const std = @import("std");
const builtin = @import("builtin");
const limits = @import("memory.zig").limits;

// scoped, not bare std.log: main.zig's logFn drops the unscoped .default scope
// wholesale (ghostty and uucode log there too), and a corrupt dump's parse
// diagnostic is the only thing that says WHICH field went bad.
const log = std.log.scoped(.dump);
const pardes = @import("pardes.zig");
const tagline = @import("tagline.zig");
const layout = @import("layout.zig");
const filesystem = @import("fs.zig");
const ctlfs = @import("ninep/tree.zig");
const exec = @import("exec.zig");
const body_layer = @import("body_layer.zig");
const colors = @import("colors.zig");
const themes = colors.themes;
const config = @import("config.zig");
const pdf_enabled = pardes.pdf_enabled;
const platform = pardes.platform;
const isolated = pardes.isolated;
const terminal_panes = pardes.terminal_panes;
const MAX_PANES = pardes.MAX_PANES;
const MAX_COLS = pardes.MAX_COLS;
const column_weight_unit = layout.column_weight_unit;
const max_column_weight = layout.max_column_weight;
const effect_path_cap = pardes.effect_path_cap;
const Options = pardes.Options;
const Pardes = pardes.Pardes;

/// Where the next dump goes. $PARDES_DUMP wins verbatim (the snapshot harness
/// pins it for deterministic goldens); else $XDG_DATA_HOME|~/.local/share
/// /pardes/pardes-<utc>.zon — timestamped so dumps never overwrite each other.
/// Creates the pardes dir (parents assumed; a failure surfaces at open).
pub fn outPath(buf: *[1024:0]u8, dir_setting: []const u8) ?[:0]const u8 {
    if (std.c.getenv("PARDES_DUMP")) |p|
        return std.fmt.bufPrintSentinel(buf, "{s}", .{std.mem.span(p)}, 0) catch null;
    var dir_buf: [900]u8 = undefined;
    const dir = directory(&dir_buf, dir_setting) orelse return null;
    var dz: [901:0]u8 = undefined;
    @memcpy(dz[0..dir.len], dir);
    dz[dir.len] = 0;
    _ = std.c.mkdir(dz[0..dir.len :0], 0o755); // EEXIST is fine
    var ts: std.c.timespec = undefined;
    _ = std.c.clock_gettime(.REALTIME, &ts);
    const es: std.time.epoch.EpochSeconds = .{ .secs = @intCast(@max(0, ts.sec)) };
    const yd = es.getEpochDay().calculateYearDay();
    const md = yd.calculateMonthDay();
    const ds = es.getDaySeconds();
    return std.fmt.bufPrintSentinel(buf, "{s}/pardes-{d:0>4}{d:0>2}{d:0>2}-{d:0>2}{d:0>2}{d:0>2}.zon", .{
        dir,                       yd.year,              md.month.numeric(),
        @as(u8, md.day_index) + 1, ds.getHoursIntoDay(), ds.getMinutesIntoHour(),
        ds.getSecondsIntoMinute(),
    }, 0) catch null;
}
/// Where dumps go and relative Restore names are looked up: the `DumpDir`
/// setting when set (a leading `~/` is the home directory), else the default.
pub fn directory(buf: []u8, dir_setting: []const u8) ?[]const u8 {
    if (dir_setting.len == 0) return defaultDirectory(buf);
    if (std.mem.startsWith(u8, dir_setting, "~/")) if (std.c.getenv("HOME")) |h|
        return std.fmt.bufPrint(buf, "{s}/{s}", .{ std.mem.span(h), dir_setting[2..] }) catch null;
    return std.fmt.bufPrint(buf, "{s}", .{dir_setting}) catch null;
}

/// The standard dump directory, without creating it or generating a filename.
pub fn defaultDirectory(buf: []u8) ?[]const u8 {
    if (std.c.getenv("XDG_DATA_HOME")) |x|
        return std.fmt.bufPrint(buf, "{s}/pardes", .{std.mem.span(x)}) catch null;
    if (std.c.getenv("HOME")) |h|
        return std.fmt.bufPrint(buf, "{s}/.local/share/pardes", .{std.mem.span(h)}) catch null;
    return null;
}

pub const magic = "pardes-dump";
pub const version: u32 = 1;
pub const max_panes: usize = 16;
pub const max_cols: usize = 6;
/// Output arguments are typed in the same bounded one-line tag storage. Keep
/// the schema limit named independently so a dump reader can validate it
/// without importing the output-pane implementation. The bound itself is
/// `limits.max_tag_tail` — the one place a board-shaped capacity is chosen.
pub const max_origin_arg: usize = limits.max_tag_tail;

