mushroomdb-query 0.2.0

//! Cypher subset AST. Types match the Plan 3 Task 6 interface block.

use crate::filter::CmpOp;
use core_storage::Value;

/// A LIMIT or SKIP value: either an exact count or a named query parameter.
///
/// `$name` parameters are resolved at execution time from the params map and
/// validated to be a non-negative integer.
#[derive(Debug, Clone, PartialEq)]
pub enum LimitSkip {
    Exact(u64),
    Param(String),
}

/// One `OPTIONAL MATCH pattern [WHERE expr]` clause.
///
/// If the pattern produces no rows for a given input row, the input row
/// survives with the optional variables set to `null` (left-outer-join
/// semantics, openCypher §10.1.3).
///
/// `where_expr`, when present, is applied INSIDE the optional scope:
/// it filters candidate rows before the left-outer fallback fires.  This
/// differs from a post-filter that would eliminate the null row entirely.
#[derive(Debug, Clone, PartialEq)]
pub struct OptionalClause {
    pub patterns: Vec<Pattern>,
    /// WHERE clause scoped to this optional match (applied before nullification).
    pub where_expr: Option<Expr>,
}

#[derive(Debug, Clone, PartialEq)]
pub struct Query {
    pub matches: Vec<Pattern>,
    /// `OPTIONAL MATCH` clauses that follow the required matches.
    pub optional_clauses: Vec<OptionalClause>,
    /// Top-level WHERE filter, evaluated before UNWIND expansion.
    pub where_expr: Option<Expr>,
    /// Top-level UNWIND clauses (after WHERE, before post_unwind_where/WITH/RETURN).
    pub unwinds: Vec<UnwindClause>,
    /// Optional WHERE evaluated after UNWIND expansion (references UNWIND aliases).
    pub post_unwind_where: Option<Expr>,
    /// WITH pipeline stages. Each stage carries a WITH clause and optional
    /// MATCH / UNWIND / WHERE that follow it.
    pub stages: Vec<WithStage>,
    pub returns: Vec<RetItem>,
    /// `RETURN DISTINCT …` — executor hashes projected rows after `Project`.
    pub distinct: bool,
    pub order_by: Vec<OrderItem>,
    pub skip: Option<LimitSkip>,
    pub limit: Option<LimitSkip>,
}

/// One `UNWIND <expr> AS <alias>` clause.
#[derive(Debug, Clone, PartialEq)]
pub struct UnwindClause {
    pub list: UnwindExpr,
    pub alias: String,
}

/// The expression whose value is iterated in UNWIND.
#[derive(Debug, Clone, PartialEq)]
pub enum UnwindExpr {
    /// Inline list literal: `[1, 2, 3]`.
    Lit(Vec<Value>),
    /// Property on a bound node: `n.tags`.
    Prop { var: String, field: String },
    /// A previously bound alias (from a prior WITH): `alias`.
    Var(String),
}

/// One WITH stage in a pipeline:
/// ```text
/// WITH <items> [WHERE <expr>] [ORDER BY …] [SKIP n] [LIMIT n]
/// [MATCH …]* [OPTIONAL MATCH …]* [UNWIND …]* [WHERE <expr>]
/// ```
#[derive(Debug, Clone, PartialEq)]
pub struct WithStage {
    /// The projected items in the WITH clause.
    pub items: Vec<RetItem>,
    /// Optional WHERE / HAVING filter immediately after the WITH keyword.
    pub where_expr: Option<Expr>,
    pub order_by: Vec<OrderItem>,
    pub skip: Option<LimitSkip>,
    pub limit: Option<LimitSkip>,
    /// MATCH clauses that follow this WITH.
    pub matches: Vec<Pattern>,
    /// OPTIONAL MATCH clauses that follow the required MATCHes in this stage.
    pub optional_clauses: Vec<OptionalClause>,
    /// UNWIND clauses that follow this WITH.
    pub unwinds: Vec<UnwindClause>,
    /// WHERE clause that follows those MATCHes (pre-next-WITH/RETURN filter).
    pub post_where: Option<Expr>,
}

/// Aggregate function in a RETURN clause.
#[derive(Debug, Clone, PartialEq)]
pub enum AggFunc {
    Count,
    Sum,
    Avg,
    Min,
    Max,
}

/// Argument to an aggregate function.
#[derive(Debug, Clone, PartialEq)]
pub enum AggArg {
    /// `COUNT(*)` — every matched row counts regardless of binding.
    Star,
    /// `COUNT(var)` — counts rows where `var` is bound (non-null).
    Var(String),
    /// `SUM(var.field)`, `AVG(var.field)`, etc.
    Prop { var: String, field: String },
}

/// Hop-count range for variable-length relationship patterns (`*min..max`).
/// Both bounds are inclusive.  `min = max` is a fixed-hop pattern.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct HopRange {
    pub min: u8,
    pub max: u8,
}

