//! CSS Paged Media Pagination Engine - "Infinite Canvas with Physical Spacers"

//!

//! This module implements a pagination architecture where content is laid out

//! on a single "infinite" vertical canvas, with "dead zones" representing page

//! breaks (including headers, footers, and margins).

//!

//! ## Core Concept: Physical Spacers

//!

//! Instead of assigning nodes to logical pages, we map pages onto a single vertical

//! coordinate system where page breaks are physical empty spaces:

//!

//! ```text

//! 0px      ─────────────────────────────

//!          │ Page 1 Content             │

//! 1000px   ─────────────────────────────

//!          │ Dead Space (Footer+Margin) │  ← Page break zone

//! 1100px   ─────────────────────────────

//!          │ Page 2 Content             │

//! 2100px   ─────────────────────────────

//!          │ Dead Space (Footer+Margin) │

//! 2200px   ─────────────────────────────

//! ```

//!

//! ## CSS Generated Content for Paged Media (GCPM) Level 3 Support

//!

//! This module provides the foundation for CSS GCPM Level 3 features:

//!

//! - **Running Elements** (`position: running(name)`) - Elements extracted from flow and displayed

//!   in margin boxes (headers/footers)

//! - **Page Selectors** (`@page :first`, `@page :left/:right`) - Per-page styling

//! - **Named Strings** (`string-set`, `content: string(name)`) - Captured text for headers

//! - **Page Counters** (`counter(page)`, `counter(pages)`) - Page numbering

//!

//! **Note:** Running elements, named strings, and page selectors are currently

//! stub implementations. Only page counters and header/footer configuration

//! are functional.

//!

//! See: https://www.w3.org/TR/css-gcpm-3/

use std::{collections::BTreeMap, sync::Arc};

use azul_core::geom::LogicalSize;

use azul_css::props::{

    basic::ColorU,

    layout::fragmentation::PageBreak,

};

/// Manages the infinite canvas coordinate system with page boundaries.

///

/// The `PageGeometer` tracks page dimensions and provides utilities for:

///

/// - Determining which page a Y coordinate falls on

/// - Calculating the next page start position

/// - Checking if content crosses page boundaries

#[derive(Debug, Clone)]

pub struct PageGeometer {

    /// Total height of each page (including margins, headers, footers)

    pub page_size: LogicalSize,

    /// Content area margins (space reserved at top/bottom of each page)

    pub page_margins: PageMargins,

    /// Height reserved for page header (if any)

    pub header_height: f32,

    /// Height reserved for page footer (if any)

    pub footer_height: f32,

    /// Current Y position on the infinite canvas

    pub current_y: f32,

}

/// Page margin configuration

#[derive(Debug, Clone, Copy, Default)]

pub struct PageMargins {

    pub top: f32,

    pub right: f32,

    pub bottom: f32,

    pub left: f32,

}

impl PageMargins {

}

impl PageGeometer {

    /// Create a new PageGeometer for paged layout.

    /// Create with header and footer space reserved.

    /// Get the usable content height per page (page height minus margins/headers/footers).

    /// Get the usable content width per page (page width minus left/right margins).

    /// Calculate which page a given Y coordinate falls on (0-indexed).

    ///

    /// Negative Y values are clamped to page 0.

        // Account for dead zones between pages

    /// Get the Y coordinate where a page's content area starts.

    /// Get the Y coordinate where a page's content area ends.

    /// Get the height of the "dead zone" between pages (footer + margin + header of next page).

    /// Calculate the Y coordinate where the NEXT page's content starts from a given position.

    /// Check if a range [start_y, end_y) crosses a page boundary.

    /// Get remaining space on the current page from a given Y position.

    /// Check if content of given height can fit starting at Y position.

    /// Calculate the additional Y offset needed to push content to the next page.

    /// Returns 0 if content fits on current page.

        // Content doesn't fit - calculate offset to move to next page

    /// Get the number of pages needed to contain content ending at Y.

}

/// CSS break behavior classification for a box.

