package rosa

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"io/fs"
	"net/http"
	"path/filepath"
	"reflect"
	"runtime"
	"slices"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"unique"
	"unsafe"

	"hakurei.app/internal/pkg"
	"hakurei.app/internal/rosa/azalea"
)

// ArtifactH is a handle of the unique name of a prepared [pkg.Artifact].
type ArtifactH unique.Handle[string]

// H is a convenient function for acquiring an [ArtifactH] by name.
func H(name string) ArtifactH { return ArtifactH(unique.Make(name)) }

// String returns the name of p.
func (handle ArtifactH) String() string {
	return unique.Handle[string](handle).Value()
}

// MarshalJSON represents [ArtifactH] by its [Artifact.Name].
func (handle ArtifactH) MarshalJSON() ([]byte, error) {
	return json.Marshal(handle.String())
}

// UnmarshalJSON resolves [ArtifactH] by its [Artifact.Name].
func (handle *ArtifactH) UnmarshalJSON(data []byte) error {
	var name string
	if err := json.Unmarshal(data, &name); err != nil {
		return err
	}
	*handle = ArtifactH(unique.Make(name))
	return nil
}

// A HandleError is panicked when attempting to acquire an [Artifact] via an
// invalid [ArtifactH] with the Must suite of methods.
type HandleError ArtifactH

func (e HandleError) Error() string {
	return "package " + strconv.Quote(ArtifactH(e).String()) + " not available"
}

type (
	// Stage denotes the infrastructure to compile a [pkg.Artifact] on.
	Stage uint32
	// Toolchain refers to an instance of [S], and a [Stage] to compile on.
	Toolchain struct {
		stage Stage

		*S
	}
)

// P represents multiple [ArtifactH].
type P []ArtifactH

// Metadata is stage-agnostic immutable data around [Artifact] not directly
// representable in the resulting [pkg.Artifact].
type Metadata struct {
	// Unique package name.
	Name string `json:"name"`
	// Short user-facing description.
	Description string `json:"description"`
	// Project home page.
	Website string `json:"website,omitempty"`

	// Runtime dependencies.
	Dependencies P `json:"dependencies"`

	// Package version.
	Version string `json:"version"`
	// Project identifier on [Anitya].
	//
	// [Anitya]: https://release-monitoring.org/
	ID int `json:"-"`

	// Whether to exclude from exported functions.
	Exclude bool `json:"exclude,omitempty"`

	// Optional custom version checking behaviour.
	latest func(v *Versions) string
}

// GetLatest returns the latest version described by v.
func (meta *Metadata) GetLatest(v *Versions) string {
	if meta.latest != nil {
		return meta.latest(v)
	}
	return v.Latest
}

// Unversioned denotes an unversioned [Artifact].
const Unversioned = "\x00"

// UnpopulatedIDError is returned by [Artifact.GetLatest] for an instance of
// [Artifact] where ID is not populated.
type UnpopulatedIDError struct{}

func (UnpopulatedIDError) Unwrap() error { return errors.ErrUnsupported }
func (UnpopulatedIDError) Error() string { return "Anitya ID is not populated" }

// Versions are package versions returned by Anitya.
type Versions struct {
	// The latest version for the project, as determined by the version sorting algorithm.
	Latest string `json:"latest_version"`
	// List of all versions that aren’t flagged as pre-release.
	Stable []string `json:"stable_versions"`
	// List of all versions stored, sorted from newest to oldest.
	All []string `json:"versions"`
}

// getStable returns the first Stable version, or Latest if that is unavailable.
func (v *Versions) getStable() string {
	if len(v.Stable) == 0 {
		return v.Latest
	}
	return v.Stable[0]
}

