package engine

import (
	"context"
	"encoding/json"
	"fmt"
	"net/url"
	"regexp"
	"slices"
	"strings"
	"time"

	"jarl/internal/auth"
	"jarl/internal/blocking"
	"jarl/internal/model"
)

// ---- blocking: blocklists and rules (docs/blocking.md)

var blocklistNameRe = regexp.MustCompile(`^[a-z0-9]([a-z0-9-]{0,38}[a-z0-9])?$`)

func blockingAction() auth.Action { return auth.Action{Resource: auth.ResBlocking, Write: true} }

// viewIDs resolves the views of a blocklist or rule input: names or IDs,
// in view order, without duplicates. nil, nil means "not given".
func viewIDs(st *model.State, names *[]string, ids *[]int64) ([]int64, error) {
	if names == nil && ids == nil {
		return nil, nil
	}
	want := map[int64]bool{}
	if names != nil {
		for _, n := range *names {
			v := st.ViewByName(strings.TrimSpace(n))
			if v == nil {
				return nil, errf(KindBadRequest, "view %q does not exist", n)
			}
			want[v.ID] = true
		}
	}
	if ids != nil {
		for _, id := range *ids {
			if st.Views[id] == nil {
				return nil, errf(KindBadRequest, "view %d does not exist", id)
			}
			want[id] = true
		}
	}
	out := []int64{}
	for _, v := range st.OrderedViews() {
		if want[v.ID] {
			out = append(out, v.ID)
		}
	}
	return out, nil
}

// CheckBlocklistURL checks a blocklist URL: http or https, with a host.
func CheckBlocklistURL(raw string) (string, error) {
	raw = strings.TrimSpace(raw)
	u, err := url.Parse(raw)
	if err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
		return "", fmt.Errorf("%q is not an http or https URL", raw)
	}
	return raw, nil
}

func applyBlocklistPut(st *model.State, op model.Op, c *applyCtx) error {
	if err := c.require(blockingAction()); err != nil {
		return err
	}
	var in BlocklistInput
	if err := decode(op.Data, &in); err != nil {
		return err
	}
	var b *model.Blocklist
	if op.Kind == OpBlocklistCreate {
		if op.ID == 0 || st.Blocklists[op.ID] != nil {
			return errf(KindConflict, "blocklist ID %d is already in use", op.ID)
		}
		if in.Name == nil || in.URL == nil {
			return errf(KindBadRequest, "a blocklist needs a name and a URL")
		}
		b = &model.Blocklist{ID: op.ID, ViewIDs: []int64{}}
	} else {
		b = st.Blocklists[op.ID]
		if b == nil {
			return errf(KindNotFound, "blocklist %d does not exist", op.ID)
		}
		if err := checkVersion(op, b.Version, "blocklist "+b.Name); err != nil {
			return err
		}
	}
	if in.Name != nil {
		name := strings.ToLower(strings.TrimSpace(*in.Name))
		if !blocklistNameRe.MatchString(name) {
			return errf(KindBadRequest, "blocklist name %q: use 1 to 40 lowercase letters, digits and hyphens, like hagezi-pro", *in.Name)
		}
		if other := st.BlocklistByName(name); other != nil && other.ID != b.ID {
			return errf(KindConflict, "blocklist %s already exists", name)
		}
		b.Name = name
	}
	if in.URL != nil {
		u, err := CheckBlocklistURL(*in.URL)
		if err != nil {
			return errf(KindBadRequest, "%v", err)
		}
		b.URL = u
	}
	ids, err := viewIDs(st, in.Views, in.ViewIDs)
	if err != nil {
		return err
	}
	if ids != nil {
		b.ViewIDs = ids
	}
	if in.Disabled != nil {
		b.Disabled = *in.Disabled
	}
	if in.Comment != nil {
		b.Comment = *in.Comment
	}
	b.Touch(c.user(), c.now)
	st.Blocklists[b.ID] = b
	return nil
}

func applyBlocklistDelete(st *model.State, op model.Op, c *applyCtx) error {
	if err := c.require(blockingAction()); err != nil {
		return err
	}
	b := st.Blocklists[op.ID]
	if b == nil {
		return errf(KindNotFound, "blocklist %d does not exist", op.ID)
	}
	if err := checkVersion(op, b.Version, "blocklist "+b.Name); err != nil {
		return err
	}
	delete(st.Blocklists, b.ID)
	return nil
}

