// Package builder is responsible for building fully rendered kubernetes api
// objects from various input directories. A directory may contain a platform
// spec or a component spec.
package builder

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"cuelang.org/go/cue"
	"cuelang.org/go/cue/cuecontext"
	"cuelang.org/go/cue/load"

	"github.com/holos-run/holos"
	core_v1alpha2 "github.com/holos-run/holos/api/core/v1alpha2"
	core_v1alpha3 "github.com/holos-run/holos/api/core/v1alpha3"
	meta_v1alpha2 "github.com/holos-run/holos/api/meta/v1alpha2"
	"github.com/holos-run/holos/api/v1alpha1"
	"github.com/holos-run/holos/internal/client"
	"github.com/holos-run/holos/internal/errors"
	"github.com/holos-run/holos/internal/logger"
	"github.com/holos-run/holos/internal/render"
)

const (
	KubernetesObjects = core_v1alpha3.KubernetesObjectsKind
	// Helm is the value of the kind field of holos build output indicating helm
	// values and helm command information.
	Helm = core_v1alpha3.HelmChartKind
	// Skip is the value when the instance should be skipped
	Skip = "Skip"
	// KustomizeBuild is the value of the kind field of cue output indicating
	// holos should process the component using kustomize build to render output.
	KustomizeBuild = v1alpha1.KustomizeBuildKind
)

// An Option configures a Builder
type Option func(*config)

type config struct {
	args    []string
	cluster string
	tags    []string
}

type Builder struct {
	cfg config
	ctx *cue.Context
}

type buildPlanWrapper struct {
	buildPlan *core_v1alpha3.BuildPlan
}

func (b *buildPlanWrapper) validate() error {
	if b == nil {
		return fmt.Errorf("invalid BuildPlan: is nil")
	}
	bp := b.buildPlan
	if bp == nil {
		return fmt.Errorf("invalid BuildPlan: is nil")
	}
	errs := make([]string, 0, 2)
	if bp.Kind != core_v1alpha3.BuildPlanKind {
		errs = append(errs, fmt.Sprintf("kind invalid: want: %s have: %s", v1alpha1.BuildPlanKind, bp.Kind))
	}
	if len(errs) > 0 {
		return errors.New("invalid BuildPlan: " + strings.Join(errs, ", "))
	}
	return nil
}

func (b *buildPlanWrapper) resultCapacity() (count int) {
	if b == nil {
		return 0
	}
	bp := b.buildPlan
	count = len(bp.Spec.Components.HelmChartList) +
		len(bp.Spec.Components.KubernetesObjectsList) +
		len(bp.Spec.Components.KustomizeBuildList) +
		len(bp.Spec.Components.Resources)
	return count
}

// New returns a new *Builder configured by opts Option.
func New(opts ...Option) *Builder {
	var cfg config
	for _, f := range opts {
		f(&cfg)
	}
	b := &Builder{
		cfg: cfg,
		ctx: cuecontext.New(),
	}
	return b
}

// Entrypoints configures the leaf directories Builder builds.
func Entrypoints(args []string) Option {
	return func(cfg *config) { cfg.args = args }
}

// Cluster configures the cluster name for the holos component instance.
func Cluster(name string) Option {
	return func(cfg *config) { cfg.cluster = name }
}

// Tags configures tags to pass to cue when building the instance.
func Tags(tags []string) Option {
	return func(cfg *config) { cfg.tags = tags }
}

// Cluster returns the cluster name of the component instance being built.
func (b *Builder) Cluster() string {
	return b.cfg.cluster
}

func (b *Builder) Discriminate(ctx context.Context) (tm holos.TypeMeta, err error) {
	cueModDir, err := b.findCueMod()
	if err != nil {
		err = errors.Wrap(err)
		return
	}

	cueConfig := load.Config{
		Dir:        string(cueModDir),
		ModuleRoot: string(cueModDir),
	}
	bd := &holos.BuildData{ModuleRoot: string(cueModDir)}

	if len(b.cfg.args) > 1 {
		return tm, errors.Wrap(errors.New("cannot provide more than one argument"))
	}

