//! Vimwiki parser.
//!
//! Hand-rolled recursive-descent over `Vec<VimwikiToken>` (SPEC.md §6.7).
//! Resilient: never aborts the document. Anything the dispatcher can't
//! claim becomes a `BlockNode::Error(ErrorNode)` so progress is
//! guaranteed.
//!
//! ## Inline marker precedence
//!
//! Within a text run, the lexer emits delimiter tokens
//! (`BoldDelim` / `ItalicDelim` / `StrikethroughDelim` /
//! `SuperscriptDelim` / `SubscriptDelim`) one at a time. The parser pairs
//! them by scanning forward for the *next* token of the same kind, then
//! recursing on the slice between them:
//!
//!   - `*foo*`     → Bold
//!   - `_foo_`     → Italic
//!   - `~~foo~~`   → Strikethrough
//!   - `^foo^`     → Superscript
//!   - `,,foo,,`   → Subscript
//!   - `_*foo*_`   → Italic(Bold(...))   — semantically bold-italic
//!   - `*_foo_*`   → Bold(Italic(...))   — semantically bold-italic
//!
//! Unmatched delimiters fall back to literal `Text` nodes so input like
//! `2 * 3 = 6` survives without a closing pair.
//!
//! ## Link target classification
//!
//! `[[ ]]` payloads are inspected to choose between `WikiLinkNode`
//! (the default) and `ExternalLinkNode` (when the target is a URL). The
//! `LinkTarget` enum follows SPEC §9: leading `/` is root-relative,
//! `//` is filesystem-absolute, `wiki<N>:` / `wn.<Name>:` are interwiki,
//! `diary:` / `file:` / `local:` are their own kinds, and a trailing `/`
//! marks a directory link.

use crate::ast::{
    BlockNode, BlockquoteNode, BoldNode, CodeNode, CommentNode, DefinitionItemNode,
    DefinitionListNode, DocumentNode, ErrorNode, ExternalLinkNode, HeadingNode, HorizontalRuleNode,
    InlineNode, ItalicNode, KeywordNode, LinkKind, LinkTarget, ListItemNode, ListNode, ListSymbol,
    MathBlockNode, MathInlineNode, PageMetadata, ParagraphNode, PreformattedNode, RawUrlNode, Span,
    StrikethroughNode, SubscriptNode, SuperscriptNode, TableCellNode, TableNode, TableRowNode,
    TagNode, TagScope, TextNode, TransclusionNode, WikiLinkNode,
};
use crate::syntax::{Parser, TokenStream};

use super::lexer::{VimwikiToken, VimwikiTokenKind as K};

#[derive(Debug, Default, Clone)]
pub struct VimwikiParser;

impl VimwikiParser {
    pub fn new() -> Self {
        Self
    }
}

impl Parser for VimwikiParser {
    type Token = VimwikiToken;

    fn parse(&self, tokens: TokenStream<VimwikiToken>) -> DocumentNode {
        let v = tokens.into_vec();
        let mut state = ParseState::new(&v);
        state.parse_document()
    }
}

// ===== Cursor =====

struct ParseState<'a> {
    toks: &'a [VimwikiToken],
    pos: usize,
    /// Phase 12: count of `HeadingNode`s already pushed to `children`.
    /// `headings_seen - 1` is the most recent heading's index.
    headings_seen: usize,
    /// Phase 12: source line of the most recently-emitted heading.
    /// `tag_line - last_heading_line ∈ {1, 2}` is a header-scope tag.
    last_heading_line: Option<u32>,
}

impl<'a> ParseState<'a> {
    fn new(toks: &'a [VimwikiToken]) -> Self {
        Self {
            toks,
            pos: 0,
            headings_seen: 0,
            last_heading_line: None,
        }
    }

    fn at_eof(&self) -> bool {
        self.pos >= self.toks.len()
    }

    fn peek(&self) -> Option<&'a VimwikiToken> {
        self.toks.get(self.pos)
    }

    fn peek_kind(&self) -> Option<&'a K> {
        self.peek().map(|t| &t.kind)
    }

    fn advance(&mut self) -> Option<&'a VimwikiToken> {
        let t = self.toks.get(self.pos);
        if t.is_some() {
            self.pos += 1;
        }
        t
    }

    fn skip_blanks(&mut self) {
        while matches!(self.peek_kind(), Some(K::Newline) | Some(K::BlankLine)) {
            self.pos += 1;
        }
    }

    fn eat_newline(&mut self) -> bool {
        if matches!(self.peek_kind(), Some(K::Newline)) {
            self.pos += 1;
            true
        } else {
            false
        }
    }

