const debug = @import("./debug.zig");

const math = @import("./math.zig");

const std = @import("std");

pub const AllocationError = error {
	OutOfMemory,
};

pub const Allocator = struct {
	context: *anyopaque,

	actions: *const struct {
		deallocate: *const fn (context: *anyopaque, allocation: []Byte) void,
		reallocate: *const fn (context: *anyopaque, return_address: usize, existing_allocation: ?[]Byte, size: usize) AllocationError![]Byte,
	},

	pub fn Actions(comptime State: type) type {
		return struct {
			deallocate: fn (state: *State, allocation: []Byte) void,
			reallocate: fn (state: *State, return_address: usize, existing_allocation: ?[]Byte, size: usize) AllocationError![]Byte,
		};
	}

	pub fn bind(comptime State: type, state: *State, comptime actions: Actions(State)) Allocator {
		const is_zero_aligned = @alignOf(State) == 0;

		const ErasedActions = struct {
			fn deallocate(context: *anyopaque, allocation: []Byte) void {
				if (is_zero_aligned) {
					return actions.deallocate(@ptrCast(context), allocation);
				}

				return actions.deallocate(@ptrCast(@alignCast(context)), allocation);
			}

			fn reallocate(context: *anyopaque, return_address: usize, existing_allocation: ?[]Byte, size: usize) AllocationError![]Byte {
				if (is_zero_aligned) {
					return actions.reallocate(@ptrCast(context), return_address, existing_allocation, size);
				}

				return actions.reallocate(@ptrCast(@alignCast(context)), return_address, existing_allocation, size);
			}
		};

		return .{
			.context = if (is_zero_aligned) state else @ptrCast(state),

			.actions = &.{
				.deallocate = ErasedActions.deallocate,
				.reallocate = ErasedActions.reallocate,
			}
		};
	}

	pub fn deallocate(self: Allocator, allocation: anytype) void {
		switch (@typeInfo(@TypeOf(allocation))) {
			.Pointer => |pointer| {
				self.actions.deallocate(self.context, switch (pointer.size) {
					.One => @as([*]Byte, @ptrCast(allocation))[0 .. @sizeOf(pointer.child)],
					.Slice => @as([*]Byte, @ptrCast(allocation.ptr))[0 .. (@sizeOf(pointer.child) * allocation.len)],
					.Many, .C => @compileError("length of allocation must be known to deallocate"),
				});
			},

			else => @compileError("cannot deallocate " ++ allocation),
		}
	}

	pub fn reallocate(self: Allocator, allocation: ?[]Byte, allocation_size: usize) AllocationError![]Byte {
		return self.actions.reallocate(self.context, @returnAddress(), allocation, allocation_size);
	}
};

pub const Byte = u8;

pub const FixedBuffer = struct {
	bytes: []Byte,

	pub fn as_writer(self: *FixedBuffer) Writer {
		return Writer.bind(FixedBuffer, self, struct {
			fn write(writable_memory: *FixedBuffer, data: []const Byte) ?usize {
				return writable_memory.write(data);
			}
		}.write);
	}

	pub fn put(self: *FixedBuffer, byte: Byte) bool {
		if (self.bytes.len == 0) {
			return false;
		}

		self.bytes[0] = byte;
		self.bytes = self.bytes[1 ..];

		return true;
	}

	pub fn write(self: *FixedBuffer, bytes: []const Byte) usize {
		const writable = @min(self.bytes.len, bytes.len);

		copy(self.bytes, bytes);

		self.bytes = self.bytes[writable ..];

		return writable;
	}
};

pub fn Functor(comptime Output: type, comptime Input: type) type {
	return struct {
		context: *const anyopaque,
		invoker: *const fn (capture: *const anyopaque, input: Input) Output,

		const Self = @This();

		pub fn bind(comptime State: type, state: *const State, comptime invoker: fn (capture: *const State, input: Input) Output) Self {
			const is_zero_aligned = @alignOf(State) == 0;

			const Invoker = struct {
				fn invoke(context: *const anyopaque, input: Input) Output {
					if (is_zero_aligned) {
						return invoker(@ptrCast(context), input);
					}

					return invoker(@ptrCast(@alignCast(context)), input);
				}
			};

			return .{
				.context = if (is_zero_aligned) state else @ptrCast(state),
				.invoker = Invoker.invoke,
			};
		}

		pub fn from(comptime invoker: fn (input: Input) Output) Self {
			const Invoker = struct {
				fn invoke(_: *const anyopaque, input: Input) Output {
					return invoker(input);
				}
			};

			return .{
				.context = &.{},
				.invoker = Invoker.invoke,
			};
		}

		pub fn invoke(self: Self, input: Input) Output {
			return self.invoker(self.context, input);
		}
	};
}

pub fn Generator(comptime Output: type, comptime Input: type) type {
	return struct {
		context: *anyopaque,
		invoker: *const fn (capture: *anyopaque, input: Input) Output,

		const Self = @This();

		pub fn bind(comptime State: type, state: *State, comptime invoker: fn (capture: *State, input: Input) Output) Self {
			const is_zero_aligned = @alignOf(State) == 0;

			return .{
				.context = if (is_zero_aligned) state else @ptrCast(state),

				.invoker = struct {
					fn invoke(context: *anyopaque, input: Input) Output {
						if (is_zero_aligned) {
							return invoker(@ptrCast(context), input);
						}

						return invoker(@ptrCast(@alignCast(context)), input);
					}
				}.invoke,
			};
		}

		pub fn from_fn(comptime invoker: fn (input: Input) Output) Self {
			const Invoker = struct {
				fn invoke(_: *const anyopaque, input: Input) Output {
					return invoker(input);
				}
			};

