// Conversation transcript abstraction.
//
// Core code consumes normalized user/assistant messages through this module.
// Product-specific log formats live in the small compatibility sources below.

use memmap2::Mmap;
use serde_json::Value;
use std::fs;
use std::path::Path;

pub mod claude;
pub mod codex;
pub mod jsonl;

pub use jsonl::JsonlBackwardIter;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TranscriptRole {
    User,
    Assistant,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TranscriptMessage {
    pub role: TranscriptRole,
    pub text: String,
    pub timestamp: Option<String>,
    pub offset: u64,
}

pub trait ConversationSource {
    fn parse_message(&self, obj: &Value, offset: u64) -> Option<TranscriptMessage>;
    fn is_compaction(&self, obj: &Value) -> bool;

    fn may_contain_compaction(&self, _obj_bytes: &[u8]) -> bool {
        true
    }
}

pub struct AnyConversationSource;

impl ConversationSource for AnyConversationSource {
    fn parse_message(&self, obj: &Value, offset: u64) -> Option<TranscriptMessage> {
        claude::ClaudeSource.parse_message(obj, offset)
            .or_else(|| codex::CodexSource.parse_message(obj, offset))
    }

    fn is_compaction(&self, obj: &Value) -> bool {
        claude::ClaudeSource.is_compaction(obj) || codex::CodexSource.is_compaction(obj)
    }

    fn may_contain_compaction(&self, obj_bytes: &[u8]) -> bool {
        claude::ClaudeSource.may_contain_compaction(obj_bytes)
            || codex::CodexSource.may_contain_compaction(obj_bytes)
    }
}

/// Find the byte offset of the last compaction marker in mmap'd transcript data.
/// Returns the byte offset of the JSON object's opening brace.
pub(crate) fn find_last_compaction(data: &[u8]) -> Option<usize> {
    find_last_compaction_with(data, &AnyConversationSource)
}

pub(crate) fn find_last_compaction_with(
    data: &[u8],
    source: &impl ConversationSource,
) -> Option<usize> {
    for (offset, obj_bytes) in JsonlBackwardIter::new(data) {
        // Quick byte check before parsing large transcript entries.
        if !source.may_contain_compaction(obj_bytes) {
            continue;
        }

        let obj: Value = match serde_json::from_slice(obj_bytes) {
            Ok(v) => v,
            Err(_) => continue,
        };

        if source.is_compaction(&obj) {
            return Some(offset);
        }
    }

    None
}

/// Find the byte offset of the last compaction in a transcript file.
/// Returns None if the file can't be opened or has no compaction.
pub(crate) fn find_last_compaction_in_file(path: &str) -> Option<u64> {
    if path.is_empty() { return None; }

    let file = fs::File::open(path).ok()?;
    let meta = file.metadata().ok()?;
    if meta.len() == 0 { return None; }

    let mmap = unsafe { Mmap::map(&file).ok()? };
    find_last_compaction(&mmap).map(|off| off as u64)
}

/// Mmap a transcript file. Returns (Mmap, File) to keep both alive.
pub(crate) fn mmap_transcript(path: &str) -> Option<(Mmap, fs::File)> {
    let file = fs::File::open(path).ok()?;
    let meta = file.metadata().ok()?;
    if meta.len() == 0 { return None; }
    let mmap = unsafe { Mmap::map(&file).ok()? };
    Some((mmap, file))
}

/// Reverse iterator over user/assistant messages in a transcript file.
/// Yields normalized transcript messages newest-first. The caller decides
/// when to stop (byte budget, count, etc).
pub struct TailMessages {
    _file: fs::File,
    mmap: Mmap,
    pos: usize,
}

impl TailMessages {
    pub fn open(path: &str) -> Option<Self> {
        let (mmap, file) = mmap_transcript(path)?;
        let pos = mmap.len();
        Some(Self { _file: file, mmap, pos })
    }
}

impl Iterator for TailMessages {
    type Item = TranscriptMessage;

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            let (offset, obj_bytes) = jsonl::JsonlBackwardIter::new(&self.mmap[..self.pos]).next()?;
            self.pos = offset;

            let obj: Value = match serde_json::from_slice(obj_bytes) {
                Ok(v) => v,
                Err(_) => continue,
            };

            if let Some(message) = AnyConversationSource.parse_message(&obj, offset as u64) {
                return Some(message);
            }
        }
    }
}

