package regression

import (
	"context"
	"fmt"

	"gorm.io/gorm"
)

// Result holds the regression comparison between two commits.
type Result struct {
	BaseSHA      string   `json:"base_sha"`
	HeadSHA      string   `json:"head_sha"`
	RepoName     string   `json:"repo_name"`
	New          []string `json:"new"`       // Fingerprints in head but not base.
	Fixed        []string `json:"fixed"`     // Fingerprints in base but not head.
	Recurring    []string `json:"recurring"` // Fingerprints in both.
	IsRegression bool     `json:"is_regression"`
}

// Compare computes the set difference of crash fingerprints between a base and head commit.
func Compare(ctx context.Context, db *gorm.DB, repoID uint, baseSHA, headSHA string) (*Result, error) {
	baseFingerprints, err := fingerprintsForCommit(ctx, db, repoID, baseSHA)
	if err != nil {
		return nil, fmt.Errorf("base commit fingerprints: %w", err)
	}

	headFingerprints, err := fingerprintsForCommit(ctx, db, repoID, headSHA)
	if err != nil {
		return nil, fmt.Errorf("head commit fingerprints: %w", err)
	}

	baseSet := toSet(baseFingerprints)
	headSet := toSet(headFingerprints)

	var newFPs, fixedFPs, recurringFPs []string

	for fp := range headSet {
		if baseSet[fp] {
			recurringFPs = append(recurringFPs, fp)
		} else {
			newFPs = append(newFPs, fp)
		}
	}

	for fp := range baseSet {
		if !headSet[fp] {
			fixedFPs = append(fixedFPs, fp)
		}
	}

	return &Result{
		BaseSHA:      baseSHA,
		HeadSHA:      headSHA,
		New:          newFPs,
		Fixed:        fixedFPs,
		Recurring:    recurringFPs,
		IsRegression: len(newFPs) > 0,
	}, nil
}

func fingerprintsForCommit(ctx context.Context, db *gorm.DB, repoID uint, sha string) ([]string, error) {
	var fps []string
	err := db.WithContext(ctx).
		Table("artifacts").
		Distinct("crash_signatures.fingerprint").
		Joins("JOIN commits ON commits.id = artifacts.commit_id").
		Joins("JOIN crash_signatures ON crash_signatures.id = artifacts.crash_signature_id").
		Where("artifacts.repository_id = ? AND commits.sha = ?", repoID, sha).
		Where("artifacts.crash_signature_id IS NOT NULL").
		Pluck("crash_signatures.fingerprint", &fps).Error
	if err != nil {
		return nil, err
	}
	return fps, nil
}

func toSet(items []string) map[string]bool {
	s := make(map[string]bool, len(items))
	for _, item := range items {
		s[item] = true
	}
	return s
}