package engine

import (
	"context"
	"errors"
	"fmt"
	"sort"

	"github.com/MDietermann/ArduinoArchSetup/internal/module"
)

// RunOptions controls a single engine run.
type RunOptions struct {
	Selected    []string // module IDs to run; empty = all
	DryRun      bool     // Detect + Plan only, no Apply/Verify
	HaltOnError bool     // stop at first failure instead of continuing siblings
	Reporter    module.Reporter
}

// ModuleStatus is the terminal state of a module within a run.
type ModuleStatus string

const (
	StatusSucceeded ModuleStatus = "succeeded"
	StatusFailed    ModuleStatus = "failed"
	StatusSkipped   ModuleStatus = "skipped"
	StatusPlanned   ModuleStatus = "planned" // dry-run only
)

// ModuleResult captures what happened for one module.
type ModuleResult struct {
	ID     string
	Status ModuleStatus
	Plan   module.Plan
	Err    error
}

// Summary aggregates results.
type Summary struct {
	Results []ModuleResult
}

// Counts returns (succeeded, failed, skipped).
func (s Summary) Counts() (int, int, int) {
	var ok, fail, skip int
	for _, r := range s.Results {
		switch r.Status {
		case StatusSucceeded, StatusPlanned:
			ok++
		case StatusFailed:
			fail++
		case StatusSkipped:
			skip++
		}
	}
	return ok, fail, skip
}

// Run drives the selected modules through the four phases in DAG order.
// Parallelism is intentionally omitted in this foundation; a later plan
// will introduce it. Sequential execution is a correct baseline.
func Run(ctx context.Context, reg *module.Registry, opts RunOptions) (Summary, error) {
	mods, err := resolveSelection(reg, opts.Selected)
	if err != nil {
		return Summary{}, err
	}

	metas := make([]module.Meta, 0, len(mods))
	for _, m := range mods {
		metas = append(metas, m.Meta())
	}
	order, err := TopoSort(metas)
	if err != nil {
		return Summary{}, fmt.Errorf("module graph: %w", err)
	}

	byID := make(map[string]module.Module, len(mods))
	for _, m := range mods {
		byID[m.Meta().ID] = m
	}

	results := make(map[string]*ModuleResult, len(mods))
	skipped := make(map[string]bool)

	for _, id := range order {
		if skipped[id] {
			results[id] = &ModuleResult{ID: id, Status: StatusSkipped, Err: errors.New("skipped: upstream failed")}
			continue
		}
		m := byID[id]
		res := &ModuleResult{ID: id}
		results[id] = res

		state, err := m.Detect(ctx)
		if err != nil {
			res.Status = StatusFailed
			res.Err = fmt.Errorf("detect: %w", err)
			markFailed(metas, id, skipped)
			if opts.HaltOnError {
				break
			}
			continue
		}

		plan, err := m.Plan(ctx, state)
		if err != nil {
			res.Status = StatusFailed
			res.Err = fmt.Errorf("plan: %w", err)
			markFailed(metas, id, skipped)
			if opts.HaltOnError {
				break
			}
			continue
		}
		res.Plan = plan

		if opts.DryRun {
			res.Status = StatusPlanned
			continue
		}

		if err := m.Apply(ctx, plan, opts.Reporter); err != nil {
			res.Status = StatusFailed
			res.Err = fmt.Errorf("apply: %w", err)
			markFailed(metas, id, skipped)
			if opts.HaltOnError {
				break
			}
			continue
		}
		if err := m.Verify(ctx); err != nil {
			res.Status = StatusFailed
			res.Err = fmt.Errorf("verify: %w", err)
			markFailed(metas, id, skipped)
			if opts.HaltOnError {
				break
			}
			continue
		}
		res.Status = StatusSucceeded
	}

	summary := Summary{}
	// Emit results in topo order for stable output.
	ids := make([]string, 0, len(results))
	for id := range results {
		ids = append(ids, id)
	}
	sort.SliceStable(ids, func(i, j int) bool {
		return indexOf(order, ids[i]) < indexOf(order, ids[j])
	})
	for _, id := range ids {
		summary.Results = append(summary.Results, *results[id])
	}
	return summary, nil
}

func resolveSelection(reg *module.Registry, selected []string) ([]module.Module, error) {
	all := reg.All()
	if len(selected) == 0 {
		return all, nil
	}
	out := make([]module.Module, 0, len(selected))
	for _, id := range selected {
		m, ok := reg.Get(id)
		if !ok {
			return nil, fmt.Errorf("unknown module %q", id)
		}
		out = append(out, m)
	}
	return out, nil
}

func markFailed(metas []module.Meta, id string, skipped map[string]bool) {
	for d := range Descendants(metas, id) {
		skipped[d] = true
	}
}

func indexOf(s []string, v string) int {
	for i, x := range s {
		if x == v {
			return i
		}
	}
	return -1
}