//! Helpers shared by the Phase 8 navigation handlers (definition,
//! references, hover, completion).
//!
//! Two responsibilities:
//!
//! 1. **Position conversion** — clients send LSP `Position`s in either
//!    UTF-8 or UTF-16 encoding; nuwiki AST spans are byte offsets.
//!    `lsp_to_byte_pos` translates the LSP position into the same shape
//!    so it can be compared against AST spans.
//! 2. **Position lookup** — given a byte position, find the most specific
//!    `InlineNode` whose span covers it. Used to identify the link under
//!    the cursor.

use nuwiki_core::ast::{BlockNode, DocumentNode, InlineNode, ListItemNode, Span};
use tower_lsp::lsp_types::Position as LspPosition;

use crate::semantic_tokens::LineIndex;

/// Translate an LSP `Position` (whose `character` is a UTF-16 code-unit
/// offset by default, or a UTF-8 byte offset when negotiated) into our
/// internal `(line, byte_col)` shape.
pub fn lsp_to_byte_pos(p: LspPosition, text: &str, utf8: bool) -> (u32, u32) {
    if utf8 {
        return (p.line, p.character);
    }
    let idx = LineIndex::new(text);
    let line_str = idx.line_str(p.line, text);
    let byte_col = utf16_to_byte_col(line_str, p.character);
    (p.line, byte_col)
}

fn utf16_to_byte_col(line: &str, target_utf16: u32) -> u32 {
    let mut byte = 0u32;
    let mut units = 0u32;
    for ch in line.chars() {
        if units >= target_utf16 {
            break;
        }
        units += ch.len_utf16() as u32;
        byte += ch.len_utf8() as u32;
    }
    byte
}

/// Find the most specific inline node whose span covers the given byte
/// position. Walks block structure first, then descends into inline
/// containers (bold, italic, …) until no child claims the position.
pub fn find_inline_at(doc: &DocumentNode, line: u32, byte_col: u32) -> Option<&InlineNode> {
    for block in &doc.children {
        if let Some(node) = find_in_block(block, line, byte_col) {
            return Some(node);
        }
    }
    None
}

fn find_in_block(block: &BlockNode, line: u32, col: u32) -> Option<&InlineNode> {
    match block {
        BlockNode::Heading(h) => find_in_inlines(&h.children, line, col),
        BlockNode::Paragraph(p) => find_in_inlines(&p.children, line, col),
        BlockNode::Blockquote(b) => b.children.iter().find_map(|c| find_in_block(c, line, col)),
        BlockNode::List(l) => l
            .items
            .iter()
            .find_map(|it| find_in_list_item(it, line, col)),
        BlockNode::DefinitionList(dl) => dl.items.iter().find_map(|it| {
            it.term
                .as_ref()
                .and_then(|t| find_in_inlines(t, line, col))
                .or_else(|| {
                    it.definitions
                        .iter()
                        .find_map(|d| find_in_inlines(d, line, col))
                })
        }),
        BlockNode::Table(t) => t.rows.iter().find_map(|r| {
            r.cells
                .iter()
                .find_map(|c| find_in_inlines(&c.children, line, col))
        }),
        _ => None,
    }
}

fn find_in_list_item(item: &ListItemNode, line: u32, col: u32) -> Option<&InlineNode> {
    find_in_inlines(&item.children, line, col).or_else(|| {
        item.sublist.as_ref().and_then(|sub| {
            sub.items
                .iter()
                .find_map(|i| find_in_list_item(i, line, col))
        })
    })
}

fn find_in_inlines(inlines: &[InlineNode], line: u32, col: u32) -> Option<&InlineNode> {
    for n in inlines {
        if !span_contains(span_of_inline(n), line, col) {
            continue;
        }
        // Descend into inline containers so we return the *innermost* hit.
        let deeper = match n {
            InlineNode::Bold(b) => find_in_inlines(&b.children, line, col),
            InlineNode::Italic(i) => find_in_inlines(&i.children, line, col),
            InlineNode::BoldItalic(bi) => find_in_inlines(&bi.children, line, col),
            InlineNode::Strikethrough(s) => find_in_inlines(&s.children, line, col),
            InlineNode::Superscript(s) => find_in_inlines(&s.children, line, col),
            InlineNode::Subscript(s) => find_in_inlines(&s.children, line, col),
            InlineNode::Color(c) => find_in_inlines(&c.children, line, col),
            InlineNode::WikiLink(w) => w
                .description
                .as_ref()
                .and_then(|d| find_in_inlines(d, line, col)),
            InlineNode::ExternalLink(e) => e
                .description
                .as_ref()
                .and_then(|d| find_in_inlines(d, line, col)),
            _ => None,
        };
        return Some(deeper.unwrap_or(n));
    }
    None
}

fn span_contains(s: Span, line: u32, col: u32) -> bool {
    let start = (s.start.line, s.start.column);
    let end = (s.end.line, s.end.column);
    let p = (line, col);
    p >= start && p < end
}

pub 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,
    }
}