app.py

"""

Speed Reader — WebM Converter
Flask app for HuggingFace Spaces (Docker SDK).

Endpoints:
  GET  /          → health check / status page
  POST /convert   → multipart upload: file=<webm>, format=mp4|gif, fps=15
                    returns the converted file as a binary download
"""

import io
import os
import subprocess
import tempfile
from pathlib import Path
from flask import Flask, request, send_file, jsonify
from flask_cors import CORS

app = Flask(__name__)
CORS(app, resources={r"/*": {"origins": "*"}})


# ── Health check ──────────────────────────────────────────────────────────────

@app.route("/", methods=["GET"])
def index():
    return jsonify({
        "status": "ok",
        "service": "Speed Reader — WebM Converter",
        "endpoints": {
            "POST /convert": {
                "params": {
                    "file":   "WebM file (multipart)",
                    "format": "'mp4' or 'gif'",
                    "fps":    "GIF frame rate, default 15 (ignored for mp4)"
                },
                "returns": "Converted file download"
            }
        }
    })


# ── Conversion endpoint ───────────────────────────────────────────────────────

@app.route("/convert", methods=["POST"])
def convert():
    if "file" not in request.files:
        return jsonify({"error": "No file uploaded. Send as multipart field 'file'."}), 400

    uploaded = request.files["file"]
    fmt      = request.form.get("format", "mp4").lower().strip()
    fps      = request.form.get("fps", "15")

    if fmt not in ("mp4", "gif"):
        return jsonify({"error": f"Unsupported format '{fmt}'. Use 'mp4' or 'gif'."}), 400

    try:
        fps = max(5, min(30, int(fps)))
    except ValueError:
        fps = 15

    # ── Write upload to temp dir, run ffmpeg, read result into memory ─────────
    #
    # IMPORTANT: send_file is called AFTER the with-block so the tempdir is
    # already deleted by then. We must read the output file into a BytesIO
    # buffer while we are still inside the with-block.
    #
    buf = None
    with tempfile.TemporaryDirectory() as tmpdir:
        tmp = Path(tmpdir)
        src = tmp / "input.webm"
        out = tmp / f"output.{fmt}"

        uploaded.save(str(src))

        if src.stat().st_size == 0:
            return jsonify({"error": "Uploaded file is empty."}), 400

        try:
            if fmt == "mp4":
                _run([
                    "ffmpeg", "-y",
                    "-i",        str(src),
                    "-c:v",      "libx264",
                    "-preset",   "fast",
                    "-crf",      "22",
                    "-pix_fmt",  "yuv420p",
                    "-movflags", "+faststart",
                    "-an",
                    str(out)
                ])

            else:  # gif — two-pass palette encode
                palette = tmp / "palette.png"

                # Pass 1: build optimised palette from the full video
                _run([
                    "ffmpeg", "-y",
                    "-i",  str(src),
                    "-vf", f"fps={fps},scale=iw:ih:flags=lanczos,palettegen=stats_mode=diff",
                    str(palette)
                ])

                # Pass 2: encode GIF using palette
                # [0:v] is required to tell ffmpeg which stream feeds the filter
                _run([
                    "ffmpeg", "-y",
                    "-i", str(src),
                    "-i", str(palette),
                    "-filter_complex",
                    f"[0:v]fps={fps},scale=iw:ih:flags=lanczos[x];[x][1:v]paletteuse=dither=bayer",
                    str(out)
                ])

        except subprocess.CalledProcessError as e:
            return jsonify({"error": f"ffmpeg failed:\n{e.stderr[-800:]}"}), 500

        if not out.exists() or out.stat().st_size == 0:
            return jsonify({"error": "Conversion produced an empty file."}), 500

        # Read into memory NOW, while the tempdir still exists
        buf = io.BytesIO(out.read_bytes())

    # tempdir is deleted here — but buf is safely in memory
    buf.seek(0)
    mime = "video/mp4" if fmt == "mp4" else "image/gif"
    return send_file(
        buf,
        mimetype=mime,
        as_attachment=True,
        download_name=f"speed-read.{fmt}"
    )


# ── Helper ────────────────────────────────────────────────────────────────────

def _run(cmd: list[str]):
    result = subprocess.run(cmd, capture_output=True, text=True)
    if result.returncode != 0:
        raise subprocess.CalledProcessError(
            result.returncode, cmd, output=result.stdout, stderr=result.stderr
        )
    return result


# ── Entry point ───────────────────────────────────────────────────────────────

if __name__ == "__main__":
    port = int(os.environ.get("PORT", 7860))
    app.run(host="0.0.0.0", port=port)