	// Make args relative to the module directory
	args := make([]string, 0, len(b.cfg.args)+2)
	for _, path := range b.cfg.args {
		target, err := filepath.Abs(path)
		if err != nil {
			return tm, errors.Wrap(fmt.Errorf("could not find absolute path: %w", err))
		}
		relPath, err := filepath.Rel(bd.ModuleRoot, target)
		if err != nil {
			return tm, errors.Wrap(fmt.Errorf("invalid argument, must be relative to cue.mod: %w", err))
		}

		bd.InstancePath = holos.InstancePath(target)
		bd.Dir = relPath

		relPath = "./" + relPath
		args = append(args, relPath)
	}

	instances := load.Instances(args, &cueConfig)
	values, err := b.ctx.BuildInstances(instances)
	if err != nil {
		return tm, errors.Wrap(err)
	}
	bd.Value = values[0]
	tm, err = bd.TypeMeta()
	return
}

// Unify returns a cue.Value representing the kind of build holos is meant to
// execute. This function unifies a cue package entrypoint with
// platform.config.json and user data json files located recursively within the
// userdata directory at the cue module root.
//
// Deprecated: use Discriminate instead.
func (b *Builder) Unify(ctx context.Context, cfg *client.Config) (bd holos.BuildData, err error) {
	// Ensure the value is from the same runtime, otherwise cue panics.
	bd.Value = b.ctx.CompileString("")

	cueModDir, err := b.findCueMod()
	if err != nil {
		err = errors.Wrap(err)
		return
	}
	bd.ModuleRoot = string(cueModDir)

	platformConfigData, err := os.ReadFile(filepath.Join(bd.ModuleRoot, client.PlatformConfigFile))
	if err != nil {
		return bd, errors.Wrap(fmt.Errorf("could not load platform model: %w", err))
	}

	// TODO(jeff): Changing these tag names breaks backwards compatibility. We
	// need to refactor this unification into a versioned builder, at least at the
	// component level.  Right now it's executed when rendering the initial
	// Platform spec, which should be backwards compatible but isn't because this
	// package is shared by all versions.
	tags := make([]string, 0, len(b.cfg.tags)+2)
	// TODO: Use instance.FillPath to fill the platform config.
	// Refer to https://pkg.go.dev/cuelang.org/go/cue#Value.FillPath
	tags = append(tags, "holos_platform_config="+string(platformConfigData))
	// TODO(jeff): This is hacky after I switched to reserved holos_ tag names in
	// v1alpha4.  Could use some serious clean up now that --cluster-name is
	// deprecated for --inject holos_cluster=foo, but it was kind of nice to have
	// a required argument.
	if cluster := cfg.Holos().ClusterName(); cluster != "" {
		tags = append(tags, "holos_cluster="+cluster)
	}
	tags = append(tags, b.cfg.tags...)

	cueConfig := load.Config{
		Dir:        bd.ModuleRoot,
		ModuleRoot: bd.ModuleRoot,
		Tags:       tags,
	}

	// Make args relative to the module directory
	args := make([]string, 0, len(b.cfg.args)+2)
	for _, path := range b.cfg.args {
		target, err := filepath.Abs(path)
		if err != nil {
			return bd, errors.Wrap(fmt.Errorf("could not find absolute path: %w", err))
		}
		relPath, err := filepath.Rel(bd.ModuleRoot, target)
		if err != nil {
			return bd, errors.Wrap(fmt.Errorf("invalid argument, must be relative to cue.mod: %w", err))
		}

		// WATCH OUT: Assumes only one instance path is provided via args, which is
		// true when I added this, but may be a poor assumption by the time you read
		// this.
		bd.InstancePath = holos.InstancePath(target)
		bd.Dir = relPath

		relPath = "./" + relPath
		args = append(args, relPath)
	}

	instances := load.Instances(args, &cueConfig)

	values, err := b.ctx.BuildInstances(instances)
	if err != nil {
		err = errors.Wrap(err)
		return
	}

	// Unify into a single Value
	for _, v := range values {
		bd.Value = bd.Value.Unify(v)
	}

