//! Freestanding WebAssembly boundary for the DOM backend.
//!
//! JavaScript owns the clock and nothing else: it calls `pardes_tick` (one
//! `Pardes.pump`) and reads the packed cell buffer `present` left behind. The
//! host vtable below is only what a page genuinely has — pixels, the
//! clipboard, links, downloads. Processes, a real filesystem, a language
//! backend and subprocess pipes are left null, so the core answers them itself
//! with a virtual filesystem, a virtual clipboard and silent ptys instead of
//! forwarding effects that JavaScript cannot honour anyway.

const std = @import("std");
const pardes = @import("pardes.zig");

const gpa = std.heap.wasm_allocator;
const embedded_dump = @embedFile("embedded.dump.zon");
const input_capacity = 64 * 1024;
const c_alloc_header_size = 16;
const attr_tagline: u16 = 1 << 7;

comptime {
    if (c_alloc_header_size < @sizeOf(usize)) @compileError("C allocation header is too small");
}

/// Tree-sitter's C runtime is linked into this module. Its conventional
/// allocation symbols share the same wasm allocator as the Zig core and keep
/// the original allocation size in a 16-byte, max-aligned prefix.
export fn malloc(size_arg: usize) callconv(.c) ?*anyopaque {
    const size = @max(size_arg, 1);
    const total = std.math.add(usize, c_alloc_header_size, size) catch return null;
    const bytes = gpa.alignedAlloc(u8, .@"16", total) catch return null;
    const header: *align(16) usize = @ptrCast(bytes.ptr);
    header.* = total;
    return @ptrCast(bytes.ptr + c_alloc_header_size);
}

export fn calloc(count: usize, size: usize) callconv(.c) ?*anyopaque {
    const len = std.math.mul(usize, count, size) catch return null;
    const ptr = malloc(len) orelse return null;
    if (len != 0) {
        const bytes: [*]u8 = @ptrCast(ptr);
        @memset(bytes[0..len], 0);
    }
    return ptr;
}

export fn free(ptr: ?*anyopaque) callconv(.c) void {
    const data = ptr orelse return;
    const data_bytes: [*]u8 = @ptrCast(data);
    const base: [*]align(16) u8 = @ptrCast(@alignCast(data_bytes - c_alloc_header_size));
    const header: *align(16) usize = @ptrCast(base);
    gpa.free(base[0..header.*]);
}

export fn realloc(ptr: ?*anyopaque, size: usize) callconv(.c) ?*anyopaque {
    if (ptr == null) return malloc(size);
    if (size == 0) {
        free(ptr);
        return null;
    }
    const data_bytes: [*]u8 = @ptrCast(ptr.?);
    const base: [*]align(16) u8 = @ptrCast(@alignCast(data_bytes - c_alloc_header_size));
    const header: *align(16) usize = @ptrCast(base);
    const old_size = header.* - c_alloc_header_size;
    const replacement = malloc(size) orelse return null;
    const replacement_bytes: [*]u8 = @ptrCast(replacement);
    @memcpy(replacement_bytes[0..@min(old_size, size)], data_bytes[0..@min(old_size, size)]);
    free(ptr);
    return replacement;
}

pub const std_options: std.Options = .{ .logFn = logFn };
pub const panic = std.debug.FullPanic(panicImpl);

fn logFn(
    comptime _: std.log.Level,
    comptime _: @EnumLiteral(),
    comptime _: []const u8,
    _: anytype,
) void {}

fn panicImpl(_: []const u8, _: ?usize) noreturn {
    @trap();
}

const WebCell = extern struct {
    // UTF-8 graphemes in the core are at most seven bytes. The eighth byte is
    // always zero, which also makes a debugger's memory view pleasant.
    text: [8]u8,
    fg: u32,
    bg: u32,
    attrs: u16,
    len: u8,
    flags: u8,
};

comptime {
    if (@sizeOf(WebCell) != 20) @compileError("the JS frame ABI changed");
}

const State = struct {
    core: *pardes.Pardes,
    tag_cells: [pardes.MAX_TAG_LAYERS][]WebCell = @splat(&.{}),
    layer_cells: [pardes.MAX_PANES][]WebCell = @splat(&.{}),
    cells: []WebCell = &.{},
    frame_len: usize = 0,
    frame_cols: u16 = 0,
    frame_rows: u16 = 0,