// GetVersions returns versions fetched from Anitya.
func (meta *Metadata) GetVersions(ctx context.Context) (*Versions, error) {
	if meta.ID == 0 {
		return nil, UnpopulatedIDError{}
	}

	var resp *http.Response
	if req, err := http.NewRequestWithContext(
		ctx,
		http.MethodGet,
		"https://release-monitoring.org/api/v2/versions/?project_id="+
			strconv.Itoa(meta.ID),
		nil,
	); err != nil {
		return nil, err
	} else {
		req.Header.Set("User-Agent", "Rosa/1.1")
		if resp, err = http.DefaultClient.Do(req); err != nil {
			return nil, err
		}
	}

	var v Versions
	err := json.NewDecoder(resp.Body).Decode(&v)
	return &v, errors.Join(err, resp.Body.Close())
}

// Artifact is a lazily initialised [pkg.Artifact] with associated [Metadata].
type Artifact func(t Toolchain) (meta *Metadata, a pkg.Artifact)

// A cachedArtifact caches satisfied [Artifact].
type cachedArtifact struct {
	meta *Metadata
	a    pkg.Artifact
}

const (
	// OptSkipCheck skips running all test suites.
	OptSkipCheck = 1 << iota
	// OptLLVMNoLTO disables LTO in all [LLVM] stages.
	OptLLVMNoLTO
)

// S holds a set of [Artifact].
type S struct {
	// [ArtifactH] to [Artifact].
	artifacts sync.Map
	// Size of artifacts.
	artifactCount atomic.Uint64

	// Target architecture.
	arch string
	// For initialising arch.
	archOnce sync.Once

	// Built-in functions.
	frame azalea.Frame
	// For initialising frame.
	frameOnce sync.Once
	// Must only be accessed after a call to getFrame.
	spool sync.Pool

	// Options for [pkg.Artifact] created against [S].
	opts int

	// Cached [pkg.Artifact].
	c [_stageEnd]sync.Map

	// URL of a Gentoo stage3 tarball.
	gentooStage3 string
	// Expected checksum of gentooStage3.
	gentooStage3Checksum pkg.Checksum
}

// Clone returns a copy of s.
func (s *S) Clone() *S {
	v := S{arch: s.arch}
	s.artifacts.Range(func(key, value any) bool {
		v.artifacts.Store(key, value)
		v.artifactCount.Add(1)
		return true
	})
	return &v
}

// wantsArch must be called before accessing arch.
func (s *S) wantsArch() {
	s.archOnce.Do(func() {
		if s.arch == "" {
			s.arch = runtime.GOARCH
		}
	})
}

// Arch returns the target architecture.
func (s *S) Arch() string { s.wantsArch(); return s.arch }

// Flags returns the current preset flags.
func (s *S) Flags() int { return s.opts }

// DropCaches arranges for all cached [pkg.Artifact] to be freed some time after
// it returns. Must not be used concurrently with any other method.
func (s *S) DropCaches(targetArch string, flags int) {
	if targetArch == "" {
		targetArch = runtime.GOARCH
	}

	s.arch = targetArch
	s.opts = flags
	for i := range s.c {
		s.c[i].Clear()
	}
}

// get returns the named [Artifact].
func (s *S) get(handle ArtifactH) (f Artifact) {
	s.wantsArch()
	v, ok := s.artifacts.Load(handle)
	if ok {
		f = v.(Artifact)
	}
	return
}

// mustGet is like get, but panics if the named [Artifact] is not registered.
func (s *S) mustGet(handle ArtifactH) (f Artifact) {
	f = s.get(handle)
	if f == nil {
		panic(HandleError(handle))
	}
	return
}

// New returns a [Toolchain] for the specified [Stage].
func (s *S) New(stage Stage) Toolchain {
	return Toolchain{S: s, stage: stage}
}

// Std is a convenience method that returns a [Toolchain] for the [Std] stage.
func (s *S) Std() Toolchain { return s.New(Std) }

// LoadError wraps panicked errors reaching [Toolchain.Load].
type LoadError struct {
	// Offending artifact handle.
	Handle ArtifactH
	// Recovered error.
	Err error
}

func (e LoadError) Unwrap() error { return e.Err }
func (e LoadError) Error() string {
	return "cannot load " + strconv.Quote(e.Handle.String()) + ": " + e.Err.Error()
}

