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piecetable impl with undo

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panda
2026-06-17 00:43:43 +12:00
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const std = @import("std");
// Although this function looks imperative, it does not perform the build
// directly and instead it mutates the build graph (`b`) that will be then
// executed by an external runner. The functions in `std.Build` implement a DSL
// for defining build steps and express dependencies between them, allowing the
// build runner to parallelize the build automatically (and the cache system to
// know when a step doesn't need to be re-run).
pub fn build(b: *std.Build) void {
// Standard target options allow the person running `zig build` to choose
// what target to build for. Here we do not override the defaults, which
// means any target is allowed, and the default is native. Other options
// for restricting supported target set are available.
const target = b.standardTargetOptions(.{});
// Standard optimization options allow the person running `zig build` to select
// between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
// set a preferred release mode, allowing the user to decide how to optimize.
const optimize = b.standardOptimizeOption(.{});
// It's also possible to define more custom flags to toggle optional features
// of this build script using `b.option()`. All defined flags (including
// target and optimize options) will be listed when running `zig build --help`
// in this directory.
// This creates a module, which represents a collection of source files alongside
// some compilation options, such as optimization mode and linked system libraries.
// Zig modules are the preferred way of making Zig code available to consumers.
// addModule defines a module that we intend to make available for importing
// to our consumers. We must give it a name because a Zig package can expose
// multiple modules and consumers will need to be able to specify which
// module they want to access.
const mod = b.addModule("zig_piecetable", .{
// The root source file is the "entry point" of this module. Users of
// this module will only be able to access public declarations contained
// in this file, which means that if you have declarations that you
// intend to expose to consumers that were defined in other files part
// of this module, you will have to make sure to re-export them from
// the root file.
.root_source_file = b.path("src/root.zig"),
// Later on we'll use this module as the root module of a test executable
// which requires us to specify a target.
.target = target,
});
// Here we define an executable. An executable needs to have a root module
// which needs to expose a `main` function. While we could add a main function
// to the module defined above, it's sometimes preferable to split business
// logic and the CLI into two separate modules.
//
// If your goal is to create a Zig library for others to use, consider if
// it might benefit from also exposing a CLI tool. A parser library for a
// data serialization format could also bundle a CLI syntax checker, for example.
//
// If instead your goal is to create an executable, consider if users might
// be interested in also being able to embed the core functionality of your
// program in their own executable in order to avoid the overhead involved in
// subprocessing your CLI tool.
//
// If neither case applies to you, feel free to delete the declaration you
// don't need and to put everything under a single module.
const exe = b.addExecutable(.{
.name = "zig_piecetable",
.root_module = b.createModule(.{
// b.createModule defines a new module just like b.addModule but,
// unlike b.addModule, it does not expose the module to consumers of
// this package, which is why in this case we don't have to give it a name.
.root_source_file = b.path("src/main.zig"),
// Target and optimization levels must be explicitly wired in when
// defining an executable or library (in the root module), and you
// can also hardcode a specific target for an executable or library
// definition if desireable (e.g. firmware for embedded devices).
.target = target,
.optimize = optimize,
// List of modules available for import in source files part of the
// root module.
.imports = &.{
// Here "zig_piecetable" is the name you will use in your source code to
// import this module (e.g. `@import("zig_piecetable")`). The name is
// repeated because you are allowed to rename your imports, which
// can be extremely useful in case of collisions (which can happen
// importing modules from different packages).
.{ .name = "zig_piecetable", .module = mod },
},
}),
});
// This declares intent for the executable to be installed into the
// install prefix when running `zig build` (i.e. when executing the default
// step). By default the install prefix is `zig-out/` but can be overridden
// by passing `--prefix` or `-p`.
b.installArtifact(exe);
// This creates a top level step. Top level steps have a name and can be
// invoked by name when running `zig build` (e.g. `zig build run`).
// This will evaluate the `run` step rather than the default step.
