package rosa

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"runtime"
	"slices"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"unique"

	"hakurei.app/internal/pkg"
)

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

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

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

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

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

// Artifact is stage-agnostic immutable data with a deterministic resulting
// [pkg.Artifact]. It can be created natively or through evaluation.
type Artifact struct {
	f func(t Toolchain, s *S) (a pkg.Artifact, version string)

	// 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"`

	// 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 *Artifact) 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 *Artifact) 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())
}

// A cachedArtifact holds [pkg.Artifact] and its corresponding version string.
type cachedArtifact struct {
	a pkg.Artifact
	v string
}

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

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

	// Cached [pkg.Artifact].
	c [_toolchainEnd]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 address of the named [Artifact].
func (s *S) Get(p ArtifactH) (meta *Artifact) {
	s.wantsArch()
	v, ok := s.artifacts.Load(p)
	if ok {
		meta = v.(*Artifact)
	}
	return
}

// MustGet is like Get, but panics if the named [Artifact] is not registered.
func (s *S) MustGet(p ArtifactH) (meta *Artifact) {
	meta = s.Get(p)
	if meta == nil {
		panic("artifact " + strconv.Quote(p.String()) + " not available")
	}
	return
}

// Load returns the resulting [pkg.Artifact] of [ArtifactH].
func (s *S) Load(t Toolchain, p ArtifactH) (pkg.Artifact, string) {
	s.wantsArch()
	e, ok := s.c[t].Load(p)
	if ok {
		r := e.(cachedArtifact)
		return r.a, r.v
	}

	meta := s.Get(p)
	if meta == nil {
		return nil, ""
	}
	var r cachedArtifact
	r.a, r.v = meta.f(t, s)
	s.c[t].Store(p, r)
	return r.a, r.v
}

// MustLoad is like Load, but panics if the named [Artifact] is not registered.
func (s *S) MustLoad(t Toolchain, p ArtifactH) (pkg.Artifact, string) {
	a, version := s.Load(t, p)
	if a == nil {
		panic("artifact " + strconv.Quote(p.String()) + " not available")
	}
	return a, version
}

// 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(meta *Artifact) bool {
	if meta.Name == "" {
		return false
	}
	p := ArtifactH(unique.Make(meta.Name))
	_, ok := s.artifacts.LoadOrStore(p, meta)
	if !ok {
		s.artifactCount.Add(1)
	}
	return !ok
}

// MustRegister is like Register, but panics if registration fails.
func (s *S) MustRegister(meta *Artifact) {
	if !s.Register(meta) {
		panic("attempting to register " + strconv.Quote(meta.Name) + " twice")
	}
}

// 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 []ArtifactH) {
	handles = make([]ArtifactH, 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
}

// 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())
}