// Load satisfies an [Artifact] referred to by an [ArtifactH].
func (t Toolchain) Load(handle ArtifactH) (*Metadata, pkg.Artifact) {
	defer func() {
		r := recover()
		if r == nil {
			return
		}

		err, ok := r.(error)
		if !ok {
			panic(r)
		}

		if _, ok = err.(LoadError); ok {
			panic(err)
		}
		panic(LoadError{handle, err})
	}()

	t.wantsArch()
	e, ok := t.c[t.stage].Load(handle)
	if ok {
		r := e.(cachedArtifact)
		return r.meta, r.a
	}

	f := t.get(handle)
	if f == nil {
		return nil, nil
	}
	var r cachedArtifact
	r.meta, r.a = f(t)
	t.c[t.stage].Store(handle, r)
	return r.meta, r.a
}

// MustLoad is like Load, but panics if the named [Artifact] is not registered.
func (t Toolchain) MustLoad(handle ArtifactH) (*Metadata, pkg.Artifact) {
	meta, a := t.Load(handle)
	if meta == nil {
		panic(HandleError(handle))
	}
	return meta, a
}

// Register arranges for a new [Artifact] to be cured under s. It returns false
// if another [Artifact] is already registered under the same name.
func (s *S) Register(name string, f Artifact) bool {
	if name == "" {
		return false
	}
	p := ArtifactH(unique.Make(name))
	_, ok := s.artifacts.LoadOrStore(p, f)
	if !ok {
		s.artifactCount.Add(1)
	}
	return !ok
}

// RegisterError is returned or panicked when attempting to register multiple
// [Artifact] with the same name.
type RegisterError ArtifactH

func (e RegisterError) Error() string {
	if ArtifactH(e).String() == "" {
		return "attempting to register invalid name"
	}
	return "attempting to register " + strconv.Quote(ArtifactH(e).String()) + " twice"
}

// MustRegister is like Register, but panics if registration fails.
func (s *S) MustRegister(name string, f Artifact) {
	if !s.Register(name, f) {
		panic(RegisterError(H(name)))
	}
}

// mustRegister registers an [Artifact] with the old function signature.
//
// Deprecated: Artifacts should be migrated to Register.
func (s *S) mustRegister(
	f func(t Toolchain) (pkg.Artifact, string),
	meta *Metadata,
) {
	s.MustRegister(meta.Name, func(t Toolchain) (*Metadata, pkg.Artifact) {
		v := *meta
		a, version := f(t)
		v.Version = version
		return &v, a
	})
}

// Count returns the number of [Artifact] registered to s.
func (s *S) Count() int {
	return int(s.artifactCount.Load())
}

// Collect returns all [ArtifactH] registered to s.
func (s *S) Collect() (handles P) {
	handles = make(P, 0, s.Count())
	s.artifacts.Range(func(key, _ any) bool {
		handles = append(handles, key.(ArtifactH))
		return true
	})
	slices.SortFunc(handles, func(a, b ArtifactH) int {
		return strings.Compare(a.String(), b.String())
	})
	return
}

// deferredGit is a call to Toolchain.newTagRemote from azalea.
type deferredGit struct {
	url      string
	tag      string
	checksum string
}

// getFrame must be called before accessing s.
func (s *S) getFrame() azalea.Frame {
	s.frameOnce.Do(func() {
		s.spool.New = func() any {
			v := make([]azalea.Frame, 1, 1<<4)
			v[0] = s.getFrame()
			return v
		}

		s.wantsArch()
		k := func(name string) unique.Handle[azalea.Ident] {
			return unique.Make(azalea.Ident(name))
		}

		var (
			identDefault = k("default")
			identArch    = k(s.arch)
		)

		s.frame.Val = map[unique.Handle[azalea.Ident]]any{
			k("linuxArch"): s.linuxArch(),

			k("jobsE"):      jobsE,
			k("jobsFlagE"):  jobsFlagE,
			k("jobsLE"):     jobsLE,
			k("jobsLFlagE"): jobsLFlagE,
		}
		s.frame.Func = map[unique.Handle[azalea.Ident]]azalea.F{