pub const Size = struct {
    cols: u16,
    rows: u16,
};

pub const Cursor = struct {
    col: u16 = 0,
    row: u16 = 0,
};

pub const PaneKind = enum {
    terminal,
    file,
    image,
};

pub const Terminal = struct {
    cwd: []const u8 = "",
    /// The rendered scrollback and screen as plain text, one row per line.
    stream: []const u8 = "",
    stream_b64: []const u8 = "",
    /// `stream_b64` is the emulator's primary screen and scrollback as clean
    /// VT (ghostty's formatter), which replays to what the screen showed.
    /// Absent (older dumps), it is the raw tail of the pty's output, which
    /// replays faithfully only if it holds the whole session at one size.
    stream_is_screen: bool = false,
    cursor: Cursor = .{},
};

pub const LocationRow = struct {
    kind: enum { match, context, preview },
    declaration: bool = false,
    path: []const u8,
    line: usize,
    col: usize = 0,
    end_line: usize = 0,
    end_col: usize = 0,
    location_end: usize,
    code_start: usize,
    colors_b64: []const u8 = "",
};

pub const File = struct {
    path: []const u8 = "",
    content: []const u8 = "",
    content_b64: []const u8 = "",
    dirty: bool = false,
    tree_context: bool = false,
    location_rows: []const LocationRow = &.{},
    // Builtin names remain stable when enum ordinals change.
    origin: []const u8 = "",
    origin_arg: []const u8 = "",
    mini_source: []const u8 = "",
    mini_colors_b64: []const u8 = "",
};

pub const ImagePalette = enum {
    commodore,
    terminal,
};

pub const Image = struct {
    path: []const u8 = "",
    bytes_b64: []const u8 = "",
    // Defaults are the renderer's historical state, so version-1 dumps which
    // predate these fields remain readable without a schema fork.
    petscii: bool = false,
    palette: ImagePalette = .commodore,
    ascii: bool = true,
};

pub const Pane = struct {
    kind: PaneKind,
    tag: []const u8,
    body: []const u8,
    scroll: usize = 0,
    cols: u16 = 0,
    rows: u16 = 0,
    vweight: f32 = 1,
    collapsed: bool = false,
    /// Exact editable tail when the user touched it. Null retains the live
    /// default; a present empty slice deliberately restores an empty tail.
    tag_tail: ?[]const u8 = null,
    terminal: ?Terminal = null,
    file: ?File = null,
    image: ?Image = null,
};

pub const Column = struct {
    tag: ?[]const u8 = null,
    weight: f32 = 1,
    panes: []const usize = &.{},
};

pub const Mount = struct { name: []const u8, dial: []const u8 };

pub const State = struct {
    magic: []const u8 = magic,
    version: u32 = version,
    screen: Size,
    active: usize = 0,
    topbar: []const u8 = "",
    topbar_custom: ?[]const u8 = null,
    theme: []const u8 = "dark",
    locations_config: @import("locations_config.zig").Config = .{},
    tree_context_tag_style: bool = true,
    columns: []const Column = &.{},
    panes: []const Pane = &.{},
    mounts: []const Mount = &.{},
};

/// A header is a text like any other: it may hold newlines, but not a
/// carriage return or a NUL.
fn validateTag(bar: []const u8) !void {
    if (bar.len > limits.max_tag_tail or std.mem.indexOfAny(u8, bar, "\r\x00") != null or !std.unicode.utf8ValidateSlice(bar)) return error.BadDumpTag;
}

