// Copyright 2018 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 source

import (
	"bytes"
	"context"
	"fmt"
	"go/token"
	"strconv"
	"strings"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/analysis/passes/asmdecl"
	"golang.org/x/tools/go/analysis/passes/assign"
	"golang.org/x/tools/go/analysis/passes/atomic"
	"golang.org/x/tools/go/analysis/passes/atomicalign"
	"golang.org/x/tools/go/analysis/passes/bools"
	"golang.org/x/tools/go/analysis/passes/buildtag"
	"golang.org/x/tools/go/analysis/passes/cgocall"
	"golang.org/x/tools/go/analysis/passes/composite"
	"golang.org/x/tools/go/analysis/passes/copylock"
	"golang.org/x/tools/go/analysis/passes/httpresponse"
	"golang.org/x/tools/go/analysis/passes/loopclosure"
	"golang.org/x/tools/go/analysis/passes/lostcancel"
	"golang.org/x/tools/go/analysis/passes/nilfunc"
	"golang.org/x/tools/go/analysis/passes/printf"
	"golang.org/x/tools/go/analysis/passes/shift"
	"golang.org/x/tools/go/analysis/passes/stdmethods"
	"golang.org/x/tools/go/analysis/passes/structtag"
	"golang.org/x/tools/go/analysis/passes/tests"
	"golang.org/x/tools/go/analysis/passes/unmarshal"
	"golang.org/x/tools/go/analysis/passes/unreachable"
	"golang.org/x/tools/go/analysis/passes/unsafeptr"
	"golang.org/x/tools/go/analysis/passes/unusedresult"

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

type Diagnostic struct {
	Range
	Message  string
	Source   string
	Severity DiagnosticSeverity
}

type DiagnosticSeverity int

const (
	SeverityWarning DiagnosticSeverity = iota
	SeverityError
)

func Diagnostics(ctx context.Context, v View, uri URI) (map[string][]Diagnostic, error) {
	f, err := v.GetFile(ctx, uri)
	if err != nil {
		return nil, err
	}
	pkg := f.GetPackage(ctx)
	// Prepare the reports we will send for this package.
	reports := make(map[string][]Diagnostic)
	for _, filename := range pkg.CompiledGoFiles {
		reports[filename] = []Diagnostic{}
	}
	var parseErrors, typeErrors []packages.Error
	for _, err := range pkg.Errors {
		switch err.Kind {
		case packages.ParseError:
			parseErrors = append(parseErrors, err)
		case packages.TypeError:
			typeErrors = append(typeErrors, err)
		default:
			// ignore other types of errors
			continue
		}
	}
	// Don't report type errors if there are parse errors.
	diags := typeErrors
	if len(parseErrors) > 0 {
		diags = parseErrors
	}
	for _, diag := range diags {
		pos := errorPos(diag)
		diagFile, err := v.GetFile(ctx, ToURI(pos.Filename))
		if err != nil {
			continue
		}
		diagTok := diagFile.GetToken(ctx)
		end, err := identifierEnd(diagFile.GetContent(ctx), pos.Line, pos.Column)
		// Don't set a range if it's anything other than a type error.
		if err != nil || diag.Kind != packages.TypeError {
			end = 0
		}
		startPos := fromTokenPosition(diagTok, pos.Line, pos.Column)
		if !startPos.IsValid() {
			continue
		}
		endPos := fromTokenPosition(diagTok, pos.Line, pos.Column+end)
		if !endPos.IsValid() {
			continue
		}
		diagnostic := Diagnostic{
			Range: Range{
				Start: startPos,
				End:   endPos,
			},
			Message:  diag.Msg,
			Severity: SeverityError,
		}
		if _, ok := reports[pos.Filename]; ok {
			reports[pos.Filename] = append(reports[pos.Filename], diagnostic)
		}
	}
	if len(diags) > 0 {
		return reports, nil
	}
	// Type checking and parsing succeeded. Run analyses.
	runAnalyses(v.GetAnalysisCache(), pkg, func(a *analysis.Analyzer, diag analysis.Diagnostic) {
		pos := pkg.Fset.Position(diag.Pos)
		category := a.Name
		if diag.Category != "" {
			category += "." + category
		}

		reports[pos.Filename] = append(reports[pos.Filename], Diagnostic{
			Source:   category,
			Range:    Range{Start: diag.Pos, End: diag.Pos},
			Message:  fmt.Sprintf(diag.Message),
			Severity: SeverityWarning,
		})
	})

	return reports, nil
}

// fromTokenPosition converts a token.Position (1-based line and column
// number) to a token.Pos (byte offset value). This requires the token.File
// to which the token.Pos belongs.
func fromTokenPosition(f *token.File, line, col int) token.Pos {
	linePos := lineStart(f, line)
	// TODO: This is incorrect, as pos.Column represents bytes, not characters.
	// This needs to be handled to address golang.org/issue/29149.
	return linePos + token.Pos(col-1)
}

func errorPos(pkgErr packages.Error) token.Position {
	remainder1, first, hasLine := chop(pkgErr.Pos)
	remainder2, second, hasColumn := chop(remainder1)
	var pos token.Position
	if hasLine && hasColumn {
		pos.Filename = remainder2
		pos.Line = second
		pos.Column = first
	} else if hasLine {
		pos.Filename = remainder1
		pos.Line = first
	}
	return pos
}

func chop(text string) (remainder string, value int, ok bool) {
	i := strings.LastIndex(text, ":")
	if i < 0 {
		return text, 0, false
	}
	v, err := strconv.ParseInt(text[i+1:], 10, 64)
	if err != nil {
		return text, 0, false
	}
	return text[:i], int(v), true
}

// identifierEnd returns the length of an identifier within a string,
// given the starting line and column numbers of the identifier.
func identifierEnd(content []byte, l, c int) (int, error) {
	lines := bytes.Split(content, []byte("\n"))
	if len(lines) < l {
		return 0, fmt.Errorf("invalid line number: got %v, but only %v lines", l, len(lines))
	}
	line := lines[l-1]
	if len(line) < c {
		return 0, fmt.Errorf("invalid column number: got %v, but the length of the line is %v", c, len(line))
	}
	return bytes.IndexAny(line[c-1:], " \n,():;[]"), nil
}

func runAnalyses(c *AnalysisCache, pkg *packages.Package, report func(a *analysis.Analyzer, diag analysis.Diagnostic)) error {
	// the traditional vet suite:
	analyzers := []*analysis.Analyzer{
		asmdecl.Analyzer,
		assign.Analyzer,
		atomic.Analyzer,
		atomicalign.Analyzer,
		bools.Analyzer,
		buildtag.Analyzer,
		cgocall.Analyzer,
		composite.Analyzer,
		copylock.Analyzer,
		httpresponse.Analyzer,
		loopclosure.Analyzer,
		lostcancel.Analyzer,
		nilfunc.Analyzer,
		printf.Analyzer,
		shift.Analyzer,
		stdmethods.Analyzer,
		structtag.Analyzer,
		tests.Analyzer,
		unmarshal.Analyzer,
		unreachable.Analyzer,
		unsafeptr.Analyzer,
		unusedresult.Analyzer,
	}

	roots := c.analyze([]*packages.Package{pkg}, analyzers)

	// Report diagnostics and errors from root analyzers.
	for _, r := range roots {
		for _, diag := range r.diagnostics {
			if r.err != nil {
				// TODO(matloob): This isn't quite right: we might return a failed prerequisites error,
				// which isn't super useful...
				return r.err
			}
			report(r.a, diag)
		}
	}

	return nil
}
