//! This file contains the implementation for tmux control mode. See
//! tmux(1) for more information on control mode. Some basics are documented
//! here but this is not meant to be a comprehensive source of protocol
//! documentation.

const std = @import("std");
const assert = std.debug.assert;
const oni = @import("oniguruma");

const log = std.log.scoped(.terminal_tmux);

/// A tmux control mode client. It is expected that the caller establishes
/// the connection in some way (i.e. detects the opening DCS sequence). This
/// just works on a byte stream.
pub const Client = struct {
    /// Current state of the client.
    state: State = .idle,

    /// The buffer used to store in-progress notifications, output, etc.
    buffer: std.ArrayList(u8),

    /// The maximum size in bytes of the buffer. This is used to limit
    /// memory usage. If the buffer exceeds this size, the client will
    /// enter a broken state (the control mode session will be forcibly
    /// exited and future data dropped).
    max_bytes: usize = 1024 * 1024,

    const State = enum {
        /// Outside of any active notifications. This should drop any output
        /// unless it is '%' on the first byte of a line. The buffer will be
        /// cleared when it sees '%', this is so that the previous notification
        /// data is valid until we receive/process new data.
        idle,

        /// We experienced unexpected input and are in a broken state
        /// so we cannot continue processing.
        broken,

        /// Inside an active notification (started with '%').
        notification,

        /// Inside a begin/end block.
        block,
    };

    pub fn deinit(self: *Client) void {
        self.buffer.deinit();
    }

    // Handle a byte of input.
    pub fn put(self: *Client, byte: u8) !?Notification {
        if (self.buffer.items.len >= self.max_bytes) {
            self.broken();
            return error.OutOfMemory;
        }

        switch (self.state) {
            // Drop because we're in a broken state.
            .broken => return null,

            // Waiting for a notification so if the byte is not '%' then
            // we're in a broken state. Control mode output should always
            // be wrapped in '%begin/%end' orelse we expect a notification.
            // Return an exit notification.
            .idle => if (byte != '%') {
                self.broken();
                return .{ .exit = {} };
            } else {
                self.buffer.clearRetainingCapacity();
                self.state = .notification;
            },

            // If we're in a notification and its not a newline then
            // we accumulate. If it is a newline then we have a
            // complete notification we need to parse.
            .notification => if (byte == '\n') {
                // We have a complete notification, parse it.
                return try self.parseNotification();
            },

            // If we're in a block then we accumulate until we see a newline
            // and then we check to see if that line ended the block.
            .block => if (byte == '\n') {
                const idx = if (std.mem.lastIndexOfScalar(
                    u8,
                    self.buffer.items,
                    '\n',
                )) |v| v + 1 else 0;
                const line = self.buffer.items[idx..];

                if (std.mem.startsWith(u8, line, "%end") or
                    std.mem.startsWith(u8, line, "%error"))
                {
                    const err = std.mem.startsWith(u8, line, "%error");
                    const output = std.mem.trimRight(u8, self.buffer.items[0..idx], "\r\n");

                    // If it is an error then log it.
                    if (err) log.warn("tmux control mode error={s}", .{output});

                    // Important: do not clear buffer since the notification
                    // contains it.
                    self.state = .idle;
                    return if (err) .{ .block_err = output } else .{ .block_end = output };
                }

                // Didn't end the block, continue accumulating.
            },
        }

        try self.buffer.append(byte);

        return null;
    }

    fn parseNotification(self: *Client) !?Notification {
        assert(self.state == .notification);

        const line = line: {
            var line = self.buffer.items;
            if (line[line.len - 1] == '\r') line = line[0 .. line.len - 1];
            break :line line;
        };
        const cmd = cmd: {
            const idx = std.mem.indexOfScalar(u8, line, ' ') orelse line.len;
            break :cmd line[0..idx];
        };

        // The notification MUST exist because we guard entering the notification
        // state on seeing at least a '%'.
        if (std.mem.eql(u8, cmd, "%begin")) {
            // We don't use the rest of the tokens for now because tmux
            // claims to guarantee that begin/end are always in order and
            // never intermixed. In the future, we should probably validate
            // this.
            // TODO(tmuxcc): do this before merge?

            // Move to block state because we expect a corresponding end/error
            // and want to accumulate the data.
            self.state = .block;
            self.buffer.clearRetainingCapacity();
            return null;
        } else if (std.mem.eql(u8, cmd, "%output")) cmd: {
            var re = try oni.Regex.init(
                "^%output %([0-9]+) (.+)$",
                .{ .capture_group = true },
                oni.Encoding.utf8,
                oni.Syntax.default,
                null,
            );
            defer re.deinit();

            var region = re.search(line, .{}) catch |err| {
                log.warn("failed to match notification cmd={s} line=\"{s}\" err={}", .{ cmd, line, err });
                break :cmd;
            };
            defer region.deinit();
            const starts = region.starts();
            const ends = region.ends();

            const id = std.fmt.parseInt(
                usize,
                line[@intCast(starts[1])..@intCast(ends[1])],
                10,
            ) catch unreachable;
            const data = line[@intCast(starts[2])..@intCast(ends[2])];

            // Important: do not clear buffer here since name points to it
            self.state = .idle;
            return .{ .output = .{ .pane_id = id, .data = data } };
        } else if (std.mem.eql(u8, cmd, "%session-changed")) cmd: {
            var re = try oni.Regex.init(
                "^%session-changed \\$([0-9]+) (.+)$",
                .{ .capture_group = true },
                oni.Encoding.utf8,
                oni.Syntax.default,
                null,
            );
            defer re.deinit();

            var region = re.search(line, .{}) catch |err| {
                log.warn("failed to match notification cmd={s} line=\"{s}\" err={}", .{ cmd, line, err });
                break :cmd;
            };
            defer region.deinit();
            const starts = region.starts();
            const ends = region.ends();

            const id = std.fmt.parseInt(
                usize,
                line[@intCast(starts[1])..@intCast(ends[1])],
                10,
            ) catch unreachable;
            const name = line[@intCast(starts[2])..@intCast(ends[2])];

