//! This is a non-allocating, non-fallible, and thread-safe API for printing
//! progress indicators to the terminal.
//! The tradeoff is that users of this API must provide the storage
//! for each `Progress.Node`.
//!
//! This library purposefully keeps its output simple and is ASCII-compatible.
//!
//! Initialize the struct directly, overriding these fields as desired:
//! * `refresh_rate_ms`
//! * `initial_delay_ms`
//! * `dont_print_on_dumb`
//! * `max_width`

const std = @import("std");
const builtin = @import("builtin");
const windows = std.os.windows;
const testing = std.testing;
const assert = std.debug.assert;
const os = std.os;
const time = std.time;
const Progress = @This();

/// `null` if the current node (and its children) should
/// not print on update()
terminal: ?std.fs.File = undefined,

/// Is this a Windows API terminal (note: this is not the same as being run on Windows
/// because other terminals exist like MSYS/git-bash)
is_windows_terminal: bool = false,

/// Whether the terminal supports ANSI escape codes.
supports_ansi_escape_codes: bool = false,

/// If the terminal is "dumb", don't print output.
/// This can be useful if you don't want to print all
/// the stages of code generation if there are a lot.
/// You should not use it if the user should see output
/// for example showing the user what tests run.
dont_print_on_dumb: bool = false,

root: Node = undefined,

/// Keeps track of how much time has passed since the beginning.
/// Used to compare with `initial_delay_ms` and `refresh_rate_ms`.
timer: ?time.Timer = null,

/// When the previous refresh was written to the terminal.
/// Used to compare with `refresh_rate_ms`.
prev_refresh_timestamp: u64 = undefined,

/// This is the maximum number of bytes that can be written to the terminal each refresh.
/// Anything larger than this is truncated.
// we can bump this up if we need to
output_buffer: [256]u8 = undefined,
output_buffer_slice: []u8 = undefined,

/// This is the maximum number of bytes written to the terminal with each refresh.
///
/// It is recommended to leave this as `null` so that `start` can automatically decide an
/// optimal width for the terminal.
///
/// Note that this will be clamped to at least 4 and output will appear malformed if it is < 4.
max_width: ?usize = null,

/// How many nanoseconds between writing updates to the terminal.
refresh_rate_ns: u64 = 50 * time.ns_per_ms,

/// How many nanoseconds to keep the output hidden.
initial_delay_ns: u64 = 500 * time.ns_per_ms,

done: bool = true,

/// Protects the `refresh` function, as well as `node.recently_updated_child`.
/// Without this, callsites would call `Node.end` and then free `Node` memory
/// while it was still being accessed by the `refresh` function.
update_mutex: std.Thread.Mutex = .{},

/// Keeps track of how many columns in the terminal have been output, so that
/// we can move the cursor back later.
columns_written: usize = undefined,

const truncation_suffix = "... ";

/// Represents one unit of progress. Each node can have children nodes, or
/// one can use integers with `update`.
pub const Node = struct {
    context: *Progress,
    parent: ?*Node,
    /// The name that will be displayed for this node.
    name: []const u8,
    /// Must be handled atomically to be thread-safe.
    recently_updated_child: ?*Node = null,
    /// Must be handled atomically to be thread-safe. 0 means null.
    unprotected_estimated_total_items: usize,
    /// Must be handled atomically to be thread-safe.
    unprotected_completed_items: usize,

    /// Create a new child progress node. Thread-safe.
    /// Call `Node.end` when done.
    /// TODO solve https://github.com/ziglang/zig/issues/2765 and then change this
    /// API to set `self.parent.recently_updated_child` with the return value.
    /// Until that is fixed you probably want to call `activate` on the return value.
    /// Passing 0 for `estimated_total_items` means unknown.
    pub fn start(self: *Node, name: []const u8, estimated_total_items: usize) Node {
        return Node{
            .context = self.context,
            .parent = self,
            .name = name,
            .unprotected_estimated_total_items = estimated_total_items,
            .unprotected_completed_items = 0,
        };
    }