pub fn validate(state: State) !void {
    if (state.topbar_custom) |bar| try validateTag(bar);
    for (state.columns) |column| if (column.tag) |bar| try validateTag(bar);
    if (!std.mem.eql(u8, state.magic, magic)) return error.BadDumpMagic;
    if (state.version != version) return error.BadDumpVersion;
    if (state.panes.len == 0 or state.panes.len > max_panes) return error.BadDumpPanes;
    if (state.columns.len == 0 or state.columns.len > max_cols) return error.BadDumpColumns;
    if (state.active >= state.panes.len) return error.BadDumpActive;
    if (state.mounts.len > 8) return error.BadDumpMounts;
    for (state.mounts, 0..) |mount, i| {
        if (mount.name.len == 0 or mount.name.len > 255 or mount.dial.len == 0 or
            std.mem.indexOfScalar(u8, mount.dial, 0) != null) return error.BadDumpMounts;
        if (std.mem.eql(u8, mount.name, ".") or std.mem.eql(u8, mount.name, "..") or
            std.mem.eql(u8, mount.name, "os") or std.mem.eql(u8, mount.name, "self")) return error.BadDumpMounts;
        for (mount.name) |c| if (!std.ascii.isAlphanumeric(c) and c != '_' and c != '-' and c != '.') return error.BadDumpMounts;
        for (state.mounts[0..i]) |previous| if (std.mem.eql(u8, mount.name, previous.name)) return error.BadDumpMounts;
    }
    for (state.columns) |col| {
        if (!std.math.isFinite(col.weight) or col.weight <= 0) return error.BadDumpColumns;
        if (col.panes.len == 0 or col.panes.len > max_panes) return error.BadDumpColumns;
        for (col.panes) |pane| {
            if (pane >= state.panes.len) return error.BadDumpPaneRef;
        }
    }
    for (state.panes) |pane| {
        if (!std.math.isFinite(pane.vweight) or pane.vweight <= 0)
            return error.BadDumpPaneWeight;
        if (pane.scroll > std.math.maxInt(i32)) return error.BadDumpPaneScroll;
        if (pane.tag_tail) |tail| if (tail.len > limits.max_tag_tail)
            return error.BadDumpTagTail;
        if (pane.file) |file| if (file.origin_arg.len > max_origin_arg)
            return error.BadDumpOriginArg;
        if (pane.file) |file| {
            if (file.mini_source.len > 4096 or std.mem.indexOfScalar(u8, file.mini_source, 0) != null or
                (file.mini_source.len == 0 and file.mini_colors_b64.len != 0) or
                (file.mini_source.len != 0 and !std.mem.eql(u8, file.origin, "Mini"))) return error.BadDumpMini;
        }
        switch (pane.kind) {
            .terminal => if (pane.terminal == null) return error.BadDumpPaneKind,
            .file => if (pane.file == null) return error.BadDumpPaneKind,
            .image => if (pane.image == null) return error.BadDumpPaneKind,
        }
    }
}

test "oversized recognized output argument is rejected before restore" {
    var oversized: [max_origin_arg + 1]u8 = @splat('x');
    const pane_ids = [_]usize{0};
    const columns = [_]Column{.{ .panes = &pane_ids }};
    const panes = [_]Pane{.{
        .kind = .file,
        .tag = "+Search",
        .body = "",
        .file = .{
            .path = "/tmp/+Search",
            .origin = "Find",
            .origin_arg = &oversized,
        },
    }};
    const state: State = .{
        .screen = .{ .cols = 80, .rows = 24 },
        .columns = &columns,
        .panes = &panes,
    };

    // Serialize without writeFile: that writer correctly rejects the state
    // too, while this exercises the hostile bytes a restore actually reads.
    var encoded: std.Io.Writer.Allocating = .init(std.testing.allocator);
    defer encoded.deinit();
    try std.zon.stringify.serialize(state, .{}, &encoded.writer);
    try std.testing.expectError(
        error.BadDumpOriginArg,
        readZon(std.testing.allocator, encoded.written(), "oversized-origin-arg"),
    );
}

pub fn writeFile(io: std.Io, gpa: std.mem.Allocator, path: []const u8, state: State) !void {
    try validate(state);
    var out: std.Io.Writer.Allocating = .init(gpa);
    defer out.deinit();
    try std.zon.stringify.serialize(state, .{ .whitespace = true }, &out.writer);

    var file = try std.Io.Dir.createFileAbsolute(io, path, .{});
    defer file.close(io);
    try file.writeStreamingAll(io, out.written());
}

pub const Parsed = struct {
    value: State,
    arena: std.heap.ArenaAllocator,

    pub fn deinit(parsed: *Parsed) void {
        parsed.arena.deinit();
    }
};

pub fn readZon(gpa: std.mem.Allocator, bytes: []const u8, label: []const u8) !Parsed {
    var parsed: Parsed = .{ .value = undefined, .arena = .init(gpa) };
    errdefer parsed.deinit();
    const arena = parsed.arena.allocator();
    const source = try gpa.dupeZ(u8, bytes);
    defer gpa.free(source);

    parsed.value = if (builtin.os.tag == .emscripten or builtin.os.tag == .freestanding)
        std.zon.parse.fromSliceAlloc(State, arena, source, null, .{ .free_on_error = false }) catch |err| {
            if (err == error.ParseZon) log.err("parse dump {s}: {s}", .{ label, @errorName(err) });
            return err;
        }
    else blk: {
        var diag: std.zon.parse.Diagnostics = .{};
        defer diag.deinit(arena);
        break :blk std.zon.parse.fromSliceAlloc(State, arena, source, &diag, .{ .free_on_error = false }) catch |err| {
            if (err == error.ParseZon) log.err("parse dump {s}: {f}", .{ label, diag });
            return err;
        };
    };
    try validate(parsed.value);
    return parsed;
}