    // ===== Document =====

    fn parse_document(&mut self) -> DocumentNode {
        let start_pos = self.toks.first().map(|t| t.span.start).unwrap_or_default();
        let end_pos = self.toks.last().map(|t| t.span.end).unwrap_or(start_pos);

        let mut metadata = PageMetadata::default();
        let mut children = Vec::new();

        loop {
            self.skip_blanks();
            if self.at_eof() {
                break;
            }
            if self.consume_placeholder(&mut metadata) {
                continue;
            }
            let before = self.pos;
            let block = self.parse_block();
            // Phase 12: file-scope tags get accumulated into metadata so
            // callers can read page-level tag membership without walking
            // the AST. The TagNode itself stays in `children` so renderers
            // see it too.
            if let BlockNode::Tag(t) = &block {
                if t.scope == TagScope::File {
                    for name in &t.tags {
                        if !metadata.tags.iter().any(|t| t == name) {
                            metadata.tags.push(name.clone());
                        }
                    }
                }
            }
            children.push(block);
            // Resilience: guarantee forward progress.
            if self.pos == before {
                let span = self.toks.get(self.pos).map(|t| t.span).unwrap_or_default();
                children.push(BlockNode::Error(ErrorNode {
                    span,
                    raw: format!("{:?}", self.toks.get(self.pos).map(|t| &t.kind)),
                    message: "parser made no progress".to_owned(),
                }));
                self.pos += 1;
            }
        }

        DocumentNode {
            span: Span::new(start_pos, end_pos),
            children,
            metadata,
        }
    }

    fn consume_placeholder(&mut self, metadata: &mut PageMetadata) -> bool {
        let updated = match self.peek_kind() {
            Some(K::PlaceholderTitle(v)) => {
                metadata.title = v.clone();
                true
            }
            Some(K::PlaceholderNohtml) => {
                metadata.nohtml = true;
                true
            }
            Some(K::PlaceholderTemplate(v)) => {
                metadata.template = v.clone();
                true
            }
            Some(K::PlaceholderDate(v)) => {
                metadata.date = v.clone();
                true
            }
            _ => false,
        };
        if updated {
            self.advance();
            self.eat_newline();
        }
        updated
    }

    // ===== Block dispatch =====

    fn parse_block(&mut self) -> BlockNode {
        let kind = self.peek_kind().expect("parse_block called at EOF");
        match kind {
            K::HeadingOpen { .. } => self.parse_heading(),
            K::HorizontalRule => self.parse_horizontal_rule(),
            K::ListMarker { .. } => self.parse_list(),
            K::BlockquoteMarker | K::BlockquoteIndent => self.parse_blockquote(),
            K::TableSep | K::TableHeaderRow => self.parse_table(),
            K::PreformattedOpen { .. } => self.parse_preformatted(),
            K::MathBlockOpen { .. } => self.parse_math_block(),
            K::CommentLine(_) => self.parse_single_comment(),
            K::CommentMultiOpen => self.parse_multi_comment(),
            K::Tag(_) => self.parse_tag(),
            _ => {
                if self.is_definition_start() {
                    self.parse_definition_list()
                } else {
                    self.parse_paragraph()
                }
            }
        }
    }

    // ===== Tag =====

    fn parse_tag(&mut self) -> BlockNode {
        let t = self.advance().unwrap();
        let names = match &t.kind {
            K::Tag(v) => v.clone(),
            _ => unreachable!(),
        };
        let span = t.span;
        let scope = self.scope_for_tag(span.start.line);
        self.eat_newline();
        BlockNode::Tag(TagNode {
            span,
            tags: names,
            scope,
        })
    }

    /// Decide the placement-determined scope of a tag at the given source
    /// line, matching vimwiki's rules:
    ///   - lines 0 or 1 → `File`
    ///   - within two lines after the most recent heading → `Heading(idx)`
    ///   - otherwise → `Standalone`
    fn scope_for_tag(&self, tag_line: u32) -> TagScope {
        if tag_line <= 1 {
            return TagScope::File;
        }
        if let Some(h_line) = self.last_heading_line {
            let delta = tag_line.saturating_sub(h_line);
            if (1..=2).contains(&delta) && self.headings_seen > 0 {
                return TagScope::Heading(self.headings_seen - 1);
            }
        }
        TagScope::Standalone
    }

    // ===== Heading =====

    fn parse_heading(&mut self) -> BlockNode {
        let open = self.advance().unwrap();
        let span_start = open.span.start;
        let (level, centered) = match &open.kind {
            K::HeadingOpen { level, centered } => (*level, *centered),
            _ => unreachable!(),
        };
        let inline_start = self.pos;
        let mut span_end = open.span.end;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::HeadingClose => {
                    span_end = t.span.end;
                    let inline = parse_inline_seq(&self.toks[inline_start..self.pos]);
                    self.advance();
                    self.eat_newline();
                    // Record for tag-scope resolution (Phase 12).
                    self.headings_seen += 1;
                    self.last_heading_line = Some(span_end.line);
                    return BlockNode::Heading(HeadingNode {
                        span: Span::new(span_start, span_end),
                        level,
                        centered,
                        children: inline,
                    });
                }
                K::Newline | K::BlankLine => break,
                _ => {
                    self.advance();
                }
            }
        }
        // No closing `=` seen: emit a paragraph from what we collected.
        let inline = parse_inline_seq(&self.toks[inline_start..self.pos]);
        self.eat_newline();
        BlockNode::Paragraph(ParagraphNode {
            span: Span::new(span_start, span_end),
            children: inline,
        })
    }

