ws/internal/uri/parser.go

package uri

import (
	"fmt"
	"strings"
)

// === WILDCARDS ===
//
// The star       '*'  -> matches 0 or 1 slash-bounded string
// The multi star '**' -> matches 0 or more slash-separated strings
// The dot        '.'  -> matches 1 slash-bounded string
// The multi dot  '..' -> matches 1 or more slash-separated strings
//
// === SCHEME POLICY ===
//
// - The last '/' is optional
// - Any '**' at the very end will match anything that starts with the given prefix
//
// === LIMITATIONS ==
//
// - A scheme must begin with '/'
// - A scheme cannot contain something else than a STRING or WILDCARD between 2 '/' separators
// - A scheme STRING cannot contain the symbols '/' as a character
// - A scheme STRING containing '*' or '.' characters will be treating as STRING only
// - A maximum of 16 slash-separated matchers (STRING or WILDCARD) are allowed

const maxMatch = 16

// Represents an URI matcher
type matcher struct {
	pat string // pattern to match (empty if wildcard)
	req bool   // whether it is required
	mul bool   // whether multiple matches are allowed

	buf []string // matched content (when matching)
}

// Scheme represents an URI scheme
type Scheme []*matcher

// FromString builds an URI scheme from a pattern string
func FromString(s string) (*Scheme, error) {

	// 1. Manage '/' at the start
	if len(s) < 1 || s[0] != '/' {
		return nil, fmt.Errorf("invalid URI; must start with '/'")
	}

	// 2. Split by '/'
	parts := strings.Split(s, "/")

	// 3. Max exceeded
	if len(parts)-2 > maxMatch {
		for i, p := range parts {
			fmt.Printf("%d: '%s'\n", i, p)
		}
		return nil, fmt.Errorf("URI must not exceed %d slash-separated components, got %d", maxMatch, len(parts))
	}

	// 4. Build for each part
	sch, err := buildScheme(parts)
	if err != nil {
		return nil, err
	}

	// 5. Optimise structure
	opti, err := sch.optimise()
	if err != nil {
		return nil, err
	}

	return &opti, nil

}

// Match returns if the given URI is matched by the scheme
func (s Scheme) Match(str string) bool {

	// 1. Nothing -> match all
	if len(s) == 0 {
		return true
	}

	// 2. Check for string match
	clearURI, match := s.matchString(str)
	if !match {
		return false
	}

	// 3. Check for non-string match (wildcards)
	match = s.matchWildcards(clearURI)
	if !match {
		return false
	}

	return true
}

// GetMatch returns the indexed match (excluding string matchers)
func (s Scheme) GetMatch(n uint8) ([]string, error) {

	// 1. Index out of range
	if n > uint8(len(s)) {
		return nil, fmt.Errorf("index out of range")
	}

	// 2. Iterate to find index (exclude strings)
	ni := -1
	for _, m := range s {

		// ignore strings
		if len(m.pat) > 0 {
			continue
		}

		// increment match counter : ni
		ni++

		// if expected index -> return matches
		if uint8(ni) == n {
			return m.buf, nil
		}

	}

	// 3. If nothing found -> return empty set
	return nil, fmt.Errorf("index out of range (max: %d)", ni)

}

// GetAllMatch returns all the indexed match (excluding string matchers)
func (s Scheme) GetAllMatch() [][]string {

	match := make([][]string, 0, len(s))

	for _, m := range s {

		// ignore strings
		if len(m.pat) > 0 {
			continue
		}

		match = append(match, m.buf)

	}

	return match

}

// buildScheme builds a 'basic' scheme
// from a pattern string
func buildScheme(ss []string) (Scheme, error) {

	// 1. Build scheme
	sch := make(Scheme, 0, maxMatch)

	for _, s := range ss {

		// 2. ignore empty
		if len(s) == 0 {
			continue
		}

		m := &matcher{}

		switch s {

		// 3. Card: 0, N
		case "**":
			m.req = false
			m.mul = true
			sch = append(sch, m)

		// 4. Card: 1, N
		case "..":
			m.req = true
			m.mul = true
			sch = append(sch, m)

