const std = @import("std");
const lmdb = @import("lmdb");
const http = @import("http");

// db {{{

const Prng = struct {
    var prng: std.Random.DefaultPrng = std.Random.DefaultPrng.init(0);

    fn IdType(comptime T: type) type {
        const ti = @typeInfo(@TypeOf(T.get));
        return ti.Fn.params[1].type.?;
    }

    pub fn gen_id(dbi: anytype) IdType(@TypeOf(dbi)) {
        var id: IdType(@TypeOf(dbi)) = @enumFromInt(Prng.prng.next());

        while (dbi.has(id)) {
            id = @enumFromInt(Prng.prng.next());
        }

        return id;
    }

    pub fn gen_str(dbi: anytype, comptime len: usize) [len]u8 {
        var buf: [len / 2]u8 = undefined;
        var res: [len]u8 = undefined;
        Prng.prng.fill(&buf);
        for (0..len / 2) |i| {
            res[i * 2 + 0] = 'a' + (buf[i] % 16);
            res[i * 2 + 1] = 'a' + (buf[i] >> 4 % 16);
        }

        while (dbi.has(res)) {
            Prng.prng.fill(&buf);
            for (0..len / 2) |i| {
                res[i * 2 + 0] = 'a' + (buf[i] % 16);
                res[i * 2 + 1] = 'a' + (buf[i] >> 4 % 16);
            }
        }

        return res;
    }
};

const Db = struct {
    fn Key(types: anytype) type {
        return std.meta.Tuple(&types);
    }
    fn users(txn: *const lmdb.Txn) !lmdb.Dbi(UserId, User) {
        return try txn.dbi("users", UserId, User);
    }
    fn user_ids(txn: *const lmdb.Txn) !lmdb.Dbi(Username, UserId) {
        return try txn.dbi("user_ids", Username, UserId);
    }
    fn sessions(txn: *const lmdb.Txn) !lmdb.Dbi(SessionToken, UserId) {
        return try txn.dbi("sessions", SessionToken, UserId);
    }
    fn posts(txn: *const lmdb.Txn) !lmdb.Dbi(PostId, Post) {
        return try txn.dbi("posts", PostId, Post);
    }
    fn lists(txn: *const lmdb.Txn, comptime T: type) !lmdb.Dbi(ListId, ListNode(T)) {
        return try txn.dbi("lists", ListId, ListNode(T));
    }
    fn sets(txn: *const lmdb.Txn, comptime T: type) !lmdb.Dbi(Key(.{ SetId, T }), u0) {
        return try txn.dbi("sets", Key(.{ SetId, T }), u0);
    }

    const ListId = enum(u64) { _ };

    pub fn ListNode(comptime T: type) type {
        return struct {
            next: ?ListId,
            prev: ?ListId,
            data: T,
        };
    }

    pub fn List(comptime T: type) type {
        return struct {
            const Self = @This();

            first: ListId = undefined,
            last: ListId = undefined,
            len: usize = 0,

            pub const Iterator = struct {
                dbi: lmdb.Dbi(ListId, ListNode(T)),
                id_maybe: ?ListId,

                pub fn next(self: *Iterator) ?T {
                    const id = self.id_maybe orelse return null;

                    // TODO: how to handle this?
                    const ln = self.dbi.get(id) orelse return null;
                    self.id_maybe = ln.next;
                    return ln.data;
                }
            };
            pub fn it(self: *const Self, txn: *const lmdb.Txn) !Iterator {
                const list = try Db.lists(txn, T);
                return .{ .dbi = list, .id_maybe = if (self.len > 0) self.first else null };
            }
            pub fn append(self: *Self, txn: *const lmdb.Txn, t: T) !void {
                const list = try Db.lists(txn, T);
                const new_id = Prng.gen_id(list);

                if (self.len == 0) {
                    self.first = new_id;
                    self.last = new_id;
                    self.len = 1;
                    list.put(new_id, .{
                        .next = null,
                        .prev = null,
                        .data = t,
                    });
                } else {
                    const prev_id = self.last;
                    var last = list.get(prev_id).?;
                    last.next = new_id;
                    list.put(prev_id, last);

                    list.put(new_id, .{
                        .next = null,
                        .prev = prev_id,
                        .data = t,
                    });

