// journal.rs — Journal parsing for conversation compaction
//
// Parses the poc-journal format (## TIMESTAMP\n\nContent) and matches
// entries to conversation time ranges. Journal entries are the
// compression layer: old conversation messages get replaced by the
// journal entry that covers their time period.
//
// The journal file is append-only and managed by `poc-journal write`.
// We only read it here — never modify it.

use chrono::{DateTime, NaiveDateTime, Utc};
use std::path::Path;

/// A single journal entry with its timestamp and content.
#[derive(Debug, Clone)]
pub struct JournalEntry {
    pub timestamp: DateTime<Utc>,
    pub content: String,
}

/// Parse journal entries from the journal file. Returns entries sorted
/// by timestamp (oldest first). Entries with unparseable timestamps
/// are skipped.
pub fn parse_journal(path: &Path) -> Vec<JournalEntry> {
    let text = match std::fs::read_to_string(path) {
        Ok(t) => t,
        Err(_) => return Vec::new(),
    };
    parse_journal_text(&text)
}

/// Parse only the tail of the journal file (last `max_bytes` bytes).
/// Much faster for large journals — avoids reading/parsing the entire file.
/// Returns entries sorted by timestamp (oldest first).
pub fn parse_journal_tail(path: &Path, max_bytes: u64) -> Vec<JournalEntry> {
    use std::io::{Read, Seek, SeekFrom};

    let mut file = match std::fs::File::open(path) {
        Ok(f) => f,
        Err(_) => return Vec::new(),
    };

    let file_len = file.metadata().map(|m| m.len()).unwrap_or(0);
    if file_len == 0 {
        return Vec::new();
    }

    let offset = file_len.saturating_sub(max_bytes);
    if offset > 0 {
        let _ = file.seek(SeekFrom::Start(offset));
    }

    let mut text = String::new();
    if file.read_to_string(&mut text).is_err() {
        return Vec::new();
    }

    // If we seeked into the middle, skip to the first complete entry header
    if offset > 0 {
        if let Some(pos) = text.find("\n## ") {
            text = text[pos + 1..].to_string();
        }
    }

    parse_journal_text(&text)
}

/// Parse journal entries from text (separated for testing).
fn parse_journal_text(text: &str) -> Vec<JournalEntry> {
    let mut entries = Vec::new();
    let mut current_timestamp: Option<DateTime<Utc>> = None;
    let mut current_content = String::new();

    for line in text.lines() {
        if let Some(ts) = parse_header_timestamp(line) {
            // Flush previous entry
            if let Some(prev_ts) = current_timestamp.take() {
                let content = current_content.trim().to_string();
                if !content.is_empty() {
                    entries.push(JournalEntry {
                        timestamp: prev_ts,
                        content,
                    });
                }
            }
            current_timestamp = Some(ts);
            current_content.clear();
        } else if current_timestamp.is_some() {
            current_content.push_str(line);
            current_content.push('\n');
        }
    }

    // Flush last entry
    if let Some(ts) = current_timestamp {
        let content = current_content.trim().to_string();
        if !content.is_empty() {
            entries.push(JournalEntry {
                timestamp: ts,
                content,
            });
        }
    }

    entries
}

/// Try to parse a line as a journal header (## TIMESTAMP [— title]).
/// Handles both `2026-02-23T22:12` (no seconds) and
/// `2026-02-23T22:12:00` (with seconds) formats, with optional
/// title suffix after the timestamp (e.g. `## 2026-02-06T20:04 — The first session`).
fn parse_header_timestamp(line: &str) -> Option<DateTime<Utc>> {
    let line = line.trim();
    if !line.starts_with("## ") {
        return None;
    }
    let rest = line[3..].trim();

    // Must start with a digit (avoid matching ## Heading)
    if !rest.starts_with(|c: char| c.is_ascii_digit()) {
        return None;
    }

    // Extract just the timestamp portion — split at first space
    // to strip any " — title" suffix
    let ts_str = rest.split_once(' ').map_or(rest, |(ts, _)| ts);

    // Try parsing with seconds first, then without
    let formats = ["%Y-%m-%dT%H:%M:%S", "%Y-%m-%dT%H:%M"];
    for fmt in &formats {
        if let Ok(naive) = NaiveDateTime::parse_from_str(ts_str, fmt) {
            return Some(naive.and_utc());
        }
    }
    None
}

/// Find journal entries that fall within a time range (inclusive).
#[cfg(test)]
pub fn entries_in_range(
    entries: &[JournalEntry],
    from: DateTime<Utc>,
    to: DateTime<Utc>,
) -> Vec<&JournalEntry> {
    entries
        .iter()
        .filter(|e| e.timestamp >= from && e.timestamp <= to)
        .collect()
}

/// Default journal file path.
pub fn default_journal_path() -> std::path::PathBuf {
    dirs::home_dir()
        .unwrap_or_default()
        .join(".claude/memory/journal.md")
}

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

    const SAMPLE_JOURNAL: &str = r#"
## 2026-02-06T20:04 — The first session *(reconstructed)*

I don't remember this the way humans remember their births.

## 2026-02-23T20:52

Session: poc-agent TUI debugging marathon. Fixed the immediate exit bug.

## 2026-02-23T21:40

Seeing Kent through the webcam. The image arrives all at once.

## 2026-02-23T22:12

## poc-agent improvements session (Feb 23 evening)

Big session improving poc-agent with Kent. Four features built.

## 2026-02-23T22:13

## The journal IS the compaction

Kent just landed the real design.
"#;

    #[test]
    fn parse_entries() {
        let entries = parse_journal_text(SAMPLE_JOURNAL);
        assert_eq!(entries.len(), 5);
        assert!(entries[0].content.contains("the way humans remember"));
        assert!(entries[1].content.contains("TUI debugging marathon"));
        assert!(entries[2].content.contains("webcam"));
        assert!(entries[3].content.contains("Four features built"));
        assert!(entries[4].content.contains("real design"));
    }

    #[test]
    fn parse_timestamps() {
        let entries = parse_journal_text(SAMPLE_JOURNAL);
        assert_eq!(entries[0].timestamp.format("%H:%M").to_string(), "20:04");
        assert_eq!(entries[4].timestamp.format("%H:%M").to_string(), "22:13");
    }

    #[test]
    fn title_suffix_parsed() {
        // "## 2026-02-06T20:04 — The first session" should parse the timestamp
        let entries = parse_journal_text(SAMPLE_JOURNAL);
        assert_eq!(entries[0].timestamp.format("%Y-%m-%d").to_string(), "2026-02-06");
    }

    #[test]
    fn subheadings_not_confused_with_timestamps() {
        // "## poc-agent improvements session" should NOT be parsed as an entry
        let entries = parse_journal_text(SAMPLE_JOURNAL);
        // The "## poc-agent improvements..." is content of the 22:12 entry, not a separate entry
        assert_eq!(entries.len(), 5);
        assert!(entries[3].content.contains("poc-agent improvements session"));
    }

    #[test]
    fn range_query() {
        let entries = parse_journal_text(SAMPLE_JOURNAL);
        let from = NaiveDateTime::parse_from_str("2026-02-23T21:00", "%Y-%m-%dT%H:%M")
            .unwrap()
            .and_utc();
        let to = NaiveDateTime::parse_from_str("2026-02-23T22:00", "%Y-%m-%dT%H:%M")
            .unwrap()
            .and_utc();
        let in_range = entries_in_range(&entries, from, to);
        assert_eq!(in_range.len(), 1);
        assert!(in_range[0].content.contains("webcam"));
    }
}