pub fn encodeBytes(alloc: std.mem.Allocator, bytes: []const u8) ![]const u8 {
    const enc = std.base64.standard.Encoder;
    const out = try alloc.alloc(u8, enc.calcSize(bytes.len));
    return enc.encode(out, bytes);
}

pub fn decodeBytes(alloc: std.mem.Allocator, b64: []const u8) ![]u8 {
    const dec = std.base64.standard.Decoder;
    const n = try dec.calcSizeForSlice(b64);
    const out = try alloc.alloc(u8, n);
    errdefer alloc.free(out);
    try dec.decode(out, b64);
    return out;
}

test "dump zon roundtrip" {
    const gpa = std.testing.allocator;
    const tty_b64 = try encodeBytes(gpa, "old\nhello\nworld");
    defer gpa.free(tty_b64);
    const file_b64 = try encodeBytes(gpa, "alpha\nbeta\n");
    defer gpa.free(file_b64);
    const panes = [_]Pane{
        .{
            .kind = .terminal,
            .tag = "nm /tmp Del",
            .body = "hello\nworld",
            .scroll = 1,
            .cols = 40,
            .rows = 10,
            .terminal = .{ .cwd = "/tmp", .stream = "old\nhello\nworld", .stream_b64 = tty_b64, .cursor = .{ .col = 3, .row = 2 } },
        },
        .{
            .kind = .file,
            .tag = "nm /tmp/a.txt Save Del",
            .body = "   1 alpha",
            .cols = 20,
            .rows = 5,
            .file = .{ .path = "/tmp/a.txt", .content = "alpha\nbeta\n", .content_b64 = file_b64, .dirty = true },
        },
    };
    const col_panes = [_]usize{ 0, 1 };
    const columns = [_]Column{.{ .weight = 1, .panes = &col_panes }};
    const state: State = .{
        .screen = .{ .cols = 80, .rows = 24 },
        .topbar = "Kill Newcol Dump",
        .theme = "dark",
        .columns = &columns,
        .panes = &panes,
    };

    var out: std.Io.Writer.Allocating = .init(gpa);
    defer out.deinit();
    try std.zon.stringify.serialize(state, .{ .whitespace = true }, &out.writer);
    var result = try readZon(gpa, out.written(), "roundtrip");
    defer result.deinit();
    const parsed = result.value;
    try std.testing.expectEqual(@as(usize, 2), parsed.panes.len);
    try std.testing.expectEqualStrings("dark", parsed.theme);
    try std.testing.expectEqualStrings("old\nhello\nworld", parsed.panes[0].terminal.?.stream);
    try std.testing.expectEqualStrings("alpha\nbeta\n", parsed.panes[1].file.?.content);
    try std.testing.expect(parsed.panes[1].file.?.dirty);
    {
        const bytes = try decodeBytes(gpa, parsed.panes[0].terminal.?.stream_b64);
        defer gpa.free(bytes);
        try std.testing.expectEqualStrings("old\nhello\nworld", bytes);
    }
    {
        const bytes = try decodeBytes(gpa, parsed.panes[1].file.?.content_b64);
        defer gpa.free(bytes);
        try std.testing.expectEqualStrings("alpha\nbeta\n", bytes);
    }
}

test "omitted dump defaults roundtrip without borrowing input" {
    const gpa = std.testing.allocator;
    const fixture =
        \\.{
        \\    .screen = .{ .cols = 80, .rows = 24 },
        \\    .columns = .{.{ .panes = .{0, 1, 2} }},
        \\    .panes = .{
        \\        .{ .kind = .terminal, .tag = "terminal", .body = "", .terminal = .{} },
        \\        .{ .kind = .file, .tag = "file", .body = "", .file = .{ .path = "file.zig", .content = "const café = 1;" } },
        \\        .{ .kind = .image, .tag = "image", .body = "", .image = .{} },
        \\    },
        \\}
    ;
    const input = try gpa.dupe(u8, fixture);
    defer gpa.free(input);
    var parsed = try readZon(gpa, input, "omitted-defaults");
    defer parsed.deinit();
    @memset(input, 'x');
    const value = parsed.value;
    try std.testing.expectEqualStrings(magic, value.magic);
    try std.testing.expectEqualStrings("dark", value.theme);
    try std.testing.expectEqualStrings("", value.topbar);
    try std.testing.expectEqual(@as(usize, 0), value.mounts.len);
    try std.testing.expectEqual(@as(usize, 3), value.panes.len);
    try std.testing.expectEqualStrings("file.zig", value.panes[1].file.?.path);
    try std.testing.expectEqualStrings("const café = 1;", value.panes[1].file.?.content);
    try std.testing.expect(!value.panes[1].file.?.dirty);
    try std.testing.expect(value.panes[2].image.?.ascii);

