package check

import (
	"regexp"
	"strconv"
	"strings"

	"git.vakhrushev.me/av/convy/internal/doc"
	"git.vakhrushev.me/av/convy/internal/suite"
)

// refRe catches a rule identifier: four uppercase Latin letters, a hyphen, a
// number and an optional table row number.
var refRe = regexp.MustCompile(`\b([A-Z]{4})-(\d+)(?:\.(\d+))?`)

// Ref is a reference to a rule found in the text.
type Ref struct {
	Prefix string
	Num    int
	Sub    int
	Line   int
	Text   string
}

// refsIn collects the references in a range of lines. Inline code is cut out:
// inside backticks an identifier stands as a sample of the notation rather than
// as a reference to an assertion — otherwise the line "a rule is referred to by
// its identifier (`SLOG-27`)" would demand that rule SLOG-27 exist.
//
// Rule headings are skipped: a heading declares a rule instead of referring to
// one, and there is nothing to resolve against the manifest.
func refsIn(d *doc.Document, from, to int) []Ref {
	heading := make(map[int]bool, len(d.Rules))
	for _, r := range d.Rules {
		heading[r.Line] = true
	}
	var out []Ref
	for n := from; n <= to; n++ {
		if d.Fenced(n) || heading[n] {
			continue
		}
		out = append(out, refsInLine(n, doc.StripInline(d.Line(n)))...)
	}
	return out
}

func refsInLine(n int, text string) []Ref {
	var out []Ref
	for _, m := range refRe.FindAllStringSubmatch(text, -1) {
		num, err := strconv.Atoi(m[2])
		if err != nil {
			continue
		}
		ref := Ref{Prefix: m[1], Num: num, Line: n, Text: m[0]}
		if m[3] != "" {
			ref.Sub, _ = strconv.Atoi(m[3])
		}
		out = append(out, ref)
	}
	return out
}

// checkLinks verifies that every reference resolves. An unresolved identifier
// is always an error: with stubs standing in for retired rules there is no
// third outcome — a reference leads either to a rule or to the explanation of
// why it was retired (META-31, META-32).
func checkLinks(s *suite.Suite, d *doc.Document, rep *Report) {
	for _, ref := range refsIn(d, d.Body, d.Len()) {
		if strings.HasPrefix(ref.Prefix, "X") {
			// A consumer's prefix: the local rules of a foreign repository
			// are invisible to the suite and are not to be resolved.
			continue
		}
		if s.Manifest.PrefixRetired(ref.Prefix) {
			rep.Errorf(Links, d.Path, ref.Line,
				"reference %s points at retired prefix %s", ref.Text, ref.Prefix)
			continue
		}
		target, ok := s.ByPrefix[ref.Prefix]
		if !ok {
			if _, declared := s.Manifest.PathOf(ref.Prefix); declared {
				// The file is declared but was not read — the manifest check
				// has already said so, and saying it twice helps no one.
				continue
			}
			rep.Errorf(Links, d.Path, ref.Line,
				"reference %s points at prefix %s, which the suite manifest does not declare", ref.Text, ref.Prefix)
			continue
		}
		rule, ok := ruleByNum(target, ref.Num)
		if !ok {
			rep.Errorf(Links, d.Path, ref.Line,
				"reference %s does not resolve: %s holds no rule numbered %d", ref.Text, target.Path, ref.Num)
			continue
		}
		if ref.Sub > 0 && !mentions(target, rule, ref.Text) {
			rep.Errorf(Links, d.Path, ref.Line,
				"reference %s does not resolve: the area of %s holds no such row", ref.Text, rule.ID())
		}
	}
}

// mentions reports whether the text of a reference occurs inside the area of a
// rule. That is how a table row number is checked: the row itself carries it.
func mentions(d *doc.Document, rule doc.Rule, text string) bool {
	for n := rule.Line; n <= rule.End; n++ {
		if strings.Contains(d.Line(n), text) {
			return true
		}
	}
	return false
}

func ruleByNum(d *doc.Document, num int) (doc.Rule, bool) {
	for _, r := range d.Rules {
		if r.Num == num {
			return r, true
		}
	}
	return doc.Rule{}, false
}