// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
//
// Francis Bouvier <francis@lightpanda.io>
// Pierre Tachoire <pierre@lightpanda.io>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

const std = @import("std");
const builtin = @import("builtin");
const posix = std.posix;
const Allocator = std.mem.Allocator;
const ArenaAllocator = std.heap.ArenaAllocator;

const Config = @import("../Config.zig");
const libcurl = @import("../sys/libcurl.zig");

const log = @import("lightpanda").log;
const assert = @import("lightpanda").assert;

pub const ENABLE_DEBUG = false;
const IS_DEBUG = builtin.mode == .Debug;

pub const Blob = libcurl.CurlBlob;
pub const WaitFd = libcurl.CurlWaitFd;
pub const writefunc_error = libcurl.curl_writefunc_error;

const Error = libcurl.Error;
const ErrorMulti = libcurl.ErrorMulti;
const errorFromCode = libcurl.errorFromCode;
const errorMFromCode = libcurl.errorMFromCode;
const errorCheck = libcurl.errorCheck;
const errorMCheck = libcurl.errorMCheck;

pub fn curl_version() [*c]const u8 {
    return libcurl.curl_version();
}

pub const Method = enum(u8) {
    GET = 0,
    PUT = 1,
    POST = 2,
    DELETE = 3,
    HEAD = 4,
    OPTIONS = 5,
    PATCH = 6,
    PROPFIND = 7,
};

pub const Header = struct {
    name: []const u8,
    value: []const u8,
};

pub const Headers = struct {
    headers: ?*libcurl.CurlSList,
    cookies: ?[*c]const u8,

    pub fn init(user_agent: [:0]const u8) !Headers {
        const header_list = libcurl.curl_slist_append(null, user_agent);
        if (header_list == null) {
            return error.OutOfMemory;
        }
        return .{ .headers = header_list, .cookies = null };
    }

    pub fn deinit(self: *const Headers) void {
        if (self.headers) |hdr| {
            libcurl.curl_slist_free_all(hdr);
        }
    }

    pub fn add(self: *Headers, header: [*c]const u8) !void {
        // Copies the value
        const updated_headers = libcurl.curl_slist_append(self.headers, header);
        if (updated_headers == null) {
            return error.OutOfMemory;
        }

        self.headers = updated_headers;
    }

    fn parseHeader(header_str: []const u8) ?Header {
        const colon_pos = std.mem.indexOfScalar(u8, header_str, ':') orelse return null;

        const name = std.mem.trim(u8, header_str[0..colon_pos], " \t");
        const value = std.mem.trim(u8, header_str[colon_pos + 1 ..], " \t");

        return .{ .name = name, .value = value };
    }

    pub fn iterator(self: *Headers) Iterator {
        return .{
            .header = self.headers,
            .cookies = self.cookies,
        };
    }

    const Iterator = struct {
        header: [*c]libcurl.CurlSList,
        cookies: ?[*c]const u8,

        pub fn next(self: *Iterator) ?Header {
            const h = self.header orelse {
                const cookies = self.cookies orelse return null;
                self.cookies = null;
                return .{ .name = "Cookie", .value = std.mem.span(@as([*:0]const u8, cookies)) };
            };

            self.header = h.*.next;
            return parseHeader(std.mem.span(@as([*:0]const u8, @ptrCast(h.*.data))));
        }
    };
};

// In normal cases, the header iterator comes from the curl linked list.
// But it's also possible to inject a response, via `transfer.fulfill`. In that
// case, the resposne headers are a list, []const Http.Header.
// This union, is an iterator that exposes the same API for either case.
pub const HeaderIterator = union(enum) {
    curl: CurlHeaderIterator,
    list: ListHeaderIterator,

    pub fn next(self: *HeaderIterator) ?Header {
        switch (self.*) {
            inline else => |*it| return it.next(),
        }
    }

    const CurlHeaderIterator = struct {
        conn: *const Connection,
        prev: ?*libcurl.CurlHeader = null,

        pub fn next(self: *CurlHeaderIterator) ?Header {
            const h = libcurl.curl_easy_nextheader(self.conn.easy, .header, -1, self.prev) orelse return null;
            self.prev = h;

