Add a basic command-not-find binary

packages/command-not-found/build.sh

@@ -6,4 +6,10 @@ termux_step_make_install () {
 	TERMUX_SHARE_DIR=$TERMUX_PREFIX/share/termux
 	mkdir -p $TERMUX_SHARE_DIR
 	cp $TERMUX_PKG_BUILDER_DIR/commands.txt $TERMUX_SHARE_DIR/commands.txt
+
+	TERMUX_LIBEXEC_DIR=$TERMUX_PREFIX/libexec/termux
+	mkdir -p $TERMUX_LIBEXEC_DIR
+	$CC $CFLAGS $LDFLAGS -std=c11 $TERMUX_PKG_BUILDER_DIR/command-not-found.c \
+	        -DTERMUX_COMMANDS_LISTING=$TERMUX_PREFIX/share/termux/commands.txt \
+	        -o $TERMUX_LIBEXEC_DIR/command-not-found
 }

packages/command-not-found/command-not-found.c

@@ -0,0 +1,78 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+#define STRINGIFY(x) #x
+#define TOSTRING(x) STRINGIFY(x)
+
+inline int termux_min3(unsigned int a, unsigned int b, unsigned int c) {
+	return (a < b ? (a < c ? a : c) : (b < c ? b : c));
+}
+
+int termux_levenshtein_distance(char const* restrict s1, char const* restrict s2) {
+	unsigned int s1len = strlen(s1);
+	unsigned int s2len = strlen(s2);
+	unsigned int matrix[s2len+1][s1len+1];
+	matrix[0][0] = 0;
+	for (unsigned x = 1; x <= s2len; x++)
+		matrix[x][0] = matrix[x-1][0] + 1;
+	for (unsigned y = 1; y <= s1len; y++)
+		matrix[0][y] = matrix[0][y-1] + 1;
+	for (unsigned x = 1; x <= s2len; x++)
+		for (unsigned y = 1; y <= s1len; y++)
+			matrix[x][y] = termux_min3(matrix[x-1][y] + 1, matrix[x][y-1] + 1, matrix[x-1][y-1] + (s1[y-1] == s2[x-1] ? 0 : 1));
+	return matrix[s2len][s1len];
+}
+
+int main(int argc, char** argv) {
+	if (argc != 2) {
+		fprintf(stderr, "usage: termux-command-not-found <command>\n");
+		return 1;
+	}
+	char* command_not_found = argv[1];
+
+	FILE* commands_file = fopen(TOSTRING(TERMUX_COMMANDS_LISTING), "r");
+	if (commands_file == NULL) {
+		perror(TOSTRING(TERMUX_COMMANDS_LISTING));
+		return 1;
+	}
+
+	int best_distance = -1;
+	int guesses_at_best_distance = 0;
+	char current_package[128];
+	char best_package_guess[128];
+	char best_command_guess[128];
+	char* current_line = NULL;
+	while (true) {
+		size_t buffer_length = sizeof(current_line);
+		ssize_t read_bytes = getline(&current_line, &buffer_length, commands_file);
+		if (read_bytes <= 1) break;
+		size_t line_length = strlen(current_line);
+		current_line[line_length-1] = 0;
+		if (current_line[0] == ' ') { // Binary
+			char* binary_name = current_line + 1;
+			int distance = termux_levenshtein_distance(command_not_found, binary_name);
+			if (distance == 0 && strcmp(command_not_found, binary_name) == 0) {
+				printf("The program '%s' is currently not installed. You can install it by executing:\n apt install %s\n", binary_name, current_package);
+				return 0;
+			} else if (best_distance == distance) {
+				guesses_at_best_distance++;
+			} else if (best_distance == -1 || best_distance > distance) {
+				guesses_at_best_distance = 0;
+				best_distance = distance;
+				strncpy(best_command_guess, binary_name, sizeof(best_command_guess));
+				strncpy(best_package_guess, current_package, sizeof(best_package_guess));
+			}
+		} else { // Package
+			strncpy(current_package, current_line, sizeof(current_package));
+		}
+	}
+
+	if (best_distance == -1 || best_distance > 3) {
+		printf("%s: command not found\n", command_not_found);
+	} else {
+		printf("No command '%s' found, did you mean:\n", command_not_found);
+		printf(" Command '%s' from package '%s'\n", best_command_guess, best_package_guess);
+	}
+}
+