	// Fill in #UserData
	userData, err := loadUserData(b.ctx, bd.ModuleRoot)
	if err != nil {
		err = errors.Wrap(err)
		return
	}
	bd.Value = bd.Value.FillPath(cue.ParsePath("#UserData"), userData)

	return
}

// loadUserData recursively unifies userdata/**/*.json files into cue.Value val.
func loadUserData(ctx *cue.Context, moduleRoot string) (val cue.Value, err error) {
	// Ensure the value is from the same runtime, otherwise cue panics.
	val = ctx.CompileString("")

	userdataPath := filepath.Join(moduleRoot, "userdata")
	if err = os.MkdirAll(userdataPath, 0755); err != nil {
		return val, errors.Wrap(err)
	}
	err = filepath.Walk(userdataPath, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return errors.Wrap(err)
		}
		if !info.IsDir() && filepath.Ext(info.Name()) == ".json" {
			userData, err := os.ReadFile(path)
			if err != nil {
				return errors.Wrap(err)
			}
			val = val.Unify(ctx.CompileBytes(userData, cue.Filename(path)))
		}
		return nil
	})

	return val, errors.Wrap(err)
}

// Run builds the cue entrypoint into zero or more Results.  Exactly one CUE
// package entrypoint is expected in the args slice.  The platform config is
// provided to the entrypoint through a json encoded string tag named
// platform_config.  The resulting cue.Value is unified with all user data files
// at the path "#UserData".
//
// Deprecated: Use holos.Builder instead
func (b *Builder) Run(ctx context.Context, cfg *client.Config) (results []*render.Result, err error) {
	log := logger.FromContext(ctx)
	log.DebugContext(ctx, "cue: building instances")

	bd, err := b.Unify(ctx, cfg)
	if err != nil {
		return nil, err
	}
	return b.build(ctx, bd)
}

func (b *Builder) build(ctx context.Context, bd holos.BuildData) (results []*render.Result, err error) {
	log := logger.FromContext(ctx).With("dir", bd.InstancePath)
	value := bd.Value

	if err := value.Err(); err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not build %s: %w", bd.InstancePath, err))
	}

	log.DebugContext(ctx, "cue: validating instance")
	if err := value.Validate(); err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not validate: %w", err))
	}

	log.DebugContext(ctx, "cue: decoding holos build plan")
	jsonBytes, err := value.MarshalJSON()
	if err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not marshal cue instance %s: %w", bd.Dir, err))
	}
	decoder := json.NewDecoder(bytes.NewReader(jsonBytes))

	// Discriminate the type of build plan.
	tm := &v1alpha1.TypeMeta{}
	err = decoder.Decode(tm)
	if err != nil {
		return nil, errors.Wrap(fmt.Errorf("invalid BuildPlan: %s: %w", bd.Dir, err))
	}

	log.DebugContext(ctx, "cue: discriminated build kind: "+tm.Kind, "kind", tm.Kind, "apiVersion", tm.APIVersion)

	// New decoder for the full object
	decoder = json.NewDecoder(bytes.NewReader(jsonBytes))

	// TODO: When we release v1, explicitly allow unknown fields so we can add
	// fields without needing to bump the major version.  Disallow until we reach
	// v1 for clear error reporting.
	decoder.DisallowUnknownFields()

	switch tm.Kind {
	case "BuildPlan":
		var bp core_v1alpha3.BuildPlan
		if err = decoder.Decode(&bp); err != nil {
			err = errors.Wrap(fmt.Errorf("could not decode BuildPlan %s: %w", bd.Dir, err))
			return
		}
		results, err = b.buildPlan(ctx, &bp, bd.InstancePath)
		if err != nil {
			return results, err
		}
	default:
		err = errors.Wrap(fmt.Errorf("unknown kind: %v", tm.Kind))
	}

	return results, err
}

func (b *Builder) buildPlan(ctx context.Context, buildPlan *core_v1alpha3.BuildPlan, path holos.InstancePath) (results []*render.Result, err error) {
	log := logger.FromContext(ctx)

	bpw := buildPlanWrapper{buildPlan: buildPlan}

	if err := bpw.validate(); err != nil {
		log.WarnContext(ctx, "could not validate", "skipped", true, "err", err)
		return nil, errors.Wrap(fmt.Errorf("could not validate %w", err))
	}

	if buildPlan.Spec.Disabled {
		log.DebugContext(ctx, "skipped: spec.disabled is true", "skipped", true)
		return
	}

	results = make([]*render.Result, 0, bpw.resultCapacity())
	log.DebugContext(ctx, "allocated results slice", "cap", bpw.resultCapacity())

	for _, component := range buildPlan.Spec.Components.Resources {
		ko := render.KubernetesObjects{Component: component}
		if result, err := ko.Render(ctx, path); err != nil {
			return nil, errors.Wrap(fmt.Errorf("could not render: %w", err))
		} else {
			results = append(results, result)
		}
	}

