pub const TOPBAR_H: u16 = 1;
pub const GUTTER: u16 = 2;
pub const BOX_H: u16 = 1;
pub const MINW: u16 = 10;
pub const MINH: u16 = 3;
pub const PREFIX_W: u16 = 5;

pub const Rect = struct { x: u16, y: u16, w: u16, h: u16 };

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

pub const ScrollbarButton = enum { left, middle, right };

pub const Scrollbar = struct {
    total: usize,
    offset: usize,
    len: usize,
};

pub fn Layout(comptime max_cols: usize, comptime max_panes: usize) type {
    return struct {
        ncol: usize,
        col_weight: [max_cols]f32,
        col_terms: [max_cols][max_panes]usize,
        col_n: [max_cols]usize,
    };
}

pub fn layoutFindTerm(l: anytype, id: usize) ?struct { col: usize, idx: usize } {
    var c: usize = 0;
    while (c < l.ncol) : (c += 1) {
        var k: usize = 0;
        while (k < l.col_n[c]) : (k += 1) {
            if (l.col_terms[c][k] == id) return .{ .col = c, .idx = k };
        }
    }
    return null;
}

pub fn layoutRemove(l: anytype, id: usize) void {
    const f = layoutFindTerm(l, id) orelse return;
    const c = f.col;
    var k = f.idx;
    while (k + 1 < l.col_n[c]) : (k += 1) l.col_terms[c][k] = l.col_terms[c][k + 1];
    l.col_n[c] -= 1;
    if (l.col_n[c] == 0) {
        if (l.ncol > 1) l.col_weight[if (c > 0) c - 1 else c + 1] += l.col_weight[c];
        var j = c;
        while (j + 1 < l.ncol) : (j += 1) {
            l.col_terms[j] = l.col_terms[j + 1];
            l.col_n[j] = l.col_n[j + 1];
            l.col_weight[j] = l.col_weight[j + 1];
        }
        l.ncol -= 1;
    }
}

pub fn layoutInsert(l: anytype, c: usize, idx: usize, id: usize) void {
    var k = l.col_n[c];
    while (k > idx) : (k -= 1) l.col_terms[c][k] = l.col_terms[c][k - 1];
    l.col_terms[c][idx] = id;
    l.col_n[c] += 1;
}

pub fn layoutAppendColumn(l: anytype, id: usize) void {
    if (l.ncol >= l.col_weight.len) return;
    const c = l.ncol;
    l.col_weight[c] = 1;
    l.col_terms[c][0] = id;
    l.col_n[c] = 1;
    l.ncol += 1;
}

pub fn computeGeom(
    l: anytype,
    items: anytype,
    sw: u16,
    sh: u16,
    rects: anytype,
    col_x: anytype,
    col_w: anytype,
    comptime vweightFn: anytype,
) void {
    if (l.ncol == 0) return;
    var wsum: f32 = 0;
    for (0..l.ncol) |c| wsum += l.col_weight[c];
    if (wsum <= 0) wsum = 1;

    var x: u16 = 0;
    for (0..l.ncol) |c| {
        const last = c + 1 == l.ncol;
        const cw: u16 = if (last) (sw -| x) else @max(1, @as(u16, @intFromFloat(@round(@as(f32, @floatFromInt(sw)) * l.col_weight[c] / wsum))));
        col_x[c] = x;
        col_w[c] = cw;

        var vsum: f32 = 0;
        for (0..l.col_n[c]) |k| {
            if (vweightFn(items, l.col_terms[c][k])) |vweight| vsum += vweight;
        }
        if (vsum <= 0) vsum = 1;

        var y: u16 = TOPBAR_H;
        const avail_h = sh -| TOPBAR_H;
        for (0..l.col_n[c]) |k| {
            const id = l.col_terms[c][k];
            const vweight = vweightFn(items, id) orelse continue;
            const lastk = k + 1 == l.col_n[c];
            const ch: u16 = if (lastk) (sh -| y) else @max(1, @as(u16, @intFromFloat(@round(@as(f32, @floatFromInt(avail_h)) * vweight / vsum))));
            rects[id] = .{ .x = x, .y = y, .w = cw, .h = ch };
            y +|= ch;
        }
        x +|= cw;
    }
}