// For a top level step to actually do something, it must depend on other
// steps (e.g. a Run step, as we will see in a moment).
const run_step = b.step("run", "Run the app");
// This creates a RunArtifact step in the build graph. A RunArtifact step
// invokes an executable compiled by Zig. Steps will only be executed by the
// runner if invoked directly by the user (in the case of top level steps)
// or if another step depends on it, so it's up to you to define when and
// how this Run step will be executed. In our case we want to run it when
// the user runs `zig build run`, so we create a dependency link.
const run_cmd = b.addRunArtifact(exe);
run_step.dependOn(&run_cmd.step);
// By making the run step depend on the default step, it will be run from the
// installation directory rather than directly from within the cache directory.
run_cmd.step.dependOn(b.getInstallStep());
// This allows the user to pass arguments to the application in the build
// command itself, like this: `zig build run -- arg1 arg2 etc`
if (b.args) |args| {
run_cmd.addArgs(args);
}
// Creates an executable that will run `test` blocks from the provided module.
// Here `mod` needs to define a target, which is why earlier we made sure to
// set the releative field.
const mod_tests = b.addTest(.{
.root_module = mod,
});
// A run step that will run the test executable.
const run_mod_tests = b.addRunArtifact(mod_tests);
// Creates an executable that will run `test` blocks from the executable's
// root module. Note that test executables only test one module at a time,
// hence why we have to create two separate ones.
const exe_tests = b.addTest(.{
.root_module = exe.root_module,
});
// A run step that will run the second test executable.
const run_exe_tests = b.addRunArtifact(exe_tests);
// A top level step for running all tests. dependOn can be called multiple
// times and since the two run steps do not depend on one another, this will
// make the two of them run in parallel.
const test_step = b.step("test", "Run tests");
test_step.dependOn(&run_mod_tests.step);
test_step.dependOn(&run_exe_tests.step);
// Just like flags, top level steps are also listed in the `--help` menu.
//
// The Zig build system is entirely implemented in userland, which means
// that it cannot hook into private compiler APIs. All compilation work
// orchestrated by the build system will result in other Zig compiler
// subcommands being invoked with the right flags defined. You can observe
// these invocations when one fails (or you pass a flag to increase
// verbosity) to validate assumptions and diagnose problems.
//
// Lastly, the Zig build system is relatively simple and self-contained,
// and reading its source code will allow you to master it.
}

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.{
// This is the default name used by packages depending on this one. For
// example, when a user runs `zig fetch --save <url>`, this field is used
// as the key in the `dependencies` table. Although the user can choose a
// different name, most users will stick with this provided value.
//
// It is redundant to include "zig" in this name because it is already
// within the Zig package namespace.
.name = .zig_piecetable,
// This is a [Semantic Version](https://semver.org/).
// In a future version of Zig it will be used for package deduplication.
.version = "0.0.0",
// Together with name, this represents a globally unique package
// identifier. This field is generated by the Zig toolchain when the
// package is first created, and then *never changes*. This allows
// unambiguous detection of one package being an updated version of
// another.
//
// When forking a Zig project, this id should be regenerated (delete the
// field and run `zig build`) if the upstream project is still maintained.
// Otherwise, the fork is *hostile*, attempting to take control over the
// original project's identity. Thus it is recommended to leave the comment
// on the following line intact, so that it shows up in code reviews that
// modify the field.
.fingerprint = 0x9be7c0b888bfd1e9, // Changing this has security and trust implications.
// Tracks the earliest Zig version that the package considers to be a
// supported use case.
.minimum_zig_version = "0.16.0",
// This field is optional.
// Each dependency must either provide a `url` and `hash`, or a `path`.
// `zig build --fetch` can be used to fetch all dependencies of a package, recursively.
// Once all dependencies are fetched, `zig build` no longer requires
// internet connectivity.
.dependencies = .{
// See `zig fetch --save <url>` for a command-line interface for adding dependencies.
//.example = .{
// // When updating this field to a new URL, be sure to delete the corresponding
// // `hash`, otherwise you are communicating that you expect to find the old hash at
// // the new URL. If the contents of a URL change this will result in a hash mismatch
// // which will prevent zig from using it.
// .url = "https://example.com/foo.tar.gz",
//
// // This is computed from the file contents of the directory of files that is
// // obtained after fetching `url` and applying the inclusion rules given by
// // `paths`.
// //
// // This field is the source of truth; packages do not come from a `url`; they
// // come from a `hash`. `url` is just one of many possible mirrors for how to
// // obtain a package matching this `hash`.
// //
// // Uses the [multihash](https://multiformats.io/multihash/) format.
// .hash = "...",
//
// // When this is provided, the package is found in a directory relative to the
// // build root. In this case the package's hash is irrelevant and therefore not
// // computed. This field and `url` are mutually exclusive.
