1/*
2 * Copyright (c) 2026 DataPond D-Library Pty Ltd. ("The Sanctuary")
3 * Non-Profit Public Library — The World Library
4 * 
5 * D-SAFE Certification issued by POND Enterprise.
6 * Published under the D-Open Code Sovereign Licence v1.0 framework
7 * DataPond D-Library All exclusive Right reserved on modifiying the code - CC Attribution to data pond, Non modifiable, Non Commercial.
8 * https://registry.world.bibliotech.com/licence
9 * Source code donated to DataPond D-Library by it's author: data pond.
10 * 
11 * Technical Guardian ("The Shield"): Pond Enterprise Pty Ltd. (ACN 694 747 987)
12 * All liability claims about D-SAFE certification issues coming from the published D-Safe direction must be addressed with Pond Enterprise Pty Ltd.
13 * Code Modification automatically voids the certified liability protection provided by Pond Enterprise.
14 */
15// Gateway-fallback streaming fetch with progress tracking.
16
17export const DEFAULT_GATEWAYS = [
18    'https://arweave.net',
19    'https://permagate.io',
20    'https://ar-io.dev',
21];
22
23// Wraps a Response body in a counting ReadableStream — zero clone overhead (§2.11).
24export function trackProgress(
25    response: Response,
26    onProgress: (loaded: number, total?: number) => void,
27): Response {
28    const reader  = response.body!.getReader();
29    const total   = response.headers.get('content-length')
30        ? parseInt(response.headers.get('content-length')!, 10)
31        : undefined;
32    let loaded = 0;
33    const stream = new ReadableStream({
34        async pull(controller) {
35            const { done, value } = await reader.read();
36            if (done) { controller.close(); return; }
37            loaded += value.byteLength;
38            onProgress(loaded, total);
39            controller.enqueue(value);
40        },
41        cancel(reason) { return reader.cancel(reason); },
42    });
43    return new Response(stream, response);
44}
45
46export async function fetchFromGateways(
47    txId: string,
48    gateways: string[],
49    onProgress: (loaded: number, total?: number) => void,
50): Promise<Response> {
51    let lastError: unknown;
52    for (const gw of gateways) {
53        try {
54            const url  = `${gw}/${txId}`;
55            const resp = await fetch(url, { mode: 'cors' });
56            // CORS guard — opaque responses must never reach cache.put (§2.5).
57            if (resp.type === 'opaque') {
58                throw new Error(`[downloader_v2] opaque response for ${txId} — CORS not granted`);
59            }
60            if (!resp.ok) {
61                throw new Error(`[downloader_v2] HTTP ${resp.status} from ${gw}`);
62            }
63            const tracked = trackProgress(resp, onProgress);
64            
65            const reader = tracked.body!.getReader();
66            const { done, value } = await reader.read();
67            
68            let finalStream: ReadableStream;
69            if (!value) {
70                finalStream = new ReadableStream({
71                    start(controller) { controller.close(); }
72                });
73            } else {
74                const isGzip = value.length >= 2 && value[0] === 0x1f && value[1] === 0x8b;
75                
76                const combinedStream = new ReadableStream({
77                    start(controller) {
78                        controller.enqueue(value);
79                    },
80                    async pull(controller) {
81                        const { done, value: chunk } = await reader.read();
82                        if (done) {
83                            controller.close();
84                        } else {
85                            controller.enqueue(chunk);
86                        }
87                    },
88                    cancel(reason) {
89                        return reader.cancel(reason);
90                    }
91                });
92
93                finalStream = isGzip ? combinedStream.pipeThrough(new DecompressionStream('gzip')) : combinedStream;
94            }
95
96            // Mark origin for diagnostics.
97            const headers = new Headers(tracked.headers);
98            headers.set('X-DL2-Stored', new Date().toISOString());
99            headers.delete('content-length');
100            headers.delete('content-encoding');
101
102            return new Response(finalStream, { status: tracked.status, statusText: tracked.statusText, headers });
103        } catch (err) {
104            lastError = err;
105        }
106    }
107    throw lastError ?? new Error(`[downloader_v2] all gateways failed for ${txId}`);
108}
109