rustango 0.14.2

//! Query layer for rustango.
//!
//! v0.1 ships a typed `QuerySet<T>` that builds an `AND`-joined `WHERE`
//! clause and compiles to the dialect-neutral `SelectQuery` IR in
//! `rustango-core`. `UpdateBuilder<T>` mirrors the same shape for `UPDATE`,
//! and `QuerySet<T>` itself is the input to bulk delete. The dynamic
//! resolver lands in week 5.

use std::marker::PhantomData;

use crate::core::{
    Assignment, DeleteQuery, Filter, Model, ModelSchema, Op, QueryError, SelectQuery, SqlValue,
    TypedAssignment, TypedExpr, UpdateQuery, WhereExpr,
};

/// A lazy builder for a `SELECT` over `T`.
///
/// Filters are accumulated in insertion order; nothing touches the schema
/// until `compile` is called, so the builder never panics on bad input.
///
/// Two filter shapes are accepted and may be mixed freely:
/// * [`Self::filter`] / [`Self::eq`] — string-keyed, validated at
///   `compile` time.
/// * [`Self::where_`] — typed (`User::id.gt(10)`); the column is already
///   resolved, so it bypasses the schema lookup at compile time.
pub struct QuerySet<T: Model> {
    pending: Vec<PendingFilter>,
    limit: Option<i64>,
    offset: Option<i64>,
    /// FK field names registered for [`Self::select_related`] — slice
    /// 9.0d. Each name resolves to a `Join` against the FK target at
    /// `compile()` time, so the SELECT pulls the parent rows along
    /// with the children in a single SQL round trip.
    select_related: Vec<String>,
    /// `(field_name, desc)` pairs registered via [`Self::order_by`].
    /// Slice 9.0b. Resolved against the schema at `compile()` time.
    order_by: Vec<(String, bool)>,
    _model: PhantomData<fn() -> T>,
}

/// Filter accumulator entry — keeps insertion order across string-keyed and
/// typed filter calls. Each entry contributes one node to the final
/// `WhereExpr::And` clause.
enum PendingFilter {
    /// String-keyed; resolved against the schema at `compile` time.
    Raw(RawFilter),
    /// Already resolved by a typed [`Column`](crate::core::Column).
    Resolved(Filter),
    /// Typed sub-expression (built via `.and()` / `.or()` on the
    /// typed-column API). Already validated; contributes a whole
    /// sub-tree to the WHERE clause.
    Expr(WhereExpr),
}

#[derive(Debug, Clone)]
struct RawFilter {
    field: String,
    op: Op,
    value: SqlValue,
}

#[derive(Debug, Clone)]
struct RawAssignment {
    field: String,
    value: SqlValue,
}

impl<T: Model> Default for QuerySet<T> {
    fn default() -> Self {
        Self::new()
    }
}

impl<T: Model> QuerySet<T> {
    #[must_use]
    pub fn new() -> Self {
        Self {
            pending: Vec::new(),
            limit: None,
            offset: None,
            select_related: Vec::new(),
            order_by: Vec::new(),
            _model: PhantomData,
        }
    }

    /// Append `ORDER BY` columns. Slice 9.0b.
    ///
    /// Each entry is a `(field_name, desc)` pair where `field_name`
    /// is a Rust-side field on the model — schema validation runs at
    /// `compile()` time. Multiple `.order_by(...)` calls compose;
    /// subsequent calls append after earlier ones (left-to-right
    /// precedence).
    ///
    /// ```ignore
    /// let posts = Post::objects()
    ///     .order_by(&[("published_at", true)])  // newest first
    ///     .fetch_on(conn).await?;
    /// ```
    ///
    /// To sort by multiple columns:
    ///
    /// ```ignore
    /// .order_by(&[("category", false), ("published_at", true)])
    /// ```
    #[must_use]
    pub fn order_by(mut self, items: &[(&str, bool)]) -> Self {
        for (field, desc) in items {
            self.order_by.push(((*field).to_owned(), *desc));
        }
        self
    }