                    self.last = new_id;
                    self.len += 1;
                }
            }
        };
    }

    const SetId = enum(u64) { _ };

    pub fn Set(comptime T: type) type {
        return struct {
            const Self = @This();
            const SetKey = Key(.{ SetId, T });

            len: usize = 0,
            set_id: ?SetId = null,

            pub fn init(self: *Self) void {
                self.set_id = @enumFromInt(Prng.prng.next());
            }

            pub fn has(self: Self, txn: *const lmdb.Txn, t: T) !bool {
                if (self.set_id == null) return false;

                const set = try Db.sets(txn, T);
                const key = SetKey{ self.set_id.?, t };

                return set.has(key);
            }

            pub fn add(self: *Self, txn: *const lmdb.Txn, t: T) !void {
                if (self.set_id == null) self.init();

                const set = try Db.sets(txn, T);
                const key = SetKey{ self.set_id.?, t };

                if (!set.has(key)) {
                    set.put(key, 0);
                    if (set.has(key)) {
                        self.len += 1;
                    }
                }
            }

            pub fn del(self: *Self, txn: *const lmdb.Txn, t: T) !void {
                if (self.set_id == null) self.init();

                const set = try Db.sets(txn, T);
                const key = SetKey{ self.set_id.?, t };

                if (set.has(key)) {
                    set.del(key);
                    if (!set.has(key)) {
                        self.len -= 1;
                    }
                }
            }
        };
    }
};

// }}}

// content {{{

const User = struct {
    // TODO: choose sizes
    id: UserId,
    username: Username,
    password_hash: PasswordHash,
    posts: PostList = PostList{},
};

const Post = struct {
    id: PostId,

    user_id: UserId,
    time: Timestamp,

    upvotes: UserList = UserList{},
    downvotes: UserList = UserList{},
    comments: PostList = PostList{},
    // reposts

    text: PostText,
};

const SessionTokenLen = 16;

const Id = u64;
const Login = struct {
    user: User,
    user_id: UserId,
    session_token: SessionToken,
};
const UserId = enum(u64) { _ };
const PostId = enum(u64) { _ };
const Timestamp = i64;
const Username = std.BoundedArray(u8, 16);
const PasswordHash = std.BoundedArray(u8, 128);
const SessionToken = [SessionTokenLen]u8;
const CookieValue = std.BoundedArray(u8, 128);
const PostText = std.BoundedArray(u8, 1024);
const PostList = Db.List(PostId);
const UserList = Db.Set(UserId);

pub fn hash_password(password: []const u8) !PasswordHash {
    var hash_buffer = try PasswordHash.init(128);

    // TODO: choose buffer size
    // TODO: dont allocate on stack, maybe zero memory?
    var buffer: [1024 * 10]u8 = undefined;
    var alloc = std.heap.FixedBufferAllocator.init(&buffer);

    // TODO: choose limits
    const result = try std.crypto.pwhash.argon2.strHash(password, .{
        .allocator = alloc.allocator(),
        .params = std.crypto.pwhash.argon2.Params.fromLimits(1000, 1024),
    }, hash_buffer.slice());

    try hash_buffer.resize(result.len);

    return hash_buffer;
}

pub fn verify_password(password: []const u8, hash: PasswordHash) bool {
    var buffer: [1024 * 10]u8 = undefined;
    var alloc = std.heap.FixedBufferAllocator.init(&buffer);

    if (std.crypto.pwhash.argon2.strVerify(hash.constSlice(), password, .{
        .allocator = alloc.allocator(),
    })) {
        return true;
    } else |err| {
        std.debug.print("verify error: {}\n", .{err});
        return false;
    }
}

pub fn register_user(env: *lmdb.Env, username: []const u8, password: []const u8) !bool {
    const username_array = try Username.fromSlice(username);

    const txn = try env.txn();
    defer {
        txn.commit();
        env.sync();
    }

    const users = try Db.users(&txn);
    const user_ids = try Db.user_ids(&txn);

    if (user_ids.has(username_array)) {
        return false;
    } else {
        const user_id = Prng.gen_id(users);
        users.put(user_id, User{
            .id = user_id,
            .username = username_array,
            .password_hash = try hash_password(password),
        });

        user_ids.put(username_array, user_id);