    /// This is the same as calling `start` and then `end` on the returned `Node`. Thread-safe.
    pub fn completeOne(self: *Node) void {
        if (self.parent) |parent| {
            @atomicStore(?*Node, &parent.recently_updated_child, self, .Release);
        }
        _ = @atomicRmw(usize, &self.unprotected_completed_items, .Add, 1, .Monotonic);
        self.context.maybeRefresh();
    }

    /// Finish a started `Node`. Thread-safe.
    pub fn end(self: *Node) void {
        self.context.maybeRefresh();
        if (self.parent) |parent| {
            {
                self.context.update_mutex.lock();
                defer self.context.update_mutex.unlock();
                _ = @cmpxchgStrong(?*Node, &parent.recently_updated_child, self, null, .Monotonic, .Monotonic);
            }
            parent.completeOne();
        } else {
            self.context.update_mutex.lock();
            defer self.context.update_mutex.unlock();
            self.context.done = true;
            self.context.refreshWithHeldLock();
        }
    }

    /// Tell the parent node that this node is actively being worked on. Thread-safe.
    pub fn activate(self: *Node) void {
        if (self.parent) |parent| {
            @atomicStore(?*Node, &parent.recently_updated_child, self, .Release);
            self.context.maybeRefresh();
        }
    }

    /// Thread-safe. 0 means unknown.
    pub fn setEstimatedTotalItems(self: *Node, count: usize) void {
        @atomicStore(usize, &self.unprotected_estimated_total_items, count, .Monotonic);
    }

    /// Thread-safe.
    pub fn setCompletedItems(self: *Node, completed_items: usize) void {
        @atomicStore(usize, &self.unprotected_completed_items, completed_items, .Monotonic);
    }
};

/// Create a new progress node.
/// Call `Node.end` when done.
/// `estimated_total_items` value of 0 means unknown.
///
/// Note that as soon as work is started and progress output is printed,
/// `std.Progress` expects you to lean back and wait and not resize the terminal.
/// Resizing the terminal during progress output may result in malformed output.
// TODO: solve https://github.com/ziglang/zig/issues/2765 and then change this
// API to return Progress rather than accept it as a parameter.
pub fn start(self: *Progress, name: []const u8, estimated_total_items: usize) *Node {
    const stderr = std.io.getStdErr();
    self.terminal = null;
    if (stderr.supportsAnsiEscapeCodes()) {
        self.terminal = stderr;
        self.supports_ansi_escape_codes = true;
    } else if (builtin.os.tag == .windows and stderr.isTty()) {
        self.is_windows_terminal = true;
        self.terminal = stderr;
    } else if (builtin.os.tag != .windows) {
        // we are in a "dumb" terminal like in acme or writing to a file
        self.terminal = stderr;
    }
    self.calculateMaxWidth();
    self.root = Node{
        .context = self,
        .parent = null,
        .name = name,
        .unprotected_estimated_total_items = estimated_total_items,
        .unprotected_completed_items = 0,
    };
    self.columns_written = 0;
    self.prev_refresh_timestamp = 0;
    self.timer = time.Timer.start() catch null;
    self.done = false;
    return &self.root;
}

fn calculateMaxWidth(self: *Progress) void {
    if (self.max_width == null) {
        if (self.terminal) |terminal| {
            // choose an optimal width and account for progress output that could have been printed
            // before us by another `std.Progress` instance
            const terminal_width = self.getTerminalWidth(terminal.handle) catch 100;
            const chars_already_printed = self.getTerminalCursorColumn(terminal) catch 0;
            self.max_width = terminal_width - chars_already_printed;
        } else {
            self.max_width = 100;
        }
    }
    self.max_width = std.math.clamp(
        self.max_width.?,
        truncation_suffix.len, // make sure we can at least truncate
        self.output_buffer.len - 1,
    );
}

