])) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1,
+                    "Got unsupported operand types for /: '%s' and '%s'",
+                    g_variant_get_type_string(args[0]), g_variant_get_type_string(args[1]));
+        return NULL;
+    }
+
+    if (g_variant_is_of_type(args[0], G_VARIANT_TYPE_INT64) &&
+        g_variant_is_of_type(args[1], G_VARIANT_TYPE_INT64)) {
+        gint64 val0 = g_variant_get_int64(args[0]);
+        gint64 val1 = g_variant_get_int64(args[1]);
+
+        if (val1 == 0) {
+            g_set_error(error, playerctl_formatter_error_quark(), 1, "Divide by zero error");
+            return NULL;
+        }
+
+        gint64 result = val0 / val1;
+
+        return g_variant_new("x", result);
+    }
+
+    gdouble val0 = get_double_value(args[0]);
+    gdouble val1 = get_double_value(args[1]);
+
+    if (val1 == 0.0) {
+        g_set_error(error, playerctl_formatter_error_quark(), 1, "Divide by zero error");
+        return NULL;
+    }
+
+    gdouble result = val0 / val1;
+
+    return g_variant_new("d", result);
+}
+
+struct template_function {
    const gchar *name;
-    gchar *(*func)(struct token *token, GVariant **args, int nargs, GError **error);
-} helpers[] = {
+    GVariant *(*func)(struct token *token, GVariant **args, int nargs, GError **error);
+} template_functions[] = {
    {"lc", &helperfn_lc},
    {"uc", &helperfn_uc},
    {"duration", &helperfn_duration},
    {"markup_escape", &helperfn_markup_escape},
    {"default", &helperfn_default},
    {"emoji", &helperfn_emoji},
+    {INFIX_ADD, &infixfn_add},
+    {INFIX_SUB, &infixfn_sub},
+    {INFIX_MUL, &infixfn_mul},
+    {INFIX_DIV, &infixfn_div},
 };

 static GVariant *expand_token(struct token *token, GVariantDict *context, GError **error) {
@@ -457,6 +843,9 @@ static GVariant *expand_token(struct token *token, GVariantDict *context, GError
    case TOKEN_STRING:
        return g_variant_new("s", token->data);

+    case TOKEN_NUMBER:
+        return g_variant_new("d", token->numeric_data);
+
    case TOKEN_VARIABLE:
        if (g_variant_dict_contains(context, token->data)) {
            return g_variant_dict_lookup_value(context, token->data, NULL);
@@ -483,15 +872,14 @@ static GVariant *expand_token(struct token *token, GVariantDict *context, GError
            }
        }

-        for (gsize i = 0; i < LENGTH(helpers); ++i) {
-            if (g_strcmp0(helpers[i].name, token->data) == 0) {
-                gchar *result = helpers[i].func(token, args, nargs, &tmp_error);
+        for (gsize i = 0; i < LENGTH(template_functions); ++i) {
+            if (g_strcmp0(template_functions[i].name, token->data) == 0) {
+                ret = template_functions[i].func(token, args, nargs, &tmp_error);
                if (tmp_error != NULL) {
                    g_propagate_error(error, tmp_error);
                    goto func_out;
                }

-                ret = g_variant_new("s", result);
                goto func_out;
            }
        }
--- a/test/test_format.py
+++ b/test/test_format.py
@@ -3,68 +3,18 @@ from .mpris import setup_mpris
 from .playerctl import PlayerctlCli

 import pytest
+import asyncio

 # TODO: test missing function does not segv


@pytest.mark.asyncio
-async def test_format(bus_address):
-    [mpris] = await setup_mpris('format-test', bus_address=bus_address)
-    TITLE = 'A Title'
-    ARTIST = 'An Artist'
-    ALBUM = 'An Album'
-    mpris.metadata = {
-        'xesam:title': Variant('s', TITLE),
-        'xesam:artist': Variant('as', [ARTIST]),
-        'xesam:escapeme': Variant('s', '<hi>'),
-        'xesam:album': Variant('s', ALBUM),
-        'mpris:length': Variant('x', 100000)
-    }
+async def test_emoji(bus_address):
+    [mpris] = await setup_mpris('emoji-format-test', bus_address=bus_address)
+    mpris.metadata = {'mpris:length': Variant('x', 100000)}
    await mpris.ping()
-
    playerctl = PlayerctlCli(bus_address)