// .path = "foo",
//
// // When this is set to `true`, a package is declared to be lazily
// // fetched. This makes the dependency only get fetched if it is
// // actually used.
// .lazy = false,
//},
},
// Specifies the set of files and directories that are included in this package.
// Only files and directories listed here are included in the `hash` that
// is computed for this package. Only files listed here will remain on disk
// when using the zig package manager. As a rule of thumb, one should list
// files required for compilation plus any license(s).
// Paths are relative to the build root. Use the empty string (`""`) to refer to
// the build root itself.
// A directory listed here means that all files within, recursively, are included.
.paths = .{
"build.zig",
"build.zig.zon",
"src",
// For example...
//"LICENSE",
//"README.md",
},
}

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//! By convention, root.zig is the root source file when making a package.
const std = @import("std");
const Io = std.Io;
const Piece = struct {
// each piece could just be a slice however this make it easier to write
start: usize,
length: usize,
text: *const []const u8,
const nothing: []const u8 = "";
pub const none = Piece{
.start = 0,
.length = 0,
.text = &nothing,
};
pub fn format(self: Piece, writer: *std.Io.Writer) !void {
try writer.print(
"piece {{src[{},{}] : \"{s}\"}}",
.{ self.start, self.length, self.text.* },
);
}
};
const ActionType = enum {
append,
insert,
insert_splits_piece,
delete,
};
const Action = struct {
piece_table_index: usize,
old_start: usize,
old_length: usize,
};
const ActionGroup = union(ActionType) {
/// this will only occur when the table was already empty so boof it
append: void,
/// happens when a piece is cleanly inserted in to the table
insert: usize,
/// happens when the piece requires to be split before indexing
insert_splits_piece: Action,
/// happens when a piece is deletes (length set to zero)
/// appends all modifed pieces to be restored
delete: std.ArrayList(Action),
};
/// abstracted so i can implement redo
const ActionList = struct {
const Self = @This();
actions: std.ArrayList(ActionGroup) = .empty,
pub const empty = ActionList{};
pub fn append(self: *Self, alloc: std.mem.Allocator, action_group: ActionGroup) !void {
try self.actions.append(alloc, action_group);
}
pub fn pop(self: *Self) ?ActionGroup {
return self.actions.pop();
}
pub fn deinit(self: *Self, alloc: std.mem.Allocator) void {
for (self.actions.items) |*act| {
switch (act.*) {
.delete => act.delete.deinit(alloc),
else => continue,
}
}
self.actions.deinit(alloc);
}
};
/// piece table with built in undo
/// since the piece table is going in a text editor
/// if you dont have undo is not going to be a very
/// good text editor we aint trying to be ed here
const PieceTable = struct {
const Self = @This();
const Alloc = std.mem.Allocator;
pieces: std.ArrayList(Piece) = .empty,
actions: ActionList = .empty,
// i have this here because its easy
total_len: usize = 0,
pub fn init() Self {
return Self{};
}
/// self : piece table that is being operated on
/// alloc : allocator used for adding to the arraylists
/// piece : the piece to add
/// index : the index in the text where the new piece will be added
pub fn insert(self: *Self, alloc: Alloc, piece: Piece, index: usize) !void {
var currnet_start: usize = 0;
for (self.pieces.items, 0..) |p, i| {
// find the index where the split occurs
if (currnet_start + p.length > index) {
// we gotta split the piece
const pieces: [3]Piece = [3]Piece{
Piece{
.text = p.text,
.start = p.start,
.length = index - currnet_start,
},
piece,
Piece{
.text = p.text,
.start = p.start + (index - currnet_start),
.length = p.length - (index - currnet_start),
},
};
try self.pieces.replaceRange(alloc, i, 1, &pieces);
try self.actions.append(alloc, .{
.insert_splits_piece = Action{
.piece_table_index = i,
.old_length = p.length,
.old_start = p.start,
},
});
return;
}
if (currnet_start + p.length == index) {
try self.pieces.insert(alloc, i + 1, piece);
try self.actions.append(alloc, .{ .insert = i + 1 });
return;
} // just append after
if (currnet_start + p.length < index) currnet_start += p.length;
}
// if there are no items this runs
try self.pieces.append(alloc, piece);
try self.actions.append(alloc, .append);
}
/// will delete all from (index) to (index)
/// self : piece table that is being operated on
/// alloc : allocator used for adding the actions to the action list.
