// 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.

// this file contains protocol<->span converters

package protocol

import (
	"go/token"

	"golang.org/x/tools/internal/span"
	errors "golang.org/x/xerrors"
)

type ColumnMapper struct {
	URI       span.URI
	Converter *span.TokenConverter
	Content   []byte
}

func NewURI(uri span.URI) string {
	return string(uri)
}

func NewColumnMapper(uri span.URI, filename string, fset *token.FileSet, f *token.File, content []byte) *ColumnMapper {
	var converter *span.TokenConverter
	if f == nil {
		converter = span.NewContentConverter(filename, content)
	} else {
		converter = span.NewTokenConverter(fset, f)
	}
	return &ColumnMapper{
		URI:       uri,
		Converter: converter,
		Content:   content,
	}
}

func (m *ColumnMapper) Location(s span.Span) (Location, error) {
	rng, err := m.Range(s)
	if err != nil {
		return Location{}, err
	}
	return Location{URI: NewURI(s.URI()), Range: rng}, nil
}

func (m *ColumnMapper) Range(s span.Span) (Range, error) {
	if span.CompareURI(m.URI, s.URI()) != 0 {
		return Range{}, errors.Errorf("column mapper is for file %q instead of %q", m.URI, s.URI())
	}
	s, err := s.WithAll(m.Converter)
	if err != nil {
		return Range{}, err
	}
	start, err := m.Position(s.Start())
	if err != nil {
		return Range{}, err
	}
	end, err := m.Position(s.End())
	if err != nil {
		return Range{}, err
	}
	return Range{Start: start, End: end}, nil
}

func (m *ColumnMapper) Position(p span.Point) (Position, error) {
	chr, err := span.ToUTF16Column(p, m.Content)
	if err != nil {
		return Position{}, err
	}
	return Position{
		Line:      float64(p.Line() - 1),
		Character: float64(chr - 1),
	}, nil
}

func (m *ColumnMapper) Span(l Location) (span.Span, error) {
	return m.RangeSpan(l.Range)
}

func (m *ColumnMapper) RangeSpan(r Range) (span.Span, error) {
	start, err := m.Point(r.Start)
	if err != nil {
		return span.Span{}, err
	}
	end, err := m.Point(r.End)
	if err != nil {
		return span.Span{}, err
	}
	return span.New(m.URI, start, end).WithAll(m.Converter)
}

func (m *ColumnMapper) PointSpan(p Position) (span.Span, error) {
	start, err := m.Point(p)
	if err != nil {
		return span.Span{}, err
	}
	return span.New(m.URI, start, start).WithAll(m.Converter)
}

func (m *ColumnMapper) Point(p Position) (span.Point, error) {
	line := int(p.Line) + 1
	offset, err := m.Converter.ToOffset(line, 1)
	if err != nil {
		return span.Point{}, err
	}
	lineStart := span.NewPoint(line, 1, offset)
	return span.FromUTF16Column(lineStart, int(p.Character)+1, m.Content)
}