Move query to its own subpackage (#152)

Move all the query system to its own package. The reason is to
avoid it to rely on unexported methods and structures, and move
it out of the main package since this is really not a core
feature. It is still tied to the toml.TomlTree and toml.Position
structures for now.

* Move query mechanism to its own subpackage
* Rename QueryResult to Result to avoid stutter
* Add query.CompileAndExecute

Fixes #116

query/match.go

@@ -0,0 +1,232 @@
+package query
+
+import (
+	"fmt"
+	"github.com/pelletier/go-toml"
+)
+
+// base match
+type matchBase struct {
+	next pathFn
+}
+
+func (f *matchBase) setNext(next pathFn) {
+	f.next = next
+}
+
+// terminating functor - gathers results
+type terminatingFn struct {
+	// empty
+}
+
+func newTerminatingFn() *terminatingFn {
+	return &terminatingFn{}
+}
+
+func (f *terminatingFn) setNext(next pathFn) {
+	// do nothing
+}
+
+func (f *terminatingFn) call(node interface{}, ctx *queryContext) {
+	ctx.result.appendResult(node, ctx.lastPosition)
+}
+
+// match single key
+type matchKeyFn struct {
+	matchBase
+	Name string
+}
+
+func newMatchKeyFn(name string) *matchKeyFn {
+	return &matchKeyFn{Name: name}
+}
+
+func (f *matchKeyFn) call(node interface{}, ctx *queryContext) {
+	if array, ok := node.([]*toml.TomlTree); ok {
+		for _, tree := range array {
+			item := tree.Get(f.Name)
+			if item != nil {
+				ctx.lastPosition = tree.GetPosition(f.Name)
+				f.next.call(item, ctx)
+			}
+		}
+	} else if tree, ok := node.(*toml.TomlTree); ok {
+		item := tree.Get(f.Name)
+		if item != nil {
+			ctx.lastPosition = tree.GetPosition(f.Name)
+			f.next.call(item, ctx)
+		}
+	}
+}
+
+// match single index
+type matchIndexFn struct {
+	matchBase
+	Idx int
+}
+
+func newMatchIndexFn(idx int) *matchIndexFn {
+	return &matchIndexFn{Idx: idx}
+}
+
+func (f *matchIndexFn) call(node interface{}, ctx *queryContext) {
+	if arr, ok := node.([]interface{}); ok {
+		if f.Idx < len(arr) && f.Idx >= 0 {
+			if treesArray, ok := node.([]*toml.TomlTree); ok {
+				if len(treesArray) > 0 {
+					ctx.lastPosition = treesArray[0].Position()
+				}
+			}
+			f.next.call(arr[f.Idx], ctx)
+		}
+	}
+}
+
+// filter by slicing
+type matchSliceFn struct {
+	matchBase
+	Start, End, Step int
+}
+
+func newMatchSliceFn(start, end, step int) *matchSliceFn {
+	return &matchSliceFn{Start: start, End: end, Step: step}
+}
+
+func (f *matchSliceFn) call(node interface{}, ctx *queryContext) {
+	if arr, ok := node.([]interface{}); ok {
+		// adjust indexes for negative values, reverse ordering
+		realStart, realEnd := f.Start, f.End
+		if realStart < 0 {
+			realStart = len(arr) + realStart
+		}
+		if realEnd < 0 {
+			realEnd = len(arr) + realEnd
+		}
+		if realEnd < realStart {
+			realEnd, realStart = realStart, realEnd // swap
+		}
+		// loop and gather
+		for idx := realStart; idx < realEnd; idx += f.Step {
+			if treesArray, ok := node.([]*toml.TomlTree); ok {
+				if len(treesArray) > 0 {
+					ctx.lastPosition = treesArray[0].Position()
+				}
+			}
+			f.next.call(arr[idx], ctx)
+		}
+	}
+}
+
+// match anything
+type matchAnyFn struct {
+	matchBase
+}
+
+func newMatchAnyFn() *matchAnyFn {
+	return &matchAnyFn{}
+}
+
+func (f *matchAnyFn) call(node interface{}, ctx *queryContext) {
+	if tree, ok := node.(*toml.TomlTree); ok {
+		for _, k := range tree.Keys() {
+			v := tree.Get(k)
+			ctx.lastPosition = tree.GetPosition(k)
+			f.next.call(v, ctx)
+		}
+	}
+}
+
+// filter through union
+type matchUnionFn struct {
+	Union []pathFn
+}
+
+func (f *matchUnionFn) setNext(next pathFn) {
+	for _, fn := range f.Union {
+		fn.setNext(next)
+	}
+}
+
+func (f *matchUnionFn) call(node interface{}, ctx *queryContext) {
+	for _, fn := range f.Union {
+		fn.call(node, ctx)
+	}
+}
+
+// match every single last node in the tree
+type matchRecursiveFn struct {
+	matchBase
+}
+
+func newMatchRecursiveFn() *matchRecursiveFn {
+	return &matchRecursiveFn{}
+}
+
+func (f *matchRecursiveFn) call(node interface{}, ctx *queryContext) {
+	originalPosition := ctx.lastPosition
+	if tree, ok := node.(*toml.TomlTree); ok {
+		var visit func(tree *toml.TomlTree)
+		visit = func(tree *toml.TomlTree) {
+			for _, k := range tree.Keys() {
+				v := tree.Get(k)
+				ctx.lastPosition = tree.GetPosition(k)
+				f.next.call(v, ctx)
+				switch node := v.(type) {
+				case *toml.TomlTree:
+					visit(node)
+				case []*toml.TomlTree:
+					for _, subtree := range node {
+						visit(subtree)
+					}
+				}
+			}
+		}
+		ctx.lastPosition = originalPosition
+		f.next.call(tree, ctx)
+		visit(tree)
+	}
+}
+
+// match based on an externally provided functional filter
+type matchFilterFn struct {
+	matchBase
+	Pos  toml.Position
+	Name string
+}
+
+func newMatchFilterFn(name string, pos toml.Position) *matchFilterFn {
+	return &matchFilterFn{Name: name, Pos: pos}
+}
+
+func (f *matchFilterFn) call(node interface{}, ctx *queryContext) {
+	fn, ok := (*ctx.filters)[f.Name]
+	if !ok {
+		panic(fmt.Sprintf("%s: query context does not have filter '%s'",
+			f.Pos.String(), f.Name))
+	}
+	switch castNode := node.(type) {
+	case *toml.TomlTree:
+		for _, k := range castNode.Keys() {
+			v := castNode.Get(k)
+			if fn(v) {
+				ctx.lastPosition = castNode.GetPosition(k)
+				f.next.call(v, ctx)
+			}
+		}
+	case []*toml.TomlTree:
+		for _, v := range castNode {
+			if fn(v) {
+				if len(castNode) > 0 {
+					ctx.lastPosition = castNode[0].Position()
+				}
+				f.next.call(v, ctx)
+			}
+		}
+	case []interface{}:
+		for _, v := range castNode {
+			if fn(v) {
+				f.next.call(v, ctx)
+			}
+		}
+	}
+}