    /// Eagerly load a `ForeignKey<Parent>` field via a `LEFT JOIN` —
    /// Django's `select_related`. Pass the field name on `T` (not the
    /// FK column or the parent table); subsequent `fetch_on` returns
    /// rows where each `ForeignKey<Parent>` is `Loaded` after a
    /// **single** SQL query, no N+1.
    ///
    /// ```ignore
    /// let posts: Vec<Post> = Post::objects()
    ///     .select_related("author")
    ///     .fetch_on(conn).await?;
    /// // post.author is ForeignKey::Loaded { pk, value }
    /// ```
    ///
    /// Multiple `.select_related()` calls compose: each adds another
    /// `LEFT JOIN` to the same SELECT. Schema validation (the field
    /// exists, is an FK, has a primary-key target) happens at
    /// `compile()` time.
    #[must_use]
    pub fn select_related(mut self, field: impl Into<String>) -> Self {
        self.select_related.push(field.into());
        self
    }

    /// Cap the number of returned rows. `None` removes any previously set limit.
    #[must_use]
    pub fn limit(mut self, n: i64) -> Self {
        self.limit = Some(n);
        self
    }

    /// Skip the first `n` rows. Pair with [`limit`](Self::limit) for paging.
    #[must_use]
    pub fn offset(mut self, n: i64) -> Self {
        self.offset = Some(n);
        self
    }

    /// Append a `WHERE field <op> value` predicate.
    ///
    /// `field` is the Rust-side field name; the column is looked up from the
    /// schema at compile time.
    #[must_use]
    pub fn filter(mut self, field: impl Into<String>, op: Op, value: impl Into<SqlValue>) -> Self {
        self.pending.push(PendingFilter::Raw(RawFilter {
            field: field.into(),
            op,
            value: value.into(),
        }));
        self
    }

    /// Sugar for `filter(field, Op::Eq, value)`.
    #[must_use]
    pub fn eq(self, field: impl Into<String>, value: impl Into<SqlValue>) -> Self {
        self.filter(field, Op::Eq, value)
    }

    /// Append a typed predicate or boolean expression built via the
    /// [`Column`](crate::core::Column) API. Accepts either a single
    /// [`TypedFilter`](crate::core::TypedFilter) (`User::id.gt(10)`)
    /// or a composed [`TypedExpr`] (`User::id.eq(1).or(User::id.eq(2))`).
    /// Every `.where_()` call AND-joins its argument into the
    /// queryset's accumulated WHERE clause.
    #[must_use]
    pub fn where_<E: Into<TypedExpr<T>>>(mut self, predicate: E) -> Self {
        let expr = predicate.into().into_expr();
        // Hoist a bare predicate into the legacy `Resolved` slot so
        // the resulting WhereExpr stays a flat AND-of-predicates for
        // simple chains — preserves the v0.6 `as_flat_and()` shape.
        match expr {
            WhereExpr::Predicate(filter) => {
                self.pending.push(PendingFilter::Resolved(filter));
            }
            other => {
                self.pending.push(PendingFilter::Expr(other));
            }
        }
        self
    }

    /// Validate the accumulated filters against `T::SCHEMA` and lower to
    /// the dialect-neutral `SelectQuery` IR.
    ///
    /// # Errors
    /// Returns [`QueryError::UnknownField`] if a filter names a field not
    /// present on the model, and [`QueryError::TypeMismatch`] if the bound
    /// value's type does not match the field's declared type.
    pub fn compile(self) -> Result<SelectQuery, QueryError> {
        let model: &'static ModelSchema = T::SCHEMA;
        let where_clause = resolve_pending(model, self.pending)?;
        let joins = lower_select_related(model, &self.select_related)?;
        let order_by = lower_order_by(model, &self.order_by)?;
        Ok(SelectQuery {
            model,
            where_clause,
            search: None,
            joins,
            order_by,
            limit: self.limit,
            offset: self.offset,
        })
    }

