//! Focus Management - Track and navigate widget focus
//!
//! Manages which widget has keyboard focus and provides
//! Tab/Shift+Tab navigation between focusable widgets.

const std = @import("std");
const Input = @import("../core/input.zig");

/// Maximum number of focusable widgets per frame
pub const MAX_FOCUSABLES = 64;

/// Focus manager state
pub const FocusManager = struct {
    /// Currently focused widget ID
    focused_id: ?u32 = null,

    /// List of focusable widget IDs this frame (in order)
    focusables: [MAX_FOCUSABLES]u32 = undefined,
    focusable_count: usize = 0,

    /// Widget ID to focus next frame (from keyboard nav)
    pending_focus: ?u32 = null,

    /// Whether Tab was pressed this frame
    tab_pressed: bool = false,
    shift_tab_pressed: bool = false,

    const Self = @This();

    /// Reset for new frame
    pub fn beginFrame(self: *Self) void {
        self.focusable_count = 0;
        self.tab_pressed = false;
        self.shift_tab_pressed = false;

        // Apply pending focus
        if (self.pending_focus) |id| {
            self.focused_id = id;
            self.pending_focus = null;
        }
    }

    /// Process keyboard input for focus navigation
    pub fn processInput(self: *Self, input: *const Input.InputState, key_events: []const Input.KeyEvent) void {
        _ = input;
        for (key_events) |event| {
            if (event.key == .tab and event.pressed) {
                if (event.modifiers.shift) {
                    self.shift_tab_pressed = true;
                } else {
                    self.tab_pressed = true;
                }
            }
        }
    }

    /// Register a widget as focusable
    pub fn registerFocusable(self: *Self, id: u32) void {
        if (self.focusable_count >= MAX_FOCUSABLES) return;
        self.focusables[self.focusable_count] = id;
        self.focusable_count += 1;
    }

    /// Check if a widget has focus
    pub fn hasFocus(self: Self, id: u32) bool {
        return self.focused_id == id;
    }

    /// Request focus for a widget
    pub fn requestFocus(self: *Self, id: u32) void {
        self.focused_id = id;
    }

    /// Clear focus
    pub fn clearFocus(self: *Self) void {
        self.focused_id = null;
    }

    /// End of frame: process Tab navigation
    pub fn endFrame(self: *Self) void {
        if (self.focusable_count == 0) return;

        if (self.tab_pressed) {
            self.focusNext();
        } else if (self.shift_tab_pressed) {
            self.focusPrev();
        }
    }

    /// Focus next widget in order
    fn focusNext(self: *Self) void {
        if (self.focusable_count == 0) return;

        if (self.focused_id) |current| {
            // Find current index
            for (self.focusables[0..self.focusable_count], 0..) |id, i| {
                if (id == current) {
                    // Focus next (wrap around)
                    const next_idx = (i + 1) % self.focusable_count;
                    self.pending_focus = self.focusables[next_idx];
                    return;
                }
            }
        }

        // No current focus, focus first
        self.pending_focus = self.focusables[0];
    }

    /// Focus previous widget in order
    fn focusPrev(self: *Self) void {
        if (self.focusable_count == 0) return;

        if (self.focused_id) |current| {
            // Find current index
            for (self.focusables[0..self.focusable_count], 0..) |id, i| {
                if (id == current) {
                    // Focus previous (wrap around)
                    const prev_idx = if (i == 0) self.focusable_count - 1 else i - 1;
                    self.pending_focus = self.focusables[prev_idx];
                    return;
                }
            }
        }

        // No current focus, focus last
        self.pending_focus = self.focusables[self.focusable_count - 1];
    }

    /// Focus specific index
    pub fn focusIndex(self: *Self, idx: usize) void {
        if (idx < self.focusable_count) {
            self.pending_focus = self.focusables[idx];
        }
    }

    /// Get the index of the focused widget
    pub fn focusedIndex(self: Self) ?usize {
        if (self.focused_id) |current| {
            for (self.focusables[0..self.focusable_count], 0..) |id, i| {
                if (id == current) {
                    return i;
                }
            }
        }
        return null;
    }
};

/// Focus ring - circular focus navigation helper
pub const FocusRing = struct {
    ids: [MAX_FOCUSABLES]u32 = undefined,
    count: usize = 0,
    current: usize = 0,

    const Self = @This();

    /// Add a widget ID to the ring
    pub fn add(self: *Self, id: u32) void {
        if (self.count >= MAX_FOCUSABLES) return;
        self.ids[self.count] = id;
        self.count += 1;
    }

    /// Get current focused ID
    pub fn currentId(self: Self) ?u32 {
        if (self.count == 0) return null;
        return self.ids[self.current];
    }

    /// Move to next
    pub fn next(self: *Self) void {
        if (self.count == 0) return;
        self.current = (self.current + 1) % self.count;
    }

    /// Move to previous
    pub fn prev(self: *Self) void {
        if (self.count == 0) return;
        self.current = if (self.current == 0) self.count - 1 else self.current - 1;
    }

    /// Check if widget has focus
    pub fn isFocused(self: Self, id: u32) bool {
        if (self.count == 0) return false;
        return self.ids[self.current] == id;
    }

    /// Focus specific widget by ID
    pub fn focusId(self: *Self, id: u32) bool {
        for (self.ids[0..self.count], 0..) |widget_id, i| {
            if (widget_id == id) {
                self.current = i;
                return true;
            }
        }
        return false;
    }

    /// Reset the ring
    pub fn reset(self: *Self) void {
        self.count = 0;
        self.current = 0;
    }
};

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

test "FocusManager navigation" {
    var fm = FocusManager{};

    fm.beginFrame();
    fm.registerFocusable(100);
    fm.registerFocusable(200);
    fm.registerFocusable(300);

    // No focus initially
    try std.testing.expectEqual(@as(?u32, null), fm.focused_id);

    // Tab to first
    fm.tab_pressed = true;
    fm.endFrame();
    fm.beginFrame();

    try std.testing.expectEqual(@as(?u32, 100), fm.focused_id);

    // Register again for new frame
    fm.registerFocusable(100);
    fm.registerFocusable(200);
    fm.registerFocusable(300);

    // Tab to second
    fm.tab_pressed = true;
    fm.endFrame();
    fm.beginFrame();

    try std.testing.expectEqual(@as(?u32, 200), fm.focused_id);
}

test "FocusRing" {
    var ring = FocusRing{};

    ring.add(10);
    ring.add(20);
    ring.add(30);

    try std.testing.expectEqual(@as(?u32, 10), ring.currentId());
    try std.testing.expect(ring.isFocused(10));

    ring.next();
    try std.testing.expectEqual(@as(?u32, 20), ring.currentId());

    ring.prev();
    try std.testing.expectEqual(@as(?u32, 10), ring.currentId());

    ring.prev(); // Wrap to end
    try std.testing.expectEqual(@as(?u32, 30), ring.currentId());
}

test "FocusRing focusId" {
    var ring = FocusRing{};

    ring.add(100);
    ring.add(200);
    ring.add(300);

    const found = ring.focusId(200);
    try std.testing.expect(found);
    try std.testing.expectEqual(@as(?u32, 200), ring.currentId());
}