package stylecheck // import "honnef.co/go/tools/stylecheck"

import (
	"fmt"
	"go/ast"
	"go/constant"
	"go/token"
	"go/types"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"honnef.co/go/tools/lint"
	. "honnef.co/go/tools/lint/lintdsl"
	"honnef.co/go/tools/ssa"

	"golang.org/x/tools/go/types/typeutil"
)

type Checker struct {
	CheckGenerated bool
}

func NewChecker() *Checker {
	return &Checker{}
}

func (*Checker) Name() string              { return "stylecheck" }
func (*Checker) Prefix() string            { return "ST" }
func (c *Checker) Init(prog *lint.Program) {}

func (c *Checker) Checks() []lint.Check {
	return []lint.Check{
		{ID: "ST1000", FilterGenerated: false, Fn: c.CheckPackageComment},
		{ID: "ST1001", FilterGenerated: true, Fn: c.CheckDotImports},
		// {ID: "ST1002", FilterGenerated: true, Fn: c.CheckBlankImports},
		{ID: "ST1003", FilterGenerated: true, Fn: c.CheckNames},
		// {ID: "ST1004", FilterGenerated: false, Fn: nil, 			  },
		{ID: "ST1005", FilterGenerated: false, Fn: c.CheckErrorStrings},
		{ID: "ST1006", FilterGenerated: false, Fn: c.CheckReceiverNames},
		// {ID: "ST1007", FilterGenerated: true, Fn: c.CheckIncDec},
		{ID: "ST1008", FilterGenerated: false, Fn: c.CheckErrorReturn},
		// {ID: "ST1009", FilterGenerated: false, Fn: c.CheckUnexportedReturn},
		// {ID: "ST1010", FilterGenerated: false, Fn: c.CheckContextFirstArg},
		{ID: "ST1011", FilterGenerated: false, Fn: c.CheckTimeNames},
		{ID: "ST1012", FilterGenerated: false, Fn: c.CheckErrorVarNames},
		{ID: "ST1013", FilterGenerated: true, Fn: c.CheckHTTPStatusCodes},
		{ID: "ST1015", FilterGenerated: true, Fn: c.CheckDefaultCaseOrder},
		{ID: "ST1016", FilterGenerated: false, Fn: c.CheckReceiverNamesIdentical},
	}
}

func (c *Checker) CheckPackageComment(j *lint.Job) {
	// - At least one file in a non-main package should have a package comment
	//
	// - The comment should be of the form
	// "Package x ...". This has a slight potential for false
	// positives, as multiple files can have package comments, in
	// which case they get appended. But that doesn't happen a lot in
	// the real world.

	for _, pkg := range j.Program.InitialPackages {
		if pkg.Name == "main" {
			continue
		}
		hasDocs := false
		for _, f := range pkg.Syntax {
			if IsInTest(j, f) {
				continue
			}
			if f.Doc != nil && len(f.Doc.List) > 0 {
				hasDocs = true
				prefix := "Package " + f.Name.Name + " "
				if !strings.HasPrefix(strings.TrimSpace(f.Doc.Text()), prefix) {
					j.Errorf(f.Doc, `package comment should be of the form "%s..."`, prefix)
				}
				f.Doc.Text()
			}
		}

		if !hasDocs {
			for _, f := range pkg.Syntax {
				if IsInTest(j, f) {
					continue
				}
				j.Errorf(f, "at least one file in a package should have a package comment")
			}
		}
	}
}

func (c *Checker) CheckDotImports(j *lint.Job) {
	for _, pkg := range j.Program.InitialPackages {
		for _, f := range pkg.Syntax {
		imports:
			for _, imp := range f.Imports {
				path := imp.Path.Value
				path = path[1 : len(path)-1]
				for _, w := range pkg.Config.DotImportWhitelist {
					if w == path {
						continue imports
					}
				}

				if imp.Name != nil && imp.Name.Name == "." && !IsInTest(j, f) {
					j.Errorf(imp, "should not use dot imports")
				}
			}
		}
	}
}

func (c *Checker) CheckBlankImports(j *lint.Job) {
	fset := j.Program.Fset()
	for _, f := range j.Program.Files {
		if IsInMain(j, f) || IsInTest(j, f) {
			continue
		}

