//! Applying a `memory` call (M5a spec, section 5). `note` records experience in any session;
//! the identity actions change `memory.md` or `user.md`, and only a session that has not read
//! untrusted content may use them. Every refusal is a fixed sentence: it reaches the model.

use std::collections::HashSet;

use bxcore::{DataClass, MemoryArgs, MemoryFile, Timestamp};

use crate::check::check;
use crate::entries;
use crate::files::{Store, grouped};
use crate::notes::{Kind, Note, minute};

/// The session a call comes from, as `brokerd` saw it when it decided the call.
#[derive(Debug, Clone)]
pub struct Context {
    pub session: String,
    pub call: u64,
    pub taint: DataClass,
    pub untrusted: bool,
    pub now: Timestamp,
}

/// What an applied call changed: an identity file's entries before and after (both empty for a
/// note), and the notes it appended.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Change {
    pub file: Option<MemoryFile>,
    pub before: Vec<String>,
    pub after: Vec<String>,
    pub notes: Vec<Note>,
}

/// The answer to the model, and the change for the journal.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Outcome {
    pub action: &'static str,
    pub answer: String,
    pub change: Change,
}

/// The sentence for a write over a file's limit.
pub fn over_limit(file: MemoryFile, size: usize) -> String {
    format!(
        "{} would be {} of {} characters; use consolidate to move entries to notes",
        file.name(),
        grouped(size),
        grouped(file.limit())
    )
}

/// The sentence for an identity edit other than `add` from a session that read untrusted content.
pub fn untrusted_refusal(file: MemoryFile) -> String {
    format!(
        "this session has read untrusted content; it can take notes but not change {}",
        file.name()
    )
}

/// The answer when an untrusted session's `add` became a note. It names the file it did not change:
/// on the device the model read a shorter answer as success.
pub fn saved_as_note(file: MemoryFile) -> String {
    format!(
        "not added to {}: this session has read untrusted content, so it was saved in notes.md as an untrusted note",
        file.name()
    )
}

/// The answer to a `note` from a session that has not read untrusted content.
pub const NOTED: &str = "saved in notes.md";

/// The answer to a `note` from a session that has read untrusted content.
pub const NOTED_UNTRUSTED: &str =
    "saved in notes.md, marked untrusted: this session has read untrusted content";

fn stale(file: MemoryFile) -> String {
    format!(
        "no entry of {} is exactly this text; the file may have changed; nothing was changed",
        file.name()
    )
}

fn checked(text: &str) -> Result<String, String> {
    check(text).map_err(|refused| refused.sentence().to_string())?;
    Ok(text.trim().to_string())
}

fn note(ctx: &Context, kind: Kind, text: &str) -> Note {
    Note {
        kind,
        time: minute(ctx.now),
        session: ctx.session.clone(),
        text: text.to_string(),
    }
}

/// Apply `args` for the session in `ctx`. `Err` is the sentence for the model; nothing changed.
pub fn apply(store: &Store, args: &MemoryArgs, ctx: &Context) -> Result<Outcome, String> {
    // 1. `args.check()?`.
    args.check()?;
    // 2. A Note: return `noted(store, ctx, text, "note")`. Otherwise take the file.
    let file = match args {
        MemoryArgs::Note { text } => {
            return noted(store, ctx, text, "note");
        }
        MemoryArgs::Add { file, .. }
        | MemoryArgs::Replace { file, .. }
        | MemoryArgs::Remove { file, .. }
        | MemoryArgs::Consolidate { file, .. } => *file,
    };
    // 3. When `ctx.untrusted`: an Add becomes `noted(store, ctx, text, "add")?` with its answer
    //    replaced by saved_as_note(file); any other action -> Err(untrusted_refusal(file)).
    if ctx.untrusted {
        match args {
            MemoryArgs::Add { text, .. } => {
                let outcome = noted(store, ctx, text, "add")?;
                return Ok(Outcome {
                    answer: saved_as_note(file),
                    ..outcome
                });
            }
            _ => return Err(untrusted_refusal(file)),
        }
    }
    // 4. `let before = store.entries(file)?;` then `let (action, after, moved) = edited(file,
    //    &before, args, ctx)?;`.
    let before = store.entries(file)?;
    let (action, after, moved) = edited(file, &before, args, ctx)?;
    // 5. When `after` holds the same entry twice (collect into a HashSet and compare lengths):
    //    Err(format!("{} would hold the same entry twice", file.name())).
    let unique: HashSet<&String> = after.iter().collect();
    if unique.len() != after.len() {
        return Err(format!("{} would hold the same entry twice", file.name()));
    }
    // 6. `size = entries::size(&after)`; size > file.limit() -> Err(over_limit(file, size)).
    let size = entries::size(&after);
    if size > file.limit() {
        return Err(over_limit(file, size));
    }
    // 7. `store.write_entries(file, &after)?`, then `store.append("notes.md", &note.render())?` for
    //    each note in `moved`.
    store.write_entries(file, &after)?;
    for entry in &moved {
        store.append("notes.md", &entry.render())?;
    }
    // 8. Ok(Outcome { action, answer: format!("{} updated ({} of {} characters); it takes effect in
    //    the next session", file.name(), grouped(size), grouped(file.limit())), change: Change {
    //    file: Some(file), before, after, notes: moved } }).
    Ok(Outcome {
        action,
        answer: format!(
            "{} updated ({} of {} characters); it takes effect in the next session",
            file.name(),
            grouped(size),
            grouped(file.limit())
        ),
        change: Change {
            file: Some(file),
            before,
            after,
            notes: moved,
        },
    })
}

