// SPDX-License-Identifier: MIT OR Apache-2.0
// Copyright (c) 2026 Noyalib. All rights reserved.

//! Comment-aware read view over a [`crate::cst::Document`].
//!
//! The CST already round-trips comments byte-for-byte through
//! [`Document::set`] and friends — touched spans are rewritten,
//! everything else (indentation, comments, blank lines) is left alone.
//! What this module adds is the *read* side: given a path-shaped
//! query, return the human-authored YAML comments that decorate the
//! node at that path. Tools (linters, AI agents reading config files,
//! IDE plugins) need that to understand what each field *means*.
//!
//! # Definitions
//!
//! - **Inline comment**: a `#`-introduced comment on the *same* line
//!   as the node's content, after that content. `key: val # inline`.
//! - **Leading comments**: a contiguous run of comment-only or blank
//!   lines immediately above the node's first byte. `# pre\nkey: val`
//!   yields one leading comment.
//!
//! # Examples
//!
//! ```
//! use noyalib::cst::parse_document;
//!
//! let src = "# top of file\nname: noyalib  # the project\n# next field\nversion: 0.0.1\n";
//! let doc = parse_document(src).unwrap();
//!
//! let name = doc.comments_at("name");
//! assert_eq!(name.before.len(), 1);
//! assert_eq!(name.before[0].text, " top of file");
//! assert_eq!(name.inline.as_ref().unwrap().text, " the project");
//!
//! let version = doc.comments_at("version");
//! assert_eq!(version.before.len(), 1);
//! assert_eq!(version.before[0].text, " next field");
//! assert!(version.inline.is_none());
//! ```

use crate::comments::Comment;
use crate::cst::Document;
use crate::prelude::*;

/// Comments that decorate a single node, organised by their position
/// relative to the node.
///
/// Returned by [`Document::comments_at`]. Both fields are empty /
/// `None` when no comments decorate the queried path or when the path
/// does not resolve to a node in the document.
///
/// # Examples
///
/// ```
/// use noyalib::cst::parse_document;
///
/// let doc = parse_document("port: 8080  # the listen port\n").unwrap();
/// let bundle = doc.comments_at("port");
/// assert!(bundle.before.is_empty());
/// assert_eq!(bundle.inline.unwrap().text, " the listen port");
/// ```
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub struct CommentBundle {
    /// Contiguous run of comment lines that appear immediately above
    /// the node, in source order. An interleaved blank line does not
    /// break the run — only another content node does. Empty when
    /// the node has no leading comments.
    pub before: Vec<Comment>,
    /// The trailing comment on the node's own line, if any. `None`
    /// when no `#`-introduced comment follows the node's content on
    /// the same source line. Multi-line nodes (block mappings,
    /// block sequences) do not have an inline comment in this sense
    /// — query individual entries instead.
    pub inline: Option<Comment>,
}

impl CommentBundle {
    /// `true` when the bundle has neither a leading nor an inline
    /// comment. Convenience for the common "decide whether to render"
    /// branch in tooling.
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.before.is_empty() && self.inline.is_none()
    }
}

impl Document {
    /// Comments decorating the node at `path`, classified by position.
    ///
    /// Returns an empty [`CommentBundle`] when `path` does not
    /// resolve. Path syntax matches [`Document::span_at`] —
    /// `foo.bar`, `items[0]`, `items[0].name`. Wildcard /
    /// recursive-descent segments are not supported (a non-singular
    /// span has no canonical "above" line).
    ///
    /// # Examples
    ///
    /// ```
    /// use noyalib::cst::parse_document;
    ///
    /// let src = "# A multi-line\n# leading block\nport: 8080  # inline\n";
    /// let doc = parse_document(src).unwrap();
    ///
    /// let b = doc.comments_at("port");
    /// assert_eq!(b.before.len(), 2);
    /// assert_eq!(b.inline.as_ref().unwrap().text, " inline");
    /// ```
    #[must_use]
    pub fn comments_at(&self, path: &str) -> CommentBundle {
        let Some((start, end)) = self.span_at(path) else {
            return CommentBundle::default();
        };

        // Comment scanning is independent of edits — always run on the
        // current source. The comment count is small (one per line at
        // most), so per-call scanning is cheaper than caching.
        let comments = match crate::comments::load_comments(self.source()) {
            Ok(c) => c,
            // A document that successfully parsed cannot fail comment
            // scan — but if it does, treat as no comments rather than
            // bubbling up: this is a read-only convenience API.
            Err(_) => return CommentBundle::default(),
        };

        let src = self.source();
        let line_start_idx = line_start(src, start);
        let line_end_idx = line_end(src, end.saturating_sub(1).max(start));

        let mut bundle = CommentBundle::default();

        // Inline only applies to single-line nodes — a multi-line
        // block (mapping, sequence) does not have a single inline
        // comment of its own; query individual entries instead.
        let is_single_line = !src[start..end].contains('\n');
        if is_single_line {
            for c in &comments {
                if c.start >= end && c.start <= line_end_idx {
                    bundle.inline = Some(c.clone());
                    break;
                }
            }
        }