    fn init(cols: u16, rows: u16) !State {
        const allocs = pardes.memory.init(gpa);
        errdefer pardes.memory.deinit();
        pardes.image.start(std.Io.failing, allocs.image);
        errdefer pardes.image.stop();
        if (comptime pardes.pdf_enabled) pardes.pdf.start(allocs.pdf);
        errdefer if (comptime pardes.pdf_enabled) pardes.pdf.stop();
        pardes.syntax.start(allocs.tree_sitter);
        errdefer pardes.syntax.stop();

        const core = try pardes.Pardes.initFromDump(allocs.pardes, .{
            .cols = cols,
            .rows = rows,
            .frame_allocator = allocs.frame,
            .image_allocator = allocs.image,
            .pdf_allocator = allocs.pdf,
            .tree_sitter_allocator = allocs.tree_sitter,
        }, embedded_dump);
        return .{ .core = core };
    }

    fn deinit(s: *State) void {
        if (s.cells.len > 0) gpa.free(s.cells);
        for (s.layer_cells) |cells| gpa.free(cells);
        for (s.tag_cells) |cells| gpa.free(cells);
        s.core.deinit();
        pardes.image.stop();
        if (comptime pardes.pdf_enabled) pardes.pdf.stop();
        pardes.syntax.stop();
        pardes.memory.deinit();
    }
};

var state: ?State = null;
var input: [input_capacity]u8 = undefined;
var last_error: u32 = 0;

export fn pardes_init(cols_arg: u32, rows_arg: u32) u32 {
    if (state) |*old| old.deinit();
    state = null;
    last_error = 0;

    const cols: u16 = @intCast(std.math.clamp(cols_arg, 1, std.math.maxInt(u16)));
    const rows: u16 = @intCast(std.math.clamp(rows_arg, 1, std.math.maxInt(u16)));
    state = State.init(cols, rows) catch |err| {
        last_error = @intFromError(err);
        return last_error;
    };
    state.?.core.update(.{ .resize = .{ .cols = cols, .rows = rows } });
    return 0;
}

export fn pardes_deinit() void {
    if (state) |*s| s.deinit();
    state = null;
}

export fn pardes_last_error() u32 {
    return last_error;
}

export fn pardes_input_ptr() u32 {
    return @intCast(@intFromPtr(&input));
}

export fn pardes_input_capacity() u32 {
    return input_capacity;
}

export fn pardes_gui_tagline_font_percent() u32 {
    return pardes.config.gui_tagline_font_percent;
}

export fn pardes_resize(cols_arg: u32, rows_arg: u32) void {
    const s = &(state orelse return);
    const cols: u16 = @intCast(std.math.clamp(cols_arg, 1, std.math.maxInt(u16)));
    const rows: u16 = @intCast(std.math.clamp(rows_arg, 1, std.math.maxInt(u16)));
    if (s.core.screen_w == cols and s.core.screen_h == rows) return;
    s.core.update(.{ .resize = .{ .cols = cols, .rows = rows } });
}

/// `mods`: bit 0 ctrl, bit 1 alt, bit 2 shift. `len` bytes at input are the
/// browser's composed text for printable keys and zero for functional keys.
export fn pardes_key(cp_arg: u32, len_arg: u32, mods: u32) void {
    const s = &(state orelse return);
    if (cp_arg > std.math.maxInt(u21)) return;
    const len: usize = @min(len_arg, input.len);
    s.core.update(.{ .key = .{
        .cp = @intCast(cp_arg),
        .text = input[0..len],
        .ctrl = mods & 1 != 0,
        .alt = mods & 2 != 0,
        .shift = mods & 4 != 0,
    } });
}

export fn pardes_paste(len_arg: u32) void {
    const s = &(state orelse return);
    const len: usize = @min(len_arg, input.len);
    s.core.update(.{ .paste = input[0..len] });
}

/// Buttons and kinds are their boundary enum ordinals. Invalid values are
/// ignored rather than reaching an unchecked enum cast inside wasm.
export fn pardes_mouse(button_arg: u32, kind_arg: u32, col_arg: u32, row_arg: u32, mods: u32) void {
    mouseWithHit(button_arg, kind_arg, col_arg, row_arg, mods, null, null);
}