    var encoded: std.Io.Writer.Allocating = .init(gpa);
    defer encoded.deinit();
    try std.zon.stringify.serialize(value, .{}, &encoded.writer);
    var again = try readZon(gpa, encoded.written(), "default-roundtrip");
    defer again.deinit();
    try std.testing.expectEqualDeep(value, again.value);
}

test "dump parser releases its arena at every allocation failure" {
    const Check = struct {
        fn run(gpa: std.mem.Allocator) !void {
            var parsed = try readZon(gpa,
                \\.{
                \\    .screen = .{ .cols = 80, .rows = 24 },
                \\    .columns = .{.{ .panes = .{0} }},
                \\    .panes = .{.{ .kind = .file, .tag = "file", .body = "", .file = .{ .content = "owned" } }},
                \\}
            , "allocation-cleanup");
            defer parsed.deinit();
            try std.testing.expectEqualStrings("owned", parsed.value.panes[0].file.?.content);
        }
    };
    try std.testing.checkAllAllocationFailures(std.testing.allocator, Check.run, .{});
}

test "dump mount validation bounds names ownership inputs and duplicates" {
    const panes = [_]Pane{.{ .kind = .file, .tag = "", .body = "", .file = .{} }};
    const ids = [_]usize{0};
    const columns = [_]Column{.{ .panes = &ids }};
    var state: State = .{
        .screen = .{ .cols = 80, .rows = 24 },
        .columns = &columns,
        .panes = &panes,
    };
    try validate(state);
    for ([_]Mount{
        .{ .name = "peer", .dial = "/tmp/peer.sock" },
        .{ .name = "build-1.local", .dial = "tcp!127.0.0.1!5640" },
    }) |mount| {
        state.mounts = &.{mount};
        try validate(state);
    }
    for ([_]Mount{
        .{ .name = "", .dial = "/tmp/peer.sock" },
        .{ .name = ".", .dial = "/tmp/peer.sock" },
        .{ .name = "..", .dial = "/tmp/peer.sock" },
        .{ .name = "os", .dial = "/tmp/peer.sock" },
        .{ .name = "self", .dial = "/tmp/peer.sock" },
        .{ .name = "two/parts", .dial = "/tmp/peer.sock" },
        .{ .name = "two parts", .dial = "/tmp/peer.sock" },
        .{ .name = "peer", .dial = "" },
        .{ .name = "peer", .dial = "unix!/tmp/peer\x00.sock" },
    }) |mount| {
        state.mounts = &.{mount};
        try std.testing.expectError(error.BadDumpMounts, validate(state));
    }
    const duplicate = Mount{ .name = "peer", .dial = "/tmp/peer.sock" };
    state.mounts = &.{ duplicate, duplicate };
    try std.testing.expectError(error.BadDumpMounts, validate(state));
    var name: [256]u8 = @splat('x');
    state.mounts = &.{.{ .name = name[0..255], .dial = "/tmp/peer.sock" }};
    try validate(state);
    state.mounts = &.{.{ .name = &name, .dial = "/tmp/peer.sock" }};
    try std.testing.expectError(error.BadDumpMounts, validate(state));
    const mounts = [_]Mount{
        .{ .name = "a", .dial = "/tmp/a" },
        .{ .name = "b", .dial = "/tmp/b" },
        .{ .name = "c", .dial = "/tmp/c" },
        .{ .name = "d", .dial = "/tmp/d" },
        .{ .name = "e", .dial = "/tmp/e" },
        .{ .name = "f", .dial = "/tmp/f" },
        .{ .name = "g", .dial = "/tmp/g" },
        .{ .name = "h", .dial = "/tmp/h" },
        .{ .name = "i", .dial = "/tmp/i" },
    };
    state.mounts = mounts[0..8];
    try validate(state);
    state.mounts = &mounts;
    try std.testing.expectError(error.BadDumpMounts, validate(state));
}

