//! Output buffers (+Errors, search and jump results, help, messages, the
//! changelog): their rows, traits and look targets.
const panes = @import("panes.zig");
const std = @import("std");
const pardes = @import("pardes.zig");
const exec = @import("exec.zig");
const config = @import("config.zig");
const Pardes = pardes.Pardes;
const modal = @import("modal.zig");
const dump = @import("dump.zig");
const limits = @import("memory.zig").limits;
const builtins = @import("builtins.zig");
const effect_sources = @import("effect_sources.zig");
const build_options = @import("pardes_config");
const lsp = @import("lsp/lsp.zig");
const look = @import("look.zig");
const locations = @import("locations.zig");
const Pane = panes.Pane;
const File = panes.File;

const Builtin = builtins.registry.Builtin();

const fonts = if (builtins.capabilities.font_picker) @import("fonts.zig") else struct {};

pub const Origin = union(enum) {
    cmd: Builtin,
    query: lsp.Kind,
    search,
    errors,
    pdf_links,
    /// The panes a refusal (Exit, Restore, Del, Delcol, get) is over, kept
    /// in +Unsaved rather than a notice that goes.
    unsaved,
};

pub const max_arg = dump.max_origin_arg;

pub const State = struct {
    from: Origin,
    arg_buf: [max_arg]u8 = undefined,
    arg_len: u16 = 0,

    pub fn arg(o: *const State) []const u8 {
        return o.arg_buf[0..o.arg_len];
    }
};

const RowDecoration = struct {
    location_end: usize = 0,
    prefix_end: usize = 0,
    declaration: bool = false,
    mark_start: usize = 0,
    mark_end: usize = 0,
    severity: enum { none, err, warning, info, hint } = .none,

    /// Nothing in the row is decorated: most rows of most files.
    pub fn plain(row: RowDecoration) bool {
        return !row.declaration and row.location_end == 0 and row.prefix_end == 0 and row.mark_end <= row.mark_start;
    }

    /// `chrome` is the theme's own (Pardes.bodyChrome): body paper changes
    /// immediately, so its ink must change with it even while the
    /// surrounding tags are still fading. Once a frame, never a grapheme:
    /// working it out takes the contrast searches' pow calls.
    pub fn styleAt(row: RowDecoration, chrome: *const pardes.ChromeTheme, byte: usize) ?pardes.CellStyle {
        if (row.plain()) return null;
        if (row.declaration or byte < @max(row.location_end, row.prefix_end))
            return .{ .fg = .{ .rgb = chrome.lineno } };
        if (byte < row.mark_start or byte >= row.mark_end) return null;
        if (row.severity == .none) return .{
            .fg = .{ .rgb = chrome.search_fg },
            .bg = .{ .rgb = chrome.search_bg },
        };
        return .{ .fg = .{ .rgb = switch (row.severity) {
            .err => chrome.diagnostic_error,
            .warning => chrome.diagnostic_warning,
            .info => chrome.diagnostic_info,
            .hint => chrome.diagnostic_hint,
            .none => unreachable,
        } }, .bold = true };
    }
};

fn rowDecoration(output: ?State, line: []const u8) RowDecoration {
    return decorateRow(output, line, null);
}

pub fn decorateRow(output: ?State, line: []const u8, metadata: ?locations.Row) RowDecoration {
    const origin = (output orelse return .{}).from;
    if (!traits(origin).locations) return .{};
    const target = locations.parse(line);
    const spot = if (metadata) |m| m.at else target.at;
    if (spot.line == 0) return .{};
    var row: RowDecoration = .{
        .location_end = if (metadata) |m| m.location_end else target.end,
        .prefix_end = if (metadata) |m| m.code_start else target.end,
        .declaration = if (metadata) |m| m.declaration else false,
    };
    const source_start = if (metadata) |m| m.code_start else target.code_start;
    if (source_start >= line.len) return row;
    if (metadata) |m| if (m.kind == .context) return row;
    const mark_occurrence = switch (origin) {
        .search => true,
        .cmd => |cmd| cmd == .Grep,
        .query => |kind| switch (kind) {
            .definition, .declaration, .type_definition, .implementation, .references => true,
            else => false,
        },
        else => false,
    };
    if (mark_occurrence and spot.col > 0 and spot.end_line == spot.line and
        spot.end_col >= spot.col)
    {
        row.mark_start = source_start +| (spot.col - 1);
        row.mark_end = @min(line.len, source_start +| spot.end_col);
    }
    const is_diagnostic = switch (origin) {
        .query => |kind| kind == .diagnostics or kind == .workspace_diagnostics,
        else => false,
    };
    if (is_diagnostic) {
        const text = line[source_start..];
        inline for (.{ .{ "error:", .err }, .{ "warning:", .warning }, .{ "info:", .info }, .{ "hint:", .hint } }) |label| {
            if (std.mem.startsWith(u8, text, label[0])) {
                row.mark_start = source_start;
                row.mark_end = source_start + label[0].len;
                row.severity = label[1];
            }
        }
    }
    return row;
}