pub fn moveTerm(
    l: anytype,
    rects: anytype,
    col_x: anytype,
    col_w: anytype,
    id: usize,
    cur_x: u16,
    cur_y: u16,
) void {
    const src = layoutFindTerm(l, id) orelse return;
    var tc: usize = if (l.ncol > 0) l.ncol - 1 else 0;
    for (0..l.ncol) |c| {
        if (cur_x >= col_x[c] and cur_x < col_x[c] + col_w[c]) {
            tc = c;
            break;
        }
    }

    var ti: usize = 0;
    var k: usize = 0;
    while (k < l.col_n[tc]) : (k += 1) {
        const cid = l.col_terms[tc][k];
        if (cid == id) continue;
        const r = rects[cid];
        if (cur_y < r.y + r.h / 2) break;
        ti += 1;
    }

    const src_solo = l.col_n[src.col] == 1;
    if (tc == src.col and src_solo) return;
    layoutRemove(l, id);
    if (src_solo and src.col < tc) tc -= 1;
    if (tc >= l.ncol) tc = l.ncol - 1;
    if (ti > l.col_n[tc]) ti = l.col_n[tc];
    layoutInsert(l, tc, ti, id);
}

pub fn paneAt(rects: anytype, pane_count: usize, col: u16, row: u16) ?usize {
    for (0..pane_count) |i| {
        const r = rects[i];
        if (col >= r.x and col < r.x + r.w and row >= r.y and row < r.y + r.h) return i;
    }
    return null;
}

pub fn paneAtSlots(rects: anytype, slots: anytype, col: u16, row: u16) ?usize {
    for (slots.*, 0..) |slot, i| {
        if (slot == null) continue;
        const r = rects[i];
        if (col >= r.x and col < r.x + r.w and row >= r.y and row < r.y + r.h) return i;
    }
    return null;
}

pub fn clampMousePos(screen_w: u16, screen_h: u16, mouse: anytype) MousePos {
    return .{
        .col = if (mouse.col < 0) 0 else @min(@as(u16, @intCast(mouse.col)), screen_w -| 1),
        .row = if (mouse.row < 0) 0 else @min(@as(u16, @intCast(mouse.row)), screen_h -| 1),
    };
}

pub fn inMoveBox(r: Rect, col: u16, row: u16) bool {
    return col < r.x + GUTTER and row < r.y + BOX_H;
}

pub fn scrollbarClickDelta(r: Rect, button: ScrollbarButton, col: u16, row: u16) ?i32 {
    if (col >= r.x + GUTTER or row < r.y + BOX_H) return null;
    const local: i32 = @as(i32, row) - @as(i32, r.y + BOX_H);
    return switch (button) {
        .left, .middle => -local,
        .right => local,
    };
}

pub fn drawGutter(
    root: anytype,
    r: Rect,
    active: bool,
    active_box: [3]u8,
    inactive_box: [3]u8,
    track: [3]u8,
    thumb: [3]u8,
    scrollbar: ?Scrollbar,
) void {
    const gut = root.child(.{ .x_off = r.x, .y_off = r.y, .width = GUTTER, .height = r.h });
    const box_bg = if (active) active_box else inactive_box;
    var gy: u16 = 0;
    while (gy < r.h) : (gy += 1) {
        const bg = if (gy < BOX_H) box_bg else track;
        var gx: u16 = 0;
        while (gx < GUTTER) : (gx += 1) {
            gut.writeCell(gx, gy, .{ .char = .{ .grapheme = " " }, .style = .{ .bg = .{ .rgb = bg } } });
        }
    }

