//! The edit journal: one JSON line per applied edit in `memory/edits/YYYY-MM.jsonl`, the owner's
//! record of every write, and `undo` of the latest edit of a file (M5a spec, section 5).

use serde::{Deserialize, Serialize};

use proto::{MemoryFile, Timestamp};

use crate::edit::{Context, Outcome};
use crate::files::Store;

/// One line of the journal.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Record {
    /// `YYYY-MM-DD-NNNN`, numbered from 1 each day.
    pub id: String,
    pub time: String,
    pub session: String,
    pub call: u64,
    /// `add`, `replace`, `remove`, `consolidate`, `note`, or `undo`.
    pub action: String,
    /// The identity file changed, if any.
    pub file: Option<String>,
    /// Where the write went: `memory.md`, `user.md` or `notes.md`.
    pub to: String,
    pub before: Vec<String>,
    pub after: Vec<String>,
    /// The `notes.md` entries appended, as written.
    pub notes: Vec<String>,
    pub untrusted: bool,
    /// For an undo, the edit it reverted.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub undoes: Option<String>,
}

fn file_of(name: &str) -> Option<MemoryFile> {
    match name {
        "memory.md" => Some(MemoryFile::Memory),
        "user.md" => Some(MemoryFile::User),
        _ => None,
    }
}

/// Every record, oldest first, from every month's file.
pub fn records(store: &Store) -> Result<Vec<Record>, String> {
    // Read the directory `store.path("edits")`: NotFound -> Ok(empty); another error ->
    // Err(format!("{}: {e}", dir.display())). Take the names that end ".jsonl" and sort them. For
    // each file, `read_to_string` and parse every line as a Record with serde_json; a bad line ->
    // Err(format!("{}: line {}: {e}", path.display(), n + 1)) with n counted from 0. Return all
    // records, oldest first.
    let dir = store.path("edits");
    let mut paths: Vec<std::path::PathBuf> = match std::fs::read_dir(&dir) {
        Ok(rd) => rd
            .filter_map(|entry| entry.ok().map(|e| e.path()))
            .collect(),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(Vec::new()),
        Err(e) => return Err(format!("{}: {e}", dir.display())),
    };
    paths.retain(|p| {
        p.file_name()
            .and_then(|s| s.to_str())
            .is_some_and(|n| n.ends_with(".jsonl"))
    });
    paths.sort();
    let mut out: Vec<Record> = Vec::new();
    for path in paths {
        let text =
            std::fs::read_to_string(&path).map_err(|e| format!("{}: {e}", path.display()))?;
        for (n, line) in text.lines().enumerate() {
            let record: Record = serde_json::from_str(line)
                .map_err(|e| format!("{}: line {}: {e}", path.display(), n + 1))?;
            out.push(record);
        }
    }
    Ok(out)
}

/// Append a record, giving it the next id of its day.
pub(crate) fn append(store: &Store, mut record: Record, now: Timestamp) -> Result<String, String> {
    // 1. `day` is the first 10 characters of `now.to_rfc3339()` ("0000-00-00" if shorter).
    // 2. `taken` = how many of `records(store)?` have an id starting format!("{day}-").
    // 3. record.id = format!("{day}-{:04}", taken + 1).
    // 4. `create_dir_all(store.path("edits"))` (an error names the directory),
    //    `serde_json::to_string(&record)`, then `store.append(&format!("edits/{month}.jsonl"),
    //    &format!("{line}\n"))?` where month is the first 7 characters of day. Ok(record.id).
    let rfc = now.to_rfc3339();
    let day = rfc.get(..10).unwrap_or("0000-00-00");
    let taken = records(store)?
        .iter()
        .filter(|r| r.id.starts_with(&format!("{day}-")))
        .count();
    record.id = format!("{day}-{:04}", taken + 1);
    let edits_dir = store.path("edits");
    std::fs::create_dir_all(&edits_dir).map_err(|e| format!("{}: {e}", edits_dir.display()))?;
    let line = serde_json::to_string(&record).map_err(|e| e.to_string())?;
    let month = day.get(..7).unwrap_or("0000-00");
    store.append(&format!("edits/{month}.jsonl"), &format!("{line}\n"))?;
    Ok(record.id)
}

