const coral = @import("coral");

pub const CompileError = coral.io.AllocationError || error {

};

pub const Environment = struct {
	allocator: coral.io.Allocator,
	globals: ValueTable,
	stack: coral.stack.Dense(Value),
	calls: coral.stack.Dense(CallFrame),

	const CallFrame = struct {
		object: ?*Object,
		ip: usize,
		slots: []Value,
	};

	pub const InitOptions = struct {
		stack_max: u32,
		calls_max: u32,
	};

	pub const NewOptions = struct {
		userdata: []const u8 = &.{},
		identity: ?*const anyopaque = null,
		behavior: *const Object.Behavior = &.{},
	};

	pub const NewScriptOptions = struct {
		name: []const u8,
		data: []const u8,
	};

	pub fn call(self: *Environment, object: *Object, arguments: []const Value) RuntimeError!Value {
		var global_object = Object{
			.ref_count = 0,
			.identity = &self.globals,
			.userdata = &.{},
			.fields = self.globals,
			.behavior = &.{},
		};

		return object.behavior.caller(.{
			.env = self,
			.args = arguments,
			.caller = &global_object,
			.callee = object,
		});
	}

	pub fn check(self: Environment, condition: bool, failure_message: []const u8) RuntimeError!void {
		if (condition) return;

		// TODO: Emit failure message.
		_ = self;
		_ = failure_message;

		return error.CheckFailure;
	}

	pub fn deinit(self: *Environment) void {
		self.stack.deinit(self.allocator);
		self.calls.deinit(self.allocator);
	}

	pub fn global_set(self: *Environment, global_name: []const u8, value: Value) coral.io.AllocationError!void {
		try self.globals.assign(self.allocator, global_name, value);
	}

	pub fn init(allocator: coral.io.Allocator, options: InitOptions) !Environment {
		var environment = Environment{
			.allocator = allocator,
			.globals = .{},
			.stack = .{},
			.calls = .{},
		};

		errdefer {
			environment.stack.deinit(allocator);
			environment.calls.deinit(allocator);
		}

		try environment.stack.grow(allocator, options.stack_max);
		try environment.calls.grow(allocator, options.calls_max);

		return environment;
	}

	pub fn new(self: *Environment, options: NewOptions) coral.io.AllocationError!*Object {
		const object = try coral.io.allocate_one(Object, self.allocator);

		errdefer coral.io.deallocate(self.allocator, object);

		const userdata = try coral.io.allocate_many(u8, options.userdata.len, self.allocator);

		errdefer coral.io.deallocate(self.allocator, userdata);

		coral.io.copy(userdata, options.userdata);

		object.* = .{
			.userdata = userdata,
			.ref_count = 1,
			.identity = options.identity orelse userdata.ptr,
			.behavior = options.behavior,
			.fields = .{},
		};

		return object;
	}

	pub fn new_array(self: *Environment) coral.io.AllocationError!*Object {
		// TODO: Implement.
		return self.new(.none, .{});
	}

	pub fn new_script(self: *Environment, options: NewScriptOptions) coral.io.AllocationError!*Object {
		// TODO: Implement.
		_ = self;
		_ = options;

		return error.OutOfMemory;
	}

	pub fn new_string(self: *Environment, string_data: []const u8) coral.io.AllocationError!*Object {
		const object = try self.new(.{
			.userdata = string_data,
			.behavior = &.{},
		});

		errdefer self.release(object);

		return object;
	}

	pub fn new_string_from(self: *Environment, formats: []const coral.format.Value) coral.io.AllocationError!*Object {
		// TODO: Implement.
		coral.format.print(coral.io.null_writer, formats);

		return self.new_string("");
	}

	pub fn new_string_from_integer(self: *Environment, integer: Integer) coral.io.AllocationError!*Object {
		// TODO: Implement.
		_ = integer;

		return self.new_string("0");
	}

	pub fn new_table(self: *Environment) coral.io.AllocationError!*Object {
		// TODO: Implement.
		return self.new(.none, .{});
	}

	pub fn raw_get(_: Environment, object: *Object, field_name: []const u8) Value {
		return object.fields.lookup(field_name) orelse .nil;
	}

	pub fn raw_set(environment: Environment, object: *Object, field_name: []const u8, value: Value) coral.io.AllocationError!void {
		try object.fields.assign(environment.allocator, field_name, value);
	}