    // ===== Horizontal rule =====

    fn parse_horizontal_rule(&mut self) -> BlockNode {
        let t = self.advance().unwrap();
        let span = t.span;
        self.eat_newline();
        BlockNode::HorizontalRule(HorizontalRuleNode { span })
    }

    // ===== Comments =====

    fn parse_single_comment(&mut self) -> BlockNode {
        let t = self.advance().unwrap();
        let content = match &t.kind {
            K::CommentLine(s) => s.clone(),
            _ => unreachable!(),
        };
        let span = t.span;
        self.eat_newline();
        BlockNode::Comment(CommentNode { span, content })
    }

    fn parse_multi_comment(&mut self) -> BlockNode {
        let open = self.advance().unwrap();
        let span_start = open.span.start;
        let mut span_end = open.span.end;
        let mut content = String::new();
        let mut first = true;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::CommentMultiClose => {
                    span_end = t.span.end;
                    self.advance();
                    self.eat_newline();
                    return BlockNode::Comment(CommentNode {
                        span: Span::new(span_start, span_end),
                        content,
                    });
                }
                K::CommentMultiLine(s) => {
                    if !first {
                        content.push('\n');
                    }
                    content.push_str(s);
                    first = false;
                    span_end = t.span.end;
                    self.advance();
                }
                K::Newline => {
                    self.advance();
                }
                _ => {
                    self.advance();
                }
            }
        }
        // Unterminated: keep what we have.
        BlockNode::Comment(CommentNode {
            span: Span::new(span_start, span_end),
            content,
        })
    }

    // ===== Preformatted =====

    fn parse_preformatted(&mut self) -> BlockNode {
        let open = self.advance().unwrap();
        let span_start = open.span.start;
        let mut span_end = open.span.end;
        let language = match &open.kind {
            K::PreformattedOpen { language, .. } => language.clone(),
            _ => unreachable!(),
        };
        let mut content = String::new();
        let mut first = true;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::PreformattedClose => {
                    span_end = t.span.end;
                    self.advance();
                    self.eat_newline();
                    return BlockNode::Preformatted(PreformattedNode {
                        span: Span::new(span_start, span_end),
                        content,
                        language,
                    });
                }
                K::PreformattedLine(s) => {
                    if !first {
                        content.push('\n');
                    }
                    content.push_str(s);
                    first = false;
                    span_end = t.span.end;
                    self.advance();
                }
                K::Newline => {
                    self.advance();
                }
                _ => {
                    self.advance();
                }
            }
        }
        BlockNode::Preformatted(PreformattedNode {
            span: Span::new(span_start, span_end),
            content,
            language,
        })
    }

    // ===== Math block =====

    fn parse_math_block(&mut self) -> BlockNode {
        let open = self.advance().unwrap();
        let span_start = open.span.start;
        let mut span_end = open.span.end;
        let environment = match &open.kind {
            K::MathBlockOpen { environment } => environment.clone(),
            _ => unreachable!(),
        };
        let mut content = String::new();
        let mut first = true;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::MathBlockClose => {
                    span_end = t.span.end;
                    self.advance();
                    self.eat_newline();
                    return BlockNode::MathBlock(MathBlockNode {
                        span: Span::new(span_start, span_end),
                        content,
                        environment,
                    });
                }
                K::MathBlockLine(s) => {
                    if !first {
                        content.push('\n');
                    }
                    content.push_str(s);
                    first = false;
                    span_end = t.span.end;
                    self.advance();
                }
                K::Newline => {
                    self.advance();
                }
                _ => {
                    self.advance();
                }
            }
        }
        BlockNode::MathBlock(MathBlockNode {
            span: Span::new(span_start, span_end),
            content,
            environment,
        })
    }

    // ===== List =====

    fn parse_list(&mut self) -> BlockNode {
        let first = self.peek().expect("parse_list at EOF");
        let span_start = first.span.start;
        let (base_symbol, base_indent) = match &first.kind {
            K::ListMarker { symbol, indent } => (*symbol, *indent),
            _ => unreachable!(),
        };
        let mut items = Vec::new();
        let mut span_end = span_start;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::ListMarker { indent, .. } if *indent == base_indent => {
                    let item = self.parse_list_item();
                    span_end = item.span.end;
                    items.push(item);
                }
                _ => break,
            }
        }
        BlockNode::List(ListNode {
            span: Span::new(span_start, span_end),
            ordered: matches!(
                base_symbol,
                ListSymbol::Numeric
                    | ListSymbol::NumericParen
                    | ListSymbol::AlphaParen
                    | ListSymbol::AlphaUpperParen
                    | ListSymbol::RomanParen
                    | ListSymbol::RomanUpperParen
            ),
            symbol: base_symbol,
            items,
        })
    }

    fn parse_list_item(&mut self) -> ListItemNode {
        let marker = self.advance().expect("list item without marker");
        let span_start = marker.span.start;
        let mut span_end = marker.span.end;
        let (symbol, level) = match &marker.kind {
            K::ListMarker { symbol, indent } => (*symbol, *indent as usize),
            _ => unreachable!(),
        };