func applyBlockRulePut(st *model.State, op model.Op, c *applyCtx) error {
	if err := c.require(blockingAction()); err != nil {
		return err
	}
	var in BlockRuleInput
	if err := decode(op.Data, &in); err != nil {
		return err
	}
	var r *model.BlockRule
	if op.Kind == OpBlockRuleCreate {
		if op.ID == 0 || st.BlockRules[op.ID] != nil {
			return errf(KindConflict, "rule ID %d is already in use", op.ID)
		}
		if in.Name == nil {
			return errf(KindBadRequest, "a rule needs a domain name")
		}
		r = &model.BlockRule{ID: op.ID, Action: model.BlockActionBlock, ViewIDs: []int64{}}
	} else {
		r = st.BlockRules[op.ID]
		if r == nil {
			return errf(KindNotFound, "rule %d does not exist", op.ID)
		}
		if err := checkVersion(op, r.Version, "rule "+r.Name); err != nil {
			return err
		}
	}
	if in.Name != nil {
		n, err := blocking.NormalizeName(*in.Name)
		if err != nil {
			return errf(KindBadRequest, "%v", err)
		}
		r.Name = n
	}
	if in.Action != nil {
		a := strings.ToLower(strings.TrimSpace(*in.Action))
		if a != model.BlockActionBlock && a != model.BlockActionAllow {
			return errf(KindBadRequest, "a rule's action is block or allow, not %q", *in.Action)
		}
		r.Action = a
	}
	if in.Exact != nil {
		r.Exact = *in.Exact
	}
	ids, err := viewIDs(st, in.Views, in.ViewIDs)
	if err != nil {
		return err
	}
	if ids != nil {
		r.ViewIDs = ids
	}
	if in.Comment != nil {
		r.Comment = *in.Comment
	}
	r.Touch(c.user(), c.now)
	st.BlockRules[r.ID] = r
	return nil
}

func applyBlockRuleDelete(st *model.State, op model.Op, c *applyCtx) error {
	if err := c.require(blockingAction()); err != nil {
		return err
	}
	r := st.BlockRules[op.ID]
	if r == nil {
		return errf(KindNotFound, "rule %d does not exist", op.ID)
	}
	if err := checkVersion(op, r.Version, "rule "+r.Name); err != nil {
		return err
	}
	delete(st.BlockRules, r.ID)
	return nil
}

// blockingUsers lists the blocklists and rules that name a view.
func blockingUsers(st *model.State, viewID int64) []string {
	var out []string
	for _, b := range st.SortedBlocklists() {
		if slices.Contains(b.ViewIDs, viewID) {
			out = append(out, "blocklist "+b.Name)
		}
	}
	for _, r := range st.SortedBlockRules() {
		if slices.Contains(r.ViewIDs, viewID) {
			out = append(out, ruleLabel(r))
		}
	}
	return out
}

// ruleLabel describes a rule: "block ads.example (and below)".
func ruleLabel(r *model.BlockRule) string {
	s := r.Action + " " + r.Name
	if !r.Exact {
		s += " (and below)"
	}
	return s
}

// ---- expansion

func (x *expander) blocklistCreate(req Request) ([]model.Op, error) {
	return x.simpleCreate(req, OpBlocklistCreate, func(data json.RawMessage) (string, error) {
		var in BlocklistInput
		if err := decode(data, &in); err != nil {
			return "", err
		}
		if in.Name == nil || in.URL == nil {
			return "", errf(KindBadRequest, "a blocklist needs a name and a URL")
		}
		return "add blocklist " + *in.Name + " (" + *in.URL + ")", nil
	})
}

func (x *expander) blockRuleCreate(req Request) ([]model.Op, error) {
	return x.simpleCreate(req, OpBlockRuleCreate, func(data json.RawMessage) (string, error) {
		var in BlockRuleInput
		if err := decode(data, &in); err != nil {
			return "", err
		}
		if in.Name == nil {
			return "", errf(KindBadRequest, "a rule needs a domain name")
		}
		r := &model.BlockRule{Name: strings.ToLower(strings.TrimSuffix(strings.TrimSpace(*in.Name), ".")), Action: model.BlockActionBlock}
		if in.Action != nil {
			r.Action = strings.ToLower(*in.Action)
		}
		if in.Exact != nil {
			r.Exact = *in.Exact
		}
		return ruleLabel(r), nil
	})
}

func applyBlockingPause(st *model.State, op model.Op, c *applyCtx) error {
	if err := c.require(blockingAction()); err != nil {
		return err
	}
	var in BlockingPauseInput
	if err := decode(op.Data, &in); err != nil {
		return err
	}
	if in.Until != nil && in.Until.Sub(c.now) > MaxBlockingPause+time.Minute {
		return errf(KindBadRequest, "blocking can be paused for at most %s; disable lists to stop using them", MaxBlockingPause)
	}
	st.Settings.BlockingPausedUntil = in.Until
	return nil
}

// ResumeBlocking ends a pause whose time is up, and returns when the
// current pause ends (zero when blocking isn't paused).
func (e *Engine) ResumeBlocking(ctx context.Context) time.Time {
	st, err := e.store.LoadState(ctx)
	if err != nil || st.Settings.BlockingPausedUntil == nil {
		return time.Time{}
	}
	until := *st.Settings.BlockingPausedUntil
	if e.Now().Before(until) {
		return until
	}
	if _, err := e.Submit(ctx, []Request{NewRequest(OpBlockingPause, 0, BlockingPauseInput{})}, auth.System, "system", "resume blocking after the pause", ApplyOptions{}); err != nil {
		e.log.Warn("resuming blocking after the pause failed; it will be tried again", "err", err)
		return e.Now().Add(time.Minute)
	}
	e.log.Info("blocking resumed after the pause")
	return time.Time{}
}