            // Important: do not clear buffer here since name points to it
            self.state = .idle;
            return .{ .session_changed = .{ .id = id, .name = name } };
        } else if (std.mem.eql(u8, cmd, "%sessions-changed")) cmd: {
            if (!std.mem.eql(u8, line, "%sessions-changed")) {
                log.warn("failed to match notification cmd={s} line=\"{s}\"", .{ cmd, line });
                break :cmd;
            }

            self.buffer.clearRetainingCapacity();
            self.state = .idle;
            return .{ .sessions_changed = {} };
        } else if (std.mem.eql(u8, cmd, "%window-add")) cmd: {
            var re = try oni.Regex.init(
                "^%window-add @([0-9]+)$",
                .{ .capture_group = true },
                oni.Encoding.utf8,
                oni.Syntax.default,
                null,
            );
            defer re.deinit();

            var region = re.search(line, .{}) catch |err| {
                log.warn("failed to match notification cmd={s} line=\"{s}\" err={}", .{ cmd, line, err });
                break :cmd;
            };
            defer region.deinit();
            const starts = region.starts();
            const ends = region.ends();

            const id = std.fmt.parseInt(
                usize,
                line[@intCast(starts[1])..@intCast(ends[1])],
                10,
            ) catch unreachable;

            self.buffer.clearRetainingCapacity();
            self.state = .idle;
            return .{ .window_add = .{ .id = id } };
        } else if (std.mem.eql(u8, cmd, "%window-renamed")) cmd: {
            var re = try oni.Regex.init(
                "^%window-renamed @([0-9]+) (.+)$",
                .{ .capture_group = true },
                oni.Encoding.utf8,
                oni.Syntax.default,
                null,
            );
            defer re.deinit();

            var region = re.search(line, .{}) catch |err| {
                log.warn("failed to match notification cmd={s} line=\"{s}\" err={}", .{ cmd, line, err });
                break :cmd;
            };
            defer region.deinit();
            const starts = region.starts();
            const ends = region.ends();

            const id = std.fmt.parseInt(
                usize,
                line[@intCast(starts[1])..@intCast(ends[1])],
                10,
            ) catch unreachable;
            const name = line[@intCast(starts[2])..@intCast(ends[2])];

            // Important: do not clear buffer here since name points to it
            self.state = .idle;
            return .{ .window_renamed = .{ .id = id, .name = name } };
        } else {
            // Unknown notification, log it and return to idle state.
            log.warn("unknown tmux control mode notification={s}", .{cmd});
        }

        // Unknown command. Clear the buffer and return to idle state.
        self.buffer.clearRetainingCapacity();
        self.state = .idle;

        return null;
    }

    // Mark the tmux state as broken.
    fn broken(self: *Client) void {
        self.state = .broken;
        self.buffer.clearAndFree();
    }
};

/// Possible notification types from tmux control mode. These are documented
/// in tmux(1).
pub const Notification = union(enum) {
    enter: void,
    exit: void,

    block_end: []const u8,
    block_err: []const u8,

    output: struct {
        pane_id: usize,
        data: []const u8, // unescaped
    },

    session_changed: struct {
        id: usize,
        name: []const u8,
    },

    sessions_changed: void,

    window_add: struct {
        id: usize,
    },

    window_renamed: struct {
        id: usize,
        name: []const u8,
    },
};

test "tmux begin/end empty" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%begin 1578922740 269 1\n") |byte| try testing.expect(try c.put(byte) == null);
    for ("%end 1578922740 269 1") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .block_end);
    try testing.expectEqualStrings("", n.block_end);
}

test "tmux begin/error empty" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%begin 1578922740 269 1\n") |byte| try testing.expect(try c.put(byte) == null);
    for ("%error 1578922740 269 1") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .block_err);
    try testing.expectEqualStrings("", n.block_err);
}

test "tmux begin/end data" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%begin 1578922740 269 1\n") |byte| try testing.expect(try c.put(byte) == null);
    for ("hello\nworld\n") |byte| try testing.expect(try c.put(byte) == null);
    for ("%end 1578922740 269 1") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .block_end);
    try testing.expectEqualStrings("hello\nworld", n.block_end);
}

test "tmux output" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%output %42 foo bar baz") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .output);
    try testing.expectEqual(42, n.output.pane_id);
    try testing.expectEqualStrings("foo bar baz", n.output.data);
}

test "tmux session-changed" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%session-changed $42 foo") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .session_changed);
    try testing.expectEqual(42, n.session_changed.id);
    try testing.expectEqualStrings("foo", n.session_changed.name);
}

test "tmux sessions-changed" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%sessions-changed") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .sessions_changed);
}

test "tmux sessions-changed carriage return" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%sessions-changed\r") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .sessions_changed);
}

test "tmux window-add" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%window-add @14") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .window_add);
    try testing.expectEqual(14, n.window_add.id);
}

test "tmux window-renamed" {
    const testing = std.testing;
    const alloc = testing.allocator;

    var c: Client = .{ .buffer = std.ArrayList(u8).init(alloc) };
    defer c.deinit();
    for ("%window-renamed @42 bar") |byte| try testing.expect(try c.put(byte) == null);
    const n = (try c.put('\n')).?;
    try testing.expect(n == .window_renamed);
    try testing.expectEqual(42, n.window_renamed.id);
    try testing.expectEqualStrings("bar", n.window_renamed.name);
}