Self

pub fn ComponentIterator(comptime path_type: PathType, comptime T: type) type {
    return struct {
        path: []const T,
        /// Length of the root with at most one trailing path separator included (e.g. `C:/`).
        root_len: usize,
        /// Length of the root with all trailing path separators included (e.g. `C://///`).
        root_end_index: usize,
        start_index: usize = 0,
        end_index: usize = 0,

        const Self = @This();

        pub const Component = struct {
            /// The current component's path name, e.g. 'b'.
            /// This will never contain path separators.
            name: []const T,
            /// The full path up to and including the current component, e.g. '/a/b'
            /// This will never contain trailing path separators.
            path: []const T,
        };

        /// After `init`, `next` will return the first component after the root
        /// (there is no need to call `first` after `init`).
        /// To iterate backwards (from the end of the path to the beginning), call `last`
        /// after `init` and then iterate via `previous` calls.
        /// For Windows paths, paths are assumed to be in the Win32 namespace.
        pub fn init(path: []const T) Self {
            const root_len: usize = switch (path_type) {
                .posix, .uefi => posix: {
                    // Root on UEFI and POSIX only differs by the path separator
                    break :posix if (path.len > 0 and path_type.isSep(T, path[0])) 1 else 0;
                },
                .windows => windows: {
                    break :windows parsePathWindows(T, path).root.len;
                },
            };
            // If there are repeated path separators directly after the root,
            // keep track of that info so that they don't have to be dealt with when
            // iterating components.
            var root_end_index = root_len;
            for (path[root_len..]) |c| {
                if (!path_type.isSep(T, c)) break;
                root_end_index += 1;
            }
            return .{
                .path = path,
                .root_len = root_len,
                .root_end_index = root_end_index,
                .start_index = root_end_index,
                .end_index = root_end_index,
            };
        }

        /// Returns the root of the path if it is not a relative path, or null otherwise.
        /// For POSIX paths, this will be `/`.
        /// For Windows paths, this will be something like `C:\`, `\\server\share\`, etc.
        /// For UEFI paths, this will be `\`.
        pub fn root(self: Self) ?[]const T {
            if (self.root_end_index == 0) return null;
            return self.path[0..self.root_len];
        }

        /// Returns the first component (from the beginning of the path).
        /// For example, if the path is `/a/b/c` then this will return the `a` component.
        /// After calling `first`, `previous` will always return `null`, and `next` will return
        /// the component to the right of the one returned by `first`, if any exist.
        pub fn first(self: *Self) ?Component {
            self.start_index = self.root_end_index;
            self.end_index = self.start_index;
            while (self.end_index < self.path.len and !path_type.isSep(T, self.path[self.end_index])) {
                self.end_index += 1;
            }
            if (self.end_index == self.start_index) return null;
            return .{
                .name = self.path[self.start_index..self.end_index],
                .path = self.path[0..self.end_index],
            };
        }

        /// Returns the last component (from the end of the path).
        /// For example, if the path is `/a/b/c` then this will return the `c` component.
        /// After calling `last`, `next` will always return `null`, and `previous` will return
        /// the component to the left of the one returned by `last`, if any exist.
        pub fn last(self: *Self) ?Component {
            self.end_index = self.path.len;
            while (true) {
                if (self.end_index == self.root_end_index) {
                    self.start_index = self.end_index;
                    return null;
                }
                if (!path_type.isSep(T, self.path[self.end_index - 1])) break;
                self.end_index -= 1;
            }
            self.start_index = self.end_index;
            while (true) {
                if (self.start_index == self.root_end_index) break;
                if (path_type.isSep(T, self.path[self.start_index - 1])) break;
                self.start_index -= 1;
            }
            if (self.start_index == self.end_index) return null;
            return .{
                .name = self.path[self.start_index..self.end_index],
                .path = self.path[0..self.end_index],
            };
        }

        /// Returns the next component (the component to the right of the most recently
        /// returned component), or null if no such component exists.
        /// For example, if the path is `/a/b/c` and the most recently returned component
        /// is `b`, then this will return the `c` component.
        pub fn next(self: *Self) ?Component {
            const peek_result = self.peekNext() orelse return null;
            self.start_index = peek_result.path.len - peek_result.name.len;
            self.end_index = peek_result.path.len;
            return peek_result;
        }

        /// Like `next`, but does not modify the iterator state.
        pub fn peekNext(self: Self) ?Component {
            var start_index = self.end_index;
            while (start_index < self.path.len and path_type.isSep(T, self.path[start_index])) {
                start_index += 1;
            }
            var end_index = start_index;
            while (end_index < self.path.len and !path_type.isSep(T, self.path[end_index])) {
                end_index += 1;
            }
            if (start_index == end_index) return null;
            return .{
                .name = self.path[start_index..end_index],
                .path = self.path[0..end_index],
            };
        }

        /// Returns the previous component (the component to the left of the most recently
        /// returned component), or null if no such component exists.
        /// For example, if the path is `/a/b/c` and the most recently returned component
        /// is `b`, then this will return the `a` component.
        pub fn previous(self: *Self) ?Component {
            const peek_result = self.peekPrevious() orelse return null;
            self.start_index = peek_result.path.len - peek_result.name.len;
            self.end_index = peek_result.path.len;
            return peek_result;
        }

        /// Like `previous`, but does not modify the iterator state.
        pub fn peekPrevious(self: Self) ?Component {
            var end_index = self.start_index;
            while (true) {
                if (end_index == self.root_end_index) return null;
                if (!path_type.isSep(T, self.path[end_index - 1])) break;
                end_index -= 1;
            }
            var start_index = end_index;
            while (true) {
                if (start_index == self.root_end_index) break;
                if (path_type.isSep(T, self.path[start_index - 1])) break;
                start_index -= 1;
            }
            if (start_index == end_index) return null;
            return .{
                .name = self.path[start_index..end_index],
                .path = self.path[0..end_index],
            };
        }
    };
}