        // Optional Checkbox
        let checkbox = if let Some(K::Checkbox(state)) = self.peek_kind() {
            let state = *state;
            let t = self.advance().unwrap();
            span_end = t.span.end;
            Some(state)
        } else {
            None
        };

        // Inline content until end of line.
        let inline_start = self.pos;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::Newline | K::BlankLine => break,
                _ => {
                    span_end = t.span.end;
                    self.advance();
                }
            }
        }
        let inline_end = self.pos;
        let children = parse_inline_seq(&self.toks[inline_start..inline_end]);
        self.eat_newline();

        // Sublist: subsequent ListMarker tokens with deeper indent.
        let sublist = if let Some(K::ListMarker { indent, .. }) = self.peek_kind() {
            if (*indent as usize) > level {
                let block = self.parse_list();
                if let BlockNode::List(node) = block {
                    span_end = node.span.end;
                    Some(node)
                } else {
                    None
                }
            } else {
                None
            }
        } else {
            None
        };

        ListItemNode {
            span: Span::new(span_start, span_end),
            symbol,
            level,
            checkbox,
            children,
            sublist,
        }
    }

    // ===== Blockquote =====

    fn parse_blockquote(&mut self) -> BlockNode {
        let first = self.peek().unwrap();
        let span_start = first.span.start;
        let mut span_end = span_start;
        let mut lines: Vec<Vec<InlineNode>> = Vec::new();
        while let Some(t) = self.peek() {
            match &t.kind {
                K::BlockquoteMarker | K::BlockquoteIndent => {
                    self.advance();
                    let inline_start = self.pos;
                    while let Some(t2) = self.peek() {
                        match &t2.kind {
                            K::Newline | K::BlankLine => break,
                            _ => {
                                span_end = t2.span.end;
                                self.advance();
                            }
                        }
                    }
                    let inline_end = self.pos;
                    let inline = parse_inline_seq(&self.toks[inline_start..inline_end]);
                    if !inline.is_empty() {
                        lines.push(inline);
                    }
                    self.eat_newline();
                }
                _ => break,
            }
        }
        let mut children: Vec<BlockNode> = Vec::with_capacity(lines.len());
        for line in lines {
            let line_start = line
                .first()
                .and_then(span_start_of_inline)
                .unwrap_or(span_start);
            let line_end = line.last().and_then(span_end_of_inline).unwrap_or(span_end);
            children.push(BlockNode::Paragraph(ParagraphNode {
                span: Span::new(line_start, line_end),
                children: line,
            }));
        }
        BlockNode::Blockquote(BlockquoteNode {
            span: Span::new(span_start, span_end),
            children,
        })
    }

    // ===== Table =====

    fn parse_table(&mut self) -> BlockNode {
        let first = self.peek().unwrap();
        let span_start = first.span.start;
        let mut span_end = span_start;
        let mut rows: Vec<TableRowNode> = Vec::new();
        let mut next_is_header = false;
        let mut has_header = false;

        while let Some(t) = self.peek() {
            match &t.kind {
                K::TableHeaderRow => {
                    has_header = true;
                    if let Some(last) = rows.last_mut() {
                        last.is_header = true;
                    }
                    next_is_header = true;
                    span_end = t.span.end;
                    self.advance();
                    self.eat_newline();
                }
                K::TableSep => {
                    let row = self.parse_table_row();
                    span_end = row.span.end;
                    rows.push(row);
                    if next_is_header {
                        // Header sep applies to the *previous* row, not this one.
                        next_is_header = false;
                    }
                }
                _ => break,
            }
        }
        BlockNode::Table(TableNode {
            span: Span::new(span_start, span_end),
            rows,
            has_header,
        })
    }

    fn parse_table_row(&mut self) -> TableRowNode {
        // Consume leading TableSep
        let first_sep = self.advance().expect("table row without leading |");
        let span_start = first_sep.span.start;
        let mut span_end = first_sep.span.end;
        let mut cells: Vec<TableCellNode> = Vec::new();