		// Collect imports of the form `import _ "foo"`, i.e. with no
		// parentheses, as their comment will be associated with the
		// (paren-free) GenDecl, not the import spec itself.
		//
		// We don't directly process the GenDecl so that we can
		// correctly handle the following:
		//
		//  import _ "foo"
		//  import _ "bar"
		//
		// where only the first import should get flagged.
		skip := map[ast.Spec]bool{}
		ast.Inspect(f, func(node ast.Node) bool {
			switch node := node.(type) {
			case *ast.File:
				return true
			case *ast.GenDecl:
				if node.Tok != token.IMPORT {
					return false
				}
				if node.Lparen == token.NoPos && node.Doc != nil {
					skip[node.Specs[0]] = true
				}
				return false
			}
			return false
		})
		for i, imp := range f.Imports {
			pos := fset.Position(imp.Pos())

			if !IsBlank(imp.Name) {
				continue
			}
			// Only flag the first blank import in a group of imports,
			// or don't flag any of them, if the first one is
			// commented
			if i > 0 {
				prev := f.Imports[i-1]
				prevPos := fset.Position(prev.Pos())
				if pos.Line-1 == prevPos.Line && IsBlank(prev.Name) {
					continue
				}
			}

			if imp.Doc == nil && imp.Comment == nil && !skip[imp] {
				j.Errorf(imp, "a blank import should be only in a main or test package, or have a comment justifying it")
			}
		}
	}
}

func (c *Checker) CheckIncDec(j *lint.Job) {
	// TODO(dh): this can be noisy for function bodies that look like this:
	// 	x += 3
	// 	...
	// 	x += 2
	// 	...
	// 	x += 1
	fn := func(node ast.Node) bool {
		assign, ok := node.(*ast.AssignStmt)
		if !ok || (assign.Tok != token.ADD_ASSIGN && assign.Tok != token.SUB_ASSIGN) {
			return true
		}
		if (len(assign.Lhs) != 1 || len(assign.Rhs) != 1) ||
			!IsIntLiteral(assign.Rhs[0], "1") {
			return true
		}

		suffix := ""
		switch assign.Tok {
		case token.ADD_ASSIGN:
			suffix = "++"
		case token.SUB_ASSIGN:
			suffix = "--"
		}

		j.Errorf(assign, "should replace %s with %s%s", Render(j, assign), Render(j, assign.Lhs[0]), suffix)
		return true
	}
	for _, f := range j.Program.Files {
		ast.Inspect(f, fn)
	}
}

func (c *Checker) CheckErrorReturn(j *lint.Job) {
fnLoop:
	for _, fn := range j.Program.InitialFunctions {
		sig := fn.Type().(*types.Signature)
		rets := sig.Results()
		if rets == nil || rets.Len() < 2 {
			continue
		}

		if rets.At(rets.Len()-1).Type() == types.Universe.Lookup("error").Type() {
			// Last return type is error. If the function also returns
			// errors in other positions, that's fine.
			continue
		}
		for i := rets.Len() - 2; i >= 0; i-- {
			if rets.At(i).Type() == types.Universe.Lookup("error").Type() {
				j.Errorf(rets.At(i), "error should be returned as the last argument")
				continue fnLoop
			}
		}
	}
}

