tree.go

package gow

import (
	"net/url"
	"strings"
	"unicode"
)

// Param is a single URL parameter, consisting of a key and a value.
type Param struct {
	Key   string
	Value string
}

// Params is a Param-slice, as returned by the router.
// The slice is ordered, the first URL parameter is also the first slice value.
// It is therefore safe to read values by the index.
type Params []Param

// Get returns the value of the first Param which key matches the given name.
// If no matching Param is found, an empty string is returned.
func (ps Params) Get(name string) (string, bool) {
	for _, entry := range ps {
		if entry.Key == name {
			return entry.Value, true
		}
	}
	return "", false
}

// ByName returns the value of the first Param which key matches the given name.
// If no matching Param is found, an empty string is returned.
func (ps Params) ByName(name string) (va string) {
	va, _ = ps.Get(name)
	return
}

type methodTree struct {
	method string
	root   *node
}

type methodTrees []methodTree

func (trees methodTrees) get(method string) *node {
	for _, tree := range trees {
		if tree.method == method {
			return tree.root
		}
	}
	return nil
}

func min(a, b int) int {
	if a <= b {
		return a
	}
	return b
}

func longestCommonPrefix(a, b string) int {
	i := 0
	max := min(len(a), len(b))
	for i < max && a[i] == b[i] {
		i++
	}
	return i
}

func countParams(path string) uint8 {
	var n uint
	for i := 0; i < len(path); i++ {
		if path[i] == ':' || path[i] == '*' {
			n++
		}
	}
	if n >= 255 {
		return 255
	}
	return uint8(n)
}

type nodeType uint8

const (
	static nodeType = iota // default
	root
	param
	catchAll
)

type node struct {
	path      string
	indices   string
	children  []*node
	handlers  HandlersChain
	priority  uint32
	nType     nodeType
	maxParams uint8
	wildChild bool
	fullPath  string
}

// increments priority of the given child and reorders if necessary.
func (n *node) incrementChildPrio(pos int) int {
	cs := n.children
	cs[pos].priority++
	prio := cs[pos].priority

	// Adjust position (move to front)
	newPos := pos
	for ; newPos > 0 && cs[newPos-1].priority < prio; newPos-- {
		// Swap node positions
		cs[newPos-1], cs[newPos] = cs[newPos], cs[newPos-1]
	}

	// build new index char string
	if newPos != pos {
		n.indices = n.indices[:newPos] + // unchanged prefix, might be empty
			n.indices[pos:pos+1] + // the index char we move
			n.indices[newPos:pos] + n.indices[pos+1:] // rest without char at 'pos'
	}

	return newPos
}

// addRoute adds a node with the given handle to the path.
// Not concurrency-safe!
func (n *node) addRoute(path string, handlers HandlersChain) {
	fullPath := path
	n.priority++
	numParams := countParams(path)
	// Empty tree
	if len(n.path) == 0 && len(n.children) == 0 {
		n.insertChild(numParams, path, fullPath, handlers)
		n.nType = root
		return
	}

	parentFullPathIndex := 0

walk:
	for {
		// Update maxParams of the current node
		if numParams > n.maxParams {
			n.maxParams = numParams
		}

		// Find the longest common prefix.
		// This also implies that the common prefix contains no ':' or '*'
		// since the existing key can't contain those chars.
		i := longestCommonPrefix(path, n.path)

		// Split edge
		if i < len(n.path) {
			child := node{
				path:      n.path[i:],
				wildChild: n.wildChild,
				indices:   n.indices,
				children:  n.children,
				handlers:  n.handlers,
				priority:  n.priority - 1,
				fullPath:  n.fullPath,
			}

			// Update maxParams (max of all children)
			for _, v := range child.children {
				if v.maxParams > child.maxParams {
					child.maxParams = v.maxParams
				}
			}

			n.children = []*node{&child}
			// []byte for proper unicode char conversion, see #65
			n.indices = string([]byte{n.path[i]})
			n.path = path[:i]
			n.handlers = nil
			n.wildChild = false
			n.fullPath = fullPath[:parentFullPathIndex+i]
		}

		// Make new node a child of this node
		if i < len(path) {
			path = path[i:]

			if n.wildChild {
				parentFullPathIndex += len(n.path)
				n = n.children[0]
				n.priority++

				// Update maxParams of the child node
				if numParams > n.maxParams {
					n.maxParams = numParams
				}
				numParams--

