zcatgui/src/widgets/split.zig

//! Split Widget - Resizable split panels
//!
//! HSplit and VSplit divide an area into two resizable panels.
//! The divider can be dragged with mouse or adjusted with Ctrl+arrows.

const std = @import("std");
const Context = @import("../core/context.zig").Context;
const Command = @import("../core/command.zig");
const Layout = @import("../core/layout.zig");
const Style = @import("../core/style.zig");
const Input = @import("../core/input.zig");

/// Split direction
pub const Direction = enum {
    horizontal, // Left | Right
    vertical, // Top / Bottom
};

/// Split state (caller-managed)
pub const SplitState = struct {
    /// Split offset (0.0 to 1.0)
    offset: f32 = 0.5,
    /// Whether the divider is being dragged
    dragging: bool = false,
    /// Minimum offset (prevents panels from being too small)
    min_offset: f32 = 0.1,
    /// Maximum offset
    max_offset: f32 = 0.9,

    const Self = @This();

    /// Set offset with clamping
    pub fn setOffset(self: *Self, new_offset: f32) void {
        self.offset = std.math.clamp(new_offset, self.min_offset, self.max_offset);
    }

    /// Adjust offset by delta
    pub fn adjustOffset(self: *Self, delta: f32) void {
        self.setOffset(self.offset + delta);
    }
};

/// Split configuration
pub const SplitConfig = struct {
    /// Divider thickness in pixels
    divider_size: u32 = 6,
    /// Whether divider is draggable
    draggable: bool = true,
    /// Divider color
    divider_color: Style.Color = Style.Color.rgb(60, 60, 60),
    /// Divider hover color
    divider_hover_color: Style.Color = Style.Color.rgb(80, 80, 80),
    /// Divider drag color
    divider_drag_color: Style.Color = Style.Color.primary,
};

/// Result of split operation - returns the two panel rectangles
pub const SplitResult = struct {
    /// First panel (left or top)
    first: Layout.Rect,
    /// Second panel (right or bottom)
    second: Layout.Rect,
    /// Divider was moved
    changed: bool,
};

/// Calculate split layout without rendering
pub fn splitLayout(
    bounds: Layout.Rect,
    state: *const SplitState,
    direction: Direction,
    divider_size: u32,
) SplitResult {
    if (bounds.isEmpty()) {
        return .{
            .first = Layout.Rect.zero(),
            .second = Layout.Rect.zero(),
            .changed = false,
        };
    }

    const div_size = @as(i32, @intCast(divider_size));

    return switch (direction) {
        .horizontal => blk: {
            const available_w = bounds.w -| divider_size;
            const first_w: u32 = @intFromFloat(@as(f32, @floatFromInt(available_w)) * state.offset);
            const second_w = available_w -| first_w;

            break :blk .{
                .first = Layout.Rect.init(bounds.x, bounds.y, first_w, bounds.h),
                .second = Layout.Rect.init(
                    bounds.x + @as(i32, @intCast(first_w)) + div_size,
                    bounds.y,
                    second_w,
                    bounds.h,
                ),
                .changed = false,
            };
        },
        .vertical => blk: {
            const available_h = bounds.h -| divider_size;
            const first_h: u32 = @intFromFloat(@as(f32, @floatFromInt(available_h)) * state.offset);
            const second_h = available_h -| first_h;

            break :blk .{
                .first = Layout.Rect.init(bounds.x, bounds.y, bounds.w, first_h),
                .second = Layout.Rect.init(
                    bounds.x,
                    bounds.y + @as(i32, @intCast(first_h)) + div_size,
                    bounds.w,
                    second_h,
                ),
                .changed = false,
            };
        },
    };
}

/// Draw a horizontal split (left | right)
pub fn hsplit(
    ctx: *Context,
    state: *SplitState,
) SplitResult {
    return hsplitEx(ctx, state, .{});
}

/// Draw a horizontal split with config
pub fn hsplitEx(
    ctx: *Context,
    state: *SplitState,
    config: SplitConfig,
) SplitResult {
    const bounds = ctx.layout.nextRect();
    return splitRect(ctx, bounds, state, .horizontal, config);
}

/// Draw a vertical split (top / bottom)
pub fn vsplit(
    ctx: *Context,
    state: *SplitState,
) SplitResult {
    return vsplitEx(ctx, state, .{});
}

/// Draw a vertical split with config
pub fn vsplitEx(
    ctx: *Context,
    state: *SplitState,
    config: SplitConfig,
) SplitResult {
    const bounds = ctx.layout.nextRect();
    return splitRect(ctx, bounds, state, .vertical, config);
}

/// Draw a split in a specific rectangle
pub fn splitRect(
    ctx: *Context,
    bounds: Layout.Rect,
    state: *SplitState,
    direction: Direction,
    config: SplitConfig,
) SplitResult {
    if (bounds.isEmpty()) {
        return .{
            .first = Layout.Rect.zero(),
            .second = Layout.Rect.zero(),
            .changed = false,
        };
    }

    var result = splitLayout(bounds, state, direction, config.divider_size);