// CheckUnexportedReturn checks that exported functions on exported
// types do not return unexported types.
func (c *Checker) CheckUnexportedReturn(j *lint.Job) {
	for _, fn := range j.Program.InitialFunctions {
		if fn.Synthetic != "" || fn.Parent() != nil {
			continue
		}
		if !ast.IsExported(fn.Name()) || IsInMain(j, fn) || IsInTest(j, fn) {
			continue
		}
		sig := fn.Type().(*types.Signature)
		if sig.Recv() != nil && !ast.IsExported(Dereference(sig.Recv().Type()).(*types.Named).Obj().Name()) {
			continue
		}
		res := sig.Results()
		for i := 0; i < res.Len(); i++ {
			if named, ok := DereferenceR(res.At(i).Type()).(*types.Named); ok &&
				!ast.IsExported(named.Obj().Name()) &&
				named != types.Universe.Lookup("error").Type() {
				j.Errorf(fn, "should not return unexported type")
			}
		}
	}
}

func (c *Checker) CheckReceiverNames(j *lint.Job) {
	for _, pkg := range j.Program.InitialPackages {
		for _, m := range pkg.SSA.Members {
			if T, ok := m.Object().(*types.TypeName); ok {
				ms := typeutil.IntuitiveMethodSet(T.Type(), nil)
				for _, sel := range ms {
					fn := sel.Obj().(*types.Func)
					recv := fn.Type().(*types.Signature).Recv()
					if Dereference(recv.Type()) != T.Type() {
						// skip embedded methods
						continue
					}
					if recv.Name() == "self" || recv.Name() == "this" {
						j.Errorf(recv, `receiver name should be a reflection of its identity; don't use generic names such as "this" or "self"`)
					}
					if recv.Name() == "_" {
						j.Errorf(recv, "receiver name should not be an underscore, omit the name if it is unused")
					}
				}
			}
		}
	}
}

func (c *Checker) CheckReceiverNamesIdentical(j *lint.Job) {
	for _, pkg := range j.Program.InitialPackages {
		for _, m := range pkg.SSA.Members {
			names := map[string]int{}

			var firstFn *types.Func
			if T, ok := m.Object().(*types.TypeName); ok {
				ms := typeutil.IntuitiveMethodSet(T.Type(), nil)
				for _, sel := range ms {
					fn := sel.Obj().(*types.Func)
					recv := fn.Type().(*types.Signature).Recv()
					if Dereference(recv.Type()) != T.Type() {
						// skip embedded methods
						continue
					}
					if firstFn == nil {
						firstFn = fn
					}
					if recv.Name() != "" && recv.Name() != "_" {
						names[recv.Name()]++
					}
				}
			}

			if len(names) > 1 {
				var seen []string
				for name, count := range names {
					seen = append(seen, fmt.Sprintf("%dx %q", count, name))
				}

				j.Errorf(firstFn, "methods on the same type should have the same receiver name (seen %s)", strings.Join(seen, ", "))
			}
		}
	}
}

func (c *Checker) CheckContextFirstArg(j *lint.Job) {
	// TODO(dh): this check doesn't apply to test helpers. Example from the stdlib:
	// 	func helperCommandContext(t *testing.T, ctx context.Context, s ...string) (cmd *exec.Cmd) {
fnLoop:
	for _, fn := range j.Program.InitialFunctions {
		if fn.Synthetic != "" || fn.Parent() != nil {
			continue
		}
		params := fn.Signature.Params()
		if params.Len() < 2 {
			continue
		}
		if types.TypeString(params.At(0).Type(), nil) == "context.Context" {
			continue
		}
		for i := 1; i < params.Len(); i++ {
			param := params.At(i)
			if types.TypeString(param.Type(), nil) == "context.Context" {
				j.Errorf(param, "context.Context should be the first argument of a function")
				continue fnLoop
			}
		}
	}
}

func (c *Checker) CheckErrorStrings(j *lint.Job) {
	fnNames := map[*ssa.Package]map[string]bool{}
	for _, fn := range j.Program.InitialFunctions {
		m := fnNames[fn.Package()]
		if m == nil {
			m = map[string]bool{}
			fnNames[fn.Package()] = m
		}
		m[fn.Name()] = true
	}

