const std = @import("std");
const testing = std.testing;
const fmt = std.fmt;

const net = std.net;

const ipc = @import("./main.zig");
const Message  = ipc.Message;
const CBEventType = ipc.CBEvent.Type;

const Allocator = std.mem.Allocator;

const print_eq = @import("./util.zig").print_eq;
const print = std.debug.print;

const Event = ipc.Event;

/// SwitchDB 
/// Functions read and write: handle 

pub const SwitchDB = struct {
    const Self = @This();

    db: std.AutoArrayHashMap(i32, ManagedConnection),

    pub fn init (allocator: Allocator) Self {
        return Self {
            .db = std.AutoArrayHashMap(i32, ManagedConnection).init(allocator),
        };
    }

    pub fn deinit (self: *Self) void {
        self.db.deinit();
    }

    pub fn format(self: Self, comptime _: []const u8, _: fmt.FormatOptions, out_stream: anytype) !void {
        for(self.db.keys()) |k,i| {
            try fmt.format(out_stream, "({},{})", .{k, self.db.values()[i].dest});
        }
    }

    pub fn set_callbacks(self: *Self, fd: i32
        , in  : *const fn (origin: i32, m: *Message) CBEventType
        , out : *const fn (origin: i32, m: *const Message) CBEventType) !void {

        var managedconnection = self.db.get(fd) orelse return error.unregisteredFD;
        managedconnection.in = in;
        managedconnection.out = out;
    }

    /// Dig the "db" hashmap, perform "in" fn, may provide a message.
    /// Errors from the "in" fn are reported as Zig errors.
    pub fn read (self: *Self, fd: i32) !?Message {
        // assert there is an entry with this fd as a key.
        var managedconnection = self.db.get(fd) orelse return error.unregisteredFD;
        var message: Message = undefined;

        var r: CBEventType = managedconnection.in(fd, &message);

        switch (r) {
            // The message should be ignored (protocol specific).
            CBEventType.IGNORE => { return null; },
            // No error. A message was generated.
            CBEventType.NO_ERROR => {
                message.fd = managedconnection.dest;
                return message;
            },
            CBEventType.FD_CLOSING => { return error.closeFD; },
            // Generic error, or the message was read but with errors.
            CBEventType.ERROR => {
                return error.generic;
            },
        }

        unreachable;
    }

    /// Dig the "db" hashmap and perform "out" fn.
    /// Errors from the "out" fn are reported as Zig errors.
    pub fn write (self: *Self, message: Message) !void {
        // assert there is an entry with this fd as a key.
        var managedconnection = self.db.get(message.fd) orelse return error.unregisteredFD;
        var r = managedconnection.out(managedconnection.dest, &message);

        switch (r) {
            // The message should be ignored (protocol specific).
            // No error. A message was generated.
            CBEventType.NO_ERROR => {
                return;
            },
            CBEventType.FD_CLOSING => { return error.closeFD; },
            // Generic error, or the message was read but with errors.
            CBEventType.IGNORE,
            CBEventType.ERROR => {
                return error.generic;
            },
        }

        unreachable;
    }

    pub fn handle_event_read (self: *Self, index: usize, fd: i32) Event {
        var message: ?Message = null;
        message = self.read (fd) catch |err| switch(err) {
            error.closeFD => {
                return Event.init(Event.Type.DISCONNECTION, index, fd, null);
            },
            error.unregisteredFD,
            error.generic => {
                return Event.init(Event.Type.ERROR, index, fd, null);
            },
        };
        return Event.init(Event.Type.SWITCH_RX, index, fd, message);
    }

    /// Message is free'd in any case.
    pub fn handle_event_write (self: *Self, index: usize, message: Message) Event {
        defer message.deinit();
        var fd = message.fd;
        self.write(message) catch |err| switch(err) {
            error.closeFD => {
                return Event.init(Event.Type.DISCONNECTION, index, fd, null);
            },
            error.unregisteredFD,
            error.generic => {
                return Event.init(Event.Type.ERROR, index, fd, null);
            },
        };
        return Event.init(Event.Type.SWITCH_TX, index, fd, null);
    }

    /// Simple wrapper around self.db.get.
    pub fn getDest (self: *Self, fd: i32) !i32 {
        return self.db.get(fd).?.dest;
    }

    pub fn nuke (self: *Self, fd: i32) void {
        if (self.db.fetchSwapRemove(fd)) |kv| {
            _ = self.db.swapRemove(kv.value.dest);
        }
    }
};

const ManagedConnection = struct {
    dest : i32,
    in  : *const fn (origin: i32, m: *Message) CBEventType = default_in,
    out : *const fn (origin: i32, m: *const Message) CBEventType = default_out,
};

test "creation and display" {
   const config = .{.safety = true};
   var gpa = std.heap.GeneralPurposeAllocator(config){};
   defer _ = gpa.deinit();
   const allocator = gpa.allocator();

   var switchdb = SwitchDB.init(allocator);
   defer switchdb.deinit();