#[derive(Debug, Clone, Copy, PartialEq, Eq)]

pub enum BreakBehavior {

    /// Box can be split at internal break points (paragraphs, containers)

    Splittable,

    /// Box should be kept together if possible (break-inside: avoid)

    AvoidBreak,

    /// Box cannot be split (replaced elements, overflow:scroll, etc.)

    Monolithic,

}

/// Result of evaluating break properties for a box.

#[derive(Debug, Clone)]

pub struct BreakEvaluation {

    /// Whether to force a page break before this element

    pub force_break_before: bool,

    /// Whether to force a page break after this element  

    pub force_break_after: bool,

    /// How this box should behave at potential break points

    pub behavior: BreakBehavior,

    /// For text: minimum lines to keep at page start (orphans)

    pub orphans: u32,

    /// For text: minimum lines to keep at page end (widows)

    pub widows: u32,

}

impl Default for BreakEvaluation {

}

/// Check if a break-before/after value forces a page break.

        PageBreak::Always

            | PageBreak::Page

            | PageBreak::Left

            | PageBreak::Right

            | PageBreak::Recto

            | PageBreak::Verso

            | PageBreak::All

    )

/// Check if a break-before/after value avoids breaks.

/// Metadata about table header repetition for a specific page.

#[derive(Debug, Clone)]

pub struct RepeatedTableHeader {

    /// The Y position on the infinite canvas where this header should appear

    pub inject_at_y: f32,

    /// The display list items for the table header (cloned from original)

    pub header_items: Vec<usize>, // Indices into the original display list

    /// The height of the header

    pub header_height: f32,

}

/// Context for pagination during layout.

///

/// This is passed into layout functions to allow them to make page-aware decisions.

#[derive(Debug)]

pub struct PaginationContext<'a> {

    /// The page geometry calculator

    pub geometer: &'a PageGeometer,

    /// Accumulated break-inside: avoid depth from ancestors

    pub break_avoid_depth: usize,

    /// Track table headers that need to repeat on new pages

    pub repeated_headers: Vec<RepeatedTableHeader>,

}

impl<'a> PaginationContext<'a> {

    /// Enter a box with break-inside: avoid

    /// Exit a box with break-inside: avoid

    /// Check if we're inside an ancestor with break-inside: avoid

    /// Register a table header for repetition on subsequent pages.

}

/// Calculate the position adjustment for a child element considering pagination.

///

/// This is called during BFC/IFC layout to determine if content needs to be

/// pushed to the next page.

///

/// # Arguments

/// * `geometer` - Page geometry calculator

/// * `main_pen` - Current Y position in infinite canvas coordinates

/// * `child_height` - Estimated height of the child element

/// * `break_eval` - Break property evaluation for the child

/// * `is_avoiding_breaks` - Whether an ancestor has break-inside: avoid

///

/// # Returns

/// The Y offset to add to `main_pen` (0 if no adjustment needed, positive if pushing to next page)

    // 1. Handle forced break-before

            // Not at the start of a page - force break

    // 2. Check if content fits on current page

    // 3. Handle monolithic content (cannot be split)

    // +spec:inline-formatting-context:cb2a20 - initial letter boxes are monolithic for block-axis fragmentation; breaks between lines alongside an initial letter should be avoided (like widows/orphans), but forced breaks take precedence

            // Fits on current page

            // Doesn't fit but would fit on empty page - move to next

        // Too large for any page - let it overflow (no adjustment)

    // 4. Handle avoid-break content

            // Fits on current page

            // Move to next page to keep together

        // Too large to keep together - must allow splitting

    // 5. Splittable content - check orphans/widows constraints

    // For now, just ensure we have at least some minimum space

        // Not enough space for even a small amount - move to next page

// CSS GCPM Level 3: Running Elements & Page Margin Boxes

//

// This section provides infrastructure for CSS Generated Content for Paged Media

// Level 3 (https://www.w3.org/TR/css-gcpm-3/).

//

// Key concepts:

//

// 1. **Running Elements** - Elements with `position: running(header)` are removed from the normal

//    flow and available for display in page margin boxes.