/// from : the index to be deleted from
/// to : the index the deletion will stop
pub fn delete(self: *Self, alloc: std.mem.Allocator, from: usize, to: usize) !void {
var currnet_index: usize = 0;
var edited_piece_index: usize = 0;
var delete_actions: std.ArrayList(Action) = .empty;
// from set
for (self.pieces.items, 0..) |p, i| {
// find the index where the split occurs
if (currnet_index + p.length > from) {
// we gotta split the piece
var current_piece = &self.pieces.items[i];
try delete_actions.append(
alloc,
Action{
.piece_table_index = i,
.old_start = current_piece.start,
.old_length = current_piece.length,
},
);
current_piece.length -= from - currnet_index;
edited_piece_index = i;
break;
}
if (currnet_index + p.length <= from) currnet_index += p.length;
}
// to set
for (self.pieces.items, edited_piece_index..) |p, i| {
if (currnet_index + p.length < to) {
var current_piece = &self.pieces.items[i];
try delete_actions.append(
alloc,
Action{
.piece_table_index = i,
.old_start = current_piece.start,
.old_length = current_piece.length,
},
);
current_piece.length = 0;
currnet_index += p.length;
}
if (currnet_index + p.length >= to) {
var current_piece = &self.pieces.items[i];
try delete_actions.append(
alloc,
Action{
.piece_table_index = i,
.old_start = current_piece.start,
.old_length = current_piece.length,
},
);
// shrink it
current_piece.start += to - currnet_index;
current_piece.length -= to - currnet_index;
break;
}
}
try self.actions.append(alloc, .{ .delete = delete_actions });
}
pub fn undo(self: *Self, alloc: std.mem.Allocator) !void {
var action_to_undo = self.actions.pop() orelse return;
switch (action_to_undo) {
.append => {
self.pieces.deinit(alloc);
self.pieces = .empty;
},
.insert => |insert_index| {
// for the small price of one alloc you too can just swap nothing in
// might be faster, dont know should test
// [TODO] test if this is faster
try self.pieces.append(alloc, .none);
_ = self.pieces.swapRemove(insert_index);
},
.insert_splits_piece => |action| {
// remove the 2 addtional pieces
self.pieces.orderedRemoveMany(&.{
action.piece_table_index + 1,
action.piece_table_index + 2,
});
const first_half_of_split_piece = &self.pieces.items[action.piece_table_index];
first_half_of_split_piece.length = action.old_length;
first_half_of_split_piece.start = action.old_start;
},
.delete => |deletes| {
for (deletes.items) |action| {
const piece = &self.pieces.items[action.piece_table_index];
piece.length = action.old_length;
piece.start = action.old_start;
}
action_to_undo.delete.deinit(alloc);
},
}
}
pub fn format(self: Self, writer: *std.Io.Writer) !void {
_ = try writer.write("table : \"");
for (self.pieces.items) |p| {
_ = try writer.write(p.text.*[p.start .. p.start + p.length]);
}
_ = try writer.write("\"");
}
// pub fn undo(self: Self) !void {}
pub fn deinit(self: *Self, alloc: std.mem.Allocator) void {
self.actions.deinit(alloc);
self.pieces.deinit(alloc);
}
};
test "PieceTable insert" {
const orignal_text: []const u8 = "damn these are some cool toads";
const new_text: []const u8 = "frogs and ";
const even_newer_text: []const u8 = "cats but not ";
var piece_table = PieceTable.init();
try piece_table.insert(std.testing.allocator, .{
.start = 0,
.length = orignal_text.len,
.text = &orignal_text,
}, 0);
std.debug.print("{f}\n", .{piece_table});
try piece_table.insert(std.testing.allocator, .{
.text = &new_text,
.start = 0,
.length = new_text.len,
}, 20);
std.debug.print("{f}\n", .{piece_table});
try piece_table.delete(std.testing.allocator, 20, 20 + new_text.len);
std.debug.print("{f}\n", .{piece_table});
try piece_table.insert(std.testing.allocator, .{
.text = &even_newer_text,
.start = 0,
.length = even_newer_text.len,
}, 20);
std.debug.print("{f}\n", .{piece_table});
try piece_table.undo(std.testing.allocator);
std.debug.print("{f}\n", .{piece_table});
piece_table.deinit(std.testing.allocator);
}