const std = @import("std");

const pad = @import("padding.zig");
const validate = @import("validate.zig");
const compress = @import("compress.zig");
const InvalidRecord = validate.InvalidRecord;

const mem = std.mem;
const Allocator = mem.Allocator;
const ArrayList = std.ArrayList;
const BufSet = std.BufSet;

pub const Group = struct {
    gid: u32,
    name: []const u8,
    members: BufSet,

    pub fn clone(self: *const Group, allocator: Allocator) Allocator.Error!Group {
        var name = try allocator.dupe(u8, self.name);
        return Group{
            .gid = self.gid,
            .name = name,
            .members = try self.members.cloneWithAllocator(allocator),
        };
    }

    pub fn deinit(self: *Group, allocator: Allocator) void {
        allocator.free(self.name);
        self.members.deinit();
        self.* = undefined;
    }
};

pub const GroupStored = struct {
    gid: u32,
    name: []const u8,
    members_offset: u64,
};

pub const PackedGroup = struct {
    pub const alignment_bits = 3;

    const Inner = packed struct {
        gid: u32,
        padding: u3 = 0,
        groupname_len: u5,

        pub fn groupnameLen(self: *const Inner) usize {
            return @as(usize, self.groupname_len) + 1;
        }
    };

    inner: *const Inner,
    groupdata: []const u8,
    members_offset: u64,

    pub const Entry = struct {
        group: PackedGroup,
        next: ?[]const u8,
    };

    pub fn fromBytes(bytes: []const u8) error{Overflow}!Entry {
        const inner = mem.bytesAsValue(Inner, bytes[0..@sizeOf(Inner)]);
        const start_blob = @sizeOf(Inner);
        const end_strings = @sizeOf(Inner) + inner.groupnameLen();
        const members_offset = try compress.uvarint(bytes[end_strings..]);
        const end_blob = end_strings + members_offset.bytes_read;
        const next_start = pad.roundUp(usize, alignment_bits, end_blob);

        var next: ?[]const u8 = null;
        if (next_start < bytes.len)
            next = bytes[next_start..];

        return Entry{
            .group = PackedGroup{
                .inner = inner,
                .groupdata = bytes[start_blob..end_strings],
                .members_offset = members_offset.value,
            },
            .next = next,
        };
    }

    fn validateUtf8(s: []const u8) InvalidRecord!void {
        if (!std.unicode.utf8ValidateSlice(s))
            return error.InvalidRecord;
    }

    pub const Iterator = struct {
        section: ?[]const u8,

        pub fn next(it: *Iterator) error{Overflow}!?PackedGroup {
            if (it.section) |section| {
                const entry = try fromBytes(section);
                it.section = entry.next;
                return entry.group;
            }
            return null;
        }
    };

    pub fn iterator(section: []const u8) Iterator {
        return Iterator{ .section = section };
    }

    pub fn gid(self: *const PackedGroup) u32 {
        return self.inner.gid;
    }

    pub fn membersOffset(self: *const PackedGroup) u64 {
        return self.members_offset;
    }

    pub fn name(self: *const PackedGroup) []const u8 {
        return self.groupdata;
    }

    const packErr = validate.InvalidRecord || Allocator.Error || error{Overflow};
    pub fn packTo(
        arr: *ArrayList(u8),
        group: GroupStored,
    ) packErr!void {
        std.debug.assert(arr.items.len & 7 == 0);
        try validate.utf8(group.name);
        const len = try validate.downCast(u5, group.name.len - 1);
        const inner = Inner{ .gid = group.gid, .groupname_len = len };
        try arr.*.appendSlice(mem.asBytes(&inner));
        try arr.*.appendSlice(group.name);
        try compress.appendUvarint(arr, group.members_offset);
    }
};

const testing = std.testing;

// someMembers constructs a bufset from an allocator and a list of strings.
pub fn someMembers(
    allocator: Allocator,
    members: []const []const u8,
) Allocator.Error!BufSet {
    var bufset = BufSet.init(allocator);
    errdefer bufset.deinit();
    for (members) |member|
        try bufset.insert(member);
    return bufset;
}

test "PackedGroup alignment" {
    try testing.expectEqual(@sizeOf(PackedGroup) * 8, @bitSizeOf(PackedGroup));
}

test "construct PackedGroups" {
    var buf = ArrayList(u8).init(testing.allocator);
    defer buf.deinit();

    const groups = [_]GroupStored{
        GroupStored{
            .gid = 1000,
            .name = "sudo",
            .members_offset = 1,
        },
        GroupStored{
            .gid = std.math.maxInt(u32),
            .name = "Name" ** 8, // 32
            .members_offset = std.math.maxInt(u64),
        },
    };

    for (groups) |group| {
        try PackedGroup.packTo(&buf, group);
        try pad.arrayList(&buf, PackedGroup.alignment_bits);
    }

    var i: u29 = 0;
    var it = PackedGroup.iterator(buf.items);
    while (try it.next()) |group| : (i += 1) {
        try testing.expectEqual(groups[i].gid, group.gid());
        try testing.expectEqualStrings(groups[i].name, group.name());
        try testing.expectEqual(groups[i].members_offset, group.membersOffset());
    }
    try testing.expectEqual(groups.len, i);
}

test "Group.clone" {
    var allocator = testing.allocator;
    var arena = std.heap.ArenaAllocator.init(allocator);
    defer arena.deinit();

    var members = BufSet.init(allocator);
    try members.insert("member1");
    try members.insert("member2");
    defer members.deinit();

    var cloned = try members.cloneWithAllocator(arena.allocator());

    cloned.remove("member1");
    try cloned.insert("member4");
    try testing.expect(members.contains("member1"));
    try testing.expect(!members.contains("member4"));

    try testing.expect(!cloned.contains("member1"));
    try testing.expect(cloned.contains("member4"));
}