test "version-one image records default old fields and roundtrip new state" {
    const gpa = std.testing.allocator;
    const legacy =
        \\.{
        \\    .magic = "pardes-dump",
        \\    .version = 1,
        \\    .screen = .{ .cols = 80, .rows = 24 },
        \\    .active = 0,
        \\    .topbar = "",
        \\    .theme = "dark",
        \\    .columns = .{.{ .panes = .{0} }},
        \\    .panes = .{.{
        \\        .kind = .image,
        \\        .tag = "img /tmp/old.ppm New Del",
        \\        .body = "",
        \\        .image = .{ .path = "/tmp/old.ppm", .bytes_b64 = "" },
        \\    }},
        \\}
    ;
    var old = try readZon(gpa, legacy, "legacy-image");
    defer old.deinit();
    const old_image = old.value.panes[0].image.?;
    try std.testing.expect(!old_image.petscii);
    try std.testing.expectEqual(ImagePalette.commodore, old_image.palette);
    try std.testing.expect(old_image.ascii);
    try std.testing.expect(old.value.panes[0].tag_tail == null);

    const pane = Pane{
        .kind = .image,
        .tag = "img petscii:on palette:terminal ascii:off /tmp/new.ppm",
        .body = "",
        .tag_tail = "",
        .image = .{
            .path = "/tmp/new.ppm",
            .petscii = true,
            .palette = .terminal,
            .ascii = false,
        },
    };
    const ids = [_]usize{0};
    const columns = [_]Column{.{ .panes = &ids }};
    const panes = [_]Pane{pane};
    const state = State{
        .screen = .{ .cols = 80, .rows = 24 },
        .columns = &columns,
        .panes = &panes,
    };
    var out: std.Io.Writer.Allocating = .init(gpa);
    defer out.deinit();
    try std.zon.stringify.serialize(state, .{ .whitespace = true }, &out.writer);
    var parsed = try readZon(gpa, out.written(), "new-image");
    defer parsed.deinit();
    const restored = parsed.value.panes[0].image.?;
    try std.testing.expect(restored.petscii);
    try std.testing.expectEqual(ImagePalette.terminal, restored.palette);
    try std.testing.expect(!restored.ascii);
    try std.testing.expect(parsed.value.panes[0].tag_tail != null);
    try std.testing.expectEqualStrings("", parsed.value.panes[0].tag_tail.?);
}

test "validation bounds pane restore state" {
    const ids = [_]usize{0};
    const columns = [_]Column{.{ .panes = &ids }};
    var panes = [_]Pane{.{
        .kind = .terminal,
        .tag = "term",
        .body = "",
        .terminal = .{},
    }};
    const state = State{
        .screen = .{ .cols = 80, .rows = 24 },
        .columns = &columns,
        .panes = &panes,
    };
    try validate(state);

    panes[0].vweight = 0;
    try std.testing.expectError(error.BadDumpPaneWeight, validate(state));
    panes[0].vweight = std.math.inf(f32);
    try std.testing.expectError(error.BadDumpPaneWeight, validate(state));
    panes[0].vweight = 1;

    panes[0].scroll = @as(usize, @intCast(std.math.maxInt(i32))) + 1;
    try std.testing.expectError(error.BadDumpPaneScroll, validate(state));
    panes[0].scroll = 0;

    var oversized_tail: [limits.max_tag_tail + 1]u8 = @splat('x');
    panes[0].tag_tail = &oversized_tail;
    try std.testing.expectError(error.BadDumpTagTail, validate(state));
    panes[0].tag_tail = oversized_tail[0..limits.max_tag_tail];
    try validate(state);
}

// ---- a whole editor to and from a dump (acme keeps this in rows.c) ----

pub fn dumpState(p: *Pardes) !void {
    const arena = p.scratch.allocator();
    var slot_to_pane: [MAX_PANES]?usize = @splat(null);
    var dump_panes: [MAX_PANES]Pane = undefined;
    var panes_len: usize = 0;
    for (p.panes, 0..) |slot, id| {
        const pane = slot orelse continue;
        slot_to_pane[id] = panes_len;
        const tag = try tagline.tagText(p, arena, pane);
        const body = try body_layer.bodyText(p, arena, pane);
        const scroll: usize = @intCast(@max(0, pane.scroll()));
        var dp: Pane = if (pane.file) |*f| try pardes.panes.File.dumpPane(
            arena,
            pane,
            f,
            tag,
            body,
            scroll,
            if (f.output) |o| pardes.panes.Output.word(o.from) else "",
            if (f.output) |*o| o.arg() else "",
        ) else if (pane.hasPdf()) blk: {
            if (comptime !pdf_enabled) unreachable;
            const pv = &pane.pdf.?;
            break :blk try pardes.panes.Image.dumpPane(p, arena, pane, tag, body, pv.page, pv.path, &.{});
        } else if (pane.image) |iv|
            try pardes.panes.Image.dumpPane(p, arena, pane, tag, body, scroll, iv.path, iv.raw)
        else
            try pardes.panes.Terminal.dumpPane(pane, arena, tag, body, scroll);
        dp.tag_tail = pane.tag.own;
        dump_panes[panes_len] = dp;
        panes_len += 1;
    }