//

// 2. **Page Margin Boxes** - 16 margin boxes around each page (@top-left, @top-center, @top-right,

//    @bottom-left, etc.) that can contain running elements or generated content.

//

// 3. **Named Strings** - Text captured with `string-set: header content(text)` and displayed with

//    `content: string(header)`.

//

// 4. **Page Counters** - `counter(page)` and `counter(pages)` for page numbering.

/// Position of a margin box on a page (CSS GCPM margin box names).

///

/// CSS defines 16 margin boxes around the page content area:

/// ```text

/// ┌─────────┬─────────────────┬─────────┐

/// │top-left │   top-center    │top-right│

/// ├─────────┼─────────────────┼─────────┤

/// │         │                 │         │

/// │  left   │                 │  right  │

/// │  -top   │                 │  -top   │

/// │         │                 │         │

/// │  left   │    CONTENT      │  right  │

/// │-middle  │      AREA       │-middle  │

/// │         │                 │         │

/// │  left   │                 │  right  │

/// │-bottom  │                 │-bottom  │

/// │         │                 │         │

/// ├─────────┼─────────────────┼─────────┤

/// │bot-left │  bottom-center  │bot-right│

/// └─────────┴─────────────────┴─────────┘

/// ```

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]

pub enum MarginBoxPosition {

    // Top row

    TopLeftCorner,

    TopLeft,

    TopCenter,

    TopRight,

    TopRightCorner,

    // Left column

    LeftTop,

    LeftMiddle,

    LeftBottom,

    // Right column

    RightTop,

    RightMiddle,

    RightBottom,

    // Bottom row

    BottomLeftCorner,

    BottomLeft,

    BottomCenter,

    BottomRight,

    BottomRightCorner,

}

impl MarginBoxPosition {

    /// Returns true if this margin box is in the top margin area.

            Self::TopLeftCorner

                | Self::TopLeft

                | Self::TopCenter

                | Self::TopRight

                | Self::TopRightCorner

        )

    /// Returns true if this margin box is in the bottom margin area.

            Self::BottomLeftCorner

                | Self::BottomLeft

                | Self::BottomCenter

                | Self::BottomRight

                | Self::BottomRightCorner

        )

}

/// A running element that was extracted from the document flow.

///

/// CSS GCPM allows elements to be "running" - removed from normal flow

/// and made available for display in page margin boxes.

///

/// ```css

/// h1 { position: running(chapter-title); }

/// @page { @top-center { content: element(chapter-title); } }

/// ```

#[derive(Debug, Clone)]

pub struct RunningElement {

    /// The name of this running element (e.g., "chapter-title")

    pub name: String,

    /// The display list items for this element (captured when encountered in flow)

    pub display_items: Vec<super::display_list::DisplayListItem>,

    /// The size of this element when rendered

    pub size: LogicalSize,

    /// Which page this element was defined on (for `running()` selector specificity)

    pub source_page: usize,

}

/// Content that can appear in a page margin box.

///

/// This enum represents the various types of content that CSS GCPM

/// allows in margin boxes.

#[derive(Clone)]

pub enum MarginBoxContent {

    /// Empty margin box

    None,

    /// A running element referenced by name: `content: element(header)`

    RunningElement(String),

    /// A named string: `content: string(chapter)`

    NamedString(String),

    /// Page counter: `content: counter(page)`

    PageCounter,

    /// Total pages counter: `content: counter(pages)`

    PagesCounter,

    /// Page counter with format: `content: counter(page, lower-roman)`

    PageCounterFormatted { format: CounterFormat },

    /// Combined content (e.g., "Page " counter(page) " of " counter(pages))

    Combined(Vec<MarginBoxContent>),

    /// Literal text

    Text(String),

    /// Custom callback for dynamic content generation

    Custom(Arc<dyn Fn(PageInfo) -> String + Send + Sync>),

}

impl std::fmt::Debug for MarginBoxContent {

        }

}

/// Counter formatting styles (subset of CSS list-style-type).