fn edited(
    file: MemoryFile,
    before: &[String],
    args: &MemoryArgs,
    ctx: &Context,
) -> Result<(&'static str, Vec<String>, Vec<Note>), String> {
    match args {
        MemoryArgs::Add { text, .. } => {
            let text = checked(text)?;
            if before.contains(&text) {
                return Err(format!("{} already has this entry", file.name()));
            }
            let mut after = before.to_vec();
            after.push(text);
            Ok(("add", after, Vec::new()))
        }
        MemoryArgs::Replace { old, text, .. } => {
            let pos = position(before, old).ok_or_else(|| stale(file))?;
            let text = checked(text)?;
            if before
                .iter()
                .enumerate()
                .any(|(i, e)| i != pos && *e == text)
            {
                return Err(format!("{} already has this entry", file.name()));
            }
            let mut after = before.to_vec();
            after[pos] = text;
            Ok(("replace", after, Vec::new()))
        }
        MemoryArgs::Remove { old, .. } => {
            let pos = position(before, old).ok_or_else(|| stale(file))?;
            let gone = before[pos].clone();
            let mut after = before.to_vec();
            after.remove(pos);
            Ok(("remove", after, vec![note(ctx, Kind::Dropped(file), &gone)]))
        }
        MemoryArgs::Consolidate { entries, .. } => {
            let (after, notes) = consolidate(file, before, entries, ctx)?;
            Ok(("consolidate", after, notes))
        }
        MemoryArgs::Note { .. } => Err(
            "a note is not an identity edit".to_string(), // `apply` takes notes before it asks for an identity edit.
        ),
    }
}

/// Where `old` is, matched exactly (after trimming, as entries are stored).
fn position(list: &[String], old: &str) -> Option<usize> {
    list.iter().position(|e| e == old.trim())
}

fn noted(
    store: &Store,
    ctx: &Context,
    text: &str,
    action: &'static str,
) -> Result<Outcome, String> {
    let text = checked(text)?;
    let entry = note(
        ctx,
        Kind::Noted {
            class: ctx.taint,
            untrusted: ctx.untrusted,
        },
        &text,
    );
    store.append("notes.md", &entry.render())?;
    Ok(Outcome {
        action,
        answer: if ctx.untrusted {
            NOTED_UNTRUSTED
        } else {
            NOTED
        }
        .to_string(),
        change: Change {
            file: None,
            before: Vec::new(),
            after: Vec::new(),
            notes: vec![entry],
        },
    })
}

/// Mark the entry `old` names as named: stale if `before` has no such entry, an error if it was
/// named already.
fn claim(
    file: MemoryFile,
    before: &[String],
    named: &mut HashSet<usize>,
    old: &str,
) -> Result<(), String> {
    let pos = position(before, old).ok_or_else(|| stale(file))?;
    if named.insert(pos) {
        Ok(())
    } else {
        Err(format!(
            "consolidate names an entry of {} twice",
            file.name()
        ))
    }
}

fn consolidate(
    file: MemoryFile,
    before: &[String],
    lines: &[bxcore::ConsolidateEntry],
    ctx: &Context,
) -> Result<(Vec<String>, Vec<Note>), String> {
    let mut named: HashSet<usize> = HashSet::new();
    let mut after = Vec::new();
    let mut out = Vec::new();
    for line in lines {
        let action = line.action().map_err(|e| e.to_string())?;
        match action {
            bxcore::EntryAction::Keep(old) => {
                claim(file, before, &mut named, &old)?;
                after.push(old.trim().to_string());
            }
            bxcore::EntryAction::Rewrite { old, text } => {
                claim(file, before, &mut named, &old)?;
                after.push(checked(&text)?);
            }
            bxcore::EntryAction::Move(old) => {
                claim(file, before, &mut named, &old)?;
                out.push(note(ctx, Kind::Moved(file), old.trim()));
            }
            bxcore::EntryAction::Drop(old) => {
                claim(file, before, &mut named, &old)?;
                out.push(note(ctx, Kind::Dropped(file), old.trim()));
            }
            bxcore::EntryAction::New(text) => {
                after.push(checked(&text)?);
            }
        }
    }
    let missing = before.len() - named.len();
    if missing != 0 {
        return Err(format!(
            "consolidate must name every entry of {}; it leaves out {missing}",
            file.name()
        ));
    }
    Ok((after, out))
}