package gitea

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
)

type DeliveryState string

const (
	DeliveryNotAttempted DeliveryState = "not_attempted"
	DeliveryComplete     DeliveryState = "complete"
	DeliveryPartial      DeliveryState = "partial"
	DeliveryConflict     DeliveryState = "conflict"
	DeliveryUnknown      DeliveryState = "unknown"
)

type AssetIdentity struct {
	Filename string
	SHA256   string
}

// UploadResult reports the current asset observations from one upload attempt.
// Each identity appears in at most one category; early failures can leave some
// declared assets unreported.
type UploadResult struct {
	State DeliveryState
	// Matching contains existing attachments with the declared content.
	Matching []AssetIdentity
	// Uploaded contains assets whose upload was confirmed during this invocation.
	Uploaded []AssetIdentity
	// Pending contains assets known to be missing.
	Pending []AssetIdentity
	// Conflicting contains assets with detected content conflicts.
	Conflicting []AssetIdentity
	// Uncertain contains assets whose remote state could not be resolved.
	Uncertain []AssetIdentity
}

// VerifyLocalAssets checks that every expected file still matches its declared
// size and digest before delivery begins.
func VerifyLocalAssets(assets []ExpectedAsset) error {
	if err := validateExpectedAssets(assets); err != nil {
		return err
	}
	for _, asset := range assets {
		if err := verifyLocalAsset(asset); err != nil {
			return err
		}
	}
	return nil
}

// UploadMissing uploads assets classified missing by InspectAssets. It stops
// before the first write if any declared existing asset conflicts or cannot be
// verified, and never replaces an existing attachment.
func (c Client) UploadMissing(ctx context.Context, destination Destination, releaseID int64, inspection Inspection) (UploadResult, error) {
	return c.uploadMissing(ctx, destination, releaseID, inspection, true)
}

// UploadVerifiedMissing uploads missing assets whose local contents have already
// passed VerifyLocalAssets. It reuses that verification while retaining remote
// inspection, conflict handling, and upload reconciliation.
func (c Client) UploadVerifiedMissing(ctx context.Context, destination Destination, releaseID int64, inspection Inspection) (UploadResult, error) {
	return c.uploadMissing(ctx, destination, releaseID, inspection, false)
}

func (c Client) uploadMissing(ctx context.Context, destination Destination, releaseID int64, inspection Inspection, verifyLocal bool) (UploadResult, error) {
	if releaseID <= 0 {
		return UploadResult{State: DeliveryPartial}, failure(FailureInvalid, "upload release assets", 0, errors.New("release ID must be positive"))
	}
	if strings.TrimSpace(destination.Token) == "" {
		return UploadResult{State: DeliveryPartial}, failure(FailureInvalid, "upload release assets", 0, errors.New("Gitea token is required"))
	}
	base, err := parseBaseURL(destination.BaseURL)
	if err != nil {
		return UploadResult{State: DeliveryPartial}, failure(FailureInvalid, "validate destination", 0, err)
	}
	if strings.TrimSpace(destination.Owner) == "" || strings.ContainsAny(destination.Owner, "/\\") || strings.TrimSpace(destination.Repository) == "" || strings.ContainsAny(destination.Repository, "/\\") {
		return UploadResult{State: DeliveryPartial}, failure(FailureInvalid, "upload release assets", 0, errors.New("Gitea owner and repository must be path segments"))
	}
	expected := orderedExpected(inspection.Assets)
	if err := validateExpectedAssets(expected); err != nil {
		return UploadResult{State: DeliveryPartial}, err
	}
	result := UploadResult{State: DeliveryPartial}
	preflightConflict := false
	preflightUnknown := false
	for _, observation := range inspection.Assets {
		switch observation.State {
		case AssetMatching:
			result.Matching = append(result.Matching, identity(observation.Expected))
		case AssetMissing:
			result.Pending = append(result.Pending, identity(observation.Expected))
		case AssetConflicting:
			preflightConflict = true
			result.Conflicting = append(result.Conflicting, identity(observation.Expected))
		case AssetUnverifiable:
			preflightUnknown = true
			result.Uncertain = append(result.Uncertain, identity(observation.Expected))
		default:
			return result, failure(FailureInvalid, "preflight release assets", 0, fmt.Errorf("asset %q has no inspection result", observation.Expected.Filename))
		}
	}
	if preflightConflict {
		result.State = DeliveryConflict
		return result, failure(FailureConflict, "preflight release assets", 0, errors.New("one or more existing attachments conflict"))
	}
	if preflightUnknown {
		result.State = DeliveryNotAttempted
		return result, failure(FailureUnverifiable, "preflight release assets", 0, errors.New("one or more existing attachments could not be verified"))
	}
	if len(expected) == 0 {
		result.State = DeliveryComplete
		return result, nil
	}
	if len(result.Pending) == 0 {
		result.State = DeliveryComplete
		return result, nil
	}

