Blame for server.py

#!/usr/bin/env python3
"""Local Gurbani waveform section editor server.

Parent-folder convention:

  parent/
    Project One/
      recording.mp3
      aligned_transcript.json
    Project Two/
      another.mp3
      transcript_sections.json

Project folders are discovered recursively. A project folder must contain an
MP3 and a transcript JSON with a ``sections`` array. The JSON filename can be
``aligned_transcript.json``, ``aligned_transcript copy.json``, or
``transcript_sections.json``. When present, ``audio_file`` selects the MP3.
Hidden files and hidden directories are ignored.

Run:
  python server.py
  python server.py --parent-folder /path/to/parent --port 8000
  python server.py --parent-folder /path/to/parent --longer 20
"""
from __future__ import annotations

import argparse
import array
import json
import mimetypes
import os
import shutil
import subprocess
import sys
import tempfile
import math
from datetime import datetime
from http import HTTPStatus
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path
from urllib.parse import parse_qs, quote, unquote, urlparse

HOST = "127.0.0.1"
DEFAULT_PORT = 8000
AUDIO_EXTENSIONS = {".mp3", ".wav", ".m4a", ".flac", ".ogg"}
TRANSCRIPT_JSON_NAME = "aligned_transcript.json"
ROOT_PROJECT_KEY = "__root__"
BASE_DIR = Path(__file__).resolve().parent
INDEX_FILE = BASE_DIR / "index.html"


def clean_payload(payload: object) -> dict:
    """Return the input schema without adding, deleting, or normalising fields."""
    if isinstance(payload, dict):
        return payload
    elif isinstance(payload, list):
        return {"sections": payload}
    return {"sections": []}


def transcript_payload(json_path: Path) -> dict | None:
    """Read a transcript JSON candidate, rejecting unrelated JSON files."""
    try:
        payload = json.loads(json_path.read_text(encoding="utf-8"))
    except (OSError, json.JSONDecodeError):
        return None
    sections = payload.get("sections") if isinstance(payload, dict) else None
    if not isinstance(sections, list):
        return None
    if not any(
        isinstance(section, dict)
        and "start_time" in section
        and "end_time" in section
        and "transcript" in section
        for section in sections
    ):
        return None
    return payload


def transcript_json_priority(path: Path) -> tuple[int, str]:
    name = path.name.casefold()
    preferred = {
        "aligned_transcript.json": 0,
        "aligned_transcript copy.json": 1,
        "transcript_sections.json": 2,
    }
    if name in preferred:
        rank = preferred[name]
    elif name.startswith("aligned_transcript"):
        rank = 3
    elif name.startswith("transcript_sections"):
        rank = 4
    else:
        rank = 5
    return rank, name


def merge_editable_fields(
    original: object,
    submitted: object,
    preserve_section_ids: list[str] | None = None,
    renumber_section_ids: bool = False,
) -> dict:
    """Apply edits while optionally retaining sections hidden by a duration filter."""
    if isinstance(original, dict):
        result = dict(original)
        original_sections = original.get("sections", [])
    else:
        result = {}
        original_sections = original if isinstance(original, list) else []

    submitted_sections = submitted.get("sections", []) if isinstance(submitted, dict) else []
    if not isinstance(original_sections, list):
        original_sections = []
    if not isinstance(submitted_sections, list):
        submitted_sections = []

    originals_by_id = {
        str(section.get("section_id")): section
        for section in original_sections
        if isinstance(section, dict) and section.get("section_id") is not None
    }
    replacements: dict[str, dict] = {}
    new_sections: list[dict] = []
    submitted_order: list[dict] = []
    editable = ("section_id", "transcript", "start_time", "end_time")
    for edited in submitted_sections:
        if not isinstance(edited, dict):
            continue
        # The editor renumbers serial IDs after a split/join. Its transient
        # source ID identifies the original section whose other fields must be
        # retained. Older clients without this marker still match by section ID.
        source_id = (
            edited.get("__source_section_id")
            if "__source_section_id" in edited
            else edited.get("section_id")
        )
        original_section = originals_by_id.get(str(source_id)) if source_id is not None else None
        if original_section is None:
            # Split/insert creates a new section. Keep only the fields required
            # by this transcript/timing schema; never copy unrelated metadata.
            new_section = {key: edited[key] for key in ("section_id", *editable) if key in edited}
            new_sections.append(new_section)
            submitted_order.append(new_section)
            continue
        new_section = dict(original_section)
        for key in editable:
            if key in edited:
                new_section[key] = edited[key]
        replacements[str(source_id)] = new_section
        submitted_order.append(new_section)

