//! Memory writes mirrored in Honcho (M5c spec, section 4): each journalled edit is decided into
//! the ledger the moment it is journalled, one item per Honcho action, in the order they must be
//! sent. Only decided here; the worker sends (task 13). The text is kept as journalled.

use std::sync::{Arc, Mutex};

use bxcore::{SessionId, Timestamp};

use crate::files::Store;
use crate::honcho::ledger::{self, Action, Item, Ledger, Record, Workspace};
use crate::honcho::report;
use crate::journal;
use crate::notes::{self, Kind};

/// The session the journal gives an owner's edit (`bxctl memory undo`).
pub const OWNER: &str = "owner";

/// The part of an edit that has no Boxmaker session to stamp its conclusion with.
pub const NO_SESSION: &str = "the edit has no Boxmaker session";

/// `before` and `after` as multisets of entry text: what `before` has more of (dropped, in
/// `before`'s order), and what `after` has more of (added, in `after`'s order).
pub fn diff(before: &[String], after: &[String]) -> (Vec<String>, Vec<String>) {
    (minus(before, after), minus(after, before))
}

/// `a` without one occurrence of each text of `b`, in `a`'s order.
fn minus(a: &[String], b: &[String]) -> Vec<String> {
    let mut left: Vec<&String> = b.iter().collect();
    let mut out: Vec<String> = Vec::new();
    for text in a {
        match left.iter().position(|t| *t == text) {
            Some(at) => {
                left.swap_remove(at);
            }
            None => out.push(text.clone()),
        }
    }
    out
}

/// The journalled notes of `record`, read back.
fn notes_of(record: &journal::Record) -> Vec<notes::Note> {
    record.notes.iter().flat_map(|n| notes::parse(n)).collect()
}

/// The session an edit's conclusions carry: its own, or for an owner's undo the undone edit's,
/// following `undoes` back through undos of undos. `None` when there is none.
pub fn session_of(record: &journal::Record, records: &[journal::Record]) -> Option<SessionId> {
    let mut current = record;
    for _ in 0..=records.len() {
        if current.session != OWNER {
            return SessionId::new(&current.session).ok();
        }
        let undone = current.undoes.as_deref()?;
        current = records.iter().find(|r| r.id == undone)?;
    }
    None
}

/// A conclusion about `peer` in the trusted workspace, stamped with `session`; without a session
/// it cannot be stamped, and is a `Skip`.
fn conclusion(peer: &str, session: Option<&SessionId>, text: &str) -> Action {
    match session {
        Some(session) => Action::Conclude {
            workspace: Workspace::Trusted,
            peer: peer.to_string(),
            session: session.clone(),
            text: text.to_string(),
        },
        None => Action::Skip {
            why: NO_SESSION.to_string(),
        },
    }
}

/// An identity edit (an undo included), `file` its name: each entry dropped, a conclusion
/// deleted, then each entry added, a conclusion made, about the owner for `user.md` and the agent
/// for `memory.md`. Entries `consolidate` moved to notes are not dropped: they are still held.
fn identity_actions(
    record: &journal::Record,
    file: &str,
    notes: &[notes::Note],
    session: Option<&SessionId>,
    agent: &str,
    owner: &str,
) -> Vec<Action> {
    let moved: Vec<String> = notes
        .iter()
        .filter(|n| matches!(n.kind, Kind::Moved(_)))
        .map(|n| n.text.clone())
        .collect();
    let (dropped, added) = diff(&record.before, &record.after);
    let peer = if file == "user.md" { owner } else { agent };
    let mut out: Vec<Action> = minus(&dropped, &moved)
        .into_iter()
        .map(|text| Action::Unconclude {
            workspace: Workspace::Trusted,
            text,
        })
        .collect();
    out.extend(added.iter().map(|text| conclusion(peer, session, text)));
    out
}

/// A write saved as notes: when flagged, one `Skip` naming the rule; otherwise each `noted` note,
/// a fleet message when the write was untrusted, else a conclusion about the agent.
fn note_actions(
    record: &journal::Record,
    notes: &[notes::Note],
    session: Option<&SessionId>,
    agent: &str,
) -> Vec<Action> {
    if let Some(rule) = &record.flag {
        return vec![Action::Skip {
            why: format!("flagged: {rule}"),
        }];
    }
    notes
        .iter()
        .filter(|n| matches!(n.kind, Kind::Noted { .. }))
        .map(|n| {
            if record.untrusted {
                match session {
                    Some(session) => Action::Fleet {
                        session: session.clone(),
                        text: n.text.clone(),
                    },
                    None => Action::Skip {
                        why: NO_SESSION.to_string(),
                    },
                }
            } else {
                conclusion(agent, session, &n.text)
            }
        })
        .collect()
}

/// What `record` asks of Honcho, in the order to send it: an identity edit's, or a write saved as
/// notes. Anything else (a rejection) asks nothing.
pub fn actions(
    record: &journal::Record,
    session: Option<&SessionId>,
    agent: &str,
    owner: &str,
) -> Vec<Action> {
    let notes = notes_of(record);
    match &record.file {
        Some(file) => identity_actions(record, file, &notes, session, agent, owner),
        None => note_actions(record, &notes, session, agent),
    }
}

/// With `[honcho]`: decides each journalled edit into the ledger.
pub struct Mirror {
    ledger: Arc<Mutex<Ledger>>,
    agent: String,
    owner: String,
}

impl Mirror {
    pub fn new(ledger: Arc<Mutex<Ledger>>, agent: &str, owner: &str) -> Mirror {
        Mirror {
            ledger,
            agent: agent.to_string(),
            owner: owner.to_string(),
        }
    }

    /// `bxctl memory sync`'s report of the ledger, under the ledger's lock alone.
    pub fn report(&self) -> String {
        report::report(&self.ledger.lock().unwrap_or_else(|p| p.into_inner()))
    }

    /// Decide the journalled edit `id` (the latest when `None`), called under the index lock
    /// right after it was journalled, so the ledger has the journal's order. Its parts are
    /// `Edit { id, part }` from 0. An edit already decided, or asking nothing, adds no line. A
    /// failure is logged; the edit itself stands.
    pub fn journalled(&self, store: &Store, id: Option<&str>, now: Timestamp, log: &dyn Fn(&str)) {
        let records = match journal::records(store) {
            Ok(records) => records,
            Err(e) => {
                log(&format!(
                    "memoryd: {e}; the edit is not mirrored in Honcho; {}",
                    ledger::RUNBOOK
                ));
                return;
            }
        };
        let found = match id {
            Some(id) => records.iter().find(|r| r.id == id),
            None => records.last(),
        };
        let Some(record) = found else {
            return;
        };
        let session = session_of(record, &records);
        let actions = actions(record, session.as_ref(), &self.agent, &self.owner);
        let mut book = self.ledger.lock().unwrap_or_else(|p| p.into_inner());
        for (part, action) in actions.into_iter().enumerate() {
            let Ok(part) = u32::try_from(part) else {
                return;
            };
            let item = Item::Edit {
                id: record.id.clone(),
                part,
            };
            if book.is_decided(&item) {
                continue;
            }
            if let Err(e) = book.append(Record::Decided {
                time: now,
                item,
                action,
            }) {
                log(&format!("memoryd: {e}; {}", ledger::RUNBOOK));
                return;
            }
        }
    }
}