// Copyright 2023 Harness, Inc.
//
// 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 pullreq

import (
	"context"
	"fmt"
	"strconv"
	"strings"
	"time"

	apiauth "github.com/harness/gitness/app/api/auth"
	"github.com/harness/gitness/app/api/controller"
	"github.com/harness/gitness/app/api/usererror"
	"github.com/harness/gitness/app/auth"
	pullreqevents "github.com/harness/gitness/app/events/pullreq"
	"github.com/harness/gitness/app/services/instrument"
	labelsvc "github.com/harness/gitness/app/services/label"
	"github.com/harness/gitness/errors"
	"github.com/harness/gitness/git"
	gitenum "github.com/harness/gitness/git/enum"
	"github.com/harness/gitness/git/sha"
	"github.com/harness/gitness/types"
	"github.com/harness/gitness/types/enum"

	"github.com/rs/zerolog/log"
)

type CreateInput struct {
	IsDraft bool `json:"is_draft"`

	Title       string `json:"title"`
	Description string `json:"description"`

	SourceRepoRef string `json:"source_repo_ref"`
	SourceBranch  string `json:"source_branch"`
	TargetBranch  string `json:"target_branch"`

	ReviewerIDs []int64 `json:"reviewer_ids"`

	Labels []*types.PullReqLabelAssignInput `json:"labels"`
}

func (in *CreateInput) Sanitize() error {
	in.Title = strings.TrimSpace(in.Title)
	in.Description = strings.TrimSpace(in.Description)

	if err := validateTitle(in.Title); err != nil {
		return err
	}

	if err := validateDescription(in.Description); err != nil {
		return err
	}

	return nil
}

// Create creates a new pull request.
func (c *Controller) Create(
	ctx context.Context,
	session *auth.Session,
	repoRef string,
	in *CreateInput,
) (*types.PullReq, error) {
	if err := in.Sanitize(); err != nil {
		return nil, err
	}

	targetRepo, err := c.getRepoCheckAccess(ctx, session, repoRef, enum.PermissionRepoPush)
	if err != nil {
		return nil, fmt.Errorf("failed to acquire access to target repo: %w", err)
	}

	sourceRepo := targetRepo
	if in.SourceRepoRef != "" {
		sourceRepo, err = c.getRepoCheckAccess(ctx, session, in.SourceRepoRef, enum.PermissionRepoPush)
		if err != nil {
			return nil, fmt.Errorf("failed to acquire access to source repo: %w", err)
		}
	}

	if sourceRepo.ID == targetRepo.ID && in.TargetBranch == in.SourceBranch {
		return nil, usererror.BadRequest("target and source branch can't be the same")
	}

	var sourceSHA sha.SHA

	if sourceSHA, err = c.verifyBranchExistence(ctx, sourceRepo, in.SourceBranch); err != nil {
		return nil, err
	}

	if _, err = c.verifyBranchExistence(ctx, targetRepo, in.TargetBranch); err != nil {
		return nil, err
	}

	if err = c.checkIfAlreadyExists(ctx, targetRepo.ID, sourceRepo.ID, in.TargetBranch, in.SourceBranch); err != nil {
		return nil, err
	}

	targetWriteParams, err := controller.CreateRPCInternalWriteParams(ctx, c.urlProvider, session, targetRepo)
	if err != nil {
		return nil, fmt.Errorf("failed to create RPC write params: %w", err)
	}

	mergeBaseResult, err := c.git.MergeBase(ctx, git.MergeBaseParams{
		ReadParams: git.ReadParams{RepoUID: sourceRepo.GitUID},
		Ref1:       in.SourceBranch,
		Ref2:       in.TargetBranch,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to find merge base: %w", err)
	}

	mergeBaseSHA := mergeBaseResult.MergeBaseSHA

	if mergeBaseSHA == sourceSHA {
		return nil, usererror.BadRequest("The source branch doesn't contain any new commits")
	}

	prStats, err := c.git.DiffStats(ctx, &git.DiffParams{
		ReadParams: git.ReadParams{RepoUID: targetRepo.GitUID},
		BaseRef:    mergeBaseSHA.String(),
		HeadRef:    sourceSHA.String(),
	})
	if err != nil {
		return nil, fmt.Errorf("failed to fetch PR diff stats: %w", err)
	}

	var pr *types.PullReq

	targetRepoID := targetRepo.ID

	labelAssignInputMap, err := c.prepareLabels(
		ctx, in.Labels, session.Principal.ID, targetRepo.ID, targetRepo.ParentID,
	)
	if err != nil {
		return nil, fmt.Errorf("failed to prepare labels: %w", err)
	}

	var labelAssignOuts []*labelsvc.AssignToPullReqOut

	err = controller.TxOptLock(ctx, c.tx, func(ctx context.Context) error {
		// Always re-fetch at the start of the transaction because the repo we have is from a cache.