    /// Lower this queryset to a `DeleteQuery` — same WHERE clause, no projection.
    ///
    /// # Errors
    /// As [`QuerySet::compile`].
    pub fn compile_delete(self) -> Result<DeleteQuery, QueryError> {
        let model: &'static ModelSchema = T::SCHEMA;
        let where_clause = resolve_pending(model, self.pending)?;
        Ok(DeleteQuery {
            model,
            where_clause,
        })
    }

    /// Start an `UpdateBuilder` carrying this queryset's filters as the WHERE clause.
    #[must_use]
    pub fn update(self) -> UpdateBuilder<T> {
        UpdateBuilder {
            qs: self,
            set: Vec::new(),
        }
    }
}

/// Accumulates `SET column = value` assignments, then compiles to an `UpdateQuery`.
///
/// Constructed via [`QuerySet::update`]. The queryset's filters become the
/// WHERE clause; an empty queryset produces an unfiltered update affecting
/// every row.
pub struct UpdateBuilder<T: Model> {
    qs: QuerySet<T>,
    set: Vec<PendingAssignment>,
}

enum PendingAssignment {
    Raw(RawAssignment),
    Resolved(Assignment),
}

impl<T: Model> UpdateBuilder<T> {
    /// Append a `SET field = value` assignment. Last write wins for repeated fields.
    #[must_use]
    pub fn set(mut self, field: impl Into<String>, value: impl Into<SqlValue>) -> Self {
        self.set.push(PendingAssignment::Raw(RawAssignment {
            field: field.into(),
            value: value.into(),
        }));
        self
    }

    /// Append a typed `SET column = value` from a [`Column`](crate::core::Column).
    #[must_use]
    pub fn set_typed(mut self, assignment: TypedAssignment<T>) -> Self {
        self.set
            .push(PendingAssignment::Resolved(assignment.into_assignment()));
        self
    }

    /// Validate against `T::SCHEMA` and lower to an `UpdateQuery`.
    ///
    /// # Errors
    /// Returns [`QueryError::UnknownField`] if any `set` or filter names an
    /// unknown field, and [`QueryError::TypeMismatch`] if any bound value's
    /// type doesn't match the field's declared type.
    pub fn compile(self) -> Result<UpdateQuery, QueryError> {
        let model: &'static ModelSchema = T::SCHEMA;

        let assignments = self
            .set
            .into_iter()
            .map(|p| match p {
                PendingAssignment::Raw(raw) => resolve_assignment(model, raw),
                PendingAssignment::Resolved(assignment) => Ok(assignment),
            })
            .collect::<Result<Vec<_>, _>>()?;

        let where_clause = resolve_pending(model, self.qs.pending)?;

        Ok(UpdateQuery {
            model,
            set: assignments,
            where_clause,
        })
    }
}

/// Convert `(field_name, desc)` pairs into `OrderClause`s by
/// resolving each field name on the schema. Slice 9.0b.
fn lower_order_by(
    model: &'static ModelSchema,
    items: &[(String, bool)],
) -> Result<Vec<crate::core::OrderClause>, QueryError> {
    let mut out = Vec::with_capacity(items.len());
    for (field_name, desc) in items {
        let field = model
            .field(field_name)
            .ok_or_else(|| QueryError::UnknownField {
                model: model.name,
                field: field_name.clone(),
            })?;
        out.push(crate::core::OrderClause {
            column: field.column,
            desc: *desc,
        });
    }
    Ok(out)
}