            const header = h.*;
            return .{
                .name = std.mem.span(header.name),
                .value = std.mem.span(header.value),
            };
        }
    };

    const ListHeaderIterator = struct {
        index: usize = 0,
        list: []const Header,

        pub fn next(self: *ListHeaderIterator) ?Header {
            const idx = self.index;
            if (idx == self.list.len) {
                return null;
            }
            self.index = idx + 1;
            return self.list[idx];
        }
    };
};

const HeaderValue = struct {
    value: []const u8,
    amount: usize,
};

pub const AuthChallenge = struct {
    status: u16,
    source: ?enum { server, proxy },
    scheme: ?enum { basic, digest },
    realm: ?[]const u8,

    pub fn parse(status: u16, header: []const u8) !AuthChallenge {
        var ac: AuthChallenge = .{
            .status = status,
            .source = null,
            .realm = null,
            .scheme = null,
        };

        const sep = std.mem.indexOfPos(u8, header, 0, ": ") orelse return error.InvalidHeader;
        const hname = header[0..sep];
        const hvalue = header[sep + 2 ..];

        if (std.ascii.eqlIgnoreCase("WWW-Authenticate", hname)) {
            ac.source = .server;
        } else if (std.ascii.eqlIgnoreCase("Proxy-Authenticate", hname)) {
            ac.source = .proxy;
        } else {
            return error.InvalidAuthChallenge;
        }

        const pos = std.mem.indexOfPos(u8, std.mem.trim(u8, hvalue, std.ascii.whitespace[0..]), 0, " ") orelse hvalue.len;
        const _scheme = hvalue[0..pos];
        if (std.ascii.eqlIgnoreCase(_scheme, "basic")) {
            ac.scheme = .basic;
        } else if (std.ascii.eqlIgnoreCase(_scheme, "digest")) {
            ac.scheme = .digest;
        } else {
            return error.UnknownAuthChallengeScheme;
        }

        return ac;
    }
};

pub const ResponseHead = struct {
    pub const MAX_CONTENT_TYPE_LEN = 64;

    status: u16,
    url: [*c]const u8,
    redirect_count: u32,
    _content_type_len: usize = 0,
    _content_type: [MAX_CONTENT_TYPE_LEN]u8 = undefined,
    // this is normally an empty list, but if the response is being injected
    // than it'll be populated. It isn't meant to be used directly, but should
    // be used through the transfer.responseHeaderIterator() which abstracts
    // whether the headers are from a live curl easy handle, or injected.
    _injected_headers: []const Header = &.{},

    pub fn contentType(self: *ResponseHead) ?[]u8 {
        if (self._content_type_len == 0) {
            return null;
        }
        return self._content_type[0..self._content_type_len];
    }
};

pub const Connection = struct {
    easy: *libcurl.Curl,
    node: Handles.HandleList.Node = .{},

    pub fn init(
        ca_blob_: ?libcurl.CurlBlob,
        config: *const Config,
    ) !Connection {
        const easy = libcurl.curl_easy_init() orelse return error.FailedToInitializeEasy;
        errdefer libcurl.curl_easy_cleanup(easy);

        // timeouts
        try libcurl.curl_easy_setopt(easy, .timeout_ms, config.httpTimeout());
        try libcurl.curl_easy_setopt(easy, .connect_timeout_ms, config.httpConnectTimeout());

        // redirect behavior
        try libcurl.curl_easy_setopt(easy, .max_redirs, config.httpMaxRedirects());
        try libcurl.curl_easy_setopt(easy, .follow_location, 2);
        try libcurl.curl_easy_setopt(easy, .redir_protocols_str, "HTTP,HTTPS"); // remove FTP and FTPS from the default

        // proxy
        const http_proxy = config.httpProxy();
        if (http_proxy) |proxy| {
            try libcurl.curl_easy_setopt(easy, .proxy, proxy.ptr);
        }