		targetRepoFull, err := c.repoStore.Find(ctx, targetRepoID)
		if err != nil {
			return fmt.Errorf("failed to find repository: %w", err)
		}

		// Update the repository's pull request sequence number

		targetRepoFull.PullReqSeq++
		err = c.repoStore.Update(ctx, targetRepoFull)
		if err != nil {
			return fmt.Errorf("failed to update pullreq sequence number: %w", err)
		}

		// Create pull request in the DB

		pr = newPullReq(session, targetRepoFull.PullReqSeq, sourceRepo.ID, targetRepo.ID, in, sourceSHA, mergeBaseSHA)
		pr.Stats = types.PullReqStats{
			DiffStats:       types.NewDiffStats(prStats.Commits, prStats.FilesChanged, prStats.Additions, prStats.Deletions),
			Conversations:   0,
			UnresolvedCount: 0,
		}

		targetRepo = targetRepoFull.Core()

		// Calculate the activity sequence
		pr.ActivitySeq = int64(len(in.Labels) + len(in.ReviewerIDs))

		err = c.pullreqStore.Create(ctx, pr)
		if err != nil {
			return fmt.Errorf("pullreq creation failed: %w", err)
		}

		// Assign reviewers and labels if any

		if err := c.createReviewers(ctx, session, in.ReviewerIDs, targetRepo, pr); err != nil {
			return err
		}

		if labelAssignOuts, err = c.assignLabels(ctx, pr, session.Principal.ID, labelAssignInputMap); err != nil {
			return err
		}

		c.storeLabelAssignActivity(ctx, pr, session.Principal.ID, labelAssignOuts)

		// Create PR head reference in the git repository

		err = c.git.UpdateRef(ctx, git.UpdateRefParams{
			WriteParams: targetWriteParams,
			Name:        strconv.FormatInt(targetRepoFull.PullReqSeq, 10),
			Type:        gitenum.RefTypePullReqHead,
			NewValue:    sourceSHA,
			OldValue:    sha.None, // we don't care about the old value
		})
		if err != nil {
			return fmt.Errorf("failed to create PR head ref: %w", err)
		}

		return nil
	})
	if err != nil {
		return nil, fmt.Errorf("failed to create pullreq: %w", err)
	}

	backfillWithLabelAssignInfo(pr, labelAssignOuts)

	c.eventReporter.Created(ctx, &pullreqevents.CreatedPayload{
		Base:         eventBase(pr, &session.Principal),
		SourceBranch: in.SourceBranch,
		TargetBranch: in.TargetBranch,
		SourceSHA:    sourceSHA.String(),
	})

	c.sseStreamer.Publish(ctx, targetRepo.ParentID, enum.SSETypePullReqUpdated, pr)

	err = c.instrumentation.Track(ctx, instrument.Event{
		Type:      instrument.EventTypeCreatePullRequest,
		Principal: session.Principal.ToPrincipalInfo(),
		Path:      sourceRepo.Path,
		Properties: map[instrument.Property]any{
			instrument.PropertyRepositoryID:   sourceRepo.ID,
			instrument.PropertyRepositoryName: sourceRepo.Identifier,
			instrument.PropertyPullRequestID:  pr.Number,
		},
	})
	if err != nil {
		log.Ctx(ctx).Warn().Msgf("failed to insert instrumentation record for create pull request operation: %s", err)
	}

	return pr, nil
}

func (c *Controller) createReviewers(
	ctx context.Context,
	session *auth.Session,
	reviewers []int64,
	repo *types.RepositoryCore,
	pr *types.PullReq,
) error {
	if len(reviewers) == 0 {
		return nil
	}

	addedByInfo := session.Principal.ToPrincipalInfo()
	reviewerType := enum.PullReqReviewerTypeRequested

	for _, id := range reviewers {
		if id == addedByInfo.ID {
			return usererror.BadRequest("PR creator cannot be added as a reviewer.")
		}

		reviewerPrincipal, err := c.principalStore.Find(ctx, id)
		if err != nil {
			return usererror.BadRequest("Failed to find principal reviewer.")
		}