			return .{
				.context = &.{},
				.invoker = Invoker.invoke,
			};
		}

		pub fn invoke(self: Self, input: Input) Output {
			return self.invoker(self.context, input);
		}
	};
}

pub fn Tag(comptime Element: type) type {
	return switch (@typeInfo(Element)) {
		.Enum => |info| info.tag_type,
		.Union => |info| info.tag_type orelse @compileError(@typeName(Element) ++ " has no tag type"),
		else => @compileError("expected enum or union type, found '" ++ @typeName(Element) ++ "'"),
	};
}

pub const Writer = Generator(?usize, []const Byte);

pub fn all_equals(target: []const Byte, match: Byte) bool {
	for (0 .. target.len) |index| {
		if (target[index] != match) {
			return false;
		}
	}

	return true;
}

pub fn allocate_copy(comptime Element: type, allocator: Allocator, source: []const Element) AllocationError![]Element {
	const allocation = try allocator.actions.reallocate(allocator.context, @returnAddress(), null, @sizeOf(Element) * source.len);

	copy(allocation, bytes_of(source));

	return @as([*]Element, @ptrCast(@alignCast(allocation.ptr)))[0 .. source.len];
}

pub fn allocate_many(allocator: Allocator, count: usize, value: anytype) AllocationError![]@TypeOf(value) {
	const Type = @TypeOf(value);
	const typeSize = @sizeOf(Type);

	if (typeSize == 0) {
		@compileError("Cannot allocate memory for 0-byte sized type " ++ @typeName(Type));
	}

	const allocations = @as([*]Type, @ptrCast(@alignCast(try allocator.actions.reallocate(
		allocator.context,
		@returnAddress(),
		null,
		typeSize * count))))[0 .. count];

	for (allocations) |*allocation| {
		allocation.* = value;
	}

	return allocations;
}

pub fn allocate_one(allocator: Allocator, value: anytype) AllocationError!*@TypeOf(value) {
	const Type = @TypeOf(value);
	const typeSize = @sizeOf(Type);

	if (typeSize == 0) {
		@compileError("Cannot allocate memory for 0-byte sized type " ++ @typeName(Type));
	}

	const allocation = @as(*Type, @ptrCast(@alignCast(try allocator.actions.reallocate(
		allocator.context,
		@returnAddress(),
		null,
		typeSize))));

	allocation.* = value;

	return allocation;
}

pub fn allocate_string(allocator: Allocator, source: []const Byte) AllocationError![:0]Byte {
	const allocation = try allocator.actions.reallocate(allocator.context, @returnAddress(), null, source.len + 1);

	copy(allocation[0 .. source.len], source);

	allocation[source.len] = 0;

	return @ptrCast(allocation);
}

pub fn are_equal(target: []const Byte, match: []const Byte) bool {
	if (target.len != match.len) {
		return false;
	}

	for (0 .. target.len) |index| {
		if (target[index] != match[index]) {
			return false;
		}
	}

	return true;
}

pub fn bytes_of(value: anytype) []const Byte {
	const pointer_info = @typeInfo(@TypeOf(value)).Pointer;

	return switch (pointer_info.size) {
		.One => @as([*]const Byte, @ptrCast(value))[0 .. @sizeOf(pointer_info.child)],
		.Slice => @as([*]const Byte, @ptrCast(value.ptr))[0 .. @sizeOf(pointer_info.child) * value.len],
		else => @compileError("`value` must be single-element pointer or slice type"),
	};
}

pub fn copy(target: []Byte, source: []const Byte) void {
	var index: usize = 0;

	while (index < source.len) : (index += 1) {
		target[index] = source[index];
	}
}

pub fn compare(this: []const Byte, that: []const Byte) isize {
	const range = @min(this.len, that.len);
	var index: usize = 0;

	while (index < range) : (index += 1) {
		const difference = @as(isize, @intCast(this[index])) - @as(isize, @intCast(that[index]));

		if (difference != 0) {
			return difference;
		}
	}

	return @as(isize, @intCast(this.len)) - @as(isize, @intCast(that.len));
}

pub fn djb2_hash(comptime int: std.builtin.Type.Int, target: []const Byte) math.Int(int) {
	var hash_code = @as(math.Int(int), 5381);

	for (target) |byte| {
		hash_code = ((hash_code << 5) +% hash_code) +% byte;
	}

	return hash_code;
}

pub fn find_first(haystack: []const Byte, needle: Byte) ?usize {
	for (0 .. haystack.len) |i| {
		if (haystack[i] == needle) {
			return i;
		}
	}

	return null;
}

pub fn jenkins_hash(comptime int: std.builtin.Type.Int, bytes: []const Byte) math.Int(int) {
    var hash = @as(math.Int(int), 0);

    for (bytes) |byte| {
        hash +%= byte;
        hash +%= (hash << 10);
        hash ^= (hash >> 6);
    }

    hash +%= (hash << 3);
    hash ^= (hash >> 11);
    hash +%= (hash << 15);

    return hash;
}

pub const null_writer = Writer.from_fn(write_null);

pub fn slice_sentineled(comptime sen: anytype, ptr: [*:sen]const @TypeOf(sen)) [:sen]const @TypeOf(sen) {
    var len = @as(usize, 0);

    while (ptr[len] != sen) {
        len += 1;
    }

    return ptr[0 .. len:sen];
}

pub fn tag_of(comptime value: anytype) Tag(@TypeOf(value)) {
	return @as(Tag(@TypeOf(value)), value);
}

fn write_null(buffer: []const u8) ?usize {
	return buffer.len;
}

pub fn zero(target: []Byte) void {
	for (target) |*t| t.* = 0;
}