//! DatePicker Widget - Date selection with calendar
//!
//! A date picker with calendar view, supporting single date
//! and date range selection.

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");

/// Date structure
pub const Date = struct {
    year: u16,
    month: u8, // 1-12
    day: u8, // 1-31

    const Self = @This();

    /// Create a date
    pub fn init(year: u16, month: u8, day: u8) Self {
        return .{
            .year = year,
            .month = @min(12, @max(1, month)),
            .day = @min(31, @max(1, day)),
        };
    }

    /// Get today's date (simplified - uses epoch calculation)
    pub fn today() Self {
        const ts = std.time.timestamp();
        return fromTimestamp(ts);
    }

    /// Create from unix timestamp
    pub fn fromTimestamp(ts: i64) Self {
        // Simplified calculation - doesn't handle all edge cases
        const days_since_epoch = @divTrunc(ts, 86400);
        const remaining_days = days_since_epoch + 719468; // Days from year 0

        const era: i64 = @divTrunc(if (remaining_days >= 0) remaining_days else remaining_days - 146096, 146097);
        const doe: u32 = @intCast(remaining_days - era * 146097);
        const yoe = @divTrunc(doe - @divTrunc(doe, 1460) + @divTrunc(doe, 36524) - @divTrunc(doe, 146096), 365);
        const y: i64 = @as(i64, @intCast(yoe)) + era * 400;
        const doy = doe - (365 * yoe + @divTrunc(yoe, 4) - @divTrunc(yoe, 100));
        const mp = @divTrunc(5 * doy + 2, 153);
        const d: u8 = @intCast(doy - @divTrunc(153 * mp + 2, 5) + 1);
        const m: u8 = @intCast(if (mp < 10) mp + 3 else mp - 9);
        const year: u16 = @intCast(y + @as(i64, if (m <= 2) 1 else 0));

        return .{ .year = year, .month = m, .day = d };
    }

    /// Check if dates are equal
    pub fn eql(self: Self, other: Self) bool {
        return self.year == other.year and self.month == other.month and self.day == other.day;
    }

    /// Compare dates
    pub fn compare(self: Self, other: Self) std.math.Order {
        if (self.year != other.year) {
            return std.math.order(self.year, other.year);
        }
        if (self.month != other.month) {
            return std.math.order(self.month, other.month);
        }
        return std.math.order(self.day, other.day);
    }

    /// Check if this date is before another
    pub fn isBefore(self: Self, other: Self) bool {
        return self.compare(other) == .lt;
    }

    /// Check if this date is after another
    pub fn isAfter(self: Self, other: Self) bool {
        return self.compare(other) == .gt;
    }

    /// Get days in month
    pub fn daysInMonth(self: Self) u8 {
        return getDaysInMonth(self.year, self.month);
    }

    /// Get day of week (0 = Sunday, 6 = Saturday)
    pub fn dayOfWeek(self: Self) u8 {
        // Zeller's congruence
        var y = @as(i32, self.year);
        var m = @as(i32, self.month);

        if (m < 3) {
            m += 12;
            y -= 1;
        }

        const q = @as(i32, self.day);
        const k = @mod(y, 100);
        const j = @divTrunc(y, 100);

        const h = @mod(q + @divTrunc(13 * (m + 1), 5) + k + @divTrunc(k, 4) + @divTrunc(j, 4) - 2 * j, 7);

        // Convert to 0=Sunday
        return @intCast(@mod(h + 6, 7));
    }

    /// Format as string (YYYY-MM-DD)
    pub fn format(self: Self, buf: []u8) []const u8 {
        const result = std.fmt.bufPrint(buf, "{d:0>4}-{d:0>2}-{d:0>2}", .{
            self.year,
            self.month,
            self.day,
        }) catch return "";
        return result;
    }
};

/// Get days in a month
fn getDaysInMonth(year: u16, month: u8) u8 {
    const days = [_]u8{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    if (month < 1 or month > 12) return 0;

    if (month == 2 and isLeapYear(year)) {
        return 29;
    }
    return days[month - 1];
}

/// Check if year is a leap year
fn isLeapYear(year: u16) bool {
    return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0);
}

/// Date picker state
pub const State = struct {
    /// Selected date
    selected: ?Date = null,
    /// Range start (for range selection)
    range_start: ?Date = null,
    /// Range end (for range selection)
    range_end: ?Date = null,
    /// Currently viewed month
    view_month: u8 = 1,
    /// Currently viewed year
    view_year: u16 = 2025,
    /// Is picker open (for popup variant)
    open: bool = false,
    /// Hover date
    hover_date: ?Date = null,

    const Self = @This();