        while let Some(t) = self.peek() {
            match &t.kind {
                K::Newline | K::BlankLine => break,
                K::TableSep => {
                    span_end = t.span.end;
                    self.advance();
                }
                K::TableColSpan => {
                    let span = t.span;
                    span_end = span.end;
                    self.advance();
                    cells.push(TableCellNode {
                        span,
                        children: Vec::new(),
                        col_span: true,
                        row_span: false,
                    });
                }
                K::TableRowSpan => {
                    let span = t.span;
                    span_end = span.end;
                    self.advance();
                    cells.push(TableCellNode {
                        span,
                        children: Vec::new(),
                        col_span: false,
                        row_span: true,
                    });
                }
                _ => {
                    let cell_start_idx = self.pos;
                    let cell_start_pos = t.span.start;
                    let mut cell_end_pos = t.span.end;
                    while let Some(tt) = self.peek() {
                        match &tt.kind {
                            K::TableSep | K::Newline | K::BlankLine => break,
                            _ => {
                                cell_end_pos = tt.span.end;
                                self.advance();
                            }
                        }
                    }
                    let inline = parse_inline_seq(&self.toks[cell_start_idx..self.pos]);
                    span_end = cell_end_pos;
                    cells.push(TableCellNode {
                        span: Span::new(cell_start_pos, cell_end_pos),
                        children: inline,
                        col_span: false,
                        row_span: false,
                    });
                }
            }
        }
        self.eat_newline();
        TableRowNode {
            span: Span::new(span_start, span_end),
            cells,
            is_header: false,
        }
    }

    // ===== Definition list =====

    fn is_definition_start(&self) -> bool {
        // Walk forward on the current line. If we find a DefinitionTermMarker
        // before a Newline/BlankLine, treat as a definition.
        let mut i = self.pos;
        while let Some(t) = self.toks.get(i) {
            match &t.kind {
                K::Newline | K::BlankLine => return false,
                K::DefinitionTermMarker => return true,
                _ => i += 1,
            }
        }
        false
    }

    fn parse_definition_list(&mut self) -> BlockNode {
        let first = self.peek().unwrap();
        let span_start = first.span.start;
        let mut span_end = span_start;
        let mut items: Vec<DefinitionItemNode> = Vec::new();
        while self.is_definition_start() {
            let item = self.parse_definition_item();
            span_end = item.span.end;
            items.push(item);
        }
        BlockNode::DefinitionList(DefinitionListNode {
            span: Span::new(span_start, span_end),
            items,
        })
    }

    fn parse_definition_item(&mut self) -> DefinitionItemNode {
        let item_start_idx = self.pos;
        let item_span_start = self.toks[item_start_idx].span.start;

        // Term: tokens until DefinitionTermMarker
        let term_start = self.pos;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::DefinitionTermMarker | K::Newline | K::BlankLine => break,
                _ => {
                    self.advance();
                }
            }
        }
        let term_end = self.pos;
        let term_inline = if term_end > term_start {
            let v = parse_inline_seq(&self.toks[term_start..term_end]);
            if v.is_empty() {
                None
            } else {
                Some(v)
            }
        } else {
            None
        };

        let mut span_end = self
            .toks
            .get(term_end.saturating_sub(1))
            .map(|t| t.span.end)
            .unwrap_or(item_span_start);

        // DefinitionTermMarker
        if matches!(self.peek_kind(), Some(K::DefinitionTermMarker)) {
            span_end = self.peek().unwrap().span.end;
            self.advance();
        }

        // Definition tokens until end of line
        let def_start = self.pos;
        while let Some(t) = self.peek() {
            match &t.kind {
                K::Newline | K::BlankLine => break,
                _ => {
                    span_end = t.span.end;
                    self.advance();
                }
            }
        }
        let def_end = self.pos;
        let mut definitions = Vec::new();
        if def_end > def_start {
            let v = parse_inline_seq(&self.toks[def_start..def_end]);
            if !v.is_empty() {
                definitions.push(v);
            }
        }
        self.eat_newline();

        DefinitionItemNode {
            span: Span::new(item_span_start, span_end),
            term: term_inline,
            definitions,
        }
    }

    // ===== Paragraph =====

    fn parse_paragraph(&mut self) -> BlockNode {
        let span_start = self.peek().unwrap().span.start;
        let inline_start = self.pos;
        // `content_end` excludes a trailing newline that just terminates
        // the paragraph (instead of joining two content lines), so it
        // doesn't leak into `parse_inline_seq` as a stray soft-break " ".
        let mut content_end = self.pos;
        let mut span_end = span_start;

        loop {
            match self.peek_kind() {
                None => break,
                Some(K::Newline) => {
                    span_end = self.peek().unwrap().span.end;
                    self.advance();
                    match self.peek_kind() {
                        None => break,
                        Some(k) if starts_new_block(k) => break,
                        // Soft-break: the newline joins two content lines.
                        // Pull it into the inline range as a space.
                        _ => content_end = self.pos,
                    }
                }
                Some(k) if starts_new_block(k) => break,
                Some(_) => {
                    span_end = self.peek().unwrap().span.end;
                    self.advance();
                    content_end = self.pos;
                }
            }
        }

