// Copyright 2020 The Fuchsia 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 state

import (
	"fmt"
	"regexp"
	"strings"

	"fidl-lsp/third_party/fidlgen"
)

var (
	// https://fuchsia.dev/fuchsia-src/development/languages/fidl/reference/language.md#identifiers
	fidlIdentifierPattern = `[a-zA-Z](?:[a-zA-Z0-9_]*[a-zA-Z0-9])?`

	// Although "library" can be used anywhere (e.g. as a type name), this regex
	// is robust because the the library declaration must appear at the top of
	// the file (only comments and whitespace can precede it).
	libraryRegexp = regexp.MustCompile(`` +
		`^(?:\s*//[^\n]*\n)*\s*` +
		`library\s+(` +
		fidlIdentifierPattern +
		`(?:\.` + fidlIdentifierPattern + `)*` +
		`)\s*;`)

	// TODO: make this agnostic to platform

	// Although "using" can be used anywhere (e.g. as a type name), this regex
	// is robust because it only matches imports of platform libraries (ones
	// that start with fidl, fuchsia, or test) and the special library zx. The
	// only problem is it can match commented imports, so we have to check for
	// this after matching.
	platformImportRegexp = regexp.MustCompile(`` +
		`\busing\s+(` +
		`zx|` +
		`(?:fidl|fuchsia|test)` +
		`(?:\.` + fidlIdentifierPattern + `)+` +
		`)` +
		`(?:\s+as\s+` + fidlIdentifierPattern + `)?` +
		`\s*;`)
)

// LibraryMatch is the result of ParseLibraryMatch and ParsePlatformImportsMatch
// and represents the location and value of a `library` or `using` declaration
// in a FIDL file.
type LibraryMatch struct {
	Lib   fidlgen.LibraryName
	Range Range
}

// TODO: we should keep track of URI <-> fidlLibrary mapping, so we don't have
// to parse for `library` name each time

// LibraryOfFile extracts the name of the FIDL library of the provided FIDL
// file, by extracting its `library` declaration.
func LibraryOfFile(file string) (fidlgen.LibraryName, error) {
	fidlLib, ok := ParseLibraryMatch(file)
	if !ok {
		return fidlgen.LibraryName{}, fmt.Errorf("Could not find library declaration in file")
	}
	return fidlLib.Lib, nil
}

// ParseLibraryMatch extracts with regex the `library __;` declaration from the
// FIDL file passed in, if there is one, or returns false if not.
func ParseLibraryMatch(fidl string) (LibraryMatch, bool) {
	m := libraryRegexp.FindStringSubmatchIndex(fidl)
	if m == nil {
		return LibraryMatch{}, false
	}
	return toLibraryMatch(fidl, m[2], m[3]), true
}

// ParsePlatformImportsMatch extracts with regex the `using __;` import
// declarations in the FIDL file passed in.
func ParsePlatformImportsMatch(fidl string) []LibraryMatch {
	var libs []LibraryMatch
	for _, m := range platformImportRegexp.FindAllStringSubmatchIndex(fidl, -1) {
		// See the comment in parsePlatformImports.
		i := strings.LastIndexByte(fidl[:m[2]], '\n')
		if i == -1 || !strings.Contains(fidl[i:m[2]], "//") {
			libs = append(libs, toLibraryMatch(fidl, m[2], m[3]))
		}
	}
	return libs
}

func toLibraryMatch(fidl string, start, end int) LibraryMatch {
	return LibraryMatch{
		Lib: fidlgen.MustReadLibraryName(fidl[start:end]),
		Range: Range{
			Start: Position{
				Line:      strings.Count(fidl[:start], "\n"),
				Character: start - strings.LastIndexByte(fidl[:start], '\n') - 1,
			},
			End: Position{
				Line:      strings.Count(fidl[:end], "\n"),
				Character: end - strings.LastIndexByte(fidl[:end], '\n') - 1,
			},
		},
	}
}

// https://fuchsia.dev/fuchsia-src/development/languages/fidl/reference/language.md#identifiers
//
// This also includes a '.' as long as it is not initial or trailing, so we can
// capture fully-qualified names and library names.
var identRegexp = regexp.MustCompile(`\b[a-zA-Z](?:[a-zA-Z0-9_.]*[a-zA-Z0-9])?\b`)

// Symbol represents a FIDL identifier.
// It could be a fully-qualified name, a local declaration name, a library name,
// etc.
type Symbol struct {
	Name     string
	Location Location
}

// SymbolAtPos returns the FIDL identifier that is at `pos` in `file`.
func (fs *FileSystem) SymbolAtPos(path FileID, pos Position) (Symbol, error) {
	lines, ok := fs.files[path]
	if !ok {
		return Symbol{}, fmt.Errorf("could not find file `%s`", path)
	}

	if pos.Line >= len(lines) {
		return Symbol{}, fmt.Errorf("position %#v in file `%s` is out of bounds", pos, path)
	}
	line := lines[pos.Line]
	tokens := identRegexp.FindAllStringIndex(line, -1)
	if len(tokens) == 0 {
		return Symbol{}, fmt.Errorf("could not find any symbols in line %d in file `%s`", pos.Line, path)
	}

	var name string
	r := Range{
		Start: Position{Line: pos.Line},
		End:   Position{Line: pos.Line},
	}
	for _, token := range tokens {
		if pos.Character >= token[0] &&
			pos.Character <= token[1] {
			name = line[token[0]:token[1]]
			r.Start.Character = token[0]
			r.End.Character = token[1]
			break
		}
	}
	if name == "" {
		return Symbol{}, fmt.Errorf("could not find symbol at pos %#v in file `%s`", pos, path)
	}

	// TODO: could exclude all FIDL keywords, to save work

	// TODO: check that the symbol is not part of a comment: if the line
	// contains "//" and the symbol is after the "//", then don't return the
	// symbol. "//" could also be part of a string const, but that also wouldn't
	// be an identifer.

	return Symbol{
		Name: name,
		Location: Location{
			FileID: path,
			Range:  r,
		},
	}, nil
}