// Copyright 2013 gopm authors.
//
// Licensed under the Apache License, Version 2.0 (the "License"): you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations
// under the License.

package doc

import (
	"bytes"
	"go/ast"
	"go/build"
	"go/doc"
	"go/parser"
	"go/token"
	"io"
	"io/ioutil"
	"os"
	"path"
	"runtime"
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/gpmgo/gopm/log"
)

type sliceWriter struct{ p *[]byte }

func (w sliceWriter) Write(p []byte) (int, error) {
	*w.p = append(*w.p, p...)
	return len(p), nil
}

func (w *walker) readDir(dir string) ([]os.FileInfo, error) {
	if dir != w.ImportPath {
		panic("unexpected")
	}
	fis := make([]os.FileInfo, 0, len(w.srcs))
	for _, src := range w.srcs {
		fis = append(fis, src)
	}
	return fis, nil
}

func (w *walker) openFile(path string) (io.ReadCloser, error) {
	if strings.HasPrefix(path, w.ImportPath+"/") {
		if src, ok := w.srcs[path[len(w.ImportPath)+1:]]; ok {
			return ioutil.NopCloser(bytes.NewReader(src.data)), nil
		}
	}
	panic("unexpected")
}

func simpleImporter(imports map[string]*ast.Object, path string) (*ast.Object, error) {
	pkg := imports[path]
	if pkg == nil {
		// Guess the package name without importing it. Start with the last
		// element of the path.
		name := path[strings.LastIndex(path, "/")+1:]

		// Trim commonly used prefixes and suffixes containing illegal name
		// runes.
		name = strings.TrimSuffix(name, ".go")
		name = strings.TrimSuffix(name, "-go")
		name = strings.TrimPrefix(name, "go.")
		name = strings.TrimPrefix(name, "go-")
		name = strings.TrimPrefix(name, "biogo.")

		// It's also common for the last element of the path to contain an
		// extra "go" prefix, but not always. TODO: examine unresolved ids to
		// detect when trimming the "go" prefix is appropriate.

		pkg = ast.NewObj(ast.Pkg, name)
		pkg.Data = ast.NewScope(nil)
		imports[path] = pkg
	}
	return pkg, nil
}

// build gets imports from source files.
func (w *walker) build(srcs []*source, nod *Node) ([]string, error) {
	// Add source files to walker, I skipped references here.
	w.srcs = make(map[string]*source)
	for _, src := range srcs {
		w.srcs[src.name] = src
	}

	w.fset = token.NewFileSet()

	// Find the package and associated files.
	ctxt := build.Context{
		GOOS:          runtime.GOOS,
		GOARCH:        runtime.GOARCH,
		CgoEnabled:    true,
		JoinPath:      path.Join,
		IsAbsPath:     path.IsAbs,
		SplitPathList: func(list string) []string { return strings.Split(list, ":") },
		IsDir:         func(path string) bool { panic("unexpected") },
		HasSubdir:     func(root, dir string) (rel string, ok bool) { panic("unexpected") },
		ReadDir:       func(dir string) (fi []os.FileInfo, err error) { return w.readDir(dir) },
		OpenFile:      func(path string) (r io.ReadCloser, err error) { return w.openFile(path) },
		Compiler:      "gc",
	}

	bpkg, err := ctxt.ImportDir(w.ImportPath, 0)
	// Continue if there are no Go source files; we still want the directory info.
	_, nogo := err.(*build.NoGoError)
	if err != nil {
		if nogo {
			err = nil
		} else {
			log.Warn("walker: %s", err.Error())
			return nil, nil
		}
	}

	// Parse the Go files

	files := make(map[string]*ast.File)
	for _, name := range append(bpkg.GoFiles, bpkg.CgoFiles...) {
		file, err := parser.ParseFile(w.fset, name, w.srcs[name].data, parser.ParseComments)
		if err != nil {
			//beego.Error("doc.walker.build():", err)
			continue
		}
		files[name] = file
	}

	w.ImportPath = strings.Replace(w.ImportPath, "\\", "/", -1)
	var imports []string
	for _, v := range bpkg.Imports {
		// Skip strandard library.
		if !IsGoRepoPath(v) &&
			(GetProjectPath(v) != GetProjectPath(w.ImportPath)) {
			imports = append(imports, v)
		}
	}

	apkg, _ := ast.NewPackage(w.fset, files, simpleImporter, nil)

	mode := doc.Mode(0)
	if w.ImportPath == "builtin" {
		mode |= doc.AllDecls
	}

	pdoc := doc.New(apkg, w.ImportPath, mode)

	if nod != nil {
		nod.Synopsis = Synopsis(pdoc.Doc)
		if i := strings.Index(nod.Synopsis, "\n"); i > -1 {
			nod.Synopsis = nod.Synopsis[:i]
		}
	}

	return imports, err
}

var badSynopsisPrefixes = []string{
	"Autogenerated by Thrift Compiler",
	"Automatically generated ",
	"Auto-generated by ",
	"Copyright ",
	"COPYRIGHT ",
	`THE SOFTWARE IS PROVIDED "AS IS"`,
	"TODO: ",
	"vim:",
}

// Synopsis extracts the first sentence from s. All runs of whitespace are
// replaced by a single space.
func Synopsis(s string) string {

	parts := strings.SplitN(s, "\n\n", 2)
	s = parts[0]

	var buf []byte
	const (
		other = iota
		period
		space
	)
	last := space
Loop:
	for i := 0; i < len(s); i++ {
		b := s[i]
		switch b {
		case ' ', '\t', '\r', '\n':
			switch last {
			case period:
				break Loop
			case other:
				buf = append(buf, ' ')
				last = space
			}
		case '.':
			last = period
			buf = append(buf, b)
		default:
			last = other
			buf = append(buf, b)
		}
	}

	// Ensure that synopsis fits an App Engine datastore text property.
	const m = 400
	if len(buf) > m {
		buf = buf[:m]
		if i := bytes.LastIndex(buf, []byte{' '}); i >= 0 {
			buf = buf[:i]
		}
		buf = append(buf, " ..."...)
	}

	s = string(buf)

	r, n := utf8.DecodeRuneInString(s)
	if n < 0 || unicode.IsPunct(r) || unicode.IsSymbol(r) {
		// ignore Markdown headings, editor settings, Go build constraints, and * in poorly formatted block comments.
		s = ""
	} else {
		for _, prefix := range badSynopsisPrefixes {
			if strings.HasPrefix(s, prefix) {
				s = ""
				break
			}
		}
	}

	return s
}