export fn pardes_mouse_pixel(button_arg: u32, kind_arg: u32, col_arg: u32, row_arg: u32, mods: u32, x: f32, y: f32, bw: f32, bh: f32, tw: f32, th: f32) void {
    const s = &(state orelse return);
    const source = s.core.presentation.pointerFractional(s.core.screen_w, s.core.screen_h, x / @max(1, bw), y / @max(1, bh));
    var hit: ?pardes.Mouse.BodyHit = null;
    for (&s.core.surface.body_layers) |*layer| {
        const point = source orelse break;
        hit = layer.hitAt(point.x * bw, point.y * bh, bw, bh, tw, th);
        if (hit != null) break;
    }
    var tag_hit: ?pardes.TagHit = null;
    for (&s.core.surface.tag_layers) |*layer| {
        const point = source orelse break;
        tag_hit = layer.hitAt(point.x * bw, point.y * bh, bw, bh, tw, th);
        if (tag_hit != null) break;
    }
    mouseWithHit(button_arg, kind_arg, col_arg, row_arg, mods, hit, tag_hit);
}

fn mouseWithHit(button_arg: u32, kind_arg: u32, col_arg: u32, row_arg: u32, mods: u32, hit: ?pardes.Mouse.BodyHit, tag_hit: ?pardes.TagHit) void {
    const s = &(state orelse return);
    const button: pardes.Mouse.Button = switch (button_arg) {
        0 => .left,
        1 => .middle,
        2 => .right,
        3 => .wheel_up,
        4 => .wheel_down,
        5 => .wheel_left,
        6 => .wheel_right,
        7 => .none,
        8 => .back,
        9 => .forward,
        else => return,
    };
    const kind: pardes.Mouse.Kind = switch (kind_arg) {
        0 => .press,
        1 => .release,
        2 => .motion,
        3 => .drag,
        else => return,
    };
    s.core.update(.{ .mouse = .{
        .body_hit = hit,
        .tag_hit = tag_hit,
        .button = button,
        .kind = kind,
        .col = @intCast(@min(col_arg, std.math.maxInt(u16))),
        .row = @intCast(@min(row_arg, std.math.maxInt(u16))),
        .ctrl = mods & 1 != 0,
    } });
}

export fn pardes_touch_scroll(delta: f32) void {
    const s = &(state orelse return);
    s.core.update(.{ .touch_scroll = delta });
}

export fn pardes_pointer_leave() void {
    const s = &(state orelse return);
    s.core.update(.pointer_leave);
}

/// One iteration of the core's own loop: queued input, effects, render,
/// present. JS calls it once per animation frame, after spending that frame's
/// animation ticks.
export fn pardes_tick() void {
    const s = &(state orelse return);
    s.core.pump(host(s)) catch |err| {
        last_error = @intFromError(err);
    };
}

/// Spend one fixed 60 Hz animation step, the only writer of animated time in
/// this host. Separate from the pump for the reason the AppKit shell keeps them
/// separate: if every input pump also advanced the transition, a burst of keys
/// would collapse a ten-frame fade into one display frame.
export fn pardes_animation_tick() void {
    const s = &(state orelse return);
    s.core.update(.tick);
}

export fn pardes_animating() u32 {
    const s = &(state orelse return 0);
    return @intFromBool(s.core.animationActive());
}

/// The Exit builtin, or the last pane closing. JS stops its frame loop.
export fn pardes_should_quit() u32 {
    const s = &(state orelse return 0);
    return @intFromBool(s.core.quit);
}

/// The number of cells in the frame `present` last packed, or zero before the
/// first tick. `pardes_frame_ptr` is valid until the next one.
export fn pardes_frame() u32 {
    const s = &(state orelse return 0);
    return @intCast(s.frame_len);
}

export fn pardes_frame_ptr() u32 {
    const s = &(state orelse return 0);
    return if (s.frame_len == 0) 0 else @intCast(@intFromPtr(s.cells.ptr));
}

export fn pardes_frame_cols() u32 {
    const s = &(state orelse return 0);
    return s.frame_cols;
}

export fn pardes_frame_rows() u32 {
    const s = &(state orelse return 0);
    return s.frame_rows;
}

export fn pardes_cursor_x() i32 {
    const s = &(state orelse return -1);
    return if (s.core.surface.cursor) |cursor| cursor.x else -1;
}

export fn pardes_tag_text_inset() u32 {
    return pardes.TAG_TEXT_INSET;
}

export fn pardes_grip_columns() u32 {
    return @import("config.zig").GUTTER;
}

export fn pardes_tag_layer_limit() u32 {
    return pardes.MAX_TAG_LAYERS;
}

export fn pardes_tag_layer_value(index: u32, field: u32) u32 {
    const s = &(state orelse return 0);
    if (index >= pardes.MAX_TAG_LAYERS) return 0;
    const layer = &s.core.surface.tag_layers[index];
    return switch (field) {
        0 => layer.cols,
        1 => @intFromEnum(layer.kind),
        2 => layer.id,
        3 => layer.serial,
        4 => layer.viewport.x,
        5 => layer.viewport.y,
        6 => layer.viewport.w,
        7 => layer.viewport.h,
        8 => if (layer.cursor) |c| c.col else 65535,
        9 => if (layer.cursor) |c| @intFromBool(c.bar) else 0,
        10 => @as(u32, layer.bg[0]) << 16 | @as(u32, layer.bg[1]) << 8 | layer.bg[2],
        else => 0,
    };
}

