package checkers

import (
	"go/ast"
	"regexp"
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/go-critic/go-critic/checkers/internal/astwalk"
	"github.com/go-critic/go-critic/linter"
)

func init() {
	var info linter.CheckerInfo
	info.Name = "commentFormatting"
	info.Tags = []string{linter.StyleTag}
	info.Summary = "Detects comments with non-idiomatic formatting"
	info.Before = `//This is a comment`
	info.After = `// This is a comment`

	collection.AddChecker(&info, func(ctx *linter.CheckerContext) (linter.FileWalker, error) {
		regexpPatterns := []*regexp.Regexp{
			regexp.MustCompile(`^//[\w-]+:.*$`), // e.g.: key: value
		}
		equalPatterns := []string{
			"//nolint",
		}
		parts := []string{
			"//go:generate ",   // e.g.: go:generate value
			"//line /",         // e.g.: line /path/to/file:123
			"//nolint ",        // e.g.: nolint
			"//noinspection ",  // e.g.: noinspection ALL, some GoLand and friends versions
			"//region",         // e.g.: region awawa, used by GoLand and friends for custom folding
			"//endregion",      // e.g.: endregion awawa or endregion, closes GoLand regions
			"//<editor-fold",   // e.g.: <editor-fold desc="awawa"> or <editor-fold>, used by VSCode for custom folding
			"//</editor-fold>", // e.g.: </editor-fold>, closes VSCode regions
			"//export ",        // e.g.: export Foo
			"///",              // e.g.: vertical breaker /////////////
			"//+",
			"//#",
			"//-",
			"//!",
		}

		return astwalk.WalkerForComment(&commentFormattingChecker{
			ctx:            ctx,
			partPatterns:   parts,
			equalPatterns:  equalPatterns,
			regexpPatterns: regexpPatterns,
		}), nil
	})
}

type commentFormattingChecker struct {
	astwalk.WalkHandler
	ctx *linter.CheckerContext

	partPatterns   []string
	equalPatterns  []string
	regexpPatterns []*regexp.Regexp
}

func (c *commentFormattingChecker) VisitComment(cg *ast.CommentGroup) {
	if strings.HasPrefix(cg.List[0].Text, "/*") {
		return
	}

outerLoop:
	for _, comment := range cg.List {
		commentLen := len(comment.Text)
		if commentLen <= len("// ") {
			continue
		}

		for _, p := range c.partPatterns {
			if commentLen < len(p) {
				continue
			}

			if strings.EqualFold(comment.Text[:len(p)], p) {
				continue outerLoop
			}
		}

		for _, p := range c.equalPatterns {
			if strings.EqualFold(comment.Text, p) {
				continue outerLoop
			}
		}

		for _, p := range c.regexpPatterns {
			if p.MatchString(comment.Text) {
				continue outerLoop
			}
		}

		// Make a decision based on a first comment text rune.
		r, _ := utf8.DecodeRuneInString(comment.Text[len("//"):])
		if !c.specialChar(r) && !unicode.IsSpace(r) {
			c.warn(comment)
			return
		}
	}
}

func (c *commentFormattingChecker) specialChar(r rune) bool {
	// Permitted list to avoid false-positives.
	switch r {
	case '+', '-', '#', '!':
		return true
	default:
		return false
	}
}

func (c *commentFormattingChecker) warn(comment *ast.Comment) {
	c.ctx.WarnFixable(comment, linter.QuickFix{
		From:        comment.Pos(),
		To:          comment.End(),
		Replacement: []byte(strings.Replace(comment.Text, "//", "// ", 1)),
	}, "put a space between `//` and comment text")
}