        let children = parse_inline_seq(&self.toks[inline_start..content_end]);
        BlockNode::Paragraph(ParagraphNode {
            span: Span::new(span_start, span_end),
            children,
        })
    }
}

fn starts_new_block(kind: &K) -> bool {
    matches!(
        kind,
        K::BlankLine
            | K::HeadingOpen { .. }
            | K::HorizontalRule
            | K::ListMarker { .. }
            | K::BlockquoteMarker
            | K::BlockquoteIndent
            | K::TableSep
            | K::TableHeaderRow
            | K::PreformattedOpen { .. }
            | K::MathBlockOpen { .. }
            | K::CommentLine(_)
            | K::CommentMultiOpen
            | K::PlaceholderTitle(_)
            | K::PlaceholderNohtml
            | K::PlaceholderTemplate(_)
            | K::PlaceholderDate(_)
            | K::Tag(_)
    )
}

// ===== Inline pairing =====

fn parse_inline_seq(toks: &[VimwikiToken]) -> Vec<InlineNode> {
    let mut out = Vec::new();
    let mut i = 0;
    while i < toks.len() {
        let token = &toks[i];
        match &token.kind {
            K::Text(s) => {
                out.push(InlineNode::Text(TextNode {
                    span: token.span,
                    content: s.clone(),
                }));
                i += 1;
            }
            K::Code(s) => {
                out.push(InlineNode::Code(CodeNode {
                    span: token.span,
                    content: s.clone(),
                }));
                i += 1;
            }
            K::MathInline(s) => {
                out.push(InlineNode::MathInline(MathInlineNode {
                    span: token.span,
                    content: s.clone(),
                }));
                i += 1;
            }
            K::Keyword(k) => {
                out.push(InlineNode::Keyword(KeywordNode {
                    span: token.span,
                    keyword: *k,
                }));
                i += 1;
            }
            K::RawUrl(u) => {
                out.push(InlineNode::RawUrl(RawUrlNode {
                    span: token.span,
                    url: u.clone(),
                }));
                i += 1;
            }
            K::Newline => {
                // Soft break inside a multi-line block: render as space.
                out.push(InlineNode::Text(TextNode {
                    span: token.span,
                    content: " ".into(),
                }));
                i += 1;
            }
            K::BoldDelim => {
                i = pair_or_text(toks, i, "*", &mut out, K::BoldDelim, |span, kids| {
                    InlineNode::Bold(BoldNode {
                        span,
                        children: kids,
                    })
                })
            }
            K::ItalicDelim => {
                i = pair_or_text(toks, i, "_", &mut out, K::ItalicDelim, |span, kids| {
                    InlineNode::Italic(ItalicNode {
                        span,
                        children: kids,
                    })
                })
            }
            K::StrikethroughDelim => {
                i = pair_or_text(
                    toks,
                    i,
                    "~~",
                    &mut out,
                    K::StrikethroughDelim,
                    |span, kids| {
                        InlineNode::Strikethrough(StrikethroughNode {
                            span,
                            children: kids,
                        })
                    },
                )
            }
            K::SuperscriptDelim => {
                i = pair_or_text(toks, i, "^", &mut out, K::SuperscriptDelim, |span, kids| {
                    InlineNode::Superscript(SuperscriptNode {
                        span,
                        children: kids,
                    })
                })
            }
            K::SubscriptDelim => {
                i = pair_or_text(toks, i, ",,", &mut out, K::SubscriptDelim, |span, kids| {
                    InlineNode::Subscript(SubscriptNode {
                        span,
                        children: kids,
                    })
                })
            }
            K::WikiLinkOpen => {
                let (node, next) = parse_wikilink(toks, i);
                out.push(node);
                i = next;
            }
            K::TransclusionOpen => {
                let (node, next) = parse_transclusion(toks, i);
                out.push(node);
                i = next;
            }
            // Tokens that shouldn't appear in inline context (e.g. dangling
            // close delimiters, separators outside their owners): emit as
            // literal text so nothing is silently dropped.
            K::WikiLinkClose => push_literal(token, "]]", &mut out, &mut i),
            K::WikiLinkSep => push_literal(token, "|", &mut out, &mut i),
            K::TransclusionClose => push_literal(token, "}}", &mut out, &mut i),
            K::TransclusionSep => push_literal(token, "|", &mut out, &mut i),
            K::HeadingClose => push_literal(token, "=", &mut out, &mut i),
            // Other tokens (block markers, etc.) should not appear here; skip.
            _ => {
                i += 1;
            }
        }
    }
    out
}

fn push_literal(token: &VimwikiToken, lit: &str, out: &mut Vec<InlineNode>, i: &mut usize) {
    out.push(InlineNode::Text(TextNode {
        span: token.span,
        content: lit.into(),
    }));
    *i += 1;
}