	missing := make(map[string]ExpectedAsset, len(result.Pending))
	for _, observation := range inspection.Assets {
		if observation.State == AssetMissing {
			missing[observation.Expected.Filename] = observation.Expected
		}
	}
	if verifyLocal {
		for _, item := range expected {
			if _, needsUpload := missing[item.Filename]; !needsUpload {
				continue
			}
			if err := verifyLocalAsset(item); err != nil {
				return result, err
			}
		}
	}

	baseAPI := strings.TrimRight(base.String(), "/") + "/api/v1/repos/" + url.PathEscape(destination.Owner) + "/" + url.PathEscape(destination.Repository)
	client := c.httpClient()
	for _, item := range expected {
		if _, needsUpload := missing[item.Filename]; !needsUpload {
			continue
		}
		status, uploadErr := c.uploadAsset(ctx, client, destination.Token, baseAPI, releaseID, item)
		if uploadErr == nil {
			result.Uploaded = append(result.Uploaded, identity(item))
			result.Pending = removeIdentity(result.Pending, item.Filename)
			continue
		}
		if !shouldReconcileWrite(status, uploadErr) {
			return result, uploadErr
		}
		inspection, inspectErr := c.InspectAssets(ctx, destination, releaseID, []ExpectedAsset{item})
		if inspectErr != nil || len(inspection.Assets) != 1 {
			result.State = DeliveryUnknown
			result.Pending = removeIdentity(result.Pending, item.Filename)
			result.Uncertain = append(result.Uncertain, identity(item))
			return result, failure(FailureUnknown, "resolve asset upload", status, errors.Join(uploadErr, inspectErr))
		}
		observation := inspection.Assets[0]
		switch observation.State {
		case AssetMatching:
			result.Matching = append(result.Matching, identity(item))
			result.Pending = removeIdentity(result.Pending, item.Filename)
		case AssetConflicting:
			result.State = DeliveryConflict
			result.Pending = removeIdentity(result.Pending, item.Filename)
			result.Conflicting = append(result.Conflicting, identity(item))
			return result, failure(FailureConflict, "resolve asset upload", status, uploadErr)
		case AssetMissing:
			if status == http.StatusConflict {
				result.State = DeliveryConflict
				result.Pending = removeIdentity(result.Pending, item.Filename)
				result.Conflicting = append(result.Conflicting, identity(item))
				return result, failure(FailureConflict, "resolve asset upload", status, uploadErr)
			}
			result.State = DeliveryUnknown
			result.Pending = removeIdentity(result.Pending, item.Filename)
			result.Uncertain = append(result.Uncertain, identity(item))
			return result, failure(FailureUnknown, "resolve asset upload", status, uploadErr)
		default:
			result.State = DeliveryUnknown
			result.Pending = removeIdentity(result.Pending, item.Filename)
			result.Uncertain = append(result.Uncertain, identity(item))
			return result, failure(FailureUnknown, "resolve asset upload", status, errors.Join(uploadErr, observation.Err))
		}
	}
	if len(result.Pending) == 0 {
		result.State = DeliveryComplete
	} else {
		result.State = DeliveryPartial
	}
	return result, nil
}

func (c Client) uploadAsset(ctx context.Context, client *http.Client, token, apiRoot string, releaseID int64, asset ExpectedAsset) (int, error) {
	uploadURL := apiRoot + "/releases/" + strconv.FormatInt(releaseID, 10) + "/assets"
	parsed, err := url.Parse(uploadURL)
	if err != nil {
		return 0, failure(FailureInvalid, "prepare asset upload", 0, err)
	}
	query := parsed.Query()
	query.Set("name", asset.Filename)
	parsed.RawQuery = query.Encode()
	reader, writer := io.Pipe()
	multipartWriter := multipart.NewWriter(writer)
	writeDone := make(chan error, 1)
	go func() {
		part, partErr := multipartWriter.CreateFormFile("attachment", asset.Filename)
		if partErr == nil {
			var source io.Reader
			if len(asset.Content) > 0 {
				source = bytes.NewReader(asset.Content)
			} else {
				file, openErr := os.Open(asset.Path)
				if openErr != nil {
					partErr = openErr
				} else {
					defer file.Close()
					source = file
				}
			}
			if partErr == nil {
				_, partErr = io.Copy(part, source)
			}
		}
		closeErr := multipartWriter.Close()
		if partErr == nil {
			partErr = closeErr
		}
		_ = writer.CloseWithError(partErr)
		writeDone <- partErr
	}()

