"""Paths, constants, and the timebase convention.

Timebase convention (FROZEN CONTRACT — do not change without a change request):

    ``t_global`` is the master timeline in seconds.
    For a video *v* with ``offset_ms`` and ``drift_ppm``::

        t_video = (t_global - offset_ms / 1000) * (1 + drift_ppm * 1e-6)

    The reference video has ``offset_ms == 0`` (and ``drift_ppm == 0``). A positive
    ``offset_ms`` means the video started recording *later* than the master zero, so at a
    given ``t_global`` its local playhead is earlier. Use :func:`t_video_from_global` and
    :func:`t_global_from_video` everywhere — never re-derive the algebra inline. The
    frontend mirrors :func:`t_video_from_global` in ``transport.js``.
"""

from __future__ import annotations

import os
from pathlib import Path

# ---------------------------------------------------------------------------
# Paths. The data root can be overridden with FESTIVAL4D_DATA_DIR (used by tests
# to run against a temporary project without touching the repo's data/).
# ---------------------------------------------------------------------------
REPO_ROOT = Path(__file__).resolve().parents[2]


def _data_dir() -> Path:
    env = os.environ.get("FESTIVAL4D_DATA_DIR")
    return Path(env).resolve() if env else REPO_ROOT / "data"


DATA_DIR = _data_dir()
RAW_DIR = DATA_DIR / "raw"          # user drops source videos here (gitignored)
WORK_DIR = DATA_DIR / "work"        # extracted wavs, frames, colmap workspace (gitignored)
AUDIO_DIR = WORK_DIR / "audio"      # per-video mono 16 kHz wavs (ingest)
FRAMES_DIR = WORK_DIR / "frames"    # sampled JPEGs for SfM
COLMAP_DIR = WORK_DIR / "colmap"    # COLMAP workspace
DB_PATH = DATA_DIR / "project.db"   # SQLite (gitignored)

POINTS_PLY = WORK_DIR / "points.ply"        # reconstructed / synthetic point cloud
SPLAT_PLY = WORK_DIR / "splat.ply"          # optional 3DGS splat (trained externally, e.g. via MODELBEAST — see docs/modelbeast-crossover.md); viewer prefers it over the point cloud
SYNC_JSON = WORK_DIR / "sync.json"          # exported sync solution (lane A)
GROUND_TRUTH_JSON = WORK_DIR / "ground_truth.json"  # synthetic fixture ground truth

# ---------------------------------------------------------------------------
# Constants
# ---------------------------------------------------------------------------
FRONTEND_ORIGINS = [
    "http://localhost:5173",
    "http://127.0.0.1:5173",
]
# Local-only, single-user, offline tool: allow any localhost origin so a Vite dev server on
# a fallback port (5174, …) still works. Kept alongside the explicit 5173 default.
FRONTEND_ORIGIN_REGEX = r"http://(localhost|127\.0\.0\.1)(:\d+)?"
API_HOST = "127.0.0.1"
API_PORT = 8000

AUDIO_SAMPLE_RATE = 16_000          # ingest extracts mono 16 kHz for sync (M1)

# Synthetic fixture parameters (M0). Ground-truth offsets are deliberately odd,
# non-round numbers so a naive integer-second guesser can't accidentally "pass".
SYNTH_VIDEO_W = 640
SYNTH_VIDEO_H = 360
SYNTH_FPS = 30
SYNTH_DURATION_S = 20.0
SYNTH_AUDIO_SR = 48_000
SYNTH_OFFSETS_MS = (0.0, 1370.0, -842.0)   # cam0 is the reference (offset 0)


def t_video_from_global(t_global: float, offset_ms: float, drift_ppm: float = 0.0) -> float:
    """Map master-timeline seconds to a video's local playhead seconds (FROZEN)."""
    return (t_global - offset_ms / 1000.0) * (1.0 + drift_ppm * 1e-6)


def t_global_from_video(t_video: float, offset_ms: float, drift_ppm: float = 0.0) -> float:
    """Inverse of :func:`t_video_from_global` (FROZEN)."""
    return t_video / (1.0 + drift_ppm * 1e-6) + offset_ms / 1000.0