fn getTerminalWidth(self: Progress, file_handle: os.fd_t) !u16 {
    if (builtin.os.tag == .linux) {
        // TODO: figure out how to get this working on FreeBSD, macOS etc. too.
        //       they too should have capabilities to figure out the cursor column.
        var winsize: os.linux.winsize = undefined;
        switch (os.errno(os.linux.ioctl(file_handle, os.linux.T.IOCGWINSZ, @ptrToInt(&winsize)))) {
            .SUCCESS => return winsize.ws_col,
            else => return error.Unexpected,
        }
    } else if (builtin.os.tag == .windows) {
        std.debug.assert(self.is_windows_terminal);
        var info: windows.CONSOLE_SCREEN_BUFFER_INFO = undefined;
        if (windows.kernel32.GetConsoleScreenBufferInfo(file_handle, &info) != windows.TRUE)
            return error.Unexpected;
        return @intCast(u16, info.dwSize.X);
    } else {
        return error.Unsupported;
    }
}

fn getTerminalCursorColumn(self: Progress, file: std.fs.File) !u16 {
    // TODO: figure out how to get this working on FreeBSD, macOS etc. too.
    //       they too should have termios or capabilities to figure out the terminal width.
    if (builtin.os.tag == .linux and self.supports_ansi_escape_codes) {
        // First, disable echo and enable non-canonical mode
        // (so that no enter press required for us to read the output of the escape sequence below)
        const original_termios = try os.tcgetattr(file.handle);
        var new_termios = original_termios;
        new_termios.lflag &= ~(os.linux.ECHO | os.linux.ICANON);
        try os.tcsetattr(file.handle, .NOW, new_termios);
        defer os.tcsetattr(file.handle, .NOW, original_termios) catch {
            // Sorry for ruining your terminal
        };

        try file.writeAll("\x1b[6n");
        var buf: ["\x1b[65536;65536R".len]u8 = undefined;
        const output = try file.reader().readUntilDelimiter(&buf, 'R');
        var splitter = std.mem.split(u8, output, ";");
        _ = splitter.next().?; // skip first half
        const column_half = splitter.next() orelse return error.UnexpectedEnd;
        const column = try std.fmt.parseUnsigned(u16, column_half, 10);
        return column - 1; // it's one-based
    } else if (builtin.os.tag == .windows) {
        std.debug.assert(self.is_windows_terminal);
        var info: windows.CONSOLE_SCREEN_BUFFER_INFO = undefined;
        if (windows.kernel32.GetConsoleScreenBufferInfo(file.handle, &info) != windows.TRUE)
            return error.Unexpected;
        return @intCast(u16, info.dwCursorPosition.X);
    } else {
        return error.Unsupported;
    }
}

/// Updates the terminal if enough time has passed since last update. Thread-safe.
pub fn maybeRefresh(self: *Progress) void {
    if (self.timer) |*timer| {
        if (!self.update_mutex.tryLock()) return;
        defer self.update_mutex.unlock();
        const now = timer.read();
        if (now < self.initial_delay_ns) return;
        // TODO I have observed this to happen sometimes. I think we need to follow Rust's
        // lead and guarantee monotonically increasing times in the std lib itself.
        if (now < self.prev_refresh_timestamp) return;
        if (now - self.prev_refresh_timestamp < self.refresh_rate_ns) return;
        return self.refreshWithHeldLock();
    }
}

/// Updates the terminal and resets `self.next_refresh_timestamp`. Thread-safe.
pub fn refresh(self: *Progress) void {
    if (!self.update_mutex.tryLock()) return;
    defer self.update_mutex.unlock();

    return self.refreshWithHeldLock();
}

fn refreshWithHeldLock(self: *Progress) void {
    const is_dumb = !self.supports_ansi_escape_codes and !self.is_windows_terminal;
    if (is_dumb and self.dont_print_on_dumb) return;

    const file = self.terminal orelse return;

