"""Shared media type constants and helpers.

Single source of truth for the file extensions and MIME types handled by the
image support (roadmap #108) and reused by the audio/video players (#109).
Keeping these sets here avoids the previous duplication (``indexer.py``,
``attachment_indexer.py`` and ``main.py`` each carried their own copy).
"""

from __future__ import annotations

import mimetypes

# Image extensions viewable in the browser (HEIC/HEIF deliberately excluded —
# no browser decodes them natively; see roadmap #108).
IMAGE_EXTENSIONS: frozenset[str] = frozenset({
    ".png", ".jpg", ".jpeg", ".gif", ".svg", ".webp", ".bmp", ".ico",
})

# Audio extensions (socle for #109, not wired into the index yet).
AUDIO_EXTENSIONS: frozenset[str] = frozenset({
    ".mp3", ".m4a", ".aac", ".wav", ".ogg", ".oga", ".opus", ".flac",
})

# Video extensions (socle for #109, not wired into the index yet).
VIDEO_EXTENSIONS: frozenset[str] = frozenset({
    ".mp4", ".webm", ".mov", ".m4v",
})

MEDIA_EXTENSIONS: frozenset[str] = IMAGE_EXTENSIONS | AUDIO_EXTENSIONS | VIDEO_EXTENSIONS

# Explicit MIME types for extensions ``mimetypes`` gets wrong or does not know.
_MIME_OVERRIDES: dict[str, str] = {
    ".jpg": "image/jpeg",
    ".jpeg": "image/jpeg",
    ".svg": "image/svg+xml",
    ".ico": "image/x-icon",
    ".webp": "image/webp",
    ".m4a": "audio/mp4",
    ".oga": "audio/ogg",
    ".opus": "audio/ogg",
    ".mov": "video/quicktime",
    ".m4v": "video/mp4",
}


def is_image(ext: str) -> bool:
    """Return True when *ext* (with leading dot, any case) is an image."""
    return ext.lower() in IMAGE_EXTENSIONS


def is_audio(ext: str) -> bool:
    """Return True when *ext* is an audio extension."""
    return ext.lower() in AUDIO_EXTENSIONS


def is_video(ext: str) -> bool:
    """Return True when *ext* is a video extension."""
    return ext.lower() in VIDEO_EXTENSIONS


def is_media(ext: str) -> bool:
    """Return True when *ext* is any supported image/audio/video extension."""
    return ext.lower() in MEDIA_EXTENSIONS


def media_mime_type(path: str) -> str:
    """Return the best MIME type for *path* (extension based).

    Falls back to ``application/octet-stream`` when the type is unknown.
    """
    lower = path.lower()
    for ext, mime in _MIME_OVERRIDES.items():
        if lower.endswith(ext):
            return mime
    guessed, _ = mimetypes.guess_type(path)
    return guessed or "application/octet-stream"