test "result decoration follows source byte ranges and diagnostic provenance" {
    const row = rowDecoration(.{ .from = .search }, "src/a.rs:3:5-7 let abc = 1;");
    try std.testing.expectEqualStrings("abc", "src/a.rs:3:5-7 let abc = 1;"[row.mark_start..row.mark_end]);
    const prose = rowDecoration(.{ .from = .{ .query = .hover } }, "src/a.rs:3:5-7 error: prose");
    try std.testing.expectEqual(@as(usize, 0), prose.mark_end);
    const diagnostic = rowDecoration(.{ .from = .{ .query = .diagnostics } }, "src/a.rs:3:5-7 warning: unused");
    try std.testing.expectEqual(.warning, diagnostic.severity);
    try std.testing.expectEqualStrings("warning:", "src/a.rs:3:5-7 warning: unused"[diagnostic.mark_start..diagnostic.mark_end]);
    const malformed = rowDecoration(.{ .from = .search }, "src/a.rs:3:99999999999999999999-99999999999999999999 text");
    try std.testing.expect(malformed.mark_end <= "src/a.rs:3:99999999999999999999-99999999999999999999 text".len);
    const snippet = "src/a.rs:3:14-16 \t\tfoo + 界 + foo";
    for ([_]lsp.Kind{ .definition, .declaration, .type_definition, .implementation, .references }) |kind| {
        const occurrence = rowDecoration(.{ .from = .{ .query = kind } }, snippet);
        try std.testing.expectEqualStrings("foo", snippet[occurrence.mark_start..occurrence.mark_end]);
    }
    for ([_]lsp.Kind{ .document_symbols, .workspace_symbols, .completion, .incoming_calls, .outgoing_calls, .supertypes, .subtypes, .rename }) |kind| {
        const label = rowDecoration(.{ .from = .{ .query = kind } }, snippet);
        try std.testing.expectEqual(@as(usize, 0), label.mark_end);
    }
}

test "stacked empty previews distinguish separators from trailing newlines" {
    var path = [_]u8{ 'x', '.', 'c' };
    const rows = [_]locations.Row{
        .{ .kind = .match, .path = &path, .at = .{ .line = 1, .col = 1 }, .location_end = 7, .code_start = 7 },
        .{ .kind = .preview, .path = &path, .at = .{ .line = 1, .col = 1 }, .location_end = 0, .code_start = 0 },
    };
    try std.testing.expect(locations.sameInput("x.c:1:1 ", "x.c:1:1\n", &rows, .stacked));
    try std.testing.expect(locations.sameInput("x.c:1:1 \n", "x.c:1:1\n\n", &rows, .stacked));
    try std.testing.expect(!locations.sameInput("x.c:1:1 ", "x.c:1:1\n\n", &rows, .stacked));
    try std.testing.expect(!locations.sameInput("x.c:1:1 \n", "x.c:1:1\n", &rows, .stacked));
}

test "Lspinfo and Lspwhy fill one +Lsp in a directory" {
    const p = try Pardes.init(std.testing.allocator, .{ .tty_only = true });
    defer p.deinit();
    _ = try p.setTestFile("x\n");
    try fillResults(p, 0, "/work", .{ .query = .status }, "", try p.gpa.dupe(u8, "servers\n"), null);
    try fillResults(p, 0, "/work", .{ .query = .explain }, "", try p.gpa.dupe(u8, "why\n"), null);
    var lsp_panes: usize = 0;
    for (p.panes) |slot| {
        const f = (slot orelse continue).file orelse continue;
        if (std.mem.eql(u8, f.path, "/work/+Lsp")) {
            lsp_panes += 1;
            try std.testing.expectEqualStrings("why\n", f.content);
        }
    }
    try std.testing.expectEqual(@as(usize, 1), lsp_panes);
}

test "plain output does not opt into location decoration" {
    const report = rowDecoration(.{ .from = .{ .cmd = .LocationsConfig } }, "LocationsConfig context:5 tscontext:on");
    try std.testing.expectEqualDeep(RowDecoration{}, report);
    const prose = rowDecoration(.{ .from = .{ .query = .hover } }, "src/a.rs:3:5-7 error: prose");
    try std.testing.expectEqualDeep(RowDecoration{}, prose);
    const errors = rowDecoration(.{ .from = .errors }, "src/a.rs:3:5-7 error: prose");
    try std.testing.expectEqualDeep(RowDecoration{}, errors);
    try std.testing.expect(!traits(.{ .cmd = .Find }).locations);
    try std.testing.expect(traits(.{ .cmd = .Grep }).locations);
    try std.testing.expect(traits(.{ .query = .completion }).locations);
}

pub fn setArg(o: *State, text: []const u8) error{ArgumentTooLong}!void {
    if (text.len > max_arg) return error.ArgumentTooLong;
    o.arg_len = @intCast(text.len);
    @memcpy(o.arg_buf[0..o.arg_len], text);
}

pub const Traits = builtins.OutputTraits;

const file_row: Traits = .{ .name = "", .doc = true, .saves = true };

