// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package cache

import (
	"context"
	"fmt"
	"go/scanner"
	"go/token"
	"go/types"
	"regexp"
	"strconv"
	"strings"

	errors "golang.org/x/xerrors"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/packages"
	"golang.org/x/tools/internal/analysisinternal"
	"golang.org/x/tools/internal/event"
	"golang.org/x/tools/internal/lsp/debug/tag"
	"golang.org/x/tools/internal/lsp/protocol"
	"golang.org/x/tools/internal/lsp/source"
	"golang.org/x/tools/internal/span"
	"golang.org/x/tools/internal/typesinternal"
)

func sourceDiagnostics(ctx context.Context, snapshot *snapshot, pkg *pkg, severity protocol.DiagnosticSeverity, e interface{}) ([]*source.Diagnostic, error) {
	fset := snapshot.view.session.cache.fset
	var (
		spn     span.Span
		err     error
		msg     string
		code    typesinternal.ErrorCode
		diagSrc source.DiagnosticSource
		fixes   []source.SuggestedFix
		related []source.RelatedInformation
	)
	switch e := e.(type) {
	case packages.Error:
		diagSrc = toDiagnosticSource(e.Kind)
		var ok bool
		if msg, spn, ok = parseGoListImportCycleError(ctx, snapshot, e, pkg); ok {
			diagSrc = source.TypeError
			break
		}
		if e.Pos == "" {
			spn = parseGoListError(e.Msg)

			// We may not have been able to parse a valid span.
			if _, err := spanToRange(snapshot, pkg, spn); err != nil {
				var diags []*source.Diagnostic
				for _, cgf := range pkg.compiledGoFiles {
					diags = append(diags, &source.Diagnostic{
						URI:      cgf.URI,
						Severity: severity,
						Source:   diagSrc,
						Message:  msg,
					})
				}
				return diags, nil
			}
		} else {
			spn = span.Parse(e.Pos)
		}
	case *scanner.Error:
		msg = e.Msg
		diagSrc = source.ParseError
		spn, err = scannerErrorRange(snapshot, pkg, e.Pos)
		if err != nil {
			if ctx.Err() != nil {
				return nil, ctx.Err()
			}
			event.Error(ctx, "no span for scanner.Error pos", err, tag.Package.Of(pkg.ID()))
			spn = span.Parse(e.Pos.String())
		}

	case scanner.ErrorList:
		// The first parser error is likely the root cause of the problem.
		if e.Len() <= 0 {
			return nil, errors.Errorf("no errors in %v", e)
		}
		msg = e[0].Msg
		diagSrc = source.ParseError
		spn, err = scannerErrorRange(snapshot, pkg, e[0].Pos)
		if err != nil {
			if ctx.Err() != nil {
				return nil, ctx.Err()
			}
			event.Error(ctx, "no span for scanner.Error pos", err, tag.Package.Of(pkg.ID()))
			spn = span.Parse(e[0].Pos.String())
		}
	case types.Error:
		msg = e.Msg
		diagSrc = source.TypeError
		if !e.Pos.IsValid() {
			return nil, fmt.Errorf("invalid position for type error %v", e)
		}
		code, spn, err = typeErrorData(fset, pkg, e)
		if err != nil {
			return nil, err
		}
	case extendedError:
		perr := e.primary
		msg = perr.Msg
		diagSrc = source.TypeError
		if !perr.Pos.IsValid() {
			return nil, fmt.Errorf("invalid position for type error %v", e)
		}
		code, spn, err = typeErrorData(fset, pkg, e.primary)
		if err != nil {
			return nil, err
		}
		for _, s := range e.secondaries {
			var x source.RelatedInformation
			x.Message = s.Msg
			_, xspn, err := typeErrorData(fset, pkg, s)
			if err != nil {
				return nil, fmt.Errorf("invalid position for type error %v", s)
			}
			x.URI = xspn.URI()
			rng, err := spanToRange(snapshot, pkg, xspn)
			if err != nil {
				return nil, err
			}
			x.Range = rng
			related = append(related, x)
		}
	case *analysis.Diagnostic:
		spn, err = span.NewRange(fset, e.Pos, e.End).Span()
		if err != nil {
			return nil, err
		}
		msg = e.Message
		diagSrc = source.AnalyzerErrorKind(e.Category)
		fixes, err = suggestedAnalysisFixes(snapshot, pkg, e)
		if err != nil {
			return nil, err
		}
		related, err = relatedInformation(snapshot, pkg, e)
		if err != nil {
			return nil, err
		}
	default:
		panic(fmt.Sprintf("%T unexpected", e))
	}
	rng, err := spanToRange(snapshot, pkg, spn)
	if err != nil {
		return nil, err
	}
	sd := &source.Diagnostic{
		URI:            spn.URI(),
		Range:          rng,
		Severity:       severity,
		Source:         diagSrc,
		Message:        msg,
		Related:        related,
		SuggestedFixes: fixes,
	}
	if code != 0 {
		sd.Code = code.String()
		sd.CodeHref = typesCodeHref(snapshot, code)
	}
	return []*source.Diagnostic{sd}, nil
}

func typesCodeHref(snapshot *snapshot, code typesinternal.ErrorCode) string {
	target := snapshot.View().Options().LinkTarget
	return fmt.Sprintf("https://%s/golang.org/x/tools/internal/typesinternal#%s", target, code.String())
}