		// TODO: To check the reviewer's access to the repo we create a dummy session object. Fix it.
		if err = apiauth.CheckRepo(
			ctx,
			c.authorizer,
			&auth.Session{
				Principal: *reviewerPrincipal,
				Metadata:  nil,
			},
			repo,
			enum.PermissionRepoReview,
		); err != nil {
			if errors.Is(err, apiauth.ErrNotAuthorized) {
				return usererror.BadRequest(
					"The reviewer doesn't have enough permissions for the repository.",
				)
			}
			return fmt.Errorf(
				"reviewer principal: %s access error: %w", reviewerPrincipal.UID, err)
		}

		reviewer := newPullReqReviewer(
			session, pr, repo,
			reviewerPrincipal.ToPrincipalInfo(),
			addedByInfo, reviewerType,
			&ReviewerAddInput{
				ReviewerID: id,
			},
		)

		if err = c.reviewerStore.Create(ctx, reviewer); err != nil {
			return fmt.Errorf("failed to create pull request reviewer: %w", err)
		}
	}

	return nil
}

// prepareLabels fetches data (labels and label values) necessary for the pr label assignment.
// The data recency is not critical: labels/values might change and the op will either be valid or fail.
// Because it makes db calls, we use it before, i.e. outside of the PR creation tx.
func (c *Controller) prepareLabels(
	ctx context.Context,
	labelAssignInputs []*types.PullReqLabelAssignInput,
	principalID int64,
	repoID int64,
	repoParentID int64,
) (map[*types.PullReqLabelAssignInput]*labelsvc.WithValue, error) {
	labelAssignInputMap := make(
		map[*types.PullReqLabelAssignInput]*labelsvc.WithValue,
		len(labelAssignInputs),
	)

	for _, labelAssignInput := range labelAssignInputs {
		labelWithValue, err := c.labelSvc.PreparePullReqLabel(
			ctx,
			principalID, repoID, repoParentID,
			labelAssignInput,
		)
		if err != nil {
			return nil, fmt.Errorf("failed to prepare label assignment data: %w", err)
		}

		labelAssignInputMap[labelAssignInput] = &labelWithValue
	}

	return labelAssignInputMap, nil
}

// assignLabels is a critical op for PR creation, so we use it in the PR creation tx.
func (c *Controller) assignLabels(
	ctx context.Context,
	pr *types.PullReq,
	principalID int64,
	labelAssignInputMap map[*types.PullReqLabelAssignInput]*labelsvc.WithValue,
) ([]*labelsvc.AssignToPullReqOut, error) {
	assignOuts := make([]*labelsvc.AssignToPullReqOut, len(labelAssignInputMap))

	var err error
	var i int
	for labelAssignInput, labelWithValue := range labelAssignInputMap {
		assignOuts[i], err = c.labelSvc.AssignToPullReqOnCreation(
			ctx,
			pr.ID,
			principalID,
			labelWithValue,
			labelAssignInput,
		)
		if err != nil {
			return nil, fmt.Errorf("failed to assign label to pullreq: %w", err)
		}

		i++
	}

	return assignOuts, nil
}

func backfillWithLabelAssignInfo(
	pr *types.PullReq,
	labelAssignOuts []*labelsvc.AssignToPullReqOut,
) {
	pr.Labels = make([]*types.LabelPullReqAssignmentInfo, len(labelAssignOuts))
	for i, assignOut := range labelAssignOuts {
		pr.Labels[i] = assignOut.ToLabelPullReqAssignmentInfo()
	}
}

func (c *Controller) storeLabelAssignActivity(
	ctx context.Context,
	pr *types.PullReq,
	principalID int64,
	labelAssignOuts []*labelsvc.AssignToPullReqOut,
) {
	for _, out := range labelAssignOuts {
		payload := activityPayload(out)
		pr.ActivitySeq++
		if _, err := c.activityStore.CreateWithPayload(
			ctx, pr, principalID, payload, nil,
		); err != nil {
			log.Ctx(ctx).Err(err).Msg("failed to write label assign pull req activity")
		}
	}
}

// newPullReq creates new pull request object.
func newPullReq(
	session *auth.Session,
	number int64,
	sourceRepoID int64,
	targetRepoID int64,
	in *CreateInput,
	sourceSHA, mergeBaseSHA sha.SHA,
) *types.PullReq {
	now := time.Now().UnixMilli()
	return &types.PullReq{
		ID:                0, // the ID will be populated in the data layer
		Version:           0,
		Number:            number,
		CreatedBy:         session.Principal.ID,
		Created:           now,
		Updated:           now,
		Edited:            now,
		State:             enum.PullReqStateOpen,
		IsDraft:           in.IsDraft,
		Title:             in.Title,
		Description:       in.Description,
		SourceRepoID:      sourceRepoID,
		SourceBranch:      in.SourceBranch,
		SourceSHA:         sourceSHA.String(),
		TargetRepoID:      targetRepoID,
		TargetBranch:      in.TargetBranch,
		ActivitySeq:       0,
		MergedBy:          nil,
		Merged:            nil,
		MergeMethod:       nil,
		MergeBaseSHA:      mergeBaseSHA.String(),
		MergeCheckStatus:  enum.MergeCheckStatusUnchecked,
		RebaseCheckStatus: enum.MergeCheckStatusUnchecked,
		Author:            *session.Principal.ToPrincipalInfo(),
		Merger:            nil,
	}
}