	for _, fn := range j.Program.InitialFunctions {
		if IsInTest(j, fn) {
			// We don't care about malformed error messages in tests;
			// they're usually for direct human consumption, not part
			// of an API
			continue
		}
		for _, block := range fn.Blocks {
		instrLoop:
			for _, ins := range block.Instrs {
				call, ok := ins.(*ssa.Call)
				if !ok {
					continue
				}
				if !IsCallTo(call.Common(), "errors.New") && !IsCallTo(call.Common(), "fmt.Errorf") {
					continue
				}

				k, ok := call.Common().Args[0].(*ssa.Const)
				if !ok {
					continue
				}

				s := constant.StringVal(k.Value)
				if len(s) == 0 {
					continue
				}
				switch s[len(s)-1] {
				case '.', ':', '!', '\n':
					j.Errorf(call, "error strings should not end with punctuation or a newline")
				}
				idx := strings.IndexByte(s, ' ')
				if idx == -1 {
					// single word error message, probably not a real
					// error but something used in tests or during
					// debugging
					continue
				}
				word := s[:idx]
				first, n := utf8.DecodeRuneInString(word)
				if !unicode.IsUpper(first) {
					continue
				}
				for _, c := range word[n:] {
					if unicode.IsUpper(c) {
						// Word is probably an initialism or
						// multi-word function name
						continue instrLoop
					}
				}

				word = strings.TrimRightFunc(word, func(r rune) bool { return unicode.IsPunct(r) })
				if fnNames[fn.Package()][word] {
					// Word is probably the name of a function in this package
					continue
				}
				// First word in error starts with a capital
				// letter, and the word doesn't contain any other
				// capitals, making it unlikely to be an
				// initialism or multi-word function name.
				//
				// It could still be a proper noun, though.

				j.Errorf(call, "error strings should not be capitalized")
			}
		}
	}
}

func (c *Checker) CheckTimeNames(j *lint.Job) {
	suffixes := []string{
		"Sec", "Secs", "Seconds",
		"Msec", "Msecs",
		"Milli", "Millis", "Milliseconds",
		"Usec", "Usecs", "Microseconds",
		"MS", "Ms",
	}
	fn := func(T types.Type, names []*ast.Ident) {
		if !IsType(T, "time.Duration") && !IsType(T, "*time.Duration") {
			return
		}
		for _, name := range names {
			for _, suffix := range suffixes {
				if strings.HasSuffix(name.Name, suffix) {
					j.Errorf(name, "var %s is of type %v; don't use unit-specific suffix %q", name.Name, T, suffix)
					break
				}
			}
		}
	}
	for _, f := range j.Program.Files {
		ast.Inspect(f, func(node ast.Node) bool {
			switch node := node.(type) {
			case *ast.ValueSpec:
				T := TypeOf(j, node.Type)
				fn(T, node.Names)
			case *ast.FieldList:
				for _, field := range node.List {
					T := TypeOf(j, field.Type)
					fn(T, field.Names)
				}
			}
			return true
		})
	}
}

func (c *Checker) CheckErrorVarNames(j *lint.Job) {
	for _, f := range j.Program.Files {
		for _, decl := range f.Decls {
			gen, ok := decl.(*ast.GenDecl)
			if !ok || gen.Tok != token.VAR {
				continue
			}
			for _, spec := range gen.Specs {
				spec := spec.(*ast.ValueSpec)
				if len(spec.Names) != len(spec.Values) {
					continue
				}

				for i, name := range spec.Names {
					val := spec.Values[i]
					if !IsCallToAST(j, val, "errors.New") && !IsCallToAST(j, val, "fmt.Errorf") {
						continue
					}

					prefix := "err"
					if name.IsExported() {
						prefix = "Err"
					}
					if !strings.HasPrefix(name.Name, prefix) {
						j.Errorf(name, "error var %s should have name of the form %sFoo", name.Name, prefix)
					}
				}
			}
		}
	}
}