#[derive(Debug, Clone, Copy, PartialEq, Eq)]

pub enum CounterFormat {

    Decimal,

    DecimalLeadingZero,

    LowerRoman,

    UpperRoman,

    LowerAlpha,

    UpperAlpha,

    LowerGreek,

}

impl Default for CounterFormat {

}

impl CounterFormat {

    /// Format a number according to this counter style.

        }

}

/// Convert number to roman numerals.

    }

    } else {

    }

/// Convert number to alphabetic (a-z, aa-az, etc.).

    }

/// Convert number to Greek letters (α, β, γ, ...).

    const GREEK: &[char] = &[

        'α', 'β', 'γ', 'δ', 'ε', 'ζ', 'η', 'θ', 'ι', 'κ', 'λ', 'μ', 'ν', 'ξ', 'ο', 'π', 'ρ', 'σ',

        'τ', 'υ', 'φ', 'χ', 'ψ', 'ω',

    ];

    // For numbers > 24, use αα, αβ, etc.

/// Information about the current page, passed to content generators.

#[derive(Debug, Clone, Copy)]

pub struct PageInfo {

    /// Current page number (1-indexed for display)

    pub page_number: usize,

    /// Total number of pages (may be 0 if unknown during first pass)

    pub total_pages: usize,

    /// Whether this is the first page

    pub is_first: bool,

    /// Whether this is the last page

    pub is_last: bool,

    /// Whether this is a left (verso) page (for duplex printing)

    pub is_left: bool,

    /// Whether this is a right (recto) page

    pub is_right: bool,

    /// Whether this is a blank page (inserted for left/right alignment)

    pub is_blank: bool,

}

impl PageInfo {

    /// Create PageInfo for a specific page.

        Self {

            is_blank: false,

        }

}

/// Default height for page headers and footers (in points).

const DEFAULT_HEADER_FOOTER_HEIGHT: f32 = 30.0;

/// Default font size for header/footer text (in points).

const DEFAULT_HEADER_FOOTER_FONT_SIZE: f32 = 10.0;

/// Configuration for page headers and footers.

///

/// This is a simplified interface for the common case of adding

/// headers and footers. For full GCPM support, use `PageTemplate`.

#[derive(Debug, Clone)]

pub struct HeaderFooterConfig {

    /// Whether to show a header on each page

    pub show_header: bool,

    /// Whether to show a footer on each page

    pub show_footer: bool,

    /// Height of the header area (if shown)

    pub header_height: f32,

    /// Height of the footer area (if shown)  

    pub footer_height: f32,

    /// Content generator for the header

    pub header_content: MarginBoxContent,

    /// Content generator for the footer

    pub footer_content: MarginBoxContent,

    /// Font size for header/footer text

    pub font_size: f32,

    /// Text color for header/footer

    pub text_color: ColorU,

    /// Whether to skip header/footer on first page

    pub skip_first_page: bool,

}

impl Default for HeaderFooterConfig {

}

impl HeaderFooterConfig {

    /// Create a config with page numbers in the footer.

    /// Create a config with page numbers in both header and footer.

    /// Set custom header text.

    /// Set custom footer text.

    /// Generate the text content for a margin box given page info.

            MarginBoxContent::PagesCounter => {

                } else {

                }

            }

                // TODO: Look up named string from document context

            }

                // Running elements are rendered as display items, not text

            }

        }

    /// Get the header text for a specific page.

    /// Get the footer text for a specific page.

}

/// Full page template with all 16 margin boxes (CSS GCPM @page support).

///

/// This provides complete control over page layout following the CSS

/// Paged Media and GCPM specifications.

#[derive(Debug, Clone, Default)]

pub struct PageTemplate {

    /// Content for each margin box position

    pub margin_boxes: BTreeMap<MarginBoxPosition, MarginBoxContent>,

    /// Page margins (space allocated for margin boxes)

    pub margins: PageMargins,

    /// Named strings captured from the document

    pub named_strings: BTreeMap<String, String>,

    /// Running elements available for this page

    pub running_elements: BTreeMap<String, RunningElement>,

}

impl PageTemplate {

    /// Create a new empty page template.

