pub const EnvMap = struct {
    hash_map: HashMap,

    const HashMap = std.HashMap(
        []const u8,
        []const u8,
        EnvNameHashContext,
        std.hash_map.default_max_load_percentage,
    );

    pub const Size = HashMap.Size;

    pub const EnvNameHashContext = struct {
        fn upcase(c: u21) u21 {
            if (c <= std.math.maxInt(u16))
                return windows.ntdll.RtlUpcaseUnicodeChar(@as(u16, @intCast(c)));
            return c;
        }

        pub fn hash(self: @This(), s: []const u8) u64 {
            _ = self;
            if (native_os == .windows) {
                var h = std.hash.Wyhash.init(0);
                var it = unicode.Wtf8View.initUnchecked(s).iterator();
                while (it.nextCodepoint()) |cp| {
                    const cp_upper = upcase(cp);
                    h.update(&[_]u8{
                        @as(u8, @intCast((cp_upper >> 16) & 0xff)),
                        @as(u8, @intCast((cp_upper >> 8) & 0xff)),
                        @as(u8, @intCast((cp_upper >> 0) & 0xff)),
                    });
                }
                return h.final();
            }
            return std.hash_map.hashString(s);
        }

        pub fn eql(self: @This(), a: []const u8, b: []const u8) bool {
            _ = self;
            if (native_os == .windows) {
                var it_a = unicode.Wtf8View.initUnchecked(a).iterator();
                var it_b = unicode.Wtf8View.initUnchecked(b).iterator();
                while (true) {
                    const c_a = it_a.nextCodepoint() orelse break;
                    const c_b = it_b.nextCodepoint() orelse return false;
                    if (upcase(c_a) != upcase(c_b))
                        return false;
                }
                return if (it_b.nextCodepoint()) |_| false else true;
            }
            return std.hash_map.eqlString(a, b);
        }
    };

    /// Create a EnvMap backed by a specific allocator.
    /// That allocator will be used for both backing allocations
    /// and string deduplication.
    pub fn init(allocator: Allocator) EnvMap {
        return EnvMap{ .hash_map = HashMap.init(allocator) };
    }

    /// Free the backing storage of the map, as well as all
    /// of the stored keys and values.
    pub fn deinit(self: *EnvMap) void {
        var it = self.hash_map.iterator();
        while (it.next()) |entry| {
            self.free(entry.key_ptr.*);
            self.free(entry.value_ptr.*);
        }

        self.hash_map.deinit();
    }

    /// Same as `put` but the key and value become owned by the EnvMap rather
    /// than being copied.
    /// If `putMove` fails, the ownership of key and value does not transfer.
    /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
    pub fn putMove(self: *EnvMap, key: []u8, value: []u8) !void {
        assert(unicode.wtf8ValidateSlice(key));
        const get_or_put = try self.hash_map.getOrPut(key);
        if (get_or_put.found_existing) {
            self.free(get_or_put.key_ptr.*);
            self.free(get_or_put.value_ptr.*);
            get_or_put.key_ptr.* = key;
        }
        get_or_put.value_ptr.* = value;
    }

    /// `key` and `value` are copied into the EnvMap.
    /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
    pub fn put(self: *EnvMap, key: []const u8, value: []const u8) !void {
        assert(unicode.wtf8ValidateSlice(key));
        const value_copy = try self.copy(value);
        errdefer self.free(value_copy);
        const get_or_put = try self.hash_map.getOrPut(key);
        if (get_or_put.found_existing) {
            self.free(get_or_put.value_ptr.*);
        } else {
            get_or_put.key_ptr.* = self.copy(key) catch |err| {
                _ = self.hash_map.remove(key);
                return err;
            };
        }
        get_or_put.value_ptr.* = value_copy;
    }

    /// Find the address of the value associated with a key.
    /// The returned pointer is invalidated if the map resizes.
    /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
    pub fn getPtr(self: EnvMap, key: []const u8) ?*[]const u8 {
        assert(unicode.wtf8ValidateSlice(key));
        return self.hash_map.getPtr(key);
    }

    /// Return the map's copy of the value associated with
    /// a key.  The returned string is invalidated if this
    /// key is removed from the map.
    /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
    pub fn get(self: EnvMap, key: []const u8) ?[]const u8 {
        assert(unicode.wtf8ValidateSlice(key));
        return self.hash_map.get(key);
    }

    /// Removes the item from the map and frees its value.
    /// This invalidates the value returned by get() for this key.
    /// On Windows `key` must be a valid [WTF-8](https://simonsapin.github.io/wtf-8/) string.
    pub fn remove(self: *EnvMap, key: []const u8) void {
        assert(unicode.wtf8ValidateSlice(key));
        const kv = self.hash_map.fetchRemove(key) orelse return;
        self.free(kv.key);
        self.free(kv.value);
    }

    /// Returns the number of KV pairs stored in the map.
    pub fn count(self: EnvMap) HashMap.Size {
        return self.hash_map.count();
    }

    /// Returns an iterator over entries in the map.
    pub fn iterator(self: *const EnvMap) HashMap.Iterator {
        return self.hash_map.iterator();
    }

    fn free(self: EnvMap, value: []const u8) void {
        self.hash_map.allocator.free(value);
    }

    fn copy(self: EnvMap, value: []const u8) ![]u8 {
        return self.hash_map.allocator.dupe(u8, value);
    }
}