// 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/packages"
)

type Diagnostic struct {
	Range
	Message string
}

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, err := f.GetPackage()
	if err != nil {
		return nil, err
	}
	// Prepare the reports we will send for this package.
	reports := make(map[string][]Diagnostic)
	for _, filename := range pkg.GoFiles {
		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, err := diagFile.GetToken()
		if err != nil {
			continue
		}
		content, err := diagFile.Read()
		if err != nil {
			continue
		}
		end, err := identifierEnd(content, 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,
		}
		if _, ok := reports[pos.Filename]; ok {
			reports[pos.Filename] = append(reports[pos.Filename], diagnostic)
		}
	}
	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
}