    // Calculate divider bounds
    const divider = switch (direction) {
        .horizontal => Layout.Rect.init(
            result.first.right(),
            bounds.y,
            config.divider_size,
            bounds.h,
        ),
        .vertical => Layout.Rect.init(
            bounds.x,
            result.first.bottom(),
            bounds.w,
            config.divider_size,
        ),
    };

    // Check mouse interaction with divider
    const mouse = ctx.input.mousePos();
    const divider_hovered = divider.contains(mouse.x, mouse.y);

    // Handle dragging
    if (config.draggable) {
        if (divider_hovered and ctx.input.mousePressed(.left)) {
            state.dragging = true;
        }

        if (state.dragging) {
            if (ctx.input.mouseDown(.left)) {
                // Calculate new offset based on mouse position
                const new_offset: f32 = switch (direction) {
                    .horizontal => blk: {
                        const rel_x = mouse.x - bounds.x;
                        break :blk @as(f32, @floatFromInt(rel_x)) / @as(f32, @floatFromInt(bounds.w));
                    },
                    .vertical => blk: {
                        const rel_y = mouse.y - bounds.y;
                        break :blk @as(f32, @floatFromInt(rel_y)) / @as(f32, @floatFromInt(bounds.h));
                    },
                };

                const old_offset = state.offset;
                state.setOffset(new_offset);

                if (state.offset != old_offset) {
                    result.changed = true;
                    // Recalculate layout
                    result = splitLayout(bounds, state, direction, config.divider_size);
                }
            } else {
                state.dragging = false;
            }
        }
    }

    // Draw divider
    const divider_color = if (state.dragging)
        config.divider_drag_color
    else if (divider_hovered)
        config.divider_hover_color
    else
        config.divider_color;

    ctx.pushCommand(Command.rect(divider.x, divider.y, divider.w, divider.h, divider_color));

    // Draw grip lines on divider
    const grip_color = divider_color.lighten(20);
    const num_grips: u32 = 3;
    const grip_spacing: u32 = 4;

    switch (direction) {
        .horizontal => {
            const grip_h: u32 = 20;
            const grip_y = divider.y + @as(i32, @intCast((divider.h -| grip_h) / 2));
            const grip_x = divider.x + @as(i32, @intCast(config.divider_size / 2));

            for (0..num_grips) |i| {
                const y = grip_y + @as(i32, @intCast(i * grip_spacing + grip_spacing));
                ctx.pushCommand(Command.line(grip_x - 1, y, grip_x + 1, y, grip_color));
            }
        },
        .vertical => {
            const grip_w: u32 = 20;
            const grip_x = divider.x + @as(i32, @intCast((divider.w -| grip_w) / 2));
            const grip_y = divider.y + @as(i32, @intCast(config.divider_size / 2));

            for (0..num_grips) |i| {
                const x = grip_x + @as(i32, @intCast(i * grip_spacing + grip_spacing));
                ctx.pushCommand(Command.line(x, grip_y - 1, x, grip_y + 1, grip_color));
            }
        },
    }

    return result;
}

// =============================================================================
// Tests
// =============================================================================

test "SplitState offset clamping" {
    var state = SplitState{};

    state.setOffset(0.7);
    try std.testing.expectApproxEqAbs(@as(f32, 0.7), state.offset, 0.001);

    state.setOffset(0.05); // Below min
    try std.testing.expectApproxEqAbs(@as(f32, 0.1), state.offset, 0.001);

    state.setOffset(0.95); // Above max
    try std.testing.expectApproxEqAbs(@as(f32, 0.9), state.offset, 0.001);
}

test "splitLayout horizontal" {
    const state = SplitState{ .offset = 0.5 };
    const bounds = Layout.Rect.init(0, 0, 206, 100); // 206 = 200 + 6 divider

    const result = splitLayout(bounds, &state, .horizontal, 6);

    try std.testing.expectEqual(@as(u32, 100), result.first.w);
    try std.testing.expectEqual(@as(u32, 100), result.second.w);
    try std.testing.expectEqual(@as(i32, 106), result.second.x); // 100 + 6
}

test "splitLayout vertical" {
    const state = SplitState{ .offset = 0.5 };
    const bounds = Layout.Rect.init(0, 0, 100, 206);

    const result = splitLayout(bounds, &state, .vertical, 6);

    try std.testing.expectEqual(@as(u32, 100), result.first.h);
    try std.testing.expectEqual(@as(u32, 100), result.second.h);
    try std.testing.expectEqual(@as(i32, 106), result.second.y);
}

test "hsplit generates commands" {
    var ctx = try Context.init(std.testing.allocator, 800, 600);
    defer ctx.deinit();

    var state = SplitState{};

    ctx.beginFrame();
    ctx.layout.row_height = 400;

    const result = hsplit(&ctx, &state);

    try std.testing.expect(result.first.w > 0);
    try std.testing.expect(result.second.w > 0);
    try std.testing.expect(ctx.commands.items.len >= 1); // At least divider

    ctx.endFrame();
}