    const sb = scrollbar orelse return;
    const track_h: usize = if (r.h > BOX_H) r.h - BOX_H else 0;
    if (track_h == 0) return;
    const total = if (sb.total == 0) 1 else sb.total;
    const len = @max(1, (track_h * @max(1, sb.len)) / total);
    const pos = (track_h * sb.offset) / total;
    var sy: usize = 0;
    while (sy < track_h) : (sy += 1) {
        if (sy < pos or sy >= pos + len) continue;
        var gx: u16 = 0;
        while (gx < GUTTER) : (gx += 1) {
            gut.writeCell(gx, @intCast(BOX_H + sy), .{ .char = .{ .grapheme = " " }, .style = .{ .bg = .{ .rgb = thumb } } });
        }
    }
}

pub fn overlayDash(win: anytype, col: u16, row: u16, glyph: []const u8) void {
    var cell = win.readCell(col, row) orelse return;
    cell.char.grapheme = glyph;
    cell.default = false;
    win.writeCell(col, row, cell);
}

pub fn drawBorderV(win: anytype, col: u16, screen_h: u16) void {
    var row: u16 = TOPBAR_H;
    while (row < screen_h) : (row += 1) overlayDash(win, col, row, "╎");
}

pub fn drawBorderH(win: anytype, x: u16, width: u16, row: u16) void {
    var col = x;
    while (col < x + width) : (col += 1) overlayDash(win, col, row, "╌");
}

pub fn drawMovePreview(win: anytype, l: anytype, col_x: anytype, col_w: anytype, cur_x: u16, cur_y: u16, color: [3]u8) void {
    var tc: usize = if (l.ncol > 0) l.ncol - 1 else 0;
    for (0..l.ncol) |c| {
        if (cur_x >= col_x[c] and cur_x < col_x[c] + col_w[c]) {
            tc = c;
            break;
        }
    }
    var col: u16 = col_x[tc];
    while (col < col_x[tc] + col_w[tc]) : (col += 1) {
        win.writeCell(col, cur_y, .{ .char = .{ .grapheme = "╌" }, .style = .{ .fg = .{ .rgb = color } } });
    }
    win.writeCell(cur_x, cur_y, .{ .char = .{ .grapheme = "▌" }, .style = .{ .fg = .{ .rgb = color } } });
}

pub fn drawHoverResizeHints(
    win: anytype,
    l: anytype,
    rects: anytype,
    col_x: anytype,
    col_w: anytype,
    screen_h: u16,
    hover_col: u16,
    hover_row: u16,
) void {
    var c: usize = 0;
    while (c + 1 < l.ncol) : (c += 1) {
        if (hover_col == col_x[c] + col_w[c] -| 1) drawBorderV(win, hover_col, screen_h);
    }
    var cc: usize = 0;
    while (cc < l.ncol) : (cc += 1) {
        if (hover_col < col_x[cc] or hover_col >= col_x[cc] + col_w[cc]) continue;
        var k: usize = 0;
        while (k + 1 < l.col_n[cc]) : (k += 1) {
            const r = rects[l.col_terms[cc][k]];
            if (hover_row == r.y + r.h -| 1) drawBorderH(win, col_x[cc], col_w[cc], hover_row);
        }
    }
}

pub fn drawInteractionPreview(
    win: anytype,
    l: anytype,
    rects: anytype,
    col_x: anytype,
    col_w: anytype,
    screen_h: u16,
    drag: anytype,
    hover_col: u16,
    hover_row: u16,
    move_color: [3]u8,
) void {
    switch (drag) {
        .border_v => |d| drawBorderV(win, d.cur_x, screen_h),
        .border_h => |d| drawBorderH(win, col_x[d.col], col_w[d.col], d.cur_y),
        .move => |d| drawMovePreview(win, l, col_x, col_w, d.cur_x, d.cur_y, move_color),
        else => drawHoverResizeHints(win, l, rects, col_x, col_w, screen_h, hover_col, hover_row),
    }
}