package app

import "github.com/hjbdev/patterm/internal/scratchpad"

// navEntry is one row in the unified sidebar navigation list. Exactly
// one of childID or pad is set. childID points at a Child by ID; pad
// names a scratchpad entry. Empty zero-value means "no target".
type navEntry struct {
	childID string
	pad     string
}

func (n navEntry) empty() bool   { return n.childID == "" && n.pad == "" }
func (n navEntry) isPad() bool   { return n.pad != "" }
func (n navEntry) isChild() bool { return n.childID != "" }

// visibleAgentTree returns the running entries under the active agent
// tab (root agent + its sub-agents). With the new Processes pane,
// command processes live in their own section and never show up here —
// the agent tree is for KindAgent (and KindTerminal sub-entries) only.
func visibleAgentTree(children []*Child, activeAgentID string) []*Child {
	if activeAgentID == "" {
		return nil
	}
	out := make([]*Child, 0, len(children))
	for _, c := range children {
		if c.Status() != StatusRunning {
			continue
		}
		if c.Kind == KindCommand && c.ParentID == "" {
			continue
		}
		if c.ID == activeAgentID || c.ParentID == activeAgentID {
			out = append(out, c)
		}
	}
	return out
}

// visibleSessionTree is retained for the test suite and any pre-Processes
// callers — it returns the active agent's tree given the focused id,
// resolving the active agent root from focus the same way the previous
// implementation did.
func visibleSessionTree(children []*Child, focusID string) []*Child {
	rootID := activeRootID(children, focusID)
	if rootID == "" {
		return nil
	}
	out := make([]*Child, 0, len(children))
	for _, c := range children {
		if c.Status() != StatusRunning {
			continue
		}
		if c.ID == rootID || c.ParentID == rootID {
			out = append(out, c)
		}
	}
	return out
}

// activeRootID resolves the agent root the user is "inside" right now.
// If focus is on a sub-agent, it walks up. If focus is on a top-level
// process (KindCommand), it falls through to the first running agent
// root so the agent tree section keeps showing something coherent.
func activeRootID(children []*Child, focusID string) string {
	if focusID != "" {
		for _, c := range children {
			if c.ID != focusID {
				continue
			}
			if c.Kind == KindCommand && c.ParentID == "" {
				break
			}
			if c.ParentID == "" {
				return c.ID
			}
			if parent := findChildInSnapshot(children, c.ParentID); parent != nil {
				return parent.ID
			}
			return ""
		}
	}
	return firstRunningAgentID(children)
}

func firstRunningAgentID(children []*Child) string {
	for _, c := range children {
		if c.Kind != KindAgent {
			continue
		}
		if c.ParentID == "" && c.Status() == StatusRunning {
			return c.ID
		}
	}
	return ""
}

// processList returns every top-level command/terminal entry in spawn
// order, regardless of running state. The Processes sidebar section
// keeps showing exited entries so the user can see what just died (and
// because Session retains KindCommand entries for restart).
func processList(children []*Child) []*Child {
	out := make([]*Child, 0, len(children))
	for _, c := range children {
		if c.ParentID != "" {
			continue
		}
		if c.Kind == KindCommand || c.Kind == KindTerminal {
			out = append(out, c)
		}
	}
	return out
}

func findChildInSnapshot(children []*Child, id string) *Child {
	for _, c := range children {
		if c.ID == id {
			return c
		}
	}
	return nil
}

func firstRunningTopLevel(children []*Child) *Child {
	for _, c := range children {
		if c.ParentID == "" && c.Status() == StatusRunning {
			return c
		}
	}
	return nil
}

// runningTopLevels lists every running top-level agent session in the
// order they appear in the snapshot. Tabs only show agents — command
// processes live in the Processes sidebar section — so Ctrl+A/D
// navigation cycles through agent tabs exclusively.
func runningTopLevels(children []*Child) []*Child {
	out := make([]*Child, 0, len(children))
	for _, c := range children {
		if c.Kind != KindAgent {
			continue
		}
		if c.ParentID == "" && c.Status() == StatusRunning {
			out = append(out, c)
		}
	}
	return out
}

