/*
 * Media extraction: classify one core message into media items.
 * Rules: docs/media-scraper.md. Third-party embeds are never downloaded.
 */

import type { CoreAttachment, CoreEmbed, CoreSticker, CoreMessage, MediaKind, MediaMessage } from "./types.js";

const IMAGE_EXT = new Set(["png", "jpg", "jpeg", "webp", "bmp", "avif"]);
const GIF_EXT = new Set(["gif"]);
const VIDEO_EXT = new Set(["mp4", "webm", "mov", "mkv"]);
const AUDIO_EXT = new Set(["mp3", "m4a", "ogg", "wav", "flac"]);

/** Sticker formatType to file extension. 3 is Lottie JSON; not archived. */
const STICKER_EXT: Record<number, string | undefined> = { 1: "png", 2: "apng", 4: "gif" };

/** A media item extracted from a message. `url` is the original source link. */
export interface ExtractedMedia {
    kind: MediaKind;
    url: string;
    provider: string | null;
    contentType: string | null;
    size: number | null;
    width: number | null;
    height: number | null;
    durationSecs: number | null;
    /** False for every embed. Downloads are a later step, never for third-party embeds. */
    downloaded: boolean;
    previewUrl: string | null;
}

function extension(filename: string | null | undefined): string {
    const match = /\.([a-z0-9]+)$/i.exec(filename ?? "");
    return match ? match[1].toLowerCase() : "";
}

function classifyAttachment(attachment: CoreAttachment, voiceMessage: boolean): MediaKind | null {
    const ext = extension(attachment.filename);
    const type = (attachment.contentType ?? "").toLowerCase();

    // A voice-message flag wins unless the file is clearly an image or a video.
    if (
        voiceMessage &&
        !IMAGE_EXT.has(ext) &&
        !GIF_EXT.has(ext) &&
        !VIDEO_EXT.has(ext) &&
        !type.startsWith("image/") &&
        !type.startsWith("video/")
    ) {
        return "audio";
    }

    if (AUDIO_EXT.has(ext) || type.startsWith("audio/")) return "audio";
    if (VIDEO_EXT.has(ext) || type.startsWith("video/")) return "video";
    if (GIF_EXT.has(ext) || type === "image/gif") return "gif";
    if (IMAGE_EXT.has(ext) || type.startsWith("image/")) return "image";
    return null;
}

function hostname(url: string | null): string | null {
    if (!url) return null;
    try {
        return new URL(url).hostname;
    } catch {
        return null;
    }
}

function extractEmbed(embed: CoreEmbed): ExtractedMedia | null {
    const provider = embed.provider ?? hostname(embed.url);
    const common = {
        provider,
        downloaded: false,
        size: null,
        width: null,
        height: null,
        durationSecs: null
    };

    if (embed.videoUrl) {
        return {
            ...common,
            kind: "video",
            url: embed.url ?? embed.videoUrl,
            contentType: null,
            previewUrl: embed.thumbnailUrl ?? embed.imageUrl
        };
    }

    const providerKey = (provider ?? "").toLowerCase();
    if (embed.type === "gifv" || providerKey.includes("tenor") || providerKey.includes("giphy")) {
        return {
            ...common,
            kind: "gif",
            url: embed.url ?? embed.imageUrl ?? "",
            contentType: null,
            previewUrl: embed.thumbnailUrl ?? embed.imageUrl
        };
    }

    if (embed.imageUrl) {
        return {
            ...common,
            kind: "image",
            url: embed.url ?? embed.imageUrl,
            contentType: null,
            previewUrl: embed.thumbnailUrl ?? embed.imageUrl
        };
    }

    return null;
}

function extractSticker(sticker: CoreSticker): ExtractedMedia | null {
    if (!sticker.id) return null;
    const ext = STICKER_EXT[sticker.formatType ?? 1];
    if (!ext) return null;

    return {
        kind: ext === "gif" ? "gif" : "image",
        url: `https://cdn.discordapp.com/stickers/${sticker.id}.${ext}`,
        provider: "discord",
        contentType: null,
        size: null,
        width: null,
        height: null,
        durationSecs: null,
        downloaded: false,
        previewUrl: null
    };
}

function extractFrom(message: MediaMessage): ExtractedMedia[] {
    const items: ExtractedMedia[] = [];

    for (const attachment of message.attachments ?? []) {
        if (!attachment.url) continue;
        const kind = classifyAttachment(attachment, message.voiceMessage);
        if (!kind) continue;
        items.push({
            kind,
            url: attachment.url,
            provider: "discord",
            contentType: attachment.contentType,
            size: attachment.size,
            width: attachment.width,
            height: attachment.height,
            durationSecs: attachment.durationSecs,
            downloaded: false,
            previewUrl: null
        });
    }

    for (const embed of message.embeds ?? []) {
        const item = extractEmbed(embed);
        if (item?.url) items.push(item);
    }

    for (const sticker of message.stickerItems ?? []) {
        const item = extractSticker(sticker);
        if (item) items.push(item);
    }

    return items;
}

/** Extract every media item from a message, including forwarded snapshots. Deduped by URL. */
export function extractMedia(message: CoreMessage): ExtractedMedia[] {
    const items = extractFrom(message);

    for (const snapshot of message.forwarded ?? []) {
        items.push(...extractFrom(snapshot));
    }

    const seen = new Set<string>();
    return items.filter(item => {
        if (seen.has(item.url)) return false;
        seen.add(item.url);
        return true;
    });
}