        // tls
        if (ca_blob_) |ca_blob| {
            try libcurl.curl_easy_setopt(easy, .ca_info_blob, ca_blob);
            if (http_proxy != null) {
                try libcurl.curl_easy_setopt(easy, .proxy_ca_info_blob, ca_blob);
            }
        } else {
            assert(config.tlsVerifyHost() == false, "Http.init tls_verify_host", .{});

            try libcurl.curl_easy_setopt(easy, .ssl_verify_host, false);
            try libcurl.curl_easy_setopt(easy, .ssl_verify_peer, false);

            if (http_proxy != null) {
                try libcurl.curl_easy_setopt(easy, .proxy_ssl_verify_host, false);
                try libcurl.curl_easy_setopt(easy, .proxy_ssl_verify_peer, false);
            }
        }

        // compression, don't remove this. CloudFront will send gzip content
        // even if we don't support it, and then it won't be decompressed.
        // empty string means: use whatever's available
        try libcurl.curl_easy_setopt(easy, .accept_encoding, "");

        // debug
        if (comptime ENABLE_DEBUG) {
            try libcurl.curl_easy_setopt(easy, .verbose, true);

            // Sometimes the default debug output hides some useful data. You can
            // uncomment the following line (BUT KEEP THE LIVE ABOVE AS-IS), to
            // get more control over the data (specifically, the `CURLINFO_TEXT`
            // can include useful data).

            // try libcurl.curl_easy_setopt(easy, .debug_function, debugCallback);
        }

        return .{
            .easy = easy,
        };
    }

    pub fn deinit(self: *const Connection) void {
        libcurl.curl_easy_cleanup(self.easy);
    }

    pub fn setURL(self: *const Connection, url: [:0]const u8) !void {
        try libcurl.curl_easy_setopt(self.easy, .url, url.ptr);
    }

    // a libcurl request has 2 methods. The first is the method that
    // controls how libcurl behaves. This specifically influences how redirects
    // are handled. For example, if you do a POST and get a 301, libcurl will
    // change that to a GET. But if you do a POST and get a 308, libcurl will
    // keep the POST (and re-send the body).
    // The second method is the actual string that's included in the request
    // headers.
    // These two methods can be different - you can tell curl to behave as though
    // you made a GET, but include "POST" in the request header.
    //
    // Here, we're only concerned about the 2nd method. If we want, we'll set
    // the first one based on whether or not we have a body.
    //
    // It's important that, for each use of this connection, we set the 2nd
    // method. Else, if we make a HEAD request and re-use the connection, but
    // DON'T reset this, it'll keep making HEAD requests.
    // (I don't know if it's as important to reset the 1st method, or if libcurl
    // can infer that based on the presence of the body, but we also reset it
    // to be safe);
    pub fn setMethod(self: *const Connection, method: Method) !void {
        const easy = self.easy;
        const m: [:0]const u8 = switch (method) {
            .GET => "GET",
            .POST => "POST",
            .PUT => "PUT",
            .DELETE => "DELETE",
            .HEAD => "HEAD",
            .OPTIONS => "OPTIONS",
            .PATCH => "PATCH",
            .PROPFIND => "PROPFIND",
        };
        try libcurl.curl_easy_setopt(easy, .custom_request, m.ptr);
    }

    pub fn setBody(self: *const Connection, body: []const u8) !void {
        const easy = self.easy;
        try libcurl.curl_easy_setopt(easy, .post, true);
        try libcurl.curl_easy_setopt(easy, .post_field_size, body.len);
        try libcurl.curl_easy_setopt(easy, .copy_post_fields, body.ptr);
    }

    pub fn setGetMode(self: *const Connection) !void {
        try libcurl.curl_easy_setopt(self.easy, .http_get, true);
    }

    pub fn setHeaders(self: *const Connection, headers: *Headers) !void {
        try libcurl.curl_easy_setopt(self.easy, .http_header, headers.headers);
    }

    pub fn setCookies(self: *const Connection, cookies: [*c]const u8) !void {
        try libcurl.curl_easy_setopt(self.easy, .cookie, cookies);
    }

    pub fn setPrivate(self: *const Connection, ptr: *anyopaque) !void {
        try libcurl.curl_easy_setopt(self.easy, .private, ptr);
    }

    pub fn setProxyCredentials(self: *const Connection, creds: [:0]const u8) !void {
        try libcurl.curl_easy_setopt(self.easy, .proxy_user_pwd, creds.ptr);
    }