export fn pardes_tag_layer_cells(index: u32) ?[*]const WebCell {
    const s = &(state orelse return null);
    if (index >= pardes.MAX_TAG_LAYERS) return null;
    const layer = &s.core.surface.tag_layers[index];
    if (layer.cols == 0) return null;
    const cells = &s.tag_cells[index];
    if (cells.len != layer.cells.len) cells.* = gpa.realloc(cells.*, layer.cells.len) catch return null;
    for (layer.cells, cells.*) |source, *out| out.* = encodeWebCell(source);
    return cells.ptr;
}

export fn pardes_tagline_band_offset(row: u16, canvas_h: f32, cell_h: u32, tagline_h: u32) u32 {
    return pardes.taglineBandOffset(row, canvas_h, cell_h, tagline_h);
}

export fn pardes_body_layer_value(index: u32, field: u32) u32 {
    const s = &(state orelse return 0);
    if (index >= pardes.MAX_PANES) return 0;
    const layer = &s.core.surface.body_layers[index];
    return switch (field) {
        0 => layer.rows,
        1 => layer.cols,
        2 => layer.context_rows,
        3 => layer.viewport.x,
        4 => layer.viewport.y,
        5 => layer.viewport.w,
        6 => layer.viewport.h,
        7 => layer.serial,
        8 => if (layer.cursor) |c| c.x else 65535,
        9 => if (layer.cursor) |c| c.y else 65535,
        10 => if (layer.cursor) |c| @intFromBool(c.bar) else 0,
        else => @intFromBool(layer.hasContextBorderAfter(field - 11)),
    };
}

export fn pardes_body_layer_cells(index: u32) ?[*]const WebCell {
    const s = &(state orelse return null);
    if (index >= pardes.MAX_PANES) return null;
    const layer = &s.core.surface.body_layers[index];
    if (layer.rows == 0) return null;
    const cells = &s.layer_cells[index];
    if (cells.len != layer.cells.len) cells.* = gpa.realloc(cells.*, layer.cells.len) catch return null;
    for (layer.cells, cells.*) |cell, *out| out.* = encodeWebCell(cell);
    return cells.ptr;
}

export fn pardes_body_layer_limit() u32 {
    return pardes.MAX_PANES;
}

export fn pardes_row_metrics(body_w: u16, body_h: u16, tagline_w: u16, tagline_h: u16) void {
    const s = &(state orelse return);
    s.core.update(.{ .resize = .{ .cols = s.core.screen_w, .rows = s.core.screen_h, .cell_pixels = s.core.cell_pixels, .row_metrics = .{ .body_w = @max(1, body_w), .body_h = @max(1, body_h), .tagline_w = @max(1, tagline_w), .tagline_h = @max(1, tagline_h) } } });
}

export fn pardes_pointer_shape() u32 {
    const s = &(state orelse return 0);
    return @intFromEnum(s.core.surface.pointer_shape);
}

export fn pardes_cursor_y() i32 {
    const s = &(state orelse return -1);
    return if (s.core.surface.cursor) |cursor| cursor.y else -1;
}

export fn pardes_cursor_bar() u32 {
    const s = &(state orelse return 0);
    return @intFromBool(if (s.core.surface.cursor) |cursor| cursor.bar else false);
}

/// The browser's touch policy asks whether a gesture began on layout chrome.
/// A hit returns row:col packed into u32, including snapping near a separator;
/// 0xffffffff means body text and therefore one-finger scroll/tap-as-LOOK.
export fn pardes_chrome_target(col_arg: u32, row_arg: u32) u32 {
    const s = &(state orelse return std.math.maxInt(u32));
    const col: u16 = @intCast(@min(col_arg, std.math.maxInt(u16)));
    const row: u16 = @intCast(@min(row_arg, std.math.maxInt(u16)));
    const target = s.core.chromeTarget(col, row) orelse return std.math.maxInt(u32);
    return (@as(u32, target.row) << 16) | target.col;
}

