//! 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;
use crate::notes::Note;

/// 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.
    todo!()
}

/// 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).
    todo!()
}

/// 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.
    todo!()
}

/// 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".
    todo!()
}

/// 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})")).
    todo!()
}