    pub fn setCredentials(self: *const Connection, creds: [:0]const u8) !void {
        try libcurl.curl_easy_setopt(self.easy, .user_pwd, creds.ptr);
    }

    pub fn setCallbacks(
        self: *const Connection,
        comptime header_cb: libcurl.CurlHeaderFunction,
        comptime data_cb: libcurl.CurlWriteFunction,
    ) !void {
        try libcurl.curl_easy_setopt(self.easy, .header_data, self.easy);
        try libcurl.curl_easy_setopt(self.easy, .header_function, header_cb);
        try libcurl.curl_easy_setopt(self.easy, .write_data, self.easy);
        try libcurl.curl_easy_setopt(self.easy, .write_function, data_cb);
    }

    pub fn setProxy(self: *const Connection, proxy: ?[*:0]const u8) !void {
        try libcurl.curl_easy_setopt(self.easy, .proxy, proxy);
    }

    pub fn setTlsVerify(self: *const Connection, verify: bool, use_proxy: bool) !void {
        try libcurl.curl_easy_setopt(self.easy, .ssl_verify_host, verify);
        try libcurl.curl_easy_setopt(self.easy, .ssl_verify_peer, verify);
        if (use_proxy) {
            try libcurl.curl_easy_setopt(self.easy, .proxy_ssl_verify_host, verify);
            try libcurl.curl_easy_setopt(self.easy, .proxy_ssl_verify_peer, verify);
        }
    }

    pub fn getEffectiveUrl(self: *const Connection) ![*c]const u8 {
        var url: [*c]u8 = undefined;
        try libcurl.curl_easy_getinfo(self.easy, .effective_url, &url);
        return url;
    }

    pub fn getResponseCode(self: *const Connection) !u16 {
        var status: c_long = undefined;
        try libcurl.curl_easy_getinfo(self.easy, .response_code, &status);
        if (status < 0 or status > std.math.maxInt(u16)) {
            return 0;
        }
        return @intCast(status);
    }

    pub fn getRedirectCount(self: *const Connection) !u32 {
        var count: c_long = undefined;
        try libcurl.curl_easy_getinfo(self.easy, .redirect_count, &count);
        return @intCast(count);
    }

    pub fn getResponseHeader(self: *const Connection, name: [:0]const u8, index: usize) ?HeaderValue {
        var hdr: ?*libcurl.CurlHeader = null;
        libcurl.curl_easy_header(self.easy, name, index, .header, -1, &hdr) catch |err| {
            // ErrorHeader includes OutOfMemory — rare but real errors from curl internals.
            // Logged and returned as null since callers don't expect errors.
            log.err(.http, "get response header", .{
                .name = name,
                .err = err,
            });
            return null;
        };
        const h = hdr orelse return null;
        return .{
            .amount = h.amount,
            .value = std.mem.span(h.value),
        };
    }

    pub fn getPrivate(self: *const Connection) !*anyopaque {
        var private: *anyopaque = undefined;
        try libcurl.curl_easy_getinfo(self.easy, .private, &private);
        return private;
    }

    // These are headers that may not be send to the users for inteception.
    pub fn secretHeaders(_: *const Connection, headers: *Headers, http_headers: *const Config.HttpHeaders) !void {
        if (http_headers.proxy_bearer_header) |hdr| {
            try headers.add(hdr);
        }
    }

    pub fn request(self: *const Connection, http_headers: *const Config.HttpHeaders) !u16 {
        var header_list = try Headers.init(http_headers.user_agent_header);
        defer header_list.deinit();
        try self.secretHeaders(&header_list, http_headers);
        try self.setHeaders(&header_list);

