From 2b12c41095bd31de83b8fe03dddedac507fd6b35 Mon Sep 17 00:00:00 2001
From: Richard Newman <rnewman@twinql.com>
Date: Mon, 7 May 2018 22:33:35 -0700
Subject: [PATCH] WIP: nested pull.

---
 query-parser/src/parse.rs |  6 +++++-
 query-pull/src/errors.rs  |  5 +++++
 query-pull/src/lib.rs     | 30 ++++++++++++++++++++++++++++--
 query/src/lib.rs          | 26 +++++++++++++++++++++++++-
 4 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/query-parser/src/parse.rs b/query-parser/src/parse.rs
index 244a0cca..886917e4 100644
--- a/query-parser/src/parse.rs
+++ b/query-parser/src/parse.rs
@@ -366,7 +366,11 @@ fn validate_attributes<'a, I>(attrs: I) -> std::result::Result<(), &'static str>
                     return Err("wildcard with specified attributes");
                 }
             },
-            // TODO: map form.
+            &PullAttributeSpec::Nested(ref _attr, ref patterns) => {
+                if patterns.is_empty() {
+                    return Err("empty nested pull map");
+                }
+            },
         }
     }
     Ok(())
diff --git a/query-pull/src/errors.rs b/query-pull/src/errors.rs
index 94c38426..871bb47f 100644
--- a/query-pull/src/errors.rs
+++ b/query-pull/src/errors.rs
@@ -27,6 +27,11 @@ error_chain! {
             description(":db/id repeated")
             display(":db/id repeated")
         }
+
+        NonRefNestedPullAttribute {
+            description("nested pull attribute is non-ref")
+            display("nested pull attribute is non-ref")
+        }
     }
 
     links {
diff --git a/query-pull/src/lib.rs b/query-pull/src/lib.rs
index 26ee1895..2af6fe0e 100644
--- a/query-pull/src/lib.rs
+++ b/query-pull/src/lib.rs
@@ -88,6 +88,7 @@ use mentat_core::{
     StructuredMap,
     TypedValue,
     ValueRc,
+    ValueType,
 };
 
 use mentat_db::cache;
@@ -144,8 +145,18 @@ pub struct Puller {
     // The domain of this map is the set of attributes to fetch.
     // The range is the set of aliases to use in the output.
     attributes: BTreeMap<Entid, ValueRc<NamespacedKeyword>>,
+
+    // The original spec for this puller.
     attribute_spec: cache::AttributeSpec,
+
+    // If :db/id is mentioned in the attribute list, its alias is this.
     db_id_alias: Option<ValueRc<NamespacedKeyword>>,
+
+    // A pull expression can be arbitrarily nested. We represent this both
+    // within the `attribute_spec` itself and also as a nested set of `Puller`s.
+    // When an attribute in the list above returns an entity -- and it should! --
+    // it is accumulated and we recurse down into these nested layers.
+    nested: BTreeMap<Entid, Puller>,
 }
 
 impl Puller {
@@ -156,8 +167,8 @@ impl Puller {
         let lookup_name = |i: &Entid| {
             // In the unlikely event that we have an attribute with no name, we bail.
             schema.get_ident(*i)
-                    .map(|ident| ValueRc::new(ident.clone()))
-                    .ok_or_else(|| ErrorKind::UnnamedAttribute(*i))
+                  .map(|ident| ValueRc::new(ident.clone()))
+                  .ok_or_else(|| ErrorKind::UnnamedAttribute(*i))
         };
 
         let mut names: BTreeMap<Entid, ValueRc<NamespacedKeyword>> = Default::default();
@@ -204,6 +215,20 @@ impl Puller {
                         },
                     }
                 },
+
+                // An attribute that nests must be ref-typed.
+                &PullAttributeSpec::Nested(ref attribute, ref patterns) => {
+                    let value_type = attribute.get_attribute(schema)
+                                              .map(|(a, _e)| a.value_type);
+                    let is_ref_typed = value_type.map(|v| v == ValueType::Ref)
+                                                 .unwrap_or(false);
+                    if !is_ref_typed {
+                        bail!(ErrorKind::NonRefNestedPullAttribute);
+                    }
+
+                    // TODO
+                    unimplemented!();
+                },
             }
         }
 
@@ -211,6 +236,7 @@ impl Puller {
             attributes: names,
             attribute_spec: cache::AttributeSpec::specified(&attrs, schema),
             db_id_alias,
+            nested: Default::default(),
         })
     }
 
diff --git a/query/src/lib.rs b/query/src/lib.rs
index cae69051..2eb2ee1a 100644
--- a/query/src/lib.rs
+++ b/query/src/lib.rs
@@ -55,7 +55,11 @@ pub use edn::{
 };
 
 use mentat_core::{
+    Attribute,
     FromRc,
+    HasSchema,
+    KnownEntid,
+    Schema,
     TypedValue,
     ValueRc,
     ValueType,
@@ -499,6 +503,19 @@ pub enum PullConcreteAttribute {
     Entid(i64),
 }
 
+impl PullConcreteAttribute {
+    pub fn get_attribute<'s>(&self, schema: &'s Schema) -> Option<(&'s Attribute, KnownEntid)> {
+        match self {
+            &PullConcreteAttribute::Ident(ref rc) => {
+                schema.attribute_for_ident(rc.as_ref())
+            },
+            &PullConcreteAttribute::Entid(e) => {
+                schema.attribute_for_entid(e).map(|a| (a, KnownEntid(e)))
+            },
+        }
+    }
+}
+
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct NamedPullAttribute {
     pub attribute: PullConcreteAttribute,
@@ -518,7 +535,7 @@ impl From<PullConcreteAttribute> for NamedPullAttribute {
 pub enum PullAttributeSpec {
     Wildcard,
     Attribute(NamedPullAttribute),
-    // PullMapSpec(Vec<…>),
+    Nested(PullConcreteAttribute, Vec<PullAttributeSpec>),
     // LimitedAttribute(PullConcreteAttribute, u64),  // Limit nil => Attribute instead.
     // DefaultedAttribute(PullConcreteAttribute, PullDefaultValue),
 }
@@ -556,6 +573,13 @@ impl std::fmt::Display for PullAttributeSpec {
             &PullAttributeSpec::Attribute(ref attr) => {
                 write!(f, "{}", attr)
             },
+            &PullAttributeSpec::Nested(ref attr, ref patterns) => {
+                write!(f, "{{{} [", attr)?;
+                for p in patterns {
+                    write!(f, " {}", p)?;
+                }
+                write!(f, "]}}")
+            },
         }
     }
 }