fn pair_or_text<F>(
    toks: &[VimwikiToken],
    open_idx: usize,
    literal: &str,
    out: &mut Vec<InlineNode>,
    target: K,
    build: F,
) -> usize
where
    F: FnOnce(Span, Vec<InlineNode>) -> InlineNode,
{
    if let Some(close_idx) = find_close(toks, open_idx, &target) {
        let inner = parse_inline_seq(&toks[open_idx + 1..close_idx]);
        let span = Span::new(toks[open_idx].span.start, toks[close_idx].span.end);
        out.push(build(span, inner));
        close_idx + 1
    } else {
        out.push(InlineNode::Text(TextNode {
            span: toks[open_idx].span,
            content: literal.into(),
        }));
        open_idx + 1
    }
}

fn find_close(toks: &[VimwikiToken], start: usize, target: &K) -> Option<usize> {
    for (offset, t) in toks.iter().enumerate().skip(start + 1) {
        if &t.kind == target {
            return Some(offset);
        }
    }
    None
}

// ===== Wikilink + transclusion =====

fn parse_wikilink(toks: &[VimwikiToken], open_idx: usize) -> (InlineNode, usize) {
    let span_start = toks[open_idx].span.start;
    let mut i = open_idx + 1;
    let target_start = i;
    let mut target_end = i;
    let mut sep_idx: Option<usize> = None;
    let mut close_idx: Option<usize> = None;
    while i < toks.len() {
        match &toks[i].kind {
            K::WikiLinkClose => {
                close_idx = Some(i);
                break;
            }
            K::WikiLinkSep if sep_idx.is_none() => {
                sep_idx = Some(i);
                target_end = i;
            }
            _ => {}
        }
        i += 1;
    }
    let close_idx = match close_idx {
        Some(c) => c,
        None => {
            // Unterminated link: emit literal `[[`.
            return (
                InlineNode::Text(TextNode {
                    span: toks[open_idx].span,
                    content: "[[".into(),
                }),
                open_idx + 1,
            );
        }
    };

    if sep_idx.is_none() {
        target_end = close_idx;
    }

    let target_text = collect_text(&toks[target_start..target_end]);
    let span = Span::new(span_start, toks[close_idx].span.end);

    let description: Option<Vec<InlineNode>> = sep_idx.map(|sep| {
        let inner = parse_inline_seq(&toks[sep + 1..close_idx]);
        if inner.is_empty() {
            vec![]
        } else {
            inner
        }
    });

    if is_url(&target_text) {
        (
            InlineNode::ExternalLink(ExternalLinkNode {
                span,
                url: target_text,
                description,
            }),
            close_idx + 1,
        )
    } else {
        let target = parse_link_target(&target_text);
        (
            InlineNode::WikiLink(WikiLinkNode {
                span,
                target,
                description,
            }),
            close_idx + 1,
        )
    }
}

fn parse_transclusion(toks: &[VimwikiToken], open_idx: usize) -> (InlineNode, usize) {
    let span_start = toks[open_idx].span.start;
    let mut i = open_idx + 1;
    let url_start = i;
    let mut url_end = i;
    let mut seps: Vec<usize> = Vec::new();
    let mut close_idx: Option<usize> = None;
    while i < toks.len() {
        match &toks[i].kind {
            K::TransclusionClose => {
                close_idx = Some(i);
                break;
            }
            K::TransclusionSep => {
                if seps.is_empty() {
                    url_end = i;
                }
                seps.push(i);
            }
            _ => {}
        }
        i += 1;
    }
    let close_idx = match close_idx {
        Some(c) => c,
        None => {
            return (
                InlineNode::Text(TextNode {
                    span: toks[open_idx].span,
                    content: "{{".into(),
                }),
                open_idx + 1,
            );
        }
    };
    if seps.is_empty() {
        url_end = close_idx;
    }
    let url = collect_text(&toks[url_start..url_end]);
    let span = Span::new(span_start, toks[close_idx].span.end);

    // After URL: optional alt, then key=val attrs.
    let mut alt = None;
    let mut attrs = std::collections::HashMap::new();
    if !seps.is_empty() {
        let alt_start = seps[0] + 1;
        let alt_end = if seps.len() >= 2 { seps[1] } else { close_idx };
        let alt_text = collect_text(&toks[alt_start..alt_end]);
        if !alt_text.is_empty() {
            alt = Some(alt_text);
        }
        for window in seps.windows(2) {
            let s = window[0];
            let e = window[1];
            // attr segment is at [s+1..e]; format key=val
            let segment = collect_text(&toks[s + 1..e]);
            if let Some(eq) = segment.find('=') {
                let k = segment[..eq].trim().to_owned();
                let v = segment[eq + 1..].trim().to_owned();
                if !k.is_empty() {
                    attrs.insert(k, v);
                }
            }
        }
        // Last attribute segment between final sep and close.
        if let Some(&last) = seps.last() {
            if last + 1 < close_idx && seps.len() >= 2 {
                let segment = collect_text(&toks[last + 1..close_idx]);
                if let Some(eq) = segment.find('=') {
                    let k = segment[..eq].trim().to_owned();
                    let v = segment[eq + 1..].trim().to_owned();
                    if !k.is_empty() {
                        attrs.insert(k, v);
                    }
                }
            }
        }
    }