/// Journal an applied call; the id it was given.
pub fn record(store: &Store, ctx: &Context, outcome: &Outcome) -> Result<String, String> {
    // `append` a Record: id empty (append sets it), time `ctx.now.to_rfc3339()`, session and call
    // from ctx, action `outcome.action`, file `change.file` as its name, to that name or "notes.md"
    // when there is no file, before and after from the change, notes the change's notes each
    // `render()`ed, untrusted `ctx.untrusted`, undoes None; `now` is ctx.now.
    let change = &outcome.change;
    let notes: Vec<String> = change.notes.iter().map(|n| n.render()).collect();
    let file = change.file.map(|f| f.name().to_string());
    let to = match &file {
        Some(name) => name.clone(),
        None => "notes.md".to_string(),
    };
    append(
        store,
        Record {
            id: String::new(),
            time: ctx.now.to_rfc3339(),
            session: ctx.session.clone(),
            call: ctx.call,
            action: outcome.action.to_string(),
            file,
            to,
            before: change.before.clone(),
            after: change.after.clone(),
            notes,
            untrusted: ctx.untrusted,
            undoes: None,
        },
        ctx.now,
    )
}

/// The last `count` records, one line each, oldest first.
pub fn log(store: &Store, count: usize) -> Result<String, String> {
    // The last `count` of `records(store)?` (all of them when fewer), oldest first, one line each:
    // format!("{}  {}  {}  {}  {}{}", id, time, session, action, to, and "  untrusted" when the
    // record is untrusted), joined by newlines. With no records at all: "no memory edits yet".
    let all = records(store)?;
    if all.is_empty() {
        return Ok("no memory edits yet".to_string());
    }
    let selected = &all[all.len().saturating_sub(count)..];
    let lines: Vec<String> = selected
        .iter()
        .map(|r| {
            if r.untrusted {
                format!(
                    "{}  {}  {}  {}  {}  untrusted",
                    r.id, r.time, r.session, r.action, r.to
                )
            } else {
                format!(
                    "{}  {}  {}  {}  {}",
                    r.id, r.time, r.session, r.action, r.to
                )
            }
        })
        .collect();
    Ok(lines.join("\n"))
}

/// Revert edit `id`, if it is the latest edit of its identity file and the file still holds
/// exactly what it left. Notes it appended stay (the file is append-only). The undo is journalled.
pub fn undo(store: &Store, id: &str, now: Timestamp) -> Result<String, String> {
    // 1. Find the record with this id in `records(store)?`, else Err(format!("no edit {id}")).
    // 2. Its file must be Some and known to `file_of`, else Err(format!("{id} changed no identity
    //    file; notes are append-only")).
    // 3. The latest record whose file is the same name must be this one, else Err(format!("{id} is
    //    not the latest edit of {name}")).
    // 4. `store.entries(file)?` must equal record.after, else Err(format!("{name} has changed since
    //    {id}; nothing was undone")).
    // 5. `store.write_entries(file, &record.before)?`, then `append` a Record: session "owner",
    //    call 0, action "undo", file and to the name, before the current entries, after
    //    record.before, no notes, untrusted false, undoes Some(id).
    // 6. Ok(format!("undone: {id} ({name} restored; journalled as {undo_id})")).
    let all = records(store)?;
    let record = all
        .iter()
        .find(|r| r.id == id)
        .ok_or_else(|| format!("no edit {id}"))?;
    let name: &str = match &record.file {
        Some(n) => n,
        None => {
            return Err(format!(
                "{id} changed no identity file; notes are append-only"
            ));
        }
    };
    let file = match file_of(name) {
        Some(f) => f,
        None => {
            return Err(format!(
                "{id} changed no identity file; notes are append-only"
            ));
        }
    };
    let latest = all.iter().rev().find(|r| r.file.as_deref() == Some(name));
    if latest.is_none_or(|r| r.id != id) {
        return Err(format!("{id} is not the latest edit of {name}"));
    }
    let current = store.entries(file)?;
    if current != record.after {
        return Err(format!("{name} has changed since {id}; nothing was undone"));
    }
    store.write_entries(file, &record.before)?;
    let undo_id = append(
        store,
        Record {
            id: String::new(),
            time: now.to_rfc3339(),
            session: "owner".to_string(),
            call: 0,
            action: "undo".to_string(),
            file: Some(name.to_string()),
            to: name.to_string(),
            before: current,
            after: record.before.clone(),
            notes: Vec::new(),
            untrusted: false,
            undoes: Some(id.to_string()),
        },
        now,
    )?;
    Ok(format!(
        "undone: {id} ({name} restored; journalled as {undo_id})"
    ))
}