//! The order of the articles of a section, a module (ADR 0009) — the rules are
//! the engine's (`ld_engine::order`); here, the database and the door to
//! propose one.
//!
//! - The version in force is the order the section reads in now: its articles
//!   one can see, by position. The text the engine compares for it is that live
//!   order, so it always reads what the reader shows.
//! - A proposal is another order of the same articles, each once. While it is
//!   under vote, articles may enter the section or leave it: it is completed at
//!   the end (`ld_engine::order::fit`), and its votes stay.
//! - Entering into force gives the section's places out again in the new order;
//!   the articles keep their texts, their votes, their sections.

use crate::AppState;
use crate::auth::User;
use crate::docs::{self, DocState, ProposalRow, UnitRow};
use crate::error::{AppError, AppResult};
use crate::modules::{self, ModuleKind, NewVersion};
use crate::util;
use axum::Json;
use axum::extract::{Path, State};
use ld_engine::order::{self, Article, OrderError};
use serde::Deserialize;
use serde_json::{Value, json};
use sqlx::SqliteConnection;

/// More articles than any section will hold: a longer list is refused unread.
const MAX_ARTICLES: usize = 500;

/// Every section of a document, in the order of the document, with the articles
/// of its order now (read inside a transaction: the seed writes them in it).
pub async fn sections_now(conn: &mut SqliteConnection, doc_id: &str) -> sqlx::Result<Vec<(String, Vec<String>)>> {
    #[derive(sqlx::FromRow)]
    struct Row {
        id: String,
        section: Option<String>,
        position: f64,
        visible: bool,
    }
    // Seen: a text in force, or an open version (`DocState::members` says the same). It reads
    // only the columns of before 0012: a document born now, or given its modules by an
    // amendment, holds no retired unit (ADR 0014); `article_amend` keeps the live ones.
    let rows = sqlx::query_as::<_, Row>(
        "SELECT u.id, u.section, u.position,
                (u.in_force_id IS NOT NULL OR EXISTS (SELECT 1 FROM proposals p
                   WHERE p.unit_id = u.id AND p.status = 'open' AND p.kind IN ('text', 'remove'))) AS visible
           FROM units u WHERE u.doc_id = ? AND u.kind = 'article' ORDER BY u.position, u.id",
    )
    .bind(doc_id)
    .fetch_all(&mut *conn)
    .await?;
    let articles: Vec<Article<'_>> = rows
        .iter()
        .map(|r| Article { id: &r.id, section: r.section.as_deref(), position: r.position, visible: r.visible })
        .collect();
    let mut sections: Vec<String> = Vec::new();
    for r in &rows {
        if let Some(s) = &r.section
            && !sections.contains(s)
        {
            sections.push(s.clone());
        }
    }
    Ok(sections
        .into_iter()
        .map(|s| {
            let members = order::members(&articles, &s);
            (s, members)
        })
        .collect())
}

/// The order an order version gives its section now, as the screen tells it.
pub fn version_json(st: &DocState, unit: &UnitRow, p: &ProposalRow) -> Value {
    let members = st.members(unit.section.as_deref().unwrap_or_default());
    if p.status == "in_force" {
        return json!({ "ids": members, "added": [], "dropped": [], "same": true });
    }
    match order::decode(&p.body) {
        Some(proposed) => {
            let f = order::fit(&proposed, &members);
            let same = f.order == members;
            json!({ "ids": f.order, "added": f.added, "dropped": f.dropped, "same": same })
        }
        None => json!({ "ids": [], "added": [], "dropped": [], "same": false, "unreadable": true }),
    }
}

/// The order enters into force: its articles take the section's places in its order.
pub async fn enter(conn: &mut SqliteConnection, st: &DocState, unit: &UnitRow, p: &ProposalRow) -> AppResult<()> {
    let members = st.members(unit.section.as_deref().unwrap_or_default());
    // An unreadable order is blocked: it never comes this far.
    let Some(proposed) = order::decode(&p.body) else { return Ok(()) };
    let fitted = order::fit(&proposed, &members);
    let current: Vec<(String, f64)> = members
        .iter()
        .filter_map(|id| st.units.iter().find(|u| &u.id == id).map(|u| (id.clone(), u.position)))
        .collect();
    for (id, position) in order::positions(&fitted.order, &current) {
        sqlx::query("UPDATE units SET position = ? WHERE id = ? AND doc_id = ? AND kind = 'article'")
            .bind(position)
            .bind(&id)
            .bind(&st.doc.id)
            .execute(&mut *conn)
            .await?;
    }
    tracing::info!(doc = %st.doc.id, unit = %unit.code, added = fitted.added.len(), dropped = fitted.dropped.len(), "order of a section in force");
    Ok(())
}

#[derive(Deserialize)]
pub struct OrderBody {
    /// Every article of the section (unit ids), each once, in the order proposed.
    order: Vec<String>,
}

/// Propose another order for a section. An open proposal that already reads in
/// this order is given back rather than doubled.
pub async fn propose(
    State(state): State<AppState>,
    User(user): User,
    Path(unit_id): Path<String>,
    Json(b): Json<OrderBody>,
) -> AppResult<Json<Value>> {
    let doc_id: String = sqlx::query_scalar("SELECT doc_id FROM units WHERE id = ?")
        .bind(&unit_id)
        .fetch_optional(&state.db)
        .await?
        .ok_or(AppError::NotFound)?;
    let st = docs::load_state(&state, &doc_id).await?;
    docs::require_open(&state, &user, &st.group).await?;
    let unit = st.units.iter().find(|u| u.id == unit_id).ok_or(AppError::NotFound)?;
    if st.module_of(&unit.id) != Some(ModuleKind::Order) {
        return Err(AppError::Invalid("not_an_order"));
    }
    if b.order.len() > MAX_ARTICLES {
        return Err(AppError::Invalid("order"));
    }
    let members = st.members(unit.section.as_deref().unwrap_or_default());
    order::check(&b.order, &members).map_err(|e| match e {
        OrderError::NotTheSection => AppError::Invalid("order"),
        OrderError::Unchanged => AppError::Invalid("same_order"),
    })?;
    if let Some(existing) = st.proposals.iter().find(|p| {
        p.unit_id == unit.id
            && p.status == "open"
            && p.kind == ModuleKind::Order.as_str()
            && order::decode(&p.body).is_some_and(|o| order::fit(&o, &members).order == b.order)
    }) {
        return Ok(Json(json!({ "id": existing.id, "existing": true })));
    }
    let now = util::now();
    let mut conn = state.db.acquire().await?;
    let id = modules::insert_version(
        &mut conn,
        NewVersion {
            unit_id: &unit.id,
            kind: ModuleKind::Order,
            title: &unit.code,
            body: &order::canonical(&b.order),
            author: Some(&user.id),
            in_force: false,
            now: &now,
        },
    )
    .await?;
    Ok(Json(json!({ "id": id, "existing": false })))
}