			// library functions

			k("join"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var elems []string
				var sep string
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("elems"): &elems,
					k("sep"):   &sep,
				}); err != nil {
					return
				}
				v = strings.Join(elems, sep)
				set = true
				return
			}},

			// intenral/pkg built-ins

			k("remoteTar"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var url, checksum string
				var compress uint32
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("url"):      &url,
					k("checksum"): &checksum,
					k("compress"): &compress,
				}); err != nil {
					return
				}
				v = pkg.NewHTTPGetTar(nil, url, mustDecode(checksum), compress)
				set = true
				return
			}, V: map[unique.Handle[azalea.Ident]]any{
				k("uncompressed"): uint32(pkg.TarUncompressed),
				k("gzip"):         uint32(pkg.TarGzip),
				k("bzip2"):        uint32(pkg.TarBzip2),
			}},

			k("remoteFile"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var url, checksum string
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("url"):      &url,
					k("checksum"): &checksum,
				}); err != nil {
					return
				}
				v = pkg.NewHTTPGet(nil, url, mustDecode(checksum))
				set = true
				return
			}},

			// state helpers

			k("arch"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var fallback any
				for _, arg := range args {
					switch arg.K {
					case identDefault:
						fallback = arg.V
						continue

					case identArch:
						return arg.V, true, nil
					}
				}

				return fallback, fallback != nil, nil
			}},

			// convenience functions

			k("remoteGit"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var a deferredGit
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("url"):      &a.url,
					k("tag"):      &a.tag,
					k("checksum"): &a.checksum,
				}); err != nil {
					return
				}
				v = a
				set = true
				return
			}},

			k("remoteGitLab"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var domain, suffix, ref, checksum string
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("domain"):   &domain,
					k("suffix"):   &suffix,
					k("ref"):      &ref,
					k("checksum"): &checksum,
				}); err != nil {
					return
				}
				v = newFromGitLab(domain, suffix, ref, checksum)
				set = true
				return
			}},

			k("remoteCPAN"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var author, name, version, checksum string
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("author"):   &author,
					k("name"):     &name,
					k("version"):  &version,
					k("checksum"): &checksum,
				}); err != nil {
					return
				}
				v = newFromCPAN(author, name, version, checksum)
				set = true
				return
			}},

			k("remoteGitHub"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var suffix, tag, checksum string
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("suffix"):   &suffix,
					k("tag"):      &tag,
					k("checksum"): &checksum,
				}); err != nil {
					return
				}
				v = newFromGitHub(suffix, tag, checksum)
				set = true
				return
			}},

			// high-level helpers

			k("make"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var attr MakeHelper
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("omitDefaults"):  &attr.OmitDefaults,
					k("generate"):      &attr.Generate,
					k("preMake"):       &attr.ScriptMakeEarly,
					k("preCheck"):      &attr.ScriptCheckEarly,
					k("postInstall"):   &attr.Script,
					k("inPlace"):       &attr.InPlace,
					k("skipConfigure"): &attr.SkipConfigure,
					k("configureName"): &attr.ConfigureName,
					k("configure"):     &attr.Configure,
					k("host"):          &attr.Host,
					k("build"):         &attr.Build,
					k("make"):          &attr.Make,
					k("skipCheck"):     &attr.SkipCheck,
					k("check"):         &attr.Check,
					k("install"):       &attr.Install,

					k("skipEarlyStageCheck"): &attr.SkipCheckEarly,
				}); err != nil {
					return
				}
				v = &attr
				set = true
				return
			}},

			k("makeMaker"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var attr MakeMakerHelper
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("skipCheck"): &attr.SkipCheck,
				}); err != nil {
					return
				}
				v = &attr
				set = true
				return
			}},

			k("pip"): {F: func(
				args azalea.FArgs,
			) (v any, set bool, err error) {
				var attr PipHelper
				if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
					k("append"):         &attr.Append,
					k("buildIsolation"): &attr.BuildIsolation,
					k("enterSource"):    &attr.EnterSource,
					k("install"):        &attr.Install,
					k("skipCheck"):      &attr.SkipCheck,
					k("check"):          &attr.Check,
					k("postInstall"):    &attr.Script,
				}); err != nil {
					return
				}
				v = &attr
				set = true
				return
			}},
		}
	})
	return s.frame
}