    if preserve_section_ids is None:
        # Normal mode submits every section; omission means intentional deletion.
        merged = submitted_order
    else:
        # Longer-only mode submits just the visible sections. Retain source
        # sections that were hidden by the threshold and omit deleted visible
        # sections. Then put new split sections back in audio-time order.
        preserve_ids = {str(section_id) for section_id in preserve_section_ids}
        merged = []
        for section in original_sections:
            if not isinstance(section, dict):
                continue
            source_id = section.get("section_id")
            key = str(source_id) if source_id is not None else None
            if key in replacements:
                merged.append(replacements[key])
            elif key in preserve_ids:
                merged.append(section)
        merged.extend(new_sections)
        def section_start(section: dict) -> tuple[float, float]:
            try:
                start = float(section.get("start_time", 0))
            except (TypeError, ValueError):
                start = 0.0
            try:
                end = float(section.get("end_time", start))
            except (TypeError, ValueError):
                end = start
            return start, end
        merged.sort(key=section_start)

    if renumber_section_ids:
        for index, section in enumerate(merged, 1):
            section["section_id"] = f"section-{index}"

    result["sections"] = merged
    return result


class EditorServer(ThreadingHTTPServer):
    daemon_threads = True

    def __init__(
        self, address, handler, parent_folder: Path, sections: bool,
        longer_seconds: float | None = None,
    ):
        super().__init__(address, handler)
        self.parent_folder = parent_folder.resolve()
        self.sections = sections
        self.longer_seconds = longer_seconds

    @staticmethod
    def _has_hidden_part(relative_path: Path) -> bool:
        return any(part.startswith(".") for part in relative_path.parts)

    def project_folders(self) -> list[Path]:
        """Return valid project folders found recursively below the parent."""
        projects: list[Path] = []
        try:
            candidates = list(self.parent_folder.rglob("*.json"))
            # The configured root can itself be one project.
            candidates.extend(self.parent_folder.glob("*.json"))

            for json_path in candidates:
                if not json_path.is_file() or json_path.name.startswith("."):
                    continue
                if transcript_payload(json_path) is None:
                    continue
                folder = json_path.parent.resolve()
                try:
                    relative = folder.relative_to(self.parent_folder)
                except ValueError:
                    continue
                if self._has_hidden_part(relative):
                    continue
                if self.resolve_project(self.project_key(folder)) is not None:
                    projects.append(folder)
        except OSError:
            return []

        return sorted(
            set(projects),
            key=lambda path: path.relative_to(self.parent_folder).as_posix().casefold(),
        )

    def project_key(self, folder: Path) -> str:
        relative = folder.resolve().relative_to(self.parent_folder)
        return ROOT_PROJECT_KEY if not relative.parts else relative.as_posix()

    def resolve_project(self, name: str) -> tuple[Path, Path, Path] | None:
        """Resolve a recursive project path safely below the parent folder."""
        raw_name = str(name).strip().replace("\\", "/")
        if raw_name == ROOT_PROJECT_KEY:
            folder = self.parent_folder
        else:
            relative = Path(raw_name)
            if (
                not raw_name
                or relative.is_absolute()
                or any(part in {"", ".", ".."} or part.startswith(".") for part in relative.parts)
            ):
                return None

            folder = (self.parent_folder / relative).resolve()
            try:
                checked_relative = folder.relative_to(self.parent_folder)
            except ValueError:
                return None
            if self._has_hidden_part(checked_relative):
                return None
        if not folder.is_dir():
            return None

        audio_candidates = sorted(
            (
                path for path in folder.iterdir()
                if path.is_file() and path.suffix.casefold() == ".mp3"
                and not path.name.startswith(".")
            ),
            key=lambda path: path.name.casefold(),
        )
        if not audio_candidates:
            return None