#[derive(Debug, Clone, PartialEq)]
pub struct Pattern {
    pub start: NodePat,
    pub chain: Vec<(RelPat, NodePat)>,
    /// True when parsed as `MATCH shortestPath(...)`.
    pub shortest: bool,
}

#[derive(Debug, Clone, PartialEq)]
pub struct NodePat {
    pub var: Option<String>,
    pub label: Option<String>,
    pub props: Vec<(String, Operand)>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum RelDir {
    Right,
    Left,
    Undirected,
}

#[derive(Debug, Clone, PartialEq)]
pub struct RelPat {
    pub var: Option<String>,
    pub etype: Option<String>,
    pub dir: RelDir,
    /// `None` = single-hop (normal `Expand`).  `Some(r)` = variable-length
    /// (`VarExpand`) with the given min/max hop bounds.
    pub hops: Option<HopRange>,
}

#[derive(Debug, Clone, PartialEq)]
pub enum Expr {
    And(Box<Expr>, Box<Expr>),
    Or(Box<Expr>, Box<Expr>),
    Not(Box<Expr>),
    Cmp {
        lhs: Operand,
        op: CmpOp,
        rhs: Operand,
    },
    /// Standalone operand used as a boolean predicate.
    ///
    /// Enables `WHERE textMatches(n.bio, 'query')` without requiring an
    /// explicit comparison.  Truthiness: `Bool(true)` → true, `Bool(false)`
    /// → false, null → false, any other non-null non-false value → true.
    Truthy(Operand),
    /// `operand IS NULL` — true iff the operand evaluates to null.
    IsNull(Operand),
    /// `operand IS NOT NULL` — true iff the operand is non-null.
    IsNotNull(Operand),
    /// `expr IN [a, b, $p]` or `expr IN $list` (`$list` is `Value::List`).
    In {
        expr: Operand,
        list: Vec<Operand>,
    },
}

#[derive(Debug, Clone, PartialEq)]
pub enum Operand {
    Prop {
        var: String,
        field: String,
    },
    Lit(Value),
    Param(String),
    /// Bare variable reference (used in `WITH … WHERE alias > 2`).
    Var(String),
    /// Scalar function call: `toLower(n.name)`, `size(n.tags)`, `type(r)`, etc.
    ///
    /// Supported functions (case-insensitive): `toLower`, `toUpper`, `size`,
    /// `coalesce`, `type`, `abs`, `round`.  Unknown names → named error at
    /// execution time listing the supported set.
    FuncCall {
        name: String,
        args: Vec<Operand>,
    },
    /// Arithmetic expression inside a function argument: `abs(n.age - 27)`,
    /// `round(n.score * 1.5)`.  Supports `+`, `-`, `*`, `/`.
    BinArith {
        op: ArithOp,
        left: Box<Operand>,
        right: Box<Operand>,
    },
}

/// Arithmetic operators for `Operand::BinArith`.
#[derive(Debug, Clone, PartialEq)]
pub enum ArithOp {
    Add,
    Sub,
    Mul,
    Div,
}

/// RETURN item value: bare variable, `var.field`, an aggregate call, a
/// scalar function call, or an arbitrary scalar expression (arithmetic etc.).
#[derive(Debug, Clone, PartialEq)]
pub enum RetVal {
    Var(String),
    Prop {
        var: String,
        field: String,
    },
    /// Single aggregate function call.  When combined with non-aggregate items
    /// in the same RETURN clause, the planner routes to `GroupAggregate`.
    /// Multiple aggregate items are also supported via `GroupAggregate`.
    Agg {
        func: AggFunc,
        arg: AggArg,
    },
    /// Scalar function call in a RETURN position, e.g. `toLower(n.name)`.
    /// The same function set as `Operand::FuncCall`.
    FuncCall {
        name: String,
        args: Vec<Operand>,
    },
    /// Arbitrary scalar expression in a RETURN/WITH position, e.g. `n.age + 1`.
    /// Evaluated via `resolve_operand` at execution time; null propagates.
    ScalarExpr(Operand),
}

#[derive(Debug, Clone, PartialEq)]
pub struct RetItem {
    pub value: RetVal,
    pub alias: Option<String>,
}

/// ORDER BY target. Bare identifiers that match a RETURN alias become `Alias`;
/// otherwise they stay `Var`. `var.field` is always `Prop`.
#[derive(Debug, Clone, PartialEq)]
pub enum OrderTarget {
    Alias(String),
    Var(String),
    Prop { var: String, field: String },
}

#[derive(Debug, Clone, PartialEq)]
pub struct OrderItem {
    pub target: OrderTarget,
    pub descending: bool,
}

// ─── Write statement AST ──────────────────────────────────────────────────────

/// Top-level write statement (CREATE / MATCH…SET / MATCH…DELETE / MATCH…DETACH DELETE / MERGE).
/// Produced by `parse_write`; executed by `GraphDb::query_write`.
#[derive(Debug, Clone, PartialEq)]
pub enum WriteStatement {
    Create(CreateStmt),
    MatchSet(MatchSetStmt),
    MatchDelete(MatchDeleteStmt),
    MatchDeleteNode(MatchDeleteNodeStmt),
    Merge(MergeStmt),
}