		// 5. Card: 0, 1
		case "*":
			m.req = false
			m.mul = false
			sch = append(sch, m)

		// 6. Card: 1
		case ".":
			m.req = true
			m.mul = false
			sch = append(sch, m)

		// 7. Card: 1, literal string
		default:
			m.req = true
			m.mul = false
			m.pat = fmt.Sprintf("/%s", s)
			sch = append(sch, m)

		}

	}

	return sch, nil
}

// optimise optimised the scheme for further parsing
func (s Scheme) optimise() (Scheme, error) {

	// 1. Nothing to do if only 1 element
	if len(s) <= 1 {
		return s, nil
	}

	// 2. Init reshifted scheme
	rshift := make(Scheme, 0, maxMatch)
	rshift = append(rshift, s[0])

	// 2. Iterate over matchers
	for p, i, l := 0, 1, len(s); i < l; i++ {

		pre, cur := s[p], s[i]

		/* Merge: 2 following literals */
		if len(pre.pat) > 0 && len(cur.pat) > 0 {

			// merge strings into previous
			pre.pat = fmt.Sprintf("%s%s", pre.pat, cur.pat)

			// delete current
			s[i] = nil

		}

		// increment previous (only if current is not nul)
		if s[i] != nil {
			rshift = append(rshift, s[i])
			p = i
		}

	}

	return rshift, nil

}

// matchString checks the STRING matchers from an URI
// it returns a boolean : false when not matching, true eitherway
// it returns a cleared uri, without STRING data
func (s Scheme) matchString(uri string) (string, bool) {

	// 1. Initialise variables
	clr := uri  // contains cleared input string
	minOff := 0 // minimum offset

	// 2. Iterate over strings
	for _, m := range s {

		ls := len(m.pat)

		// {1} If not STRING matcher -> ignore //
		if ls == 0 {
			continue
		}

		// {2} Get offset in URI (else -1) //
		off := strings.Index(clr, m.pat)
		if off < 0 {
			return "", false
		}

		// {3} Fail on invalid offset range //
		if off < minOff {
			return "", false
		}

		// {4} Check for trailing '/' //
		hasSlash := 0
		if off+ls < len(clr) && clr[off+ls] == '/' {
			hasSlash = 1
		}

		// {5} Remove the current string (+trailing slash) from the URI //
		beg, end := clr[:off], clr[off+ls+hasSlash:]
		clr = fmt.Sprintf("%s\a/%s", beg, end) // separate matches by '\a' character

		// {6} Update offset range //
		minOff = len(beg) + 2 - 1 // +2 slash separators
		// -1 because strings begin with 1 slash already

	}

	// 3. If exists, remove trailing '/'
	if clr[len(clr)-1] == '/' {
		clr = clr[:len(clr)-1]
	}

	// 4. If exists, remove trailing '\a'
	if clr[len(clr)-1] == '\a' {
		clr = clr[:len(clr)-1]
	}

	return clr, true

}

// matchWildcards check the WILCARDS (non-string) matchers from
// a cleared URI. it returns if the string matches
// + it sets the matchers buffers for later extraction
func (s Scheme) matchWildcards(clear string) bool {

	// 1. Extract wildcards (ref)
	wildcards := make(Scheme, 0, maxMatch)

	for _, m := range s {
		if len(m.pat) == 0 {
			m.buf = nil // flush buffers
			wildcards = append(wildcards, m)
		}
	}

	// 2. If no wildcards -> match
	if len(wildcards) == 0 {
		return true
	}

	// 3. Break uri by '\a' characters
	matches := strings.Split(clear, "\a")[1:]

	// 4. Iterate over matches
	for n, match := range matches {

		// {1} If no more matcher //
		if n >= len(wildcards) {
			return false
		}

		// {2} Split by '/' //
		data := strings.Split(match, "/")[1:] // from index 1 because it begins with '/'

		// {3} If required and missing //
		if wildcards[n].req && len(data) < 1 {
			return false
		}

		// {4} If not multi but got multi //
		if !wildcards[n].mul && len(data) > 1 {
			return false
		}

		// {5} Store data into matcher //
		wildcards[n].buf = data

	}

	// 5. Match
	return true

}