package main

import (
	api "code.dlmw.ch/dlmw/qv/internal"
	"code.dlmw.ch/dlmw/qv/internal/validator"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"math/rand"
	"net/http"
	"slices"
	"time"
)

type createElectionRequestWithValidator struct {
	api.CreateElectionRequest
	validator.Validator
}

func (r *createElectionRequestWithValidator) isValid() bool {
	r.CheckField(validator.NotBlank(r.Name), "name", "must not be blank")
	r.CheckField(validator.GreaterThan(r.Tokens, 0), "tokens", "must be greater than 0")
	r.CheckField(validator.After(r.ExpiresAt, time.Now()), "expiresAt", "must expire in a future date")
	r.CheckField(validator.GreaterThan(len(r.Choices), 1), "choices", "there must be more than 1 choice")
	r.CheckField(validator.UniqueValues(r.Choices), "choices", "must not contain duplicate values")

	for _, choice := range r.Choices {
		r.CheckField(validator.NotBlank(choice), "choice", "must not be blank")
	}

	if r.AreVotersKnown {
		r.CheckField(
			validator.GreaterThan(r.MaxVoters, 0),
			"maxVoters",
			"must be greater than 0 when voters are known",
		)
	} else {
		r.CheckField(
			validator.GreaterThanOrEquals(r.MaxVoters, 0),
			"maxVoters",
			"must be a positive number",
		)
	}

	return r.Valid()
}

func (app *application) createElection(w http.ResponseWriter, r *http.Request) {
	var request createElectionRequestWithValidator

	if err := app.unmarshalRequest(r, &request); err != nil {
		app.clientError(w, http.StatusBadRequest, err.Error())
		return
	}

	if !request.isValid() {
		app.unprocessableEntityError(w, request.Validator)
		return
	}

	electionId, err := app.elections.Insert(
		request.Name,
		request.Tokens,
		request.AreVotersKnown,
		request.MaxVoters,
		request.Choices,
		request.ExpiresAt,
	)
	if err != nil {
		app.serverError(w, r, err)
		return
	}

	var res []byte
	if request.AreVotersKnown {
		voterIdentities := make([]string, 0, request.MaxVoters)
		for i := 0; i < request.MaxVoters; i++ {
			randomIdentity := randomVoterIdentity()
			_, err := app.voters.Insert(randomIdentity, electionId)
			if err != nil {
				app.serverError(w, r, err)
			}
			voterIdentities = append(voterIdentities, randomIdentity)
		}

		res, err = json.Marshal(api.CreateElectionResponse{VoterIdentities: &voterIdentities})
		if err != nil {
			app.serverError(w, r, err)
			return
		}
	}

	w.Header().Set("Location", fmt.Sprintf("/election/%v", electionId))
	w.Write(res)
}

func randomVoterIdentity() string {
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	b := make([]byte, 16)
	for i := range b {
		b[i] = charset[rand.Intn(len(charset))]
	}
	return string(b)
}

type createVotesRequestWithValidator struct {
	api.CreateVotesRequest
	validator.Validator
}

func (r *createVotesRequestWithValidator) isValid() bool {
	r.CheckField(validator.GreaterThan(r.ElectionId, 0), "electionId", "must be greater than 0")

	for _, choice := range r.Choices {
		r.CheckField(validator.NotBlank(choice.ChoiceText), "choiceText", "must not be blank")
	}

	return r.Valid()
}

func (app *application) createVotes(w http.ResponseWriter, r *http.Request) {
	var request createVotesRequestWithValidator

	if err := app.unmarshalRequest(r, &request); err != nil {
		app.clientError(w, http.StatusBadRequest, err.Error())
		return
	}

	if !request.isValid() {
		app.unprocessableEntityError(w, request.Validator)
		return
	}

	election, err := app.elections.GetById(request.ElectionId)
	if err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			app.unprocessableEntityErrorSingle(w, fmt.Errorf("election with id %v doesn't exist", request.ElectionId))
			return
		}
		app.serverError(w, r, err)
	}

	for _, c := range request.Choices {
		choiceExists := slices.Contains(election.Choices, c.ChoiceText)
		if !choiceExists {
			app.unprocessableEntityErrorSingle(w, fmt.Errorf("choice %v doesn't exist", c.ChoiceText))
			return
		}
	}

	tokensUsed := 0
	for _, c := range request.Choices {
		tokensUsed += c.Tokens
	}

	if tokensUsed > election.Tokens {
		app.unprocessableEntityErrorSingle(w, fmt.Errorf("you used too many tokens; must not exceed %v tokens", election.Tokens))
		return
	}

	electionHasExpired := election.ExpiresAt.Before(time.Now())
	if electionHasExpired {
		app.unprocessableEntityErrorSingle(w, fmt.Errorf("election has expired"))
		return
	}

	// this snippet of code also inserts in the `voters` table
	voterIdentity := func() string {
		var voterIdentity string
		if election.AreVotersKnown {
			if request.VoterIdentity == nil || validator.Blank(*request.VoterIdentity) {
				app.unprocessableEntityErrorSingle(w, fmt.Errorf("election has known voters; you must provide an identity provided by the organizer"))
				return ""
			}

			voterIdentity = *request.VoterIdentity
			hasCastVotes, err := app.votes.Exists(voterIdentity, election.ID)
			if err != nil {
				app.serverError(w, r, err)
				return ""
			}
			if hasCastVotes {
				app.unprocessableEntityErrorSingle(w, fmt.Errorf("you already voted"))
				return ""
			}

			voterExists, err := app.voters.Exists(voterIdentity, election.ID)
			if err != nil {
				app.serverError(w, r, err)
				return ""
			}
			if !voterExists {
				app.unprocessableEntityErrorSingle(w, fmt.Errorf("invalid voter identity"))
				return ""
			}
		} else {
			voterIdentity = r.RemoteAddr

			// if voters are known, voter will always exist
			voterExists, err := app.voters.Exists(voterIdentity, election.ID)
			if err != nil {
				app.serverError(w, r, err)
				return ""
			}
			if voterExists {
				app.unprocessableEntityErrorSingle(w, fmt.Errorf("you already voted"))
				return ""
			}

			_, err = app.voters.Insert(voterIdentity, election.ID)
			if err != nil {
				app.serverError(w, r, err)
				return ""
			}
		}
		return voterIdentity
	}()

	if voterIdentity == "" {
		return
	}

	if !election.AreVotersKnown {
		voterCount, err := app.voters.CountByElection(election.ID)
		if err != nil && !errors.Is(sql.ErrNoRows, err) {
			app.serverError(w, r, err)
			return
		}
		// if voters are known, voterCount == election.MaxVoters in all cases
		if voterCount == election.MaxVoters {
			app.unprocessableEntityErrorSingle(w, fmt.Errorf("maximum voters reached"))
			return
		}
	}

	for _, c := range request.Choices {
		_, err := app.votes.Insert(voterIdentity, election.ID, c.ChoiceText, c.Tokens)
		if err != nil {
			app.serverError(w, r, err)
		}
	}

	w.WriteHeader(http.StatusCreated)
}