pub fn traits(o: Origin) Traits {
    return switch (o) {
        // rows are `location text`, so n/N walk them
        .search => .{ .name = config.search_buffer, .steps = true, .locations = true },
        .errors => .{ .name = config.errors_buffer, .doc = true },
        .pdf_links => .{ .name = config.pdf_links_buffer, .steps = true, .locations = true },
        .unsaved => .{ .name = config.unsaved_buffer, .doc = true },
        .cmd => |b| builtins.registry.outputTraits(b) orelse unreachable,
        .query => |k| switch (k) {
            .hover => .{ .name = config.hover_buffer },
            // prose: an action list, a diff, a report about the backend
            .code_action, .format, .status, .explain => .{ .name = config.lsp_buffer },
            .rename => .{ .name = config.search_buffer, .steps = true, .locations = true },
            .definition, .declaration, .type_definition, .implementation, .references => .{
                .name = config.search_buffer,
                .steps = true,
                .locations = true,
                .jumps = true,
            },
            // The hierarchy kinds behave like references: a list of places,
            // and a lone answer (one caller, one subtype) is a jump.
            .incoming_calls, .outgoing_calls, .supertypes, .subtypes => .{
                .name = config.search_buffer,
                .steps = true,
                .locations = true,
                .jumps = true,
            },
            .document_symbols, .workspace_symbols, .diagnostics, .workspace_diagnostics, .select_refs, .completion => .{
                .name = config.search_buffer,
                .steps = true,
                .locations = true,
            },
        },
    };
}

pub fn usesLocationsConfig(from: Origin) bool {
    const tr = traits(from);
    return tr.steps and !tr.commands and from != .pdf_links and
        !std.meta.eql(from, Origin{ .cmd = .Find }) and
        !std.meta.eql(from, Origin{ .query = .completion });
}

pub fn fileTraits(out: ?State) Traits {
    return traits((out orelse return file_row).from);
}

pub const Grain = enum {
    word,
    line,
    whole,
};

pub fn grain(out: ?State) Grain {
    const tr = fileTraits(out);
    if (tr.commands) return .whole;
    return if (tr.steps) .line else .word;
}

pub fn word(o: Origin) []const u8 {
    return switch (o) {
        .cmd => |b| @tagName(b),
        .query => |k| @tagName(k),
        .search => "/",
        .errors => config.errors_buffer,
        .pdf_links => config.pdf_links_buffer,
        .unsaved => config.unsaved_buffer,
    };
}

pub fn fromWord(w: []const u8) ?Origin {
    if (w.len == 0) return null;
    if (std.mem.eql(u8, w, "/")) return .search;
    if (std.mem.eql(u8, w, config.errors_buffer)) return .errors;
    if (std.mem.eql(u8, w, config.pdf_links_buffer)) return .pdf_links;
    if (std.mem.eql(u8, w, config.unsaved_buffer)) return .unsaved;
    if (std.meta.stringToEnum(Builtin, w)) |b|
        if (builtins.registry.outputTraits(b) != null) return .{ .cmd = b };
    if (std.meta.stringToEnum(lsp.Kind, w)) |k| return .{ .query = k };
    return null;
}

pub fn resultsFrom(p: *Pardes, pane: *Pane, from: Origin) bool {
    const rp = p.panes[pane.search_pane orelse return false] orelse return false;
    const f = rp.file orelse return false;
    const o = f.output orelse return false;
    return std.meta.eql(o.from, from);
}

pub const Location = struct {
    path: []const u8,
    at: look.Spot,
    end: usize,

    fn order(a: Location, b: Location) std.math.Order {
        const path = std.mem.order(u8, a.path, b.path);
        if (path != .eq) return path;
        if (a.at.line != b.at.line) return std.math.order(a.at.line, b.at.line);
        return std.math.order(a.at.col, b.at.col);
    }
};

pub fn location(line: []const u8) Location {
    const target = locations.parse(std.mem.trimEnd(u8, line, " \t\r\n"));
    return .{ .path = target.path, .at = target.at, .end = target.end };
}

pub fn isResultRow(file: *const File.State, row: usize) bool {
    if (row < file.location_rows.len) return file.location_rows[row].kind == .match;
    return !locations.isContextLine(modal.lineSlice(file.content, row));
}

fn sortResults(arena: std.mem.Allocator, from: Origin, content: []u8, anchor: ?usize) !?usize {
    switch (from) {
        .search => {},
        .cmd => |cmd| switch (cmd) {
            .Find, .Grep => {},
            else => return anchor,
        },
        .query => |kind| switch (kind) {
            .definition,
            .declaration,
            .type_definition,
            .implementation,
            .references,
            .incoming_calls,
            .outgoing_calls,
            .supertypes,
            .subtypes,
            .document_symbols,
            .workspace_symbols,
            .diagnostics,
            .workspace_diagnostics,
            .select_refs,
            .rename,
            => {},
            else => return anchor,
        },
        .errors, .pdf_links, .unsaved => return anchor,
    }
    if (content.len == 0) return anchor;
    const path_only = std.meta.eql(from, Origin{ .cmd = .Find });
    const trailing_newline = content[content.len - 1] == '\n';
    const body = content[0 .. content.len - @intFromBool(trailing_newline)];
    var lines = std.mem.splitScalar(u8, body, '\n');
    var previous: ?Location = null;
    var sorted = true;
    var count: usize = 0;
    while (lines.next()) |line| {
        const current: Location = if (path_only) .{ .path = line, .at = .{}, .end = line.len } else location(line);
        if (!path_only and current.at.line == 0) return anchor;
        if (previous) |last| if (last.order(current) == .gt) {
            sorted = false;
        };
        previous = current;
        count += 1;
    }
    if (sorted) return anchor;