// ---- the host ----
//
// Four imports, because four things here are the browser's and not the core's.
// Everything else in `Host.VTable` stays null: see the file comment.
extern "pardes" fn host_open_link(url: [*]const u8, url_len: usize) callconv(.c) void;
extern "pardes" fn host_set_clipboard(text: [*]const u8, text_len: usize) callconv(.c) void;
extern "pardes" fn host_read_clipboard() callconv(.c) void;
/// A file a page writes is a download. `path` names it; both slices are
/// borrowed for the length of the call.
extern "pardes" fn host_download(
    path: [*]const u8,
    path_len: usize,
    bytes: [*]const u8,
    bytes_len: usize,
) callconv(.c) void;

const vtable: pardes.Host.VTable = .{
    .present = present,
    .write_file = writeFile,
    .write_dump = writeDump,
    .set_clipboard = setClipboard,
    .read_clipboard = readClipboard,
    .open_link = openLink,
};

fn host(s: *State) pardes.Host {
    return .{ .ctx = s, .vtable = &vtable };
}

/// Pack the canonical Surface into the stable, JS-facing cell array.
fn present(ctx: ?*anyopaque, surface: *const pardes.Surface) void {
    const s: *State = @ptrCast(@alignCast(ctx.?));
    s.frame_len = 0;
    s.frame_cols = 0;
    s.frame_rows = 0;
    const count: usize = @as(usize, surface.cols) * surface.rows;
    if (count != s.cells.len) {
        if (count == 0) {
            if (s.cells.len > 0) gpa.free(s.cells);
            s.cells = &.{};
        } else {
            const resized = if (s.cells.len == 0)
                gpa.alloc(WebCell, count)
            else
                gpa.realloc(s.cells, count);
            s.cells = resized catch |err| {
                last_error = @intFromError(err);
                return;
            };
        }
    }
    s.frame_len = count;
    s.frame_cols = surface.cols;
    s.frame_rows = surface.rows;
    for (surface.cells, s.cells[0..count]) |cell, *out| out.* = encodeWebCell(cell);
}

fn encodeWebCell(cell: pardes.Cell) WebCell {
    var out: WebCell = .{ .text = @splat(0), .fg = encodeColor(cell.style.fg), .bg = encodeColor(cell.style.bg), .attrs = encodeAttrs(cell.style), .len = if (cell.default) 1 else cell.len, .flags = @intFromBool(cell.default) };
    if (cell.default) out.text[0] = ' ' else @memcpy(out.text[0..cell.len], cell.grapheme());
    return out;
}

fn writeFile(_: ?*anyopaque, _: u8, path: []const u8, bytes: []const u8) void {
    // A download the browser has been handed IS the save here: there is no
    // filesystem to fail against, so there is no `saveFailed` to report.
    host_download(path.ptr, path.len, bytes.ptr, bytes.len);
}

fn writeDump(_: ?*anyopaque, bytes: []const u8) void {
    const name = "pardes-dump.zon";
    host_download(name.ptr, name.len, bytes.ptr, bytes.len);
}

fn setClipboard(_: ?*anyopaque, text: []const u8) void {
    host_set_clipboard(text.ptr, text.len);
}

/// Asynchronous and permission-gated, unlike everything else here: the answer
/// arrives later as an ordinary `pardes_paste`, or never if the prompt says no.
fn readClipboard(_: ?*anyopaque) void {
    host_read_clipboard();
}

fn openLink(_: ?*anyopaque, url: []const u8) void {
    host_open_link(url.ptr, url.len);
}

fn encodeColor(color: pardes.Color) u32 {
    return switch (color) {
        .default => 0x01000000,
        .index => |index| 0x02000000 | @as(u32, index),
        .rgb => |rgb| (@as(u32, rgb[0]) << 16) | (@as(u32, rgb[1]) << 8) | rgb[2],
    };
}

fn encodeAttrs(style: pardes.CellStyle) u16 {
    var attrs: u16 = 0;
    attrs |= @as(u16, @intFromBool(style.bold)) << 0;
    attrs |= @as(u16, @intFromBool(style.dim)) << 1;
    attrs |= @as(u16, @intFromBool(style.italic)) << 2;
    attrs |= @as(u16, @intFromBool(style.blink)) << 3;
    attrs |= @as(u16, @intFromBool(style.reverse)) << 4;
    attrs |= @as(u16, @intFromBool(style.invisible)) << 5;
    attrs |= @as(u16, @intFromBool(style.strikethrough)) << 6;
    attrs |= @as(u16, @intFromBool(style.font_role == .tagline)) * attr_tagline;
    attrs |= @as(u16, @intFromEnum(style.ul)) << 8;
    return attrs;
}