-    cmd = await playerctl.run('metadata --format "{{artist}} - {{title}}"')
-    assert cmd.stdout == f'{ARTIST} - {TITLE}', cmd.stderr
-
-    cmd = await playerctl.run(
-        'metadata --format "{{markup_escape(xesam:escapeme)}}"')
-    assert cmd.stdout == '&lt;hi&gt;', cmd.stderr
-
-    cmd = await playerctl.run('metadata --format "{{lc(artist)}}"')
-    assert cmd.stdout == ARTIST.lower(), cmd.stderr
-
-    cmd = await playerctl.run('metadata --format "{{uc(title)}}"')
-    assert cmd.stdout == TITLE.upper(), cmd.stderr
-
-    cmd = await playerctl.run('metadata --format "{{uc(lc(title))}}"')
-    assert cmd.stdout == TITLE.upper(), cmd.stderr
-
-    cmd = await playerctl.run('metadata --format \'{{uc("Hi")}}\'')
-    assert cmd.stdout == "HI", cmd.stderr
-
-    cmd = await playerctl.run('metadata --format "{{mpris:length}}"')
-    assert cmd.stdout == "100000", cmd.stderr
-
-    cmd = await playerctl.run(
-        'metadata --format \'@{{ uc( "hi" ) }} - {{uc( lc( "HO"  ) ) }} . {{lc( uc(  title ) )   }}@\''
-    )
-    assert cmd.stdout == f'@HI - HO . {TITLE.lower()}@', cmd.stderr
-
-    cmd = await playerctl.run(
-        'metadata --format \'{{default(xesam:missing, artist)}}\'')
-    assert cmd.stdout == ARTIST, cmd.stderr
-
-    cmd = await playerctl.run(
-        'metadata --format \'{{default(title, artist)}}\'')
-    assert cmd.stdout == TITLE, cmd.stderr
-
-    cmd = await playerctl.run('metadata --format \'{{default("", "ok")}}\'')
-    assert cmd.stdout == 'ok', cmd.stderr
-
-    cmd = await playerctl.run('metadata --format \'{{default("ok", "not")}}\'')
-    assert cmd.stdout == 'ok', cmd.stderr
-
    status_emoji_cmd = 'metadata --format \'{{emoji(status)}}\''

    mpris.playback_status = 'Playing'
@@ -99,7 +49,127 @@ async def test_format(bus_address):
                              )
    assert cmd.returncode == 1, cmd.stderr