    (
        InlineNode::Transclusion(TransclusionNode {
            span,
            url,
            alt,
            attrs,
        }),
        close_idx + 1,
    )
}

fn collect_text(toks: &[VimwikiToken]) -> String {
    let mut out = String::new();
    for t in toks {
        if let K::Text(s) = &t.kind {
            out.push_str(s);
        }
    }
    out
}

fn is_url(s: &str) -> bool {
    s.starts_with("http://")
        || s.starts_with("https://")
        || s.starts_with("ftp://")
        || s.starts_with("mailto:")
        || s.starts_with("file://")
}

// ===== LinkTarget classification =====

fn parse_link_target(text: &str) -> LinkTarget {
    let mut target = LinkTarget {
        kind: LinkKind::Wiki,
        path: None,
        wiki_index: None,
        wiki_name: None,
        anchor: None,
        is_absolute: false,
        is_directory: false,
    };

    // Split off anchor first.
    let (path_part, anchor) = match text.split_once('#') {
        Some((p, a)) => (p, Some(a.to_owned())),
        None => (text, None),
    };
    target.anchor = anchor;

    if path_part.is_empty() {
        target.kind = LinkKind::AnchorOnly;
        return target;
    }

    // `//path` — filesystem-absolute.
    if let Some(rest) = path_part.strip_prefix("//") {
        target.kind = LinkKind::Local;
        target.is_absolute = true;
        let (path, is_dir) = strip_directory(rest);
        target.is_directory = is_dir;
        target.path = Some(path);
        return target;
    }

    // `/Page` — root-relative wiki link.
    if let Some(rest) = path_part.strip_prefix('/') {
        target.kind = LinkKind::Wiki;
        target.is_absolute = true;
        let (path, is_dir) = strip_directory(rest);
        target.is_directory = is_dir;
        target.path = Some(path);
        return target;
    }

    // Scheme prefixes.
    if let Some(rest) = path_part.strip_prefix("file:") {
        target.kind = LinkKind::File;
        target.path = Some(rest.to_owned());
        return target;
    }
    if let Some(rest) = path_part.strip_prefix("local:") {
        target.kind = LinkKind::Local;
        target.path = Some(rest.to_owned());
        return target;
    }
    if let Some(rest) = path_part.strip_prefix("diary:") {
        target.kind = LinkKind::Diary;
        target.path = Some(rest.to_owned());
        return target;
    }
    if let Some(rest) = path_part.strip_prefix("wn.") {
        if let Some((name, page)) = rest.split_once(':') {
            target.kind = LinkKind::Interwiki;
            target.wiki_name = Some(name.to_owned());
            target.path = Some(page.to_owned());
            return target;
        }
    }
    if let Some((scheme, rest)) = path_part.split_once(':') {
        if let Some(num) = scheme.strip_prefix("wiki") {
            if let Ok(idx) = num.parse::<usize>() {
                target.kind = LinkKind::Interwiki;
                target.wiki_index = Some(idx);
                target.path = Some(rest.to_owned());
                return target;
            }
        }
    }

    // Default: plain wiki link, possibly directory.
    let (path, is_dir) = strip_directory(path_part);
    target.kind = LinkKind::Wiki;
    target.is_directory = is_dir;
    target.path = Some(path);
    target
}

fn strip_directory(s: &str) -> (String, bool) {
    if let Some(stripped) = s.strip_suffix('/') {
        (stripped.to_owned(), true)
    } else {
        (s.to_owned(), false)
    }
}

// ===== Span helpers =====

fn span_start_of_inline(node: &InlineNode) -> Option<crate::ast::Position> {
    Some(span_of_inline(node).start)
}

fn span_end_of_inline(node: &InlineNode) -> Option<crate::ast::Position> {
    Some(span_of_inline(node).end)
}

fn span_of_inline(node: &InlineNode) -> Span {
    match node {
        InlineNode::Text(n) => n.span,
        InlineNode::Bold(n) => n.span,
        InlineNode::Italic(n) => n.span,
        InlineNode::BoldItalic(n) => n.span,
        InlineNode::Strikethrough(n) => n.span,
        InlineNode::Code(n) => n.span,
        InlineNode::Superscript(n) => n.span,
        InlineNode::Subscript(n) => n.span,
        InlineNode::MathInline(n) => n.span,
        InlineNode::Keyword(n) => n.span,
        InlineNode::Color(n) => n.span,
        InlineNode::WikiLink(n) => n.span,
        InlineNode::ExternalLink(n) => n.span,
        InlineNode::Transclusion(n) => n.span,
        InlineNode::RawUrl(n) => n.span,
    }
}