Fix display for longer command lines

This largely means being more careful about how we move the cursor
around, to avoid doing the wrong thing when the command line wraps
or is exactly one screen width.

We now "reset" the cursor to the beginning of the command line before
doing anything else, it's just too hard to move the cursor consistently
otherwise. The readline redraw takes care of moving the cursor back
to its current place in the command.

This fixes #10 and some other issues that I found while testing
the change.

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Fixed
+
+- Fix display errors when the command line wraps or the cursor is in the middle of a longer command.
+
 ## [1.5] - 2020-02-24
 
 ### Fixed

src/main.c

@@ -24,6 +24,8 @@
 
 #define PROGRAM_NAME "pipeline"
 char *program_name = PROGRAM_NAME;
+const char *prompt = "pipeline> ";
+const size_t prompt_width = 10;
 
 bool truncate_lines = false;
 int s_lines, s_cols;
@@ -100,9 +102,9 @@ ssize_t read_line(FILE *s, size_t max_display_len) {
 // which can be more than `count` when long logical lines wrap to multiple lines on-screen.
 // `total` is the total number of logical lines in the output.
 // (where "logical lines" means lines separated by \n chars)
-void read_show_output(FILE *s, size_t *count, size_t *shown, size_t *total) {
+void read_show_output(size_t max_to_show, FILE *s, size_t *count, size_t *shown, size_t *total) {
  termput0("cd");
- int lines_left = s_lines - 2;
+ int lines_left = max_to_show;
  for (;;) {
  size_t max_display_len;
  if (truncate_lines)
@@ -127,7 +129,7 @@ void read_show_output(FILE *s, size_t *count, size_t *shown, size_t *total) {
 
 // Fork the child process, run the given command in shell. Prints the first page
 // of stdout on success, or stderr on failure.
-int read_command(const char *command, size_t *count, size_t *shown, size_t *total) {
+int read_command(size_t max_to_show, const char *command, size_t *count, size_t *shown, size_t *total) {
  int child_stdout[2];
  int child_stderr[2];
  abort_ltz(pipe(child_stdout));
@@ -152,7 +154,7 @@ int read_command(const char *command, size_t *count, size_t *shown, size_t *tota
  FILE *c_stderr = abort_null(fdopen(child_stderr[0], "r"));
  *count = *shown = *total = 0;
 
- read_show_output(c_stdout, count, shown, total);
+ read_show_output(max_to_show, c_stdout, count, shown, total);
 
  fclose(c_stdout);
  int status = 0;
@@ -162,7 +164,7 @@ int read_command(const char *command, size_t *count, size_t *shown, size_t *tota
  if ((*shown) > 0)
  termput1("UP", *shown);
  *count = *shown = *total = 0;
- read_show_output(c_stderr, count, shown, total);
+ read_show_output(max_to_show, c_stderr, count, shown, total);
  }
  fclose(c_stderr);
 
@@ -171,18 +173,43 @@ int read_command(const char *command, size_t *count, size_t *shown, size_t *tota
 
 // Run the current command string and display the first page of results.
 // Args are passed in by readline and ignored.
-int show_preview(const char *a, int b) {
+int show_preview(const char *_a, int _b) {
  // Get the current window dimensions
  struct winsize sizes;
  abort_ltz(ioctl(0, TIOCGWINSZ, &sizes));
  s_lines = sizes.ws_row;
  s_cols = sizes.ws_col;
 
- printf("\n");
+ // Add 1 to the width for the cursor on the end, it makes the output
+ // cleaner when the command is exactly at the screen width.
+ size_t command_width = prompt_width + rl_end + 1;
+ size_t command_lines = (size_t)ceil((double)command_width / s_cols);
+
+ // Move the cursor to the beginning of the command line
+ // so we know where we are.
+ size_t cursor_pos = prompt_width + rl_point;
+ while (cursor_pos >= s_cols) {
+ termput0("up");
+ cursor_pos -= s_cols;
+ }
+ if (cursor_pos > 0)
+ termput1("LE", cursor_pos);
+
+ // Now move the cursor one line below the command line.
+ // Printing newlines rather than using termput("DO") here because
+ // we might be at the bottom of the window, and we can't just
+ // move down from there.
+ for (int i = 0; i < command_lines; ++i)
+ printf("\n");
+
+ // Display the output
+ size_t max_to_show = s_lines - (command_lines + 1);
  size_t count = 0;
  size_t shown = 0;
  size_t total = 0;
- int last_status = read_command(rl_line_buffer, &count, &shown, &total);
+ int last_status = read_command(max_to_show, rl_line_buffer, &count, &shown, &total);
+
+ // Display the status line in reversed video
  termput0("mr");
  int statsize = 0;
  if (last_status == 0) {
@@ -192,10 +219,13 @@ int show_preview(const char *a, int b) {
  }
  printf("%*s", s_cols - statsize, "");
  termput0("me");
- termput1("UP", shown + 1);
- // moving the cursor fully left, necessary for libreadline but not libedit
- termput1("LE", 9999);
+ termput1("LE", s_cols);
+
+ // Now move the cursor back to the beginning of the command line,
+ // and tell readline to redraw.
+ termput1("UP", shown + command_lines);
  rl_forced_update_display();
+
  return 0;
 }
 
@@ -274,7 +304,7 @@ int main(int argc, char *const *argv) {
  setupterm(NULL, 1, NULL);
  rl_startup_hook = setup;
  signal(SIGINT, cleanup);
- char *line = readline("pipeline> ");
+ char *line = readline(prompt);
  // as far as I'm aware, we'll never reach this point because
  // we always exit with Ctrl-C.
  free(line);