/// `CREATE (a:L {id: 'x', ...})[-[:T]->(b:L2 {id: 'y', ...})] [RETURN …]`
///
/// `nodes` is in encounter order. `edges` reference node vars that appear in
/// `nodes`. Each node must have a string-valued `id` property (used as key).
///
/// `returns`, when `Some`, projects the created bindings as a read result.
/// The write and the projection are committed as a single WAL batch frame.
#[derive(Debug, Clone, PartialEq)]
pub struct CreateStmt {
    pub nodes: Vec<CreateNode>,
    pub edges: Vec<CreateEdge>,
    /// Optional RETURN clause: project created bindings after commit.
    pub returns: Option<Vec<RetItem>>,
}

/// One node in a CREATE pattern.
#[derive(Debug, Clone, PartialEq)]
pub struct CreateNode {
    /// Optional binding variable (`a` in `(a:Label {…})`).
    pub var: Option<String>,
    pub label: String,
    /// Literal property pairs.  Must include a string-valued `id` field.
    pub props: Vec<(String, core_storage::Value)>,
}

/// One edge in a CREATE pattern, referencing vars from `CreateStmt.nodes`.
#[derive(Debug, Clone, PartialEq)]
pub struct CreateEdge {
    pub src_var: String,
    pub etype: String,
    pub dst_var: String,
}

/// `MATCH patterns [WHERE expr] SET var.field = literal [, …] [RETURN …]`
#[derive(Debug, Clone, PartialEq)]
pub struct MatchSetStmt {
    pub matches: Vec<Pattern>,
    pub where_expr: Option<Expr>,
    pub sets: Vec<SetClause>,
    /// Optional RETURN clause: project matched bindings from post-write state.
    pub returns: Option<Vec<RetItem>>,
}

/// One `var.field = literal_or_param` assignment in a SET clause.
///
/// `value` is an `Operand` rather than a bare `Value` so that `$param`
/// references are legal on the RHS (resolved at execution time from the
/// query's parameter map).  Only `Operand::Lit` and `Operand::Param` are
/// accepted by the parser; other variants produce a named parse error.
#[derive(Debug, Clone, PartialEq)]
pub struct SetClause {
    pub var: String,
    pub field: String,
    pub value: Operand,
}

/// `MATCH patterns [WHERE expr] DELETE rel_var [, …]`
///
/// Each `EdgeDelete` carries the etype, src node var, and dst node var resolved
/// from the MATCH patterns at parse time so the executor can emit a read query
/// returning node keys without extra pattern-scanning.
#[derive(Debug, Clone, PartialEq)]
pub struct MatchDeleteStmt {
    pub matches: Vec<Pattern>,
    pub where_expr: Option<Expr>,
    pub deletes: Vec<EdgeDelete>,
}

/// One edge variable to delete, with resolved topology.
#[derive(Debug, Clone, PartialEq)]
pub struct EdgeDelete {
    pub rel_var: String,
    pub etype: String,
    pub src_var: String,
    pub dst_var: String,
}

/// `MATCH patterns [WHERE expr] [DETACH] DELETE node_var [, …]`
///
/// When `detach` is `true` (DETACH DELETE), all incident edges are removed
/// before the node is tombstoned (openCypher semantics).  When `false`
/// (bare DELETE), the node must have no incident edges; the executor returns
/// an error if any remain.
#[derive(Debug, Clone, PartialEq)]
pub struct MatchDeleteNodeStmt {
    pub matches: Vec<Pattern>,
    pub where_expr: Option<Expr>,
    /// Node variable names whose nodes are to be deleted (resolved from MATCH patterns).
    pub node_vars: Vec<String>,
    /// `true` → DETACH DELETE (allowed regardless of edges).
    /// `false` → bare DELETE (error if any edges touch the node).
    pub detach: bool,
}

/// `MERGE (n:Label {id: 'x'}) [ON CREATE SET …] [ON MATCH SET …] [RETURN …]`
///
/// Exactly one property is allowed (the key). More properties → named error.
/// `ON CREATE SET` / `ON MATCH SET` apply inside the same write batch as the
/// insert-or-skip. `returns`, when `Some`, projects the node after commit.
#[derive(Debug, Clone, PartialEq)]
pub struct MergeStmt {
    pub label: String,
    /// The single property that identifies the node. Value must be a string.
    pub key_field: String,
    pub key_value: core_storage::Value,
    /// Optional bound variable for the MERGE node (for RETURN projection).
    pub var: Option<String>,
    /// `ON CREATE SET` assignments, applied only when the node is inserted.
    pub on_create: Vec<SetClause>,
    /// `ON MATCH SET` assignments, applied only when the node already exists.
    pub on_match: Vec<SetClause>,
    /// Optional RETURN clause: project the node after commit.
    pub returns: Option<Vec<RetItem>>,
}