    const Row = struct {
        text: []const u8,
        target: Location,
        original: usize,

        fn lessThan(_: void, a: @This(), b: @This()) bool {
            return switch (a.target.order(b.target)) {
                .lt => true,
                .eq => a.original < b.original,
                .gt => false,
            };
        }
    };
    const rows = try arena.alloc(Row, count);
    const copy = try arena.dupe(u8, body);
    lines = std.mem.splitScalar(u8, copy, '\n');
    for (rows, 0..) |*row, original| {
        const text = lines.next().?;
        const target: Location = if (path_only) .{ .path = text, .at = .{}, .end = text.len } else location(text);
        row.* = .{
            .text = text,
            .target = target,
            .original = original,
        };
    }
    std.mem.sort(Row, rows, {}, Row.lessThan);
    var mapped = anchor;
    var offset: usize = 0;
    for (rows, 0..) |row, i| {
        if (anchor == row.original) mapped = i;
        @memcpy(content[offset..][0..row.text.len], row.text);
        offset += row.text.len;
        if (i + 1 < rows.len or trailing_newline) {
            content[offset] = '\n';
            offset += 1;
        }
    }
    std.debug.assert(offset == content.len);
    return mapped;
}

pub fn nextResult(content: []const u8, rows: []const locations.Row, path: []const u8, at: look.Spot) usize {
    const current: Location = .{ .path = path, .at = at, .end = 0 };
    var lines = std.mem.splitScalar(u8, content, '\n');
    var first: ?usize = null;
    var row: usize = 0;
    while (lines.next()) |line| : (row += 1) {
        if (row < rows.len) {
            if (rows[row].kind != .match) continue;
        } else if (locations.isContextLine(line)) continue;
        const target = location(line);
        if (target.at.line == 0) continue;
        if (first == null) first = row;
        if (target.order(current) == .gt) return row;
    }
    return first orelse 0;
}

pub fn open(p: *Pardes, id: usize, dir: []const u8, from: Origin, arg: []const u8, content: []u8) !*Pane {
    const path = try std.fmt.allocPrint(p.gpa, "{s}/{s}", .{
        std.mem.trimEnd(u8, dir, "/"), traits(from).name,
    });
    errdefer p.gpa.free(path);
    var out: State = .{ .from = from };
    try setArg(&out, arg);
    const history = try File.History.create(p.gpa);
    errdefer p.gpa.destroy(history);
    const pane = try p.newDocPane(id);
    pane.file = .{ .path = path, .content = content, .output = out, .history = history };
    pane.body.cur_pinned = true;
    return pane;
}

/// Find and Grep share one +Search a directory, each run replacing what
/// the last showed, as acme reuses a directory's +Errors; a pane's own
/// search (LookWord list) keeps a pane a pattern.
/// Whether `dir` has its Find/Grep +Search open.
pub fn hasFileSearch(p: *Pardes, dir: []const u8) bool {
    for (p.panes) |slot| {
        const f = (slot orelse continue).file orelse continue;
        const o = f.output orelse continue;
        if (fileSearch(o.from) and std.mem.eql(u8, std.fs.path.dirname(f.path) orelse "", dir)) return true;
    }
    return false;
}

/// Whether `from` fills its directory's one +Search, whatever filled it
/// last (Find, Grep, Symbols, Diagnostics, any language server's list),
/// each run replacing the last. A plain word's search (in a file or a PDF)
/// keeps a +Search a pattern: n/N walk from one such list to the next.
fn fileSearch(from: Origin) bool {
    return from != .search and std.mem.eql(u8, traits(from).name, config.search_buffer);
}

/// A language server's prose (Lspinfo, Lspwhy, a code action list, a
/// format diff): one `+Lsp` a directory holds for all of them.
fn lspProse(from: Origin) bool {
    return from == .query and std.mem.eql(u8, traits(from).name, config.lsp_buffer);
}