        json_options = []
        for candidate in folder.glob("*.json"):
            if candidate.name.startswith("."):
                continue
            payload = transcript_payload(candidate)
            if payload is None:
                continue
            audio_name = Path(str(payload.get("audio_file") or "")).name if isinstance(payload, dict) else ""
            matching_audio = next(
                (audio for audio in audio_candidates if audio.name.casefold() == audio_name.casefold()),
                None,
            )
            json_options.append((0 if matching_audio else 1, *transcript_json_priority(candidate), candidate, matching_audio))
        if not json_options:
            return None
        json_options.sort(key=lambda option: option[:3])
        _, _, _, json_path, audio = json_options[0]
        if audio is None:
            audio = audio_candidates[0]
        return folder, audio.resolve(), json_path.resolve()

    def resolve_audio(self, project_name: str) -> Path | None:
        project = self.resolve_project(project_name)
        return project[1] if project else None

    def resolve_json_for_audio(
        self,
        project_name: str,
        existing_only: bool = False,
    ) -> Path | None:
        project = self.resolve_project(project_name)
        return project[2] if project else None


# Auto-align tuning. These values are intentionally grouped here.
AUTO_ALIGN_FRAME_MS = 10
AUTO_ALIGN_SMOOTH_MS = 80
AUTO_ALIGN_CONTEXT_SECONDS = 1.5
AUTO_ALIGN_MIN_QUIET_SECONDS = 0.28
AUTO_ALIGN_ALLOWED_SPIKE_SECONDS = 0.03
AUTO_ALIGN_END_PADDING_SECONDS = 0.00
AUTO_ALIGN_ABSOLUTE_FLOOR = 0.00075
AUTO_ALIGN_NOISE_MULTIPLIER = 2.6
AUTO_ALIGN_CONTEXT_RATIO = 0.040
AUTO_ALIGN_MAX_THRESHOLD = 0.0060


def _percentile(values: list[float], fraction: float) -> float:
    if not values:
        return 0.0
    ordered = sorted(values)
    index = max(0, min(len(ordered) - 1, round((len(ordered) - 1) * fraction)))
    return ordered[index]


def analyse_section_tail(
    audio_path: Path,
    section_start: float,
    current_end: float,
    next_start: float | None = None,
) -> dict:
    """Extend forward to the minimum point of the first sustained low-energy valley.

    The threshold is based mainly on audio immediately before ``current_end``.
    Later bursts before the next section cannot influence that threshold. Once
    the first genuine quiet valley is confirmed, all later energy is ignored.
    The returned boundary never moves backwards and never passes ``next_start``.
    """
    sample_rate = 16000
    frame_ms = AUTO_ALIGN_FRAME_MS
    frame_seconds = frame_ms / 1000.0
    frame_samples = sample_rate * frame_ms // 1000

    scan_start = max(0.0, current_end - AUTO_ALIGN_CONTEXT_SECONDS)
    search_offset = current_end - scan_start

    if next_start is not None:
        hard_limit = max(current_end, next_start)
    else:
        hard_limit = current_end + 15.0

    scan_seconds = max(frame_seconds, min(60.0, hard_limit - scan_start))
    command = [
        "ffmpeg", "-v", "error", "-ss", f"{scan_start:.3f}",
        "-t", f"{scan_seconds:.3f}", "-i", str(audio_path),
        "-ac", "1", "-ar", str(sample_rate), "-f", "f32le", "pipe:1",
    ]
    try:
        result = subprocess.run(
            command,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            check=True,
        )
    except FileNotFoundError as exc:
        raise RuntimeError(
            "ffmpeg is required for Align Unvalidated but was not found"
        ) from exc
    except subprocess.CalledProcessError as exc:
        message = exc.stderr.decode("utf-8", errors="replace").strip()
        raise RuntimeError(
            f"ffmpeg could not decode the audio: {message or exc}"
        ) from exc

    samples = array.array("f")
    samples.frombytes(result.stdout)
    if not samples:
        return {"aligned_end": round(current_end, 3), "mode": "no_audio"}