   try switchdb.db.put(5, ManagedConnection {.dest = 6});
   try switchdb.db.put(6, ManagedConnection {.dest = 5});

   try print_eq("{ (5,6)(6,5) }", .{switchdb});
}

fn successful_in (_: i32, m: *Message) CBEventType {
    m.* = Message.init(8, std.heap.c_allocator, "coucou") catch {
        return CBEventType.ERROR;
    };
    return CBEventType.NO_ERROR;
}

fn successful_out (_: i32, _: *const Message) CBEventType {
    return CBEventType.NO_ERROR;
}

test "successful exchanges" {
    const config = .{.safety = true};
    var gpa = std.heap.GeneralPurposeAllocator(config){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    var switchdb = SwitchDB.init(allocator);
    defer switchdb.deinit();

    try switchdb.db.put(5, ManagedConnection {.dest = 6, .in = successful_in, .out = successful_out});
    try switchdb.db.put(6, ManagedConnection {.dest = 5, .in = successful_in, .out = successful_out});

    // should return a new message (hardcoded: fd 8, payload "coucou")
    var event_1: Event = switchdb.handle_event_read (1, 5);
    if (event_1.m) |m| { m.deinit(); }
    else               { return error.NoMessage; }

    // should return a new message (hardcoded: fd 8, payload "coucou")
    var event_2: Event = switchdb.handle_event_read (1, 6);
    if (event_2.m) |m| { m.deinit(); }
    else               { return error.NoMessage; }

    var message = try Message.init(6, allocator, "coucou");
    var event_3 = switchdb.handle_event_write (5, message);
    if (event_3.m) |_| { return error.ShouldNotCarryMessage; }
}

fn unsuccessful_in (_: i32, _: *Message) CBEventType {
    return CBEventType.ERROR;
}

fn unsuccessful_out (_: i32, _: *const Message) CBEventType {
    return CBEventType.ERROR;
}

test "unsuccessful exchanges" {
    const config = .{.safety = true};
    var gpa = std.heap.GeneralPurposeAllocator(config){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    var switchdb = SwitchDB.init(allocator);
    defer switchdb.deinit();

    try switchdb.db.put(5, ManagedConnection {.dest = 6, .in = unsuccessful_in, .out = unsuccessful_out});
    try switchdb.db.put(6, ManagedConnection {.dest = 5, .in = unsuccessful_in, .out = unsuccessful_out});

    // should return a new message (hardcoded: fd 8, payload "coucou")
    var event_1: Event = switchdb.handle_event_read (1, 5);
    if (event_1.m) |_| { return error.ShouldNotCarryMessage; }

    // should return a new message (hardcoded: fd 8, payload "coucou")
    var event_2: Event = switchdb.handle_event_read (1, 6);
    if (event_2.m) |_| { return error.ShouldNotCarryMessage; }

    var message = try Message.init(6, allocator, "coucou");
    var event_3 = switchdb.handle_event_write (5, message);
    if (event_3.m) |_| { return error.ShouldNotCarryMessage; }
}

test "nuke 'em" {
    const config = .{.safety = true};
    var gpa = std.heap.GeneralPurposeAllocator(config){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    var switchdb = SwitchDB.init(allocator);
    defer switchdb.deinit();

    try switchdb.db.put(5, ManagedConnection {.dest = 6, .in = unsuccessful_in, .out = unsuccessful_out});
    try switchdb.db.put(6, ManagedConnection {.dest = 5, .in = unsuccessful_in, .out = unsuccessful_out});

    try testing.expect(switchdb.db.count() == 2);
    switchdb.nuke(5);
    try testing.expect(switchdb.db.count() == 0);
}

fn default_in (origin: i32, m: *Message) CBEventType {
    print ("receiving a message originated from {}\n", .{origin});
    var buffer: [2000000]u8 = undefined; // TODO: FIXME??
    var packet_size: usize = undefined;

    // This may be kinda hacky, idk.
    var stream: net.Stream = .{ .handle = origin };
    packet_size = stream.read(buffer[0..]) catch return CBEventType.ERROR;

    // Let's handle this as a disconnection.
    if (packet_size <= 4) {
        return CBEventType.FD_CLOSING;
    }

    m.* = Message.read(origin, buffer[0..], std.heap.c_allocator)
          catch return CBEventType.ERROR;

    return CBEventType.NO_ERROR;
}

fn default_out (origin: i32, m: *const Message) CBEventType {
    print ("sending a message originated from {}\n", .{origin});
    // Message contains the fd, no need to search for
    // the right structure to copy, let's just recreate
    // a Stream from the fd.
    var stream = net.Stream { .handle = m.fd };

    var buffer: [200000]u8 = undefined; // TODO: buffer size
    var fbs = std.io.fixedBufferStream(&buffer);
    var writer = fbs.writer();

    // returning basic errors, no details.
    _ = m.write(writer) catch return CBEventType.ERROR;
    _ = stream.write (fbs.getWritten()) catch return CBEventType.ERROR;

    return CBEventType.NO_ERROR;
}