        return true;
    }
}

pub fn login_user(env: *lmdb.Env, username: []const u8, password: []const u8) !SessionToken {
    const username_array = try Username.fromSlice(username);

    const txn = try env.txn();
    defer {
        txn.commit();
        env.sync();
    }

    const user_ids = try Db.user_ids(&txn);
    const user_id = user_ids.get(username_array) orelse return error.UnknownUsername;
    std.debug.print("id: {}\n", .{user_id});

    const users = try Db.users(&txn);
    if (users.get(user_id)) |user| {
        if (verify_password(password, user.password_hash)) {
            const sessions = try Db.sessions(&txn);
            const session_token = Prng.gen_str(sessions, SessionTokenLen);
            sessions.put(session_token, user_id);
            return session_token;
        } else {
            return error.IncorrectPassword;
        }
    } else {
        return error.UserNotFound;
    }
}

fn logout_user(env: *lmdb.Env, session_token: SessionToken) !void {
    const txn = try env.txn();
    defer {
        txn.commit();
        env.sync();
    }

    const sessions = try Db.sessions(&txn);
    sessions.del(session_token);
}

fn post(env: *lmdb.Env, user_id: UserId, text: []const u8) !void {
    var post_id: PostId = undefined;

    var txn = try env.txn();
    {
        const posts = try Db.posts(&txn);
        post_id = Prng.gen_id(posts);
        posts.put(post_id, Post{
            .id = post_id,
            .user_id = user_id,
            .time = std.time.timestamp(),
            .text = try PostText.fromSlice(text),
        });

        txn.commit();
        env.sync();
    }

    txn = try env.txn();
    {
        const users = try Db.users(&txn);
        var user = users.get(user_id) orelse return error.UserNotFound;
        try user.posts.append(&txn, post_id);
        users.put(user_id, user);

        txn.commit();
        env.sync();
    }
}

fn vote(env: *lmdb.Env, post_id: PostId, user_id: UserId, dir: enum { Up, Down }) !void {
    const txn = try env.txn();
    defer {
        txn.commit();
        env.sync();
    }

    const posts = try Db.posts(&txn);

    var p = posts.get(post_id) orelse return error.PostNotFound;
    if (dir == .Up) {
        try p.upvotes.add(&txn, user_id);
    } else {
        try p.downvotes.add(&txn, user_id);
    }
    posts.put(post_id, p);
}

fn unvote(env: *lmdb.Env, post_id: PostId, user_id: UserId, dir: enum { Up, Down }) !void {
    const txn = try env.txn();
    defer {
        txn.commit();
        env.sync();
    }

    const posts = try Db.posts(&txn);

    var p = posts.get(post_id) orelse return error.PostNotFound;
    if (dir == .Up) {
        try p.upvotes.del(&txn, user_id);
    } else {
        try p.downvotes.del(&txn, user_id);
    }
    posts.put(post_id, p);
}

fn get_session_user_id(env: *lmdb.Env, session_token: SessionToken) !UserId {
    const txn = try env.txn();
    defer txn.abort();

    const sessions = try Db.sessions(&txn);

    if (sessions.get(session_token)) |user_id| {
        return user_id;
    } else {
        return error.SessionNotFound;
    }
}

fn get_user(env: *lmdb.Env, user_id: UserId) !?User {
    const txn = try env.txn();
    defer txn.abort();

    const users = try Db.users(&txn);
    return users.get(user_id);
}

// }}}

// html {{{
fn html_form(res: *http.Response, comptime fmt_action: []const u8, args_action: anytype, inputs: anytype) !void {
    try res.write("<form style=\"display: inline-block!important;\" action=\"", .{});
    try res.write(fmt_action, args_action);
    try res.write("\" method=\"post\">", .{});

    inline for (inputs) |input| {
        switch (@typeInfo(@TypeOf(input))) {
            .Struct => {
                try res.write("<input ", .{});
                try res.write(input[0], input[1]);
                try res.write(" />", .{});
            },
            else => {
                try res.write("<input ", .{});
                try res.write(input, .{});
                try res.write(" />", .{});
            },
        }
    }