	pub fn release(self: Environment, object: *Object) void {
		coral.debug.assert(object.ref_count != 0);

		object.ref_count -= 1;

		if (object.ref_count == 0) {
			coral.io.deallocate(self.allocator, object.userdata);
			coral.io.deallocate(self.allocator, object);
		}
	}

	pub fn user_cast(self: *Environment, object: *Object, expected_identity: *const anyopaque, comptime CastTarget: type) RuntimeError!*CastTarget {
		// TODO: Emit failure message.
		_ = self;

		if (object.identity != expected_identity) {
			// Identity does not match what was expected.
			return error.InvalidOperation;
		}

		if (object.userdata.len != @sizeOf(CastTarget)) {
			// Userdata size does not match target type.
			return error.InvalidOperation;
		}

		return @ptrCast(*CastTarget, @alignCast(@alignOf(CastTarget), object.userdata));
	}

	pub fn virtual_call(self: *Environment, object: *Object, index: Value, arguments: []const Value) RuntimeError!Value {
		const value = try self.virtual_get(object, index);

		switch (value) {
			.object => |callee| {
				defer self.release(callee);

				return callee.behavior.caller(.{
					.environment = self,
					.object = callee,
					.caller = object,
					.arguments = arguments,
				});
			},

			else => return error.InvalidOperation,
		}
	}

	pub fn virtual_get(self: *Environment, object: *Object, index: Value) RuntimeError!Value {
		return object.behavior.getter(.{
			.environment = self,
			.object = object,
			.index = index,
		});
	}

	pub fn virtual_set(self: *Environment, object: *Object, index: Value, value: Value) RuntimeError!void {
		return object.behavior.setter(.{
			.environment = self,
			.object = object,
			.index = index,
			.value = value,
		});
	}
};

pub const Float = f32;

pub const Integer = i32;

pub const Object = struct {
	ref_count: usize,
	identity: *const anyopaque,
	userdata: []u8,
	behavior: *const Behavior,
	fields: ValueTable,

	pub const Behavior = struct {
		caller: *const Caller = default_call,
		deinitialize: *const Deinitializer = default_deinitialize,
		getter: *const Getter = default_get,
		setter: *const Setter = default_set,

		fn default_call(_: CallContext) RuntimeError!Value {
			return error.InvalidOperation;
		}

		fn default_deinitialize(_: DeinitializeContext) void {
			// Nothing to deinitialize by default.
		}

		fn default_get(context: GetContext) RuntimeError!Value {
			switch (context.index) {
				.object => |index| {
					if (!index.is_string()) return error.InvalidOperation;

					return context.obj.fields.lookup(index.userdata) orelse .nil;
				},

				.integer => |integer| {
					const index = context.env.new_string_from(&.{.{.signed = integer}});

					defer context.env.release(index);

					return context.obj.fields.lookup(index.userdata) orelse .nil;
				},

				else => return error.InvalidOperation,
			}
		}

		fn default_set(_: SetContext) RuntimeError!void {
			return error.InvalidOperation;
		}
	};

	pub const CallContext = struct {
		env: *Environment,
		caller: *Object,
		callee: *Object,
		args: []const Value,
	};

	pub const Caller = fn (context: CallContext) RuntimeError!Value;

	pub const DeinitializeContext = struct {
		env: *Environment,
		obj: *Object,
	};

	pub const Deinitializer = fn (context: DeinitializeContext) void;

	pub const GetContext = struct {
		env: *Environment,
		obj: *const Object,
		index: Value,
	};

	pub const Getter = fn (context: GetContext) RuntimeError!Value;

	pub const SetContext = struct {
		env: *Environment,
		obj: *Object,
		index: Value,
		value: Value,
	};

	pub const Setter = fn (context: SetContext) RuntimeError!void;

	pub fn as_value(self: *Object) Value {
		return .{.object = self};
	}

	pub fn is_string(self: Object) bool {
		// Userdata represents a string (of bytes) if it's identity is it's userdata.
		return self.identity == @ptrCast(*const anyopaque, self.userdata.ptr);
	}
};

pub const RuntimeError = coral.io.AllocationError || error {
	InvalidOperation,
	CheckFailure,
};

pub const Value = union(enum) {
	nil,
	false,
	true,
	float: Float,
	integer: Integer,
	object: *Object,
};

const ValueTable = coral.table.Hashed(coral.table.string_key, Value);