// Copyright 2024, Pulumi Corporation.
//
// 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 internal

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"hash"
	"io"
	gofs "io/fs"
	"os"
	"path"
	"path/filepath"
	"slices"
	"syscall"

	buildx "github.com/docker/buildx/build"
	"github.com/moby/patternmatcher/ignorefile"
	"github.com/spf13/afero"
	"github.com/tonistiigi/fsutil"
	"golang.org/x/exp/maps"

	"github.com/pulumi/pulumi-go-provider/infer"
	"github.com/pulumi/pulumi/sdk/v3/go/common/util/contract"
)

var (
	_ infer.Annotated = (*Context)(nil)
	_ infer.Annotated = (*BuildContext)(nil)
)

// Context represents Docker's `PATH | URL | -` context argument. Inline
// context isn't supported yet.
type Context struct {
	Location string `pulumi:"location"` // Location is a local directory or URL.
}

// BuildContext represents Docker's named and unamed contexts.
type BuildContext struct {
	Context
	Named NamedContexts `pulumi:"named,optional"`
}

func (bc *BuildContext) namedMap() map[string]string {
	if bc == nil {
		return nil
	}
	return bc.Named.Map()
}

// NamedContexts correspond to Docker's `--build-context name=path` options.
// The path can be local or a remote URL.
type NamedContexts map[string]Context

// Map returns NamedContexts as a simple map.
func (nc NamedContexts) Map() map[string]string {
	m := map[string]string{}
	for k, v := range nc {
		m[k] = v.Location
	}
	return m
}

// Annotate sets docstrings on Context.
func (c *Context) Annotate(a infer.Annotator) {
	a.Describe(&c.Location, dedent(`
		Resources to use for build context.

		The location can be:
		* A relative or absolute path to a local directory (".", "./app",
		  "/app", etc.).
		* A remote URL of a Git repository, tarball, or plain text file
		  ("https://github.com/user/myrepo.git", "http://server/context.tar.gz",
		  etc.).
	`))
}

// validate returns a non-nil CheckError if the Context is invalid. The
// returned Dockerfile may have defaults set to match Docker's default
// handling. The returned Dockerfile should be validated separately. Non-nil
// values are returned even in the case of errors to allow additional
// validation to be performed.
func (bc *BuildContext) validate(preview bool, d *Dockerfile) (*Dockerfile, *Context, error) {
	if d == nil {
		d = &Dockerfile{}
	}
	c := &Context{}
	if bc != nil {
		c = &bc.Context
	}

	if c.Location == "" && preview {
		// The field is required so we normally wouldn't need to check if it
		// exists, but during previews it can still be empty if the value is
		// unknown. This isn't an error, but it does prevent us from performing
		// a build later.
		return d, c, nil
	}
	// If this isn't a preview but our location still isn't set, default it to
	// the current directory.
	if c.Location == "" {
		c.Location = "."
	}

	if buildx.IsRemoteURL(c.Location) {
		// We assume remote URLs are always valid.
		return d, c, nil
	}

	abs, err := filepath.Abs(c.Location)
	if err != nil {
		return d, c, newCheckFailure(err, "context.location")
	}

	if d.Location == "" && d.Inline == "" {
		// If a Dockerfile wasn't provided and our context is on-disk, then
		// set our Dockerfile to a default of <PATH>/Dockerfile.
		d.Location = filepath.Join(c.Location, "Dockerfile")
	}

	if isLocalDir(afero.NewOsFs(), abs) {
		// Our context exists -- nothing else to check.
		return d, c, nil
	}

	if c.Location != "-" {
		return d, c, newCheckFailure(
			fmt.Errorf("%q: not a valid directory or URL", c.Location),
			"context.location",
		)
	}

	return d, c, nil
}

// Annotate sets docstrings on BuildContext.
func (bc *BuildContext) Annotate(a infer.Annotator) {
	a.Describe(&bc.Named, dedent(`
		Additional build contexts to use.

		These contexts are accessed with "FROM name" or "--from=name"
		statements when using Dockerfile 1.4+ syntax.

		Values can be local paths, HTTP URLs, or  "docker-image://" images.
	`))
}

// hashFile hashes a file's contents and accumulates it into the provider Hash.
func hashFile(
	h hash.Hash,
	fs fsutil.FS,
	relativePath string,
	fileMode gofs.FileMode,
) error {
	if fileMode.IsDir() {
		return nil
	}
	if !fileMode.IsRegular() && fileMode.Type() != os.ModeSymlink {
		return nil
	}

	f, err := fs.Open(relativePath)
	if err != nil {
		return fmt.Errorf("could not open %q: %w", relativePath, err)
	}
	defer contract.IgnoreClose(f)