    rms_values: list[float] = []
    for offset in range(0, len(samples) - frame_samples + 1, frame_samples):
        frame = samples[offset:offset + frame_samples]
        energy = sum(float(value) * float(value) for value in frame) / len(frame)
        rms_values.append(math.sqrt(energy))
    if not rms_values:
        return {"aligned_end": round(current_end, 3), "mode": "no_frames"}

    smooth_frames = max(1, round(AUTO_ALIGN_SMOOTH_MS / frame_ms))
    half_window = smooth_frames // 2
    smoothed: list[float] = []
    for i in range(len(rms_values)):
        lo = max(0, i - half_window)
        hi = min(len(rms_values), i + half_window + 1)
        smoothed.append(sum(rms_values[lo:hi]) / (hi - lo))

    search_index = max(
        0,
        min(len(smoothed) - 1, round(search_offset / frame_seconds)),
    )

    # The context ends at the existing boundary and therefore represents the
    # current section only. A later high-energy burst cannot raise or lower the
    # threshold used to identify the first valley.
    context_start = max(0, search_index - round(1.2 / frame_seconds))
    context_values = smoothed[context_start:search_index + 1]
    context_level = _percentile(context_values, 0.75)

    # Estimate the local floor from the forward search, but use only its lowest
    # portion. This adapts to recording hiss while remaining independent of a
    # later spoken or sung burst.
    forward_values = smoothed[search_index:]
    noise_floor = _percentile(forward_values, 0.10)

    threshold = max(
        AUTO_ALIGN_ABSOLUTE_FLOOR,
        noise_floor * AUTO_ALIGN_NOISE_MULTIPLIER,
        context_level * AUTO_ALIGN_CONTEXT_RATIO,
    )
    threshold = min(threshold, AUTO_ALIGN_MAX_THRESHOLD)

    quiet_frames_required = max(
        1,
        round(AUTO_ALIGN_MIN_QUIET_SECONDS / frame_seconds),
    )
    allowed_spike_frames = max(
        0,
        round(AUTO_ALIGN_ALLOWED_SPIKE_SECONDS / frame_seconds),
    )

    quiet_start: int | None = None
    quiet_count = 0
    spike_count = 0

    for i in range(search_index, len(smoothed)):
        value = smoothed[i]

        if value <= threshold:
            if quiet_start is None:
                quiet_start = i
            quiet_count += 1
            spike_count = 0
        elif quiet_start is not None and spike_count < allowed_spike_frames:
            # Permit a very short click or isolated noisy frame inside an
            # otherwise continuous valley.
            spike_count += 1
        else:
            quiet_start = None
            quiet_count = 0
            spike_count = 0

        if quiet_start is not None and quiet_count >= quiet_frames_required:
            # The valley is now confirmed. Place the boundary at the lowest
            # energy frame inside this first confirmed valley, not at the first
            # frame that crossed the threshold. This better matches the visual
            # low point in the waveform and still prevents a later burst from
            # being included.
            confirmed_end = i + 1
            valley_values = smoothed[quiet_start:confirmed_end]
            minimum_offset = min(
                range(len(valley_values)),
                key=valley_values.__getitem__,
            )
            minimum_index = quiet_start + minimum_offset
            minimum_time = scan_start + minimum_index * frame_seconds
            valley_start_time = scan_start + quiet_start * frame_seconds

            aligned_end = max(
                current_end,
                minimum_time + AUTO_ALIGN_END_PADDING_SECONDS,
            )
            if next_start is not None:
                aligned_end = min(aligned_end, next_start)
            return {
                "aligned_end": round(aligned_end, 3),
                "mode": "first_valley_minimum",
                "threshold": threshold,
                "noise_floor": noise_floor,
                "context_level": context_level,
                "valley_start": round(valley_start_time, 3),
                "valley_minimum": round(minimum_time, 3),
                "valley_minimum_energy": valley_values[minimum_offset],
            }

    if next_start is not None:
        aligned_end = next_start
        mode = "next_section_start"
    else:
        aligned_end = scan_start + len(smoothed) * frame_seconds
        mode = "scan_limit"

    return {
        "aligned_end": round(max(current_end, aligned_end), 3),
        "mode": mode,
        "threshold": threshold,
        "noise_floor": noise_floor,
        "context_level": context_level,
    }


