From 937c8b31d759d868c6b27c6bd8431c6cb97cbd9e Mon Sep 17 00:00:00 2001
From: Gregory Eremin <g@erem.in>
Date: Tue, 17 Feb 2015 22:47:02 +0700
Subject: [PATCH] Parser context

---
 parser/context.go | 120 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 parser/context.go

diff --git a/parser/context.go b/parser/context.go
new file mode 100644
index 0000000..90af6da
--- /dev/null
+++ b/parser/context.go
@@ -0,0 +1,120 @@
+package parser
+
+import (
+	"strconv"
+	"strings"
+)
+
+type (
+	context struct {
+		exps []expectation
+	}
+
+	// Context building block
+	expectation struct {
+		typ   expectationType
+		key   string // Object key
+		index int64  // Array index
+	}
+
+	// Type of expectation: object or array
+	expectationType int
+)
+
+const (
+	unknown expectationType = iota
+	object
+	array
+)
+
+func (c *context) compare(c2 *context) bool {
+	if len(c.exps) != len(c2.exps) {
+		return false
+	}
+
+	for i, exp := range c.exps {
+		exp2 := c2.exps[i]
+		if exp.typ != exp2.typ {
+			return false
+		}
+		switch exp.typ {
+		case array:
+			if exp.index != -1 && exp2.index != -1 && exp.index != exp2.index {
+				return false
+			}
+		case object:
+			if exp.key != exp2.key {
+				return false
+			}
+		}
+	}
+
+	return true
+}
+
+func (c *context) push(typ expectationType) {
+	c.exps = append(c.exps, expectation{
+		typ: typ,
+	})
+}
+
+func (c *context) pop() {
+	if len(c.exps) == 0 {
+		return
+	}
+	c.exps = c.exps[:len(c.exps)-1]
+}
+
+func (c *context) setKey(key string) {
+	c.exps[len(c.exps)-1].key = key
+}
+
+func (c *context) setIndex(i int64) {
+	c.exps[len(c.exps)-1].index = i
+}
+
+func parseSelectors(sels []string) map[string]*context {
+	ctxs := map[string]*context{}
+	for _, sel := range sels {
+		ctxs[sel] = &context{
+			exps: parseSelector(sel),
+		}
+	}
+	return ctxs
+}
+
+func parseSelector(sel string) []expectation {
+	exps := []expectation{}
+	parts := strings.Split(sel[1:], "/")
+	for _, part := range parts {
+		c := expectation{}
+		if len(part) > 2 && part[:1] == "[" && part[len(part)-1:] == "]" {
+			c.typ = array
+			part = part[1 : len(part)-1]
+			if part == "*" {
+				c.index = -1
+			} else if i, err := strconv.ParseInt(part, 10, 64); err == nil {
+				c.index = i
+			} else {
+				panic("Array index should be numeric: " + part)
+			}
+		} else {
+			c.typ = object
+			c.key = part
+		}
+		exps = append(exps, c)
+	}
+
+	return exps
+}
+
+func (e expectationType) String() string {
+	switch e {
+	case array:
+		return "Index"
+	case object:
+		return "Key"
+	default:
+		return "Unknown"
+	}
+}