package party

import (
	"fmt"
	"strings"
	"sync"

	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/pact"
	"git.golem15.com/golem15/summercms/modules/phrasebook"
	"git.golem15.com/golem15/summercms/modules/postcard"
)

// Plugin is the required descriptor every compiled plugin implements.
type Plugin interface {
	ID() string
	Requires() []string
	Register(app *backpack.App) error
	Boot(app *backpack.App) error
}

var (
	mu      sync.Mutex
	plugins []Plugin
)

// Register appends a plugin to the process-wide registry. Plugins call this
// from init() after a blank import; Activate selects and orders them.
func Register(p Plugin) {
	if p == nil {
		return
	}
	mu.Lock()
	defer mu.Unlock()
	plugins = append(plugins, p)
}

func snapshot() []Plugin {
	mu.Lock()
	defer mu.Unlock()
	out := make([]Plugin, len(plugins))
	copy(out, plugins)
	return out
}

// Activate resolves ids in manifest order, topologically sorts Requires(),
// then runs every Register before any Boot.
func Activate(app *backpack.App, ids []string) ([]Plugin, error) {
	if app == nil {
		return nil, fmt.Errorf("party: app is nil")
	}
	return activate(snapshot(), app, ids)
}

func activate(registered []Plugin, app *backpack.App, ids []string) ([]Plugin, error) {
	byID := make(map[string]Plugin, len(registered))
	for _, p := range registered {
		if p == nil {
			continue
		}
		id := p.ID()
		if id == "" {
			return nil, fmt.Errorf("party: registered plugin has empty id")
		}
		if _, exists := byID[id]; exists {
			return nil, fmt.Errorf("party: duplicate plugin id %q", id)
		}
		byID[id] = p
	}

	seen := make(map[string]struct{}, len(ids))
	selected := make([]Plugin, 0, len(ids))
	index := make(map[string]int, len(ids))
	for _, id := range ids {
		if id == "" {
			return nil, fmt.Errorf("party: empty plugin id in manifest")
		}
		if _, dup := seen[id]; dup {
			return nil, fmt.Errorf("party: duplicate plugin id %q", id)
		}
		seen[id] = struct{}{}
		p, ok := byID[id]
		if !ok {
			return nil, fmt.Errorf("party: plugin %q is not registered", id)
		}
		index[id] = len(selected)
		selected = append(selected, p)
	}

	for _, p := range selected {
		for _, req := range p.Requires() {
			if _, ok := seen[req]; !ok {
				return nil, fmt.Errorf("party: plugin %q requires %q, which is not registered", p.ID(), req)
			}
		}
	}

	ordered, err := topoSort(selected, index)
	if err != nil {
		return nil, err
	}

	orderedIDs := make([]string, len(ordered))
	for i, p := range ordered {
		orderedIDs[i] = p.ID()
	}
	app.SetPlugins(orderedIDs)

	for _, p := range ordered {
		if hc, ok := p.(pact.HasConfig); ok && app.Config != nil {
			if err := app.Config.MergePlugin(p.ID(), hc.ConfigFS()); err != nil {
				return nil, fmt.Errorf("party: config %s: %w", p.ID(), err)
			}
		}
	}
	for _, p := range ordered {
		if err := p.Register(app); err != nil {
			return nil, fmt.Errorf("party: register %s: %w", p.ID(), err)
		}
	}
	if err := phrasebook.Activate(app, ordered); err != nil {
		return nil, fmt.Errorf("party: lang: %w", err)
	}
	if err := postcard.Activate(app, ordered); err != nil {
		return nil, fmt.Errorf("party: mail: %w", err)
	}
	for _, p := range ordered {
		if err := postcard.BootPlugin(app, p); err != nil {
			return nil, fmt.Errorf("party: boot %s: %w", p.ID(), err)
		}
		if err := p.Boot(app); err != nil {
			return nil, fmt.Errorf("party: boot %s: %w", p.ID(), err)
		}
	}
	return ordered, nil
}

func topoSort(plugins []Plugin, index map[string]int) ([]Plugin, error) {
	byID := make(map[string]Plugin, len(plugins))
	indeg := make(map[string]int, len(plugins))
	dependents := make(map[string][]string, len(plugins))
	for _, p := range plugins {
		byID[p.ID()] = p
		indeg[p.ID()] = 0
	}
	for _, p := range plugins {
		seenReq := make(map[string]struct{})
		for _, req := range p.Requires() {
			if _, ok := seenReq[req]; ok {
				continue
			}
			seenReq[req] = struct{}{}
			if _, ok := byID[req]; !ok {
				continue
			}
			indeg[p.ID()]++
			dependents[req] = append(dependents[req], p.ID())
		}
	}

	ready := make([]string, 0, len(plugins))
	for _, p := range plugins {
		if indeg[p.ID()] == 0 {
			ready = append(ready, p.ID())
		}
	}

	out := make([]Plugin, 0, len(plugins))
	for len(ready) > 0 {
		id := ready[0]
		ready = ready[1:]
		out = append(out, byID[id])
		next := append([]string(nil), dependents[id]...)
		sortByIndex(next, index)
		for _, dep := range next {
			indeg[dep]--
			if indeg[dep] == 0 {
				ready = insertByIndex(ready, dep, index)
			}
		}
	}
	if len(out) != len(plugins) {
		leftover := make([]string, 0)
		done := make(map[string]struct{}, len(out))
		for _, p := range out {
			done[p.ID()] = struct{}{}
		}
		for _, p := range plugins {
			if _, ok := done[p.ID()]; !ok {
				leftover = append(leftover, p.ID())
			}
		}
		return nil, fmt.Errorf("party: dependency cycle involving %s", strings.Join(leftover, ", "))
	}
	return out, nil
}

func sortByIndex(ids []string, index map[string]int) {
	for i := 1; i < len(ids); i++ {
		j := i
		for j > 0 && index[ids[j]] < index[ids[j-1]] {
			ids[j], ids[j-1] = ids[j-1], ids[j]
			j--
		}
	}
}

func insertByIndex(ready []string, id string, index map[string]int) []string {
	at := len(ready)
	for i, existing := range ready {
		if index[id] < index[existing] {
			at = i
			break
		}
	}
	ready = append(ready, "")
	copy(ready[at+1:], ready[at:])
	ready[at] = id
	return ready
}