const std = @import("std");
const bencode = @import("bencode.zig");

// https://wiki.theory.org/BitTorrentSpecification#Tracker_Response
pub const TrackerResp = struct {
    // interval: u64,
    peers: []std.net.Address,

    pub fn parse(a: std.mem.Allocator, b: bencode.BValue) !TrackerResp {
        var ipl = std.ArrayList(std.net.Address).init(a);
        defer ipl.deinit();
        var d = b.asDict() catch return error.Malformatted;
        var pb = d.get("peers") orelse return error.Malformatted;
        var ps = pb.asString() catch return error.Malformatted;
        if ((ps.len % 6) != 0) return error.Malformatted;
        for (0..ps.len / 6) |ix| {
            const start = ix * 6;
            const port = std.mem.readInt(u16, ps[start + 4 .. start + 6][0..2], .big);
            var ip = [_]u8{0} ** 4;
            @memcpy(&ip, ps[start .. start + 4]);
            try ipl.append(std.net.Address.initIp4(ip, port));
        }
        return .{
            .peers = try ipl.toOwnedSlice(),
        };
    }

    pub fn deinit(self: *TrackerResp, a: std.mem.Allocator) void {
        a.free(self.peers);
    }
};

pub fn trackerRequestUrl(a: std.mem.Allocator, info_hash: [20]u8, peer_id: [20]u8, left: usize, announce: []const u8) ![]const u8 {
    var q = std.StringHashMap([]const u8).init(a);
    defer q.deinit();
    try q.put("info_hash", &info_hash);
    try q.put("peer_id", &peer_id);
    try q.put("port", "6881");
    try q.put("uploaded", "0");
    try q.put("downloaded", "0");
    var buf_left = [_]u8{0} ** 1024;
    try q.put("left", try std.fmt.bufPrint(&buf_left, "{}", .{left}));
    try q.put("compact", "1");
    var qs = try toqs(a, q);
    defer a.free(qs);
    return try std.fmt.allocPrint(a, "{s}?{s}", .{ announce, qs });
}

fn toqs(a: std.mem.Allocator, hm: std.StringHashMap([]const u8)) ![]const u8 {
    var al = std.ArrayList(u8).init(a);
    defer al.deinit();
    var w = al.writer();
    var it = hm.iterator();
    var first = true;
    while (it.next()) |entry| {
        if (!first) try w.writeByte('&');
        try std.Uri.writeEscapedQuery(w, entry.key_ptr.*);
        try w.writeByte('=');
        try std.Uri.writeEscapedQuery(w, entry.value_ptr.*);
        first = false;
    }
    return try al.toOwnedSlice();
}