	_, err = io.Copy(h, f)
	if errors.Is(err, syscall.EISDIR) {
		// Ignore symlinks to directories.
		return nil
	}
	if err != nil {
		return fmt.Errorf("could not copy %q to hash: %w", relativePath, err)
	}

	h.Write([]byte(filepath.ToSlash(path.Clean(relativePath))))
	h.Write([]byte(fileMode.String()))

	return nil
}

// hashBuildContext accumulates hashes for files in a directory. If the file is
// a symlink, the location it points to is hashed. If it is a regular file, we
// hash the contents of the file. In order to detect file renames and mode
// changes, we also write to the accumulator a relative name and file mode.
func hashBuildContext(
	contextPath, dockerfilePath string,
	namedContexts map[string]string,
) (string, error) {
	h := sha256.New()
	fs := afero.NewOsFs()

	// Grab .dockerignore if our context and/or Dockerfile is on-disk.
	excludes := []string{}
	if isLocalDir(fs, contextPath) || isLocalFile(fs, dockerfilePath) {
		e, err := getIgnorePatterns(fs, dockerfilePath, contextPath)
		if err != nil {
			return "", err
		}
		excludes = e
	}

	if isLocalFile(fs, dockerfilePath) {
		err := hashDockerfile(h, dockerfilePath)
		if err != nil {
			return "", nil
		}
	}

	if isLocalDir(fs, contextPath) {
		// Hash our context if it's on-disk.
		fs, err := rootFS(contextPath, excludes)
		if err != nil {
			return "", err
		}
		if _, err := hashPath(h, fs); err != nil {
			return "", err
		}
	}

	// Hash any local named contexts. Sort keys for stable iteration order.
	keys := maps.Keys(namedContexts)
	slices.Sort(keys)
	for _, key := range keys {
		namedContext := namedContexts[key]
		if isLocalDir(fs, namedContext) {
			fs, err := rootFS(namedContext, excludes)
			if err != nil {
				return "", err
			}
			if _, err := hashPath(h, fs); err != nil {
				return "", err
			}
		}
	}

	return hex.EncodeToString(h.Sum(nil)), nil
}

// hashPath hashes all paths within the provided FS.
func hashPath(h hash.Hash, fs fsutil.FS) (string, error) {
	err := fs.Walk(
		context.Background(),
		"/",
		func(filePath string, dir gofs.DirEntry, err error) error {
			if err != nil {
				return err
			}
			if dir.IsDir() {
				return nil
			}
			// fsutil.Walk makes filePath relative to the root, we join it back to get an absolute path to
			// the file to hash.
			fi, err := dir.Info()
			if err != nil {
				return err
			}
			return hashFile(h, fs, filePath, fi.Mode())
		},
	)
	if err != nil {
		return "", fmt.Errorf("unable to hash build context: %w", err)
	}
	// create a hash of the entire input of the hash accumulator
	return hex.EncodeToString(h.Sum(nil)), nil
}

// hashDockerfile hashes the contents of a Dockerfile.
func hashDockerfile(h hash.Hash, path string) error {
	// The Dockerfile might be capture by .dockerignore, so we explicitly hash
	// its content (but not filename -- to match Docker) in order to detect
	// changes in it.
	df, err := os.ReadFile(filepath.Clean(path))
	if err != nil {
		return fmt.Errorf("error reading dockerfile %q: %w", path, err)
	}
	_, err = h.Write(df)
	if err != nil {
		return fmt.Errorf("error hashing dockerfile %q: %w", path, err)
	}
	return nil
}

// getIgnorePatterns returns all patterns to ignore when constructing a build
// context for the given Dockerfile, if any such patterns exist.
//
// Precedence is given to Dockerfile-specific ignore-files as per
// https://docs.docker.com/build/building/context/#filename-and-location.
func getIgnorePatterns(fs afero.Fs, dockerfilePath, contextRoot string) ([]string, error) {
	paths := []string{
		// Prefer <Dockerfile>.dockerignore if it's present.
		dockerfilePath + ".dockerignore",
	}

	if isLocalDir(fs, contextRoot) {
		// Otherwise fall back to the ignore-file at the root of our build context.
		paths = append(paths, filepath.Join(contextRoot, ".dockerignore"))
	}

	// Attempt to parse our candidate ignore-files, skipping any that don't
	// exist.
	for _, p := range paths {
		f, err := fs.Open(p)
		if errors.Is(err, afero.ErrFileNotFound) {
			continue
		}
		if err != nil {
			return nil, fmt.Errorf("reading %q: %w", p, err)
		}

		ignorePatterns, err := ignorefile.ReadAll(f)
		if err != nil {
			contract.IgnoreClose(f)
			return nil, fmt.Errorf("unable to parse %q: %w", p, err)
		}
		contract.IgnoreClose(f)
		return ignorePatterns, nil
	}

	return nil, nil
}

func isLocalDir(fs afero.Fs, path string) bool {
	stat, err := fs.Stat(path)
	return err == nil && stat.IsDir()
}

func isLocalFile(fs afero.Fs, path string) bool {
	stat, err := fs.Stat(path)
	return err == nil && !stat.IsDir()
}

// rootFS returns a new fsutil.FS scoped to the given root and with the given
// exclusions.
func rootFS(root string, excludes []string) (fsutil.FS, error) {
	fs, err := fsutil.NewFS(root)
	if err != nil {
		return nil, err
	}
	return fsutil.NewFilterFS(fs, &fsutil.FilterOpt{ExcludePatterns: excludes})
}