/// Get the timestamp of the compaction message at a given byte offset.
/// Returns a human-readable datetime string, or None if unavailable.
pub fn compaction_timestamp(path: &str, offset: u64) -> Option<String> {
    let (mmap, _file) = mmap_transcript(path)?;
    let start = offset as usize;
    if start >= mmap.len() { return None; }

    // Find the end of this JSONL line
    let end = mmap[start..].iter().position(|&b| b == b'\n')
        .map(|p| start + p)
        .unwrap_or(mmap.len());

    let obj: Value = serde_json::from_slice(&mmap[start..end]).ok()?;

    if let Some(ts) = obj.get("timestamp").and_then(|v| v.as_str()) {
        return Some(ts.to_string());
    }

    for field in &["createdAt", "created_at", "time"] {
        if let Some(ts) = obj.get(*field).and_then(|v| v.as_str()) {
            return Some(ts.to_string());
        }
    }

    None
}

/// Detect whether a compaction has occurred since the last check.
///
/// Compares the current compaction offset against a saved value in
/// `state_dir/compaction-{session_id}`. Returns true if a new
/// compaction was found. Updates the saved offset.
pub fn detect_new_compaction(
    state_dir: &Path,
    session_id: &str,
    transcript_path: &str,
) -> bool {
    let offset = find_last_compaction_in_file(transcript_path);

    let save_path = state_dir.join(format!("compaction-{}", session_id));
    let saved: Option<u64> = fs::read_to_string(&save_path)
        .ok()
        .and_then(|s| s.trim().parse().ok());

    let is_new = match (offset, saved) {
        (Some(cur), Some(prev)) => cur != prev,
        (Some(_), None) => true,
        _ => false,
    };

    // Save current offset
    if let Some(off) = offset {
        fs::write(&save_path, off.to_string()).ok();
    }

    is_new
}

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

    fn write_temp_jsonl(content: &str) -> tempfile::NamedTempFile {
        let mut file = tempfile::NamedTempFile::new().unwrap();
        file.write_all(content.as_bytes()).unwrap();
        file.flush().unwrap();
        file
    }

    #[test]
    fn tail_messages_yields_normalized_messages_newest_first() {
        let file = write_temp_jsonl(
            r#"{"timestamp":"2026-06-15T15:00:00.000Z","type":"user","message":{"content":"claude user"}}
{"timestamp":"2026-06-15T15:00:01.000Z","type":"assistant","message":{"content":[{"type":"text","text":"claude assistant"}]}}
{"timestamp":"2026-06-15T15:00:02.000Z","type":"event_msg","payload":{"type":"user_message","message":"codex user"}}
{"timestamp":"2026-06-15T15:00:03.000Z","type":"event_msg","payload":{"type":"task_started"}}
{"timestamp":"2026-06-15T15:00:04.000Z","type":"event_msg","payload":{"type":"agent_message","message":"codex assistant"}}
"#,
        );

        let messages: Vec<_> = TailMessages::open(&file.path().to_string_lossy())
            .unwrap()
            .collect();

        assert_eq!(messages.len(), 4);
        assert_eq!(messages[0].text, "codex assistant");
        assert_eq!(messages[1].text, "codex user");
        assert_eq!(messages[2].text, "claude assistant");
        assert_eq!(messages[3].text, "claude user");
        assert!(messages[0].offset > messages[1].offset);
    }

    #[test]
    fn detects_claude_and_codex_compactions() {
        let claude = br#"{"timestamp":"2026-06-15T15:00:00.000Z","type":"user","message":{"content":"normal"}}
{"timestamp":"2026-06-15T15:00:01.000Z","type":"user","message":{"content":"This session is being continued from a previous conversation."}}
"#;
        let codex = br#"{"timestamp":"2026-06-15T15:00:00.000Z","type":"event_msg","payload":{"type":"user_message","message":"normal"}}
{"timestamp":"2026-06-15T15:00:01.000Z","type":"event_msg","payload":{"type":"context_compacted"}}
"#;

        assert!(find_last_compaction(claude).is_some());
        assert!(find_last_compaction(codex).is_some());
    }

    #[test]
    fn detect_new_compaction_tracks_offset_changes() {
        let transcript = write_temp_jsonl(
            r#"{"timestamp":"2026-06-15T15:00:00.000Z","type":"event_msg","payload":{"type":"context_compacted"}}
"#,
        );
        let state = tempfile::tempdir().unwrap();

        assert!(detect_new_compaction(
            state.path(),
            "session",
            &transcript.path().to_string_lossy(),
        ));
        assert!(!detect_new_compaction(
            state.path(),
            "session",
            &transcript.path().to_string_lossy(),
        ));
    }
}