// getStack returns a new stack for azalea evaluation.
func (s *S) getStack() []azalea.Frame {
	s.getFrame()
	return s.spool.Get().([]azalea.Frame)
}

// putStack returns a stack to spool.
func (s *S) putStack(v []azalea.Frame) { s.spool.Put(v) }

// toHandles makes handles out of an [azalea.Array] of identifiers.
func toHandles(idents azalea.Array) (P, error) {
	handles := make(P, len(idents))
	for i, p := range idents {
		if len(p) != 1 {
			return nil, azalea.EvaluationError{
				Expr: p,
				Err:  errors.New("concatenation not allowed for handles"),
			}
		}
		s, ok := p[0].(azalea.Ident)
		if !ok {
			return nil, azalea.EvaluationError{
				Expr: p[0],
				Err:  errors.New("identifiers expected for handles"),
			}
		}
		handles[i] = H(string(s))
	}
	return handles, nil
}

// evalContext holds per-artifact context.
type evalContext struct {
	// Backing filesystem.
	b fs.FS
	// Pending azalea function.
	expr *azalea.Func
	// Current toolchain.
	t Toolchain
}

// pf implements [azalea.PF].
func (ctx *evalContext) pf(
	name azalea.Ident,
	args azalea.FArgs,
) (v any, set bool, err error) {
	k := func(name string) unique.Handle[azalea.Ident] {
		return unique.Make(azalea.Ident(name))
	}

	meta := Metadata{Name: string(name)}
	var (
		attr    PackageAttr
		patches []string
		excl    bool
		early   bool

		anitya  int64
		sourceA any
		helper  Helper

		inputs, runtimes azalea.Array

		anityaFallback   bool
		anityaLegacyCPAN bool
	)
	if err = args.Apply(map[unique.Handle[azalea.Ident]]any{
		k("description"): &meta.Description,
		k("website"):     &meta.Website,
		k("version"):     &meta.Version,
		k("anitya"):      &anitya,

		k("writable"):    &attr.Writable,
		k("chmod"):       &attr.Chmod,
		k("enterSource"): &attr.EnterSource,
		k("env"):         &attr.Env,
		k("early"):       &attr.ScriptEarly,
		k("patches"):     &patches,
		k("exclusive"):   &excl,
		k("toyboxEarly"): &early,

		k("source"):  &sourceA,
		k("exec"):    &helper,
		k("inputs"):  &inputs,
		k("runtime"): &runtimes,

		k("anityaFallback"):   &anityaFallback,
		k("anityaLegacyCPAN"): &anityaLegacyCPAN,
	}); err != nil {
		return
	}
	var inputsH P
	if inputsH, err = toHandles(inputs); err != nil {
		return
	} else if meta.Dependencies, err = toHandles(runtimes); err != nil {
		return
	}

	for _, pathname := range patches {
		var p []byte
		p, err = fs.ReadFile(ctx.b, pathname)
		if err != nil {
			return
		}
		attr.Patches = append(attr.Patches, KV{
			strings.TrimSuffix(filepath.Base(pathname), ".patch"),
			unsafe.String(unsafe.SliceData(p), len(p)),
		})
	}
	if excl {
		attr.Flag |= TExclusive
	}
	if early {
		attr.Flag |= TEarly
	}

