;;;; raylib [text] example - text writing anim
;;;;
;;;; examples/text/text_writing_anim.c. Sixty lines of C whose whole substance
;;;; is one call this package cannot bind:
;;;;
;;;;     DrawText(TextSubtext(message, 0, framesCounter/10), ...)
;;;;
;;;; TextSubtext is in raylib.h and is not in the bindings, on the rule
;;;; raylib.fln states for the whole Text* family: it answers a `char *` into
;;;; a rotating static buffer, and declare-c refuses a returned pointer to
;;;; memory the caller does not own. There is no missing line to add — the
;;;; binding would be wrong at any signature.
;;;;
;;;; And it does not matter, because Flan has the operation as a primitive.
;;;; `slice(a, lo, hi)` takes a view of an array, `string(b)` reinterprets the
;;;; bytes as a string at no cost, and `string(slice(message, 0, n))` is
;;;; TextSubtext with the static buffer removed — no copy, no shared state, no
;;;; rotation to run out of. Porting the example is therefore how the gap gets
;;;; *closed* rather than reported: the C's workaround for not having slices
;;;; is the thing Flan did not need.
;;;;
;;;; The one place they differ, and it is why the clamp below is here rather
;;;; than in the C: TextSubtext clips its length to the string, so the C can
;;;; pass a counter that runs past the end for ever and see nothing happen.
;;;; `slice` does not clip — an out-of-range bound is an error, and a bound
;;;; computed at run time is checked at run time — so the length has to be
;;;; brought inside the string before the call. That is a better failure than
;;;; the C's, and it costs one `min`.
;;;;
;;;; The message is a `[u8]` and not a `string` because `slice` takes an array
;;;; or a slice; `bytes-view("…")` is the bridge in the other direction from
;;;; `string(…)` and costs nothing either. The embedded newline is written as
;;;; an escape, and raylib's draw-text breaks the line on it.

import rl "vendor:raylib"

const screen-width = 800
const screen-height = 450

const message = "This sample illustrates a text writing\nanimation effect! Check it out! ;)"

once frames-counter: i32

fn main() -> ()
  rl/init-window(screen-width, screen-height,
                 "raylib [text] example - text writing anim")
  defer rl/close-window()
  frames-counter = 0
  rl/set-target-fps(60)
  until rl/window-should-close()
    ;; Update. Holding space runs the counter eight times faster; enter starts
    ;; it over.
    if rl/is-key-down(:key-space)
      frames-counter += 8
    else
      frames-counter += 1
    if rl/is-key-pressed(:key-enter)
      frames-counter = 0
    ;; Draw
    rl/with-drawing:
      rl/clear-background(rl/raywhite)
      ;; One character every ten frames. The clamp is the whole difference from
      ;; the C — see the header comment.
      let b = bytes-view(message)
          n = min(i32(length(b)), frames-counter / 10)
      rl/draw-text(str(slice(b, 0, n)), 210, 160, 20, rl/maroon)
      rl/draw-text("PRESS [ENTER] to RESTART!", 240, 260, 20, rl/lightgray)
      rl/draw-text("HOLD [SPACE] to SPEED UP!", 239, 300, 20, rl/lightgray)