    /// Initialize with today's date
    pub fn init() Self {
        const today = Date.today();
        return .{
            .view_month = today.month,
            .view_year = today.year,
        };
    }

    /// Navigate to previous month
    pub fn prevMonth(self: *Self) void {
        if (self.view_month == 1) {
            self.view_month = 12;
            self.view_year -|= 1;
        } else {
            self.view_month -= 1;
        }
    }

    /// Navigate to next month
    pub fn nextMonth(self: *Self) void {
        if (self.view_month == 12) {
            self.view_month = 1;
            self.view_year += 1;
        } else {
            self.view_month += 1;
        }
    }

    /// Navigate to previous year
    pub fn prevYear(self: *Self) void {
        self.view_year -|= 1;
    }

    /// Navigate to next year
    pub fn nextYear(self: *Self) void {
        self.view_year += 1;
    }

    /// Set view to show selected date
    pub fn showSelected(self: *Self) void {
        if (self.selected) |date| {
            self.view_month = date.month;
            self.view_year = date.year;
        }
    }
};

/// Date picker configuration
pub const Config = struct {
    /// Minimum selectable date
    min_date: ?Date = null,
    /// Maximum selectable date
    max_date: ?Date = null,
    /// First day of week (0 = Sunday, 1 = Monday)
    first_day_of_week: u8 = 1,
    /// Show week numbers
    show_week_numbers: bool = false,
    /// Enable range selection
    range_selection: bool = false,
    /// Show navigation arrows
    show_navigation: bool = true,
    /// Cell size
    cell_size: u32 = 28,
};

/// Date picker colors
pub const Colors = struct {
    background: Style.Color = Style.Color.rgba(40, 40, 40, 255),
    header_bg: Style.Color = Style.Color.rgba(50, 50, 50, 255),
    text: Style.Color = Style.Color.rgba(220, 220, 220, 255),
    text_muted: Style.Color = Style.Color.rgba(120, 120, 120, 255),
    today: Style.Color = Style.Color.rgba(100, 149, 237, 255),
    selected: Style.Color = Style.Color.rgba(70, 130, 180, 255),
    range: Style.Color = Style.Color.rgba(70, 130, 180, 100),
    hover: Style.Color = Style.Color.rgba(60, 60, 60, 255),
    disabled: Style.Color = Style.Color.rgba(80, 80, 80, 255),
    border: Style.Color = Style.Color.rgba(80, 80, 80, 255),
    weekend: Style.Color = Style.Color.rgba(180, 100, 100, 255),

    pub fn fromTheme(theme: Style.Theme) Colors {
        return .{
            .background = theme.background,
            .header_bg = theme.background.lighten(10),
            .text = theme.foreground,
            .text_muted = theme.secondary,
            .today = theme.primary,
            .selected = theme.selection_bg,
            .range = theme.selection_bg.withAlpha(100),
            .hover = theme.background.lighten(15),
            .disabled = theme.secondary,
            .border = theme.border,
            .weekend = theme.error_color.lighten(30),
        };
    }
};

/// Date picker result
pub const Result = struct {
    /// Date was selected/changed
    changed: bool = false,
    /// Selected date
    date: ?Date = null,
    /// Selected range (if range selection enabled)
    range_start: ?Date = null,
    range_end: ?Date = null,
};

/// Draw a date picker / calendar
pub fn datePicker(ctx: *Context, state: *State) Result {
    return datePickerEx(ctx, state, .{}, .{});
}

/// Draw a date picker with configuration
pub fn datePickerEx(
    ctx: *Context,
    state: *State,
    config: Config,
    colors: Colors,
) Result {
    const bounds = ctx.layout.nextRect();
    return datePickerRect(ctx, bounds, state, config, colors);
}

/// Draw a date picker in specific rectangle
pub fn datePickerRect(
    ctx: *Context,
    bounds: Layout.Rect,
    state: *State,
    config: Config,
    colors: Colors,
) Result {
    var result = Result{
        .date = state.selected,
        .range_start = state.range_start,
        .range_end = state.range_end,
    };

    if (bounds.isEmpty()) return result;

    const mouse = ctx.input.mousePos();
    const mouse_pressed = ctx.input.mousePressed(.left);

    // Draw background
    ctx.pushCommand(Command.rect(bounds.x, bounds.y, bounds.w, bounds.h, colors.background));
    ctx.pushCommand(Command.rectOutline(bounds.x, bounds.y, bounds.w, bounds.h, colors.border));

    const padding: i32 = 8;
    var y = bounds.y + padding;