	for _, component := range buildPlan.Spec.Components.KubernetesObjectsList {
		ko := render.KubernetesObjects{Component: component}
		if result, err := ko.Render(ctx, path); err != nil {
			return nil, errors.Wrap(fmt.Errorf("could not render: %w", err))
		} else {
			results = append(results, result)
		}
	}
	for _, component := range buildPlan.Spec.Components.HelmChartList {
		hc := render.HelmChart{Component: component}
		if result, err := hc.Render(ctx, path); err != nil {
			return nil, errors.Wrap(fmt.Errorf("could not render: %w", err))
		} else {
			results = append(results, result)
		}
	}
	for _, component := range buildPlan.Spec.Components.KustomizeBuildList {
		kb := render.KustomizeBuild{Component: component}
		if result, err := kb.Render(ctx, path); err != nil {
			return nil, errors.Wrap(fmt.Errorf("could not render: %w", err))
		} else {
			results = append(results, result)
		}
	}

	log.DebugContext(ctx, "returning results", "len", len(results))

	return results, nil
}

// findCueMod returns the root module location containing the cue.mod file or
// directory or an error if the builder arguments do not share a common root
// module.
func (b *Builder) findCueMod() (dir holos.PathCueMod, err error) {
	for _, origPath := range b.cfg.args {
		absPath, err := filepath.Abs(origPath)
		if err != nil {
			return "", err
		}
		path := holos.PathCueMod(absPath)
		for {
			if _, err := os.Stat(filepath.Join(string(path), "cue.mod")); err == nil {
				if dir != "" && dir != path {
					return "", fmt.Errorf("multiple modules not supported: %v is not %v", dir, path)
				}
				dir = path
				break
			} else if !os.IsNotExist(err) {
				return "", err
			}
			parentPath := holos.PathCueMod(filepath.Dir(string(path)))
			if parentPath == path {
				return "", fmt.Errorf("no cue.mod from root to leaf: %v", origPath)
			}
			path = parentPath
		}
	}
	return dir, nil
}

// Platform builds a platform
// TODO: Refactor, lift up into NewPlatform RunE.
func (b *Builder) Platform(ctx context.Context, cfg *client.Config) (*core_v1alpha2.Platform, error) {
	log := logger.FromContext(ctx)
	log.DebugContext(ctx, "cue: building platform instance")
	bd, err := b.Unify(ctx, cfg)
	if err != nil {
		return nil, errors.Wrap(err)
	}
	return b.runPlatform(ctx, bd)
}

func (b *Builder) runPlatform(ctx context.Context, bd holos.BuildData) (*core_v1alpha2.Platform, error) {
	path := holos.InstancePath(bd.Dir)
	log := logger.FromContext(ctx).With("dir", path)

	value := bd.Value
	if err := bd.Value.Err(); err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not load: %w", err))
	}

	log.DebugContext(ctx, "cue: validating instance")
	if err := value.Validate(); err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not validate: %w", err))
	}

	log.DebugContext(ctx, "cue: decoding holos platform")
	jsonBytes, err := value.MarshalJSON()
	if err != nil {
		return nil, errors.Wrap(fmt.Errorf("could not marshal cue instance %s: %w", bd.Dir, err))
	}

	decoder := json.NewDecoder(bytes.NewReader(jsonBytes))
	// Discriminate the type of build plan.
	tm := &meta_v1alpha2.TypeMeta{}
	err = decoder.Decode(tm)
	if err != nil {
		return nil, errors.Wrap(fmt.Errorf("invalid platform: %s: %w", bd.Dir, err))
	}

	log.DebugContext(ctx, "cue: discriminated build kind: "+tm.GetKind(), "kind", tm.GetKind(), "apiVersion", tm.GetAPIVersion())
	decoder = json.NewDecoder(bytes.NewReader(jsonBytes))
	decoder.DisallowUnknownFields()

	var pf core_v1alpha2.Platform
	switch tm.GetKind() {
	case "Platform":
		if err = decoder.Decode(&pf); err != nil {
			err = errors.Wrap(fmt.Errorf("could not decode platform %s: %w", bd.Dir, err))
			return nil, err
		}
		return &pf, nil
	default:
		err = errors.Wrap(fmt.Errorf("unknown kind: %v", tm.GetKind()))
	}

	return nil, err
}