//! Media types for files served byte for byte.
//!
//! A fixed table rather than a system lookup: Python's `mimetypes` consults
//! `/etc/mime.types` where it exists, so smolweb's `Content-Type` for the same
//! file differs between hosts. Determinism is worth more here than coverage of
//! the long tail, and an unknown extension has a correct answer anyway.

use std::path::Path;

/// Returned when the extension is absent or unrecognised.
pub const DEFAULT: &str = "application/octet-stream";

/// The media type to serve `path` as, by extension, compared case-insensitively.
pub fn media_type(path: &Path) -> &'static str {
    let Some(extension) = path.extension().and_then(|e| e.to_str()) else { return DEFAULT };
    let extension = extension.to_ascii_lowercase();
    TABLE
        .iter()
        .find(|(known, _)| *known == extension)
        .map(|(_, media_type)| *media_type)
        .unwrap_or(DEFAULT)
}

/// Extensions a folder of Markdown actually carries. Text types name their
/// charset, since a client has no other way to know it.
const TABLE: &[(&str, &str)] = &[
    // Images
    ("png", "image/png"),
    ("jpg", "image/jpeg"),
    ("jpeg", "image/jpeg"),
    ("gif", "image/gif"),
    ("webp", "image/webp"),
    ("svg", "image/svg+xml"),
    ("ico", "image/vnd.microsoft.icon"),
    ("avif", "image/avif"),
    // Documents and data
    ("txt", "text/plain; charset=utf-8"),
    ("gmi", "text/gemini; charset=utf-8"),
    ("css", "text/css; charset=utf-8"),
    ("html", "text/html; charset=utf-8"),
    ("xml", "application/xml"),
    ("json", "application/json"),
    ("toml", "application/toml"),
    ("pdf", "application/pdf"),
    ("asc", "text/plain; charset=utf-8"),
    // Audio and video
    ("mp3", "audio/mpeg"),
    ("ogg", "audio/ogg"),
    ("opus", "audio/ogg"),
    ("flac", "audio/flac"),
    ("wav", "audio/wav"),
    ("mp4", "video/mp4"),
    ("webm", "video/webm"),
    // Archives and fonts
    ("gz", "application/gzip"),
    ("zip", "application/zip"),
    ("tar", "application/x-tar"),
    ("woff2", "font/woff2"),
];

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn recognises_common_extensions() {
        assert_eq!(media_type(Path::new("img.png")), "image/png");
        assert_eq!(media_type(Path::new("a/b/photo.JPEG")), "image/jpeg");
        assert_eq!(media_type(Path::new("notes.txt")), "text/plain; charset=utf-8");
    }

    #[test]
    fn falls_back_for_the_unknown_and_the_extensionless() {
        assert_eq!(media_type(Path::new("mystery.xyz")), DEFAULT);
        assert_eq!(media_type(Path::new("LICENSE")), DEFAULT);
        assert_eq!(media_type(Path::new("archive.tar.zst")), DEFAULT);
    }
}