        // Add cookies.
        if (header_list.cookies) |cookies| {
            try self.setCookies(cookies);
        }

        try libcurl.curl_easy_perform(self.easy);
        return self.getResponseCode();
    }
};

pub const Handles = struct {
    connections: []Connection,
    dirty: HandleList,
    in_use: HandleList,
    available: HandleList,
    multi: *libcurl.CurlM,
    performing: bool = false,

    pub const HandleList = std.DoublyLinkedList;

    pub fn init(
        allocator: Allocator,
        ca_blob: ?libcurl.CurlBlob,
        config: *const Config,
    ) !Handles {
        const count: usize = config.httpMaxConcurrent();
        if (count == 0) return error.InvalidMaxConcurrent;

        const multi = libcurl.curl_multi_init() orelse return error.FailedToInitializeMulti;
        errdefer libcurl.curl_multi_cleanup(multi) catch {};

        try libcurl.curl_multi_setopt(multi, .max_host_connections, config.httpMaxHostOpen());

        const connections = try allocator.alloc(Connection, count);
        errdefer allocator.free(connections);

        var available: HandleList = .{};
        for (0..count) |i| {
            connections[i] = try Connection.init(ca_blob, config);
            available.append(&connections[i].node);
        }

        return .{
            .dirty = .{},
            .in_use = .{},
            .connections = connections,
            .available = available,
            .multi = multi,
        };
    }

    pub fn deinit(self: *Handles, allocator: Allocator) void {
        for (self.connections) |*conn| {
            conn.deinit();
        }
        allocator.free(self.connections);
        libcurl.curl_multi_cleanup(self.multi) catch {};
    }

    pub fn hasAvailable(self: *const Handles) bool {
        return self.available.first != null;
    }

    pub fn get(self: *Handles) ?*Connection {
        if (self.available.popFirst()) |node| {
            self.in_use.append(node);
            return @as(*Connection, @fieldParentPtr("node", node));
        }
        return null;
    }

    pub fn add(self: *Handles, conn: *const Connection) !void {
        try libcurl.curl_multi_add_handle(self.multi, conn.easy);
    }

    pub fn remove(self: *Handles, conn: *Connection) void {
        if (libcurl.curl_multi_remove_handle(self.multi, conn.easy)) {
            self.isAvailable(conn);
        } else |err| {
            // can happen if we're in a perform() call, so we'll queue this
            // for cleanup later.
            const node = &conn.node;
            self.in_use.remove(node);
            self.dirty.append(node);
            log.warn(.http, "multi remove handle", .{ .err = err });
        }
    }

    pub fn isAvailable(self: *Handles, conn: *Connection) void {
        const node = &conn.node;
        self.in_use.remove(node);
        self.available.append(node);
    }

    pub fn perform(self: *Handles) !c_int {
        self.performing = true;
        defer self.performing = false;

        const multi = self.multi;
        var running: c_int = undefined;
        try libcurl.curl_multi_perform(self.multi, &running);

        {
            const list = &self.dirty;
            while (list.first) |node| {
                list.remove(node);
                const conn: *Connection = @fieldParentPtr("node", node);
                if (libcurl.curl_multi_remove_handle(multi, conn.easy)) {
                    self.available.append(node);
                } else |err| {
                    log.fatal(.http, "multi remove handle", .{ .err = err, .src = "perform" });
                    @panic("multi_remove_handle");
                }
            }
        }

        return running;
    }

    pub fn poll(self: *Handles, extra_fds: []libcurl.CurlWaitFd, timeout_ms: c_int) !void {
        try libcurl.curl_multi_poll(self.multi, extra_fds, timeout_ms, null);
    }

    pub const MultiMessage = struct {
        conn: Connection,
        err: ?Error,
    };

    pub fn readMessage(self: *Handles) ?MultiMessage {
        var messages_count: c_int = 0;
        const msg = libcurl.curl_multi_info_read(self.multi, &messages_count) orelse return null;
        return switch (msg.data) {
            .done => |err| .{
                .conn = .{ .easy = msg.easy_handle },
                .err = err,
            },
            else => unreachable,
        };
    }
};

fn debugCallback(_: *libcurl.Curl, msg_type: libcurl.CurlInfoType, raw: [*c]u8, len: usize, _: *anyopaque) c_int {
    const data = raw[0..len];
    switch (msg_type) {
        .text => std.debug.print("libcurl [text]: {s}\n", .{data}),
        .header_out => std.debug.print("libcurl [req-h]: {s}\n", .{data}),
        .header_in => std.debug.print("libcurl [res-h]: {s}\n", .{data}),
        // .data_in => std.debug.print("libcurl [res-b]: {s}\n", .{data}),
        else => std.debug.print("libcurl ?? {d}\n", .{msg_type}),
    }
    return 0;
}