var httpStatusCodes = map[int]string{
	100: "StatusContinue",
	101: "StatusSwitchingProtocols",
	102: "StatusProcessing",
	200: "StatusOK",
	201: "StatusCreated",
	202: "StatusAccepted",
	203: "StatusNonAuthoritativeInfo",
	204: "StatusNoContent",
	205: "StatusResetContent",
	206: "StatusPartialContent",
	207: "StatusMultiStatus",
	208: "StatusAlreadyReported",
	226: "StatusIMUsed",
	300: "StatusMultipleChoices",
	301: "StatusMovedPermanently",
	302: "StatusFound",
	303: "StatusSeeOther",
	304: "StatusNotModified",
	305: "StatusUseProxy",
	307: "StatusTemporaryRedirect",
	308: "StatusPermanentRedirect",
	400: "StatusBadRequest",
	401: "StatusUnauthorized",
	402: "StatusPaymentRequired",
	403: "StatusForbidden",
	404: "StatusNotFound",
	405: "StatusMethodNotAllowed",
	406: "StatusNotAcceptable",
	407: "StatusProxyAuthRequired",
	408: "StatusRequestTimeout",
	409: "StatusConflict",
	410: "StatusGone",
	411: "StatusLengthRequired",
	412: "StatusPreconditionFailed",
	413: "StatusRequestEntityTooLarge",
	414: "StatusRequestURITooLong",
	415: "StatusUnsupportedMediaType",
	416: "StatusRequestedRangeNotSatisfiable",
	417: "StatusExpectationFailed",
	418: "StatusTeapot",
	422: "StatusUnprocessableEntity",
	423: "StatusLocked",
	424: "StatusFailedDependency",
	426: "StatusUpgradeRequired",
	428: "StatusPreconditionRequired",
	429: "StatusTooManyRequests",
	431: "StatusRequestHeaderFieldsTooLarge",
	451: "StatusUnavailableForLegalReasons",
	500: "StatusInternalServerError",
	501: "StatusNotImplemented",
	502: "StatusBadGateway",
	503: "StatusServiceUnavailable",
	504: "StatusGatewayTimeout",
	505: "StatusHTTPVersionNotSupported",
	506: "StatusVariantAlsoNegotiates",
	507: "StatusInsufficientStorage",
	508: "StatusLoopDetected",
	510: "StatusNotExtended",
	511: "StatusNetworkAuthenticationRequired",
}

func (c *Checker) CheckHTTPStatusCodes(j *lint.Job) {
	for _, pkg := range j.Program.InitialPackages {
		whitelist := map[string]bool{}
		for _, code := range pkg.Config.HTTPStatusCodeWhitelist {
			whitelist[code] = true
		}
		fn := func(node ast.Node) bool {
			call, ok := node.(*ast.CallExpr)
			if !ok {
				return true
			}

			var arg int
			switch CallNameAST(j, call) {
			case "net/http.Error":
				arg = 2
			case "net/http.Redirect":
				arg = 3
			case "net/http.StatusText":
				arg = 0
			case "net/http.RedirectHandler":
				arg = 1
			default:
				return true
			}
			lit, ok := call.Args[arg].(*ast.BasicLit)
			if !ok {
				return true
			}
			if whitelist[lit.Value] {
				return true
			}

			n, err := strconv.Atoi(lit.Value)
			if err != nil {
				return true
			}
			s, ok := httpStatusCodes[n]
			if !ok {
				return true
			}
			j.Errorf(lit, "should use constant http.%s instead of numeric literal %d", s, n)
			return true
		}
		for _, f := range pkg.Syntax {
			ast.Inspect(f, fn)
		}
	}
}

func (c *Checker) CheckDefaultCaseOrder(j *lint.Job) {
	fn := func(node ast.Node) bool {
		stmt, ok := node.(*ast.SwitchStmt)
		if !ok {
			return true
		}
		list := stmt.Body.List
		for i, c := range list {
			if c.(*ast.CaseClause).List == nil && i != 0 && i != len(list)-1 {
				j.Errorf(c, "default case should be first or last in switch statement")
				break
			}
		}
		return true
	}
	for _, f := range j.Program.Files {
		ast.Inspect(f, fn)
	}
}