// nextTabID returns the id of the top-level session `step` positions
// away from the current focus in the runningTopLevels list, wrapping
// at both ends. Returns "" when there's nothing to switch to.
func nextTabID(children []*Child, focusID string, step int) string {
	roots := runningTopLevels(children)
	if len(roots) == 0 {
		return ""
	}
	rootID := activeRootID(children, focusID)
	idx := -1
	for i, r := range roots {
		if r.ID == rootID {
			idx = i
			break
		}
	}
	if idx < 0 {
		idx = 0
	}
	idx = (idx + step) % len(roots)
	if idx < 0 {
		idx += len(roots)
	}
	if roots[idx].ID == focusID {
		return ""
	}
	return roots[idx].ID
}

// currentTabFlat returns the focused tab's processes (root first, then
// its running children) in display order. Used to step focus with
// Ctrl+W/S.
func currentTabFlat(children []*Child, focusID string) []*Child {
	rootID := activeRootID(children, focusID)
	if rootID == "" {
		return nil
	}
	out := make([]*Child, 0, 4)
	for _, c := range children {
		if c.ID == rootID && c.Status() == StatusRunning {
			out = append(out, c)
			break
		}
	}
	for _, c := range children {
		if c.ParentID == rootID && c.Status() == StatusRunning {
			out = append(out, c)
		}
	}
	return out
}

// sidebarNavList combines the Processes section and the active Agent
// Tree into one flat list — top-to-bottom matching what the user sees
// in the sidebar. Ctrl+W/S walks this list so the user can step out of
// the agent tree, into the Processes section, and back.
func sidebarNavList(children []*Child, activeAgentID string) []*Child {
	out := make([]*Child, 0, 8)
	for _, c := range processList(children) {
		out = append(out, c)
	}
	for _, c := range visibleAgentTree(children, activeAgentID) {
		out = append(out, c)
	}
	return out
}

// sidebarNav returns the combined Processes + Agent Tree + Scratchpads
// navigation list. Scratchpads always appear after children so the
// existing "step past the tree" expectation still holds.
func sidebarNav(children []*Child, activeAgentID string, pads []scratchpad.Entry) []navEntry {
	flat := sidebarNavList(children, activeAgentID)
	out := make([]navEntry, 0, len(flat)+len(pads))
	for _, c := range flat {
		out = append(out, navEntry{childID: c.ID})
	}
	for _, p := range pads {
		out = append(out, navEntry{pad: p.Name})
	}
	return out
}

// nextNavEntry returns the entry `step` positions away from the
// current focus in the unified nav list. Either focusChildID or
// focusPad will be set (or both empty for "nothing focused yet").
// Empty when there's nothing else to land on.
func nextNavEntry(children []*Child, focusChildID, focusPad, activeAgentID string, pads []scratchpad.Entry, step int) navEntry {
	flat := sidebarNav(children, activeAgentID, pads)
	if len(flat) == 0 {
		return navEntry{}
	}
	matches := func(e navEntry) bool {
		if focusPad != "" && e.pad != "" {
			return e.pad == focusPad
		}
		if focusChildID != "" && e.childID != "" {
			return e.childID == focusChildID
		}
		return false
	}
	if len(flat) == 1 {
		if matches(flat[0]) {
			return navEntry{}
		}
		return flat[0]
	}
	idx := -1
	for i, e := range flat {
		if matches(e) {
			idx = i
			break
		}
	}
	if idx < 0 {
		idx = 0
	}
	idx = (idx + step) % len(flat)
	if idx < 0 {
		idx += len(flat)
	}
	if matches(flat[idx]) {
		return navEntry{}
	}
	return flat[idx]
}

// nextChildID is retained for tests; it ignores scratchpads.
func nextChildID(children []*Child, focusID, activeAgentID string, step int) string {
	flat := sidebarNavList(children, activeAgentID)
	if len(flat) == 0 {
		return ""
	}
	if len(flat) == 1 {
		if flat[0].ID == focusID {
			return ""
		}
		return flat[0].ID
	}
	idx := -1
	for i, c := range flat {
		if c.ID == focusID {
			idx = i
			break
		}
	}
	if idx < 0 {
		idx = 0
	}
	idx = (idx + step) % len(flat)
	if idx < 0 {
		idx += len(flat)
	}
	if flat[idx].ID == focusID {
		return ""
	}
	return flat[idx].ID
}