    try res.write("</form>", .{});
}
// }}}

// write {{{
fn write_header(res: *http.Response, logged_in: ?Login) !void {
    if (logged_in) |login| {
        try res.write(
            \\<a href="/user/{s}">Home</a><br />
        , .{login.user.username.constSlice()});
        try html_form(res, "/logout", .{}, .{
            \\type="submit" value="Logout"
        });
        try html_form(res, "/quit", .{}, .{
            \\type="submit" value="Quit"
        });
        try res.write("<br />", .{});
        try html_form(res, "/post", .{}, .{
            \\type="text" name="text"
            ,
            \\type="submit" value="Post"
        });
    } else {
        try res.write(
            \\<a href="/">Home</a><br />
            \\<a href="/register">Register</a>
            \\<a href="/login">Login</a><br />
        , .{});
        try html_form(res, "/quit", .{}, .{
            \\type="submit" value="Quit"
        });
    }
}
fn write_posts(res: *http.Response, txn: *const lmdb.Txn, user: User, login: ?Login) !void {
    const posts = try Db.posts(txn);
    var it = try user.posts.it(txn);
    while (it.next()) |post_id| {
        const p = posts.get(post_id) orelse break;
        try res.write(
            \\<div>
            \\<p>{s}</p>
        , .{p.text.constSlice()});
        if (login != null and try p.upvotes.has(txn, login.?.user_id)) {
            try html_form(res, "/unupvote/{}", .{@intFromEnum(post_id)}, .{
                .{ "type=\"submit\" value=\"&#x2B06; {}\"", .{p.upvotes.len} },
            });
        } else {
            try html_form(res, "/upvote/{}", .{@intFromEnum(post_id)}, .{
                .{ "type=\"submit\" value=\"&#x2B06; {}\"", .{p.upvotes.len} },
            });
        }
        if (login != null and try p.downvotes.has(txn, login.?.user_id)) {
            try html_form(res, "/undownvote/{}", .{@intFromEnum(post_id)}, .{
                .{ "type=\"submit\" value=\"&#x2B07; {}\"", .{p.downvotes.len} },
            });
        } else {
            try html_form(res, "/downvote/{}", .{@intFromEnum(post_id)}, .{
                .{ "type=\"submit\" value=\"&#x2B07; {}\"", .{p.downvotes.len} },
            });
        }
        try res.write(
            \\<span>&#x1F4AD; {}</span>
            \\</div>
        , .{p.comments.len});
    }
}
// }}}

fn list_users(env: lmdb.Env) !void {
    const txn = try env.txn();
    defer txn.abort();

    // const users = try Db.users(&txn);
    const users = try txn.dbi("users", UserId, User);
    var cursor = try users.cursor();

    var key: UserId = undefined;
    var user_maybe = cursor.get(&key, .First);

    while (user_maybe) |*user| {
        std.debug.print("[{}] {s}\n", .{ key, user.username.constSlice() });

        user_maybe = cursor.get(&key, .Next);
    }
}
fn list_user_ids(env: lmdb.Env) !void {
    const txn = try env.txn();
    defer txn.abort();

    const user_ids = try Db.user_ids(&txn);
    var cursor = try user_ids.cursor();

    var key: Username = undefined;
    var user_id_maybe = cursor.get(&key, .First);

    while (user_id_maybe) |user_id| {
        std.debug.print("[{s}] {}\n", .{ key.constSlice(), user_id });

        user_id_maybe = cursor.get(&key, .Next);
    }
}

fn list_sessions(env: lmdb.Env) !void {
    const txn = try env.txn();
    defer txn.abort();

    const sessions = try Db.sessions(&txn);
    var cursor = try sessions.cursor();

    var key: SessionToken = undefined;
    var user_id_maybe = cursor.get(&key, .First);

    while (user_id_maybe) |user_id| {
        std.debug.print("[{s}] {}\n", .{ key, user_id });

        user_id_maybe = cursor.get(&key, .Next);
    }
}

fn list_posts(env: lmdb.Env) !void {
    const txn = try env.txn();
    defer txn.abort();

    const posts = try Db.posts(&txn);
    var cursor = try posts.cursor();

    var key: PostId = undefined;
    var post_maybe = cursor.get(&key, .First);

    while (post_maybe) |p| {
        std.debug.print("[{}] {s}\n", .{ key, p.text.constSlice() });

        post_maybe = cursor.get(&key, .Next);
    }
}

const ReqBufferSize = 4096;
const ResHeadBufferSize = 1024 * 16;
const ResBodyBufferSize = 1024 * 16;

pub fn main() !void {
    // server
    var server = try http.Server.init("::", 8080);
    defer server.deinit();

