const std = @import("std");
const HTTPClient = std.http.Client;
const Io = std.Io;
const json = std.json;

const models = @import("models.zig");

const TIME_SLEEP_FACTOR: f64 = 0.98;

const log = std.log.scoped(.SpaceTraders);

const Semaphore = struct {
    mutex: Io.Mutex = .{ .state = .unlocked },
    cond: Io.Condition = .{},
    /// It is OK to initialise this field to any value.
    permits: u64 = 0,

    pub fn post(sem: *Semaphore, io: Io) void {
        sem.mutex.lockUncancelable(io);
        defer sem.mutex.unlock(io);

        sem.permits += 1;
        sem.cond.signal(io);
    }

    pub fn set(sem: *Semaphore, io: Io, permits: u64) void {
        sem.mutex.lockUncancelable(io);
        defer sem.mutex.unlock(io);

        sem.permits = permits;
        sem.cond.signal(io);
    }

    pub fn wait(sem: *Semaphore, io: Io) !void {
        sem.mutex.lockUncancelable(io);
        defer sem.mutex.unlock(io);

        while (sem.permits == 0)
            try sem.cond.wait(io, &sem.mutex);

        sem.permits -= 1;
        if (sem.permits > 0)
            sem.cond.signal(io);
    }

    pub fn available(sem: *Semaphore, io: Io) u64 {
        sem.mutex.lockUncancelable(io);
        defer sem.mutex.unlock(io);

        return sem.permits;
    }
};

pub const Limiter = struct {
    points: u64,
    duration: i64,
    time: ?Io.Timestamp,

    mutex: Io.Mutex = .{ .state = .unlocked },
    semaphor: Semaphore,

    pub fn init(opts: struct { points: u54 = 2, duration: i64 = 1000 }) Limiter {
        return .{
            .points = opts.points,
            .duration = opts.duration,
            .time = null,
            .semaphor = Semaphore{ .permits = opts.points },
        };
    }

    pub fn checkReset(l: *Limiter, io: Io) bool {
        l.mutex.lock(io) catch return false;
        defer l.mutex.unlock(io);

        if (l.time) |t| {
            const dur = t.durationTo(Io.Clock.now(.real, io) catch return false);
            if (dur.toSeconds() > 0) {
                l.semaphor.set(io, l.points);
                l.time = null;
                return true;
            }
        }

        return false;
    }

    pub fn aquire(l: *Limiter, io: Io) !void {
        try l.mutex.lock(io);
        defer l.mutex.unlock(io);

        if (l.time == null) {
            const now = try Io.Clock.now(.real, io);
            l.time = now.addDuration(.fromMilliseconds(l.duration));
        }

        return l.semaphor.wait(io);
    }

    pub fn timeToReset(l: *Limiter, io: Io) Io.Duration {
        if (l.time) |t| {
            return t.durationTo(Io.Clock.now(.real, io) catch return .zero);
        }
        return .zero;
    }

    pub fn available(l: *Limiter, io: Io) bool {
        return l.semaphor.available(io) > 0;
    }
};

pub const BurstyLimiter = struct {
    static: Limiter,
    burst: Limiter,

    pub fn wait(bl: *BurstyLimiter, io: Io) !void {
        _ = bl.static.checkReset(io);
        _ = bl.burst.checkReset(io);

        if (!bl.static.available(io)) {
            if (bl.burst.available(io)) {
                log.debug("Using Burst", .{});
                try bl.burst.aquire(io);
                return;
            } else {
                log.warn("No request available, waiting", .{});

                var static = bl.static.checkReset(io);
                var burst = bl.burst.checkReset(io);

                while (!static and !burst and !bl.static.available(io)) {
                    try io.sleep(bl.static.timeToReset(io), .real);
                    static = bl.static.checkReset(io);
                    burst = bl.burst.checkReset(io);
                }

                log.debug("sleep done", .{});

