// Copyright 2018 The Hugo Authors. All rights reserved.
//
// 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 filecache provides a file based cache for Hugo.
package filecache

import (
	"encoding/json"
	"errors"
	"fmt"
	"path"
	"path/filepath"
	"strings"
	"time"

	"github.com/gohugoio/hugo/common/hmaps"
	"github.com/gohugoio/hugo/config"

	"github.com/mitchellh/mapstructure"
	"github.com/spf13/afero"
)

const (
	resourcesGenDir = ":resourceDir/_gen"
	cacheDirProject = ":cacheDir/:project"
)

const (
	CacheKeyImages        = "images"
	CacheKeyAssets        = "assets"
	CacheKeyModules       = "modules"
	CacheKeyModuleQueries = "modulequeries"
	CacheKeyModuleGitInfo = "modulegitinfo"
	CacheKeyGetResource   = "getresource"
	CacheKeyMisc          = "misc"
)

type Configs map[string]FileCacheConfig

// CacheDirModules returns the compiled path to the modules cache.
// For internal use.
func (c Configs) CacheDirModules() string {
	return c[CacheKeyModules].DirCompiled
}

// CacheDirMisc returns the compiled path to the misc cache.
// For internal use.
func (c Configs) CacheDirMisc() string {
	return c[CacheKeyMisc].DirCompiled
}

var defaultCacheConfigs = Configs{
	CacheKeyModules: {
		MaxAge: -1,
		Dir:    ":cacheDir/modules",
		fileCacheConfigInternal: fileCacheConfigInternal{
			entryIsDir: true,
			isReadOnly: true, // we need to make it writable when pruning.
		},
	},
	CacheKeyModuleQueries: {
		MaxAge: 24 * time.Hour,
		Dir:    ":cacheDir/modules",
	},
	CacheKeyModuleGitInfo: {
		MaxAge: 24 * time.Hour,
		Dir:    ":cacheDir/modules",
		fileCacheConfigInternal: fileCacheConfigInternal{
			entryIsDir: true,
		},
	},
	CacheKeyImages: {
		MaxAge: -1,
		Dir:    resourcesGenDir,
	},
	CacheKeyAssets: {
		MaxAge: -1,
		Dir:    resourcesGenDir,
	},
	CacheKeyGetResource: {
		MaxAge: -1, // Never expire
		Dir:    cacheDirProject,
	},
	CacheKeyMisc: {
		MaxAge: -1,
		Dir:    cacheDirProject,
	},
}

func init() {
	for k, v := range defaultCacheConfigs {
		v.name = k
		defaultCacheConfigs[k] = v
	}
}

type FileCacheConfig struct {
	// Max age of cache entries in this cache. Any items older than this will
	// be removed and not returned from the cache.
	// A negative value means forever, 0 means cache is disabled.
	// Hugo is lenient with what types it accepts here, but we recommend using
	// a duration string, a sequence of  decimal numbers, each with optional fraction and a unit suffix,
	// such as "300ms", "1.5h" or "2h45m".
	// Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
	MaxAge time.Duration

	// The directory where files are stored.
	Dir string

	fileCacheConfigInternal `json:"-"`
}

func (cfg *FileCacheConfig) init() error {
	if cfg.DirCompiled == "" {
		// From unit tests. Just check that it does not contain any placeholders.
		if strings.Contains(cfg.Dir, ":") {
			return fmt.Errorf("cache dir %q contains unresolved placeholders", cfg.Dir)
		}
		cfg.DirCompiled = cfg.Dir
	}
	// Sanity check the config.
	if len(cfg.DirCompiled) < 5 {
		panic(fmt.Sprintf("invalid cache dir: %q", cfg.DirCompiled))
	}
	return nil
}

type fileCacheConfigInternal struct {
	DirCompiled string

	name          string // The name of this cache, e.g. "images", "modules" etc.
	entryIsDir    bool   // when set, the cache entries represents directories directly below the base dir.
	isReadOnly    bool   // when set, the cache is read only and needs to be pruned differently. This is used for the Go modules cache.
	IsResourceDir bool   //  resources/_gen will get its own composite filesystem that also checks any theme. TODO(bep) unexport this.
}

// MarshalJSON marshals FileCacheConfig to JSON with MaxAge as a human-readable string.
func (c FileCacheConfig) MarshalJSON() ([]byte, error) {
	var maxAge any
	if c.MaxAge == -1 {
		maxAge = -1
	} else {
		maxAge = strings.TrimSuffix(c.MaxAge.String(), "0m0s")
	}
	return json.Marshal(&struct {
		MaxAge any    `json:"maxAge"`
		Dir    string `json:"dir"`
	}{
		MaxAge: maxAge,
		Dir:    c.Dir,
	})
}

// ImageCache gets the file cache for processed images.
func (f Caches) ImageCache() *Cache {
	return f[CacheKeyImages]
}