    // lmdb
    var env = try lmdb.Env.open("db", 1024 * 1024 * 10);
    defer env.close();

    std.debug.print("Users:\n", .{});
    try list_users(env);
    std.debug.print("User IDs:\n", .{});
    try list_user_ids(env);
    std.debug.print("Sessions:\n", .{});
    try list_sessions(env);
    std.debug.print("Posts:\n", .{});
    try list_posts(env);

    try handle_connection(&server, &env);
    // const ThreadCount = 1;
    // var ts: [ThreadCount]std.Thread = undefined;

    // for (0..ThreadCount) |i| {
    //     ts[i] = try std.Thread.spawn(.{}, handle_connection, .{ &server, &env });
    // }
    // for (0..ThreadCount) |i| {
    //     ts[i].join();
    // }

    std.debug.print("done\n", .{});
}

fn handle_connection(server: *http.Server, env: *lmdb.Env) !void {
    // TODO: static?
    var req_buffer: [ReqBufferSize]u8 = undefined;
    var res_head_buffer: [ResHeadBufferSize]u8 = undefined;
    var res_body_buffer: [ResBodyBufferSize]u8 = undefined;

    accept: while (true) {
        server.wait();

        while (try server.next_request(&req_buffer)) |req| {
            // std.debug.print("[{}]: {s}\n", .{ req.method, req.target });

            // reponse
            var res = http.Response.init(req.fd, &res_head_buffer, &res_body_buffer);

            // check session token
            var logged_in: ?Login = null;

            if (req.get_cookie("session_token")) |session_token_str| {
                var session_token: SessionToken = undefined;
                std.mem.copyForwards(u8, &session_token, session_token_str);
                // const session_token = try std.fmt.parseUnsigned(SessionToken, session_token_str, 10);
                // const session_token = std.mem.bytesToValue(SessionToken, session_token_str);
                if (get_session_user_id(env, session_token)) |user_id| {
                    const txn = try env.txn();
                    defer txn.abort();
                    const users = try Db.users(&txn);

                    logged_in = .{
                        .user = users.get(user_id) orelse return error.UserNotFound,
                        .user_id = user_id,
                        .session_token = session_token,
                    };
                } else |err| {
                    std.debug.print("get_session_user err: {}\n", .{err});

                    try res.add_header(
                        "Set-Cookie",
                        .{"session_token=deleted; Expires=Thu, 01 Jan 1970 00:00:00 GMT"},
                    );
                }
            }

            // html
            if (req.method == .GET) {
                try write_header(&res, logged_in);

                if (std.mem.eql(u8, req.target, "/register")) {
                    try res.write(
                        \\<form action="/register" method="post">
                        \\<input type="text" name="username" />
                        \\<input type="password" name="password" />
                        \\<input type="submit" value="Register" />
                        \\</form>
                    , .{});
                    try res.send();
                } else if (std.mem.eql(u8, req.target, "/login")) {
                    try res.write(
                        \\<form action="/login" method="post">
                        \\<input type="text" name="username" />
                        \\<input type="password" name="password" />
                        \\<input type="submit" value="Login" />
                        \\</form>
                    , .{});
                    try res.send();
                } else if (std.mem.startsWith(u8, req.target, "/user/")) {
                    const username = req.target[6..req.target.len];

                    const txn = try env.txn();
                    defer txn.abort();

                    const user_ids = try Db.user_ids(&txn);
                    if (user_ids.get(try Username.fromSlice(username))) |user_id| {
                        const users = try Db.users(&txn);
                        const user = users.get(user_id).?;
                        try write_posts(&res, &txn, user, logged_in);
                    } else {
                        try res.write(
                            \\<p>User not found</pvo>
                        , .{});
                    }
                    try res.send();
                } else {
                    if (logged_in) |login| {
                        const user = (try get_user(env, login.user_id)).?;

                        const txn = try env.txn();
                        defer txn.abort();

                        try write_posts(&res, &txn, user, logged_in);