pub fn fillResults(p: *Pardes, id: usize, dir: []const u8, from: Origin, arg: []const u8, content: []u8, initial_anchor: ?usize) !void {
    var result_content = content;
    errdefer p.gpa.free(result_content);
    var result_rows: []locations.Row = &.{};
    errdefer locations.freeRows(p.gpa, result_rows);
    const pane = p.panes[id] orelse return error.MissingPane;
    if (arg.len > max_arg) return error.ArgumentTooLong;
    var anchor = try sortResults(p.scratch.allocator(), from, content, initial_anchor);
    const by_arg = std.meta.activeTag(from) != .query;
    if (p.locations_config.context == 0 and !p.locations_config.tscontext) {
        for (p.panes, 0..) |slot, i| {
            // A directory's +Search is found by its directory, whatever
            // pane ran the search: that +Search itself too.
            if (i == id and !fileSearch(from)) continue;
            const rp = slot orelse continue;
            const rf = if (rp.file) |*f| f else continue;
            const output = if (rf.output) |*o| o else continue;
            if (!std.meta.eql(output.from, from)) continue;
            if (by_arg and !std.mem.eql(u8, output.arg(), arg)) continue;
            if (!std.mem.eql(u8, std.fs.path.dirname(rf.path) orelse "", dir)) continue;
            if (!locations.sameInput(content, rf.content, rf.location_rows, p.locations_config.layout)) continue;
            try setArg(output, arg);
            p.gpa.free(content);
            p.fs.refilled = rp.serial;
            p.active = id;
            if (traits(from).steps) {
                pane.search_pane = i;
                pane.search_row = anchor;
                look.armLookWalk(p, i);
            }
            return;
        }
    }
    if (usesLocationsConfig(from)) {
        const formatted = try locations.format(p, dir, content, anchor, true);
        p.gpa.free(result_content);
        result_content = formatted.content;
        result_rows = formatted.rows;
        anchor = formatted.anchor;
    }
    for (p.panes, 0..) |slot, i| {
        const rp = slot orelse continue;
        const rf = if (rp.file) |*f| f else continue;
        const o = if (rf.output) |*x| x else continue;
        const shared = (fileSearch(from) and fileSearch(o.from)) or (lspProse(from) and lspProse(o.from));
        if (i == id and !shared) continue;
        if (!shared and !std.meta.eql(o.from, from)) continue;
        if (!shared and by_arg and !std.mem.eql(u8, o.arg(), arg)) continue;
        if (!std.mem.eql(u8, std.fs.path.dirname(rf.path) orelse "", dir)) continue;
        o.from = from;
        p.fs.refilled = rp.serial;
        try setArg(o, arg);
        if (std.mem.eql(u8, rf.content, result_content)) {
            p.gpa.free(result_content);
        } else {
            File.setContent(p, rf, result_content);
            resetBody(p, rp);
        }
        if (locations.equalRows(rf.location_rows, result_rows)) {
            locations.freeRows(p.gpa, result_rows);
        } else {
            locations.freeRows(p.gpa, rf.location_rows);
            rf.location_rows = result_rows;
            if (rf.highlights.len > 0) p.tree_sitter_gpa.free(rf.highlights);
            rf.highlights = &.{};
            rf.highlight_start = 0;
            rf.syntax_dirty = true;
        }
        p.active = id;
        if (traits(from).steps) {
            pane.search_pane = i;
            pane.search_row = anchor;
            look.armLookWalk(p, i);
        }
        return;
    }
    const free = p.freeSlot() orelse return error.NoPaneSlots;
    const np = try open(p, free, dir, from, arg, result_content);
    np.file.?.location_rows = result_rows;
    exec.placeNew(p, id, id, free, .doc);
    p.active = id;
    if (traits(from).steps) {
        pane.search_pane = free;
        pane.search_row = anchor;
        look.armLookWalk(p, free);
    }
}

pub fn openJumps(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    for (p.jumps[0..p.njumps]) |j| {
        // A closed file's entry: marked, and a look at it opens it again.
        if (j.serial == 0) {
            const e = p.recentByHash(j.path_hash) orelse continue;
            try out.writer.print("{s}:{d}:{d} (closed)\n", .{ e.path, @max(1, j.line), @max(1, j.col) });
            continue;
        }
        const jp = p.panes[j.pane] orelse continue;
        var idbuf: [16]u8 = undefined;
        const pdf_path: ?[]const u8 = if (comptime pardes.pdf_enabled) jp.pdfPath() else null;
        const has_path = if (jp.file) |f| f.output == null else pdf_path != null;
        const loc: []const u8 = if (has_path)
            (if (jp.file) |f| f.path else pdf_path.?)
        else
            std.fmt.bufPrint(&idbuf, config.pane_addr ++ "{d}", .{jp.serial}) catch unreachable;
        const what: []const u8 = if (jp.file) |f|
            std.mem.trim(u8, modal.lineSlice(f.content, j.line -| 1), " \t\r")
        else if (jp.image) |iv|
            iv.path
        else if (pdf_path) |path|
            path
        else
            jp.cwdSlice();
        var cut = @min(what.len, 120);
        while (cut > 0 and cut < what.len and what[cut] & 0xc0 == 0x80) cut -= 1;
        if (j.line == 0)
            try out.writer.print("{s} {s}\n", .{ loc, what[0..cut] })
        else
            try out.writer.print("{s}:{d}:{d} {s}\n", .{ loc, j.line, j.col, what[0..cut] });
    }
    const content = try out.toOwnedSlice();
    try openStepped(p, id, .{ .cmd = .Jumplist }, content);
}

/// The recent list as rows: `<path>:<line>:<col> open|closed`, most recent
/// first; a look at a row opens the file there, as a +Jumps row does.
pub fn recentText(p: *Pardes, w: *std.Io.Writer, look_rows: bool) !void {
    for (p.recent.entries.items) |e| {
        var is_open = false;
        for (p.panes) |slot| if (slot) |pane| if (pane.file) |f| if (f.output == null and std.mem.eql(u8, f.path, e.path)) {
            is_open = true;
        };
        const state: []const u8 = if (is_open) "open" else "(closed)";
        if (!look_rows) {
            // A name as /index shows it: one line, a newline in it `\n`.
            var name_buf: [4 * 4096]u8 = undefined;
            try w.print("{s} {s}\n", .{ if (is_open) "open" else "closed", pardes.ctlfs.events.shown(e.path, &name_buf) });
        } else if (e.line == 0) {
            try w.print("{s} {s}\n", .{ e.path, state });
        } else if (e.aline != 0 and (e.aline != e.line or e.acol != e.col)) {
            // A selection: both its ends, in order, `path:L:C-L2:C2`.
            const a_first = e.aline < e.line or (e.aline == e.line and e.acol < e.col);
            const s = if (a_first) [2]u32{ e.aline, e.acol } else [2]u32{ e.line, e.col };
            const t = if (a_first) [2]u32{ e.line, e.col } else [2]u32{ e.aline, e.acol };
            try w.print("{s}:{d}:{d}-{d}:{d} {s}\n", .{ e.path, s[0], s[1], t[0], t[1], state });
        } else {
            try w.print("{s}:{d}:{d} {s}\n", .{ e.path, e.line, e.col, state });
        }
    }
}