func suggestedAnalysisFixes(snapshot *snapshot, pkg *pkg, diag *analysis.Diagnostic) ([]source.SuggestedFix, error) {
	var fixes []source.SuggestedFix
	for _, fix := range diag.SuggestedFixes {
		edits := make(map[span.URI][]protocol.TextEdit)
		for _, e := range fix.TextEdits {
			spn, err := span.NewRange(snapshot.view.session.cache.fset, e.Pos, e.End).Span()
			if err != nil {
				return nil, err
			}
			rng, err := spanToRange(snapshot, pkg, spn)
			if err != nil {
				return nil, err
			}
			edits[spn.URI()] = append(edits[spn.URI()], protocol.TextEdit{
				Range:   rng,
				NewText: string(e.NewText),
			})
		}
		fixes = append(fixes, source.SuggestedFix{
			Title: fix.Message,
			Edits: edits,
		})
	}
	return fixes, nil
}

func relatedInformation(snapshot *snapshot, pkg *pkg, diag *analysis.Diagnostic) ([]source.RelatedInformation, error) {
	var out []source.RelatedInformation
	for _, related := range diag.Related {
		spn, err := span.NewRange(snapshot.view.session.cache.fset, related.Pos, related.End).Span()
		if err != nil {
			return nil, err
		}
		rng, err := spanToRange(snapshot, pkg, spn)
		if err != nil {
			return nil, err
		}
		out = append(out, source.RelatedInformation{
			URI:     spn.URI(),
			Range:   rng,
			Message: related.Message,
		})
	}
	return out, nil
}

func toDiagnosticSource(kind packages.ErrorKind) source.DiagnosticSource {
	switch kind {
	case packages.ListError:
		return source.ListError
	case packages.ParseError:
		return source.ParseError
	case packages.TypeError:
		return source.TypeError
	default:
		return source.UnknownError
	}
}

func typeErrorData(fset *token.FileSet, pkg *pkg, terr types.Error) (typesinternal.ErrorCode, span.Span, error) {
	ecode, start, end, ok := typesinternal.ReadGo116ErrorData(terr)
	if !ok {
		start, end = terr.Pos, terr.Pos
		ecode = 0
	}
	posn := fset.Position(start)
	pgf, err := pkg.File(span.URIFromPath(posn.Filename))
	if err != nil {
		return 0, span.Span{}, err
	}
	if !end.IsValid() || end == start {
		end = analysisinternal.TypeErrorEndPos(fset, pgf.Src, start)
	}
	spn, err := parsedGoSpan(pgf, start, end)
	if err != nil {
		return 0, span.Span{}, err
	}
	return ecode, spn, nil
}

func parsedGoSpan(pgf *source.ParsedGoFile, start, end token.Pos) (span.Span, error) {
	return span.FileSpan(pgf.Tok, pgf.Mapper.Converter, start, end)
}

func scannerErrorRange(snapshot *snapshot, pkg *pkg, posn token.Position) (span.Span, error) {
	fset := snapshot.view.session.cache.fset
	pgf, err := pkg.File(span.URIFromPath(posn.Filename))
	if err != nil {
		return span.Span{}, err
	}
	pos := pgf.Tok.Pos(posn.Offset)
	return span.NewRange(fset, pos, pos).Span()
}

// spanToRange converts a span.Span to a protocol.Range,
// assuming that the span belongs to the package whose diagnostics are being computed.
func spanToRange(snapshot *snapshot, pkg *pkg, spn span.Span) (protocol.Range, error) {
	pgf, err := pkg.File(spn.URI())
	if err != nil {
		return protocol.Range{}, err
	}
	return pgf.Mapper.Range(spn)
}

// parseGoListError attempts to parse a standard `go list` error message
// by stripping off the trailing error message.
//
// It works only on errors whose message is prefixed by colon,
// followed by a space (": "). For example:
//
//   attributes.go:13:1: expected 'package', found 'type'
//
func parseGoListError(input string) span.Span {
	input = strings.TrimSpace(input)
	msgIndex := strings.Index(input, ": ")
	if msgIndex < 0 {
		return span.Parse(input)
	}
	return span.Parse(input[:msgIndex])
}

func parseGoListImportCycleError(ctx context.Context, snapshot *snapshot, e packages.Error, pkg *pkg) (string, span.Span, bool) {
	re := regexp.MustCompile(`(.*): import stack: \[(.+)\]`)
	matches := re.FindStringSubmatch(strings.TrimSpace(e.Msg))
	if len(matches) < 3 {
		return e.Msg, span.Span{}, false
	}
	msg := matches[1]
	importList := strings.Split(matches[2], " ")
	// Since the error is relative to the current package. The import that is causing
	// the import cycle error is the second one in the list.
	if len(importList) < 2 {
		return msg, span.Span{}, false
	}
	// Imports have quotation marks around them.
	circImp := strconv.Quote(importList[1])
	for _, cgf := range pkg.compiledGoFiles {
		// Search file imports for the import that is causing the import cycle.
		for _, imp := range cgf.File.Imports {
			if imp.Path.Value == circImp {
				spn, err := span.NewRange(snapshot.view.session.cache.fset, imp.Pos(), imp.End()).Span()
				if err != nil {
					return msg, span.Span{}, false
				}
				return msg, spn, true
			}
		}
	}
	return msg, span.Span{}, false
}