package session

import "github.com/aoagents/agent-orchestrator/backend/internal/domain"

// stackInfo is the derived position of one PR within its session's set of PRs.
// PRs form a stack when one targets the source branch of another: PR B is a
// child of PR A when B.TargetBranch == A.SourceBranch and A is open.
type stackInfo struct {
	// Blocked is true when an open PR in the set owns the branch this PR targets,
	// i.e. this PR is a child stacked on a parent that has not merged yet.
	Blocked bool
	// BottomOfStack is true when no open PR sits below this one. It is the only
	// PR in a stack that should receive a merge-conflict rebase nudge; an
	// independent PR (targeting the base branch) is its own bottom.
	BottomOfStack bool
}

// buildStacks derives the stack position of every PR from the source/target
// branch columns alone. A parent counts only while open, matching the rule that
// a merged or closed parent no longer blocks its children.
func buildStacks(prs []domain.PRFacts) map[string]stackInfo {
	openSources := make(map[string]bool, len(prs))
	for _, p := range prs {
		if !p.Merged && !p.Closed && p.SourceBranch != "" {
			openSources[p.SourceBranch] = true
		}
	}
	out := make(map[string]stackInfo, len(prs))
	for _, p := range prs {
		blocked := p.TargetBranch != "" && openSources[p.TargetBranch]
		out[p.URL] = stackInfo{Blocked: blocked, BottomOfStack: !blocked}
	}
	return out
}