/// A refusal's list of unsaved panes, kept in the one +Unsaved: filled
/// again when it is there (as +Search is), else opened below `id`. Best
/// effort: with no room for it, the notice and the log still say it.
pub fn openUnsaved(p: *Pardes, id: usize, content: []u8) void {
    for (p.panes) |slot| {
        const rp = slot orelse continue;
        const rf = if (rp.file) |*f| f else continue;
        const o = rf.output orelse continue;
        if (o.from != .unsaved) continue;
        File.setContent(p, rf, content);
        resetBody(p, rp);
        return;
    }
    const pane = p.panes[id] orelse return p.gpa.free(content);
    const dir = if (pane.file) |f| (std.fs.path.dirname(f.path) orelse "/") else pane.cwdSlice();
    const free = p.freeSlot() orelse return p.gpa.free(content);
    _ = open(p, free, dir, .unsaved, "", content) catch return;
    exec.placeNew(p, id, id, free, .doc);
    p.active = id;
}

/// Pane `gone` closed: its row goes from +Unsaved, which lists only panes
/// still there to lose.
pub fn dropUnsaved(p: *Pardes, gone: *const Pane) void {
    const gf = gone.file orelse return;
    if (gf.output != null and !(gf.output.?.from == .cmd and gf.output.?.from.cmd == .New)) return;
    for (p.panes) |slot| {
        const rp = slot orelse continue;
        if (rp == gone) continue;
        const rf = if (rp.file) |*f| f else continue;
        const o = rf.output orelse continue;
        if (o.from != .unsaved) continue;
        var scratch_name: [limits.host_path_cap + 24]u8 = undefined;
        const as_scratch = std.fmt.bufPrint(&scratch_name, "{s} (pane {d}): Modified", .{ gf.path, gone.serial }) catch "";
        var out: std.ArrayList(u8) = .empty;
        var lines = std.mem.splitScalar(u8, rf.content, '\n');
        var dropped = false;
        var first = true;
        while (lines.next()) |line| {
            const is_it = std.mem.startsWith(u8, line, gf.path) and std.mem.eql(u8, line[gf.path.len..], ": Modified");
            if (is_it or (as_scratch.len > 0 and std.mem.eql(u8, line, as_scratch))) {
                dropped = true;
                continue;
            }
            if (!first) out.append(p.gpa, '\n') catch return out.deinit(p.gpa);
            out.appendSlice(p.gpa, line) catch return out.deinit(p.gpa);
            first = false;
        }
        if (!dropped) return out.deinit(p.gpa);
        const content = out.toOwnedSlice(p.gpa) catch return out.deinit(p.gpa);
        File.setContent(p, rf, content);
        resetBody(p, rp);
        return;
    }
}

/// Recent: the one +Recent, filled again when it is there (as Find and
/// Grep's +Search is), else opened below the asking pane.
pub fn openRecent(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    try recentText(p, &out.writer, true);
    const content = try out.toOwnedSlice();
    for (p.panes, 0..) |slot, i| {
        const rp = slot orelse continue;
        const rf = if (rp.file) |*f| f else continue;
        const o = rf.output orelse continue;
        if (!std.meta.eql(o.from, Origin{ .cmd = .Recent })) continue;
        File.setContent(p, rf, content);
        resetBody(p, rp);
        p.fs.refilled = rp.serial;
        if (p.panes[id]) |pane| {
            pane.search_pane = i;
            pane.search_row = null;
        }
        look.armLookWalk(p, i);
        return;
    }
    try openStepped(p, id, .{ .cmd = .Recent }, content);
}

pub fn openThemes(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    for (pardes.themes, 0..) |t, i| {
        if (pardes.colors.groupAt(i)) |title|
            try out.writer.print("{s}# {s}\n", .{ if (i == 0) "" else "\n", title });
        try out.writer.print(comptime config.Runtime.findAction(.theme).?.word ++ " {s}\n", .{t.name});
    }
    const content = try out.toOwnedSlice();
    try openStepped(p, id, .{ .cmd = .Themes }, content);
}

pub fn isWalkRow(file: *const File.State, row: usize, line: []const u8) bool {
    const state = file.output orelse return true;
    if (usesLocationsConfig(state.from)) return isResultRow(file, row);
    if (!std.meta.eql(state.from, Origin{ .cmd = .Themes })) return true;
    // Section labels are for reading, not stops in the command walk.
    return std.mem.startsWith(u8, std.mem.trimStart(u8, line, " \t"), comptime config.Runtime.findAction(.theme).?.word ++ " ");
}