def project_validation_summary(json_path: Path) -> dict:
    """Return validation progress without modifying the project JSON."""
    try:
        payload = json.loads(json_path.read_text(encoding="utf-8"))
    except (OSError, json.JSONDecodeError):
        return {
            "all_validated": False,
            "validated_count": 0,
            "section_count": 0,
        }

    if isinstance(payload, dict):
        sections = payload.get("sections", [])
    elif isinstance(payload, list):
        sections = payload
    else:
        sections = []

    if not isinstance(sections, list):
        sections = []

    valid_sections = [section for section in sections if isinstance(section, dict)]
    validated_count = sum(
        1 for section in valid_sections if section.get("validated") is True
    )
    section_count = len(valid_sections)

    return {
        # An empty project is not treated as completed.
        "all_validated": section_count > 0 and validated_count == section_count,
        "validated_count": validated_count,
        "section_count": section_count,
    }


def sections_over_duration(json_path: Path, seconds: float) -> list[dict]:
    """Read sections whose audio span is strictly longer than the threshold."""
    try:
        payload = json.loads(json_path.read_text(encoding="utf-8"))
    except (OSError, json.JSONDecodeError):
        return []
    sections = payload.get("sections", []) if isinstance(payload, dict) else payload
    if not isinstance(sections, list):
        return []
    result = []
    for section in sections:
        if not isinstance(section, dict):
            continue
        try:
            duration = float(section.get("end_time", 0)) - float(section.get("start_time", 0))
        except (TypeError, ValueError):
            continue
        if duration > seconds:
            result.append(section)
    return result


class Handler(BaseHTTPRequestHandler):
    server_version = "GurbaniSectionEditor/recursive-projects-v6-valley-minimum"

    @property
    def app(self) -> EditorServer:
        return self.server  # type: ignore[return-value]

    def log_message(self, fmt: str, *args):
        sys.stdout.write("[%s] %s\n" % (self.log_date_time_string(), fmt % args))

    def send_json(self, data: object, status: int = 200):
        body = json.dumps(data, ensure_ascii=False).encode("utf-8")
        self.send_response(status)
        self.send_header("Content-Type", "application/json; charset=utf-8")
        self.send_header("Content-Length", str(len(body)))
        self.send_header("Cache-Control", "no-store")
        self.end_headers()
        self.wfile.write(body)

    def send_error_json(self, status: int, message: str):
        self.send_json({"error": message}, status)

    def do_GET(self):
        parsed = urlparse(self.path)
        path = parsed.path
        query = parse_qs(parsed.query)

        if path == "/":
            try:
                body = INDEX_FILE.read_bytes()
            except OSError as exc:
                return self.send_error_json(500, f"Cannot read index.html: {exc}")
            self.send_response(200)
            self.send_header("Content-Type", "text/html; charset=utf-8")
            self.send_header("Content-Length", str(len(body)))
            self.send_header("Cache-Control", "no-store")
            self.end_headers()
            self.wfile.write(body)
            return

        if path == "/api/server-info":
            return self.send_json({
                "version": "mp3-aligned-transcript-v3",
                "parent_folder": str(self.app.parent_folder),
                "longer_seconds": self.app.longer_seconds,
                "project_rule": "recursive non-hidden folders containing a transcript JSON with sections and an MP3",
            })

        if path == "/api/files":
            files = []
            for folder in self.app.project_folders():
                project_key = self.app.project_key(folder)
                project = self.app.resolve_project(project_key)
                if project is None:
                    continue
                _, audio, json_path = project
                validation = project_validation_summary(json_path)
                if self.app.longer_seconds is not None:
                    matching_sections = sections_over_duration(
                        json_path, self.app.longer_seconds
                    )
                    if not matching_sections:
                        continue
                    validated_count = sum(
                        1 for section in matching_sections
                        if section.get("validated") is True
                    )
                    validation = {
                        "all_validated": validated_count == len(matching_sections),
                        "validated_count": validated_count,
                        "section_count": len(matching_sections),
                    }
                files.append({
                    "name": project_key,
                    "display_name": (
                        self.app.parent_folder.name
                        if project_key == ROOT_PROJECT_KEY
                        else project_key.replace("/", " / ")
                    ),
                    "audio_name": audio.name,
                    "audio_file_name": audio.name,
                    "json_name": json_path.name,
                    "has_json": True,
                    "all_validated": validation["all_validated"],
                    "validated_count": validation["validated_count"],
                    "section_count": validation["section_count"],
                    "audio_size": audio.stat().st_size,
                    "modified": datetime.fromtimestamp(
                        max(audio.stat().st_mtime, json_path.stat().st_mtime)
                    ).isoformat(timespec="seconds"),
                })
            return self.send_json({
                "folder": str(self.app.parent_folder),
                "longer_seconds": self.app.longer_seconds,
                "files": files,
            })