    // prepare for printing unprintable characters
    self.output_buffer_slice = &self.output_buffer;

    var end: usize = 0;
    if (self.columns_written > 0) {
        // restore the cursor position by moving the cursor
        // `columns_written` cells to the left, then clear the rest of the line
        if (self.supports_ansi_escape_codes) {
            end += (std.fmt.bufPrint(self.output_buffer_slice[end..], "\x1b[{d}D", .{self.columns_written}) catch unreachable).len;
            end += (std.fmt.bufPrint(self.output_buffer_slice[end..], "\x1b[0K", .{}) catch unreachable).len;
        } else if (builtin.os.tag == .windows) winapi: {
            std.debug.assert(self.is_windows_terminal);

            var info: windows.CONSOLE_SCREEN_BUFFER_INFO = undefined;
            if (windows.kernel32.GetConsoleScreenBufferInfo(file.handle, &info) != windows.TRUE)
                unreachable;

            var cursor_pos = windows.COORD{
                .X = info.dwCursorPosition.X - @intCast(windows.SHORT, self.columns_written),
                .Y = info.dwCursorPosition.Y,
            };

            if (cursor_pos.X < 0)
                cursor_pos.X = 0;

            const fill_chars = @intCast(windows.DWORD, info.dwSize.X - cursor_pos.X);

            var written: windows.DWORD = undefined;
            if (windows.kernel32.FillConsoleOutputAttribute(
                file.handle,
                info.wAttributes,
                fill_chars,
                cursor_pos,
                &written,
            ) != windows.TRUE) {
                // Stop trying to write to this file.
                self.terminal = null;
                break :winapi;
            }
            if (windows.kernel32.FillConsoleOutputCharacterW(
                file.handle,
                ' ',
                fill_chars,
                cursor_pos,
                &written,
            ) != windows.TRUE) unreachable;

            if (windows.kernel32.SetConsoleCursorPosition(file.handle, cursor_pos) != windows.TRUE)
                unreachable;
        } else {
            // we are in a "dumb" terminal like in acme or writing to a file
            self.output_buffer_slice[end] = '\n';
            end += 1;
        }

        self.columns_written = 0;
    }

    // from here on we will write printable characters. we also make sure the unprintable characters
    // we possibly wrote previously don't affect whether we truncate the line in `bufWrite`.
    const unprintables = end;
    end = 0;
    self.output_buffer_slice = self.output_buffer[unprintables..@minimum(self.output_buffer.len, unprintables + self.max_width.?)];

    if (!self.done) {
        var need_ellipsis = false;
        var maybe_node: ?*Node = &self.root;
        while (maybe_node) |node| {
            if (need_ellipsis) {
                self.bufWrite(&end, "... ", .{});
            }
            need_ellipsis = false;
            const estimated_total_items = @atomicLoad(usize, &node.unprotected_estimated_total_items, .Monotonic);
            const completed_items = @atomicLoad(usize, &node.unprotected_completed_items, .Monotonic);
            const current_item = completed_items + 1;
            if (node.name.len != 0 or estimated_total_items > 0) {
                if (node.name.len != 0) {
                    self.bufWrite(&end, "{s}", .{node.name});
                    need_ellipsis = true;
                }
                if (estimated_total_items > 0) {
                    if (need_ellipsis) self.bufWrite(&end, " ", .{});
                    self.bufWrite(&end, "[{d}/{d}] ", .{ current_item, estimated_total_items });
                    need_ellipsis = false;
                } else if (completed_items != 0) {
                    if (need_ellipsis) self.bufWrite(&end, " ", .{});
                    self.bufWrite(&end, "[{d}] ", .{current_item});
                    need_ellipsis = false;
                }
            }
            maybe_node = @atomicLoad(?*Node, &node.recently_updated_child, .Acquire);
        }
        if (need_ellipsis) {
            self.bufWrite(&end, "... ", .{});
        }
    }