pub fn openFonts(p: *Pardes, id: usize) !void {
    if (builtins.capabilities.font_picker) {
        const arena = p.scratch.allocator();
        const font_list = fonts.list(arena, null);
        var out: std.Io.Writer.Allocating = .init(p.gpa);
        errdefer out.deinit();
        for (font_list) |f|
            try out.writer.print(comptime config.Runtime.findAction(.font).?.word ++ " {s}\n", .{f.name});
        const content = try out.toOwnedSlice();
        try openStepped(p, id, .{ .cmd = .Fonts }, content);
    }
}

fn openStepped(p: *Pardes, id: usize, from: Origin, content: []u8) !void {
    errdefer p.gpa.free(content);
    const pane = p.panes[id] orelse return error.MissingPane;
    const own = if (pane.file) |f| (std.fs.path.dirname(f.path) orelse "/") else pane.cwdSlice();
    // A terminal whose shell has not said where it is yet (an init file's
    // word at boot): the session's directory, not `/`.
    const dir = if (own.len == 0) p.sessionDir() else own;
    const free = p.freeSlot() orelse return error.NoPaneSlots;
    _ = try open(p, free, dir, from, "", content);
    exec.placeNew(p, id, id, free, .doc);
    p.active = id;
    pane.search_pane = free;
    pane.search_row = null;
    look.armLookWalk(p, free);
}

fn helpContent(gpa: std.mem.Allocator, prefix: []const u8) ![]u8 {
    const full_header = "pardes builtins, and how to run each:\nSPC and its keys, a chord, a button, the\ntopbar - or the name, executed anywhere.\n\n";
    const group_header = "pardes builtins under SPC";
    const language_footer =
        "\nlanguage keys (motions, not words):\n" ++
        "gd gD gy gi gr   goto: definition,\n" ++
        "                 declaration, type-def,\n" ++
        "                 implementation, refs\n" ++
        "]d [d ]D [D      diagnostics: next,\n" ++
        "                 prev, last, first\n" ++
        "=                format (applies, one\n" ++
        "                 undo step)\n" ++
        "Tab after a .    completion, in insert\n" ++
        "C-left-click     definition, by mouse\n" ++
        "SPC l ...        hover, rename, symbols,\n" ++
        "                 calls, types: above\n";
    var len: usize = if (prefix.len == 0)
        full_header.len + language_footer.len
    else
        group_header.len + prefix.len * 2 + 2;
    for (pardes.builtin_rows) |row| {
        // a path-less builtin filters as the empty path: in the full listing
        // (which starts with nothing) and out of every group
        if (!std.mem.startsWith(u8, row.path orelse "", prefix)) continue;
        len += row.line.len + 1;
    }
    const content = try gpa.alloc(u8, len);
    var at: usize = 0;
    if (prefix.len == 0) {
        @memcpy(content[0..full_header.len], full_header);
        at = full_header.len;
    } else {
        @memcpy(content[0..group_header.len], group_header);
        at = group_header.len;
        for (prefix) |c| {
            content[at] = ' ';
            content[at + 1] = c;
            at += 2;
        }
        content[at] = '\n';
        content[at + 1] = '\n';
        at += 2;
    }
    for (pardes.builtin_rows) |row| {
        if (!std.mem.startsWith(u8, row.path orelse "", prefix)) continue;
        @memcpy(content[at..][0..row.line.len], row.line);
        at += row.line.len;
        content[at] = '\n';
        at += 1;
    }
    if (prefix.len == 0) {
        @memcpy(content[at..][0..language_footer.len], language_footer);
        at += language_footer.len;
    }
    std.debug.assert(at == content.len);
    return content;
}

pub fn openHelp(p: *Pardes, id: usize, prefix: []const u8) !void {
    const content = try helpContent(p.gpa, prefix);
    // content is handed off unfreed on purpose: openRead adopts it or frees
    // it, and nothing between the alloc above and this line can fail.
    return openRead(p, id, .{ .cmd = .Help }, prefix, content);
}

test "full Help renders every builtin row, then the language keys" {
    const content = try helpContent(std.testing.allocator, "");
    defer std.testing.allocator.free(content);

    // FIRST blank line: the end of the header (the footer opens with one too)
    const body = content[(std.mem.indexOf(u8, content, "\n\n") orelse
        return error.MissingHelpHeader) + 2 ..];
    var lines = std.mem.splitScalar(u8, body, '\n');
    for (pardes.builtin_rows) |row|
        try std.testing.expectEqualStrings(row.line, lines.next() orelse
            return error.MissingBuiltinHelpRow);
    // ...and after the last row, the language-keys section: the one part of
    // the keymap no builtin row can carry, closing the page.
    try std.testing.expectEqualStrings("", lines.next() orelse
        return error.MissingLanguageKeys);
    try std.testing.expectEqualStrings("language keys (motions, not words):", lines.next() orelse
        return error.MissingLanguageKeys);
    try std.testing.expect(std.mem.indexOf(u8, body, "\ngd gD gy gi gr   goto: definition,\n") != null);
    // the group view stays a pure filter: no footer under a prefix
    const group = try helpContent(std.testing.allocator, "l");
    defer std.testing.allocator.free(group);
    try std.testing.expect(std.mem.indexOf(u8, group, "language keys") == null);
}