                        try res.send();
                    } else {
                        try res.write("[GET] {s}", .{req.target});
                        try res.send();
                    }
                }
            }
            // api
            else {
                if (std.mem.eql(u8, req.target, "/register")) {
                    // TODO: handle args not supplied
                    const username = req.get_value("username").?;
                    const password = req.get_value("password").?;

                    std.debug.print("New user: {s} {s}\n", .{ username, password });
                    if (try register_user(env, username, password)) {
                        try res.redirect("/login");
                    } else {
                        try res.redirect("/register");
                    }
                    try res.send();
                } else if (std.mem.eql(u8, req.target, "/login")) {
                    // TODO: handle args not supplied
                    const username = req.get_value("username").?;
                    const password = req.get_value("password").?;

                    std.debug.print("New login: {s} {s}\n", .{ username, password });
                    if (login_user(env, username, password)) |session_token| {
                        res.status = .see_other;
                        try res.add_header(
                            "Location",
                            .{ "/user/{s}", .{username} },
                        );
                        try res.add_header(
                            "Set-Cookie",
                            .{ "session_token={s}; Secure; HttpOnly", .{session_token} },
                        );

                        try res.send();
                    } else |err| {
                        std.debug.print("login_user err: {}\n", .{err});
                        try res.redirect("/login");
                        try res.send();
                    }
                } else if (std.mem.eql(u8, req.target, "/logout")) {
                    if (logged_in) |login| {
                        try logout_user(env, login.session_token);

                        try res.add_header(
                            "Set-Cookie",
                            .{"session_token=deleted; Expires=Thu, 01 Jan 1970 00:00:00 GMT"},
                        );

                        try res.redirect("/");
                        try res.send();
                    }
                } else if (std.mem.eql(u8, req.target, "/post")) {
                    if (logged_in) |login| {
                        const text = req.get_value("text").?;
                        try post(env, login.user_id, text);

                        try res.redirect("/");
                        try res.send();
                    }
                } else if (std.mem.eql(u8, req.target, "/quit")) {
                    try res.redirect("/");
                    try res.send();
                    break :accept;
                } else if (std.mem.startsWith(u8, req.target, "/upvote/")) {
                    const login = logged_in orelse return error.NotLoggedIn;

                    const post_id_str = req.target[8..req.target.len];
                    const post_id: PostId = @enumFromInt(try std.fmt.parseUnsigned(u64, post_id_str, 10));

                    try vote(env, post_id, login.user_id, .Up);
                    try unvote(env, post_id, login.user_id, .Down);

                    if (req.get_header("Referer")) |ref| {
                        try res.redirect(ref);
                    }
                    try res.send();
                } else if (std.mem.startsWith(u8, req.target, "/downvote/")) {
                    const login = logged_in orelse return error.NotLoggedIn;

                    const post_id_str = req.target[10..req.target.len];
                    const post_id: PostId = @enumFromInt(try std.fmt.parseUnsigned(u64, post_id_str, 10));

                    try vote(env, post_id, login.user_id, .Down);
                    try unvote(env, post_id, login.user_id, .Up);

                    if (req.get_header("Referer")) |ref| {
                        try res.redirect(ref);
                    }
                    try res.send();
                } else if (std.mem.startsWith(u8, req.target, "/unupvote/")) {
                    const login = logged_in orelse return error.NotLoggedIn;

                    const post_id_str = req.target[10..req.target.len];
                    const post_id: PostId = @enumFromInt(try std.fmt.parseUnsigned(u64, post_id_str, 10));

                    try unvote(env, post_id, login.user_id, .Up);

                    if (req.get_header("Referer")) |ref| {
                        try res.redirect(ref);
                    }
                    try res.send();
                } else if (std.mem.startsWith(u8, req.target, "/undownvote/")) {
                    const login = logged_in orelse return error.NotLoggedIn;

                    const post_id_str = req.target[12..req.target.len];
                    const post_id: PostId = @enumFromInt(try std.fmt.parseUnsigned(u64, post_id_str, 10));

                    try unvote(env, post_id, login.user_id, .Down);

                    if (req.get_header("Referer")) |ref| {
                        try res.redirect(ref);
                    }
                    try res.send();
                } else {
                    // try req.respond(
                    //     \\<p>POST</p>
                    // , .{});
                    try res.write("<p>[POST] {s}</p>", .{req.target});
                    try res.send();
                }
            }
        }
    }
}