package serv

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"

	"github.com/cespare/xxhash/v2"
	"github.com/dosco/super-graph/jsn"
	"github.com/dosco/super-graph/qcode"
	"github.com/go-pg/pg"
	"github.com/valyala/fasttemplate"
)

const (
	empty = ""
)

// var (
// 	cache, _ = bigcache.NewBigCache(bigcache.DefaultConfig(24 * time.Hour))
// )

type coreContext struct {
	req gqlReq
	res gqlResp
	context.Context
}

func (c *coreContext) handleReq(w io.Writer, req *http.Request) error {
	var err error

	qc, err := qcompile.CompileQuery(c.req.Query)
	if err != nil {
		return err
	}

	vars := varMap(c)

	data, skipped, err := c.resolveSQL(qc, vars)
	if err != nil {
		return err
	}

	if len(data) == 0 || skipped == 0 {
		return c.render(w, data)
	}

	sel := qc.Query.Selects
	h := xxhash.New()

	// fetch the field name used within the db response json
	// that are used to mark insertion points and the mapping between
	// those field names and their select objects
	fids, sfmap := parentFieldIds(h, sel, skipped)

	// fetch the field values of the marked insertion points
	// these values contain the id to be used with fetching remote data
	from := jsn.Get(data, fids)

	// replacement data for the marked insertion points
	// key and value will be replaced by whats below
	to := make([]jsn.Field, 0, len(from))

	for _, id := range from {
		// use the json key to find the related Select object
		k1 := xxhash.Sum64(id.Key)

		s, ok := sfmap[k1]
		if !ok {
			continue
		}
		p := sel[s.ParentID]

		// then use the Table nme in the Select and it's parent
		// to find the resolver to use for this relationship
		k2 := mkkey(h, s.Table, p.Table)

		r, ok := rmap[k2]
		if !ok {
			continue
		}

		id := jsn.Value(id.Value)
		if len(id) == 0 {
			continue
		}

		st := time.Now()

		b, err := r.Fn(req, id)
		if err != nil {
			return err
		}

		if conf.EnableTracing {
			c.addTrace(s, st)
		}

		if len(r.Path) != 0 {
			b = jsn.Strip(b, r.Path)
		}

		var ob bytes.Buffer

		if len(s.Cols) != 0 {
			err = jsn.Filter(&ob, b, colsToList(s.Cols))
			if err != nil {
				return err
			}

		} else {
			ob.WriteString("null")
		}

		f := jsn.Field{[]byte(s.FieldName), ob.Bytes()}
		to = append(to, f)
	}

	var ob bytes.Buffer

	err = jsn.Replace(&ob, data, from, to)
	if err != nil {
		return err
	}

	return c.render(w, ob.Bytes())
}

func (c *coreContext) resolveSQL(qc *qcode.QCode, vars variables) (
	[]byte, uint32, error) {

	// var entry []byte
	// var key string

	// cacheEnabled := (conf.EnableTracing == false)

	// if cacheEnabled {
	// 	k := sha1.Sum([]byte(req.Query))
	// 	key = string(k[:])
	// 	entry, err = cache.Get(key)

	// 	if err != nil && err != bigcache.ErrEntryNotFound {
	// 		return emtpy, err
	// 	}

	// 	if len(entry) != 0 && err == nil {
	// 		return entry, nil
	// 	}
	// }

	skipped, stmts, err := pcompile.Compile(qc)
	if err != nil {
		return nil, 0, err
	}

	t := fasttemplate.New(stmts[0], openVar, closeVar)

	var sqlStmt strings.Builder
	_, err = t.Execute(&sqlStmt, vars)

	if err == errNoUserID &&
		authFailBlock == authFailBlockPerQuery &&
		authCheck(c) == false {
		return nil, 0, errUnauthorized
	}

	if err != nil {
		return nil, 0, err
	}

	finalSQL := sqlStmt.Bytes()

	if conf.DebugLevel > 0 {
		fmt.Println(finalSQL)
	}

	// if cacheEnabled {
	// 	if err = cache.Set(key, finalSQL); err != nil {
	// 		return err
	// 	}
	// }

	var st time.Time

	if conf.EnableTracing {
		st = time.Now()
	}

	var root json.RawMessage
	_, err = db.Query(pg.Scan(&root), finalSQL)

	if err != nil {
		return nil, 0, err
	}

	if conf.EnableTracing && len(qc.Query.Selects) != 0 {
		c.addTrace(&qc.Query.Selects[0], st)
	}

	return []byte(root), skipped, nil
}

func (c *coreContext) render(w io.Writer, data []byte) error {
	c.res.Data = json.RawMessage(data)
	return json.NewEncoder(w).Encode(c.res)
}

func (c *coreContext) addTrace(sel *qcode.Select, st time.Time) {
	et := time.Now()
	du := et.Sub(st)

	if c.res.Extensions == nil {
		c.res.Extensions = &extensions{&trace{
			Version:   1,
			StartTime: st,
			Execution: execution{},
		}}
	}

	c.res.Extensions.Tracing.EndTime = et
	c.res.Extensions.Tracing.Duration = du

	tr := resolver{
		Path:        []string{sel.Table},
		ParentType:  "Query",
		FieldName:   sel.Table,
		ReturnType:  "object",
		StartOffset: 1,
		Duration:    du,
	}

	c.res.Extensions.Tracing.Execution.Resolvers =
		append(c.res.Extensions.Tracing.Execution.Resolvers, tr)
}

func parentFieldIds(h *xxhash.Digest, sel []qcode.Select, skipped uint32) (
	[][]byte,
	map[uint64]*qcode.Select) {

	c := 0
	for i := range sel {
		s := &sel[i]
		if isSkipped(skipped, s.ID) {
			c++
		}
	}

	// list of keys (and it's related value) to extract from
	// the db json response
	fm := make([][]byte, c)

	// mapping between the above extracted key and a Select
	// object
	sm := make(map[uint64]*qcode.Select, c)
	n := 0

	for i := range sel {
		s := &sel[i]

		if isSkipped(skipped, s.ID) == false {
			continue
		}

		p := sel[s.ParentID]
		k := mkkey(h, s.Table, p.Table)

		if r, ok := rmap[k]; ok {
			fm[n] = r.IDField
			n++

			k := xxhash.Sum64(r.IDField)
			sm[k] = s
		}
	}

	return fm, sm
}

func isSkipped(n uint32, pos uint16) bool {
	return ((n & (1 << pos)) != 0)
}

func authCheck(ctx *coreContext) bool {
	return (ctx.Value(userIDKey) != nil)
}

func colsToList(cols []qcode.Column) []string {
	var f []string

	for i := range cols {
		f = append(f, cols[i].Name)
	}
	return f
}