pub fn openConfig(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    var dir_buf: [1024]u8 = undefined;
    const host_fs = comptime (pardes.platform != .web and pardes.platform != .esp32p4);
    var located: std.Io.Writer.Allocating = .init(p.gpa);
    defer located.deinit();
    try p.locations_config.write(&located.writer);
    try config.Runtime.writeReport(&out.writer, .{
        .locations = located.written(),
        .default_dump_dir = if (host_fs) (pardes.dump.defaultDirectory(&dir_buf) orelse "") else "",
        .startup_config_path = p.opts.startup_config_path,
        .platform = @tagName(pardes.platform),
        .theme_name = p.theme().name,
        .compiled_default_shell = config.defaultShell(),
        .hover_delay_frames = config.look_preview_delay_frames,
        .native_images = p.native_images,
        .capabilities = builtins.capabilities,
        .state = &p.settings,
    });
    const content = try out.toOwnedSlice();
    return openRead(p, id, .{ .cmd = .DumpConfig }, "", content);
}

/// The message-row log, oldest first — the lines that were said in passing and
/// then cleared by the next keystroke.
pub fn openMessages(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    var i: usize = 0;
    while (p.messages.at(i)) |m| : (i += 1) {
        if (m.serial != 0) try out.writer.print("{d}: ", .{m.serial});
        try out.writer.writeAll(m.slice());
        if (m.repeats > 1) try out.writer.print("  (x{d})", .{m.repeats});
        try out.writer.writeByte('\n');
    }
    if (i == 0) try out.writer.writeAll("nothing has been said yet\n");
    const content = try out.toOwnedSlice();
    return openRead(p, id, .{ .cmd = .Messages }, "", content);
}

/// The version banner plus the embedded CHANGELOG, so an installed binary can
/// say what it is and what changed without a repository beside it.
pub fn openChangelog(p: *Pardes, id: usize) !void {
    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    try out.writer.print("pardes {s}\n\n", .{build_options.version});
    try out.writer.writeAll(@embedFile("CHANGELOG.md"));
    const content = try out.toOwnedSlice();
    return openRead(p, id, .{ .cmd = .Changelog }, "", content);
}

pub fn openEffectCode(p: *Pardes, id: usize, argument: []const u8) !void {
    const name = std.mem.trim(u8, argument, " \t\r\n");
    const setting = config.Runtime.find(name) orelse return error.UnknownEffect;
    switch (setting.action) {
        .transition, .scene => {},
        else => return error.NotAnEffect,
    }
    if (!setting.enabled(builtins.capabilities)) return error.EffectUnavailable;
    // Without -Dembed-sources the paths would name nothing this build can open.
    if (!limits.embedded_sources) return error.EffectUnavailable;
    const paths = effect_sources.forSetting(setting) orelse
        return error.EffectUnavailable;

    var out: std.Io.Writer.Allocating = .init(p.gpa);
    errdefer out.deinit();
    try out.writer.print("EffectCode {s} ({s})\n", .{ setting.word, @tagName(effect_sources.backend) });
    try out.writer.writeByte('\n');
    for (paths) |path| try out.writer.print("/virtual/{s}\n", .{path});
    const content = try out.toOwnedSlice();
    return openRead(p, id, .{ .cmd = .EffectCode }, setting.word, content);
}

pub fn openErrors(p: *Pardes, id: usize, content: []u8) !void {
    return openRead(p, id, .errors, "", content);
}

pub fn resetBody(p: *Pardes, pane: *Pane) void {
    pane.file.?.scroll = 0;
    pane.body.cur_row = 0;
    pane.body.cur_col = 0;
    pane.body.cur_pinned = true;
    pane.hscroll = 0;
    pane.wrap_n = 0;
    pane.body.msel = .{};
    pane.body.vsel = .{};
    pane.body.nsel = 0;
    pane.nsel_snap = 0;
    pane.body.select = false;
    pane.sel = @splat(.{});
    pane.body.sticky_col = -1;
    pane.body.restore_cursor = false;
    pane.body.normal.clear();
    pane.look_at = null;
    if (p.look_hover_wait) |wait| if (wait.serial == pane.serial) {
        p.look_hover_wait = null;
    };
    if (p.look_hover_preview) |preview| if (preview.serial == pane.serial) {
        p.look_hover_preview = null;
    };
    if (p.drag == .select and p.panes[p.drag.select.id] == pane) p.drag = .none;
}

fn openRead(p: *Pardes, id: usize, from: Origin, arg: []const u8, content: []u8) !void {
    errdefer p.gpa.free(content);
    if (p.panes[id] == null) return error.MissingPane;
    for (p.panes, 0..) |slot, i| {
        const hp = slot orelse continue;
        const hf = if (hp.file) |*f| f else continue;
        const ho = if (hf.output) |*o| o else continue;
        if (!std.meta.eql(ho.from, from)) continue;
        try setArg(ho, arg);
        File.setContent(p, hf, content);
        resetBody(p, hp);
        p.active = i;
        return;
    }
    // Where the word ran: the pane's directory, or from a column's or the
    // workspace's tag, the session's.
    const dir = p.execDir(id);
    const free = p.freeSlot() orelse return error.NoPaneSlots;
    _ = try open(p, free, dir, from, arg, content);
    exec.placeNew(p, id, id, free, if (from == .errors) .errors else .doc);
    p.active = free;
}