    // Header with month/year and navigation
    const header_h: u32 = 24;

    ctx.pushCommand(Command.rect(
        bounds.x + padding,
        y,
        bounds.w -| @as(u32, @intCast(padding * 2)),
        header_h,
        colors.header_bg,
    ));

    // Month/Year text
    var month_buf: [32]u8 = undefined;
    const month_names = [_][]const u8{
        "January", "February", "March",     "April",   "May",      "June",
        "July",    "August",   "September", "October", "November", "December",
    };
    const month_name = if (state.view_month >= 1 and state.view_month <= 12)
        month_names[state.view_month - 1]
    else
        "???";

    const header_text = std.fmt.bufPrint(&month_buf, "{s} {d}", .{ month_name, state.view_year }) catch "???";
    const text_x = bounds.x + @as(i32, @intCast(bounds.w / 2)) - @as(i32, @intCast(header_text.len * 4));
    ctx.pushCommand(Command.text(text_x, y + 8, header_text, colors.text));

    // Navigation arrows
    if (config.show_navigation) {
        const nav_y = y + 8;

        // Prev month
        const prev_rect = Layout.Rect.init(bounds.x + padding, y, 24, header_h);
        ctx.pushCommand(Command.text(bounds.x + padding + 8, nav_y, "<", colors.text));
        if (prev_rect.contains(mouse.x, mouse.y) and mouse_pressed) {
            state.prevMonth();
        }

        // Next month
        const next_rect = Layout.Rect.init(
            bounds.x + @as(i32, @intCast(bounds.w)) - padding - 24,
            y,
            24,
            header_h,
        );
        ctx.pushCommand(Command.text(next_rect.x + 8, nav_y, ">", colors.text));
        if (next_rect.contains(mouse.x, mouse.y) and mouse_pressed) {
            state.nextMonth();
        }
    }

    y += @as(i32, @intCast(header_h)) + 4;

    // Day headers
    const cell_size = config.cell_size;
    const week_num_w: u32 = if (config.show_week_numbers) 24 else 0;
    const grid_x = bounds.x + padding + @as(i32, @intCast(week_num_w));

    const day_headers = if (config.first_day_of_week == 0)
        [_][]const u8{ "Su", "Mo", "Tu", "We", "Th", "Fr", "Sa" }
    else
        [_][]const u8{ "Mo", "Tu", "We", "Th", "Fr", "Sa", "Su" };

    for (day_headers, 0..) |header, i| {
        const hx = grid_x + @as(i32, @intCast(i * cell_size));
        ctx.pushCommand(Command.text(hx + 8, y, header, colors.text_muted));
    }

    y += 16;

    // Calendar grid
    const first_day = Date.init(state.view_year, state.view_month, 1);
    var first_dow = first_day.dayOfWeek();

    // Adjust for first day of week
    if (config.first_day_of_week == 1) {
        first_dow = if (first_dow == 0) 6 else first_dow - 1;
    }

    const days_in_month = first_day.daysInMonth();
    const today = Date.today();

    var day: u8 = 1;
    var row: u32 = 0;

    while (day <= days_in_month) {
        const row_y = y + @as(i32, @intCast(row * cell_size));

        // Week number
        if (config.show_week_numbers and row == 0) {
            // Simplified week number calculation
            var week_buf: [4]u8 = undefined;
            const week_text = std.fmt.bufPrint(&week_buf, "{d}", .{row + 1}) catch "";
            ctx.pushCommand(Command.text(bounds.x + padding + 4, row_y + 8, week_text, colors.text_muted));
        }

        var col: u32 = if (row == 0) first_dow else 0;
        while (col < 7 and day <= days_in_month) : (col += 1) {
            const cell_x = grid_x + @as(i32, @intCast(col * cell_size));
            const cell_rect = Layout.Rect.init(cell_x, row_y, cell_size, cell_size);
            const current_date = Date.init(state.view_year, state.view_month, day);

            // Check if date is disabled
            const is_disabled = (config.min_date != null and current_date.isBefore(config.min_date.?)) or
                (config.max_date != null and current_date.isAfter(config.max_date.?));

            // Check states
            const is_today = current_date.eql(today);
            const is_selected = state.selected != null and current_date.eql(state.selected.?);
            const is_hovered = cell_rect.contains(mouse.x, mouse.y);
            const is_weekend = (col == 5 or col == 6); // Sat/Sun when Monday first

