package sa4019

import (
	"fmt"
	"go/ast"
	"sort"
	"strings"

	"honnef.co/go/tools/analysis/facts/generated"
	"honnef.co/go/tools/analysis/lint"
	"honnef.co/go/tools/analysis/report"
	"honnef.co/go/tools/go/ast/astutil"

	"golang.org/x/tools/go/analysis"
)

var SCAnalyzer = lint.InitializeAnalyzer(&lint.Analyzer{
	Analyzer: &analysis.Analyzer{
		Name:     "SA4019",
		Run:      run,
		Requires: []*analysis.Analyzer{generated.Analyzer},
	},
	Doc: &lint.RawDocumentation{
		Title:    `Multiple, identical build constraints in the same file`,
		Since:    "2017.1",
		Severity: lint.SeverityWarning,
		MergeIf:  lint.MergeIfAny,
	},
})

var Analyzer = SCAnalyzer.Analyzer

func buildTagsIdentical(s1, s2 []string) bool {
	if len(s1) != len(s2) {
		return false
	}
	s1s := make([]string, len(s1))
	copy(s1s, s1)
	sort.Strings(s1s)
	s2s := make([]string, len(s2))
	copy(s2s, s2)
	sort.Strings(s2s)
	for i, s := range s1s {
		if s != s2s[i] {
			return false
		}
	}
	return true
}

func run(pass *analysis.Pass) (interface{}, error) {
	for _, f := range pass.Files {
		constraints := buildTags(f)
		for i, constraint1 := range constraints {
			for j, constraint2 := range constraints {
				if i >= j {
					continue
				}
				if buildTagsIdentical(constraint1, constraint2) {
					msg := fmt.Sprintf("identical build constraints %q and %q",
						strings.Join(constraint1, " "),
						strings.Join(constraint2, " "))
					report.Report(pass, f, msg, report.FilterGenerated(), report.ShortRange())
				}
			}
		}
	}
	return nil, nil
}

func buildTags(f *ast.File) [][]string {
	var out [][]string
	for _, line := range strings.Split(astutil.Preamble(f), "\n") {
		if !strings.HasPrefix(line, "+build ") {
			continue
		}
		line = strings.TrimSpace(strings.TrimPrefix(line, "+build "))
		fields := strings.Fields(line)
		out = append(out, fields)
	}
	return out
}