    _ = file.write(self.output_buffer[0 .. end + unprintables]) catch {
        // Stop trying to write to this file once it errors.
        self.terminal = null;
    };
    if (self.timer) |*timer| {
        self.prev_refresh_timestamp = timer.read();
    }
}

pub fn log(self: *Progress, comptime format: []const u8, args: anytype) void {
    const file = self.terminal orelse {
        std.debug.print(format, args);
        return;
    };
    self.refresh();
    file.writer().print(format, args) catch {
        self.terminal = null;
        return;
    };
    self.columns_written = 0;
}

fn bufWrite(self: *Progress, end: *usize, comptime format: []const u8, args: anytype) void {
    if (std.fmt.bufPrint(self.output_buffer_slice[end.*..], format, args)) |written| {
        const amt = written.len;
        end.* += amt;
        self.columns_written += amt;
    } else |err| switch (err) {
        error.NoSpaceLeft => {
            // truncate the line with a suffix.
            // for example if we have "hello world" (len=11) and 10 is the limit,
            // it would become "hello w... "
            self.columns_written += self.output_buffer_slice.len - end.*;
            end.* = self.output_buffer_slice.len;
            std.mem.copy(
                u8,
                self.output_buffer_slice[self.output_buffer_slice.len - truncation_suffix.len ..],
                truncation_suffix,
            );
        },
    }
}

// By default these tests are disabled because they use time.sleep()
// and are therefore slow. They also prints bogus progress data to stderr.
const skip_tests = true;

test "behavior on buffer overflow" {
    if (skip_tests)
        return error.SkipZigTest;

    // uncomment this to move the cursor
    //std.debug.print("{s}", .{"A" ** 300});

    var progress = Progress{};

    const long_string = "A" ** 300;
    var node = progress.start(long_string, 0);

    const speed_factor = time.ns_per_s / 4;

    time.sleep(speed_factor);
    node.activate();
    time.sleep(speed_factor);
    node.end();
}

test "multiple tasks with long names" {
    if (skip_tests)
        return error.SkipZigTest;

    var progress = Progress{};

    const tasks = [_][]const u8{
        "A" ** 99,
        "A" ** 100,
        "A" ** 101,
        "A" ** 102,
        "A" ** 103,
    };

    const speed_factor = time.ns_per_s / 6;

    for (tasks) |task| {
        var node = progress.start(task, 3);
        time.sleep(speed_factor);
        node.activate();

        time.sleep(speed_factor);
        node.completeOne();
        time.sleep(speed_factor);
        node.completeOne();
        time.sleep(speed_factor);
        node.completeOne();

        node.end();
    }
}

test "very short max width" {
    if (skip_tests)
        return error.SkipZigTest;

    var progress = Progress{ .max_width = 4 };

    const task = "A" ** 300;

    const speed_factor = time.ns_per_s / 2;

    var node = progress.start(task, 3);
    time.sleep(speed_factor);
    node.activate();

    time.sleep(speed_factor);
    node.completeOne();
    time.sleep(speed_factor);
    node.completeOne();

    node.end();
}

test "basic functionality" {
    if (skip_tests)
        return error.SkipZigTest;

    var progress = Progress{};
    const root_node = progress.start("", 100);
    defer root_node.end();

    const speed_factor = time.ns_per_ms;

    const sub_task_names = [_][]const u8{
        "reticulating splines",
        "adjusting shoes",
        "climbing towers",
        "pouring juice",
    };
    var next_sub_task: usize = 0;

    var i: usize = 0;
    while (i < 100) : (i += 1) {
        var node = root_node.start(sub_task_names[next_sub_task], 5);
        node.activate();
        next_sub_task = (next_sub_task + 1) % sub_task_names.len;

        node.completeOne();
        time.sleep(5 * speed_factor);
        node.completeOne();
        node.completeOne();
        time.sleep(5 * speed_factor);
        node.completeOne();
        node.completeOne();
        time.sleep(5 * speed_factor);

        node.end();

        time.sleep(5 * speed_factor);
    }
    {
        var node = root_node.start("this is a really long name designed to activate the truncation code. let's find out if it works", 0);
        node.activate();
        time.sleep(10 * speed_factor);
        progress.refresh();
        time.sleep(10 * speed_factor);
        node.end();
    }
}