	meta.ID = int(anitya)
	if anityaFallback {
		meta.latest = (*Versions).getStable
	} else if anityaLegacyCPAN {
		meta.latest = func(v *Versions) string {
			for _, s := range v.Stable {
				_, m, ok := strings.Cut(s, ".")
				if !ok {
					continue
				}
				if len(m) > 1 && m[0] == '0' {
					continue
				}
				return s
			}
			return v.Latest
		}
	}
	var source pkg.Artifact
	switch p := sourceA.(type) {
	case pkg.Artifact:
		source = p

	case deferredGit:
		source = ctx.t.newTagRemote(p.url, p.tag, p.checksum)

	default:
		panic(azalea.TypeError{
			Concrete: reflect.TypeOf(sourceA),
			Asserted: reflect.TypeFor[pkg.Artifact](),
		})
	}

	v = cachedArtifact{&meta, ctx.t.NewPackage(
		meta.Name,
		meta.Version,
		source,
		&attr,
		helper,
		inputsH...,
	)}
	set = true
	return
}

var (
	// ErrToplevel is returned by [S.Evaluate] when encountering a toplevel
	// expression other than a package declaration.
	ErrToplevel = errors.New("top level must only contain package declarations")
)

// RegisterAzalea registers all package declarations from r. The backing
// filesystem is directly exposed to azalea pathnames.
func (s *S) RegisterAzalea(r io.Reader, b fs.FS) error {
	var pending []*azalea.Func
	if expressions, err := azalea.Parse(r); err != nil {
		return err
	} else {
		pending = make([]*azalea.Func, len(expressions))
		for i, expr := range expressions {
			f, ok := expr.(azalea.Func)
			if !ok || !f.Package {
				return ErrToplevel
			}
			pending[i] = &f
		}
	}

	for _, f := range pending {
		if !s.Register(string(f.Ident), func(t Toolchain) (*Metadata, pkg.Artifact) {
			v, set, err := azalea.Evaluate[cachedArtifact](
				(&evalContext{b, f, t}).pf,
				s.getStack(),
				*f,
			)
			if err != nil {
				panic(err)
			} else if !set {
				panic(errors.New("unexpected unset"))
			}
			return v.meta, v.a
		}) {
			return RegisterError(H(string(f.Ident)))
		}
	}
	return nil
}

// RegisterFS registers from azalea files discovered in fsys. A file is
// evaluated if it is at the top level and its name has the suffix ".az", or it
// is in a top-level directory with the exact file name "package.az". The
// backing filesystem is directly exposed to azalea pathnames.
func (s *S) RegisterFS(fsys fs.FS) error {
	dents, err := fs.ReadDir(fsys, ".")
	if err != nil {
		return err
	}

	var r fs.File
	for _, dent := range dents {
		if dent.IsDir() {
			var sub fs.FS
			sub, err = fs.Sub(fsys, dent.Name())
			if err != nil {
				return err
			}

			r, err = sub.Open("package.az")
			if errors.Is(err, fs.ErrNotExist) {
				continue
			}
			if err != nil {
				return err
			}

			err = s.RegisterAzalea(r, sub)
			if _err := r.Close(); err == nil {
				err = _err
			}
			if err != nil {
				return err
			}
			continue
		}

		if !dent.Type().IsRegular() ||
			!strings.HasSuffix(dent.Name(), ".az") {
			continue
		}

		r, err = fsys.Open(dent.Name())
		if err != nil {
			return err
		}

		err = s.RegisterAzalea(r, fsys)
		if _err := r.Close(); err == nil {
			err = _err
		}
		if err != nil {
			return err
		}
	}
	return nil
}

// SetGentooStage3 sets the Gentoo stage3 tarball url and checksum. It panics
// if given zero values or if these values have already been set.
func (s *S) SetGentooStage3(url string, checksum pkg.Checksum) {
	if s.gentooStage3 != "" {
		panic(errors.New("attempting to set Gentoo stage3 url twice"))
	}
	if url == "" {
		panic(errors.New("attempting to set Gentoo stage3 url to the zero value"))
	}
	s.gentooStage3, s.gentooStage3Checksum = url, checksum
	s.DropCaches(s.Arch(), s.Flags())
}