    var columns: [MAX_COLS]Column = undefined;
    var columns_len: usize = 0;
    var column_ids: [MAX_COLS][MAX_PANES]usize = undefined;
    for (0..p.ncol) |c| {
        var ids_len: usize = 0;
        for (0..p.col_n[c]) |k| if (slot_to_pane[p.col_panes[c][k]]) |compact| {
            column_ids[c][ids_len] = compact;
            ids_len += 1;
        };
        if (ids_len > 0) {
            columns[columns_len] = .{
                .tag = p.col_tags[c].own,
                .weight = @as(f32, @floatFromInt(p.col_weight[c])) / @as(f32, @floatFromInt(column_weight_unit)),
                .panes = column_ids[c][0..ids_len],
            };
            columns_len += 1;
        }
    }

    var mounts: [filesystem.max_mounts]Mount = undefined;
    for (p.fs.mounts.items, 0..) |mount, i| mounts[i] = .{ .name = mount.name, .dial = mount.dial };
    const state: State = .{
        .screen = .{ .cols = p.screen_w, .rows = p.screen_h },
        .active = slot_to_pane[p.active] orelse 0,
        .topbar = config.topbar_str,
        .topbar_custom = p.global_tag.own,
        .theme = p.theme().name,
        .locations_config = p.locations_config,
        .tree_context_tag_style = p.settings.tree_context_tag_style,
        .columns = columns[0..columns_len],
        .panes = dump_panes[0..panes_len],
        .mounts = mounts[0..p.fs.mounts.items.len],
    };
    try validate(state);
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    try std.zon.stringify.serialize(state, .{ .whitespace = true }, &out.writer);
    if (p.dump_out) |d| p.gpa.free(d);
    p.dump_out = try out.toOwnedSlice();
    p.emit(.write_dump);
}

/// The replacement core for a Restore of the dump at `from`, whose log says
/// so after its panes' `new`s, for a client that reconnects to read.
pub fn restore(p: *Pardes, zon_bytes: []const u8, from: []const u8) !*Pardes {
    var opts = p.opts;
    opts.cols = p.screen_w;
    opts.rows = p.screen_h;
    const replacement = try initDump(p.gpa, opts, zon_bytes, p);
    pardes.ctlfs.events.notePath(replacement, "restore", from);
    return replacement;
}

pub fn initFromDump(gpa: std.mem.Allocator, opts: Options, zon_bytes: []const u8) !*Pardes {
    return initDump(gpa, opts, zon_bytes, null);
}

fn initDump(gpa: std.mem.Allocator, opts: Options, zon_bytes: []const u8, previous: ?*const Pardes) !*Pardes {
    const image_gpa = opts.image_allocator orelse gpa;
    const pdf_gpa = opts.pdf_allocator orelse gpa;
    const tree_sitter_gpa = opts.tree_sitter_allocator orelse gpa;
    const p = try gpa.create(Pardes);
    p.* = .{
        .gpa = gpa,
        .image_gpa = image_gpa,
        .pdf_gpa = pdf_gpa,
        .tree_sitter_gpa = tree_sitter_gpa,
        .opts = opts,
        .fs = .{},
        .screen_w = opts.cols,
        .screen_h = opts.rows,
        .scratch = .init(gpa),
        .frame_arena = .init(opts.frame_allocator orelse gpa),
        .fallback = .{ .gpa = gpa },
    };
    errdefer p.deinit();
    if (previous) |old| {
        p.next_serial = old.next_serial;
        p.lsp_seq = old.lsp_seq;
        p.pipe.seq = old.pipe.seq;
        p.cell_pixels = old.cell_pixels;
        p.row_metrics = old.row_metrics;
        p.native_images = old.native_images;
    }
    for (opts.mounts) |mount| try p.fs.mount(gpa, mount.name, mount.dial);
    p.opts.mounts = &.{};
    var parsed = try readZon(gpa, zon_bytes, "load");
    defer parsed.deinit();
    const st = parsed.value;
    p.locations_config = st.locations_config;
    p.settings.tree_context_tag_style = st.tree_context_tag_style;
    for (st.mounts) |mount| {
        var already_mounted = false;
        for (p.fs.mounts.items) |existing| {
            if (!std.mem.eql(u8, mount.name, existing.name)) continue;
            if (!std.mem.eql(u8, mount.dial, existing.dial)) return error.MountConflict;
            already_mounted = true;
            break;
        }
        if (!already_mounted) try p.fs.mount(gpa, mount.name, mount.dial);
    }