            // Check if in range
            var is_in_range = false;
            if (config.range_selection and state.range_start != null and state.range_end != null) {
                is_in_range = !current_date.isBefore(state.range_start.?) and
                    !current_date.isAfter(state.range_end.?);
            }

            // Draw cell background
            if (is_selected) {
                ctx.pushCommand(Command.rect(cell_x, row_y, cell_size, cell_size, colors.selected));
            } else if (is_in_range) {
                ctx.pushCommand(Command.rect(cell_x, row_y, cell_size, cell_size, colors.range));
            } else if (is_hovered and !is_disabled) {
                ctx.pushCommand(Command.rect(cell_x, row_y, cell_size, cell_size, colors.hover));
            }

            // Draw today indicator
            if (is_today) {
                ctx.pushCommand(Command.rectOutline(cell_x + 2, row_y + 2, cell_size - 4, cell_size - 4, colors.today));
            }

            // Draw day number
            var day_buf: [4]u8 = undefined;
            const day_text = std.fmt.bufPrint(&day_buf, "{d}", .{day}) catch "";
            const text_color = if (is_disabled)
                colors.disabled
            else if (is_selected)
                colors.text
            else if (is_weekend)
                colors.weekend
            else
                colors.text;

            const tx = cell_x + @as(i32, @intCast((cell_size - day_text.len * 8) / 2));
            ctx.pushCommand(Command.text(tx, row_y + @as(i32, @intCast((cell_size - 8) / 2)), day_text, text_color));

            // Handle click
            if (is_hovered and mouse_pressed and !is_disabled) {
                if (config.range_selection) {
                    if (state.range_start == null or state.range_end != null) {
                        state.range_start = current_date;
                        state.range_end = null;
                    } else {
                        if (current_date.isBefore(state.range_start.?)) {
                            state.range_end = state.range_start;
                            state.range_start = current_date;
                        } else {
                            state.range_end = current_date;
                        }
                    }
                    result.changed = true;
                    result.range_start = state.range_start;
                    result.range_end = state.range_end;
                } else {
                    state.selected = current_date;
                    result.changed = true;
                    result.date = current_date;
                }
            }

            day += 1;
        }

        row += 1;
    }

    return result;
}

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

test "Date init" {
    const date = Date.init(2025, 12, 25);
    try std.testing.expectEqual(@as(u16, 2025), date.year);
    try std.testing.expectEqual(@as(u8, 12), date.month);
    try std.testing.expectEqual(@as(u8, 25), date.day);
}

test "Date compare" {
    const d1 = Date.init(2025, 1, 1);
    const d2 = Date.init(2025, 1, 2);
    const d3 = Date.init(2025, 1, 1);

    try std.testing.expect(d1.isBefore(d2));
    try std.testing.expect(d2.isAfter(d1));
    try std.testing.expect(d1.eql(d3));
}

test "Date daysInMonth" {
    try std.testing.expectEqual(@as(u8, 31), Date.init(2025, 1, 1).daysInMonth());
    try std.testing.expectEqual(@as(u8, 28), Date.init(2025, 2, 1).daysInMonth());
    try std.testing.expectEqual(@as(u8, 29), Date.init(2024, 2, 1).daysInMonth()); // Leap year
    try std.testing.expectEqual(@as(u8, 30), Date.init(2025, 4, 1).daysInMonth());
}

test "isLeapYear" {
    try std.testing.expect(isLeapYear(2024));
    try std.testing.expect(!isLeapYear(2025));
    try std.testing.expect(isLeapYear(2000));
    try std.testing.expect(!isLeapYear(1900));
}

test "State navigation" {
    var state = State{
        .view_month = 1,
        .view_year = 2025,
    };

    state.prevMonth();
    try std.testing.expectEqual(@as(u8, 12), state.view_month);
    try std.testing.expectEqual(@as(u16, 2024), state.view_year);

    state.nextMonth();
    try std.testing.expectEqual(@as(u8, 1), state.view_month);
    try std.testing.expectEqual(@as(u16, 2025), state.view_year);
}

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

    var state = State.init();

    ctx.beginFrame();
    ctx.layout.row_height = 300;

    _ = datePicker(&ctx, &state);

    try std.testing.expect(ctx.commands.items.len >= 2);

    ctx.endFrame();
}

test "Date format" {
    const date = Date.init(2025, 12, 9);
    var buf: [16]u8 = undefined;
    const formatted = date.format(&buf);
    try std.testing.expectEqualStrings("2025-12-09", formatted);
}