-    cmd = await playerctl.run('metadata --format " {{lc(album)}} "')
-    assert cmd.stdout == ALBUM.lower()
+
+class MetadataTest:
+    def __init__(self, playerctl):
+        self.tests = []
+        self.playerctl = playerctl
+
+    def add(self, fmt, expected, ret=0):
+        fmt = fmt.replace("'", r"\'")
+        self.tests.append((f"metadata --format '{fmt}'", expected, ret))
+
+    async def run(self):
+        coros = []
+        for fmt, _, _ in self.tests:
+            coros.append(self.playerctl.run(fmt))
+
+        results = await asyncio.gather(*coros)
+
+        for i, cmd in enumerate(results):
+            fmt, expected, ret = self.tests[i]
+            assert cmd.returncode == ret, cmd.stderr
+            if ret == 0:
+                assert cmd.stdout == expected, cmd.stderr
+
+
+@pytest.mark.asyncio
+async def test_format(bus_address):
+    [mpris] = await setup_mpris('format-test', bus_address=bus_address)
+    TITLE = 'A Title'
+    ARTIST = 'An Artist'
+    ALBUM = 'An Album'
+    mpris.metadata = {
+        'xesam:title': Variant('s', TITLE),
+        'xesam:artist': Variant('as', [ARTIST]),
+        'xesam:escapeme': Variant('s', '<hi>'),
+        'xesam:album': Variant('s', ALBUM),
+        'mpris:length': Variant('x', 100000)
+    }
+    mpris.volume = 2.0
+    await mpris.ping()
+
+    playerctl = PlayerctlCli(bus_address)
+
+    test = MetadataTest(playerctl)
+
+    test.add('{{artist}} - {{title}}', f'{ARTIST} - {TITLE}')
+    test.add("{{markup_escape(xesam:escapeme)}}", "&lt;hi&gt;")
+    test.add("{{lc(artist)}}", ARTIST.lower())
+    test.add("{{uc(title)}}", TITLE.upper())
+    test.add("{{uc(lc(title))}}", TITLE.upper())
+    test.add('{{uc("Hi")}}', "HI")
+    test.add("{{mpris:length}}", "100000")
+    test.add(
+        '@{{ uc( "hi" ) }} - {{uc( lc( "HO"  ) ) }} . {{lc( uc(  title ) )   }}@',
+        f'@HI - HO . {TITLE.lower()}@')
+    test.add("{{default(xesam:missing, artist)}}", ARTIST)
+    test.add("{{default(title, artist)}}", TITLE)
+    test.add('{{default("", "ok")}}', 'ok')
+    test.add('{{default("ok", "not")}}', 'ok')
+    test.add(' {{lc(album)}} ', ALBUM.lower())
+
+    await test.run()
+
+    # numbers
+    math = [
+        '10',
+        '-10 + 20',
+        '10 + 10',
+        '10 * 10',
+        '10 / 10',
+        '10 + 10 * 10 + 10',
+        '10 + 10 * -10 + 10',
+        '10 + 10 * -10 + -10',
+        '-10 * 10 + 10',
+        '-10 * -10 * -1 + -10',
+        '-10 * 10 + -10 * -10 + 20 / 10 * -20 + -10',
+        '8+-+--++-4',
+        '2 - 10 * 1 + 1',
+        '2 / -2 + 2 * 2 * -2 - 2 - 2 * -2',
+        '2 * (2 + 2)',
+        '10 * (10 + 12) - 4',
+        '-(10)',
+        '-(10 + 12 * -2)',
+        '14 - (10 * 2 + 5) * -6',
+        '(14 - 2 * 3) * (14 * -2 - 6) + -(4 - 2) * 5',
+    ]
+
+    # variables
+    math += [
+        'volume',
+        'volume + 10',
+        '-volume',
+        '-volume * -1',
+        '-volume + volume',
+        'volume * volume',
+        'volume * -volume',
+        'volume + volume * -volume * volume + -volume',
+        'volume / -volume + volume * volume * -volume - volume - volume * -volume',
+        '-(volume + 3) * 5 * (volume + 2)',
+    ]
+
+    # functions
+    math += [
+        'default(5+5, None)',
+        '-default(5 + 5, None)',
+        '(-default(5 - 5, None) + 2) * 8',
+        '2 + (5 * 4 + 3 * -default(5, default(6 * (3 + 4 * (6 + 2)) / 2, None)) + -56)',
+    ]
+
+    def default_shim(arg1, arg2):
+        if arg1 is None:
+            return arg2
+        return arg1
+
+    async def math_test(math):
+        cmd = await playerctl.run("metadata --format '{{" + math + "}}'")
+        assert cmd.returncode == 0, cmd.stderr
+        assert float(cmd.stdout) == eval(math, {
+            'volume': mpris.volume,
+            'default': default_shim
+        }), math
+
+    await asyncio.gather(*[math_test(m) for m in math])

    mpris.disconnect()