#!/usr/bin/env bash
set -euo pipefail

DEMO_DIR="${1:-muse-git-demo}"

setup() {
  rm -rf "$DEMO_DIR"
  mkdir -p "$DEMO_DIR"
  cd "$DEMO_DIR"

  git init -q

  cat > calculator.py <<'PY'
def calculate_total(items):
    return sum(item["price"] for item in items)

if __name__ == "__main__":
    cart = [{"price": 10}, {"price": 15}]
    print(calculate_total(cart))
PY

  mkdir -p app
  for i in $(seq -w 1 20); do
    cat > "app/module_${i}.py" <<PY
from calculator import calculate_total

def report_${i}(items):
    return calculate_total(items)
PY
  done

  python3 - <<'PY'
from pathlib import Path

notes = [60, 64, 67, 72]
track = bytearray()
track += bytes([0x00, 0xFF, 0x51, 0x03, 0x07, 0xA1, 0x20])

for note in notes:
    track += bytes([0x00, 0x90, note, 100])
    track += bytes([0x60, 0x80, note, 64])

track += bytes([0x00, 0xFF, 0x2F, 0x00])

header = b"MThd" + (6).to_bytes(4, "big") + (0).to_bytes(2, "big") + (1).to_bytes(2, "big") + (96).to_bytes(2, "big")
chunk = b"MTrk" + len(track).to_bytes(4, "big") + track
Path("melody.mid").write_bytes(header + chunk)
PY

  git add .
  git commit -qm "Initial demo state"

  echo
  echo "Created: $(pwd)"
  echo "Baseline commit:"
  git --no-pager log --oneline -1
}

python_change() {
  cd "$DEMO_DIR"
  python3 - <<'PY'
from pathlib import Path
p = Path("calculator.py")
s = p.read_text()
s = s.replace(
    'return sum(item["price"] for item in items)',
    'return round(sum(item["price"] for item in items), 2)'
)
p.write_text(s)
PY
}

rename_change() {
  cd "$DEMO_DIR"
  python3 - <<'PY'
from pathlib import Path
for p in [Path("calculator.py"), *sorted(Path("app").glob("*.py"))]:
    s = p.read_text().replace("calculate_total", "compute_total")
    p.write_text(s)
PY
}

midi_change() {
  cd "$DEMO_DIR"
  python3 - <<'PY'
from pathlib import Path
p = Path("melody.mid")
data = bytearray(p.read_bytes())
mapping = {60: 62, 64: 65, 67: 69, 72: 74}
for i in range(1, len(data)):
    if data[i-1] in (0x90, 0x80) and data[i] in mapping:
        data[i] = mapping[data[i]]
p.write_bytes(data)
PY
}

reset_demo() {
  cd "$DEMO_DIR"
  git reset --hard -q HEAD
  git clean -fdq
}

case "${2:-setup}" in
  setup) setup ;;
  python-change) python_change ;;
  rename-change) rename_change ;;
  midi-change) midi_change ;;
  reset) reset_demo ;;
  *)
    echo "Usage: $0 [demo-dir] {setup|python-change|rename-change|midi-change|reset}"
    exit 1
    ;;
esac