				// Check if the wildcard matches
				if len(path) >= len(n.path) && n.path == path[:len(n.path)] {
					// check for longer wildcard, e.g. :name and :names
					if len(n.path) >= len(path) || path[len(n.path)] == '/' {
						continue walk
					}
				}

				pathSeg := path
				if n.nType != catchAll {
					pathSeg = strings.SplitN(path, "/", 2)[0]
				}
				prefix := fullPath[:strings.Index(fullPath, pathSeg)] + n.path
				panic("'" + pathSeg +
					"' in new path '" + fullPath +
					"' conflicts with existing wildcard '" + n.path +
					"' in existing prefix '" + prefix +
					"'")
			}

			c := path[0]

			// slash after param
			if n.nType == param && c == '/' && len(n.children) == 1 {
				parentFullPathIndex += len(n.path)
				n = n.children[0]
				n.priority++
				continue walk
			}

			// Check if a child with the next path byte exists
			for i, max := 0, len(n.indices); i < max; i++ {
				if c == n.indices[i] {
					parentFullPathIndex += len(n.path)
					i = n.incrementChildPrio(i)
					n = n.children[i]
					continue walk
				}
			}

			// Otherwise insert it
			if c != ':' && c != '*' {
				// []byte for proper unicode char conversion, see #65
				n.indices += string([]byte{c})
				child := &node{
					maxParams: numParams,
					fullPath:  fullPath,
				}
				n.children = append(n.children, child)
				n.incrementChildPrio(len(n.indices) - 1)
				n = child
			}
			n.insertChild(numParams, path, fullPath, handlers)
			return
		}

		// Otherwise and handle to current node
		if n.handlers != nil {
			panic("handlers are already registered for path '" + fullPath + "'")
		}
		n.handlers = handlers
		return
	}
}

// Search for a wildcard segment and check the name for invalid characters.
// Returns -1 as index, if no wildcard war found.
func findWildcard(path string) (wildcard string, i int, valid bool) {
	// Find start
	for start, c := range []byte(path) {
		// A wildcard starts with ':' (param) or '*' (catch-all)
		if c != ':' && c != '*' {
			continue
		}

		// Find end and check for invalid characters
		valid = true
		for end, c := range []byte(path[start+1:]) {
			switch c {
			case '/':
				return path[start : start+1+end], start, valid
			case ':', '*':
				valid = false
			}
		}
		return path[start:], start, valid
	}
	return "", -1, false
}

func (n *node) insertChild(numParams uint8, path string, fullPath string, handlers HandlersChain) {
	for numParams > 0 {
		// Find prefix until first wildcard
		wildcard, i, valid := findWildcard(path)
		if i < 0 { // No wildcard found
			break
		}

		// The wildcard name must not contain ':' and '*'
		if !valid {
			panic("only one wildcard per path segment is allowed, has: '" +
				wildcard + "' in path '" + fullPath + "'")
		}

		// check if the wildcard has a name
		if len(wildcard) < 2 {
			panic("wildcards must be named with a non-empty name in path '" + fullPath + "'")
		}

		// Check if this node has existing children which would be
		// unreachable if we insert the wildcard here
		if len(n.children) > 0 {
			panic("wildcard segment '" + wildcard +
				"' conflicts with existing children in path '" + fullPath + "'")
		}

		if wildcard[0] == ':' { // param
			if i > 0 {
				// Insert prefix before the current wildcard
				n.path = path[:i]
				path = path[i:]
			}

			n.wildChild = true
			child := &node{
				nType:     param,
				path:      wildcard,
				maxParams: numParams,
				fullPath:  fullPath,
			}
			n.children = []*node{child}
			n = child
			n.priority++
			numParams--

			// if the path doesn't end with the wildcard, then there
			// will be another non-wildcard subpath starting with '/'
			if len(wildcard) < len(path) {
				path = path[len(wildcard):]

				child := &node{
					maxParams: numParams,
					priority:  1,
					fullPath:  fullPath,
				}
				n.children = []*node{child}
				n = child
				continue
			}

			// Otherwise we're done. Insert the handle in the new leaf
			n.handlers = handlers
			return
		}

		// catchAll
		if i+len(wildcard) != len(path) || numParams > 1 {
			panic("catch-all routes are only allowed at the end of the path in path '" + fullPath + "'")
		}

		if len(n.path) > 0 && n.path[len(n.path)-1] == '/' {
			panic("catch-all conflicts with existing handle for the path segment root in path '" + fullPath + "'")
		}