	request, err := http.NewRequestWithContext(ctx, http.MethodPost, parsed.String(), reader)
	if err != nil {
		_ = reader.CloseWithError(err)
		<-writeDone
		return 0, failure(FailureInvalid, "upload release asset", 0, err)
	}
	request.Header.Set("Authorization", "token "+token)
	request.Header.Set("Accept", "application/json")
	request.Header.Set("Content-Type", multipartWriter.FormDataContentType())
	response, requestErr := client.Do(request)
	if requestErr != nil {
		_ = reader.CloseWithError(requestErr)
		<-writeDone
		return 0, failure(FailureTransport, "upload release asset", 0, requestErr)
	}
	defer response.Body.Close()
	writeErr := <-writeDone
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		return response.StatusCode, responseFailure("upload release asset", response.StatusCode)
	}
	var uploaded assetResponse
	if err := decodeJSON(response.Body, &uploaded); err != nil {
		return response.StatusCode, failure(FailureMalformed, "decode uploaded asset", response.StatusCode, err)
	}
	if uploaded.ID <= 0 || uploaded.Name != asset.Filename {
		return response.StatusCode, failure(FailureMalformed, "verify uploaded asset", response.StatusCode, errors.New("upload response does not identify the selected asset"))
	}
	if writeErr != nil {
		return response.StatusCode, failure(FailureMalformed, "stream uploaded asset", response.StatusCode, writeErr)
	}
	return response.StatusCode, nil
}

func verifyLocalAsset(asset ExpectedAsset) error {
	if len(asset.Content) > 0 {
		if int64(len(asset.Content)) != asset.Size || digest(asset.Content) != asset.SHA256 {
			return failure(FailureConflict, "verify local asset", 0, fmt.Errorf("local content does not match declared asset %q", asset.Filename))
		}
		return nil
	}
	if asset.Path == "" || filepath.Base(asset.Path) != asset.Filename {
		return failure(FailureInvalid, "verify local asset", 0, fmt.Errorf("local path for %q does not match its filename", asset.Filename))
	}
	file, err := os.Open(asset.Path)
	if err != nil {
		return failure(FailureInvalid, "verify local asset", 0, fmt.Errorf("open %q: %w", asset.Filename, err))
	}
	defer file.Close()
	info, err := file.Stat()
	if err != nil {
		return failure(FailureInvalid, "verify local asset", 0, fmt.Errorf("stat %q: %w", asset.Filename, err))
	}
	if !info.Mode().IsRegular() || info.Size() != asset.Size {
		return failure(FailureConflict, "verify local asset", 0, fmt.Errorf("local file does not match declared size for %q", asset.Filename))
	}
	hasher := sha256.New()
	size, err := io.Copy(hasher, file)
	if err != nil {
		return failure(FailureInvalid, "verify local asset", 0, fmt.Errorf("read %q: %w", asset.Filename, err))
	}
	if size != asset.Size || hex.EncodeToString(hasher.Sum(nil)) != asset.SHA256 {
		return failure(FailureConflict, "verify local asset", 0, fmt.Errorf("local content does not match declared asset %q", asset.Filename))
	}
	return nil
}

func orderedExpected(observations []AssetInspection) []ExpectedAsset {
	result := make([]ExpectedAsset, 0, len(observations))
	for _, observation := range observations {
		result = append(result, observation.Expected)
	}
	sort.Slice(result, func(i, j int) bool {
		if result[i].Filename == ManifestFilename {
			return false
		}
		if result[j].Filename == ManifestFilename {
			return true
		}
		return result[i].Filename < result[j].Filename
	})
	return result
}

func identity(asset ExpectedAsset) AssetIdentity {
	return AssetIdentity{Filename: asset.Filename, SHA256: asset.SHA256}
}

func removeIdentity(identities []AssetIdentity, filename string) []AssetIdentity {
	for index, item := range identities {
		if item.Filename == filename {
			return append(identities[:index], identities[index+1:]...)
		}
	}
	return identities
}