        // Leading: walk *upwards* from the line containing `start`,
        // collecting comment-only lines and skipping pure-blank lines.
        // Stop at the first line containing non-comment content (or at
        // the start of input).
        let mut cursor = line_start_idx;
        let mut acc: Vec<Comment> = Vec::new();
        while cursor > 0 {
            // `cursor` points at the first byte of a line; step back
            // to the previous line's start.
            let prev_line_end = cursor - 1; // the '\n' that ended the previous line
            let prev_line_start = line_start(src, prev_line_end.saturating_sub(1));
            let line_text = &src[prev_line_start..prev_line_end];
            let trimmed = line_text.trim_start_matches([' ', '\t']);

            if trimmed.is_empty() {
                // Blank line — does not break the run, does not
                // contribute a comment.
                cursor = prev_line_start;
                continue;
            }
            if trimmed.starts_with('#') {
                // Comment-only line. Find the matching scanned comment
                // (we already have spans for all of them).
                if let Some(c) = comments
                    .iter()
                    .find(|c| c.start >= prev_line_start && c.start < prev_line_end)
                {
                    acc.push(c.clone());
                }
                cursor = prev_line_start;
                continue;
            }
            // Content line — stop walking up.
            break;
        }

        // Walked upward, so the natural order is bottom-up; reverse to
        // restore source order.
        acc.reverse();
        bundle.before = acc;

        bundle
    }
}

#[inline]
fn line_start(src: &str, byte: usize) -> usize {
    let bytes = src.as_bytes();
    let mut i = byte.min(bytes.len());
    while i > 0 && bytes[i - 1] != b'\n' {
        i -= 1;
    }
    i
}

#[inline]
fn line_end(src: &str, byte: usize) -> usize {
    let bytes = src.as_bytes();
    let mut i = byte.min(bytes.len().saturating_sub(1));
    while i < bytes.len() && bytes[i] != b'\n' {
        i += 1;
    }
    i
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::cst::parse_document;

    #[test]
    fn inline_comment_on_simple_value() {
        let doc = parse_document("port: 8080  # the listen port\n").unwrap();
        let b = doc.comments_at("port");
        assert!(b.before.is_empty());
        assert_eq!(b.inline.as_ref().unwrap().text, " the listen port");
    }

    #[test]
    fn leading_single_comment() {
        let doc = parse_document("# pre\nkey: val\n").unwrap();
        let b = doc.comments_at("key");
        assert_eq!(b.before.len(), 1);
        assert_eq!(b.before[0].text, " pre");
        assert!(b.inline.is_none());
    }

    #[test]
    fn leading_multi_with_blank_lines_preserves_run() {
        let doc = parse_document(
            "# first\n\
             \n\
             # second\n\
             key: val\n",
        )
        .unwrap();
        let b = doc.comments_at("key");
        assert_eq!(b.before.len(), 2);
        assert_eq!(b.before[0].text, " first");
        assert_eq!(b.before[1].text, " second");
    }

    #[test]
    fn content_line_breaks_leading_run() {
        let doc = parse_document(
            "name: noyalib\n\
             # this comment belongs to version, not name\n\
             version: 0.0.1\n",
        )
        .unwrap();
        let name = doc.comments_at("name");
        assert!(name.before.is_empty());
        let version = doc.comments_at("version");
        assert_eq!(version.before.len(), 1);
        assert!(version.before[0].text.contains("belongs to version"));
    }

    #[test]
    fn nested_path_inline_comment() {
        let doc = parse_document(
            "server:\n\
             \x20 host: localhost  # bind address\n\
             \x20 port: 8080\n",
        )
        .unwrap();
        let host = doc.comments_at("server.host");
        assert_eq!(host.inline.as_ref().unwrap().text, " bind address");
        let port = doc.comments_at("server.port");
        assert!(port.inline.is_none());
    }

    #[test]
    fn unknown_path_returns_empty_bundle() {
        let doc = parse_document("a: 1\n").unwrap();
        let b = doc.comments_at("nonexistent");
        assert!(b.is_empty());
    }

    #[test]
    fn comments_survive_lossless_edit() {
        let mut doc = parse_document(
            "# version is bumped by Renovate\n\
             version: 0.0.1  # do not edit by hand\n",
        )
        .unwrap();
        doc.set("version", "0.0.2").unwrap();
        let b = doc.comments_at("version");
        assert_eq!(b.before.len(), 1);
        assert_eq!(b.before[0].text, " version is bumped by Renovate");
        assert_eq!(b.inline.as_ref().unwrap().text, " do not edit by hand");
        assert!(doc.to_string().contains("version: 0.0.2"));
        assert!(doc.to_string().contains("# version is bumped by Renovate"));
        assert!(doc.to_string().contains("# do not edit by hand"));
    }

    #[test]
    fn multiline_block_does_not_inherit_child_inline() {
        // Bug guard: querying a multi-line block must not return the
        // inline comment of its last child entry. The user's mental
        // model of `comments_at("server")` is "comments on `server`",
        // not "comments on `server.port`".
        let doc =
            parse_document("server:\n  host: localhost\n  port: 8080  # main HTTP port\n").unwrap();
        let server = doc.comments_at("server");
        assert!(
            server.inline.is_none(),
            "block must not inherit child inline"
        );
        let port = doc.comments_at("server.port");
        assert_eq!(port.inline.as_ref().unwrap().text, " main HTTP port");
    }

    #[test]
    fn sequence_item_inline_comment() {
        let doc = parse_document(
            "items:\n\
             \x20 - one  # the first\n\
             \x20 - two  # the second\n",
        )
        .unwrap();
        let first = doc.comments_at("items[0]");
        assert_eq!(first.inline.as_ref().unwrap().text, " the first");
        let second = doc.comments_at("items[1]");
        assert_eq!(second.inline.as_ref().unwrap().text, " the second");
    }
}