		// currently fixed width 1 for '/'
		i--
		if path[i] != '/' {
			panic("no / before catch-all in path '" + fullPath + "'")
		}

		n.path = path[:i]

		// First node: catchAll node with empty path
		child := &node{
			wildChild: true,
			nType:     catchAll,
			maxParams: 1,
			fullPath:  fullPath,
		}
		// update maxParams of the parent node
		if n.maxParams < 1 {
			n.maxParams = 1
		}
		n.children = []*node{child}
		n.indices = string('/')
		n = child
		n.priority++

		// second node: node holding the variable
		child = &node{
			path:      path[i:],
			nType:     catchAll,
			maxParams: 1,
			handlers:  handlers,
			priority:  1,
			fullPath:  fullPath,
		}
		n.children = []*node{child}

		return
	}

	// If no wildcard was found, simply insert the path and handle
	n.path = path
	n.handlers = handlers
	n.fullPath = fullPath
}

// nodeValue holds return values of (*Node).getValue method
type nodeValue struct {
	handlers HandlersChain
	params   Params
	tsr      bool
	fullPath string
}

// getValue returns the handle registered with the given path (key). The values of
// wildcards are saved to a map.
// If no handle can be found, a TSR (trailing slash redirect) recommendation is
// made if a handle exists with an extra (without the) trailing slash for the
// given path.
func (n *node) getValue(path string, po Params, unescape bool) (value nodeValue) {
	value.params = po
	//ignore case
	path = strings.ToLower(path)
walk: // Outer loop for walking the tree
	for {
		//ignore case
		prefix := strings.ToLower(n.path)
		if path == prefix {
			// We should have reached the node containing the handle.
			// Check if this node has a handle registered.
			if value.handlers = n.handlers; value.handlers != nil {
				value.fullPath = n.fullPath
				return
			}

			if path == "/" && n.wildChild && n.nType != root {
				value.tsr = true
				return
			}

			// No handle found. Check if a handle for this path + a
			// trailing slash exists for trailing slash recommendation
			indices := n.indices
			for i, max := 0, len(indices); i < max; i++ {
				if indices[i] == '/' {
					n = n.children[i]
					value.tsr = (len(n.path) == 1 && n.handlers != nil) ||
						(n.nType == catchAll && n.children[0].handlers != nil)
					return
				}
			}

			return
		}

		if len(path) > len(prefix) && path[:len(prefix)] == prefix {
			path = path[len(prefix):]
			// If this node does not have a wildcard (param or catchAll)
			// child,  we can just look up the next child node and continue
			// to walk down the tree
			if !n.wildChild {
				c := path[0]
				indices := n.indices
				for i, max := 0, len(indices); i < max; i++ {
					if c == indices[i] {
						n = n.children[i]
						continue walk
					}
				}

				// Nothing found.
				// We can recommend to redirect to the same URL without a
				// trailing slash if a leaf exists for that path.
				value.tsr = path == "/" && n.handlers != nil
				return
			}

			// handle wildcard child
			n = n.children[0]
			switch n.nType {
			case param:
				// find param end (either '/' or path end)
				end := 0
				for end < len(path) && path[end] != '/' {
					end++
				}

				// save param value
				if cap(value.params) < int(n.maxParams) {
					value.params = make(Params, 0, n.maxParams)
				}
				i := len(value.params)
				value.params = value.params[:i+1] // expand slice within preallocated capacity
				value.params[i].Key = n.path[1:]
				val := path[:end]
				if unescape {
					var err error
					if value.params[i].Value, err = url.QueryUnescape(val); err != nil {
						value.params[i].Value = val // fallback, in case of error
					}
				} else {
					value.params[i].Value = val
				}

				// we need to go deeper!
				if end < len(path) {
					if len(n.children) > 0 {
						path = path[end:]
						n = n.children[0]
						continue walk
					}