// ModulesCache gets the file cache for Hugo Modules.
func (f Caches) ModulesCache() *Cache {
	return f[CacheKeyModules]
}

// ModuleQueriesCache gets the file cache for Hugo Module version queries.
// Returns nil if not found.
func (f Caches) ModuleQueriesCache() *Cache {
	c, ok := f[CacheKeyModuleQueries]
	if !ok {
		panic("module queries cache not set")
	}
	return c
}

// ModuleGitInfoCache gets the file cache for Hugo Module git info.
func (f Caches) ModuleGitInfoCache() *Cache {
	c, ok := f[CacheKeyModuleGitInfo]
	if !ok {
		panic("module git info cache not set")
	}
	return c
}

// AssetsCache gets the file cache for assets (processed resources, SCSS etc.).
func (f Caches) AssetsCache() *Cache {
	return f[CacheKeyAssets]
}

// MiscCache gets the file cache for miscellaneous stuff.
func (f Caches) MiscCache() *Cache {
	return f[CacheKeyMisc]
}

// GetResourceCache gets the file cache for remote resources.
func (f Caches) GetResourceCache() *Cache {
	return f[CacheKeyGetResource]
}

func DecodeConfig(fs afero.Fs, bcfg config.BaseConfig, m map[string]any) (Configs, error) {
	c := make(Configs)
	valid := make(map[string]bool)
	// Add defaults
	for k, v := range defaultCacheConfigs {
		c[k] = v
		valid[k] = true
	}

	_, isOsFs := fs.(*afero.OsFs)

	for k, v := range m {
		if _, ok := v.(hmaps.Params); !ok {
			continue
		}
		var ok bool
		cc, ok := c[k]
		if !ok {
			return nil, fmt.Errorf("%q is not a valid cache name", k)
		}

		dc := &mapstructure.DecoderConfig{
			Result:           &cc,
			DecodeHook:       mapstructure.StringToTimeDurationHookFunc(),
			WeaklyTypedInput: true,
		}

		decoder, err := mapstructure.NewDecoder(dc)
		if err != nil {
			return c, err
		}

		if err := decoder.Decode(v); err != nil {
			return nil, fmt.Errorf("failed to decode filecache config: %w", err)
		}

		if cc.Dir == "" {
			return c, errors.New("must provide cache Dir")
		}

		c[k] = cc

	}

	for k, v := range c {
		dir := filepath.ToSlash(filepath.Clean(v.Dir))
		hadSlash := strings.HasPrefix(dir, "/")
		parts := strings.Split(dir, "/")

		for i, part := range parts {
			if strings.HasPrefix(part, ":") {
				resolved, isResource, err := resolveDirPlaceholder(fs, bcfg, part)
				if err != nil {
					return c, err
				}
				if isResource {
					v.IsResourceDir = true
				}
				parts[i] = resolved
			}
		}

		dir = path.Join(parts...)
		if hadSlash {
			dir = "/" + dir
		}
		v.DirCompiled = filepath.Clean(filepath.FromSlash(dir))

		if !v.IsResourceDir {
			if isOsFs && !filepath.IsAbs(v.DirCompiled) {
				return c, fmt.Errorf("%q must resolve to an absolute directory", v.DirCompiled)
			}

			// Avoid cache in root, e.g. / (Unix) or c:\ (Windows)
			if len(strings.TrimPrefix(v.DirCompiled, filepath.VolumeName(v.DirCompiled))) == 1 {
				return c, fmt.Errorf("%q is a root folder and not allowed as cache dir", v.DirCompiled)
			}
		}

		if !strings.HasPrefix(v.DirCompiled, "_gen") {
			// We do cache eviction (file removes) and since the user can set
			// his/hers own cache directory, we really want to make sure
			// we do not delete any files that do not belong to this cache.
			// We do add the cache name as the root, but this is an extra safe
			// guard. We skip the files inside /resources/_gen/ because
			// that would be breaking.
			v.DirCompiled = filepath.Join(v.DirCompiled, FilecacheRootDirname, k)
		} else {
			v.DirCompiled = filepath.Join(v.DirCompiled, k)
		}

		c[k] = v
	}

	return c, nil
}

// Resolves :resourceDir => /myproject/resources etc., :cacheDir => ...
func resolveDirPlaceholder(fs afero.Fs, bcfg config.BaseConfig, placeholder string) (cacheDir string, isResource bool, err error) {
	switch strings.ToLower(placeholder) {
	case ":resourcedir":
		return "", true, nil
	case ":cachedir":
		return bcfg.CacheDir, false, nil
	case ":project":
		return filepath.Base(bcfg.WorkingDir), false, nil
	}

	return "", false, fmt.Errorf("%q is not a valid placeholder (valid values are :cacheDir or :resourceDir)", placeholder)
}
