The Status Bar and Messages

Every serious full-screen tool reserves a strip of screen for telling you where you are: vim's status line, nano's shortcut bars, less's prompt. It's the difference between editing a file and editing blind. Ours takes the bottom row of the terminal: the text viewport gets terminal_rows - 1 rows, the status bar gets the last one. (That subtraction is why the editor struct's screen_rows is the viewport height, not the terminal height — decide once, at init, who owns which rows.)

Inverted video

The bar must read as chrome, not content. The classic trick costs five bytes: reverse video — SGR 7 swaps foreground and background, so the bar renders as a solid contrasting stripe:

\x1b[7m  ...status text padded to full width...  \x1b[m

Two details make it look right rather than almost-right:

• Pad to exactly the screen width. Reverse video colors only the cells you actually print. Print a 30-character status on an 80-column terminal and you get a 30-character stripe and 50 cells of abandoned background. The bar text must be built to precisely screen_cols characters — which is the actual programming problem here.
• Reset afterwards (\x1b[m), or the next thing drawn inherits the inversion. You knew that; it's still the #1 status-bar bug.

Left, right, and the squeeze

The conventional layout puts identity left and position right:

report.txt [+]                                    Ln 128, Col 43
└─ filename, dirty marker                         1-based, always ─┘

Building it is a fixed-width layout problem in miniature:

1. Compose the left segment: filename (or [No Name] for a fresh buffer), plus a [+] dirty marker when unsaved changes exist. (1-based Ln/Col on the right, by the way — users count from 1, programs from 0; the status bar is user territory.)
2. Compose the right segment.
3. If both fit in width, print left, width - left - right spaces, right.
4. If they don't fit, something must yield: truncate the left segment (long filenames lose their tails; a position display truncated to Ln 12 is misinformation), keeping one space between the segments. In the pathological case where even the right segment alone doesn't fit, truncate it to width — never write more than width.

This "compose segments, then resolve the squeeze" shape recurs in every TUI you'll ever write (tab bars, prompts, tmux's status) — worth doing carefully once.