#!/usr/bin/env bash
# Builds a placeholder "fly-through" from Mega's own drone stills (slow push-ins + crossfades).
# Replace with real drone / AI footage later: just run make-frames.sh on the new clip.
#
# Usage: scripts/make-placeholder.sh <photos-dir> <out.mp4>
set -euo pipefail
SRC=${1:?photos dir}
OUT=${2:?output mp4}

# Story order — each shot maps to a chapter of the scroll scene.
SHOTS=(
  "Thabzimbi-Square-16.jpg"   # 01 hero: high, wide, mountains
  "DJI_0587-Edit.jpg"         # 02 bulk earthworks: excavator in the cut
  "3415e91b-24eb-4d02-9ccf-2804afeecdb7.jpg" # 03 roads: asphalt going down
  "cd309202-9a22-40ba-ac62-c46acc80119e.jpg" # 03 roads: grader on layerworks
  "DJI_0528-Edit.jpg"         # 04 municipal + stormwater: pipe trench
  "Spark-2.jpg"               # 05 finished: delivered precinct
)
FPS=24; LEN=40; FADE=10   # frames per shot / crossfade frames

inputs=(); filters=""; i=0
for s in "${SHOTS[@]}"; do
  inputs+=(-i "$SRC/$s")
  # crop to 16:9, upscale for jitter-free zoompan, then slow push-in (alternating drift)
  dx=$([ $((i % 2)) -eq 0 ] && echo "iw/2-(iw/zoom/2)+on*1.2" || echo "iw/2-(iw/zoom/2)-on*1.2")
  filters+="[$i:v]scale=3840:2160:force_original_aspect_ratio=increase,crop=3840:2160,"
  filters+="zoompan=z='1+0.0045*on':x='$dx':y='ih/2-(ih/zoom/2)':d=$LEN:s=1920x1080:fps=$FPS,setsar=1,format=yuv420p[s$i];"
  i=$((i + 1))
done

# chain crossfades
prev="s0"; offset=0
for ((k = 1; k < i; k++)); do
  offset=$(printf "%.4f" "$(echo "$offset + ($LEN - $FADE) / $FPS" | bc -l)")
  filters+="[$prev][s$k]xfade=transition=fade:duration=$(printf "%.4f" "$(echo "$FADE / $FPS" | bc -l)"):offset=$offset[x$k];"
  prev="x$k"
done
filters=${filters%;}

ffmpeg -loglevel error -y "${inputs[@]}" -filter_complex "$filters" -map "[$prev]" \
  -c:v libx264 -preset slow -crf 18 -g 1 -pix_fmt yuv420p -movflags +faststart "$OUT"
echo "wrote $OUT"