        if path == "/api/project":
            name = query.get("name", [""])[0]
            project = self.app.resolve_project(name)
            if project is None:
                return self.send_error_json(
                    404,
                    "Project folder not found or it does not contain a transcript JSON with sections and an MP3",
                )
            folder, audio, json_path = project
            try:
                payload = json.loads(json_path.read_text(encoding="utf-8"))
            except Exception as exc:
                return self.send_error_json(500, f"Cannot read JSON: {exc}")
            return self.send_json({
                "audio_name": name,
                "audio_file_name": audio.name,
                "project_name": name,
                "json_name": json_path.name,
                "audio_url": f"/api/audio?name={quote(name)}",
                "data": clean_payload(payload),
            })

        if path == "/api/audio":
            name = query.get("name", [""])[0]
            audio = self.app.resolve_audio(name)
            if not audio:
                return self.send_error_json(404, "Project audio not found")
            return self.serve_file_with_range(audio)

        self.send_error_json(404, "Not found")

    def serve_file_with_range(self, path: Path):
        size = path.stat().st_size
        mime = mimetypes.guess_type(path.name)[0] or "application/octet-stream"
        start, end = 0, size - 1
        status = HTTPStatus.OK
        range_header = self.headers.get("Range")
        if range_header and range_header.startswith("bytes="):
            try:
                spec = range_header.removeprefix("bytes=").split(",", 1)[0]
                first, last = spec.split("-", 1)
                if first:
                    start = int(first)
                if last:
                    end = int(last)
                else:
                    end = size - 1
                start = max(0, min(start, size - 1))
                end = max(start, min(end, size - 1))
                status = HTTPStatus.PARTIAL_CONTENT
            except Exception:
                return self.send_error_json(416, "Invalid Range header")
        length = end - start + 1
        self.send_response(status)
        self.send_header("Content-Type", mime)
        self.send_header("Accept-Ranges", "bytes")
        self.send_header("Content-Length", str(length))
        if status == HTTPStatus.PARTIAL_CONTENT:
            self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
        self.send_header("Cache-Control", "no-cache")
        self.end_headers()
        with path.open("rb") as handle:
            handle.seek(start)
            remaining = length
            while remaining > 0:
                chunk = handle.read(min(1024 * 1024, remaining))
                if not chunk:
                    break
                self.wfile.write(chunk)
                remaining -= len(chunk)

    def do_POST(self):
        parsed = urlparse(self.path)
        if parsed.path not in {"/api/save", "/api/auto-align"}:
            return self.send_error_json(404, "Not found")
        try:
            length = int(self.headers.get("Content-Length", "0"))
        except ValueError:
            return self.send_error_json(400, "Invalid Content-Length")
        if length <= 0 or length > 50 * 1024 * 1024:
            return self.send_error_json(400, "Invalid request size")
        try:
            request = json.loads(self.rfile.read(length).decode("utf-8"))
        except Exception as exc:
            return self.send_error_json(400, f"Invalid JSON request: {exc}")
        if not isinstance(request, dict):
            return self.send_error_json(400, "Request must be an object")