    for (themes, 0..) |t, i| {
        if (std.mem.eql(u8, t.name, st.theme)) p.settings.theme = @intCast(i);
    }
    for (st.panes, 0..) |src, i| {
        if (i >= MAX_PANES) break;
        const pane: *pardes.panes.Pane = switch (src.kind) {
            .terminal => terminal: {
                const t = src.terminal.?;
                // A host that runs shells gets them back: the old history
                // above a new shell in the directory it was in. The web
                // shell and an isolated build only ever replay it.
                const live = comptime (terminal_panes and platform != .web and !isolated);
                const revive = live and t.cwd.len <= effect_path_cap;
                const restored = try pardes.panes.Terminal.restore(p, src, revive);
                p.installPane(i, restored);
                try restored.setOwnedCwd(t.cwd);
                if (std.mem.startsWith(u8, src.tag, "TTY ")) restored.body.mode = .tty;
                if (revive) p.emit(.{ .spawn = .{ .pane = @intCast(i), .cwd = .from(t.cwd) } });
                break :terminal restored;
            },
            .file => try pardes.panes.File.restore(p, i, src),
            .image => restore_image: {
                const im = src.image.?;
                if (pardes.panes.Pdf.isPath(im.path)) {
                    var raw: []u8 = if (im.bytes_b64.len > 0)
                        try decodeBytes(gpa, im.bytes_b64)
                    else
                        &.{};
                    errdefer if (raw.len > 0) gpa.free(raw);
                    if (comptime pdf_enabled) {
                        if (pardes.panes.Pdf.openPane(p, i, im.path, src.scroll + 1) catch null) |restored| {
                            if (raw.len > 0) gpa.free(raw);
                            raw = &.{};
                            restored.cols = @max(1, src.cols);
                            restored.rows = @max(1, src.rows);
                            break :restore_image restored;
                        }
                    }
                    // If the source path is unavailable, retain its bytes
                    // as an ordinary file rather than dropping the pane.
                    const path = try gpa.dupe(u8, im.path);
                    errdefer gpa.free(path);
                    const content = if (raw.len > 0) raw else try gpa.dupe(u8, "");
                    raw = &.{};
                    errdefer if (content.len > 0) gpa.free(content);
                    const history = try pardes.panes.File.History.create(gpa);
                    errdefer gpa.destroy(history);
                    const restored = try p.newDocPane(i);
                    restored.file = .{ .path = path, .content = content, .history = history };
                    restored.body.cur_pinned = true;
                    restored.cols = @max(1, src.cols);
                    restored.rows = @max(1, src.rows);
                    p.emit(.{ .watch = .{ .pane = @intCast(i), .on = true, .mode = .baseline_disk } });
                    break :restore_image restored;
                }
                break :restore_image try pardes.panes.Image.restore(p, i, src);
            },
        };
        tagline.restoreDumpTail(p, pane, src);
        pane.vweight = src.vweight;
        pane.collapsed = src.collapsed;
    }
    p.ncol = @min(st.columns.len, MAX_COLS);
    p.col_serial = @splat(0);
    if (st.topbar_custom) |bar| p.global_tag.own = try p.gpa.dupe(u8, bar);
    for (st.columns[0..p.ncol], 0..) |col, c| {
        if (col.tag) |bar| p.col_tags[c].own = try p.gpa.dupe(u8, bar);
        const scaled = @as(f64, @floatCast(col.weight)) * @as(f64, @floatFromInt(column_weight_unit));
        const bounded = @min(scaled, @as(f64, @floatFromInt(max_column_weight)));
        p.col_weight[c] = @max(1, @as(u64, @intFromFloat(@round(bounded))));
        p.col_n[c] = @min(col.panes.len, MAX_PANES);
        for (col.panes[0..p.col_n[c]], 0..) |pid, k| p.col_panes[c][k] = pid;
    }
    p.active = @min(st.active, MAX_PANES - 1);
    p.sync();
    exec.applyStartupConfig(p);
    colors.finishThemeInitialization(p);
    p.sync();
    p.presentation.enabled = true;
    _ = p.takeHaptic(); // see init: a restored session is not a gesture
    try p.fs.log.buf.ensureTotalCapacityPrecise(p.gpa, p.fs.log.cap);
    ctlfs.events.announce(p);
    return p;
}