                if (burst) {
                    log.debug("Using Burst", .{});
                    try bl.burst.aquire(io);
                    return;
                }
            }
        }

        try bl.static.aquire(io);
        return;
    }
};

pub const AuthType = enum { account, agent, none };

pub const Auth = struct {
    account: []const u8 = "",
    agent: []const u8 = "",
};

pub const RequestOptions = struct {
    method: std.http.Method = .GET,
    auth: AuthType = .none,
    body: Body = .empty,

    free_body_after_sending: bool = false,

    pub const Body = union(enum) {
        empty: void,
        buffer: []u8,
    };

    pub fn authorization(opts: *const RequestOptions, client: *const Client) HTTPClient.Request.Headers.Value {
        switch (opts.auth) {
            .account => return .{ .override = client.auth.account },
            .agent => return .{ .override = client.auth.agent },
            .none => return .{ .omit = {} },
        }
    }
};

pub const RequestError = error{
    OutOfMemory,
    InvalidResponse,
    RateLimiterError,
} || HTTPClient.RequestError || HTTPClient.Request.ReceiveHeadError || std.Uri.ParseError;

pub fn RawResponse(comptime T: type) type {
    return Io.Future(RequestError!json.Parsed(T));
}

pub fn Response(comptime T: type) type {
    return RawResponse(models.Wrapper(T));
}

pub const Client = struct {
    allocator: std.mem.Allocator,
    io: Io,
    limiter: BurstyLimiter,

    base_url: []const u8,
    auth: Auth,

    http: HTTPClient,

    // Stats
    total_requests: std.atomic.Value(u64) = .init(0),
    successful_requests: std.atomic.Value(u64) = .init(0),
    total_latency: std.atomic.Value(u64) = .init(0),
    average_latency: std.atomic.Value(u64) = .init(0),

    pub fn init(
        allocator: std.mem.Allocator,
        io: std.Io,
        opts: struct {
            base_url: []const u8 = "https://api.spacetraders.io/v2",
            auth: Auth = .{},
        },
    ) Client {
        return .{
            .allocator = allocator,
            .io = io,
            .limiter = .{
                .static = .init(.{}),
                .burst = .init(.{ .points = 30, .duration = 60_000 }),
            },
            .base_url = opts.base_url,
            .auth = opts.auth,
            .http = .{ .allocator = allocator, .io = io },
        };
    }

    pub fn deinit(client: *Client) void {
        client.http.deinit();
    }

    pub fn get(
        cl: *Client,
        comptime T: type,
        comptime path: []const u8,
        args: anytype,
        auth: AuthType,
    ) !RawResponse(T) {
        return cl.request(T, path, args, .{ .auth = auth });
    }

    pub fn post(
        cl: *Client,
        comptime T: type,
        comptime path: []const u8,
        args: anytype,
        body: anytype,
        auth: AuthType,
    ) !RawResponse(T) {
        const buffer = try json.Stringify.valueAlloc(cl.allocator, body, .{});
        log.debug("json body: {s}", .{buffer});
        return cl.request(T, path, args, .{
            .method = .POST,
            .auth = auth,
            .body = .{ .buffer = buffer },
            .free_body_after_sending = true,
        });
    }

    pub fn patch(
        cl: *Client,
        comptime T: type,
        comptime path: []const u8,
        args: anytype,
        body: anytype,
        auth: AuthType,
    ) !RawResponse(T) {
        const buffer = try json.Stringify.valueAlloc(cl.allocator, body, .{});
        log.debug("json body: {s}", .{buffer});
        return cl.request(T, path, args, .{
            .method = .PATCH,
            .auth = auth,
            .body = .{ .buffer = buffer },
            .free_body_after_sending = true,
        });
    }

    pub fn request(
        client: *Client,
        comptime T: type,
        comptime path: []const u8,
        args: anytype,
        opts: RequestOptions,
    ) !RawResponse(T) {
        const path_fmt = try std.fmt.allocPrint(client.allocator, path, args);
        defer client.allocator.free(path_fmt);