        if parsed.path == "/api/auto-align":
            audio_name = str(request.get("audio_name") or "")
            audio = self.app.resolve_audio(audio_name)
            if not audio:
                return self.send_error_json(404, "Project audio not found")
            try:
                section_start = float(request.get("section_start", 0))
                current_end = float(request.get("current_end", section_start))
                next_value = request.get("next_start")
                next_start = None if next_value is None else float(next_value)
            except (TypeError, ValueError):
                return self.send_error_json(400, "Invalid section timing")
            if current_end <= section_start:
                return self.send_error_json(400, "Section end must be after its start")
            if next_start is not None and next_start <= section_start + 0.02:
                return self.send_error_json(400, "Next section must start after this section")
            try:
                result = analyse_section_tail(
                    audio, section_start, current_end, next_start
                )
            except RuntimeError as exc:
                return self.send_error_json(500, str(exc))
            if result.get("mode") == "next_section_start":
                result["message"] = "Audible energy reaches the next section"
            elif result["aligned_end"] != round(current_end, 3):
                result["message"] = "Aligned to the end of the audible waveform"
            else:
                result["message"] = "No reliable waveform end was found"
            return self.send_json(result)

        audio_name = str(request.get("audio_name") or "")
        json_path = self.app.resolve_json_for_audio(audio_name)
        if not json_path:
            return self.send_error_json(400, "Invalid audio name")
        try:
            original_payload = json.loads(json_path.read_text(encoding="utf-8"))
        except Exception as exc:
            return self.send_error_json(500, f"Cannot read source JSON: {exc}")
        preserve_ids_value = request.get("preserve_section_ids")
        preserve_ids = (
            [str(value) for value in preserve_ids_value]
            if isinstance(preserve_ids_value, list)
            else None
        )
        payload = merge_editable_fields(
            original_payload,
            request.get("data"),
            preserve_section_ids=preserve_ids,
            renumber_section_ids=request.get("renumber_section_ids") is True,
        )

        try:
            json_path.parent.mkdir(parents=True, exist_ok=True)
            backup = None
            if json_path.exists():
                backup = json_path.with_suffix(json_path.suffix + ".bak")
                shutil.copy2(json_path, backup)
            fd, temp_name = tempfile.mkstemp(prefix=json_path.name + ".", suffix=".tmp", dir=json_path.parent)
            try:
                with os.fdopen(fd, "w", encoding="utf-8", newline="\n") as handle:
                    json.dump(payload, handle, ensure_ascii=False, indent=2)
                    handle.write("\n")
                    handle.flush()
                    os.fsync(handle.fileno())
                os.replace(temp_name, json_path)
            finally:
                if os.path.exists(temp_name):
                    os.unlink(temp_name)
        except Exception as exc:
            return self.send_error_json(500, f"Save failed: {exc}")

        return self.send_json({
            "saved": True,
            "json_name": json_path.name,
            "sections": len(payload["sections"]),
            "backup_name": backup.name if backup else None,
            "data": payload,
        })


def main() -> int:
    parser = argparse.ArgumentParser(
        description=(
            "Serve the editor from a parent folder and recursively discover "
            "folders containing transcript JSON files with sections and an MP3"
        )
    )
    parser.add_argument(
        "--parent-folder",
        "--kirtan-folder",
        dest="parent_folder",
        default="kirtan",
        help=(
            "Parent folder searched recursively. Each project folder must contain "
            "a transcript JSON file with sections and an MP3. "
            "--kirtan-folder remains as a backwards-compatible alias."
        ),
    )
    parser.add_argument("--host", default=HOST)
    parser.add_argument("--port", type=int, default=DEFAULT_PORT)
    parser.add_argument("--sections", default=False)
    parser.add_argument(
        "--longer",
        type=float,
        default=None,
        metavar="SECONDS",
        help="Show only projects and sections with a duration longer than SECONDS",
    )
    args = parser.parse_args()

    if args.longer is not None and args.longer <= 0:
        parser.error("--longer must be greater than 0 seconds")

    folder = Path(args.parent_folder).expanduser().resolve()
    folder.mkdir(parents=True, exist_ok=True)
    server = EditorServer(
        (args.host, args.port), Handler, folder, args.sections,
        longer_seconds=args.longer,
    )
    print("Server version: mp3-aligned-transcript-v3")
    print(f"Parent folder: {folder}")
    print("Projects: recursive non-hidden folders containing a transcript JSON with sections and an MP3")
    if args.longer is not None:
        print(f"Longer-only filter: sections longer than {args.longer:g} seconds")
    print(f"Open: http://{args.host}:{args.port}")
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        print("\nStopping server")
    finally:
        server.server_close()
    return 0


if __name__ == "__main__":
    raise SystemExit(main())