					// ... but we can't
					value.tsr = len(path) == end+1
					return
				}

				if value.handlers = n.handlers; value.handlers != nil {
					value.fullPath = n.fullPath
					return
				}
				if len(n.children) == 1 {
					// No handle found. Check if a handle for this path + a
					// trailing slash exists for TSR recommendation
					n = n.children[0]
					value.tsr = n.path == "/" && n.handlers != nil
				}
				return

			case catchAll:
				// save param value
				if cap(value.params) < int(n.maxParams) {
					value.params = make(Params, 0, n.maxParams)
				}
				i := len(value.params)
				value.params = value.params[:i+1] // expand slice within preallocated capacity
				value.params[i].Key = n.path[2:]
				if unescape {
					var err error
					if value.params[i].Value, err = url.QueryUnescape(path); err != nil {
						value.params[i].Value = path // fallback, in case of error
					}
				} else {
					value.params[i].Value = path
				}

				value.handlers = n.handlers
				value.fullPath = n.fullPath
				return

			default:
				panic("invalid node type")
			}
		}

		// Nothing found. We can recommend to redirect to the same URL with an
		// extra trailing slash if a leaf exists for that path
		value.tsr = (path == "/") ||
			(len(prefix) == len(path)+1 && prefix[len(path)] == '/' &&
				path == prefix[:len(prefix)-1] && n.handlers != nil)
		return
	}
}

// findCaseInsensitivePath makes a case-insensitive lookup of the given path and tries to find a handler.
// It can optionally also fix trailing slashes.
// It returns the case-corrected path and a bool indicating whether the lookup
// was successful.
func (n *node) findCaseInsensitivePath(path string, fixTrailingSlash bool) (ciPath []byte, found bool) {
	ciPath = make([]byte, 0, len(path)+1) // preallocate enough memory

	// Outer loop for walking the tree
	for len(path) >= len(n.path) && strings.EqualFold(path[:len(n.path)], n.path) {
		path = path[len(n.path):]
		ciPath = append(ciPath, n.path...)

		if len(path) == 0 {
			// We should have reached the node containing the handle.
			// Check if this node has a handle registered.
			if n.handlers != nil {
				return ciPath, true
			}

			// No handle found.
			// Try to fix the path by adding a trailing slash
			if fixTrailingSlash {
				for i := 0; i < len(n.indices); i++ {
					if n.indices[i] == '/' {
						n = n.children[i]
						if (len(n.path) == 1 && n.handlers != nil) ||
							(n.nType == catchAll && n.children[0].handlers != nil) {
							return append(ciPath, '/'), true
						}
						return
					}
				}
			}
			return
		}

		// If this node does not have a wildcard (param or catchAll) child,
		// we can just look up the next child node and continue to walk down
		// the tree
		if !n.wildChild {
			r := unicode.ToLower(rune(path[0]))
			for i, index := range n.indices {
				// must use recursive approach since both index and
				// ToLower(index) could exist. We must check both.
				if r == unicode.ToLower(index) {
					out, found := n.children[i].findCaseInsensitivePath(path, fixTrailingSlash)
					if found {
						return append(ciPath, out...), true
					}
				}
			}

			// Nothing found. We can recommend to redirect to the same URL
			// without a trailing slash if a leaf exists for that path
			found = fixTrailingSlash && path == "/" && n.handlers != nil
			return
		}

		n = n.children[0]
		switch n.nType {
		case param:
			// Find param end (either '/' or path end)
			end := 0
			for end < len(path) && path[end] != '/' {
				end++
			}

			// add param value to case insensitive path
			ciPath = append(ciPath, path[:end]...)

			// we need to go deeper!
			if end < len(path) {
				if len(n.children) > 0 {
					path = path[end:]
					n = n.children[0]
					continue
				}

				// ... but we can't
				if fixTrailingSlash && len(path) == end+1 {
					return ciPath, true
				}
				return
			}

			if n.handlers != nil {
				return ciPath, true
			}
			if fixTrailingSlash && len(n.children) == 1 {
				// No handle found. Check if a handle for this path + a
				// trailing slash exists
				n = n.children[0]
				if n.path == "/" && n.handlers != nil {
					return append(ciPath, '/'), true
				}
			}
			return

		case catchAll:
			return append(ciPath, path...), true

		default:
			panic("invalid node type")
		}
	}

	// Nothing found.
	// Try to fix the path by adding / removing a trailing slash
	if fixTrailingSlash {
		if path == "/" {
			return ciPath, true
		}
		if len(path)+1 == len(n.path) && n.path[len(path)] == '/' &&
			strings.EqualFold(path, n.path[:len(path)]) &&
			n.handlers != nil {
			return append(ciPath, n.path...), true
		}
	}
	return
}