/// Convert `select_related` field names into `Join`s — slice 9.0d.
///
/// For each name: look up the field on `model`, verify it's a
/// `Relation::Fk`, find the target schema in inventory, build a
/// `Join` projecting all of the target's columns. Errors out on any
/// unresolvable name with a clear `SelectRelatedInvalid` reason.
fn lower_select_related(
    model: &'static ModelSchema,
    names: &[String],
) -> Result<Vec<crate::core::Join>, QueryError> {
    use crate::core::{inventory, Join, ModelEntry, Relation};
    let mut out: Vec<Join> = Vec::with_capacity(names.len());
    for name in names {
        let field = model
            .field(name)
            .ok_or_else(|| QueryError::SelectRelatedInvalid {
                model: model.name,
                field: name.clone(),
                reason: format!("no field `{name}` on this model"),
            })?;
        let (to, on) = match field.relation {
            Some(Relation::Fk { to, on }) | Some(Relation::O2O { to, on }) => (to, on),
            _ => {
                return Err(QueryError::SelectRelatedInvalid {
                    model: model.name,
                    field: name.clone(),
                    reason: "not a `ForeignKey<T>` field".into(),
                });
            }
        };
        let target = inventory::iter::<ModelEntry>
            .into_iter()
            .find(|e| e.schema.table == to)
            .map(|e| e.schema)
            .ok_or_else(|| QueryError::SelectRelatedInvalid {
                model: model.name,
                field: name.clone(),
                reason: format!(
                    "target table `{to}` is not registered (is the parent's `#[derive(Model)]` linked into the binary?)"
                ),
            })?;
        // Project every column on the target so the decoder has the
        // full row to rebuild a `Target` instance.
        let project: Vec<&'static str> =
            target.scalar_fields().map(|f| f.column).collect();
        out.push(Join {
            target,
            on_local: field.column,
            on_remote: on,
            // The Rust field name is unique within the model, so it
            // makes a clean alias prefix that doesn't collide with
            // other JOINs the writer or admin might add later.
            alias: field.name,
            project,
        });
    }
    Ok(out)
}

fn resolve_pending(
    model: &'static ModelSchema,
    pending: Vec<PendingFilter>,
) -> Result<WhereExpr, QueryError> {
    let mut nodes: Vec<WhereExpr> = Vec::with_capacity(pending.len());
    for entry in pending {
        match entry {
            PendingFilter::Raw(raw) => {
                nodes.push(WhereExpr::Predicate(resolve_filter(model, raw)?));
            }
            PendingFilter::Resolved(filter) => {
                nodes.push(WhereExpr::Predicate(filter));
            }
            PendingFilter::Expr(expr) => {
                nodes.push(expr);
            }
        }
    }
    Ok(WhereExpr::And(nodes))
}

fn resolve_filter(model: &'static ModelSchema, raw: RawFilter) -> Result<Filter, QueryError> {
    let field = model
        .field(&raw.field)
        .ok_or_else(|| QueryError::UnknownField {
            model: model.name,
            field: raw.field.clone(),
        })?;

    // `IsNull` carries a Bool sentinel (true = IS NULL, false = IS NOT NULL),
    // not a value to compare against the field — skip the type check.
    // `In` carries a List; element-by-element checking is a follow-up.
    let skip_type_check = matches!(raw.op, Op::IsNull | Op::In);

    if !skip_type_check {
        if let Some(value_ty) = raw.value.field_type() {
            if value_ty != field.ty {
                return Err(QueryError::TypeMismatch {
                    model: model.name,
                    field: raw.field,
                    expected: field.ty,
                    actual: value_ty,
                });
            }
        }
    }

    Ok(Filter {
        column: field.column,
        op: raw.op,
        value: raw.value,
    })
}

fn resolve_assignment(
    model: &'static ModelSchema,
    raw: RawAssignment,
) -> Result<Assignment, QueryError> {
    let field = model
        .field(&raw.field)
        .ok_or_else(|| QueryError::UnknownField {
            model: model.name,
            field: raw.field.clone(),
        })?;

    if let Some(value_ty) = raw.value.field_type() {
        if value_ty != field.ty {
            return Err(QueryError::TypeMismatch {
                model: model.name,
                field: raw.field,
                expected: field.ty,
                actual: value_ty,
            });
        }
    }

    Ok(Assignment {
        column: field.column,
        value: raw.value,
    })
}