        const url = try std.fmt.allocPrint(client.allocator, "{s}{s}", .{ client.base_url, path_fmt });

        const Wrapper = struct {
            fn call(
                cl: *Client,
                url_param: []const u8,
                opts_param: RequestOptions,
            ) RequestError!json.Parsed(T) {
                defer cl.allocator.free(url_param);
                cl.limiter.wait(cl.io) catch return error.RateLimiterError;
                return Client.requestRaw(cl, T, url_param, opts_param);
            }
        };

        return client.io.concurrent(
            Wrapper.call,
            .{ client, url, opts },
        );
    }

    pub fn requestRaw(
        client: *Client,
        comptime T: type,
        url: []const u8,
        opts: RequestOptions,
    ) RequestError!json.Parsed(T) {
        const uri = std.Uri.parse(url) catch |err| {
            log.err("Error parsing url: {} - url = {s}", .{ err, url });
            return err;
        };

        var req = try client.http.request(opts.method, uri, .{
            .headers = .{
                .authorization = opts.authorization(client),
                .user_agent = .{ .override = "SPACE/0.1" },
                .content_type = .{ .override = "application/json" },
            },
        });
        defer req.deinit();

        log.debug("requesting: {s}", .{uri.path.percent_encoded});

        const start: ?Io.Timestamp = Io.Clock.now(.real, client.io) catch null;

        switch (opts.body) {
            .empty => try req.sendBodiless(),
            .buffer => |body| {
                try req.sendBodyComplete(body);
                if (opts.free_body_after_sending) client.allocator.free(body);
            },
        }

        var redirect_buffer: [1024]u8 = undefined;

        var response = try req.receiveHead(&redirect_buffer);
        const colour = blk: {
            if (@intFromEnum(response.head.status) >= 200 and @intFromEnum(response.head.status) < 300) {
                break :blk "\x1b[92m";
            } else {
                break :blk "\x1b[1m\x1b[91m";
            }
        };

        _ = client.total_requests.fetchAdd(1, .seq_cst);

        if (start) |s| blk: {
            const latency: u64 = @intCast(s.durationTo(Io.Clock.now(.real, client.io) catch break :blk).toMilliseconds());
            const old_average = client.average_latency.load(.seq_cst);
            var new_average: u64 = 0;

            if (old_average == 0) {
                new_average = latency;
            } else {
                const total_reqs = client.total_requests.load(.seq_cst);
                new_average = old_average * (total_reqs - 1) / total_reqs + latency / total_reqs;
            }

            client.average_latency.store(new_average, .seq_cst);
            _ = client.total_latency.fetchAdd(latency, .seq_cst);

            log.debug("latency: {} ms - average: {}ms", .{ latency, new_average });
        }

        log.debug(
            "\x1b[2m[path = {s}]\x1b[0m received {s}{d} {s}\x1b[0m",
            .{ url[client.base_url.len..], colour, response.head.status, response.head.reason },
        );

        // var header_iter = response.head.iterateHeaders();
        // while (header_iter.next()) |header| {
        //     log.debug("{s}: {s}", .{ header.name, header.value });
        // }

        var decompress_buffer: [std.compress.flate.max_window_len]u8 = undefined;
        var transfer_buffer: [64]u8 = undefined;
        var decompress: std.http.Decompress = undefined;

        const decompressed_body_reader = response.readerDecompressing(&transfer_buffer, &decompress, &decompress_buffer);

        var json_reader: json.Reader = .init(client.allocator, decompressed_body_reader);
        defer json_reader.deinit();

        const result = json.parseFromTokenSource(T, client.allocator, &json_reader, .{
            .ignore_unknown_fields = true,
        }) catch |err| {
            log.err("Error parsing response: {}", .{err});

            return RequestError.InvalidResponse;
        };

        _ = client.successful_requests.fetchAdd(1, .seq_cst);

        return result;
    }
};