    /// Set content for a specific margin box.

    /// Create a simple template with centered page numbers in the footer.

        );

    /// Create a template with "Page X of Y" in the bottom right.

        );

}

/// Temporary configuration for page headers/footers without CSS `@page` parsing.

///

/// Provides programmatic control over page decoration until full CSS `@page`

/// rule support is implemented.

///

/// ## Supported Features

///

/// - Page numbers in header and/or footer

/// - Custom text in header and/or footer

/// - Number format (decimal, roman numerals, alphabetic, greek)

/// - Skip first page option

///

/// ## Example

///

/// ```rust

/// use azul_layout::solver3::pagination::FakePageConfig;

///

/// let config = FakePageConfig::new()

///     .with_footer_page_numbers()

///     .with_header_text("My Document")

///     .skip_first_page(true);

///

/// let header_footer = config.to_header_footer_config();

/// ```

#[derive(Debug, Clone)]

pub struct FakePageConfig {

    /// Show header on pages

    pub show_header: bool,

    /// Show footer on pages

    pub show_footer: bool,

    /// Header text (static text, or None for page numbers only)

    pub header_text: Option<String>,

    /// Footer text (static text, or None for page numbers only)

    pub footer_text: Option<String>,

    /// Include page number in header

    pub header_page_number: bool,

    /// Include page number in footer

    pub footer_page_number: bool,

    /// Include total pages count ("of Y") in header

    pub header_total_pages: bool,

    /// Include total pages count ("of Y") in footer

    pub footer_total_pages: bool,

    /// Number format for page counters

    pub number_format: CounterFormat,

    /// Skip header/footer on first page

    pub skip_first_page: bool,

    /// Header height in points

    pub header_height: f32,

    /// Footer height in points

    pub footer_height: f32,

    /// Font size for header/footer text

    pub font_size: f32,

    /// Text color for header/footer

    pub text_color: ColorU,

}

impl Default for FakePageConfig {

}

impl FakePageConfig {

    /// Create a new empty configuration (no headers/footers).

    /// Enable footer with "Page X of Y" format.

    /// Enable header with "Page X" format.

    /// Enable both header and footer with page numbers.

    /// Set custom header text.

    /// Set custom footer text.

    /// Set the number format for page counters.

    /// Skip header/footer on the first page.

    /// Set header height.

    /// Set footer height.

    /// Set font size for header/footer text.

    /// Set text color for header/footer.

    /// Convert this fake config to the internal HeaderFooterConfig.

    ///

    /// This is the bridge between the user-facing API and the internal

    /// pagination engine.

    /// Build the MarginBoxContent for the header.

        )

    /// Build the MarginBoxContent for the footer.

        )

    /// Shared helper for building header/footer margin box content.

        } else {

        }

}

/// Information about a table that may need header repetition.

#[derive(Debug, Clone)]

pub struct TableHeaderInfo {

    /// The table's node index in the layout tree

    pub table_node_index: usize,

    /// The Y position where the table starts

    pub table_start_y: f32,

    /// The Y position where the table ends

    pub table_end_y: f32,

    /// The thead's display list items (captured during initial render)

    pub thead_items: Vec<super::display_list::DisplayListItem>,

    /// Height of the thead

    pub thead_height: f32,

    /// The Y position of the thead relative to table start

    pub thead_offset_y: f32,

}

/// Context for tracking table headers across pages.

#[derive(Debug, Default, Clone)]

pub struct TableHeaderTracker {

    /// All tables with theads that might need repetition

    pub tables: Vec<TableHeaderInfo>,

}

impl TableHeaderTracker {

    /// Register a table's thead for potential repetition.

    /// Get theads that should be repeated on a specific page.

    ///

    /// Returns the thead items that need to be injected at the top of the page,

    /// along with the Y offset where they should appear.

            // Check if this table spans into this page (but didn't start on this page)

        }

}